publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2015-07-01 | Gas Sensing with h-BN Capped MoS2 Heterostructure Thin Film Transistors | We have demonstrated selective gas sensing with molybdenum disulfide (MoS2)
thin films transistors capped with a thin layer of hexagonal boron nitride
(h-BN). The resistance change was used as a sensing parameter to detect
chemical vapors such as ethanol, acetonitrile, toluene, chloroform and
methanol. It was found that h-BN dielectric passivation layer does not prevent
gas detection via changes in the source-drain current in the active MoS2 thin
film channel. The use of h-BN cap layers (thickness H=10 nm) in the design of
MoS2 thin film gas sensors improves device stability and prevents device
degradation due to environmental and chemical exposure. The obtained results
are important for applications of van der Waals materials in chemical and
biological sensing. | 1507.00308v1 |
2016-09-13 | Gate voltage control of the $AlO_x$/$SrTiO_3$ interface electrical properties | Electron-beam deposition of an insulating granular aluminium or of an
off-stoichiometric amorphous alumina layer on a $SrTiO_3$ surface is a simple
way to get a metallic interface from insulating materials. No heating nor
specific preparation of the $SrTiO_3$ surface are needed. In this paper, we
investigate how the electrical properties of this interface can be tuned by the
use of a back gate voltage (electrical field through the $SrTiO_3$ substrate).
We demonstrate that the slow field-effect observed at room temperature can be
used to tune reversibly and in a controlled way the low temperature electrical
properties of the interface. In particular, important parameters of a
transistor such as the amplitude of the resistance response to gate voltage
changes or the existence of an "on" or an "off" state at zero gate voltage and
at low temperature can be adjusted in a single sample. This method should be
applicable to any $SrTiO_3$-based interface in which oxygen vacancies are
involved and might provide a powerful way to study the metal or superconductor
insulator transition observed in such systems. | 1609.03718v1 |
2018-07-04 | Thermal and transport properties of U3Si2 | We have studied U_3Si_2 by means of the heat capacity, electrical
resistivity, Seebeck and Hall effects, and thermal conductivity in the
temperature range 2-300 K and in magnetic fields up to 9 T. All the results
obtained point to delocalized nature of 5f-electrons in this material. The low
temperature heat capacity is enhanced (gamma_el ~ 150 mJ/mol-K2) and shows an
upturn in Cp/T (T), characteristic of spin fluctuations. The thermal
conductivity of U3Si2 is ~8.5 W/m-K at room temperature and we show that the
electronic part dominates heat transport above 300 K as expected for a metallic
system, although the lattice contribution cannot be completely neglected. | 1807.01757v1 |
2018-07-13 | Laser-beam patterned topological insulating states on thin semiconducting MoS2 | Identifying the two-dimensional (2D) topological insulating (TI) state in new
materials and its control are crucial aspects towards the development of
voltage-controlled spintronic devices with low power dissipation. Members of
the 2D transition metal dichalcogenides (TMDCs) have been recently predicted
and experimentally reported as a new class of 2D TI materials, but in most
cases edge conduction seems fragile and limited to the monolayer phase
fabricated on specified substrates. Here, we realize the controlled patterning
of the 1T'-phase embedded into the 2H-phase of thin semiconducting
molybdenum-disulfide (MoS2) by laser beam irradiation. Integer fractions of the
quantum of resistance, the dependence on laser-irradiation conditions, magnetic
field, and temperature, as well as the bulk gap observation by scanning
tunneling spectroscopy and theoretical calculations indicate the presence of
the quantum spin Hall phase in our patterned 1T' phases. | 1807.04914v3 |
2018-07-17 | Electric Field Driven Memristive Behavior at the Schottky Interface of Nb doped SrTiO3 | Computing inspired by the human brain requires a massive parallel
architecture of low-power consuming elements of which the internal state can be
changed. SrTiO3 is a complex oxide that offers rich electronic properties; here
Schottky contacts on Nb-doped SrTiO3 are demonstrated as memristive elements
for neuromorphic computing. The electric field at the Schottky interface alters
the conductivity of these devices in an analog fashion, which is important for
mimicking synaptic plasticity. Promising power consumption and endurance
characteristics are observed. The resistance states are shown to emulate the
forgetting process of the brain. A charge trapping model is proposed to explain
the switching behavior. | 1807.06274v1 |
2019-01-07 | Non-topological Origin of the Planar Hall Effect in Type-II Dirac Semimetal NiTe2 | Dirac and Weyl semimetals are new discovered topological nontrivial materials
with the linear band dispersions around the Dirac/Weyl points. When applying
non-orthogonal electric current and magnetic field, an exotic phenomenon called
chiral anomaly arises and negative longitudinal resistance can be detected.
Recently, a new phenomenon named planer Hall effect (PHE) is considered to be
another indication of chiral anomaly which has been observed in many
topological semimetals. However, it still remains a question that is the PHE
only attributed to chiral anomaly? Here we demonstrate the PHE in a
new-discovered type-II Dirac semimetal NiTe2 by low temperature transport.
However, after detailed analysis, we conclude that the PHE results from the
trivial orbital magnetoresistance. This work reveals that PHE is not a
sufficient condition of chiral anomaly and one need to take special care of
other non-topological contribution in such studies. | 1901.01749v1 |
2019-10-19 | Investigation of structural, electrical and electrochemical properties of La0.6Sr0.4Fe0.8Mn0.2O3-δ as an intermediate temperature solid oxide fuel cell cathode | La0.6Sr0.4Fe0.8Mn0.2O3 (LSFM) compound is synthesized by Sol-gel method and
evaluated as a cathode material for the intermediate temperature solid oxide
fuel cell (IT-SOFC). X-ray diffraction (XRD) indicates that the LSFM has a
Rhombohedral structure with R-3c space group symmetry. The XRD patterns reveal
very small amount of impurity phase in the LSFM and Y2O3-Stabilized ZrO2 (YSZ)
mixture powders sintered at 600, 700 and 800 C for a week. The maximum
electrical conductivity of LSFM is about 35.35 S.cm-1 at 783 C in the air. The
oxygen chemical diffusion coefficients, DChem, are increased from 1.39*10-6 up
to 7.66*10-6 .cm2. Besides, the oxygen surface exchange coefficients, kChem,
are obtained to lie between 2.9*10-3 and 8.7*10-3 cm.s-1 in a temperature range
of 600-800 C. The area-specific resistances (ASRs) of the LSFM symmetrical cell
are 7.53, 1.53, 1.13, 0.46 and 0.31 .cm2 at 600, 650, 700, 750 and 800 C
respectively, and related activation energy, Ea, is about 1.23 eV. | 1910.08754v1 |
2019-10-21 | Role of crystal lattice structure in predicting fracture toughness | We examine the atomistic scale dependence of material's resistance-to-failure
by numerical simulations and analytical analysis in electrical analogs of
brittle crystals. We show that fracture toughness depends on the lattice
geometry in a way incompatible with Griffith's relationship between fracture
and free surface energy. Its value finds its origin in the matching between the
continuum displacement field at the engineering scale, and the discrete nature
of solids at the atomic scale. The generic asymptotic form taken by this field
near the crack tip provides a solution for this matching, and subsequently a
way to predict toughness from the atomistic parameters with application to
graphene. | 1910.09343v2 |
2019-10-25 | Macroscopic visualization of fast electrochemical reaction of SrCoOx oxygen sponge | Strontium cobaltite (SrCoOx) is known as a material showing fast topotactic
electrochemical Redox reaction so-called oxygen sponge. Although atomic scale
phenomenon of the oxidation of SrCoO2.5 into SrCoO3 is known, the macroscopic
phenomenon has not been clarified yet thus far. Here, we visualize the
electrochemical oxidation of SrCoOx macroscopically. SrCoOx epitaxial films
with various oxidation states were prepared by the electrochemical oxidation of
SrCoO2.5 film into SrCoO3-d film. Steep decrease of both resistivity and the
absolute value of thermopower of electrochemically oxidized SrCoOx epitaxial
films indicated the columnar oxidation firstly occurred along with the surface
normal and then spread in the perpendicular to the normal. Further, we directly
visualized the phenomena using the conductive AFM. This macroscopic image of
the electrochemical oxidation would be useful to develop a functional device
utilizing the electrochemical redox reaction of SrCoOx. | 1910.11465v1 |
2019-10-29 | Improvement on corrosion resistance and biocompability of ZK60 magnesium alloy by carboxyl ion implantation | Magnesium alloys have been considered to be potential biocompatible metallic
materials. Further improvement on the anti-corrosion is expected to make this
type of materials more suitable for biomedical applications in the fields of
orthopedics, cardiovascular surgery and others. In this paper, we introduce a
method of carboxyl ion (COOH+) implantation to reduce the degradation of ZK60
Mg alloy and improve its functionality in physiological environment. X-ray
photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) experiments
show the formation of a smooth layer containing carbaxylic group, carbonate,
metal oxides and hydroxides on the ion implanted alloy surface. Corrosion
experiments and in vitro cytotoxicity tests demonstrate that the ion
implantation treatment can both reduce the corrosion rate and improve the
biocompatibility of the alloy. The promising results indicate that organic
functional group ion implantation may be a practical method of improving the
biological and corrosion properties of magnesium alloys. | 1910.13219v1 |
2019-11-21 | Superconducting Contact and Quantum Interference Between Two-Dimensional van der Waals and Three-Dimensional Conventional Superconductors | Two-dimensional (2D) transition-metal dichalcogenide superconductors have
unique and desirable properties for integration with conventional
superconducting circuits. However, fully superconducting contact must be made
between the 2D material and three-dimensional (3D) superconductors in order to
employ the standard microwave drive and readout of qubits in such circuits.
Here, we present a method for creating zero-resistance contacts between 2D
NbSe$_2$ and 3D aluminum that behave as Josephson junctions (JJs) with large
effective areas compared to 3D-3D JJs. We present a model for the supercurrent
flow in a 2D-3D superconducting structure by numerical solution of the
Ginzburg-Landau equations and find good agreement with experiment. These
results demonstrate a crucial step towards a new generation of hybrid
superconducting quantum circuits. | 1911.09711v2 |
2020-01-07 | Electrical transport properties of bulk tetragonal CuMnAs | Temperature-dependent resistivity and magnetoresistance are measured in bulk
tetragonal phase of antiferromagnetic CuMnAs and the latter is found to be
anisotropic both due to structure and magnetic order. We compare these findings
to model calculations with chemical disorder and finite-temperature phenomena
included. The finite-temperature ab initio calculations are based on the alloy
analogy model implemented within the coherent potential approximation and the
results are in fair agreement with experimental data. Regarding the anisotropic
magnetoresistance (AMR) which reaches a modest magnitude of 0.12%, we
phenomenologically employ the Stoner-Wohlfarth model to identify
temperature-dependent magnetic anisotropy of our samples and conclude that the
field-dependence of AMR is more similar to that of antiferromagnets than
ferromagnets, suggesting that the origin of AMR is not related to isolated Mn
magnetic moments. | 2001.01947v3 |
2020-01-18 | Microscopic aspects of artificial ageing in Al-Mg-Si alloys | Al-Mg-Si alloys with total solute contents ranging from 0.8 to 1.4 wt.% were
solutionised, quenched and then artificially aged (AA) at 180 {\deg}C, after
which positron annihilation lifetime spectroscopy was applied to obtain
information about precipitation and vacancy evolution during preceding ageing.
Hardness and electrical resistivity measurements were carried out to complement
these measurements. AA was carried out in four different heating media, which
allowed for varying the heating rate from 2.4 K/s to 170 K/s. The main result
of the study is that there is a competition between vacancy losses and
precipitation. Any precipitation taking place during quenching or during
heating to the AA temperature helps to prevent vacancies from going to sinks
and allows them to assist in solute clustering. Higher solute content, slower
heating to 180 {\deg}C and natural pre-ageing before AA were found to have a
comparable effect. | 2001.06566v1 |
2020-01-27 | Metal to insulator transition, colossal Seebeck coefficient and ultralow thermal conductivity in solution-processed monodispersed nickel nanoparticles | We report here metal to insulator transition, colossal Seebeck coefficient
and ultralow thermal conductivity (0.0057th of its bulk value, significantly
smaller than many well-known thermoelectric materials and silicon, showing
potential applications in thermoelectrics, electronics and photonics for heat
dissipation) in monodispersed well characterized Ni nanoparticles. As a
consequence, thermoelectric power factor and figure of merit are significantly
enhanced compared to their bulk counterpart. Interestingly, a systematic
crossover from metallic to semiconducting to finally electrically insulating
behavior, large negative temperature coefficient of resistance and n-type
conduction to p-type conduction with decrease in particle size have been
observed. These results are mainly attributed to formation of metal/organic
interfaces, enhancement in local electronic density of sates and multiscale
electron and phonon scattering by various defects. Thus, this study will open a
new avenue to make better thermoelectrics through incorporation of such
nanoparticles in semiconducting hosts. | 2001.09708v1 |
2020-05-21 | Thermodynamic Origin of Reaction Non-Uniformity in Battery Porous Electrodes and its Mitigation | The development of non-uniform reaction current distribution within porous
electrodes is a ubiquitous phenomenon during battery charging / discharging and
frequently controls the rate performance of battery cells. Reaction
inhomogeneity in porous electrodes is usually attributed to the kinetic
limitation of mass transport within the electrolyte and/or solid electrode
phase. In this work, however, we reveal that it is also strongly influenced by
the intrinsic thermodynamic behavior of electrode materials, specifically the
dependence of the equilibrium potential on the state of charge: electrode
reaction becomes increasingly non-uniform when the slope of the equilibrium
potential curve is reduced. We employ numerical simulation and equivalent
circuit model to elucidate such a correlation and show that the degree of
reaction inhomogeneity and the resultant discharge capacity can be predicted by
a dimensionless reaction uniformity number. For electrode materials that have
equilibrium potentials insensitive to the state of charge and exhibit
significant reaction non-uniformity, we demonstrate several approaches to
spatially homogenizing the reaction current inside porous electrodes, including
matching the electronic and ionic resistances, introducing graded electronic
conductivity and reducing the surface reaction kinetics. | 2005.10916v1 |
2020-06-16 | Ambient pressure Dirac electron system in quasi-two-dimensional molecular conductor $α$-(BETS)$_2$I$_3$ | We investigated the precise crystal structures and electronic states in a
quasi-two-dimensional molecular conductor ${\alpha}$-(BETS)$_2$I$_3$ at ambient
pressure. The electronic resistivity of this molecular solid shows
metal-to-insulator (MI) crossover at $T_{MI}$=50 K. Our x-ray diffraction and
$^{13}$C nuclear magnetic resonance experiments revealed that
${\alpha}$-(BETS)$_2$I$_3$ maintains the inversion symmetry below $T_{MI}$.
First-principles calculations found a pair of anisotropic Dirac cones at a
general k-point, with the degenerate contact points at the Fermi level. The
origin of the insulating state in this system is a small energy gap of ~2 meV
opened by the spin-orbit interaction. The Z$_2$ topological invariants indicate
that this system is a weak topological insulator. Our results suggest that
${\alpha}$-(BETS)$_2$I$_3$ is a promising material for studying the bulk Dirac
electron system in two dimensions. | 2006.08978v2 |
2020-06-18 | Dynamical vortex phase diagram of 2D superconductivity in gated MoS2 | Recent discoveries of two-dimensional (2D) superconductors have uncovered
various new aspects of physical properties including vortex matter. In this
paper, we report transport properties and a dynamical phase diagram at zero
magnetic field in ion-gated MoS2. In addition to the universal jump in the
current-voltage characteristic showing unambiguous evidence of the
Berezinskii-Kosterlitz-Thouless (BKT) transition, we observed multiple peaks in
the temperature- and current-derivative of the electrical resistance, based on
which a dynamical phase diagram in the current-temperature plane was
constructed. We found current-induced dynamical states of vortex-antivortex
pairs, containing that with the phase slip line. Also, we present a global
phase diagram of vortices in gated MoS2 which captures the nature of vortex
matter of clean 2D superconductors. | 2006.10749v1 |
2020-07-03 | From Weak Antilocalization to Kondo Scattering in a Magnetic Complex Oxide Interface | Quantum corrections to electrical resistance can serve as sensitive probes of
the magnetic landscape of a material. For example, interference between
time-reversed electron paths gives rise to weak localization effects, which can
provide information about the coupling between spins and orbital motion, while
the Kondo effect is sensitive to the presence of spin impurities. Here we use
low-temperature magnetotransport measurements to reveal a transition from weak
antilocalization (WAL) to Kondo scattering in the quasi-two-dimensional
electron gas formed at the interface between SrTiO$_3$ and the Mott insulator
NdTiO$_3$. This transition occurs as the thickness of the NdTiO$_3$ layer is
increased. Analysis of the Kondo scattering and WAL points to the presence of
atomic-scale magnetic impurities coexisting with extended magnetic regions that
affect transport via a strong magnetic exchange interaction. This leads to
distinct magnetoresistance behaviors that can serve as a sensitive probe of
magnetic properties in two dimensions. | 2007.01853v1 |
2020-08-02 | Thermal stability for domain wall mediated magnetization reversal in perpendicular STT MRAM cells with W insertion layers | We present an analytical model for calculating energy barrier for the
magnetic field-driven domain wall-mediated magnetization reversal of a
magneto-resistive random access memory (MRAM) cell and apply it to study
thermal stability factor $\Delta$ for various thicknesses of W layers inserted
into the free layer (FL) as a function of the cell size and temperature. We
find that, by increasing W thickness, the effective perpendicular magnetic
anisotropy (PMA) energy density of the FL film monotonically increases, but at
the same time, $\Delta$ of the cell mainly decreases. Our analysis shows that,
in addition to saturation magnetization $M_s$ and exchange stiffness constant
$A_\mathrm{ex}$ of the FL film, the parameter that quantifies the $\Delta$ of
the cell is its coercive field $H_c$, rather than the net PMA field $H_k$ of
the FL film comprising the cell. | 2008.00412v2 |
2020-08-03 | Intrinsic mechanism for anisotropic magnetoresistance and experimental confirmation in Co$_x$Fe$_{1-x}$ single-crystal films | Using first-principles transport calculations, we predict that the
anisotropic magnetoresistance (AMR) of single-crystal Co$_x$Fe$_{1-x}$ alloys
is strongly dependent on the current orientation and alloy concentration. An
intrinsic mechanism for AMR is found to arise from the band crossing due to
magnetization-dependent symmetry protection. These special $k$-points can be
shifted towards or away from the Fermi energy by varying the alloy composition
and hence the exchange splitting, thus allowing AMR tunability. The prediction
is confirmed by delicate transport measurements, which further reveal a
reciprocal relationship of the longitudinal and transverse resistivities along
different crystal axes. | 2008.00872v1 |
2020-08-12 | Analysis of the influence of microstructural traps on hydrogen assisted fatigue | We investigate the influence of microstructural traps on hydrogen diffusion
and embrittlement in the presence of cyclic loads. A mechanistic, multi-trap
model for hydrogen transport is developed, implemented into a finite element
framework, and used to capture the variation of crack tip lattice and trapped
hydrogen concentrations as a function of the loading frequency, the trap
binding energies and the trap densities. We show that the maximum value
attained by the lattice hydrogen concentration during the cyclic analysis
exhibits a notable sensitivity to the ratio between the loading frequency and
the effective diffusion coefficient. This is observed for both hydrogen
pre-charged samples (closed-systems) and samples exposed to a permanent source
of hydrogen (open-systems). Experiments are used to determine the critical
concentration for embrittlement, by mapping the range of frequencies where the
output is the same as testing in inert environments. We then quantitatively
investigate and discuss the implications of developing materials with higher
trap densities in mitigating embrittlement in the presence of cyclic loads. It
is shown that, unlike the static case, increasing the density of "beneficial
traps" is a viable strategy in designing alloys resistant to hydrogen assisted
fatigue for both closed- and open-systems. | 2008.05452v1 |
2020-08-18 | Preparation of Isotopically enriched $^{112,116,120,124}$Sn targets at VECC | Resistive heating and mechanical rolling methods have been employed to
prepare isotopically enriched thin target foils of 116Sn (~380 \mu g/cm2),
124Sn(~400 \mu g/cm2) and thicker foils of 112Sn (1.7 mg/cm2),120Sn (1.6
mg/cm2),respectively. Preparation of enriched targets with small amount of
material, selection of releasing agent for thin targets and separation of
deposited material insolvent were among the several challenges while
fabrication of the thin targets. Uniformity of the targets has been measured
using 241Am {\alpha}-source. NaCl has been used as releasing agent in
preparation of the thin targets. These targets have been successfully used in
nuclear physics experiments at VECC. | 2008.08081v2 |
2020-08-20 | Polarization amplification by spin-doping in nanomagnetic/graphene hybrid systems | The generation of non-equilibrium electron spin polarization, spin transport,
and spin detection are fundamental in many quantum devices. We demonstrate that
a lattice of magnetic nanodots enhances the electron spin polarization in
monolayer graphene via carrier exchange. We probed the spin polarization
through a resistively-detected variant of electron spin resonance (ESR) and
observed resonance amplification mediated by the presence of the nanodots. Each
nanodot locally injects a surplus of spin-polarized carriers into the graphene,
and the ensemble of all "spin hot spots" generates a non-equilibrium electron
spin polarization in the graphene layer at macroscopic lengths. This occurs
whenever the interdot distance is comparable or smaller than the spin diffusion
length. | 2008.08813v2 |
2020-08-21 | Fate of a soliton matter upon symmetry-breaking ferroelectric order | In a one-dimensional (1D) system with degenerate ground states, their domain
boundaries, dubbed solitons, emerge as topological excitations often carrying
unconventional charges and spins; however, the soliton excitations are only
vital in the non-ordered 1D regime. Then a question arises; how do the solitons
conform to a 3D ordered state? Here, using a quasi-1D organic ferroelectric,
TTF-CA, with degenerate polar dimers, we pursue the fate of a spin-soliton
charge-soliton composite matter in a 1D polar-dimer liquid upon its transition
to a 3D ferroelectric order by resistivity, NMR and NQR measurements. We
demonstrate that the soliton matter undergoes neutral spin-spin soliton pairing
and spin-charge soliton pairing to form polarons, coping with the 3D order. The
former contributes to the magnetism through triplet excitations whereas the
latter carries electrical current. Our results reveal the whole picture of a
soliton matter that condenses into the 3D ordered state. | 2008.09337v1 |
2020-10-09 | Electronic and magnetic properties of $α$-FeGe$_2$ films embedded in vertical spin valve devices | We studied metastable $\alpha$-FeGe$_2$, a novel layered tetragonal material,
embedded as a spacer layer in spin valve structures with ferromagnetic Fe$_3$Si
and Co$_2$FeSi electrodes. For both types of electrodes, spin valve operation
is demonstrated with a metallic transport behavior of the $\alpha$-FeGe$_2$
spacer layer. The spin valve signals are found to increase both with
temperature and spacer thickness, which is discussed in terms of a decreasing
magnetic coupling strength between the ferromagnetic bottom and top electrodes.
The temperature-dependent resistances of the spin valve structures exhibit
characteristic features, which are explained by ferromagnetic phase transitions
between 55 and 110~K. The metallic transport characteristics as well as the
low-temperature ferromagnetism are found to be consistent with the results of
first-principles calculations. | 2010.04453v2 |
2020-10-16 | Chirality induced Giant Unidirectional Magnetoresistance in Twisted Bilayer Graphene | Twisted bilayer graphene (TBG) exhibits fascinating correlation-driven
phenomena like the superconductivity and Mott insulating state, with flat bands
and a chiral lattice structure. We find by quantum transport calculations that
the chirality leads to a giant unidirectional magnetoresistance (UMR) in TBG,
where the unidirectionality refers to the resistance change under the reversal
of the direction of the current or magnetic field. We point out that flat bands
significantly enhance this effect. The UMR increases quickly upon reducing the
twist angle and reaches about 20\% for an angle of 1.5$^\circ$ in a 10 T
in-plane magnetic field. We propose the band structure topology (asymmetry),
which leads to a direction-sensitive mean free path, as a useful way to
anticipate the UMR effect. The UMR provides a probe for chirality and band
flatness in the twisted bilayers. | 2010.08385v2 |
2020-11-11 | Electron doping of the iron-arsenide superconductor CeFeAsO controlled by hydrostatic pressure | In the iron-pnictide material CeFeAsO not only the Fe moments, but also the
local 4f moments of the Ce order antiferromagnetically at low temperatures. We
elucidate on the peculiar role of the Ce on the emergence of superconductivity.
While application of pressure suppresses the iron SDW ordering temperature
monotonously up to 4 GPa, the Ce-4f magnetism is stabilized, until both types
of magnetic orders disappear abruptly and a narrow SC dome develops. With
further increasing pressure characteristics of a Kondo-lattice system become
more and more apparent in the electrical resistivity. This suggests a
connection of the emergence of superconductivity with the extinction of the
magnetic order and the onset of Kondo-screening of the Ce-4f moments. | 2011.05665v1 |
2020-11-17 | Dichotomy Between Orbital and Magnetic Nematic Instabilities in BaFe2S3 | Nematic orders emerge nearly universally in iron-based superconductors, but
elucidating their origins is challenging because of intimate couplings between
orbital and magnetic fluctuations. The iron-based ladder material BaFe2S3,
which superconducts under pressure, exhibits antiferromagnetic order below TN ~
117K and a weak resistivity anomaly at T* ~ 180K, whose nature remains elusive.
Here we report angle-resolved magnetoresistance (MR) and elastoresistance (ER)
measurements in BaFe2S3, which reveal distinct changes at T*. We find that MR
anisotropy and ER nematic response are both suppressed near T*, implying that
an orbital order promoting isotropic electronic states is stabilized at T*.
Such an isotropic state below T* competes with the antiferromagnetic order,
which is evidenced by the nonmonotonic temperature dependence of nematic
fluctuations. In contrast to the cooperative nematic orders in spin and orbital
channels in iron pnictides, the present competing orders can provide a new
platform to identify the separate roles of orbital and magnetic fluctuations. | 2011.08600v1 |
2020-11-24 | Evidence of interfacial asymmetric spin scattering at ferromagnet-Pt interfaces | We measure the spin-charge interconversion by the spin Hall effect in
ferromagnetic/Pt nanodevices. The extracted effective spin Hall angles (SHAs)
of Pt evolve drastically with the ferromagnetic (FM) materials (CoFe, Co, and
NiFe), when assuming transparent interfaces and a bulk origin of the spin
injection/detection by the FM elements. By carefully measuring the interface
resistance, we show that it is quite large and cannot be neglected. We then
evidence that the spin injection/detection at the FM/Pt interfaces are
dominated by the spin polarization of the interfaces. We show that interfacial
asymmetric spin scattering becomes the driving mechanism of the spin injection
in our samples. | 2011.12207v2 |
2020-11-25 | Electron hydrodynamics of anomalous Hall materials | We study two-dimensional electron systems in the hydrodynamic regime. We show
that a geometrical Berry curvature modifies the effective Navier-Stokes
equation for viscous electron flow in topological materials. For small electric
fields, the Hall current becomes negligible compared to the viscous
longitudinal current. In this regime, we highlight an unconventional Poiseuille
flow with an asymmetric profile and a deviation of the maximum of the current
from the center of the system. In a two-dimensional infinite geometry, the
Berry curvature leads to current whirlpools and an asymmetry of potential
profile. This phenomenon can be probed by measuring the asymmetric non-local
resistance profile. | 2011.12590v1 |
2020-11-29 | Pressure Dependent Electronic Structure in CeRh$_6$Ge$_4$ | Using the state-of-art dynamical mean-field theory combined with density
functional theory method, we have performed systematic study on the temperature
and pressure dependent electronic structure of ferromagnetic quantum critical
material candidate CeRh$_6$Ge$_4$. At -3.9 GPa and -8.3 GPa, the Ce-4$f$
occupation variation, the local magnetic susceptibility, and the low-frequency
electronic self-energy behaviors suggest the Ce-4$f$ electrons are in the
localized state; whereas at 6.5 GPa and 13.1 GPa, these quantities indicate the
Ce-4$f$ electrons are in the itinerant state. The characteristic temperatures
associated with the coherent Kondo screening is gradually suppressed to 0
around 0.8 GPa upon releasing external pressure, indicative of a local quantum
critical point. Interestingly, the momentum-resolved spectrum function shows
that even at the localized state side, highly anisotropic
$\mathbf{k}$-dependent hybridization between Ce-4$f$ and conduction electrons
is still present along $\Gamma$-A, causing hybridization gap in between. The
calculations predict 8 Fermi surface sheets at the local-moment side and 6
sheets at the Kondo coherent state. Finally, the self-energy at 0.8 GPa can be
well fitted by marginal Fermi-liquid form, giving rise to a linearly
temperature dependent resistivity. | 2011.14256v1 |
2020-12-16 | Superconductivity in the $\mathbb{Z}_2$ kagome metal KV$_3$Sb$_5$ | Here we report the observation of bulk superconductivity in single crystals
of the two-dimensional kagome metal KV$_3$Sb$_5$. Magnetic susceptibility,
resistivity, and heat capacity measurements reveal superconductivity below $T_c
= 0.93$K, and density functional theory (DFT) calculations further characterize
the normal state as a $\mathbb{Z}_2$ topological metal. Our results demonstrate
that the recent observation of superconductivity within the related kagome
metal CsV$_3$Sb$_5$ is likely a common feature across the AV$_3$Sb$_5$ (A: K,
Rb, Cs) family of compounds and establish them as a rich arena for studying the
interplay between bulk superconductivity, topological surface states, and
likely electronic density wave order in an exfoliable kagome lattice. | 2012.09097v2 |
2020-12-25 | 3D Printing Autoclavable PPE on Low-Cost Consumer 3D Printers | During the COVID-19 pandemic, medical facilities began using 3D printed PPE
sourced from their own print labs, makerspaces, universities, and individuals
with 3D printers to fill the gaps in supply as traditional manufacturing was
not widely enough distributed nor quick enough to scale to widespread spikes in
demand. However, to date this PPE has been limited to low-temperature, easy to
print thermoplastics which are not compatible with autoclave sterilization and
must be sterilized by hand washing methods. Herein, we present a method for 3D
printing a temperature resistant nylon copolymer on a common low-cost 3D
printer. We show that the resulting parts can be autoclaved without
deformation, and conduct uniaxial tensile testing showing that autoclaving the
material does not result in substantial degradation of material properties. As
a result, we demonstrate the capability to manufacture autoclavable PPE on
low-cost consumer 3D printers with only minor modification. | 2012.13476v3 |
2021-02-01 | Electronic, magnetic and galvanomagnetic properties of Co-based Heusler alloys: possible states of a half-metallic ferromagnet and spin gapless semiconductor | Parameters of the energy gap and, consequently, electronic, magnetic and
galvanomagnetic properties in different X$_2$YZ Heusler alloys can vary quite
strongly. In particular, half-metallic ferromagnets (HMFs) and spin gapless
semiconductors (SGSs) with almost 100% spin polarization of charge carriers are
promising materials for spintronics. The changes in the electrical, magnetic
and galvanomagnetic properties of the Co$_2$YSi (Y = Ti, V, Cr, Mn, Fe) and
Co$_2$MnZ Heusler alloys (Z = Al, Si, Ga, Ge) in possible HMF and/or SGS states
were followed and their interconnection was established. Significant changes in
the values of the magnetization and residual resistivity were found. At the
same time, the correlations between the changes in these electronic and
magnetic characteristics depending on the number of valence electrons and spin
polarization are observed. | 2102.00952v1 |
2021-02-14 | PCM-trace: Scalable Synaptic Eligibility Traces with Resistivity Drift of Phase-Change Materials | Dedicated hardware implementations of spiking neural networks that combine
the advantages of mixed-signal neuromorphic circuits with those of emerging
memory technologies have the potential of enabling ultra-low power pervasive
sensory processing. To endow these systems with additional flexibility and the
ability to learn to solve specific tasks, it is important to develop
appropriate on-chip learning mechanisms.Recently, a new class of three-factor
spike-based learning rules have been proposed that can solve the temporal
credit assignment problem and approximate the error back-propagation algorithm
on complex tasks. However, the efficient implementation of these rules on
hybrid CMOS/memristive architectures is still an open challenge. Here we
present a new neuromorphic building block,called PCM-trace, which exploits the
drift behavior of phase-change materials to implement long lasting eligibility
traces, a critical ingredient of three-factor learning rules. We demonstrate
how the proposed approach improves the area efficiency by >10X compared to
existing solutions and demonstrates a techno-logically plausible learning
algorithm supported by experimental data from device measurements | 2102.07260v2 |
2021-03-01 | Enhanced Superconductivity in the Se-substituted 1T-PdTe$_2$ | Two-dimensional transition metal dichalcogenide PdTe$_2$ recently attracts
much attention due to its phase coexistence of type-II Dirac semimetal and
type-I superconductivity. Here we report a 67 % enhancement of superconducting
transition temperature in the 1T-PdSeTe in comparison to that of PdTe2 through
partial substitution of Te atoms by Se. The superconductivity has been
unambiguously confirmed by the magnetization, resistivity and specific heat
measurements. 1T-PdSeTe shows type-II superconductivity with large anisotropy
and non-bulk superconductivity nature with volume fraction ~ 20 % estimated
from magnetic and heat capacity measurements. 1T-PdSeTe expands the family of
superconducting transition metal dichalcogenides and thus provides additional
insights for understanding superconductivity and topological physics in the
1T-PdTe$_2$ system | 2103.00687v1 |
2021-03-02 | Revealing atomic-scale vacancy-solute interaction in nickel | Imaging individual vacancies in solids and revealing their interactions with
solute atoms remains one of the frontiers in microscopy and microanalysis. Here
we study a creep-deformed binary Ni-2 at.% Ta alloy. Atom probe tomography
reveals a random distribution of Ta. Field ion microscopy, with contrast
interpretation supported by density-functional theory and time-of-flight mass
spectrometry, evidences a positive correlation of tantalum with vacancies. Our
results support solute-vacancy binding, which explains improvement in creep
resistance of Ta-containing Ni-based superalloys and helps guide future
material design strategies. | 2103.01639v3 |
2021-03-04 | Strange electrical transport: Colossal magnetoresistance via avoiding fully polarized magnetization in ferrimagnetic insulator Mn3Si2Te6 | Colossal magnetoresistance is of great fundamental and technological
significance and exists mostly in the manganites and a few other materials.
Here we report colossal magnetoresistance that is starkly different from that
in all other materials. The stoichiometric Mn3Si2Te6 is an insulator featuring
a ferrimagnetic transition at 78 K. The resistivity drops by 7 orders of
magnitude with an applied magnetic field above 9 Tesla, leading to an
insulator-metal transition at up to 130 K. However, the colossal
magnetoresistance occurs only when the magnetic field is applied along the
magnetic hard axis and is surprisingly absent when the magnetic field is
applied along the magnetic easy axis where magnetization is fully saturated.
The anisotropy field separating the easy and hard axes is 13 Tesla, unexpected
for the Mn ions with nominally negligible orbital momentum and spin-orbit
interactions. Double exchange and Jahn-Teller distortions that drive the
hole-doped manganites do not exist in Mn3Si2Te6. The phenomena fit no existing
models, suggesting a unique, intriguing type of electrical transport. | 2103.02764v1 |
2021-03-08 | The Efficacy of the Method of Four Coefficients to Determine Charge Carrier Scattering | The investigation of the electronic properties of semiconductors is
inherently challenging due to the ensemble averaging of fundamentals to
transport measurements (i.e., resistivity, Hall, and Seebeck coefficient
measurements). Here, we investigate the incorporation of a fourth measurement
of electronic transport, the Nernst coefficient, into the analysis, termed the
method of four-coefficients. This approach yields the Fermi level, effective
mass, scattering exponent, and relaxation time. We begin with a review of the
underlying mathematics and investigate the mapping between the four-dimensional
material property and transport coefficient spaces. We then investigate how the
traditional single parabolic band method yields a single, potentially incorrect
point on the solution sub-space. This uncertainty can be resolved through
Nernst coefficient measurements and we map the span of the ensuing sub-space.
We conclude with an investigation of how sensitive the analysis of transport
coefficients is to experimental error for different sample types. | 2103.04569v1 |
2021-03-26 | Electron-electron interactions and weak anti-localization in few-layer ZrTe5 devices | Much effort has been devoted to the electronic properties of relatively thick
ZrTe5 crystals, focusing on their three-dimensional topological effects. Thin
ZrTe5 crystals, on the other hand, were much less explored experimentally. Here
we present detailed magnetotransport studies of few-layer ZrTe5 devices, in
which electron-electron interactions and weak anti-localization are observed.
The coexistence of the two effects manifests themselves in corroborating
evidence presented in the temperature and magnetic field dependence of the
resistance. Notably, the temperature-dependent phase coherence length extracted
from weak anti-localization agrees with strong electron-electron scattering in
the sample. Meanwhile, universal conductance fluctuations have temperature and
gate voltage dependence that is similar to that of the phase coherence length.
Lastly, all the transport properties in thin ZrTe5 crystals show strong
two-dimensional characteristics. Our results provide new insight into the
highly intricate properties of topological material ZrTe5. | 2103.14329v1 |
2021-03-31 | Deciphering water-solid reactions during hydrothermal corrosion of SiC | Water solid interfacial reactions are critical to understanding corrosion.
More specifically, it is notoriously difficult to determine how water and solid
interact beyond the initial chemisorption to induce the surface dissolution.
Here, we report atomic-scale mechanisms of the elementary steps during SiC
hydrothermal corrosion, from the initial surface attack to surface dissolution.
We find that hydrogen scission reactions play a vital role in breaking Si-C
bonds, regardless of the surface orientations. Stable silica layer does not
form on the surface, but the newly identified chemical reactions on SiC are
analogous to those observed during the dissolution of silica. SiC is dissolved
directly into the water as soluble silicic acid. The rate of hydrothermal
corrosion determined based on the calculated reaction activation energies is
consistent with available experimental data. Our work sheds new light on
understanding and interpreting the experimental observations and it provides
foundation for design of materials that are resistant to corrosion in water. | 2103.16738v1 |
2021-04-14 | Low-Frequency Electronic Noise Spectroscopy of Quasi-2D van der Waals Antiferromagnetic Semiconductors | We investigated low-frequency current fluctuations, i.e. noise, in the
quasi-two-dimensional (2D) van der Waals antiferromagnetic semiconductor FePS3
with the electronic bandgap of 1.5 eV. The electrical and noise characteristics
of the p-type, highly resistive, thin films of FePS3 were measured at different
temperatures. The noise spectral density was of the 1/f - type over most of the
examined temperature range but revealed well-defined Lorentzian bulges, and
increased strongly near the Neel temperature of 118 K (f is the frequency).
Intriguingly, the noise spectral density attained its minimum at temperature
T~200 K, which was attributed to an interplay of two opposite trends in noise
scaling - one for semiconductors and another for materials with the phase
transitions. The Lorentzian corner frequencies revealed unusual dependence on
temperature and bias voltage, suggesting that their origin is different from
the generation - recombination noise in conventional semiconductors. The
obtained results are important for proposed applications of antiferromagnetic
semiconductors in spintronic devices. They also attest to the power of the
noise spectroscopy for monitoring various phase transitions. | 2104.06578v1 |
2020-12-26 | The Main Role of Thermal Annealing in Controlling the Structural and Optical Properties of ITO Thin Film Layer | Here we report on studying the electronic and optical material properties of
the technologically-relevant material indium tin oxide (ITO) as a function of
thermal annealing. In this work, ITO powder has been prepared utilizing
solid-state reaction methods. An electron beam gun technology has been used to
prepare a ITO film (325 nm). The ITO window layer has been investigated at
various temperatures. The effects of absolute temperature on the structural,
optical, and electrical properties of the prepared ITO thin film layer are
investigated. The energy band type corresponding to the orbital transitions has
been determined, and the energies of the orbital transitions have been
calculated in the Tauc region, HOMO/LUMO gap, and charge transfer gap. In
additions, the exciton and Urbach energies have been computed. It has been
found that these energies increase with increasing the annealing temperature,
except for Urbach's energies which behave differently. Thin-film quality
coefficient, surface resistance, and thermal emission in addition to the angle
of refraction as a function of wavelength, have been determined. | 2104.07464v1 |
2021-04-16 | Circuit-aware Device Modeling of Energy-efficient Monolayer WS$_2$ Trench-FinFETs | The continuous scaling of semiconductor technology has pushed the footprint
of logic devices below 50 nm. Currently, logic standard cells with one single
fin are being investigated to increase the integration density, although such
options could severely limit the performance of individual devices. In this
letter, we present a novel Trench (T-) FinFET device, composed of a monolayer
two-dimensional (2D) channel material. The device characteristics of a
monolayer WS$_2$-based T-FinFET are studied by combining the first-principles
calculations and quantum transport (QT) simulations. These results serve as
inputs to a predictive analytical model. The latter allows to benchmark the
T-FinFET with strained (s)-Si FinFETs in both quasi-ballistic and diffusive
transport regimes. The circuit-level evaluation highlights that WS$_2$
T-FinFETs exhibit a competitive energy-delay performance compared to s-Si
FinFET and WS$_2$ double-gate transistors, assuming the same mobility and
contact resistivity at small footprints. | 2104.07891v1 |
2021-04-19 | Effect of wear particles and roughness on nanoscale friction | Frictional contacts lead to the formation of a surface layer called the third
body, consisting of wear particles and structures resulting from their
agglomerates. Its behavior and properties at the nanoscale control the
macroscopic tribological performance. It is known that wear particles and
surface topography evolve with time and mutually influence one another.
However, the formation of the mature third body is largely uncharted territory
and the properties of its early stages are unknown. Here we show how a third
body initially consisting of particles acting as roller bearings transitions
into a shear-band-like state by forming adhesive bridges between the particles.
Using large-scale atomistic simulations on a brittle model material, we find
that this transition is controlled by the growth and increasing disorganization
of the particles with increasing sliding distance. Sliding resistance and wear
rate are at first controlled by the surface roughness, but upon agglomeration
wear stagnates and friction becomes solely dependent on the real contact area
in accordance with the plasticity theory of contact by Bowden and Tabor. | 2104.09217v3 |
2021-05-01 | Complementary electrochemical ICP-MS flow cell and in-situ AFM study of the anodic desorption of molecular adhesion promotors | Molecular adhesion promoters are a central component of modern coating
systems for the corrosion protection of structural materials. They are
interface active and form ultrathin corrosion inhibiting and adhesion-promoting
layers. Here we utilize thiol-based self-assembled monolayers (SAMs) as model
system for demonstrating a comprehensive combinatorial approach to understand
molecular level corrosion protection mechanisms under anodic polarization.
Specifically, we compare hydrophilic 11-Mercapto-1-undecanol and hydrophobic
1-Undecanethiol SAMs and their gold-dissolution inhibiting properties. We can
show that the intermolecular forces (hydrophobic vs hydrophilic effects)
control how SAM layers perform under oxidative conditions. Specifically, using
\textit{in situ} electrochemical AFM and a scanning-flow cell coupled to an
ICP-MS a complementary view on both corrosion resistance, as well as on changes
in surface morphology/adhesion of the SAM is possible. Protection from
oxidative dissolution is higher with hydrophobic SAMs, which detach under
micelle formation, while the hydrophilic SAM exhibits lower protective effects
on gold dissolution rates, although it stays intact as highly mobile layer
under anodic polarization. The developed multi-technique approach will prove
useful for studying the interfacial activity and corrosion suppression
mechanism of inhibiting molecules on other metals and alloys. | 2105.00280v1 |
2021-05-09 | Planar topological Hall effect in a hexagonal ferromagnetic Fe5Sn3 single crystal | The planar topological Hall effect (PTHE), appeared when the magnetic field
tended to be along the current, is believed to result from the real-space Berry
curvature of the spin spiral structure and has been experimentally observed in
skyrmion-hosting materials. In this paper, we report an experimental
observation of the PTHE in a hexagonal ferromagnetic Fe5Sn3 single crystal.
With a current along the c axis of Fe5Sn3, the transverse resistivity curves
exhibited obvious peaks near the saturation field as the magnetic field rotated
to the current and appeared more obvious with increasing temperature, which was
related to the noncoplanar spin structure in Fe5Sn3. This spin structure
induced nonzero scalar spin chirality, which acted as fictitious magnetic
fields to conduction electrons and contributed the additional transverse
signal. These findings deepen the understanding of the interaction between
conduction electrons and complex magnetic structures and are instructive for
the design of next-generation spintronic devices. | 2105.03898v1 |
2021-06-02 | Charge order dynamics in underdoped La$\mathbf{_{1.6-\textit{x}}}$Nd$\mathbf{_{0.4}}$Sr$\mathbf{_\textit{x}}$CuO$\mathbf{_{4}}$ revealed by electric pulses | The dynamics of the charge-order domains has been investigated in
La$_{1.48}$Nd$_{0.4}$Sr$_{0.12}$CuO$_{4}$, a prototypical stripe-ordered
cuprate, using pulsed current injection. We first identify the regime in which
nonthermal effects dominate over simple Joule heating, and then demonstrate
that, for small enough perturbation, pulsed current injection allows access to
nonthermally-induced resistive metastable states. The results are consistent
with pinning of the fluctuating charge order, with fluctuations being most
pronounced at the charge-order onset temperature. The nonequilibrium effects
are revealed only when the transition is approached from the charge-ordered
phase. Our experiment establishes pulsed current injection as a viable and
effective method for probing the charge-order dynamics in various other
materials. | 2106.01469v1 |
2021-06-09 | The heat equation for nanoconstrictions in 2D materials with Joule self-heating | We consider the heat equation for monolayer two-dimensional materials in the
presence of heat flow into a substrate and Joule heating due to electrical
current. We compare devices including a nanowire of constant width and a bow
tie (or wedge) constriction of varying width, and we derive approximate
one-dimensional heat equations for them; a bow tie constriction is described by
the modified Bessel equation of zero order. We compare steady state analytic
solutions of the approximate equations with numerical results obtained by a
finite element method solution of the two-dimensional equation. Using these
solutions, we describe the role of thermal conductivity, thermal boundary
resistance with the substrate and device geometry. The temperature in a device
at fixed potential difference will remain finite as the width shrinks, but will
diverge for fixed current, logarithmically with width for the bow tie as
compared to an inverse square dependence in a nanowire. | 2106.05129v2 |
2021-07-21 | Bulk superconductivity and Pauli paramagnetism in nearly stoichiometric CuCo$_2$S$_4$ | It has long remained elusive whether CuCo$_{2}$S$_{4}$ thiospinel shows bulk
superconductivity. Here we clarify the issue by studying on the samples of
sulfur-deficient CuCo$_{2}$S$_{3.7}$ and sulfurized CuCo$_{2}$S$_{4}$. The
sample CuCo$_{2}$S$_{3.7}$ has a smaller lattice constant of $a=9.454$ {\AA},
and it is not superconducting down to 1.8 K. After a full sulfurization, the
$a$ axis of the thiospinel phase increases to 9.475 {\AA}, and the thiospinel
becomes nearly stoichiometric CuCo$_{2}$S$_{4}$, although a secondary phase of
slightly Cu-doped CoS$_2$ forms. Bulk superconductivity at 4.2 K and Pauli
paramagnetism have been demonstrated for the sulfurized CuCo$_{2}$S$_{4}$ by
the measurements of electrical resistivity, magnetic susceptibility, and
specific heat. | 2107.09848v1 |
2021-09-16 | Achieving adjustable elasticity with non-affine to affine transition | For various engineering and industrial applications it is desirable to
realize mechanical systems with broadly adjustable elasticity to respond
flexibly to the external environment. Here we discover a topology-correlated
transition between affine and non-affine regimes in elasticity in both two- and
three-dimensional packing-derived networks. Based on this transition, we
numerically design and experimentally realize multifunctional systems with
adjustable elasticity. Within one system, we achieve solid-like affine
response, liquid-like non-affine response and a continuous tunability in
between. Moreover, the system also exhibits a broadly tunable Poisson's ratio
from positive to negative values, which is of practical interest for energy
absorption and for fracture-resistant materials. Our study reveals a
fundamental connection between elasticity and network topology, and
demonstrates its practical potential for designing mechanical systems and
metamaterials. | 2109.07789v1 |
2021-09-22 | Roller-Coaster in a Flatland: Magnetoresistivity in Eu-intercalated Graphite | Novel phenomena in magnetically-intercalated graphite has been a subject of
much research, pioneered and promoted by M.~S. and G.~Dresselhaus and many
others in the 1980s. Among the most enigmatic findings of that era was a
dramatic, roller-coaster-like behavior of the magnetoresistivity in EuC$_6$
compound, in which magnetic Eu$^{2+}$ ions form a triangular lattice that is
commensurate to graphite honeycomb planes. In this study, we provide a
long-awaited {\it microscopic} explanation of this behavior, demonstrating that
the resistivity of EuC$_6$ is dominated by spin excitations in Eu-planes and
their highly nontrivial evolution with the magnetic field. Together with our
theoretical analysis, the present study showcases the power of the synthetic 2D
materials as a source of potentially significant insights into the nature of
exotic spin excitations. | 2109.10916v3 |
2021-10-05 | Experimental study of transport properties of Weyl semimetal LaAlGe thin films grown by molecular beam epitaxy | Rare earth compounds display diverse electronic, magnetic, and
magneto-transport properties. Recently these compounds of the type RAlGe (R =
La, Ce, Pr) have been shown to exhibit Weyl semimetallic behavior. In this
work, we have investigated the crystal structure, electronic, and
magneto-transport properties of the Weyl semimetal LaAlGe thin films grown by
molecular beam epitaxy. The temperature dependence of longitudinal resistivity
at different magnetic fields is discussed. Observations of magnetoresistances
and Hall effect at different temperatures and their evolution with magnetic
field up to 6 T are also discussed with relevant mechanisms. We have observed
positive unsaturated magnetoresistances, with a small quadratic contribution at
low temperatures, which tends to saturate at higher fields. The Hall
measurements confirm the electron-dominated semimetallic conduction with an
average charge carrier density of ~ 9.68*10^21 cm^(-3) at room temperature. | 2110.02322v1 |
2021-11-05 | Externally controlled and switchable 2D electron gas at the Rashba interface between ferroelectrics and heavy $d$ metals | Strong spin-orbit coupling in noncentrosymmetric materials and interfaces
results in remarkable physical phenomena, such as nontrivial spin textures,
which may exhibit Rashba, Dresselhaus, and other intricated configurations.
This provides a promising basis for nonvolatile spintronic devices and further
implications. Here, we simulate from first principles a two-dimensional
electron gas in ultrathin platinum and palladium layers grown on ferroelectric
PbTiO$_3$(001). The latter allows, in principle, to switch and control the
spin-to-charge conversion by the polarization reversal. We show how the band
structure and its Rashba splitting differ in the Pt and Pd overlayers and how
these electronic features change with increasing the overlayer thickness and
upon reversal of polarization. Besides, for both overlayers, we simulated their
current-voltage ($I-V$) characteristics, the resistance of which upon the
polarization reversal changes between 20% and several hundred percent. The
reported findings can be used to model directly the Rashba-Edelstein effect. | 2111.03351v2 |
2021-11-12 | Schwarzite and schwarzynes based load-bear resistant radial cellular griding-based 3D printed structures | Nature-occurring structures exhibiting unique topological features such as
complex and gradient porosity has been the basis to create new materials and/or
structures. Most studies have been focused on complex periodic porous
structures but gradient porous ones have not been yet fully investigated for
stable structural designs. In this work, we have proposed and tested a new
approach to create cellular griding structures, in which the mass density
varies from the center to the borders, i.e, a radial gradient. To create these
new structures we exploited the topology of two carbon-based families with
different pore sizes, the schwarzites, and schwarzynes. We created fully
atomistic models that were translated into macroscale ones that were then 3D
printed. The mechanical behavior of the gradient structures was investigated by
molecular dynamics simulations and mechanical compression tests of the printed
models. Our results show that their mechanical response can be engineered (for
instance, in terms of energy absorption, ballistic performance, etc.) and can
outperform their corresponding density uniform structures. | 2111.06641v1 |
2021-12-18 | Enhanced Tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) Magnetic Tunnel Junctions | Spinel MgAl2O4 and family oxides are emerging barrier materials useful for
magnetic tunnel junctions (MTJs). We report large tunnel magnetoresistance
(TMR) ratios up to 429% at room temperature (RT) and 1,034% at 10 K in a
Fe/MgAl2O4/Fe(001)-based MTJ prepared using electron-beam evaporation of
Mg4Al-Ox. Resistance oscillations with a MTJ barrier thickness of 0.3-nm were
significantly enhanced compared to those of a Fe/MgO/Fe(001) MTJ, resulting in
a large TMR oscillation peak-to-valley difference of 125% at RT. The
differential conductance spectra were symmetric with bias polarity, and the
spectrum in the parallel magnetization state at low temperature demonstrate
significant peaks within broad local minima at |0.2-0.6| V, indicating improved
barrier interfaces by the Mg4Al-Ox barrier. This study demonstrates that TMR
ratios in Fe(001)-MTJs can still be improved. | 2112.09910v1 |
2022-01-20 | Spin valve effect in two-dimensional VSe$_2$ system | Vanadium based dichalcogenides, VSe$_2$, are two-dimensional materials in
which magnetic Vanadium atoms are arranged in a hexagonal lattice and are
coupled ferromagnetically within the plane. However, adjacent atomic planes are
coupled antiferromagnetically. This provides new and interesting opportunities
for application in spintronics and data storage and processing technologies. A
spin valve magnetoresistance may be achieved when magnetic moments of both
atomic planes are driven to parallel alignment by an external magnetic field.
The resistance change associated with the transition from antiparallel to the
parallel configuration is qualitatively similar to that observed in
artificially layered metallic magnetic structures. Detailed electronic
structure of VSe$_2$ was obtained from DFT calculations. Then, the ballistic
spin-valve magnetoresistance was determined within the Landauer formalism. In
addition, we also analyze thermal and thermoelectric properties. Both phases of
VSe$_2$, denoted as H and T, are considered. | 2201.08420v1 |
2022-03-23 | Dipolar Magnetic Interactions and A-type Antiferromagnetic Order in the Zintl Phase Insulator EuZn2P2 | Zintl phases, containing strongly covalently bonded frameworks with separate
ionically bonded ions, have emerged as a critical materials family in which to
couple magnetism and strong spin-orbit coupling to drive diverse topological
phases of matter. Here we report the single-crystal synthesis, magnetic,
thermodynamic, transport, and theoretical properties of the Zintl compound
EuZn2P2 that crystallizes in the anti-La2O3 P-3m1 structure, containing
triangular layers of Eu2+ ions. In-plane resistivity measurements reveal
insulating behavior with an estimated bandgap of Eg=0.11eV. Comparing Eu
magnetic ordering temperatures across trigonal EuM2X2 (M=divalent metal,
X=pnictide) shows that EuZn2P2 exhibits the highest ordering temperature, with
variations in TN correlating with changes in expected dipolar interaction
strengths within and between layers and independent of the magnitude of
electrical conductivity. These results provide experimental validation of the
cytochemical intuition that the cation Eu2+ layers and the anionic (M2X2)2-
framework can be treated as electronically distinct subunits, enabling further
predictive materials design. | 2203.12739v1 |
2022-04-13 | Modeling crack propagation in heterogeneous materials: Griffith's law, intrinsic crack resistance and avalanches | Various kinds of heterogeneity in solids including atomistic discreteness
affect the fracture strength as well as the failure dynamics remarkably. Here
we study the effects of an initial crack in a discrete model for fracture in
heterogeneous materials, known as the fiber bundle model. We find three
distinct regimes for fracture dynamics depending on the initial crack size. If
the initial crack is smaller than a certain value, it does not affect the
rupture dynamics and the critical stress. While for a larger initial crack, the
growth of the crack leads to a breakdown of the entire system, and the critical
stress depends on the crack size in a power-law manner with a nontrivial
exponent. The exponent, as well as the limiting crack size, depend on the
strength of heterogeneity and the range of stress relaxation in the system. | 2204.06334v1 |
2022-04-21 | Computational Design of Kinesthetic Garments | Kinesthetic garments provide physical feedback on body posture and motion
through tailored distributions of reinforced material. Their ability to
selectively stiffen a garment's response to specific motions makes them
appealing for rehabilitation, sports, robotics, and many other application
fields. However, finding designs that distribute a given amount of
reinforcement material to maximally stiffen the response to specified motions
is a challenging problem. In this work, we propose an optimization-driven
approach for automated design of reinforcement patterns for kinesthetic
garments. Our main contribution is to cast this design task as an on-body
topology optimization problem. Our method allows designers to explore a
continuous range of designs corresponding to various amounts of reinforcement
coverage. Our model captures both tight contact and lift-off separation between
cloth and body. We demonstrate our method on a variety of reinforcement design
problems for different body sites and motions. Optimal designs lead to a two-
to threefold improvement in performance in terms of energy density. A set of
manufactured designs were consistently rated as providing more resistance than
baselines in a comparative user study | 2204.09996v1 |
2022-04-24 | Large Hall electron mobilities in head-to-head BaTiO$_3$-domain walls | Strongly charged head-to-head (H2H) domain walls (DWs) that are purposely
engineered along the [110] crystallographic orientation into ferroelectric
BaTiO$_3$ single crystals have been proposed as novel 2-dimensional electron
gases (2DEGs) due to their significant domain wall conductivity (DWC). Here, we
quantify these 2DEG properties through dedicated Hall-transport measurements in
van-der-Pauw 4-point geometry at room temperature, finding the electron
mobility to reach around 400~cm$^2$(Vs)$^{-1}$, while the 2-dimensional charge
density amounts to ~7$\times$10$^3$cm$^{-2}$. We underline the necessity to
take account of thermal and geometrical-misalignment offset voltages by
evaluating the Hall resistance under magnetic-field sweeps, since otherwise
dramatic errors of several hundred percent in the derived mobility and charge
density values can occur. Apart from the specific characterization of the
conducting BaTiO$_3$ DW, we propose the method as an easy and fast way to
quantitatively characterize ferroic conducting DWs, complementary to previously
proposed scanning-probe-based Hall-potential analyses. | 2204.11265v1 |
2022-07-04 | Interdependent Superconducting Networks | Cascades are self-amplifying processes triggered by feedback mechanisms that
may cause a substantial part of a macroscopic system to change its phase in
response of a relatively small local event. The theoretical background for
these phenomena is rich and interdisciplinary with interdependent networks
providing a versatile "two-interactions" framework to study their multiscale
evolution. Yet, physics experiments aimed at validating this ever-growing
volume of predictions have remained elusive, hitherto hindered by the problem
of identifying possible physical mechanisms realizing interdependent couplings.
Here we develop and study the first experimental realization of an
interdependent system as a multilayer network of two disordered superconductors
separated by an insulating film. We show that Joule heating effects emerging at
sufficiently large driving currents act as dependency links between the
superconducting layers, igniting overheating cascades via adaptive back and
forth electro-thermal feedbacks. Through theory and experiments, we unveil a
rich phase diagram of mutual resistive transitions and cascading processes that
physically realize and generalize interdependent percolation. The present work
establishes the first physics laboratory bench for the manifestation of the
theory of interdependent systems, enabling experimental studies to control and
to further develop the multilayer phenomena of complex interdependent
materials. | 2207.01669v1 |
2022-07-06 | Ferroelastic domain walls in BiFeO$_3$ as memristive networks | Electronic conduction along individual domain walls (DWs) has been reported
in BiFeO$_3$ (BFO) and other nominally insulating ferroelectrics. DWs in these
materials separate regions of differently oriented electrical polarization
(domains) and are just a few atoms wide, providing self-assembled nanometric
conduction paths. In this work, it is shown that electronic transport is
possible also from wall to wall through the dense network of as-grown DWs in
BFO thin films. Electric field cycling at different points of the network,
performed locally by conducting atomic force microscope (cAFM), induces
resistive switching selectively at the DWs, both for vertical (single wall) and
lateral (wall-to-wall) conduction. These findings are the first step towards
investigating DWs as memristive networks for information processing and
in-materio computing. | 2207.02688v1 |
2022-07-07 | Asymmetric Ground States in La$_{0.67}$Sr$_{0.33}$MnO$_3$/BaTiO$_3$ heterostructures Induced by Flexoelectric Bending | Misfit strain delivered from single-crystal substrates typically modifies the
ground states of transition metal oxides, generating increasing interests in
designing modern transducers and sensors. Here, we demonstrate that
magnetotransport properties of La$_{0.67}$Sr$_{0.33}$MnO$_3$ (LSMO) films were
continuously tuned by uniaxial strain produced by a home-designed bending jig.
The electrical conductivity and Curie temperature of LSMO films are enhanced by
bending stresses. The resistivity of a u-shape bended LSMO decays three times
faster than that of a n-shape bended LSMO as a response to the same magnitude
of strain. The asymmetric magnetic states in uniaxially strained LSMO are
attributed to the dual actions of Jahn-Teller distortion and strain gradient
mediated flexoelectric fields in an adjacent ferroelectric layer. These
findings of multi-field regulation in a single material provide a feasible
means for developing flexible electronic and spintronic devices. | 2207.03297v1 |
2022-07-11 | Thermoelectrics: from Longitudinal to Transverse | In this article, we show fundamentals and recent advances on the transverse
thermoelectric generation, in which a thermopower is generated in the direction
perpendicular to an applied temperature gradient. Transverse thermoelectric
generation is one of the central topics in condensed matter physics, and can be
a breakthrough approach to solve long-standing technological problems with
contact resistances in thermoelectric generators. We review here the six
currently known driving mechanisms: the ordinary Nernst effect, the anomalous
Nernst effect, goniopolar materials, the spin Seebeck effect, Seebeck-driven
transverse thermoelectric generation, and ($p \times n$)-type multilayers. This
article summarizes the principles and functionalities of these transverse
thermoelectric effects and discusses their potential as "Future energy". | 2207.05005v1 |
2022-07-13 | Strong Spin-Orbit Torque Induced by the Intrinsic Spin Hall Effect in Cr1-xPtx | We report on a spin-orbit torque study of the spin current generation in
Cr1-xPtx alloy, using the light 3d ferromagnetic Co as the spin current
detector. We find that the dampinglike spin-orbit torque of Cr1-xPtx/Co
bilayers can be enhanced by tuning the Cr concentration in the Cr1-xPtx layer,
with a maximal value of 0.31 at the optimal composition of Cr0.2Pt0.8. We find
that the spin current generation in the Cr1-xPtx alloy can be fully understood
by the characteristic trade-off between the intrinsic spin Hall conductivity of
Pt and the carrier lifetime in the dirty limit. We find no evidence for the
spin current generation by other mechanisms in this material, revealing that
the role of Cr is found to be simply the same as other metals and oxides in
previous studies. This work also establishes the low-resistivity Cr0.2Pt0.8 as
an energy-efficient spin-orbit torque provider for magnetic memory and
computing technologies. | 2207.05992v2 |
2022-09-14 | Revealing the band structure of ZrTe$_5$ using Multicarrier Transport | The layered material ZrTe$_5$ appears to exhibit several exotic behaviors
which resulted in significant interest recently, although the exact properties
are still highly debated. Among these we find a Dirac/Weyl semimetallic
behavior, nontrivial spin textures revealed by low temperature transport, and a
potential weak or strong topological phase. The anomalous behavior of
resistivity has been recently elucidated as originating from band shifting in
the electronic structure. Our work examines magnetotransport behavior in
ZrTe$_5$ samples in the context of multicarrier transport. The results, in
conjunction with ab-initio band structure calculations, indicate that many of
the transport features of ZrTe$_5$ across the majority of the temperature range
can be adequately explained by the semiclassical multicarrier transport model
originating from a complex Fermi surface. | 2209.06797v2 |
2022-09-29 | Battery Testing Methods in Fuel Cell Research | This report presents some of the key laboratory electrochemical battery
testing methods that are used in fuel cell research. Methods such as
voltammetry, chronoamperometry, chronopotentiometry, and electrochemical
impedance spectroscopy are of major importance. All the electrochemical
corrosion tests are performed through a tri-electrode polarization cell setup
containing a reference electrode, a counter electrode, and the working
electrode (metal sample of interest) in an electrolyte solution. All three
electrodes are connected to a potentiostat. Corrosion of metal occurs through
an oxidation-reduction (redox) reaction. All the above testing methods can be
performed by manipulating the current and voltage responses from the cell.
Potentiostatic experiments (voltammetry and chronoamperometry) are performed
using constant potential at the working electrode and recording the current
response while galvanostatic experiments (chronopotentiometry) and vice versa.
The measured data through all these experiments can provide very useful
information regarding reaction reversibility, diffusion coefficient, reduction
potential, rate of chemical reaction, durability, adsorption, voltage losses,
and effective resistance to the mass and charge transport offered by electrode
material. | 2209.14541v1 |
2022-10-11 | New Gd-based magnetic compound GdPt$_2$B with a chiral crystal structure | Herein, we report the discovery of a novel Gd-based magnetic compound
GdPt$_2$B with a chiral crystal structure. X-ray diffraction and chemical
composition analyses reveal a CePt$_2$B-type crystal structure (space group:
$P6_422$) for GdPt$_2$B. Moreover, we successfully grew single crystals of
GdPt$_2$B using the Czochralski method. Magnetization measurements and the
Curie$-$Weiss analysis demonstrate that the ferromagnetic interaction is
dominant in GdPt$_2$B. A clear transition is observed in the temperature
dependence of electrical resistivity, magnetic susceptibility, and specific
heat at $T_{\rm O}$ = 87 K. The magnetic phase diagram of GdPt$_2$B, which
consists of a field-polarized ferromagnetic region and a magnetically ordered
region, resembles those of known chiral helimagnets. Furthermore, magnetic
susceptibility measurements reveal a possible spin reorientation within the
magnetically ordered phase in magnetic fields perpendicular to the screw axis.
The results demonstrate that GdPt$_2$B is a suitable platform for investigating
the competing effects of ferromagnetic and antisymmetric exchange interactions
in rare-earth-based chiral compounds. | 2210.05099v1 |
2022-11-09 | Coexistance of volatile and non-volatile memristive effects in phase-separated La$_{0.5}$Ca$_{0.5}$MnO$_{3}$-based devices | In this work, we have investigated the coexistance of volatile and
non-volatile memristive effects in epitaxial phase-separated
La$_{\text{0.5}}$Ca$_{\text{0.5}}$MnO$_{3}$ thin films. At low temperatures (50
K), we observed volatile resistive changes arising from self-heating effects in
the vicinity of a metal-to-insulator transition. At higher temperatures (140 K
and 200 K) we measured a combination of volatile and non-volatile effects
arising from the synergy between self-heating effects and
ferromagnetic-metallic phase growth induced by an external electrical field.
The results reported here add phase separated manganites to the list of
materials which can electrically mimic, on the same device, the behavior of
both neurons and synapses, a feature that might be useful for the development
of neuromorphic computing hardware | 2211.04955v1 |
2022-11-11 | Quantum-Hall physics and three dimensions | The discovery of the quantum Hall effect (QHE) in 1980 marked a turning point
in condensed matter physics: given appropriate experimental conditions, the
Hall conductivity {\sigma}_xy of a two-dimensional (2D) electron system is
exactly quantized. But what happens to the QHE in three dimensions (3D)?
Experiments over the past 40 years showed that some of the remarkable physics
of the QHE, in particular plateau-like Hall conductivities {\sigma}_xy
accompanied by minima in the longitudinal resistivity \r{ho}_xx, can also be
found in 3D materials. However, since typically \r{ho}_xx remains finite and a
quantitative relation between {\sigma}_xy and the conductance quantum e^2/h
could not be established, the role of quantum Hall physics in 3D remains
unsettled. Following a recent series of exciting experiments, the QHE in 3D has
now returned to the centre stage. Here, we summarize the leap in understanding
of 3D matter in magnetic fields emerging from these experiments. | 2211.06248v1 |
2022-11-25 | Microscopic parameters of the van der Waals CrSBr antiferromagnet from microwave absorption experiments | Microwave absorption experiments employing a phase-sensitive external
resistive detection are performed for a topical van der Waals antiferromagnet
CrSBr. The field dependence of two resonance modes is measured in an applied
field parallel to the three principal crystallographic directions, revealing
anisotropies and magnetic transitions in this material. To account for the
observed results, we formulate a microscopic spin model with a bi-axial
single-ion anisotropy and inter-plane exchange. Theoretical calculations give
an excellent description of full magnon spectra enabling us to precisely
determine microscopic interaction parameters for CrSBr. | 2211.14117v1 |
2022-11-30 | Unification of Nonlinear Anomalous Hall Effect and Nonreciprocal Magnetoresistance in Metals by the Quantum Geometry | The quantum geometry has significant consequences in determining transport
and optical properties in quantum materials. Here, we use a semiclassical
formalism coupled with perturbative corrections unifying the nonlinear
anomalous Hall effect (NLAHE) and nonreciprocal magnetoresistance (NMR,
longitudinal resistance) from the quantum geometry. In the dc limit, both
transverse and longitudinal nonlinear conductivities include a term due to the
normalized quantum metric dipole. The quantum metric contribution is intrinsic
and does not scale with the quasiparticle lifetime. We demonstrate the
coexistence of a NLAHE and NMR in films of the doped antiferromagentic
topological insulator MnBi$_2$Te$_4$. Our work indicates that both longitudinal
and transverse nonlinear transport provide a sensitive probe of the quantum
geometry in solids. | 2211.17213v2 |
2022-12-15 | Superconductivity by alloying the topological insulator SnBi2Te4 | Alloying indium into the topological insulator Sn1-xInxBi2Te4 induces bulk
superconductivity with critical temperatures Tc up to 1.85 K and upper critical
fields up to about 14 kOe. This is confirmed by electrical resistivity, heat
capacity, and magnetic susceptibility measurements. The heat capacity shows a
discontinuity at Tc and temperature dependence below Tc consistent with weak
coupling BCS theory, and suggests a superconducting gap near 0.25 meV. The
superconductivity is type-II and the topological surface states have been
verified by photoemission. A simple picture suggests analogies with the
isostructural magnetic topological insulator MnBi2Te4, in which a natural
heterostructure hosts complementary properties on different sublattices, and
motivates new interest in this large family of compounds. The existence of both
topological surface states and superconductivity in Sn1-xInxBi2Te4 identifies
these materials as promising candidates for the study of topological
superconductivity. | 2212.08125v1 |
2022-12-04 | Multiphase polarization in ion-intercalation nanofilms: general theory including various surface effects and memory applications | Ion concentration polarization (CP, current-induced concentration gradient
adjacent to a charge-selective interface) has been well studied for
single-phase mixed conductors (e.g., liquid electrolyte), but multiphase CP has
been rarely addressed in literature. In our recent publication, we proposed
that CP above certain threshold currents can flip the phase distribution in
multiphase ion-intercalation nanofilms sandwiched by ion-blocking electrodes.
We call this phenomenon as multiphase polarization (MP). We then proposed that
MP can further lead to nonvolatile interfacial resistive switching (RS) for
asymmetric electrodes with ion-modulated electron transfer, which theory can
reproduce the experimental results of LTO memristors. In this work, we derive a
comprehensive 2D phase-field model for coupled ion-electron transport in
ion-intercalation materials, with surface effects including electron transfer
kinetics, non-neutral wetting, energy relaxation, and surface charge. Then we
use the model to study MP. We present time evolution of phase boundaries, and
analyze the switching time, current, energy, and cyclic voltammetry, for
various boundary conditions. We find that the switching performance can be
improved significantly by manipulating surface conditions and mean
concentration. Finally, we discuss the prospects of MP-based memories and
possible extensions of the current model. | 2212.10404v1 |
2023-01-09 | Memristive Memory Enhancement by Device Miniaturization for Neuromorphic Computing | The areal footprint of memristors is a key consideration in material-based
neuromorophic computing and large-scale architecture integration. Electronic
transport in the most widely investigated memristive devices is mediated by
filaments, posing a challenge to their scalability in architecture
implementation. Here we present a compelling alternative memristive device and
demonstrate that areal downscaling leads to enhancement in memristive memory
window, while maintaining analogue behavior, contrary to expectations. Our
device designs directly integrated on semiconducting Nb-SrTiO$_3$ allows
leveraging electric field effects at edges, increasing the dynamic range in
smaller devices. Our findings are substantiated by studying the microscopic
nature of switching using scanning transmission electron microscopy, in
different resistive states, revealing an interfacial layer whose physical
extent is influenced by applied electric fields. The ability of Nb-SrTiO$_3$
memristors to satisfy hardware and software requirements with downscaling,
while significantly enhancing memristive functionalities, makes them strong
contenders for non-von Neumann computing, beyond CMOS. | 2301.03352v1 |
2023-01-13 | Multistep magnetization switching in orthogonally twisted ferromagnetic monolayers | The advent of twist-engineering in two-dimensional (2D) crystals enables the
design of van der Waals (vdW) heterostructures exhibiting emergent properties.
In the case of magnets, this approach can afford artificial antiferromagnets
with tailored spin arrangements. Here, we fabricate an orthogonally-twisted
bilayer by twisting 90 degrees two CrSBr ferromagnetic monolayers with an
easy-axis in-plane anisotropy. The magneto-transport properties reveal
multistep magnetization switching with a magnetic hysteresis opening, that is
absent in the pristine case. By tuning the magnetic field, we modulate the
remanent state and coercivity and select between hysteretic and non-hysteretic
magneto-resistance scenarios. This complexity pinpoints spin anisotropy as a
key aspect in twisted magnetic superlattices. Our results highlight the control
over the magnetic properties in vdW heterostructures, leading to a variety of
field-induced phenomena and opening a fruitful playground for creating desired
magnetic symmetries and manipulating non-collinear magnetic configurations. | 2301.05647v2 |
2023-01-17 | A robust weak topological insulator in a bismuth halide Bi4Br2I2 | We apply a topological material design concept for selecting a bulk topology
of 3D crystals by different van-der-Waals stacking of 2D topological insulator
layers, and find a bismuth halide Bi4Br2I2 to be an ideal weak topological
insulator (WTI) with the largest band gap (~230 meV) among all the WTI
candidates, by means of angle-resolved photoemission spectroscopy (ARPES),
density functional theory (DFT) calculations, and resistivity measurements. Our
results vastly expand future opportunities for fundamental research and device
applications with a robust WTI. | 2301.07158v1 |
2023-03-08 | Fast offset corrected in-memory training | In-memory computing with resistive crossbar arrays has been suggested to
accelerate deep-learning workloads in highly efficient manner. To unleash the
full potential of in-memory computing, it is desirable to accelerate the
training as well as inference for large deep neural networks (DNNs). In the
past, specialized in-memory training algorithms have been proposed that not
only accelerate the forward and backward passes, but also establish tricks to
update the weight in-memory and in parallel. However, the state-of-the-art
algorithm (Tiki-Taka version 2 (TTv2)) still requires near perfect offset
correction and suffers from potential biases that might occur due to
programming and estimation inaccuracies, as well as longer-term instabilities
of the device materials. Here we propose and describe two new and improved
algorithms for in-memory computing (Chopped-TTv2 (c-TTv2) and Analog Gradient
Accumulation with Dynamic reference (AGAD)), that retain the same runtime
complexity but correct for any remaining offsets using choppers. These
algorithms greatly relax the device requirements and thus expanding the scope
of possible materials potentially employed for such fast in-memory DNN
training. | 2303.04721v1 |
2023-03-10 | Conductivity of infinite-layer NdNiO$_{2}$ as a probe of spectator bands | Using a density-functional theory plus dynamical mean-field theory
methodology, we compute the many-body electronic structure and optical
conductivity of NdNiO$_{2}$ under the influence of large scattering rates on
the Nd($5d$) bands and including dynamical interactions on the Nd($5d$)
orbitals with shifts of the Nd-Ni $d$-level energy difference. We find a robust
conducting pathway in the out-of-plane direction arising from strong
hybridization between the Ni-$d_{z^2}$ and Nd($5d$) orbitals. This pathway can
be ``short-circuited'' if this hybridization is suppressed through large
electronic scattering rates but is not reduced to zero even by very large
beyond-DFT shifts of the Nd-Ni $d$-level energy splitting. The computed
in-plane conductivity for NdNiO$_{2}$ predicts the material to be a ``good
metal'' in contrast to experiments indicating the material is a ``bad metal''
or ``weak insulator''. Our results motivate future experiments measuring the
$c$-axis resistivity as a proxy for the spectator bands and suggests the
essential difference between the infinite-layer nickelates and the cuprates is
dimensionality of their electronic structures. | 2303.06046v1 |
2023-04-12 | Exploring the interfacial coupling between graphene and the antiferromagnetic insulator MnPSe$_3$ | Interfacial coupling between graphene and other 2D materials can give rise to
intriguing physical phenomena. In particular, several theoretical studies
predict that the interplay between graphene and an antiferromagnetic insulator
could lead to the emergence of quantum anomalous Hall phases. However, such
phases have not been observed experimentally yet, and further experimental
studies are needed to reveal the interaction between graphene and
antiferromagnetic insulators. Here, we report the study in heterostructures
composed of graphene and the antiferromagnetic insulator MnPSe$_3$. It is found
that the MnPSe$_3$ has little impact on the quantum Hall phases apart from
doping graphene via interfacial charge transfer. However, the magnetic order
can contribute indirectly via process like Kondo effect, as evidenced by the
observed minimum in the temperature-resistance curve between 20-40 K, far below
the N\'eel temperature (70 K). | 2304.05757v2 |
2023-04-27 | Magnetism and exchange bias properties in Ba$_{2}$ScRuO$_{6}$ | This paper presents structural, detailed magnetic, and exchange bias studies
in polycrystalline Ba$_{2}$ScRuO$_{6}$ synthesized at ambient pressure. In
contrast to its strontium analogue, this material crystallizes in a 6L
hexagonal structure with the space group P$\overline{3}$m1. The Rietveld
refinement using the room-temperature powder X-ray diffraction pattern suggests
a Ru-Sc disorder in the structure. The temperature variation of the
dc-electrical resistivity highlights a semiconducting behaviour with the
electron conduction corresponding to the Mott 3D-VRH model. Detailed
magnetization measurements show that Ba$_{2}$ScRuO$_{6}$ develops
antiferromagnetic ordering at T$_{N}$ $\approx$ 9 K. Interestingly, below 9 K
(T$_{N}$), the field cooled (FC) magnetic field variation of the magnetization
curves highlights exchange bias effect in the sample. The exchange bias field
reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the
magnetic ordering temperature can be attributed to inhomogeneous magnetic
correlations owing to the disorder in the structure. | 2304.13992v1 |
2023-05-10 | On the origin of permeative flows in cholesteric liquid crystals | Permeative flows, known for the explanation of the anomalous viscosity (10^5
Poise) in cholesterics at low shear rates, are still under debate due to the
difficulty of experiments. Here we use the Surface Force Balance, in which
uniform domains with regular circular defects are formed, to probe the forces
generated by compression in the direction of the helical axis. At the
quasi-static speed of the surface approach, the measured forces are shown to be
elastic (not dissipative), arising from the twist elastic deformation when the
planar anchoring at the walls is strong. A mechanism involving frictional
surface torque under strong planar surface anchoring will be proposed. The
results indicate that the strong resistance to flow observed, previously
interpreted as an enormous apparent viscosity, may in fact originate from the
intrinsic non-linear increase of elasticity when the molecules are rotated away
from equilibrium. The system is found to store energy (the force is
reversible), without dissipation, as long as the applied stress is below the
threshold for nucleating new defects. Our study underpins the importance of
boundary conditions that may dramatically change the rheology of other
viscoelastic materials and sheds light on the rational design of
strain-stiffening materials, nanomotors, and artificial muscles involving
helical architectures. | 2305.06189v1 |
2023-05-20 | Magnetic States of Graphene Proximitized Kitaev Materials | Single layer $\alpha$-ruthenium trichloride ($\rm\alpha-RuCl_3$) has been
proposed as a potential quantum spin liquid. Graphene/$\rm RuCl_3$
heterobilayers have been extensively studied with a focus on the large
interlayer electron transfer that dopes both materials. Here we examine the
interplay between the competing magnetic state of $\rm RuCl_3$ layer and
graphene electronic properties. We perform self-consistent Hartree-Fock
calculations on a Hubbard-Kanamori model of the $4d^5$ $t_{2g}$ electrons of
$\rm\alpha-RuCl_3$ and confirm that out-of-plane ferromagnetic and zigzag
antiferromagnetic states are energetically competitive. We show that the
influence of hybridization between graphene and $\rm\alpha-RuCl_3$ bands is
strongly sensitive to the magnetic configuration of $\rm RuCl_3$ and the
relative orientations of the two layers. We argue that strong hybridization
leads to graphene magneto-resistance and that it may tilt the balance between
closely competing magnetic states. Our analysis can be applied to any van der
Waals heterobilayer system with weak interlayer hybridization and allows for
arbitrary lattice constant mismatch and relative orientation. | 2305.12116v2 |
2023-05-31 | Unravelling densification during sintering by multiscale modelling of grain motion | The resulting microstructure after the sintering process determines many
materials properties of interest. In order to understand the microstructural
evolution, simulations are often employed. One such simulation method is the
phase-field method, which has garnered much interest in recent decades.
However, the method lacks a complete model for sintering, as previous works
could show unphysical effects and the inability to reach representative volume
elements. Thus the present paper aims to close this gap by employing molecular
dynamics and determining rules of motion which can be translated to a
phase-field model. The key realization is that vacancy absorption induced
motion of grains travels through a grain structure without resistance. Hence
the total displacement field of a green body is simply the superposition of all
grains reacting in isolation to local vacancy absorption events. The resulting
phase-field model is shown to be representative starting from particle counts
between 97 and 262 and contains the qualitative correct dependence of sintering
rate on particle size. | 2305.19910v2 |
2023-06-08 | Strain-stiffening elastomers fail from the edge | The accurate measurement of fracture resistance in elastomers is essential
for predicting the mechanical limits of soft devices. Usually, this is achieved
by performing tearing or peeling experiments on thin-sheet samples. Here, we
show that these tests can be surprisingly thickness-dependent, with thicker
samples being significantly stronger than thinner ones. Even for a simple
geometry, direct imaging of the fracture surface shows that the fracture
process actually involves three distinct cracks: an inner crack, and two edge
cracks. Ultimately, samples fail when two edge cracks meet at the sample's
mid-plane. The opening angle of edge crack, $2 \theta$, determines how far the
sample has to be stretched before the edge cracks meet. Conveniently, $\theta$
is a material property that can be inferred from the elastomer's non-linear
elastic response. To yield thickness-independent fracture-test results, sample
thickness should be much smaller than the smallest lateral sample dimension
divided by $\tan \theta$. Our results have direct implications for
characterizing, understanding, and modelling fracture in soft elastomers. | 2306.05575v1 |
2023-06-11 | Elasto-viscoplastic Spreading: from Plastocapillarity to Elastocapillarity | We study the spreading of elastoviscoplastic (EVP) droplets under surface
tension effects. The non- Newtonian material flows like a viscoelastic liquid
above the yield stress and behaves like a viscoelastic solid below it. Hence,
the droplet initially flows under surface tension forces but eventually reaches
a final equilibrium shape when the stress everywhere inside the droplet falls
below the resisting rheological stresses. We use numerical simulations and
combine Volume-of-Fluid (VOF) method and an EVP constitutive model to
systematically study the dynamics of spreading and the final shape of the
droplets. The spreading process examined in this study finds applications in
coating, droplet-based inkjet printing, and 3D printing, where complex fluids
such as paints, thermoplastic filaments, or bio-inks are deposited onto
surfaces. Additionally, the computational framework enables the study of a wide
range of multiphase interfacial phenomena, from elastocapillarity to
plastocapillarity. | 2306.06640v1 |
2023-06-15 | Long-Term Stability of Graphene/c-Si Schottky-Junction Solar Cells | A long operational lifetime is required for the use of solar cells in
real-life photovoltaic applications. The optimization of operational lifetimes
is achieved through understanding the inherent degradation phenomena in solar
cells. In this study, graphene/Si Schottky-junction solar cells were produced,
utilizing liquid-phase-exfoliated graphene as an active surface. The
operational and interface stability of these solar cells over a period of 5
years in ambient conditions (following ISOS-D protocols: dark storage/shelf
life) was examined, and the origin of their degradation was reported. It was
found that the dominant degradation mechanism could be attributed to the
degradation of silver contacts. This was indicated by a decrease in shunt
resistance, an increase in the ideality factor (due to a higher carrier
recombination), and a constant defect density in graphene films for up to 4
years. Measurements across the solar cell's active area during the 5-year
period revealed neither significant spatial inhomogeneity, nor shunt channel
defects. | 2306.09015v1 |
2023-06-17 | Superconductivity of Ta-Hf and Ta-Zr alloys: Potential alloys for use in superconducting devices | The electronic properties relevant to the superconductivity are reported for
bulk Ta-Hf and Ta-Zr body centered cubic alloys, in large part to determine
whether their properties are suitable for potential use in superconducting
qbits. The body centered cubic unit cell sizes increase with increasing
alloying. The results of magnetic susceptibility, electrical resistivity and
heat capacity characterization are reported. While elemental Ta is a type I
superconductor, the alloys are type II strong coupling superconductors.
Although decreasing the electron count per atom is expected to increase the
density of electronic states at the Fermi level and thus the superconducting
transition temperature (Tc) in these systems, we find that this is not
sufficient to explain the significant increases in the superconducting Tc's
observed. | 2306.10438v1 |
2023-06-30 | Role of defects on carrier dynamics and transport mechanism in Bi2Te3 single crystals | Defects play an important role in determining the type of carriers as well as
on tuning the physical properties of layered materials. In this study, we have
demonstrated that by varying the growth kinetics one can control the defects
and can achieve electrons or holes dominated Bi2Te3 single crystals using
modified Bridgman method. The correlation between structural defects and the
type of dominant charge carriers in crystals are discussed using X-Ray
diffraction and Hall resistivity. Electrons are found to be originating from Te
vacancy type defects, while holes are manifested from predominant structural
defects viz. Bi_Te antisite defects or interstitial Te atoms. We observe that
the alteration of charger carriers from electrons to holes have enhanced
magnetoresistance (MR) from 103% to 224%. The enhancement in MR emerges from 2D
multichannel quantum coherent conduction mechanism. | 2306.17487v1 |
2023-07-05 | Mechanical Energy Absorption of Architecturally Interlocked Petal-Schwarzites | We carried out fully atomistic reactive molecular dynamics simulations to
study the mechanical behavior of six newly proposed hybrid schwarzite-based
structures (interlocked petal-schwarzites). Schwarzites are carbon crystalline
nanostructures with negative Gaussian curvature created by mapping a TPMS
(Triply Periodic Minimal Surface) with carbon rings containing six to eight
atoms. Our simulations have shown that petal-schwarzite structures can
withstand uni-axial compressive stress up to the order of GPa and can be
compressed past 50 percent strain without structural collapse. Our most
resistant hierarchical structure has a calculated compressive strength of
260~GPa and specific energy absorption (SEA) of 45.95 MJ/kg, while possessing a
mass density of only 685 kg/m$^3$. These results show that these structures
could be excellent lightweight materials for applications that require
mechanical energy absorption. | 2307.02660v1 |
2023-07-09 | Optimal face-to-face coupling for fast self-folding kirigami | Kirigami-inspired designs can enable self-folding three-dimensional materials
from flat, two-dimensional sheets. Hierarchical designs of connected levels
increase the diversity of possible target structures, yet they can lead to
longer folding times in the presence of fluctuations. Here, we study the effect
of rotational coupling between levels on the self-folding of two-level kirigami
designs driven by thermal noise in a fluid. Naturally present due to
hydrodynamic resistance, we find that optimization of this coupling as control
parameter can significantly improve a structure's self-folding rate and yield. | 2307.04145v1 |
2023-07-19 | Magneto-transport and electronic structures in MoSi$_2$ bulks and thin films with different orientations | We report a comprehensive study of magneto-transport properties in MoSi$_2$
bulk and thin films. Textured MoSi$_2$ thin films of around 70 nm were
deposited on silicon substrates with different orientations. Giant
magnetoresistance of 1000% was observed in sintered bulk samples while MoSi$_2$
single crystals exhibit a magnetoresistance (MR) value of 800% at low
temperatures. At the low temperatures, the MR of the textured thin films show
weak anti-localization behaviour owing to the spin orbit coupling effects. Our
first principle calculation show the presence of surface states in this
material. The resistivity of all the MoSi$_2$ thin films is significantly low
and nearly independent of the temperature, which is important for electronic
devices. | 2307.09802v1 |
2023-07-23 | Ru doping induced spin frustration and enhancement of the room-temperature anomalous Hall effect in La2/3Sr1/3MnO3 films | In transition-metal-oxide heterostructures, the anomalous Hall effect (AHE)
is a powerful tool for detecting the magnetic state and revealing intriguing
interfacial magnetic orderings. However, achieving a larger AHE at room
temperature in oxide heterostructures is still challenging due to the dilemma
of mutually strong spin-orbit coupling and magnetic exchange interactions.
Here, we exploit the Ru doping-enhanced AHE in LSMRO epitaxial films. As the
B-site Ru doping level increases up to 20 percent, the anomalous Hall
resistivity at room temperature can be enhanced from nOhmcm to uOhmcm scale. Ru
doping leads to strong competition between ferromagnetic double-exchange
interaction and antiferromagnetic super-exchange interaction. The resultant
spin frustration and spin-glass state facilitate a strong skew-scattering
process, thus significantly enhancing the extrinsic AHE. Our findings could
pave a feasible approach for boosting the controllability and reliability of
oxide-based spintronic devices. | 2307.12253v1 |
2023-07-30 | Superconductivity in amorphous and crystalline Re-Lu films | We report on magnetron deposition and superconducting properties of a novel
superconducting material: rhenium-lutetium films on sapphire substrates.
Different compositions of Re$_{x}$Lu binary are explored from $x\approx 3.8$ to
close to pure Re stoichiometry. The highest critical temperature, up to
$T_{c}\approx $ 6.95 K, is obtained for $x\approx 10.5$. Depending on the
deposition conditions, polycrystalline or amorphous films are obtainable, both
of which are interesting for practice. Crystalline structure of polycrystalline
phase is identified using grazing incidence X-ray diffractometry as a
non-centrosymmetric superconductor. Superconducting properties were
characterized both resistively and magnetically. Demonstration of
superconductivity in this material justifies the point of view that Lu plays a
role of group 3 transition metal in period 6 of the Periodic table of elements.
In analogy with Re$_{0.82}$Nb$_{0.18}$, Re$_{6}$Ti, Re$_{6}$Hf and Re$_{6}$Zr,
one can expect that crystalline Re--Lu is also breaking the time-reversal
symmetry (this still waits confirmation). Magnetoresistivity and AC/DC
susceptibility measurements allowed us to determine H$_{c1}$ and H$_{c2}$ of
these films, as well as estimate coherence length $\xi (0)$ and magnetic
penetration depth $\lambda _{L}(0)$. We also provide information on surface
morphology of these films. | 2307.16313v1 |
2023-08-01 | Fatigue crack growth in anisotropic aluminium sheets -- phase-field modelling and experimental validation | Fatigue crack growth is decisive for the design of thin-walled structures
such as fuselage shells of air planes. The cold rolling process, used to
produce the aluminium sheets this structure is made of, leads to anisotropic
mechanical properties. In this contribution, we simulate the fatigue crack
growth with a phase-field model due to its superior ability to model arbitrary
crack paths. A fatigue variable based on the Local Strain Approach describes
the progressive weakening of the crack resistance. Anisotropy regarding the
fracture toughness is included through a structural tensor in the crack surface
density. The model is parameterised for an aluminium AA2024-T351 sheet
material. Validation with a set of experiments shows that the fitted model can
reproduce key characteristics of a growing fatigue crack, including crack path
direction and growth rate, considering the rolling direction. | 2308.00800v1 |
2023-08-11 | Metallic Quantized Anomalous Hall Effect without Chiral Edge States | The quantum anomalous Hall effect (QAHE) is a topological state of matter
with a quantized Hall resistance. It has been observed in some two-dimensional
insulating materials such as magnetic topological insulator films and twisted
bilayer graphene. These materials are insulating in the bulk, but possess
chiral edge states carrying the edge current around the systems. Here we
discover a metallic QAHE in a topological insulator film with magnetic sandwich
heterostructure, in which the Hall conductance is quantized to $e^{2}/h$, but
the longitudinal conductance remains finite. This effect is attributed to the
existence of a pair of massless Dirac cones of surface fermions, with each
contributing half of the Hall conductance due to quantum anomaly. It is not
characterized by a Chern number and not associated to any chiral edge states.
Our study offers novel insights into topological transport phenomena and
topological metallic states of matter. | 2308.05963v1 |
2023-09-16 | Investigation of the Anomalous and Topological Hall Effects in Layered Monoclinic Ferromagnet Cr$_{2.76}$Te$_4$ | We studied the electrical transport, Hall effect, and magnetic properties of
monoclinic layered ferromagnet Cr$_{2.76}$Te$_4$. Our studies demonstrate
Cr$_{2.76}$Te$_4$ to be a soft ferromagnet with strong magnetocrystalline
anisotropy. Below 50 K, the system shows an antiferromagnetic-like transition.
Interestingly, between 50 and 150 K, we observe fluctuating magnetic moments
between in-plane and out-of-plane orientations, leading to non-coplanar spin
structure. On the other hand, the electrical resistivity data suggest it to be
metallic throughout the measured temperature range, except a $kink$ at around
50 K due to AFM ordering. The Rhodes-Wohlfarth ratio
$\frac{\mu_{eff}}{\mu_{s}}=1.89 (>1)$ calculated from our magnetic studies
confirms that Cr$_{2.76}$Te$_4$ is an itinerant ferromagnet. Large anomalous
Hall effect has been observed due to the skew-scattering of impurities and the
topological Hall effect has been observed due to non-coplanar spin-structure in
the presence of strong magnetocrystalline anisotropy. We examined the mechanism
of anomalous Hall effect by employing the first principles calculations. | 2309.08898v1 |
2023-10-10 | Optical assembly of nanostructures mediated by surface roughness | Rigorous understanding of the self-assembly of colloidal nanocrystals is
crucial to the development of tailored nanostructured materials. Despite
extensive studies, a mechanistic understanding of self-assembly under
non-equilibrium driven by an external field remains an ongoing challenge. We
demonstrate self-assembly by optical tweezers imposing an external attractive
field for cubic-phase sodium yttrium fluoride nanocrystals. We show that
surface roughness of the nanocrystals is a decisive factor for contact leading
to assembly between the nanocrystals, manifested by the roughness-dependent
hydrodynamic resistivity. This provides direct evidence that dynamics are
equally important to energetics in understanding self-assembly. These results
have implications in a wide variety of different fields, such as in
understanding the factors that mediate oriented attachment-based crystal growth
or in interpreting the structure of binding sites on viruses. | 2310.06774v1 |
2023-10-20 | Surface-symmetry-driven Dzyaloshinskii--Moriya interaction and canted ferrimagnetism in collinear magnetoelectric antiferromagnet Cr$_2$O$_3$ | Antiferromagnets are normally thought of as materials with compensated
magnetic sublattices. This adds to their technological advantages but
complicates readout of the antiferromagnetic state. We demonstrate
theoretically the existence of a Dzyaloshinskii-Moriya interaction (DMI) which
is determined by the magnetic symmetry classes of Cr$_2$O$_3$ surfaces with an
in-plane magnetic easy axis. The DMI explains a previously predicted
out-of-plane magnetization at the nominally compensated surfaces of chromia,
leading to a surface-localized canted ferrimagnetism. This is in agreement with
magnetotransport measurements and with density functional theory predictions
which further allow us to quantify the strength of DMI. The temperature
dependence of the transversal resistance for these planes shows distinct
behavior in comparison with that of the Cr$_2$O$_3$ $c$ plane, which we
attribute to the influence of DMI. Our work provides a framework to analyze
surface-driven phenomena in antiferromagnets, and motivates the use of
nominally compensated chromia surfaces for antiferomagnetic spintronics and
magnonics. | 2310.13438v1 |
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