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2021-03-18 | Giant spin Hall angle in the Heusler alloy Weyl ferromagnet Co$_2$MnGa | Weyl semimetals are playing a major role in condensed matter physics due to
exotic topological properties, and their coexistence with ferromagnetism may
lead to enhanced spin-related phenomena. Here, the inverse spin Hall effect
(ISHE) in the ferromagnetic Weyl-semimetal Heusler alloy Co$_2$MnGa was
investigated at room temperature by means of electrical spin injection in
lateral spin valve structures. Spin transport properties such as spin
polarization and spin diffusion length in this material were precisely
extracted in order to estimate the spin Hall angle $\theta_{\textrm{SH}}$,
which was found to be $-0.19\pm0.04$ and is among the highest reported for a
ferromagnet. Although this value is on the same order of magnitude of known
heavy metals, the significantly higher resistivity of Co$_2$MnGa implies an
improvement on the magnitude of detection voltages, while its ferromagnetic
nature allows controlling the intensity of SHE through the magnetization
direction. It was also shown that Onsager's reciprocity does not hold for this
system, which is in part attributable to a different spin-dependent Hall
conductivity for spin-up and spin-down carriers. | 2103.10188v1 |
2021-04-06 | Relationship between the TC of smart meta-superconductor Bi(Pb)SrCaCuO and inhomogeneous phase content | A smart meta-superconductor Bi(Pb)SrCaCuO (B(P)SCCO) may increase the
critical transition temperature (TC) of B(P)SCCO by electroluminescence (EL)
energy injection of inhomogeneous phases. However, the increase amplitude
{\Delta}TC ({\Delta}TC=TC-T(C,pure)) of TC is relatively small. In this study,
a smart meta-superconductor B(P)SCCO with different matrix sizes was designed.
Three kinds of raw materials with different particle sizes were used, and
different series of Y2O3:Sm3+, Y2O3, Y2O3:Eu3+, and Y2O3:Eu3++Ag doped samples
and pure B(P)SCCO were prepared. Results indicated that the TC of the Y2O3 or
Y2O3:Sm3+ non-luminescent dopant doping sample is lower than that of pure
B(P)SCCO. However, the TC of the Y2O3:Eu3++Ag or Y2O3:Eu3+ luminescent
inhomogeneous phase doping sample is higher than that of pure B(P)SCCO. With
the decrease of the raw material particle size from 30 to 5 {\mu}m, the
particle size of the B(P)SCCO superconducting matrix in the prepared samples
decreases, and the doping content of the Y2O3:Eu3++Ag or Y2O3:Eu3+ increases
from 0.2% to 0.4%. Meanwhile, the increase of the inhomogeneous phase content
enhances the {\Delta}TC. When the particle size of raw material is 5 {\mu}m,
the doping concentration of the luminescent inhomogeneous phase can be
increased to 0.4%. At this time, the zero-resistance temperature and onset
transition temperature of the Y2O3:Eu3++Ag doped sample are 4 and 6.3 K higher
than those of pure B(P)SCCO, respectively. | 2104.02229v1 |
2021-05-12 | Superconducting diode effect via conformal-mapped nanoholes | A superconducting diode is an electronic device that conducts supercurrent
and exhibits zero resistance primarily for one direction of applied current.
Such a dissipationless diode is a desirable unit for constructing electronic
circuits with ultralow power consumption. However, realizing a superconducting
diode is fundamentally and technologically challenging, as it usually requires
a material structure without a centre of inversion, which is scarce among
superconducting materials. Here, we demonstrate a superconducting diode
achieved in a conventional superconducting film patterned with a conformal
array of nanoscale holes, which breaks the spatial inversion symmetry. We
showcase the superconducting diode effect through switchable and reversible
rectification signals, which can be three orders of magnitude larger than that
from a flux-quantum diode. The introduction of conformal potential landscapes
for creating a superconducting diode is thereby proven as a convenient,
tunable, yet vastly advantageous tool for superconducting electronics. This
could be readily applicable to any superconducting materials, including
cuprates and iron-based superconductors that have higher transition
temperatures and are desirable in device applications. | 2105.05456v1 |
2021-07-01 | Dopant-segregation to grain boundaries controls electrical conductivity of n-type NbCo(Pt)Sn half-Heusler alloy mediating thermoelectric performance | Science-driven design of future thermoelectric materials requires a deep
understanding of the fundamental relationships between microstructure and
transport properties. Grain boundaries in polycrystalline materials influence
the thermoelectric performance through the scattering of phonons or the
trapping of electrons due to space-charge effects. Yet, the current lack of
careful investigations on grain boundary-associated features hinders further
optimization of properties. Here, we study n-type NbCo1-xPtxSn half-Heusler
alloys, which were synthesized by ball milling and spark plasma sintering
(SPS). Post-SPS annealing was performed on one sample, leading to improved
low-temperature electrical conductivity. The microstructure of both samples was
examined by electron microscopy and atom probe tomography. The grain size
increases from ~230 nm to ~2.38 {\mu}m upon annealing. Pt is found within
grains and at grain boundaries, where it locally reduces the resistivity, as
assessed by in situ four-point-probe electrical conductivity measurement. Our
work showcases the correlation between microstructure and electrical
conductivity, providing opportunities for future microstructural optimization
by tuning the chemical composition at grain boundaries. | 2107.00326v1 |
2021-07-10 | Effect of characteristic size on the collective phonon transport in crystalline GeTe | We study the effect of characteristic size variation on the phonon thermal
transport in crystalline GeTe for a wide range of temperatures using the
first-principles density-functional method coupled with the kinetic collective
model approach. The characteristic size dependence of phonon thermal transport
reveals an intriguing collective phonon transport regime, located in between
the ballistic and the diffusive transport regimes. Therefore, systematic
investigations have been carried out to describe the signatures of phonon
hydrodynamics via the competitive effects between grain size and temperature. A
characteristic nonlocal length associated with phonon hydrodynamics and a heat
wave propagation length has been extracted. The connections between phonon
hydrodynamics and these length scales are discussed in terms of the Knudsen
number. Further, the scaling relation of thermal conductivity as a function of
characteristic size in the intermediate size range emerges as a crucial
indicator of the strength of the hydrodynamic behavior. A ratio concerning
normal and resistive scattering rates has been employed to understand these
different scaling relations, which seems to control the strength and prominent
visibility of the collective phonon transport in GeTe. This systematic
investigation emphasizes the importance of the competitive effects between
temperature and characteristic size on phonon hydrodynamics in GeTe, which can
lead to a better understanding of the generic behavior and consequences of the
phonon hydrodynamics and its controlling parameters in low-thermal conductivity
materials. | 2107.04731v1 |
2021-07-23 | Few-layer antimonene electrical properties | Antimonene -- a single layer of antimony atoms -- and its few layer forms are
among the latest additions to the 2D mono-elemental materials family. Numerous
predictions and experimental evidence of its remarkable properties including
(opto)electronic, energetic or biomedical, among others, together with its
robustness under ambient conditions, have attracted the attention of the
scientific community. However, experimental evidence of its electrical
properties is still lacking. Here, we characterized the electronic properties
of mechanically exfoliated flakes of few-layer (FL) antimonene of different
thicknesses (~ 2-40 nm) through photoemission electron microscopy, kelvin probe
force microscopy and transport measurements, which allows us to estimate a
sheet resistance of ~ 1200 $\Omega$sq$^{-1}$ and a mobility of ~ 150
cm$^2$V$^{-1}$s$^{-1}$ in ambient conditions, independent of the flake
thickness. Alternatively, our theoretical calculations indicate that
topologically protected surface states (TPSS) should play a key role in the
electronic properties of FL antimonene, which supports our experimental
findings. We anticipate our work will trigger further experimental studies on
TPSS in FL antimonene thanks to its simple structure and significant stability
in ambient environments. | 2107.11218v1 |
2021-07-26 | Pressure-driven electronic and structural phase transition in intrinsic magnetic topological insulator MnSb2Te4 | Intrinsic magnetic topological insulators provide an ideal platform to
achieve various exciting physical phenomena. However, this kind of materials
and related research are still very rare. In this work, we reported the
electronic and structural phase transitions in intrinsic magnetic topological
insulator MnSb2Te4 driven by hydrostatic pressure. Electric transport results
revealed that temperature dependent resistance showed a minimum value near
short-range antiferromagnetic (AFM) ordering temperature TN', the TN' values
decline with pressure, and the AFM ordering was strongly suppressed near 10 GPa
and was not visible above 11.5 GPa. The intensity of three Raman vibration
modes in MnSb2Te4 declined quickly starting from 7.5 GPa and these modes become
undetectable above 9 GPa, suggesting possible insulator-metal transition, which
is further confirmed by theoretical calculation. In situ x-ray diffraction
(XRD) demonstrated that an extra diffraction peak appears near 9.1 GPa and
MnSb2Te4 started to enter an amorphous-like state above 16.6 GPa, suggesting
the structural origin of suppressed AFM ordering and metallization. This work
has demonstrated the correlation among interlayer interaction, magnetic
ordering, and electric behavior, which could be benefit for the understanding
of the fundamental properties of this kind of materials and devices. | 2107.12071v1 |
2021-07-26 | Nitrogen-doped graphene based triboelectric nanogenerators | Harvesting all sources of available clean energy is an essential strategy to
contribute to healing current dependence on non-sustainable energy sources.
Recently, triboelectric nanogenerators (TENGs) have gained visibility as new
mechanical energy harvester offering a valid alternative to batteries, being
particularly suitable for portable devices. Here, the increased capacitance of
a few-layer graphene-based electrode is obtained by incorporating
nitrogen-doped graphene (N_graphene), enabling a 3_fold enhancement in TENGs
power output. The dependence of TENGs performance on the electronic properties
of different N_graphene types, varying in the doping concentration and in the
relative content of N-pyridinic and N-graphitic sites is investigated. These
sites have different electron affinities, and synergistically contribute to the
variation of the capacitive and resistive properties of N-graphene and
consequently, TENG performance. It is demonstrated that the power enhancement
of the TENG occurs when the N_graphene, an n-semiconductor, is interfaced
between the positive triboelectric material and the electrode, while a
deterioration of the electrical performance is observed when it is placed at
the interface with the negative triboelectric material. This behavior is
explained in terms of the dependence of N_graphene quantum capacitance on the
electrode chemical potential which shifts according to the opposite
polarization induced at the two electrodes upon triboelectrification. | 2107.12114v1 |
2021-09-19 | Float, borosilicate and tellurites as cover glasses in Si photovoltaics: optical properties and performances under sunlight | One of the most significant materials in a solar panel is the glass, which
provides transparency, UV protection as well as mechanical and chemical
resistance. In this work, we describe the production of prototypes of four
solar modules made using borosilicate, zinc-tellurite, Pr$^{3+}$ doped
zinc-tellurite, and float glass as cover materials. The performance of these
prototypes was evaluated under a solar simulator, and a device was developed to
monitor all prototypes under real conditions. A comparison between indoor and
outdoor measurements shows that outdoor results are fundamental to evaluate the
performance of modified solar modules as the ones considered in this study. In
addition, we demonstrate the fundamental role played by the refractive index of
cover glasses in the performance of the prototypes, and discuss how this
feature could be explored to achieve enhanced devices, as well as other
benefits that may arise from this field of research. | 2109.09116v3 |
2021-09-29 | Mechanical Properties and Nanostructure of Monolithic Zeolitic Imidazolate Frameworks: A Nanoindentation, Nanospectroscopy and Finite-Element Study | The synthesis of metal-organic frameworks (MOFs) in a monolithic morphology
is a promising way to achieve the transition of this class of materials from
academia to industrial applications. The sol-gel process has been widely
employed to produce MOF monoliths. It is relatively cheap and simple compared
to other techniques (e.g., mechanical densification) and moreover it allows to
produce "pure" monoliths, i.e., without the need of using binders or templates
that could affect the functional properties of the MOF. Understanding the
mechanical properties of these monoliths is crucial for their transit to
practical applications. We studied the mechanical behavior of two zeolitic
imidazolate frameworks (ZIF-8 and ZIF-71) by means of instrumented
nanoindentation and atomic force microscopy (AFM). Tip Force Microscopy (TFM),
an extension of AFM, was used to reveal the surface nanostructure of the
monoliths. We employed finite-element (FE) simulations alongside the
experiments, to establish a suitable constitutive model and determine an
improved estimate of the yield stress of ZIF monoliths. NanoFTIR was
subsequently used to pinpoint local structural alteration of the framework in
the contact area. The combination of TFM, FE simulations, and nanoFTIR enabled
us to identify the mechanical deformation mechanisms in monolithic ZIF
materials: grain boundaries sliding is dominating at low stresses, then
breakage of chemical bonds and a partial failure of the framework occurs,
eventually leading to a densification of porous framework at the contact zone.
Finally, we measured the fracture toughness using a cube corner indenter to
study the resistance of monoliths against cracking failure. | 2109.14670v1 |
2021-09-30 | Electronic and Thermal Properties of $\text{GeTe/Sb}_{2}\text{Te}_{3}$ Superlattices by ab-initio Approach: Impact of Van der Waals Gaps on Vertical Lattice Thermal Conductivity | In the last decade, several works have focused on exploring the material and
electrical properties of $\text{GeTe/Sb}_{2}\text{Te}_{3}$ superlattices (SLs)
in particular because of some first device implementations demonstrating
interesting performances such as fast switching speed, low energy consumption,
and non-volatility. However, the switching mechanism in such SL-based devices
remains under debate. In this work, we investigate the prototype
$\text{GeTe/Sb}_{2}\text{Te}_{3}$ SLs, to analyze fundamentally their
electronic and thermal properties by ab initio methods. We find that the
resistive contrast is small among the different phases of
$\text{GeTe/Sb}_{2}\text{Te}_{3}$ because of a small electronic gap (about 0.1
eV) and a consequent semi-metallic-like behavior. At the same time the
out-of-plane lattice thermal conductivity is rather small, while varying up to
four times among the different phases, from 0.11 to 0.45 W/m$^{-1}$K$^{-1}$,
intimately related to the number of Van der Waals (VdW) gaps in a unit block.
Such findings confirm the importance of the thermal improvement achievable in
$\text{GeTe/Sb}_{2}\text{Te}_{3}$ super-lattices devices, highlighting the
impact of the material stacking and the role of VdW gaps on the thermal
engineering of the Phase-Change Memory cell. | 2109.15168v2 |
2021-10-01 | A general isogeometric finite element formulation for rotation-free shells with in-plane bending of embedded fibers | This paper presents a general, nonlinear isogeometric finite element
formulation for rotation-free shells with embedded fibers that captures
anisotropy in stretching, shearing, twisting and bending -- both in-plane and
out-of-plane. These capabilities allow for the simulation of large sheets of
heterogeneous and fibrous materials either with or without matrix, such as
textiles, composites, and pantographic structures. The work is a computational
extension of our earlier theoretical work [1] that extends existing
Kirchhoff-Love shell theory to incorporate the in-plane bending resistance of
initially straight or curved fibers. The formulation requires only displacement
degrees-of-freedom to capture all mentioned modes of deformation. To this end,
isogeometric shape functions are used in order to satisfy the required
$C^1$-continuity for bending across element boundaries. The proposed
formulation can admit a wide range of material models, such as surface
hyperelasticity that does not require any explicit thickness integration. To
deal with possible material instability due to fiber compression, a
stabilization scheme is added. Several benchmark examples are used to
demonstrate the robustness and accuracy of the proposed computational
formulation. | 2110.00460v3 |
2021-10-15 | Ground state of Ce$_{3}$Bi$_{4}$Pd$_{3}$ unraveled by hydrostatic pressure | Noncentrosymmetric Ce$_{3}$Bi$_{4}$Pd$_{3}$ has attracted a lot of attention
as a candidate for strongly correlated topological material, yet its
experimental ground state remains a matter of contention. Two conflicting
scenarios have emerged from a comparison to prototypical Kondo insulator
Ce$_{3}$Bi$_{4}$Pt$_{3}$: either Ce$_{3}$Bi$_{4}$Pd$_{3}$ is a
spin-orbit-driven topological semimetal or a Kondo insulator with smaller Kondo
coupling than its Pt counterpart. Here we determine the ground state of
Ce$_{3}$Bi$_{4}$Pd$_{3}$ via electrical resistivity measurements under
hydrostatic pressure, which is a clean symmetry-preserving tuning parameter
that increases hybridization but virtually preserves spin-orbit coupling.
Ce$_{3}$Bi$_{4}$Pd$_{3}$ becomes more insulating under pressure, which is a
signature of Ce-based Kondo insulating materials. Its small zero-pressure gap
increases quadratically with pressure, similar to the behavior observed in the
series Ce$_{3}$Bi$_{4}$(Pt$_{1-x}$Pd$_{x}$)$_{3}$, which indicates that Pt
substitution and applied pressure have a similar effect. Our result not only
demonstrates that Kondo coupling, rather than spin-orbit coupling, is the main
tuning parameter in this class of materials, but it also establishes that
Ce$_{3}$Bi$_{4}$Pd$_{3}$ has a narrow-gap Kondo insulating ground state. | 2110.08230v1 |
2021-11-16 | Interpreting Angle Dependent Magnetoresistance in Layered Materials: Application to Cuprates | The evolution of the low temperature electronic structure of the cuprate
metals from the overdoped to the underdoped side has recently been addressed
through Angle-Dependant Magneto-Resistance (ADMR) experiments in
La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$. The results show a striking difference
between hole dopings $p = 0.24$ and $p = 0.21$ which lie on either side of a
putative quantum critical point at intermediate $p$. Motivated by this, we here
study the theory of ADMR in correlated layered materials, paying special
attention to the role of angle dependent quasiparticle weights
$Z_{\mathbf{k}}$. Such a $Z_{\mathbf{k}}$ is expected to characterize a number
of popular models of the cuprate materials, particularly when underdoped.
Further, in the limit of weak interlayer hopping the quasiparticle weight will
affect the $c$-axis transport measured in ADMR experiments. We show that proper
inclusion of the quasiparticle weight does not support an interpretation of the
data in terms of a $(\pi, \pi)$ spin density wave ordered state, in agreement
with the lack of direct evidence for such order. We show that a simple model of
Fermi surface reconfiguring across a van Hove point captures many of the
striking differences seen between $p = 0.21$ and $p = 0.24$. We comment on why
such a model may be appropriate for interpreting the ADMR data, despite having
a large Fermi surface at $p = 0.21$, seemingly in contradiction with other
evidence for a small Fermi surafce at that doping level. | 2111.08740v2 |
2022-01-06 | Optical properties of Au-Hf thin films | The optical properties of thin films of intermetallic Au$_{3}$Hf were
experimentally investigated for the first time, which display clear plasmonic
properties in the optical and near infrared region with negative permittivity.
In contrast to similar alloys, such as films of Au$_{3}$Zr, the films express
more negative $\epsilon'$ values and lower $\epsilon''$ values across most of
the wavelengths (370-1570 nm) investigated. The Au$_{3}$Hf films were
fabricated by DC magnetron sputtering at a range of deposition temperatures,
from room temperature to 415$^{o}$C, and annealed at different vacuum levels.
The films mostly formed as a combination of Au$_{3}$Hf, Au$_{2}$Hf and
Au$_{4}$Hf phases when deposited below 400$^{o}$C, and exclusively Au$_{3}$Hf
phase at above 400$^{o}$C, indicating key conditions for isolating this phase.
The films were stable when annealed at 10$^{-8}$ Torr, but when annealed again
at 10$^{-6}$ Torr the films oxidised and changed into a mix of Au- Hf phases,
suggesting resistance to oxidization may be an issue for un-encapsulated
applications at elevated temperatures. | 2201.02163v1 |
2022-03-31 | Thermally enhanced photoluminescence and temperature sensing properties of Sc$_2$W$_3$O$_{12}$:Eu$^{3+}$ phosphors | Currently,lanthanide ions doped luminescence materials applying as optical
thermometers have arose much concern. Basing on the different responses of two
emissions to temperature, the fluorescence intensity ratio (FIR) technique can
be executed and further estimate the sensitivities to assess the optical
thermometry performances. In this study, we introduce different doping
concentrations of Eu$^{3+}$ ions into negative expansion material
Sc$_2$W$_3$O$_{12}$:Eu$^{3+}$, accessing to the thermal enhanced luminescence
from 373 to 548 K, and investigate the temperature sensing properties in
detail. All samples exhibit good thermally enhanced luminescence behavior. The
emission intensity of Sc$_2$W$_3$O$_{12}$: 6 mol% Eu$^{3+}$ phosphors reaches
at 147.81% of initial intensity at 473 K. As the Eu doping concentration
increases, the resistance of the samples to thermal quenching decreases. The
FIR technique based on the transitions 5D0-7F1 (592 nm) and 5D0-7F2 (613 nm) of
Eu$^{3+}$ ions demonstrate a maximum relative temperature sensitivity of 3.063%
K-1 at 298 K for Sc$_2$W$_3$O$_{12}$:Eu$^{3+}$: 6 mol% Eu$^{3+}$ phosphors. The
sensitivity of sample decreases with the increase of Eu$^{3+}$ concentration.
Benefiting from the thermal enhanced luminescence performance and good
temperature sensing properties, the Sc$_2$W$_3$O$_{12}$:Eu$^{3+}$: Eu$^{3+}$
phosphors can be applies as optical thermometers. | 2203.16888v1 |
2022-04-19 | Cell barrier characterization in transwell inserts by electrical impedance spectroscopy | We describe an impedance-based method for cell barrier integrity testing. A
four-electrode electrical impedance spectroscopy (EIS) setup can be realized by
simply connecting a commercial chopstick-like electrode (STX-1) to a
potentiostat allowing monitoring cell barriers cultivated in transwell inserts.
Subsequent electric circuit modeling of the electrical impedance results the
capacitive properties of the barrier next to the well-known transepithelial
electrical resistance (TEER). The versatility of the new method was analyzed by
the EIS analysis of a Caco-2 monolayer in response to (a) different membrane
coating materials, (b) two different permeability enhancers ethylene
glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and saponin,
and (c) sonoporation. For the different membrane coating materials, the TEERs
of the standard and new protocol coincide and increase during cultivation,
while the capacitance shows a distinct maximum for three different surface
materials (no coating, Matrigel, and collagen I). The permeability enhancers
cause a decline in the TEER value, but only saponin alters the capacitance of
the cell layer by two orders of magnitude. Hence, cell layer capacitance and
TEER represent two independent properties characterizing the monolayer. The use
of commercial chopstick-like electrodes to access the impedance of a barrier
cultivated in transwell inserts enables remarkable insight into the behavior of
the cellular barrier with no extra work for the researcher. This simple method
could evolve into a standard protocol used in cell barrier research. | 2204.08886v1 |
2022-04-25 | Substrate-Dependence of Monolayer MoS$_2$ Thermal Conductivity and Thermal Boundary Conductance | The thermal properties of two-dimensional (2D) materials, like MoS$_2$, are
known to be affected by interactions with their environment, but this has
primarily been studied only with SiO$_2$ substrates. Here, we compare the
thermal conductivity (TC) and thermal boundary conductance (TBC) of monolayer
MoS$_2$ on amorphous (a-) and crystalline (c-) SiO$_2$, AlN, Al$_2$O$_3$, and
$\textit{h}$-BN monolayers using molecular dynamics. The room temperature TC of
MoS$_2$ is ~38 Wm$^{-1}$K$^{-1}$ on amorphous substrates and up to ~68
Wm$^{-1}$K$^{-1}$ on crystalline substrates, with most of the difference due to
substrate interactions with long-wavelength MoS$_2$ phonons (< 2 THz). An
$\textit{h}$-BN monolayer used as a buffer between MoS$_2$ and the substrate
causes the MoS$_2$ TC to increase by up to 50%. Length-dependent calculations
reveal TC size effects below ~2 $\mu$m and show that the MoS$_2$ TC is size-
but not substrate-limited below ~100 nm. We also find that the TBC of MoS$_2$
with c-Al$_2$O$_3$ is over twice that with c-AlN despite a similar MoS$_2$ TC
on both, indicating that the TC and TBC could be tuned independently. Finally,
we compare the thermal resistance of MoS$_2$ transistors on all substrates to
show that MoS$_2$ TBC is the most important parameter for heat removal for
long-channel (> 150 nm) devices, while TBC and TC are equally important for
short channels. This work provides important insights for electro-thermal
applications of 2D materials on various substrates. | 2204.11381v1 |
2022-05-23 | Spatial stress correlations in strong colloidal gel | In this work, we systematically investigate for the first time the nature of
stress correlations in soft colloidal gel materials which support tensile and
compressive forces as well as finite rolling torque, as a function of system
pressure. Similar to previous studies on frictional granular matter with only
compressive forces and without any rolling torque, the full stress
autocorrelation matrix is dictated by the pressure and torque autocorrelations
due to mechanical balance and material isotropy constraints. Surprisingly, it
is observed that the gel materials do not behave as a normal elastic solid
close to the gel point as assumed loosely in the literature because the real
space pressure fluctuations decay slower than the normal. We also demonstrate
that at low pressure the fractal like structural correlation determines the
pressure fluctuations and this is manifested in the real space in terms of
inhomogeneous and anisotropic force networks formed due to large voids. Far
away from the gel point, as the voids collapse under compression, the force
chain network becomes homogeneous and isotropic and the pressure fluctuations
become normal leading to normal elastic decay at long range, behaving similar
to frictionless granular matter and glass. We also observe that the torque
autocorrelation is not hyperuniform in the presence of rolling resistance close
to the gel point. Furthermore, we link the abnormal pressure fluctuations to
the non-hyperuniform behaviour of the system with respect to the local packing
fraction fluctuations, thus relating the deviations from the normal elastic
behaviour across various non-equilibrium systems under a common framework. | 2205.11575v1 |
2022-07-06 | Elastoresistivity in the incommensurate charge density wave phase of BaNi$_{\textrm{2}}$(As$_{\textrm{1-x}}$P$_{\textrm{x}}$)$_{\textrm{2}}$ | Electronic nematicity, the breaking of the crystal lattice rotational
symmetry by the electronic fluid, is a fascinating quantum state of matter.
Recently, BaNi$_2$As$_2$ has emerged as a promising candidate for a novel type
of nematicity triggered by charge fluctuations. In this work, we scrutinize the
electronic nematicity of BaNi$_2$(As$_{1-x}$P$_x$)$_2$ with $0 \leq x \leq
0.10$ using electronic transport measurements under strain. We report a large
$B_{1g}$ elastoresistance coefficient that is maximized at a temperature
slightly higher than the first-order triclinic transition, and that corresponds
to the recently discovered tetragonal-to-orthorhombic transition. The reported
elastoresistance does not follow the typical Curie-Weiss form observed in
iron-based superconductors but has a much sharper temperature dependence with a
finite elastoresistance onsetting only together with a strong enhancement of
the incommensurate charge density wave of the material. Consequently, the
$B_{1g}$ elastoresistance and the associated orthorhombic distortion appears
here as a property of this incommensurate charge density wave. Finally, we
report and track the hysteretic behavior seen in the resistance versus strain
sweeps and interpret its origin as the pinning of orthorhombic domains. Our
results revise the understanding of the interplay between nematicity, charge
density waves and structural distortions in this material. | 2207.02462v2 |
2022-07-13 | Multi-state data storage in a two-dimensional stripy antiferromagnet implemented by magnetoelectric effect | A promising approach to the next generation of low-power, functional, and
energy-efficient electronics relies on novel materials with coupled magnetic
and electric degrees of freedom. In particular, stripy antiferromagnets often
exhibit broken crystal and magnetic symmetries, which may bring about the
magnetoelectric (ME) effect and enable the manipulation of intriguing
properties and functionalities by electrical means. The demand for expanding
the boundaries of data storage and processing technologies has led to the
development of spintronics toward two-dimensional (2D) platforms. This work
reports the ME effect in the 2D stripy antiferromagnetic insulator CrOCl down
to a single layer. By measuring the tunneling resistance of CrOCl on the
parameter space of temperature, magnetic field, and applied voltage, we
verified the ME coupling down to the 2D limit and unraveled its mechanism.
Utilizing the multi-stable states and ME coupling at magnetic phase
transitions, we realize multi-state data storage in the tunneling devices. Our
work not only advances the fundamental understanding of spin-charge coupling
but also demonstrates the great potential of 2D antiferromagnetic materials to
deliver devices and circuits beyond the traditional binary operations. | 2207.05954v1 |
2022-08-09 | Discovery of Superconductivity in Nb$_4$SiSb$_2$ with a V$_4$SiSb$_2$-Type Structure and Implications of Interstitial Doping on its Physical Properties | We report on the discovery, structural analysis, and the physical properties
of Nb$_4$SiSb$_2$ -- a hitherto unknown compound crystallizing in the
V$_4$SiSb$_2$-type structure with the tetragonal space group $I4/mcm$ and unit
cell parameters $a$ = 10.3638(2) $\mathring{\mathrm{A}}$ and $c$ = 4.9151(2)
$\mathring{\mathrm{A}}$. We find Nb$_4$SiSb$_2$ to be a metal undergoing a
transition to a superconducting state at a critical temperature of $T_{\rm c}
\approx$ 1.6 K. The bulk nature of the superconductivity in this material is
confirmed by the observation of a well defined discontinuity in specific heat
with a normalized specific heat jump of $\Delta C(T_{\rm c})/\gamma T_{\rm c} =
1.33\, {\rm mJ}\, {\rm mol}^{-1}\, {\rm K}^{-2}$. We find that for
Nb$_4$SiSb$_2$, the unoccupied sites on the $4b$ Wyckoff position can be
partially occupied with Cu, Pd, or Pt. Low-temperature resistivity measurements
show transitions to superconductivity for all three compounds at $T_{\rm c}
\approx\, 1.2\, {\rm K}$ for Nb$_4$Cu$_{0.2}$SiSb$_2$, and $T_{\rm c} \approx\,
0.8\, {\rm K}$ for Nb$_4$Pd$_{0.2}$SiSb$_2$ as well as for
Nb$_4$Pt$_{0.14}$SiSb$_2$. The addition of electron-donor atoms into these void
positions, henceforth, lowers the superconducting transition temperature in
comparison to the parent compound. | 2208.04834v1 |
2022-09-07 | Ultrahigh breakdown current density of van der Waals One Dimensional $\mathrm{PdBr_2}$ | One-dimensional (1D) van der Waals (vdW) materials offer nearly defect-free
strands as channel material in the field-effect transistor (FET) devices and
probably, a better interconnect than conventional copper with higher current
density and resistance to electro-migration with sustainable down-scaling. We
report a new halide based "truly" 1D few-chain atomic thread, PdBr$_2$,
isolable from its bulk which crystallizes in a monoclinic space group C2/c.
Liquid phase exfoliated nanowires with mean length (20$\pm$1)$\mu$m transferred
onto SiO$_2$/Si wafer with a maximum aspect ratio of 5000 confirms the lower
cleavage energy perpendicular to chain direction. Moreover, an isolated
nanowire can also sustain current density of 200 MA/cm$^\mathrm{2}$ which is
atleast one-order higher than typical copper interconnects. However, local
transport measurement via conducting atomic force microscopy (CAFM) tip along
the cross direction of the single chain records a much lower current density
due to the anisotropic electronic band structure. While 1D nature of the
nanoobject can be linked with non-trivial collective quantum behavior, vdW
nature could be beneficial for the new pathways in interconnect fabrication
strategy with better control of placement in an integrated circuit (IC). | 2209.03296v6 |
2023-01-27 | A ferromagnetic Eu-Pt surface compound grown below hexagonal boron nitride | One of the fundamental applications for monolayer-thick 2D materials is their
use as protective layers of metal surfaces and in-situ intercalated reactive
materials in ambient conditions. Here we investigate the structural,
electronic, and magnetic properties, as well as the chemical stability in air
of a very reactive metal, Europium, after intercalation between a hexagonal
boron nitride (hBN) layer and a Pt substrate. We demonstrate that Eu
intercalation leads to a hBN-covered ferromagnetic EuPt$_2$ surface alloy with
divalent Eu$^{2+}$ atoms at the interface. We expose the system to ambient
conditions and find a partial conservation of the di-valent signal and hence
the Eu-Pt interface. The use of a curved Pt substrate allows us to explore the
changes in the Eu valence state and the ambient pressure protection at
different substrate planes. The interfacial EuPt$_2$ surface alloy formation
remains the same, but the resistance of the protecting hBN layer to ambient
conditions is reduced, likely due to a rougher surface and a more discontinuous
hBN coating. | 2301.11837v2 |
2023-01-31 | Elastic solids with strain-gradient elastic boundary surfaces | Recent works have shown that in contrast to classical linear elastic fracture
mechanics, endowing crack fronts in a brittle solid with Steigmann-Ogden
surface elasticity yields a model that predicts bounded strains at the crack
tips for plane-strain problems. However, a logarithmic singularity is still
present in general for anti-plane shear (mode-III fracture) even when
Steigmann-Ogden surface elasticity is incorporated. Motivated by obtaining a
model of brittle fracture capable of predicting bounded strains for all modes
of loading, we formulate an exact general theory of a bulk solid containing a
boundary surface with strain-gradient surface elasticity. For planar reference
surfaces, the form of surface elasticity reduces to that introduced by Hilgers
and Pipkin, and when the surface energy is independent of the surface gradient
of the stretching, the theory reduces to that of Steigmann and Ogden. We give a
full discussion of material symmetry using Murdoch and Cohen's extension of
Noll's theory. We present a model quadratic surface energy that incorporates
resistance to geodesic distortion, satisfies strong ellipticity, and requires
the same material constants found in the Steigmann-Ogden theory. Finally, we
derive and apply the linearized theory to mode-III fracture in an infinite
plate. We prove that there always exists a unique classical solution to the
governing integro-differential equation, and in contrast to using
Steigmann-Ogden surface elasticity, our model is consistent with the
linearization assumption in predicting finite strains at the crack tips. | 2301.13744v2 |
2023-02-10 | Cryogenic Characteristics of Graphene Composites -- Evolution from Thermal Conductors to Thermal Insulators | The development of cryogenic semiconductor electronics and superconducting
quantum computing requires composite materials that can provide both thermal
conduction and thermal insulation. We demonstrated that at cryogenic
temperatures, the thermal conductivity of graphene composites can be both
higher and lower than that of the reference pristine epoxy, depending on the
graphene filler loading and temperature. There exists a well-defined cross-over
temperature - above it, the thermal conductivity of composites increases with
the addition of graphene; below it, the thermal conductivity decreases with the
addition of graphene. The counter-intuitive trend was explained by the
specificity of heat conduction at low temperatures: graphene fillers can serve
as, both, the scattering centers for phonons in the matrix material and as the
conduits of heat. We offer a physical model that explains the experimental
trends by the increasing effect of the thermal boundary resistance at cryogenic
temperatures and the anomalous thermal percolation threshold, which becomes
temperature dependent. The obtained results suggest the possibility of using
graphene composites for, both, removing the heat and thermally insulating
components at cryogenic temperatures - a capability important for quantum
computing and cryogenically cooled conventional electronics. | 2302.05524v1 |
2023-02-23 | The influence of crystalline electric field on the magnetic properties of CeCd3X3 (X = P and As) | CeCd$_3$P$_3$ and CeCd$_3$As$_3$ compounds adopt the hexagonal
ScAl$_3$C$_3$-type structure, where magnetic Ce ions on a triangular lattice
order antiferromagnetically below $T_\text{N} \sim$0.42~K. Their crystalline
electric field (CEF) level scheme has been determined by fitting magnetic
susceptibility curves, magnetization isotherms, and Schottky anomalies in
specific heat. The calculated results, incorporating the CEF excitation, Zeeman
splitting, and molecular field, are in good agreement with the experimental
data. The CEF model, with Ce$^{3+}$ ions in a trigonal symmetry, explains the
strong easy-plane magnetic anisotropy that has been observed in this family of
materials. A detailed examination of the CEF parameters suggests that the
fourth order CEF parameter $B_{4}^{3}$ is responsible for the strong CEF
induced magnetocrystalline anisotropy, with a large $ab$-plane moment and a
small $c$-axis moment. The reliability of our CEF analysis is assessed by
comparing the current study with earlier reports of CeCd$_{3}$As$_{3}$. For
both CeCd$_{3}X_{3}$ ($X$ = P and As) compounds, less than 40 \% of $R\ln(2)$
magnetic entropy is recovered by $T_\text{N}$ and full $R\ln(2)$ entropy is
achieved at the Weiss temperature $\theta_{p}$. Although the observed magnetic
entropy is reminiscent of delocalized 4$f$-electron magnetism with significant
Kondo screening, the electrical resistivity of these compounds follows a
typical metallic behavior. Measurements of thermoelectric power further
validate the absence of Kondo contribution in CeCd$_{3}X_{3}$. | 2302.11714v1 |
2023-03-08 | Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa | Spin semimetals are amongst the most recently discovered new class of
spintronic materials, which exhibit a band gap in one spin channel and
semimetallic feature in the other, thus facilitating tunable spin transport.
Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along
with giant coercivity and spin-valve characteristics using a combined
experimental and theoretical study. The alloy crystallizes in an inverse
Heusler structure (without any martensitic transition) with a para- to
ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant
coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient,
relatively low magnitude and weak temperture dependance of electrical
resistivity suggest the semimetallic character of the alloy. This is further
supported by our specific heat measurement. Magnetoresistance (MR) confirms an
irreversible nature (with its magnitude $\sim$1\%) along with a change of sign
across the magnetic transition indicating the potentiality of Mn$_2$IrGa in
magnetic switching applications. In addition, asymmetric nature of MR in the
positive and negative field cycles is indicative of spin-valve characteristics.
Our ab-initio calculations confirm the inverse Heusler structure with
ferrimagnetic ordering to be the lowest energy state, with a saturation
magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic
axis with considerable magneto-crystalline anisotropy energy. A large positive
Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall
conductivity ($\sim$-180 S/cm). | 2303.04649v2 |
2023-03-31 | Chiral anomaly and positive longitudinal magnetoresistance in the type-II Dirac semimetals $\it{A}_x$PdTe$_2$ (\textit{A} = Cu, Ag) | The Planar Hall effect (PHE) in topological materials has been a subject of
great interest in recent years. Generally, it is understood to originate from
the chiral-anomaly (CA) induced charge pumping between doubly degenerate Weyl
nodes. However, the occurrence of PHE in the materials with positive and
anisotropic orbital magnetoresistance has raised questions about CA being the
sole origin of this effect. Here, we report the PHE, magnetoresistance, and
thermal transport properties (Seebeck and Nernst coefficients) on the Ag
intercalated PdTe$_2$. We observe positive longitudinal magnetoresistance, the
linear field dependence of the amplitude of PHE, and a prolate pattern in the
parametric plots. The planar Hall resistivity and anisotropic magnetoresitance
fits well with theoretical study of CA being the origin of PHE. So, our
observations are consistent with Weyl physics dominating the PHE in PdTe$_2$,
Cu$_{0.05}$PdTe$_2$, and Ag$_{0.05}$PdTe$_2$. We further support our data with
a theoretical model that reproduces the qualitative experimental features. In
addition, we have calculated the Seebeck ($\it{S}$) and Nernst ($\nu$)
coefficients for PdTe$_2$ and Cu and Ag intercalated compounds. The estimated
values of Fermi energy for the Cu and Ag intercalated compounds are
respectively two times and three times larger than that of PdTe$_2$. | 2303.18075v2 |
2023-07-11 | Microstructure of a spark-plasma-sintered Fe2VAl-type Heusler alloy for thermoelectric application | The influence of microstructure on thermoelectricity is increasingly
recognized. Approaches for microstructural engineering can hence be exploited
to enhance thermoelectric performance, particularly through manipulating
crystalline defects, their structure, and composition. Here, we focus on a
full-Heusler Fe2VAl-based compound that is one of the most promising
thermoelectric materials containing only Earth-abundant, non-toxic elements. A
Fe2VTa0.05Al0.95 cast alloy was atomized under a nitrogen-rich atmosphere to
induce nitride precipitation. Nanometer- to micrometer-scale microstructural
investigations by advanced scanning electron microscopy and atom probe
tomography (APT) are performed on the powder first and then on the material
consolidated by spark-plasma sintering for an increasing time. APT reveals an
unexpected pick-up of additional impurities from atomization, namely W and Mo.
The microstructure is then correlated with local and global measurements of the
thermoelectric properties. At grain boundaries, segregation and precipitation
locally reduce the electrical resistivity, as evidenced by in-situ four-point
probe measurements. The final microstructure contains a hierarchy of structural
defects, including individual point defects, dislocations, grain boundaries,
and precipitates, that allow for a strong decrease in thermal conductivity. In
combination, these effects provide an appreciable increase in thermoelectric
performance. | 2307.05051v1 |
2023-08-15 | Phases and magnetism at the microscale in compounds containing nominal Pb10-xCux(PO4)6O | Achieving superconductivity at room temperature could lead to substantial
advancements in industry and technology. Recently, a compound known as Cu-doped
lead-apatite, Pb10-xCux(PO4)6O (0.9 < x < 1.1), referred to as "LK-99", has
been reported to exhibit unusual electrical and magnetic behaviors that appear
to resemble a superconducting transition above room temperature. In this work
we collected multiphase samples containing the nominal Pb10-xCux(PO4)6O phase
(no superconductivity observed in our measured samples), synthesized by three
independent groups, and studied their chemical, magnetic, and electrical
properties at the microscale to overcome difficulties in bulk measurements.
Through the utilization of optical, scanning electron, atomic force, and
scanning diamond nitrogen-vacancy microscopy techniques, we are able to
establish a link between local magnetic properties and specific microscale
chemical phases. Our findings indicate that while the Pb10-xCux(PO4)6O phase
seems to have a mixed magnetism contribution, a significant fraction of the
diamagnetic response can be attributed to Cu-rich regions (e.g., Cu2S derived
from a reagent used in the synthesis). Additionally, our electrical
measurements reveal the phenomenon of current path switch and a change in
resistance states of Cu2S. This provides a potential explanation for the
electrical behavior observed in compounds related to Pb10-xCux(PO4)6O. | 2308.07800v3 |
2023-08-17 | Ferromagnetic and insulating behavior in both half magnetic levitation and non-levitation LK-99 like samples | Finding materials exhibiting superconductivity at room temperature has long
been one of the ultimate goals in physics and material science. Recently,
room-temperature superconducting properties have been claimed in a copper
substituted lead phosphate apatite (Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O, or called
LK-99) [1-3]. Using a similar approach, we have prepared LK-99 like samples and
confirmed the half-levitation behaviors in some small specimens under the
influence of a magnet at room temperature. To examine the magnetic properties
of our samples, we have performed systematic magnetization measurements on the
as-grown LK-99-like samples, including the half-levitated and non-levitated
samples. The magnetization measurements show the coexistence of
soft-ferromagnetic and diamagnetic signals in both half-levitated and
non-levitated samples. The electrical transport measurements on the as-grown
LK-99-like samples including both half-levitated and non-levitated samples show
an insulating behavior characterized by the increasing resistivity with the
decreasing temperature. | 2308.11768v2 |
2023-08-26 | Complex Antiferromagnetic Order in the Metallic Triangular Lattice Compound SmAuAl$_4$Ge$_2$ | The compounds $Ln$AuAl$_4$Ge$_2$ ($Ln$ $=$ lanthanide) form in a structure
that features two-dimensional triangular lattices of $Ln$ ions that are stacked
along the crystalline $c$ axis. Together with crystal electric field effects,
magnetic anisotropy, and electron-mediated spin exchange interactions, this
sets the stage for the emergence of strongly correlated spin and electron
phenomena. Here we investigate SmAuAl$_4$Ge$_2$, which exhibits weak
paramagnetism that strongly deviates from conventional Curie-Weiss behavior.
Complex antiferromagnetic ordering emerges at $T_{\rm{N1}}$ $=$ 13.2 K and
$T_{\rm{N2}}$ $=$ 7.4 K, where heat capacity measurements show that these
transitions are first and second order, respectively. These measurements also
reveal that the Sommerfeld coefficient is not enhanced compared to the
nonmagnetic analog YAuAl$_4$Ge$_2$, consistent with the charge carrier
quasiparticles exhibiting typical Fermi liquid behavior. The
temperature-dependent electrical resistivity follows standard metallic
behavior, but linear magnetoresistance unexpectedly appears within the ordered
state. We compare these results to other $Ln$AuAl$_4$Ge$_2$ materials, which
have already been established as localized $f$-electron magnets that are hosts
for interesting magnetic and electronic phases. From this, SmAuAl$_4$Ge$_2$
emerges as a complex quantum spin metal, inviting further investigations into
its properties and the broader family of related materials. | 2308.13945v2 |
2023-09-23 | Radiation Hardness and Defects Activity in PEA2PbBr4 Single Crystals | Metal halide perovskites (MHPs) are low-temperature processable hybrid
semiconductor materials with exceptional performances that are revolutionizing
the field of optoelectronic devices. Despite their great potential, commercial
deployment is hindered by MHPs lack of stability and durability, mainly
attributed to ions migration and chemical interactions with the device
electrodes. To address these issues, 2D layered MHPs have been investigated as
possible device interlayers or active material substitutes to reduce ion
migration and improve stability. Here we consider the 2D perovskite PEA2PbBr4
that was recently discussed as very promising candidate for X-ray direct
detection. While the increased resilience of PEA2PbBr4 detectors have already
been reported, the physical mechanisms responsible for such improvement
compared to the standard "3D" perovskites are not still fully understood. To
unravel the charge transport process in PEA2PbBr4 crystals thought to underly
the device better performance, we adapted an investigation technique previously
used on highly resistive inorganic semiconductors, called photo induced current
transient spectroscopy (PICTS). We demonstrate that PICTS can detect three
distinct trap states (T1, T2, and T3) with different activation energies, and
that the trap states evolution upon X-ray exposure can explain PEA2PbBr4
superior radiation tolerance and reduced aging effects. Overall, our results
provide essential insights into the stability and electrical characteristics of
2D perovskites and their potential application as reliable and direct X-ray
detectors. | 2309.13355v1 |
2023-09-28 | Extraordinary physical properties of superconducting YBa$_{1.4}$Sr$_{0.6}$Cu$_3$O$_6$Se$_{0.51}$ in a multiphase ceramic material | We report on a novel material obtained by modifying pristine YBCO
superconductor in solid phase synthesis via simultaneous partial substitution
of Ba by Sr and O by Se. Simultaneous application of EDX and EBSD confirmed
that Se atoms indeed enter the crystalline lattice cell. The detailed XRD
analysis further confirmed this conclusion and revealed that the obtained
polycrystalline material contains 5 phases, with the major phase ($>$30\%)
being a cuprate YBa$_{1.4}$Sr$_{0.6}$Cu$_{3}$O$_{6}$Se$% _{0.51}$. The obtained
superconductor demonstrates unique properties, including i) two superconducting
transitions with $T_{c1}\approx$ 35 K (granular surface phase) and
$T_{c2}\approx$ 13 K (bulk granular phase) - this granular phase arrangement
naturally yields the Wohlleben effect; ii) reentrant diamagnetism and resistive
state; iii) strong paramagnetism with Curie-Weiss behavior (% $\theta_{CW}
\approx$ 4 K) and the ferromagnetic phase overruled by superconductivity; iv)
Schottky anomaly visible in the heat capacity data and most likely delivered by
small clusters of magnetic moments. Thorough analysis of the heat capacity data
reveals a strong-coupling $d-$wave pairing in its bulk phase (with $2\Delta
/T_{c}\approx 5$), and, most importantly, a very unusual anomaly in this
cuprate. There are reasons to associate this anomaly with the quantum
criticality observed in traditional cuprate superconductors at much higher
fields (achievable only in certain laboratories). In our case, the fields
leading to quantum criticality are much weaker ($\sim $7-9 T) thus opening
avenues for exploration of the interplay between superconductivity and pair
density waves by the wider research community. | 2309.16814v1 |
2023-12-06 | Nonlinear magnetotransport in MoTe${}_2$ | The shape of the Fermi surface influences many physical phenomena in
materials and a growing interest in how the spin-dependent properties are
related to the fermiology of crystals has surged. Recently, a novel
current-dependent nonlinear magnetoresistance effect, known as bilinear
magnetoelectric resistance (BMR), has been shown to be not only sensitive to
the spin-texture in spin-polarized non-magnetic materials, but also dependent
on the convexity of the Fermi surface in topological semimetals. In this paper,
we show that the temperature dependence of the BMR signal strongly depends on
the crystal axis of the semimetallic MoTe${}_2$. For the a-axis, the amplitude
of the signal remains fairly constant, while for the b-axis it reverses sign at
about 100 K. We calculate the BMR efficiencies at 10 K to be $\chi^{J}_{A} =
(100\pm3)$ nm${}^2$T${}^{-1}$A${}^{-1}$ and $\chi^{J}_{B} = (-364\pm13)$
nm${}^2$T${}^{-1}$A${}^{-1}$ for the a- and b-axis, respectively, and we find
that they are comparable to the efficiencies measured for WTe${}_2$. We use
density functional theory calculations to compute the Fermi surfaces of both
phases at different energy levels and we observe a change in convexity of the
outer-most electron pocket as a function of the Fermi energy. Our results
suggest that the BMR signal is mostly dominated by the change in the Fermi
surface convexity. | 2312.03405v2 |
2024-01-09 | Coexistence of large anomalous Nernst effect and large coercive force in amorphous ferrimagnetic TbCo alloy films | The Anomalous Nernst Effect (ANE) has garnered significant interest for
practical applications, particularly in energy harvesting and heat flux
sensing. For these applications, it is crucial for the module to operate
without an external magnetic field, necessitating a combination of a large ANE
and a substantial coercive force. However, most materials exhibiting a large
ANE typically have a relatively small coercive force. In our research, we have
explored the ANE in amorphous ferrimagnetic TbCo alloy films, noting that the
coercive force peaks at the magnetization compensation point (MCP). We observed
that transverse Seebeck coefficients are amplified with Tb doping, reaching
more than 1.0 uV/K over a wide composition range near the MCP, which is three
times greater than that of pure Co. Our findings indicate that this enhancement
is primarily due to direct conversion, a product of the transverse
thermoelectric component and electrical resistivity. TbCo films present several
significant advantages for practical use: a large ANE, the capability to
exhibit both positive and negative ANE, the flexibility to be deposited on any
substrate due to their amorphous nature, a low thermal conductivity, and a
large coercive force. These attributes make TbCo films a promising material for
advancing ANE-based technologies. | 2401.04445v1 |
2024-02-27 | Percolating Superconductivity in Air-Stable Organic-Ion Intercalated MoS2 | When doped into a certain range of charge carrier concentrations, MoS2
departs from its pristine semiconducting character to become a strongly
correlated material characterized by exotic phenomena such as charge density
waves or superconductivity. However, the required doping levels are typically
achieved using ionic-liquid gating or air-sensitive alkali-ion intercalation,
which are not compatible with standard device fabrication processes. Here, we
report on the emergence of superconductivity and a charge density wave phase in
air-stable organic cation intercalated MoS2 crystals. By selecting two
different molecular guests, we show that these correlated electronic phases
depend dramatically on the intercalated cation, demonstrating the potential of
organic ion intercalation to finely tune the properties of 2D materials.
Moreover, we find that a fully developed zero-resistance state is not reached
in few-nm-thick flakes, indicating the presence of three-dimensional
superconductive paths which are severed by the mechanical exfoliation. We
ascribe this behavior to an inhomogeneous charge carrier distribution, which we
probe at the nanoscale using scanning near-field optical microscopy. Our
results establish organic-ion intercalated MoS2 as a platform to study the
emergence and modulation of correlated electronic phases. | 2402.17328v1 |
2024-03-28 | MaterialsMap: A CALPHAD-Based Tool to Design Composition Pathways through feasibility map for Desired Dissimilar Materials, demonstrated with RSW Joining of Ag-Al-Cu | Assembly of dissimilar metals can be achieved by different methods, for
example, casting, welding, and additive manufacturing (AM). However, undesired
phases formed in liquid-phase assembling processes due to solute segregation
during solidification diminish mechanical and other properties of the processed
parts. In the present work, an open-source software named MaterialsMap, has
been developed based on the CALculation of Phase Diagrams (CALPHAD) approach.
The primary objective of MaterialsMap is to facilitate the design of an optimal
composition pathway for assembling dissimilar alloys with liquid-phases based
on the formation of desired and undesired phases along the pathway. In
MaterialsMap, equilibrium thermodynamic calculations are used to predict
equilibrium phases formed at slow cooling rate, while Scheil-Gulliver
simulations are employed to predict non-equilibrium phases formed during rapid
cooling. By combining these two simulations, MaterialsMap offers a thorough
guide for understanding phase formation in various manufacturing processes,
assisting users in making informed decisions during material selection and
production. As a demonstration of this approach, a compositional pathway was
designed from pure Al to pure Cu through Ag using MaterialsMap. The design was
experimentally verified using resistance spot welding (RSW). | 2403.19084v1 |
2024-04-14 | Role of stress/strain in tailoring the magnetic and transport properties of magnetic thin films and multilayers | Magnetic anisotropy is a fundamental property of magnetic materials that
determines the alignment of the spins along the preferential direction, called
the easy axis of magnetization. Magnetic polycrystalline thin films offer
several advantages over magnetic epitaxial thin films because of fabrication
flexibility, higher coercivity and improved magnetic stability, higher
magnetoresistance (useful in magneto-resistive devices such as magnetic field
sensors and MRAM cells), cost-effectiveness and thermal stability, etc. In the
case of polycrystalline thin films or multilayers, Magneto-crystalline
anisotropy (MCA) is not expected due to the random orientation of grains.
Therefore, understanding the origin of uniaxial magnetic anisotropy (UMA) is
generally difficult and can't be understood in terms of crystal orientation.
The origin of UMA in polycrystalline films is often related to the preparation
conditions and substrate properties. In the present thesis, we have provided
direct in-situ real-time evidence of the stress dependence of magnetic
anisotropy through the multibeam optical stress sensor (MOSS) technique. Also,
we have tuned the magnetic anisotropy in strength and direction using
externally applied stress. To further increase the strength of the magnetic
anisotropy, we have developed a new technique that creates a multilayer using a
single magnetic material through sequential oblique and normal depositions.
This oblique angle deposition technique also helps reduce the penetration of
the top ferromagnetic layer inside the organic semiconductor layer in organic
spin valve structures. We confirm our results through various in-situ (in UHV
and HV) and ex-situ temperature-dependent conventional and unconventional
structural, morphological, and magnetic measurements (both lab-based and
synchrotron-based) that include MOKE, KERR, GIXRD, AFM, RHEED, and GISAXS, etc.
measurements. | 2405.00049v1 |
2024-05-22 | Nuclear quantum effects in structural and elastic properties of cubic silicon carbide | Silicon carbide, a semiconducting material, has gained importance in the
fields of ceramics, electronics, and renewable energy due to its remarkable
hardness and resistance. In this study, we delve into the impact of nuclear
quantum motion, or vibrational mode quantization, on the structural and elastic
properties of 3C-SiC. This aspect, elusive in conventional {\it ab-initio}
calculations, is explored through path-integral molecular dynamics (PIMD)
simulations using an efficient tight-binding (TB) Hamiltonian. This
investigation spans a wide range of temperatures and pressures, including
tensile stress, adeptly addressing the quantization and anharmonicity inherent
in solid-state vibrational modes. The accuracy of the TB model has been checked
by comparison with density-functional-theory calculations at zero temperature.
The magnitude of quantum effects is assessed by comparing PIMD outcomes with
results obtained from classical molecular dynamics simulations. Our
investigation uncovers notable reductions of 5%, 10%, and 4% in the elastic
constants $C_{11}$, $C_{12}$, and $C_{44}$, respectively, attributed to atomic
zero-point oscillations. Consequently, the bulk modulus and Poisson's ratio of
3C-SiC exhibit reduced values by 7% and 5% at low temperature. The persistence
of these quantum effects in the material's structural and elastic attributes
beyond room temperature underscores the necessity of incorporating nuclear
quantum motion for an accurate description of these fundamental properties of
SiC. | 2405.13733v1 |
1999-04-27 | The ARGO-YBJ Detector and high energy GRBs | ARGO-YBJ ia a detector optimized to study small size air showers. It consists
of a layer of Resistive Plate counters (RPCs) covering an area of about 6500
m^2 and will be located in the Yangbajing Laboratory (Tibet, China) at 4300 m
above the sea level. ARGO-YBJ will be devoted to a wide range of fundamental
issues in cosmic rays and astroparticle physics, including in particular
gamma-ray astronomy and gamma-ray bursts physics in the range 10 GeV-500 TeV.
The sensitivity of ARGO-YBJ to detect high energy GRBs is presented. | 9904373v1 |
1995-12-12 | Mechanism of thermally activated c-axis dissipation in layered High-T$_c$ superconductors at high fields | We propose a simple model which explains experimental behavior of $c$-axis
resistivity in layered High-T$_c$ superconductors at high fields in a limited
temperature range. It is generally accepted that the in-plane dissipation at
low temperatures is caused by small concentration of mobile pancake vortices
whose diffusive motion is thermally activated. We demonstrate that in such
situation a finite conductivity appears also in $c$-direction due to the phase
slips between the planes caused by the mobile pancakes. The model gives
universal relation between the components of conductivity which is in good
agreement with experimental data. | 9512097v3 |
1998-03-24 | Magnetic Penetration Depth and Surface Resistance in YBa_2Cu_3O_{7-delta}: New Results for Ultra High Purity Crystals | We have succeeded in growing very high purity (99.995%) YBa_2Cu_3O_{7-delta}
crystals in BaZrO_3 crucibles and have measured Delta-lambda(T) and R_s(T) at 1
GHz in crystals with various oxygen treatments. For an oxygen vacancy level of
delta=0.007, Delta-lambda and R_s essentially reproduce our previous results
and show no sign of the existence of the two order parameter components as
recently reported by Srikanth et al. on BaZrO_3-grown crystals. For other
oxygen concentrations, we have in some cases observed deviations from the
linear low T dependence of Delta-lambda, but never any sign of a second
transition. | 9803292v1 |
2000-02-24 | Search for Magnetic Field Induced Gap in a High-Tc Superconductor | Break junctions made of the optimally doped high temperature superconductor
Bi2Sr2Ca2CuO8 with Tc of 90 K has been investigated in magnetic fields up to 12
T, at temperatures from 4.2 K to Tc. The junction resistance varied between
1kOhm and 300kOhm. The differential conductance at low biases did not exhibit a
significant magnetic field dependence, indicating that a magnetic-field-induced
gap (Krishana et al., Science 277 83 (1997)), if exists, must be smaller than
0.25 meV. | 0002376v1 |
2001-06-11 | Microwave absorption by the Josephson-junction network in a low field: A realistic model for ceramic high-temperature superconductor | We discuss the applied magnetic field dependence of the absorption of
microwaves by a 3-dimensional array up to 30x30x30 Josephson junctions with
random parameters including the resistivity, capacity and inductance of each
junction. The numerical simulation results for the networks show characteristic
microwave absorption anomalies observed in the ceramic samples of high
temperature superconductor YBa2Cu3O(7-x). We also provide a discussion of the
absorption in simple analytical terms of Josephson loop instabilities. | 0106188v2 |
2002-03-15 | High quality MgB2 thin films in-situ grown by dc magnetron sputtering | Thin films of the recently discovered magnesium diboride (MgB2) intermetalic
superconducting compound have been grown using a magnetron sputtering
deposition technique followed by in-situ annealing at 830 C. High quality films
were obtained on both sapphire and MgO substrates. The best films showed
maximum Tc = 35 K (onset), a transition width of 0.5 K, a residual resistivity
ratio up to 1.6, a low temperature critical current density Jc > 1 MA/cm2 and
anisotropic critical field with gamma = 2.5 close to the values obtained for
single crystals. The preparation technique can be easily scaled to produce
large area in-situ films. | 0203322v1 |
2002-10-09 | Effects of In-Plane Impurity Substitution in Sr2RuO4 | We report comparative substitution effects of nonmagnetic Ti^(4+) and
magnetic Ir^(4+) impurities for Ru^(4+) in the spin-triplet superconductor
Sr2RuO4. We found that both impurities suppress the superconductivity
completely at a concentration of approximately 0.15%, reflecting the high
sensitivity to translational symmetry breaking in Sr2RuO4. In addition, a rapid
enhancement of residual resistivity is in quantitative agreement with
unitarity-limit scattering. Our result suggests that both nonmagnetic and
magnetic impurities in Sr2RuO4 act as strong potential scatterers, similar to
the nonmagnetic Zn^(2+) impurity in the high-Tc cuprates. | 0210190v1 |
2003-02-01 | Higher cumulants of voltage fluctuations in current-biased diffusive contacts | The third and fourth cumulants of voltage in a current-biased diffusive metal
contact of resistance $R$ are calculated for arbitrary temperatures and
voltages using the semiclassical cascade approach. The third cumulant equals
$e^2R^3I/3$ at high temperatures and $4e^2R^3I/15$ at low temperatures, whereas
the fourth cumulant equals $2e^2R^3T/3$ at high temperatures and
$(34/105)e^3R^4I$ at low temperatures. | 0302008v3 |
2003-05-20 | High performance temperature controller: application to the excess noise measurements of YBCO thermometers in the transition region | Dedicated read-out electronics was developed for low impedance resistive
thermometers. Using this high performance temperature controller, the
temperature dependence of the excess noise of a YBa2Cu307-d (YBCO) sample in
the superconducting transition was monitored as a function of the current bias.
The noise could reach 3.10-8 K Hz-1/2 at 1 Hz, 5 mA bias and 90 K. | 0305469v2 |
2003-08-31 | Paramagnetic Meissner effect and related dynamical phenomena | The present review is given on the paramagnetic Meissner effect observed in
conventional and ceramic high-Tc superconductors. We discuss two mechanisms
leading to this phenomenon: the d-wave and the flux compensation. It is shown
that the chiral glass phase may occur in granular superconductors possessing
d-wave pairing symmetry. Dynamical phenomena such as AC susceptibility,
compensation effect, anomalous microwave absorption, aging effect, AC
resistivity and enhancement of critical current due to the external electric
field are considered. | 0309020v1 |
2003-12-15 | Bulk antiferromagnetism in $\bf Na_{0.82}CoO_2$ single crystals | Susceptibility, specific heat, and muon spin rotation measurements on
high-quality single crystals of $\rm Na_{0.82}CoO_2$ have revealed bulk
antiferromagnetism with N\'{e}el temperature $\rm T_N = 19.8 \pm 0.1$ K and an
ordered moment perpendicular to the $\rm CoO_2$ layers. The magnetic order
encompasses nearly 100% of the crystal volume. The susceptibility exhibits a
broad peak around 30 K, characteristic of two-dimensional antiferromagnetic
fluctuations. The in-plane resistivity is metallic at high temperatures and
exhibits a minimum at $\rm T_N$. | 0312376v2 |
2004-12-31 | Numerical evaluation of the dipole-scattering model for the metal-insulator transition in gated high mobility Silicon inversion layers | The dipole trap model is able to explain the main properties of the apparent
metal-to-insulator transition in gated high mobility Si-inversion layers. Our
numerical calculations are compared with previous analytical ones and the
assumptions of the model are discussed carefully. In general we find a similar
behavior but include further details in the calculation. The calculated strong
density dependence of the resistivity is not yet in full agreement with the
experiment. | 0412762v1 |
2006-07-27 | Microwave photoresistance of a high-mobility two-dimensional electron gas in a triangular antidot lattice | The microwave (MW) photoresistance has been measured on a high-mobility
two-dimensional electron gas patterned with a shallow triangular antidot
lattice, where both the MW-induced resistance oscillations (MIRO) and
magnetoplasmon (MP) resonance are observed superposing on sharp commensurate
geometrical resonance (GR). Analysis shows that the MIRO, MP, and GR are
decoupled from each other in these experiments. | 0607740v1 |
2006-08-30 | Magnetoresistance oscillations in two-dimensional electron systems under monochromatic and bichromatic radiations | The magnetoresistance oscillations in high-mobility two-dimensional electron
systems induced by two radiation fields of frequencies 31 GHz and 47 GHz, are
analyzed in a wide magnetic-field range down to 100 G, using the
balance-equation approach to magnetotransport for high-carrier-density systems.
The frequency mixing processes are shown to be important. The predicted peak
positions, relative heights, radiation-intensity dependence and their relation
with monochromatic resistivities are in good agreement with recent experimental
finding [M. A. Zudov {\it et al.} Phys. Rev. Lett. 96, 236804 (2006)]. | 0608655v2 |
1995-01-30 | CHIRAL SYMMETRY RESTORATION AS THE GEORGI VECTOR LIMIT | I discuss recent work done with Gerry Brown on chiral phase transition at
high temperature and/or density described in terms of Georgi's vector limit.
The notion of ``mended symmetry" is suggested to play an important role in
understanding the properties of hadrons in dense and/or hot matter before
reaching the phase transition. It is shown that while the QCD vacuum in
baryon-free space is resistant to ``melting" up to the critical temperature,
baryon-rich medium can induce the vacuum to become softer in temperature: the
hadron masses drop faster in temperature when baryon matter is present. | 9501403v1 |
1998-07-22 | Carbon Coated Gas Electron Multipliers | Gas electron multipliers (GEMs) have been overcoated with a high resistivity
10e14 - 10e15 Ohms / square amorphous carbon layer. The coating avoids charging
up of the holes and provides a constant gain immediately after switching on
independent of the rate. The gain uniformity across the GEM is improved.
Coating opens the possibility to produce thick GEMs of very high gain. | 9807039v1 |
2007-04-26 | Quantum Darwinism in quantum Brownian motion: the vacuum as a witness | We study quantum Darwinism -- the redundant recording of information about a
decohering system by its environment -- in zero-temperature quantum Brownian
motion. An initially nonlocal quantum state leaves a record whose redundancy
increases rapidly with its spatial extent. Significant delocalization (e.g., a
Schroedinger's Cat state) causes high redundancy: many observers can measure
the system's position without perturbing it. This explains the objective (i.e.
classical) existence of einselected, decoherence-resistant pointer states of
macroscopic objects. | 0704.3615v1 |
2007-06-12 | High-quality all-oxide Schottky junctions fabricated on heavily Nb-doped SrTiO3 substrates | We present a detailed investigation of the electrical properties of epitaxial
La0.7Sr0.3MnO3/SrTi0.98Nb0.02O3 Schottky junctions. A fabrication process that
allows reduction of the junction dimensions to current electronic device size
has been employed. A heavily doped semiconductor has been used as a substrate
in order to suppress its series resistance. We show that, unlike standard
semiconductors, high-quality oxide-based Schottky junctions maintain a highly
rectifying behavior for doping concentration of the semiconductor larger than
10^20 cm^(-3). Moreover, the junctions show hysteretic current-voltage
characteristics. | 0706.1620v2 |
2007-07-09 | High-temperature PbTe diodes | We describe the preparation of high-temperature PbTe diodes. Satisfactory
rectification was observed up to 180-200 K. Two types of diodes, based on a
p-PbTe single crystal, were prepared: (1) by In ion-implantation, and (2) by
thermodiffusion of In. Measurements were carried-out from ~ 10 K to ~ 200 K.
The ion-implanted diodes exhibit a satisfactorily low saturation current up to
a reverse bias of ~ 400 mV, and the thermally diffused junctions up to ~ 1 V.
The junctions are linearly graded. The current-voltage characteristics have
been fitted using the Shockley model. Photosensor parameters:
zero-bias-resistance x area product, the R0C time constant and the detectivity
D* are presented. | 0707.1213v1 |
2008-02-20 | Prospects for a direct dark matter search using high resistivity CCD detectors | The possibility of using CCD detectors in a low threshold direct detection
dark matter search experiment is discussed. We present the main features of the
DECam detectors that make them a good alternative for such an experiment,
namely their low noise and their large depleted volume. The performance of the
DECam CCDs for the detection of nuclear recoils is discussed, and a measurement
of the ionization efficiency for these events is presented. Finally the plans
and expected reach for the CCD Experiment at Low Background (CELB) are
discussed. | 0802.2872v3 |
2008-08-14 | Synthesis and superconducting properties of the iron oxyarsenide TbFeAsO0.85 | The iron oxyarsenide TbFeAsO0.85 was synthesized by a high-pressure method. A
high-quality polycrystalline sample was obtained and characterized by
measurements of magnetic susceptibility and electrical resistivity. Bulk
superconductivity with Tc of 42 K was clearly established without an F doping
usually conducted to tune on superconductivity in the iron oxypnictide. | 0808.1948v1 |
2008-09-08 | Pressure Study of Superconducting Oxypnictide LaFePO | Electrical resistivity and magnetic susceptibility measurements under high
pressure were performed on an iron-based superconductor LaFePO. A steep
increase in superconducting transition temperature (Tc) of LaFePO with dTc/dP >
4 K/GPa to a maximum of 8.8 K for P = 0.8 GPa was observed. These results are
similar to isocrystalline LaFeAsO1-xFx system reported previously. X-ray
diffraction measurements were also performed under high pressure up to 10 GPa,
where linear compressibility ka and kc are presented. | 0809.1239v1 |
2008-09-29 | High-quality quantum point contact in two-dimensional GaAs (311)A hole system | We studied ballistic transport across a quantum point contact (QPC) defined
in a high-quality, GaAs (311)A two-dimensional (2D) hole system using shallow
etching and top-gating. The QPC conductance exhibits up to 11 quantized
plateaus. The ballistic one-dimensional subbands are tuned by changing the
lateral confinement and the Fermi energy of the holes in the QPC. We
demonstrate that the positions of the plateaus (in gate-voltage), the
source-drain data, and the negative magneto-resistance data can be understood
in a simple model that takes into account the variation, with gate bias, of the
hole density and the width of the QPC conducting channel. | 0809.5047v1 |
2008-10-07 | Superconductivity under high pressure in LaFeAsO | Electrical resistivity measurements under high pressures up to 29 GPa were
performed for oxypnictide compound LaFeAsO. We found a pressure-induced
superconductivity in LaFeAsO. The maximum value of Tc is 21 K at ~12 GPa. The
pressure dependence of the Tc is similar to those of LaFeAsO1-xFx series
reported previously. | 0810.1153v1 |
2009-01-06 | Fantastic Behavior of High-TC Superconductor Junctions: Tunable Superconductivity | Carrier injection performed in oxygen-deficient YBa2Cu3O7(YBCO)
hetero-structure junctions exhibited tunable resistance that was entirely
different with behaviors of semiconductor devices. Tunable superconductivity in
YBCO junctions, increasing over 20 K in transition temperature, has achieved by
using electric processes. To our knowledge, this is the first observation that
intrinsic property of high TC superconductors superconductivity can be adjusted
as tunable functional parameters of devices. The fantastic phenomenon caused by
carrier injection was discussed based on a proposed charge carrier
self-trapping model and BCS theory. | 0901.0594v1 |
2009-10-15 | ATLAS Muon Detector Commissioning | The ATLAS muon spectrometer consists of several major components: Monitored
Drift Tubes (MDTs) for precision measurements in the bending plane of the
muons, supplemented by Cathode Strip Chambers (CSC) in the high eta region;
Resistive Plate Chambers (RPCs) and Thin Gap Chambers (TGCs) for trigger and
second coordinate measurement in the barrel and endcap regions, respectively;
an optical alignment system to track the relative positions of all chambers;
and, finally, the world's largest air-core magnetic toroid system. We will
describe the status and commissioning of the muon system with cosmic rays and
plans for commissioning with early beams. | 0910.2767v1 |
2010-01-30 | High yield fabrication of chemically reduced graphene oxide field effect transistors by dielectrophoresis | We demonstrate high yield fabrication of field effect transistors (FET) using
chemically reduced graphene oxide (RGO) sheets suspended in water assembled via
dielectrophoresis. The two terminal resistances of the devices were improved by
an order of magnitude upon mild annealing at 200 0C in Ar/H2 environment for 1
hour. With the application of a backgate voltage, all of the devices showed FET
behavior with maximum hole and electron mobilities of 4.0 and 1.5 cm2/Vs
respectively. This study shows promise for scaled up fabrication of graphene
based nanoelectronic devices. | 1002.0086v2 |
2010-02-28 | Theory of acoustic-phonon assisted magnetotransport in 2D electron systems at large filling factors | A microscopic theory of the phonon-induced resistance oscillations in weak
perpendicular magnetic fields is presented. The calculations are based on the
consideration of interaction of two-dimensional electrons with
three-dimensional (bulk) acoustic phonons and take into account anisotropy of
the phonon spectrum in cubic crystals. The magnetoresistance is calculated for
[001]-grown GaAs quantum wells. The results are in agreement with available
experimental data. Apart from the numerical results, analytical expressions for
the oscillating part of magnetoresistance are obtained. These expressions are
valid in the region of high-order magnetophonon resonances and describe the
oscillating magnetoresistance determined by several groups of phonons polarized
along certain high-symmetry directions. | 1003.0176v1 |
2011-01-19 | Hidden Fermi Liquid: Self-Consistent Theory for the Normal State of High-Tc Superconductors | Hidden Fermi liquid theory explicitly accounts for the effects of Gutzwiller
projection in the t-J Hamiltonian, widely believed to contain the essential
physics of the high-Tc superconductors. We derive expressions for the entire
"strange metal", normal state relating angle-resolved photoemission,
resistivity, Hall angle, and by generalizing the formalism to include the Fermi
surface topology - angle-dependent magnetoresistance. We show this theory to be
the first self-consistent description for the normal state of the cuprates
based on transparent, fundamental assumptions. Our well-defined formalism also
serves as a guide for further experimental confirmation. | 1101.3609v1 |
2011-03-28 | Superconducting properties of FeSe wires and tapes prepared by gas diffusion technique | Superconducting FeSe in the form of wires and tapes were successfully
fabricated using a novel gas diffusion procedure. Structural analysis by mean
of x-ray diffraction shows that themain phase of tetragonal PbO-type FeSe was
obtained by this synthesis method. The zero resistivity transition temperature
of the FeSe was confirmed to be 9.3 K. The critical current density as high as
137 A/cm^2 (4 K, self field) has been observed. The results suggest that the
diffusion procedure is promising in preparing high-quality FeSe wires and
tapes. | 1103.5304v1 |
2011-06-13 | Resistant estimates for high dimensional and functional data based on random projections | We herein propose a new robust estimation method based on random projections
that is adaptive and, automatically produces a robust estimate, while enabling
easy computations for high or infinite dimensional data. Under some restricted
contamination models, the procedure is robust and attains full efficiency. We
tested the method using both simulated and real data. | 1106.2442v3 |
2011-12-01 | Superconductivity in the doped topological insulator Cu$_x$Bi$_2$Se$_3$ under high pressure | We report a high-pressure single crystal study of the topological
superconductor Cu$_x$Bi$_2$Se$_3$. Resistivity measurements under pressure show
superconductivity is depressed smoothly. At the same time the metallic behavior
is gradually lost. The upper critical field data $B_{c2}(T)$ under pressure
collapse onto a universal curve. The absence of Pauli limiting and the
comparison of $B_{c2}(T)$ to a polar state function point to spin-triplet
superconductivity, but an anisotropic spin-singlet state cannot be discarded
completely. | 1112.0102v1 |
2011-12-16 | Pseudogap and local pairs in high-Tc cuprate superconductors | Analysis of the resistivity data recently reported by Kondo et al. [1] for
(Bi,Pb)2(Sr,La)2CuO{6-delta} (Bi2201) single-crystals has been performed within
our model developed to study pseudogap (PG) in high-Tc superconductors (HTS's).
The model is based on an assumption of the existence of local pairs in HTS's at
temperatures well above Tc. Comparative analysis of our results and results of
ARPES experiments reported by Kondo et al. suggests the local pairs to be one
of the possible reason of the PG formation. | 1112.3812v1 |
2012-02-08 | A proposal to solve some puzzles in semileptonic B decays | Some long-standing problems in the experimental data for semileptonic b -> c
l nu decay rates have resisted attempts to resolve them, despite substantial
efforts. We summarize the issues, and propose a possible resolution, which may
alleviate several of these tensions simultaneously, including the "1/2 vs. 3/2
puzzle" and the composition of the inclusive decay rate in terms of exclusive
channels. | 1202.1834v3 |
2012-02-24 | The 1m3 Semidigital Hadronic Prototype | A high granularity hadronic 1 m3 calorimeter prototype with semi-digital
readout has been designed and built. This calorimeter has been made using
stainless steel as absorber and Glass Resistive Plates Chambers (GRPC) as
active medium, and read out through 1x1 cm2 pads. This prototype aims to
demonstrate that this technology fulfills the physics requirements for future
linear collider experiments, and also to test the feasibility of building a
realistic detector, taking into account design aspects as for instance a fully
embedded front-end electronics based on power pulsing system, a compact and
self-supporting mechanical structure, one-side services... | 1202.5567v1 |
2012-04-13 | Studies of Vertex Tracking with SOI Pixel Sensors for Future Lepton Colliders | This paper presents a study of vertex tracking with a beam hodoscope
consisting of three layers of monolithic pixel sensors in SOI technology on
high-resistivity substrate. We study the track extrapolation accuracy,
two-track separation and vertex reconstruction accuracy in pion-Cu interactions
with 150 and 300 GeV/c pions at the CERN SPS. Results are discussed in the
context of vertex tracking at future lepton colliders. | 1204.2910v1 |
2012-05-02 | High-field magnetoresistance revealing scattering mechanisms in graphene | We show that the type of charge carrier scattering significantly affects the
high-field magnetoresistance of graphene nanoribbons. This effect has potential
to be used in identifying the scattering mechanisms in graphene. The results
also provide an explanation for the experimentally found, intriguing
differences in the behavior of the magnetoresistance of graphene Hall bars
placed on different substrates. Additionally, our simulations indicate that the
peaks in the longitudinal resistance tend to become pinned to fractionally
quantized values, as different transport modes have very different scattering
properties. | 1205.0492v2 |
2012-05-13 | Modeling high impedance connecting links and cables below 1 Hz | High impedance connecting links and cables are modeled at low frequency in
terms of their impedance to ground and to neigbouring connecting links. The
impedance is usually considered to be the parallel combination of a resistance
and a capacitance. While this model is adequate at moderate and low frequency,
it proved to be not satisfactory at very low frequency, in the fractions of Hz
range. Deep characterization was carried out on some samples down to 10 uHz,
showing that an additional contribution to capacitance can emerge. A model was
developed to explain and account for this additional contribution. | 1205.2848v1 |
2012-07-24 | Van Kampen modes for bunch longitudinal motion | Conditions for existence, uniqueness and stability of bunch steady states are
considered. For the existence uniqueness problem, simple algebraic equations
are derived, showing the result both for the action and Hamiltonian domain
distributions. For the stability problem, van Kampen theory is used. Emerging
of discrete van Kampen modes show either loss of Landau damping, or
instability. This method can be applied for an arbitrary impedance, RF shape
and beam distribution function Available areas on intensity-emittance plane are
shown for resistive wall wake and single harmonic, bunch shortening and bunch
lengthening RF configurations. | 1207.5826v1 |
2012-11-28 | Homogeneous superconducting phase in TiN film : a complex impedance study | The low frequency complex impedance of a high resistivity 92 {\mu}{\Omega} cm
and 100 nm thick TiN superconducting film has been measured via the
transmission of several high sensitivity GHz microresonators, down to Tc/50.
The temperature dependence of the kinetic inductance follows closely BCS local
electrodynamics, with one well defined superconducting gap. This evidences the
recovery of an homogeneous superconducting phase in TiN far from the disorder
and composition driven transitions. Additionally, we observe a linearity
between resonator quality factor and frequency temperature changes, which can
be described by a two fluid model. | 1211.6678v2 |
2013-05-08 | Evidence for effective mass reduction in GaAs/AlGaAs quantum wells | We have performed microwave photoresistance measurements in high mobility
GaAs/AlGaAs quantum wells and investigated the value of the effective mass.
Surprisingly, the effective mass, obtained from the period of microwave-induced
resistance oscillations, is found to be about 12% lower than the band mass in
GaAs, $\mb$. This finding provides strong evidence for electron-electron
interactions which can be probed by microwave photoresistance in very high
Landau levels. In contrast, the measured magnetoplasmon dispersion revealed an
effective mass which is close to $\mb$, in accord with previous studies. | 1305.1814v1 |
2014-06-23 | Control of MTDC Transmission Systems under Local Information | High-voltage direct current (HVDC) is a commonly used technology for
long-distance electric power transmission, mainly due to its low resistive
losses. In this paper a distributed controller for multi-terminal high-voltage
direct current (MTDC) transmission systems is considered. Sufficient conditions
for when the proposed controller renders the closed-loop system asymptotically
stable are provided. Provided that the closed loop system is asymptotically
stable, it is shown that in steady-state a weighted average of the deviations
from the nominal voltages is zero. Furthermore, a quadratic cost of the current
injections is minimized asymptotically. | 1406.5839v2 |
2014-06-27 | Energy measurement with the SDHCAL prototype | The SDHCAL prototype that was completed in 2012 was exposed to beams of
pions, electrons of different energies at the SPS of CERN for a total time
period of 5 weeks. The data are being analyzed within the CALICE Collaboration.
However preliminary results indicate that a highly granular hadronic
calorimeter conceived for PFA application is also a powerful tool to separate
pions from electrons. The SDHCAL provides also a very good resolution of
hadronic showers energy measurement. A new calibration method that takes into
account the degradation of the Glass Resistive Plate Chambers (GRPC) response
for runs with rather high particle beam rate is presented. | 1406.7111v1 |
2014-06-29 | CMS RPC muon detector performance with 2010-2012 LHC data | The muon spectrometer of the CMS (Compact Muon Solenoid) experiment at the
Large Hadron Collider (LHC) is equipped with a redundant system made of
Resistive Plate Chambers and Drift Tube in barrel and RPC and Cathode Strip
Chamber in endcap region. In this paper, the operations and performance of the
RPC system during the first three years of LHC activity will be reported. The
stability of RPC performance, such as efficiency, cluster size and noise, will
be reported. Finally, the radiation background levels on the RPC system have
been measured as a function of the LHC luminosity. Extrapolations to the LHC
and High Luminosity LHC conditions are also discussed. | 1406.7543v1 |
2014-12-08 | Anomalous specific heat behaviour in the quadrupolar Kondo system PrV2Al20 | We have measured the specific heat of PrV$_2$Al$_{20}$ at very low
temperatures, using high quality single crystals with the residual resistivity
ratio ~ 20. The high-quality single crystals exhibit clear double transitions
at $T_{\rm Q} =$ 0.75 K and $T^* =$ 0.65 K. These transitions are clearer and
shift to higher temperature in higher quality single crystals. Besides, there
was no hysteresis in those transitions in warming and cooling process of the
heat capacity measurements. In the ordered state below $T^*$, the specific heat
shows a $T^4$ dependence, indicating the gapless mode associated with the
quadrupole and/or octupole ordering. | 1412.2583v1 |
2016-02-25 | The quantum phase slip phenomenon in superconducting nanowires with high-impedance environment | Quantum phase slip (QPS) is the particular manifestation of quantum
fluctuations of the order parameter of a current-biased quasi-1D
superconductor. The QPS event(s) can be considered a dynamic equivalent of
tunneling through conventional Josephson junction containing static in space
and time weak link(s). At low temperatures T<<Tc the QPS effect leads to finite
resistivity of narrow superconducting channels and suppresses persistent
currents in tiny nanorings. Here we demonstrate that the quantum tunneling of
phase may result in Coulomb blockade: superconducting nanowire, imbedded in
high-Ohmic environment, below a certain bias voltage behaves as an insulator. | 1602.07935v1 |
2016-05-07 | Monte-Carlo study of the MRPC prototype for the upgrade of BESIII | A GEANT4-based simulation is developed for the endcap time of flight (ETOF)
upgrade based on multi-gap resistive plate chambers (MRPC) for the BESIII
experiment. The MRPC prototype and the simulation method are described. Using a
full Monte-Carlo simulation, the influence of high voltage and threshold on
time resolution and detection efficiency are investigated. The preliminary
results from simulation are presented and are compared with the experimental
data taken with the prototype MRPC modules. | 1605.02155v1 |
2016-10-24 | Compact sorting of optical vortices by means of diffractive transformation optics | The orbital angular momentum (OAM) of light has recently attracted a growing
interest as a new degree of freedom in order to increase the information
capacity of today optical networks both for free-space and optical fiber
transmission. Here we present our work of design, fabrication and optical
characterization of diffractive optical elements for compact OAM-mode division
demultiplexing based on optical transformations. Samples have been fabricated
with 3D high-resolution electron beam lithography on polymethylmethacrylate
(PMMA) resist layer spun over a glass substrate. Their high compactness and
efficiency make these optical devices promising for integration into
next-generation platforms for OAM-modes processing in telecom applications. | 1610.07443v1 |
2017-02-22 | Interfacing of High Temperature Z-meter Setup Using Python | In this work, we interface high temperature Z-meter setup to automize the
whole measurement process. A program is built on open source programming
language Python which convert the manual measurement process into fully
automated process without any cost addition. Using this program, simultaneous
measurement of Seebeck coefficient, thermal conductivity and electrical
resistivity are performed and using all three, figure-of-merit (ZT) is
calculated. Developed program is verified by performing measurement over p-type
Bi0.36Sb1.45Te3 sample and the data obtained are found to be in good agreement
with the reported data. | 1702.06691v1 |
2017-06-01 | Nonlinear transport by vortex tangles in cuprate high-temperature superconductors | A unified model of vortex tangles is proposed to describe unconventional
transport in cuprate high-temperature superconductors, which not only captures
the fast vortices scenario at low density, but also predicts a novel mechanism
of core-core collisions in dense vortex fluid regime. The theory clarifies the
nature of vortex fluctuations being the quantum fluctuations of holes and then
resolves a discrepancy of two orders of magnitude of Anderson's damping model
$\hbar n_v$, with right prediction of the nonlinear field dependence of the
resistivity $\rho=\rho_n(B+B_T)/(B_0+B+B_T)$ and the Nernst effect, validated
by data of several samples. Consequently, Anderson's vortex tangles concept and
phase fluctuation scenario of pseudogap are verified quantitatively. | 1706.00228v1 |
2017-06-20 | Saturation of Strong Electron-Electron Umklapp Scattering at High Temperature | We consider clean metals, at finite temperature, in which the inelastic rate,
$\hbar/ \tau_{ee}$, can become of the order of, or larger, than the band
splitting energy. We show that in suchsystems, contrary to the common
knowledge, the umklapp scattering rate becomes independent of both $\tau_{ee}$
and the temperature $T,$ in three dimensional systems. We discuss the relation
of this phenomenon to the saturation of resistivity at high temperature. | 1706.06256v2 |
2018-02-05 | High Kinetic Inductance NbN Nanowire Superinductors | We demonstrate that a high kinetic inductance disordered superconductor can
realize a low microwave loss, non-dissipative circuit element with an impedance
greater than the quantum resistance ($R_Q = h/4e^2 \simeq 6.5k\Omega$). This
element, known as a superinductor, can produce a quantum circuit where charge
fluctuations are suppressed. The superinductor consists of a 40 nm wide niobium
nitride nanowire and exhibits a single photon quality factor of $2.5 \times
10^4$. Furthermore, by examining loss rates, we demonstrate that the
dissipation of our nanowire devices can be fully understood in the framework of
two-level system loss. | 1802.01723v1 |
2011-07-05 | Deep sub electron noise readout in CCD systems using digital filtering techniques | Scientific CCDs designed in thick high resistivity silicon (Si) are excellent
detectors for astronomy, high energy and nuclear physics, and instrumentation.
Many applications can benefit from CCDs ultra low noise readout systems. The
present work shows how sub electron noise CCD images can be achieved using
digital signal processing techniques. These techniques allow readout bandwidths
of up to 10 K pixels per second and keep the full CCD spatial resolution and
signal dynamic range. | 1107.0925v1 |
2013-12-13 | Recent DHCAL Developments | This talk reports on recent progress concerning the development of a Digital
Hadron Calorimeter with Resistive Plate Chambers as active elements. After the
successful testing of a Digital Hadron Calorimeter prototype, the DHCAL, in the
Fermilab and CERN test beams, the DHCAL group is now tackling some of the
remaining technical issues which were not addressed specifically with the
prototype. The talk reports on developments related to the RPC chamber design,
to improvements in the RPC rate capabilities, the high voltage distribution
system, and a gas recirculation system. | 1312.3868v1 |
2015-05-14 | High-pressure and doping studies of the superconducting antiperovskite SrPt3P | We report the results of our investigation of SrPt3P, a recently discovered
strong-coupling superconductor with Tc = 8.4 K, by application of high physical
pressure and by chemical doping. We study hole-doped SrPt3P, which was
theoretically predicted to have a higher Tc, resistively, magnetically, and
calorimetrically. Here we present the results of these studies and discuss
their implications. | 1505.03849v1 |
2016-12-18 | Power nano- and picosecond optoelectronic switches based on high-voltage silicon structures with p-n-junctions. II. Energy efficiency | Energy efficiency of optoelectronic switches based on high-voltage silicon
photodiodes, phototransistors or photothyristors and triggered-on by picosecond
laser pulses has been studied for the first time. For given values of resistive
load, amplitude and duration $t_R$ of voltage pulses it is shown that there
exist optimal sets of values for the device area, energy and absorption
coefficient for triggering illumination, which provide the maximal general
efficiency of the switch about 0.92. All three types of switches have almost
identical efficiencies at short $t_R$, and in case of long $t_R$
photothyristors possess a noticeable advantage among them. | 1701.03412v1 |
2017-01-28 | Point-contact studies of high-temperature superconductor $\rm YBa_2Cu_3O_{7-δ}$ | Point-contacts formed by the high-temperature superconductor $\rm
YBa_2Cu_3O_{7-\delta}$ prepared by cryochemical technique, and a noble metal Ag
or Cu) are investigated. The maximum value of the energy gap $\Delta\simeq
40~meV$ and the ratio $2\Delta/kT_c\simeq 12$ are obtained. It is found that
along certain crystallographic axes of the superconductor under investigation,
the electrical resistivity $\lesssim 10^{-5} \Omega\cdot cm$. | 1701.08293v1 |
2019-04-23 | Spatio-temporal crop classification of low-resolution satellite imagery with capsule layers and distributed attention | Land use classification of low resolution spatial imagery is one of the most
extensively researched fields in remote sensing. Despite significant
advancements in satellite technology, high resolution imagery lacks global
coverage and can be prohibitively expensive to procure for extended time
periods. Accurately classifying land use change without high resolution imagery
offers the potential to monitor vital aspects of global development agenda
including climate smart agriculture, drought resistant crops, and sustainable
land management. Utilizing a combination of capsule layers and long-short term
memory layers with distributed attention, the present paper achieves
state-of-the-art accuracy on temporal crop type classification at a 30x30m
resolution with Sentinel 2 imagery. | 1904.10130v1 |
2019-01-06 | Enhanced magnetic ordering in Sm metal under extreme pressure | The dependence of the magnetic ordering temperature To of Sm metal was
determined through four-point electrical resistivity measurements to pressures
as high as 150 GPa. A strong increase in To with pressure is observed above 85
GPa. In this pressure range Sm ions alloyed in dilute concentration with
superconducting Y exhibit giant Kondo pair breaking. Taken together, these
results suggest that for pressures above 85 GPa Sm is in a highly correlated
electron state, like a Kondo lattice, with an unusually high value of To. A
detailed comparison is made with similar results obtained earlier on Nd, Tb and
Dy and their dilute magnetic alloys with superconducting Y. | 1901.01563v1 |