publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
|---|---|---|---|
2017-10-03 | Holographic model for the anomalous scalings of the cuprates | We examine transport in a holographic model in which the dynamics of the
charged degrees of freedom is described by the nonlinear Dirac-Born-Infeld
(DBI) action. Axionic scalar fields are included to break translational
invariance and generate momentum dissipation in the system. Scaling exponents
are introduced by using geometries which are nonrelativistic and
hyperscaling-violating in the infrared. In the probe DBI limit the theory
reproduces the anomalous temperature dependence of the resistivity and Hall
angle of the cuprate strange metals, $\rho \sim T$ and $\cot\Theta_H \sim T^2$.
These scaling laws would not be present without the nonlinear dynamics encoded
by the DBI interactions. We further show that because of its richness the DBI
theory supports a wide spectrum of temperature scalings. This model provides
explicit examples in which transport is controlled by different relaxation
times. On the other hand, when only one quantity sets the temperature scale of
the system, the Hall angle and conductivity typically exhibit the same
temperature behavior. We illustrate this point using new fully backreacted
analytical dyonic black brane solutions. | 1710.01326v2 |
2018-01-31 | The origin of Mooij correlations in disordered metals | Sufficiently disordered metals display systematic deviations from the
behavior predicted by semi-classical Boltzmann transport theory. Here the
scattering events from impurities or thermal excitations can no longer be
considered as additive independent processes, as asserted by Matthiessen's rule
following from this picture. In the intermediate region between the regime of
good conduction and that of insulation, one typically finds a change of sign of
the temperature coefficient of resistivity (TCR), even at elevated temperature
spanning ambient conditions, a phenomenology that was first identified by Mooij
in 1973. Traditional weak coupling approaches to identify relevant corrections
to the Boltzmann picture focused on long distance interference effects such as
"weak localization", which are especially important in low dimensions (1D, 2D)
and close to the zero temperature limit. Here we formulate a strong-coupling
approach to tackle the interplay of strong disorder and lattice deformations
(phonons) in bulk three-dimensional metals at high temperatures. We identify a
polaronic mechanism of strong disorder renormalization, which describes how a
lattice locally responds to the relevant impurity potential. This mechanism,
which quantitatively captures the Mooij regime, is physically distinct and
unrelated to Anderson localization, but realizes early seminal ideas of
Anderson himself, concerning the interplay of disorder and lattice
deformations. | 1802.00065v4 |
2018-05-30 | Hikami-Larkin-Nagaoka (HLN) treatment of the Magneto Conductivity of Bi2Te3 Topological Insulator | We report the magneto-conductivity analysis at different temperatures under
magnetic field of up to 5Tesla of a well characterized Bi2Te3 crystal. Details
of crystal growth and various physical properties including high linear magneto
resistance are already reported by some of us. To elaborate upon the transport
properties of Bi2Te3 crystal, the magneto conductivity is fitted to the known
HLN (Hikami Larkin Nagaoka) equation and it is found that the conduction
mechanism is dominated by both surface driven WAL (weak anti localization) and
the bulk WL states. The value of HLN equation coefficient signifying the type
of localization (WL, WAL or both WL and WAL) falls within the range of -0.5 to
-1.5. In our case, the low field (0.25Tesla) fitting of studied crystal
exhibited value close to -0.86 for studied temperatures of up to 50K,
indicating both WAL and WL contributions. The phase coherence length is found
to decrease from 98.266 to 40.314nm with increasing temperature. Summarily, the
short letter reports the fact that bulk Bi2Te3 follows the HLN equation and
quantitative analysis of the same facilitates to know the quality of studied
crystal in terms of WAL to WL contributions and thus the surface to bulk
conduction ratio. | 1805.11822v1 |
2018-06-18 | Band structure and Fermi surfaces of the reentrant ferromagnetic superconductor Eu(Fe0.86Ir0.14)2As2 | The electronic structure of the reentrant superconductor
Eu(Fe$_{0.86}$Ir$_{0.14}$)$_{2}$As$_{2}$ (T$_c$ = 22 K) with coexisting
ferromagnetic order (T$_M$ = 18 K) is investigated using angle-resolved
photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy (STS).
We study the in-plane and out-of-plane band dispersions and Fermi surface (FS)
of Eu(Fe$_{0.86}$Ir$_{0.14}$)$_{2}$As$_{2}$. The near E$_F$ Fe 3d-derived band
dispersions near the $\Gamma$ and X high-symmetry points show changes due to Ir
substitution, but the FS topology is preserved. From momentum dependent
measurements of the superconducting gap measured at T = 5 K, we estimate an
essentially isotropic s-wave gap ($\Delta\sim5.25\pm 0.25$ meV), indicative of
strong-coupling superconductivity with 2$\Delta$/k$_{B}$T$_{c}\simeq$ 5.8. The
gap gets closed at temperatures T $\geq$ 10 K, and this is attributed to the
resistive phase which sets in at T$_M$ = 18 K due to the Eu$^{2+}$-derived
magnetic order. The modifications of the FS with Ir substitution clearly
indicates an effective hole doping with respect to the parent compound. | 1806.06563v1 |
2018-09-26 | Nanoscale Intergranular Corrosion and Relation With Grain Boundary Character as Studied In Situ on Copper | The initiation of intergranular corrosion at various types of grain
boundaries (GBs) was studied at the nanometer scale on microcrystalline copper
in 1 mM HCl aqueous solution. In situ Electrochemical Scanning Tunneling
Microscopy (ECSTM) and Electron Back-Scatter Diffraction analysis of the same
local microstructural region were combined using an innovative methodology
including micro marking performed with the STM tip. The results demonstrate
that electrochemically-induced intergranular dissolution, at the surface
termination of GBs, is dependent on the grain boundary character. It is found
that random high angle boundaries as well as sigma9 coincidence site lattice
(CSL) boundaries are susceptible to nanoscale initiation of intergranular
corrosion while for sigma3 CSL boundaries the behavior is dependent on the
deviation angle of the GB plane from the exact orientation. For the sigma3
twins, a transition from resistance to susceptibility occurs between 1{\deg}
and 1.7{\deg} of deviation as a result of the increase of the density of steps
(i.e. misorientation dislocations) in the coincidence boundary plane. The work
emphasizes the precision needed in the design of the grain boundary network in
applications where intergranular corrosion or its initiation must be controlled
at the nanoscale. | 1809.09872v1 |
2018-11-14 | Multifrequency Nanoscale Impedance Microscopy (m-NIM): A novel approach towards detection of selective and subtle modifications on the surface of polycrystalline boron-doped diamond electrodes | In this paper, we describe the modification of Nanoscale Impedance Microscopy
(NIM), namely, a combination of contact-mode atomic force microscopy with local
impedance measurements. The postulated approach is based on the application of
multifrequency voltage perturbation instead of standard frequency-by-frequency
analysis, which among others offers more time-efficient and accurate
determination of the resultant impedance spectra with high spatial resolution.
Based on the impedance spectra analysis with an appropriate electric equivalent
circuit, it was possible to map surface resistance and contact capacitance.
Polycrystalline heavy boron-doped diamond (BDD) electrodes were the research
object. Recent studies have shown that the exposure of such electrodes to
oxidizing environment may result in the modification of termination type, and
thus it is a key factor in describing the electric and electrochemical
properties of BDD. We have successfully applied multifrequency NIM, which
allowed us to prove that the modification of termination type is selective and
occurs with different propensity on the grains having specific crystallographic
orientation. Furthermore, our approach enabled the detection of even subtle
submicroscopic surface heterogeneities, created as a result of various
oxidation treatments and to distinguish them from the surface heterogeneity
related to the local distribution of boron at the grain boundaries. | 1811.05709v1 |
2019-05-12 | Nodeless superconductivity and preserved time-reversal symmetry in the noncentrosymmetric Mo3P superconductor | We report a comprehensive study of the noncentrosymmetric superconductor
Mo$_3$P. Its bulk superconductivity, with $T_c = 5.5$ K, was characterized via
electrical resistivity, magnetization, and heat-capacity measurements, while
its microscopic electronic properties were investigated by means of muon-spin
rotation/relaxation ($\mu$SR) and nuclear magnetic resonance (NMR) techniques.
In the normal state, NMR relaxation data indicate an almost ideal metallic
behavior, confirmed by band-structure calculations, which suggest a relatively
high electron density of states, dominated by the Mo $4d$-orbitals. The
low-temperature superfluid density, determined via transverse-field $\mu$SR and
electronic specific heat, suggest a fully-gapped superconducting state in
Mo$_3$P, with $\Delta_0= 0.83$ meV, the same as the BCS gap value in the
weak-coupling case, and a zero-temperature magnetic penetration depth
$\lambda_0 = 126$ nm. The absence of spontaneous magnetic fields below the
onset of superconductivity, as determined from zero-field $\mu$SR measurements,
indicates a preserved time-reversal symmetry in the superconducting state of
Mo$_3$P and, hence, spin-singlet pairing. | 1905.04726v1 |
2019-05-28 | Electronic structure and $H$-$T$ phase diagram of Eu(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ | The iron-based superconductors represent a promising platform for
high-temperature superconductivity, but the interactions underpinning their
pairing present a puzzle. The EuFe$_2$As$_2$ family is unique among these
materials for having magnetic order which onsets within the superconducting
state, just below the superconducting transition. Superconductivity and
magnetic order are normally antagonistic and often vie for the same unpaired
electrons, but in this family the magnetism arises from largely localized Eu
moments and they coexist, with the competition between these evenly-matched
opponents leading to reentrant superconducting behavior. To help elucidate the
physics in this family and the interactions between the magnetic order and
superconductivity, we investigate the $H$--$T$ phase diagram near optimal Rh
doping through specific heat, resistivity, and magnetization measurements, and
study the electronic structure by angular-resolved photoemission spectroscopy.
The competition between the Eu and FeAs layers may offer a route to directly
accessing the electronic structure under effective magnetic fields via ARPES,
which is ordinarily a strictly zero-field technique. | 1905.11554v2 |
2019-09-10 | New and fast route to black TiO2 based on hollow cathode H2 plasma | In this work, we demonstrate a new method to produce black TiO2 from pristine
anatase TiO2 films. It consists on the immersion of TiO2 films in a hollow
cathode H2 RF plasma for a few minutes, resulting in an efficient blackening of
TiO2. In this study, the pristine anatase TiO2 films were grown by magnetron
sputtering onto cover glass and c-Si substrates and then annealed at 450
{\deg}C for 2 h. Before and after the hollow cathode H2 plasma treatment, the
samples were characterized by profilometry, UV-Vis spectrophotometry, X-ray
diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field
emission scanning electron and atomic force microscopies, and four-point probe
measurements. The results show that the obtained black TiO2 thin films have a
significant light absorption on the whole solar spectrum, a very low sheet
resistance, and also a relatively high surface area when compared to the
pristine TiO2. All these characteristics lead to an important improvement on
their photocatalytic activity, as measured by the degradation rate of methylene
blue under UV irradiation. | 1909.04623v1 |
2019-09-27 | Superconducting proximity effect in InAsSb surface quantum wells with in-situ Al contact | We demonstrate robust superconducting proximity effect in
InAs$_{0.5}$Sb$_{0.5}$ quantum wells grown with epitaxial Al contact, which has
important implications for mesoscopic and topological superconductivity. Unlike
more commonly studied InAs and InSb semiconductors, bulk InAs$_{0.5}$Sb$_{0.5}$
supports stronger spin-orbit coupling and larger $g$-factor. However, these
potentially desirable properties have not been previously measured in epitaxial
heterostructures with superconductors, which could serve as a platform for
fault-tolerant topological quantum computing. Through structural and transport
characterization we observe high-quality interfaces and strong spin-orbit
coupling. We fabricate Josephson junctions based on InAs$_{0.5}$Sb$_{0.5}$
quantum wells and observe strong proximity effect. These junctions exhibit
product of normal resistance and critical current, $I_{c}R_{N} =
\SI{270}{\micro V}$, and excess current, $I_{ex}R_{N} = \SI{200}{\micro V}$ at
contact separations of 500~nm. Both of these quantities demonstrate a robust
and long-range proximity effect with highly-transparent contacts. | 1909.12571v2 |
2020-03-15 | Vacancy diffusion in multi-principal element alloys: the role of chemical disorder in the ordered lattice | Many of the purported virtues of Multi-Principal Element Alloys (MPEAs), such
as corrosion, high-temperature oxidation and irradiation resistance, are highly
sensitive to vacancy diffusivity. Similarly, solute interdiffusion is governed
by vacancy diffusion -- it is often unclear whether MPEAs are truly stable, or
effectively stabilized by slow interdiffusion. The considerable composition
space afforded to these alloys makes optimizing for desired properties a
daunting task; theoretical and computational tools are necessary to guide alloy
development. For diffusion, such tools depend on both a knowledge of the
vacancy migration barriers within a given alloy and an understanding of how
these barriers influence vacancy diffusivity. We present a generalized theory
of vacancy diffusion in rugged energy landscapes, paired with Kinetic Monte
Carlo simulations of MPEA vacancy diffusion. The barrier energy statistics are
informed by nudged elastic band calculations in the equiatomic CoNiCrFeMn
alloy. Theory and simulations show that vacancy diffusion in solid-solution
MPEAs is not necessarily sluggish, but can potentially be tuned, and that trap
models are an insufficient explanation for sluggish diffusion in the CoNiCrFeMn
HEA. These results also show that any model that endeavors to faithfully
represent diffusion-related phenomena must account for the full nature of the
energy landscape, not just the migration barriers. | 2003.06900v2 |
2017-03-28 | Indium substitution effect on the topological crystalline insulator family (Pb$_{1-x}$Sn$_{x}$)$_{1-y}$In$_{y}$Te: Topological and superconducting properties | Topological crystalline insulators (TCIs) have been of great interest in the
area of condensed matter physics. We investigated the effect of indium
substitution on the crystal structure and transport properties in the TCI
system (Pb$_{1-x}$Sn$_{x}$)$_{1-y}$In$_{y}$Te. For samples with a tin
concentration $x\le50\%$, the low-temperature resisitivities show a dramatic
variation as a function of indium concentration: with up to ~2% indium doping
the samples show weak-metallic behavior, similar to their parent compounds;
with ~6% indium doping, samples have true bulk-insulating resistivity and
present evidence for nontrivial topological surface states; with higher indium
doping levels, superconductivity was observed, with a transition temperature,
Tc, positively correlated to the indium concentration and reaching as high as
4.7 K. We address this issue from the view of bulk electronic structure
modified by the indium-induced impurity level that pins the Fermi level. The
current work summarizes the indium substitution effect on (Pb,Sn)Te, and
discusses the topological and superconducting aspects, which can be provide
guidance for future studies on this and related systems. | 1703.09836v1 |
2019-02-22 | Development of transmon qubits solely from optical lithography on 300mm wafers | Qubit information processors are increasing in footprint but currently rely
on e-beam lithography for patterning the required Josephson junctions (JJs).
Advanced optical lithography is an alternative patterning method, and we report
on the development of transmon qubits patterned solely with optical
lithography. The lithography uses 193 nm wavelength exposure and 300-mm large
silicon wafers. Qubits and arrays of evaluation JJs were patterned with process
control which resulted in narrow feature distributions: a standard deviation of
0:78% for a 220 nm linewidth pattern realized across over half the width of the
wafers. Room temperature evaluation found a 2.8-3.6% standard deviation in JJ
resistance in completed chips. The qubits used aluminum and titanium nitride
films on silicon substrates without substantial silicon etching. T1 times of
the qubits were extracted at 26 - 27 microseconds, indicating a low level of
material-based qubit defects. This study shows that large wafer optical
lithography on silicon is adequate for high-quality transmon qubits, and shows
a promising path for improving many-qubit processors. | 1902.08501v1 |
2019-06-30 | Evaluating Superconductors through Current Induced Depairing | The phenomenon of superconductivity occurs in the phase space of three
principal parameters: temperature T, magnetic field B, and current density Jd .
The critical temperature Tc is one of the first parameters that is measured and
in a certain way defines the superconductor. From the practical applications
point of view, of equal importance is the upper critical magnetic field Bc2 and
conventional critical current density Jc (above which the system begins to show
resistance without entering the normal state). However, a seldom-measured
parameter, the depairing current density Jd , holds the same fundamental
importance as Tc and Bc2, in that it defines a boundary between the
superconducting and normal states. A study of Jd sheds unique light on other
important characteristics of the superconducting state such as the superfluid
density and the nature of the normal state below Tc, information that can play
a key role in better understanding newly-discovered superconducting materials.
From a measurement perspective, the extremely high values of Jd make it
difficult to measure, which is the reason why it is seldom measured. Here, we
will review the fundamentals of current-induced depairing and the fast-pulsed
current technique that facilitates its measurement and discuss the results of
its application to the topological-insulator/chalcogenide interfacial
superconducting system.
Keywords: pairbreaking, pair-breaking, vortex, vortices, theory, tutorial,
RTS, room-temperature supeconductivity | 1907.00427v1 |
2019-07-29 | Imaging Nematic Transitions in Iron-Pnictide Superconductors with a Quantum Gas | The SQCRAMscope is a recently realized Scanning Quantum CRyogenic Atom
Microscope that utilizes an atomic Bose-Einstein condensate to measure magnetic
fields emanating from solid-state samples. The quantum sensor does so with
unprecedented DC sensitivity at micron resolution from room-to-cryogenic
temperatures. An additional advantage of the SQCRAMscope is the preservation of
optical access to the sample: Magnetometry imaging of, e.g., electron transport
may be performed in concert with other imaging techniques. This multimodal
imaging capability can be brought to bear with great effect in the study of
nematicity in iron-pnictide high-temperature superconductors, where the
relationship between electronic and structural symmetry-breaking resulting in a
nematic phase is under debate. Here, we combine the SQCRAMscope with an in situ
microscope that measures optical birefringence near the surface. This enables
simultaneous and spatially resolved detection of both bulk and near-surface
manifestations of nematicity via transport and structural deformation channels,
respectively. By performing the first local measurement of emergent resistivity
anisotropy in iron pnictides, we observe sharp, nearly concurrent transport and
structural transitions. More broadly, these measurements demonstrate the
SQCRAMscope's ability to reveal important insights into the physics of complex
quantum materials. | 1907.12601v2 |
2020-02-05 | Impact of Residual Carbon Impurities and Gallium Vacancies on Trapping Effects in AlGaN/GaN MIS-HEMTs | Effects of residual C impurities and Ga vacancies on the dynamic
instabilities of AlN/AlGaN/GaN metal insulator semiconductor high electron
mobility transistors are investigated. Secondary ion mass spectroscopy,
positron annihilation spectroscopy, steady state and time-resolved
photoluminescence (PL) measurements have been performed in conjunction with
electrical characterization and current transient analyses. The correlation
between yellow luminescence (YL), C- and Ga vacancy concentration is
investigated. Time-resolved PL indicating the C$_{\mathrm{N}}$O$_{\mathrm{N}}$
complex as the main source of the YL, while Ga vacancies or related complexes
with C seem not to play a major role. The device dynamic performance is found
to be significantly dependent on the C concentration close to the channel of
the transistor. Additionally, the magnitude of the YL is found to be in
agreement with the threshold voltage shift and with the on-resistance
degradation. Trap analysis of the GaN buffer shows an apparent activation
energy of $\sim$0.8eV for all samples, pointing to a common dominating trapping
process and that the growth parameters affect solely the density of trap
centres. It is inferred that the trapping process is likely to be directly
related to C based defects. | 2002.01952v1 |
2020-04-17 | Magnetic correlations in subsystems of the misfit [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$] cobaltate | [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], a two dimensional misfit metallic
compound, is famous for its rich phases accessed by temperature, $i.e.$ high
temperature spin-state transition, metal-insulator transition (MIT) at
intermediate temperature ($\sim$ 100 K) and low temperature spin density wave
(SDW). It enters into SDW phase below T$_{MIT}$ which becomes long range at 27
K. Information on the independent role of misfit layers (rocksalt/Ca$_2$CoO$_3$
\& triangular/CoO$_2$) in these phases is scarce. By combining a set of
complementary macroscopic (DC magnetization and resistivity) and microscopic
(neutron diffraction and X-ray absorption fine structure spectroscopy)
measurements on pure (CCO) and Tb substituted in the rocksalt layer of CCO
(CCO1), magnetic correlations in both subsystems of this misfit compound are
unraveled. CCO is found to exhibit glassiness, as well as exchange bias (EB)
effects, while CCO1 does not exhibit glassiness, albeit it shows weaker EB
effect. By combining local structure investigations from extended X-ray
absorption fine structure (EXAFS) spectroscopy and neutron diffraction results
on CCO, we confirm that the SDW arises in the CoO$_2$ layer. Our results show
that the magnetocrystalline anisotropy associated with the rocksalt layer acts
as a source of pinning, which is responsible for EB effect. Ferromagnetic
clusters in the Ca$_2$CoO$_3$ affects SDW in CoO$_2$ and ultimately glassiness
arises. | 2004.08319v2 |
2020-08-31 | Electronic properties in itinerant ferromagnet SrRu$_{1-x}$Ti$_x$O$_3$ | Here, we study the electrical transport and specific heat in 4$d$ based
ferromagnetic material SrRuO$_3$ and its Ti substituted SrRu$_{1-x}$Ti$_x$O$_3$
series ($x$ $\le$ 0.7). The SrRuO$_3$ is a metal and shows itinerant
ferromagnetism with transition temperature $T_c$ $\sim$ 160 K. The nonmagnetic
Ti$^{4+}$ (3$d^0$) substitution would not only weaken the active Ru-O-Ru
channel but is also expected to tune the electronic density and electron
correlation effect. A metal to insulator transition has been observed around
$x$ $\sim$ 0.4. The nature of charge transport in paramagnetic-metallic state
($x$ $\leq$ 0.4) and in insulating state ($x$ $>$ 0.4) follows modified Mott's
variable range hopping model. In ferromagnetic-metallic state, resistivity
shows a $T^2$ dependence below $T_c$ which though modifies to $T^{3/2}$
dependence at low temperature. In Ti substituted samples, temperature range for
$T^{3/2}$ dependence extends to higher temperature. Interestingly, this
$T^{3/2}$ dependence dominates in whole ferromagnetic regime in presence of
magnetic field. This evolution of electronic transport behavior can be
explained within the framework of Fermi liquid theory and electron-magnon
scattering mechanism. The negative magnetoresistance exhibits a hysteresis and
a crossover between negative and positive value with magnetic field which is
connected with magnetic behavior in series. The decreasing electronic
coefficient of specific heat with $x$ supports the increasing insulating
behavior in present series. We calculate a high Kadowaki-Woods ratio ($x$
$\leq$ 0.3) for SrRuO$_3$ which increases with substitution concentration. This
signifies an increasing electronic correlation effect with substitution
concentration. | 2009.00076v1 |
2007-10-21 | Change of strength of vortex pinning in YBCO due to BaZrO_3 inclusions | We probe the short-range pinning properties with the application of microwave
currents at very high driving frequencies (47.7 GHz) on
YBa$_2$Cu$_3$O$_{7-\delta}$ films with and without sub-micrometer BaZrO$_3$
inclusions. We explore the temperature and field ranges 60 K$<T<T_c$ and
0$<\mu_0H<$0.8 T, with the field applied along the c-axis. The magnetic field
induces a much smaller increase of the microwave resistivity, $\Delta
\rho_1(H)+\mathrm{i}\Delta \rho_2(H)$, in YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$
with respect to pure YBa$_2$Cu$_3$O$_{7-\delta}$. $\Delta \rho_1(H)$ is
slightly superlinear in pure YBa$_2$Cu$_3$O$_{7-\delta}$ (suggesting a possible
contribution of thermal activation), but linear or sublinear in
YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ (suggesting a possible suppression of
thermal activation as a consequence of BaZrO$_3$ inclusions). These features
persist up to close to $T_c$. We discuss our data in terms of the ratio
$r=\Delta X_s'(H)/\Delta R_s'(H)$ in the framework of the models for the
microwave surface impedance in the mixed state. Large $r$ are found in
YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$, with little field dependence. By
contrast, smaller values and stronger field dependences are found in pure
YBa$_2$Cu$_3$O$_{7-\delta}$. We discuss the different field dependence of the
pinning constant. | 0710.3943v1 |
2017-05-01 | Selective mass enhancement close to the quantum critical point in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ | A quantum critical point (QCP) is currently being conjectured for the
BaFe$_2$(As$_{1-x}$P$_x$)$_2$ system at the critical value $x_{\rm c} \approx$
0.3. In the proximity of a QCP, all thermodynamic and transport properties are
expected to scale with a single characteristic energy, given by the quantum
fluctuations. Such an universal behavior has not, however, been found in the
superconducting upper critical field $H_{\rm c2}$. Here we report $H_{\rm
c2}$-data for epitaxial thin films extracted from the electrical resistance
measured in very high magnetic fields up to 67 Tesla. Using a multi-band
analysis we find that $H_{\rm c2}$ is sensitive to the QCP, implying a
significant charge carrier effective mass enhancement at the doping-induced QCP
that is essentially band-dependent. Our results point to two qualitatively
different groups of electrons in BaFe$_2$(As$_{1-x}$P$_x$)$_2$. The first one
(possibly associated to hot spots or whole Fermi sheets) has a strong mass
enhancement at the QCP, and the second one is insensitive to the QCP. The
observed duality could also be present in many other quantum critical systems. | 1705.00695v1 |
2017-07-31 | Superconductivity at 5 K in quasi-one-dimensional Cr-based KCr3As3 single crystals | Recently a new family of Cr-based A2Cr3As3 (A = K, Rb, Cs) superconductors
were reported, which own a rare quasi-one-dimensional (Q1D) crystal structure
with infinite (Cr3As3)2- chains and exhibit intriguing superconducting
characteristics possibly derived from spin-triplet electron pairing. The
crystal structure of A2Cr3As3 is actually a slight variation of the hexagonal
TlFe3Te3 prototype although they have different lattice symmetry. Here we
report superconductivity in a 133-type KCr3As3 compound that belongs to the
latter structure. The single crystals of KCr3As3 were prepared by the
deintercalation of K ions from K2Cr3As3 crystals which were grown from a
high-temperature solution growth method, and it owns a centrosymmetric lattice
in contrast to the non-centrosymmetric K2Cr3As3. After annealing at a moderate
temperature, the KCr3As3 crystals show bulk superconductivity at 5 K revealed
by electrical resistivity, magnetic susceptibility and heat capacity
measurements. The discovery of this KCr3As3 superconductor provides a different
structural instance to study the exotic superconductivity in these Q1D Cr-based
superconductors. | 1707.09711v1 |
2019-12-23 | Antimonene/Bismuthene Vertical Van-der Waals Heterostructure: A Computational Study | In this paper, the structural, electronic, mechanical and optical properties
of antimonene-bismuthene Van-der Waals heterostructure (Sb-Bi HS) were
calculated based on the first principle density functional theory. We explored
different stacks of Sb-Bi HS to find the most and the least stable staking for
this heterostructure. At the GGA level of theory, the most stable model is a
semiconductor with an indirect band gap of 159 meV. However, when the
spin-orbit (SO) interaction is considered, the VBM and CBM touch the Fermi
level and the HS becomes a semimetal. Our results also show that the electronic
properties of the HS are robust against the external electric field and biaxial
strain. Young modulus was calculated as 64.3N/M which predicts this HS as a
resistant material against being stretched or compressed.
The calculated optical properties, similar to monolayer antimonene, are
completely dependent on the polarization of incident light and differ when
parallel or perpendicular polarization is considered. Moreover, the absorption
coefficient for perpendicular polarization in the visible region is
significantly increased in comparison with the monolayer antimonene. High
structural stability, electronic and mechanical robustness against electric
field and strain, along with polarization-dependent optical properties of this
HS, promise for its applications in beam splitters and nano-scale mirrors. | 1912.10978v2 |
2021-01-01 | An Electronic Textile Embedded Smart Cementitious Composite | Structural health monitoring (SHM) using self-sensing cement-based materials
has been reported before, where nano-fillers have been incorporated in
cementitious matrices as functional sensing elements. A percolation threshold
is always required in order for conductive nano-fillers modified concrete to be
useful for SHM. Nonetheless, the best pressure/strain sensitivity results
achieved for any self-sensing cementitious matrix are <0.01 MPa-1. In this
work, we introduce novel reduced graphene oxide (RGO) based electronic textile
(e-textile) embedded in plain and polymer-binder-modified cementitious matrix
for SHM applications. As a proof of concept, it was demonstrated that these
coated fabric-based sensors can be successfully embedded within the
cement-based structures, which are independent of any percolation threshold due
to the interconnected fabric inside the host matrix. The piezo-resistive
response was measured by applying direct and cyclic compressive loads (0.1 to
3.9 MPa). A pressure sensitivity of 1.5 MPa-1 and an ultra-high gauge factor of
2000 was obtained for the system of the self-sensing cementitious structure
with embedded e-textiles. The sensitivity of this new system with embedded
e-textile is many orders of magnitude higher than nanoparticle based
self-sensing of cementitious composites. The manufactured e-textile sensors
showed mechanical stability and functional durability over long-term cyclic
compression tests of 1000 cycles. | 2101.00140v1 |
2021-01-13 | A reusable pipeline for large-scale fiber segmentation on unidirectional fiber beds using fully convolutional neural networks | Fiber-reinforced ceramic-matrix composites are advanced materials resistant
to high temperatures, with application to aerospace engineering. Their analysis
depends on the detection of embedded fibers, with semi-supervised techniques
usually employed to separate fibers within the fiber beds. Here we present an
open computational pipeline to detect fibers in ex-situ X-ray computed
tomography fiber beds. To separate the fibers in these samples, we tested four
different architectures of fully convolutional neural networks. When comparing
our neural network approach to a semi-supervised one, we obtained Dice and
Matthews coefficients greater than $92.28 \pm 9.65\%$, reaching up to $98.42
\pm 0.03 \%$, showing that the network results are close to the
human-supervised ones in these fiber beds, in some cases separating fibers that
human-curated algorithms could not find. The software we generated in this
project is open source, released under a permissive license, and can be freely
adapted and re-used in other domains. All data and instructions on how to
download and use it are also available. | 2101.04823v2 |
2021-01-22 | Structural and transport properties of 4f electron doped Y1-x(Dy)xPdBi topological semi-metallic thin films | We report the effect of 4f electron doping on structural, electrical and
magneto-transport properties of Dy doped half Heusler Y1-x(Dy)xPdBi (x =0, 0.2,
0.5, 1) thin films grown by pulsed laser deposition. The Dy doping leads to
lattice contraction which increases from 0% for the parent x =0 sample to
approx 1.3% for x=1 sample with increase in Dy doping. The electrical transport
measurements show a typical semi-metallic behaviour in the temperature range 3K
to 300K and a sharp drop in resistivity at low temperatures (less than 3K) for
all the samples. Magnetotransport measurements and Shubnikov de-Hass
oscillations at high magnetic fields demonstrate that for these topologically
non-trivial samples, Dy doping induced lattice contraction plays an active role
in modifying the Fermi surface, carrier concentration and the effective
electron mass. There is an uniform suppression of the onset of
superconductivity with increased Dy doping which is possibly related to the
increasing local exchange field arising from the 4f electrons in Dy. Our
results indicate that we can tune various band structure parameters of YPdBi by
f electron doping and strained thin films of Y1-x(Dy)xPdBi show surface
dominated relativistic carrier transport at low temperatures. | 2101.09185v2 |
2012-06-07 | Anisotropic magnetothermoelectric power of ferromagnetic thin films | We compare the behavior of the magnetothermoelectric power (MTEP)in metallic
ferromagnetic thin films of Ni80Fe20 (Permalloy; Py), Co and CrO2 at
temperatures in the range of 100 K to 400 K. In 25 nm thick Py films and 50 nm
thick Co films both the anisotropic magnetoresistance (AMR) and MTEP show a
relative change in resistance and thermoelectric power (TEP) of the order of
0.2% when the magnetic field is reversed, and in both cases there is no
significant change in AMR or MTEP any more after the saturation field has been
reached. Surprisingly, both Py and Co films have opposite MTEP behavior
although both have the same sign for AMR and TEP. The data on 100 nm films of
fully spin-polarized CrO2, grown both on TiO2 and on sapphire, show a different
picture. The MTEP behavior at low fields shows peaks similar to the AMR in
these films, with variations up to 1%. With increasing field both the MR and
the MTEP variations keeps growing, with MTEP showing relative changes of 1.5%
with the thermal gradient along the b-axis and even 20% with the gradient along
the c-axis, with an intermediate value of 3% for the film on sapphire. It
appears that the low-field effects are due to magnetic domain switching, while
the high-field effects are intrinsic to the electronic structure of CrO2. | 1206.1527v2 |
2018-07-10 | Influence of particle size and agglomeration in solid oxide fuel cell cathodes using manganite nanoparticles | In this work we studied the influence of particle size and agglomeration in
the performance of solid oxide fuel cell cathodes made with nanoparticles of
La0.8Sr0.2MnO3. We followed two synthesis routes based on the Liquid Mix
method. In both procedures we introduced additional reagents in order to
separated the manganite particles. We evaluated cathodic performance by
Electrochemical Impedance Spectroscopy in symmetrical
(CATHODE/ELECTROLYTE/CATHODE) cells. Particle size was tuned by the temperature
used for cathode sintering. Our results show that deagglomeration of the
particles, serves to improve the cathodes performance. However, the dependence
of the performance with the size of the particles is not clear, as different
trends were obtained for each synthesis route. As a common feature, the
cathodes with the lowest area specific resistance are the ones sintered at the
largest temperature. This result indicates that an additional factor related
with the quality of the cathode/electrolyte sintering, is superimposed with the
influence of particle size, however further work is needed to clarify this
issue. The enhancement obtained by deagglomeration suggest that the use of this
kind of methods deserved to be considered to develop high performance
electrodes for solid oxide fuel cells. | 1807.03816v1 |
2019-10-25 | Interdiffusion between gadolinia doped ceria and yttria stabilized zirconia in solid oxide fuel cells: experimental investigation and kinetic modeling | Interdiffusion between the yttria stabilized zirconia (YSZ) electrolyte and
the gadolinia doped ceria (CGO) barrier layer is one of the major causes to the
degradation of solid oxide fuel cells (SOFCs). We present in this work
experimental investigations on CGO-YSZ bi-layer electrolyte sintered at 1250 C
or 1315 C and element transport as a function of sintering temperature and
dwelling time. In order to quantitatively simulate the experimental
observations, the CALPHAD-type thermodynamic assessment of the CGO-YSZ system
is performed by simplifying the system to a CeO2-ZrO2 quasi-binary system, and
the kinetic descriptions (atomic mobilities) are constructed based on critical
review of literature data. The CGO-YSZ interdiffusion is then modeled with the
DICTRA software and the simulation results are compared with the experimental
data under different sintering or long-term operating conditions. The
corresponding ohmic resistance of the bi-layer electrolyte is predicted based
on the simulated concentration profile. The results implies that the
interdiffusion across the CGO-YSZ interface happens mainly during sintering at
high temperature, while during long-term operation at relatively lower
temperature the impact of interdiffusion on cell degradation is negligible. | 1910.11947v2 |
2019-11-29 | Ultrathin 2 nm gold as ideal impedance-matched absorber for infrared light | Thermal detectors are a cornerstone of infrared (IR) and terahertz (THz)
technology due to their broad spectral range. These detectors call for suitable
broad spectral absorbers with minimalthermal mass. Often this is realized by
plasmonic absorbers, which ensure a high absorptivity butonly for a narrow
spectral band. Alternativly, a common approach is based on impedance-matching
the sheet resistance of a thin metallic film to half the free-space impedance.
Thereby, it is possible to achieve a wavelength-independent absorptivity of up
to 50 %, depending on the dielectric properties of the underlying substrate.
However, existing absorber films typicallyrequire a thickness of the order of
tens of nanometers, such as titanium nitride (14 nm), whichcan significantly
deteriorate the response of a thermal transducers. Here, we present the
application of ultrathin gold (2 nm) on top of a 1.2 nm copper oxide seed layer
as an effective IR absorber. An almost wavelength-independent and long-time
stable absorptivity of 47(3) %, ranging from 2 $\mu$m to 20 $\mu$m, could be
obtained and is further discussed. The presented gold thin-film represents
analmost ideal impedance-matched IR absorber that allows a significant
improvement of state-of-the-art thermal detector technology. | 1911.13126v1 |
2020-08-01 | Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys | Amorphous complexions in nanocrystalline metals have the potential to improve
mechanical properties and radiation tolerance, as well as resistance to grain
growth. In this study, the stability of amorphous complexions in binary and
ternary Cu-based alloys is investigated by observing the effect of cooling rate
from high temperature on the occurrence of amorphous-to-ordered complexion
transitions. Bulk Cu-Zr and Cu-Zr-Hf alloy samples were annealed to induce
boundary premelting and then quenched through a procedure that induces a
gradient of local cooling rate through the sample height. Amorphous complexion
thickness distributions were found to be invariant to local cooling rate in the
Cu-Zr-Hf alloy, demonstrating enhanced stability of the amorphous complexion
structure compared to the Cu-Zr alloy, which had thinner amorphous complexions
in the regions that were slowly cooled. The experimental results are used to
construct time-temperature-transformation diagrams of the amorphous-to-ordered
complexion transition for both the binary and ternary alloys, enabling a deeper
understanding of the influence of cooling rate and grain boundary chemistry on
complexion transitions. The critical cooling rate necessary to avoid complexion
transitions in the ternary alloy is found to be at least three orders of
magnitude slower than that for the binary alloy. | 2008.00292v2 |
2020-10-26 | Astability versus Bistability in van der Waals Tunnel Diode for Voltage Controlled Oscillator and Memory Applications | Van der Waals (vdW) tunnel junctions are attractive due to their atomically
sharp interface, gate tunablity, and robustness against lattice mismatch
between the successive layers. However, the negative differential resistance
(NDR) demonstrated in this class of tunnel diodes often exhibits noisy
behaviour with low peak current density, and lacks robustness and
repeatability, limiting their practical circuit applications. Here we propose a
strategy of using a 1L-WS$_2$ as an optimum tunnel barrier sandwiched in a
broken gap tunnel junction of highly doped black phosphorus (BP) and SnSe$_2$.
We achieve high yield tunnel diodes exhibiting highly repeatable, ultra-clean,
and gate tunable NDR characteristics with a signature of intrinsic oscillation,
and a large peak-to-valley current ratio (PVCR) of 3.6 at 300 K (4.6 at 7 K),
making them suitable for practical applications. We show that the thermodynamic
stability of the vdW tunnel diode circuit can be tuned from astability to
bistability by altering the constraint through choosing a voltage or a current
bias, respectively. In the astable mode under voltage bias, we demonstrate a
compact, voltage controlled oscillator without the need for an external tank
circuit. In the bistable mode under current bias, we demonstrate a highly
scalable, single element one-bit memory cell that is promising for dense random
access memory applications in memory intensive computation architectures. | 2010.13828v1 |
2020-12-14 | Magnetic, superconducting, and topological surface states on Fe$_{1+y}$Te$_{1-x}$Se$_{x}$ | The idea of employing non-Abelian statistics for error-free quantum computing
ignited interest in recent reports of topological surface superconductivity and
Majorana zero modes (MZMs) in FeTe$_{0.55}$Se$_{0.45}$. An associated puzzle is
that the topological features and superconducting properties are not observed
uniformly across the sample surface. Understanding and practical control of
these electronic inhomogeneities present a prominent challenge for potential
applications. Here, we combine neutron scattering, scanning angle-resolved
photoemission spectroscopy (ARPES), and microprobe composition and resistivity
measurements to characterize the electronic state of
Fe$_{1+y}$Te$_{1-x}$Se$_{x}$. We establish a phase diagram in which the
superconductivity is observed only at sufficiently low Fe concentration, in
association with distinct antiferromagnetic correlations, while the coexisting
topological surface state occurs only at sufficiently high Te concentration. We
find that FeTe$_{0.55}$Se$_{0.45}$ is located very close to both phase
boundaries, which explains the inhomogeneity of superconducting and topological
states. Our results demonstrate the compositional control required for use of
topological MZMs in practical applications. | 2012.07893v1 |
2021-02-16 | Nodal superconductivity and superconducting domes in the topological Kagome metal CsV3Sb5 | Recently superconductivity was discovered in the Kagome metal AV3Sb5 (A = K,
Rb, and Cs), which has an ideal Kagome lattice of vanadium. These V-based
superconductors also host charge density wave (CDW) and topological nontrivial
band structure. Here we report the ultralow-temperature thermal conductivity
and high pressure resistance measurements on CsV3Sb5 with Tc = 2.5 K, the
highest among AV3Sb5. A finite residual linear term of thermal conductivity at
zero magnetic field and its rapid increase in fields suggest nodal
superconductivity. By applying pressure, the Tc of CsV3Sb5 increases first,
then decreases to lower than 0.3 K at 11.4 GPa, showing a clear first
superconducting dome peaked around 0.8 GPa. Above 11.4 GPa, superconductivity
re-emerges, suggesting a second superconducting dome. Both nodal
superconductivity and superconducting domes point to unconventional
superconductivity in this V-based superconductor. While our finding of nodal
superconductivity puts a strong constrain on the pairing state of the first
dome, which should be related to the CDW instability, the superconductivity of
the second dome may present another exotic pairing state in this ideal Kagome
lattice of vanadium. | 2102.08356v2 |
2021-03-26 | Liquid Reconfigurable Stealth Window Constructed by Metamaterial Absorber | In this paper, a liquid reconfigurable stealth window constructed by
metamaterial absorber at microwave band is proposed. The stealth window
consists of an anti-reflection glass with indium tin oxide (ITO) as resistive
film and a liquid container made of polymethyl methacrylate (PMMA). Since the
materials constituting the window are all transparent, the metamaterials that
can be switched through the liquid control system can always maintain high
light transmission. The proposal can obtain a transmission passband from 2.3
GHz to 5 GHz with low insertion loss, especially at 2.45 GHz and 5 GHz with the
insertion loss of the passband reach 0.51 and 0.99 , by alcohol drainage. It
can also reflect electromagnetic waves at 2.45 GHz and absorb them from 4.5 GHz
to 10.5 GHz with a strong absorptivity over 90% by alcohol injection,
exhibiting the reconfigurable electromagnetic characteristic of switching
between transmission state and absorption state. Furthermore, the proposed
absorber shows its good transmission/absorption performance under different
polarizations and obtains absorptivity over 90% when alcohol injection in an
oblique incidence of 50{\deg}. Finally, the prototype window has been
fabricated to demonstrate the validity of the proposed structure, which
indicates that the proposal presents significant implications for smart stealth
systems and WLAN communication that require switching of working states in a
complex electromagnetic environment. | 2103.14415v1 |
2021-05-05 | Observation of current-induced switching in non-collinear antiferromagnetic IrMn$_3$ by differential voltage measurements | There is accelerating interest in developing memory devices using
antiferromagnetic (AFM) materials, motivated by the possibility for
electrically controlling AFM order via spin-orbit torques, and its read-out via
magnetoresistive effects. Recent studies have shown, however, that high current
densities create non-magnetic contributions to resistive switching signals in
AFM/heavy metal (AFM/HM) bilayers, complicating their interpretation. Here we
introduce an experimental protocol to unambiguously distinguish current-induced
magnetic and nonmagnetic switching signals in AFM/HM structures, and
demonstrate it in IrMn$_3$/Pt devices. A six-terminal double-cross device is
constructed, with an IrMn$_3$ pillar placed on one cross. The differential
voltage is measured between the two crosses with and without IrMn$_3$ after
each switching attempt. For a wide range of current densities, reversible
switching is observed only when write currents pass through the cross with the
IrMn$_3$ pillar, eliminating any possibility of non-magnetic switching
artifacts. Micromagnetic simulations support our findings, indicating a complex
domain-mediated switching process. | 2105.02277v1 |
2021-06-15 | Unusual competition of superconductivity and charge-density-wave state in a compressed topological kagome metal | Understanding the competition between superconductivity and other ordered
states (such as antiferromagnetic or charge-density-wave (CDW) state) is a
central issue in condensed matter physics. The recently discovered layered
kagome metal AV3Sb5 (A = K, Rb, and Cs) provides us a new playground to study
the interplay of superconductivity and CDW state by involving nontrivial
topology of band structures. Here, we conduct high-pressure electrical
transport and magnetic susceptibility measurements to study CsV3Sb5 with the
highest Tc of 2.7 K in AV3Sb5 family. While the CDW transition is monotonically
suppressed by pressure, superconductivity is enhanced with increasing pressure
up to P1~0.7 GPa, then an unexpected suppression on superconductivity happens
until pressure around 1.1 GPa, after that, Tc is enhanced with increasing
pressure again. The CDW is completely suppressed at a critical pressure P2~2
GPa together with a maximum Tc of about 8 K. In contrast to a common dome-like
behavior, the pressure-dependent Tc shows an unexpected double-peak behavior.
The unusual suppression of Tc at P1 is concomitant with the rapidly damping of
quantum oscillations, sudden enhancement of the residual resistivity and rapid
decrease of magnetoresistance. Our discoveries indicate an unusual competition
between superconductivity and CDW state in pressurized kagome lattice. | 2106.07896v1 |
2021-07-31 | Optical phonon modes assisted thermal conductivity in p-type ZrIrSb Half-Heusler alloy: A combined experimental and computational study | Half Heusler (HH) alloys with 18 valence electron count have attracted
significant interest in the area of research related to thermoelectrics.
Understanding the novel transport properties exhibited by these systems with
semiconducting ground state is an important focus area in this field. Large
thermal conductivity shown by most of the HH alloy possesses a major hurdle in
improving the figure of merit (ZT). Additionally, understanding the mechanism
of thermal conduction in heavy constituents HH alloys is an interesting aspect.
Here, we have investigated the high temperature thermoelectric properties of
ZrIrSb through experimental studies, phonon dispersion and electronic band
structure calculations. ZrIrSb is found to exhibit substantially lower
magnitude of resistivity and Seebeck coefficient near room temperature, owing
to existence of anti-site disorder between Ir/Sb and vacant sites.
Interestingly, in ZrIrSb, lattice thermal conductivity is governed by coupling
between the acoustic and low frequency optical phonon modes, which originates
due to heavier Ir/Sb atoms. This coupling leads to an enhancement in the
Umklapp processes due to the optical phonon excitations near zone boundary,
resulting in a lower magnitude of \k{appa}L. Our studies point to the fact that
the simultaneous existence of two heavy mass elements within a simple unit cell
can substantially decrease the lattice degrees of freedom. | 2108.00210v1 |
2021-08-18 | Thermal Transport in Graphene Composites: The Effect of Lateral Dimensions of Graphene Fillers | We report on the investigation of thermal transport in non-cured silicone
composites with graphene fillers of different lateral dimensions. Graphene
fillers are comprised of few-layer graphene flakes with lateral sizes in the
range from 400 nm to 1200 nm and number of atomic planes from one to ~100. The
distribution of the lateral dimensions and thicknesses of graphene fillers has
been determined via atomic force microscopy statistics. It was found that in
the examined range of the lateral dimensions the thermal conductivity of the
composites increases with the increasing size of the graphene fillers. The
observed difference in thermal properties can be related to the average gray
phonon mean free path in graphene, which has been estimated to be around ~800
nm at room temperature. The thermal contact resistance of composites with
graphene fillers of 1200-nm lateral dimensions was also smaller than that of
composites with graphene fillers of 400-nm lateral dimensions. The effects of
the filler loading fraction and the filler size on the thermal conductivity of
the composites were rationalized within the Kanari model. The obtained results
are important for optimization of graphene fillers for applications in thermal
interface materials for heat removal from high-power-density electronics. | 2108.08409v1 |
2021-09-15 | Superconductivity in In-doped AgSnBiTe3 with possible band inversion | We investigated the chemical pressure effects on structural and electronic
properties of SnTe-based material using partial substitution of Sn by
Ag0.5Bi0.5, which results in lattice shrinkage. For Sn1-2x(AgBi)xTe,
single-phase polycrystalline samples were obtained with a wide range of x. On
the basis of band calculations, we confirmed that the Sn1-2x(AgBi)xTe system is
basically possessing band inversion and topologically preserved electronic
states. To explore new superconducting phases related to the topological
electronic states, we investigated the In-doping effects on structural and
superconducting properties for x = 0.33 (AgSnBiTe3). For (AgSnBi)(1-y)/3InyTe,
single-phase polycrystalline samples were obtained for y = 0-0.5 by
high-pressure synthesis. Superconductivity was observed for y = 0.2-0.5. For y
= 0.4, the transition temperature estimated from zero-resistivity state was 2.4
K, and the specific heat investigation confirmed the emergence of bulk
superconductivity. Because the presence of band inversion was theoretically
predicted, and the parameters obtained from specific heat analyses were
comparable to In-doped SnTe, we expect that the (AgSnBi)(1-y)/3InyTe and other
(Ag,In,Sn,Bi)Te phases are candidate systems for studying topological
superconductivity. | 2109.07167v2 |
2021-09-17 | Visualizing band selective enhancement of quasiparticle lifetime in a metallic ferromagnet | Electrons navigate more easily in a background of ordered magnetic moments
than around randomly oriented ones. This fundamental quantum mechanical
principle is due to their Bloch wave nature and also underlies ballistic
electronic motion in a perfect crystal. As a result, a paramagnetic metal that
develops ferromagnetic order often experiences a sharp drop in the resistivity.
Despite the universality of this phenomenon, a direct observation of the impact
of ferromagnetic order on the electronic quasiparticles in a magnetic metal is
still lacking. Here we demonstrate that quasiparticles experience a significant
enhancement of their lifetime in the ferromagnetic state of the low-density
magnetic semimetal EuCd2As2, but this occurs only in selected bands and
specific energy ranges. This is a direct consequence of the magnetically
induced band splitting and the multi-orbital nature of the material. Our
detailed study allows to disentangle different electronic scattering mechanisms
due to non-magnetic disorder and magnon exchange. Such high momentum and energy
dependence quasiparticle lifetime enhancement can lead to spin selective
transport and potential spintronic applications. | 2109.08538v1 |
2021-09-23 | The Transfer Matrix Method and The Theory of Finite Periodic Systems. From Heterostructures to Superlattices | Long-period systems and superlattices, with additional periodicity, have new
effects on the energy spectrum and wave functions. Most approaches adjust
theories for infinite systems, which is acceptable for large but not small
number of unit cells $n$. In the past 30 years, a theory based entirely on
transfer matrices was developed, where the finiteness of $n$ is an essential
condition. The theory of finite periodic systems (TFPS) is also valid for any
number of propagating modes, and arbitrary potential profiles (or refractive
indices). We review this theory, the transfer matrix definition, symmetry
properties, group representations, and relations with the scattering
amplitudes. We summarize the derivation of multichannel matrix polynomials
(which reduce to Chebyshev polynomials in the one-propagating mode limit), the
analytical formulas for resonant states, energy eigenvalues, eigenfunctions,
parity symmetries, and discrete dispersion relations, for superlattices with
different confinement characteristics. After showing the inconsistencies and
limitations of hybrid approaches that combine the transfer-matrix method with
Floquet's theorem, we review some applications of the TFPS to multichannel
negative resistance, ballistic transistors, channel coupling, spintronics,
superluminal, and optical antimatter effects. We review two high-resolution
experiments using superlattices: tunneling time in photonic band-gap and
optical response of blue-emitting diodes, and show extremely accurate
theoretical predictions. | 2109.11640v4 |
2021-12-03 | Multiscale simulation of injection-induced fracture slip and wing-crack propagation in poroelastic media | In fractured poroelastic media under high differential stress, the shearing
of fractures and faults and the corresponding propagation of wing cracks can be
induced by fluid injection. Focusing on low-pressure stimulation with fluid
pressures below the minimum principal stress but above the threshold required
to overcome the fracture's frictional resistance to slip, this paper presents a
mathematical model and a numerical solution approach for coupling fluid flow
with fracture shearing and propagation. Numerical challenges are related to the
strong coupling between hydraulic and mechanical processes, the material
discontinuity the fractures represent in the medium, the wide range of spatial
scales involved, and the strong effect that fracture deformation and
propagation have on the physical processes. The solution approach is based on a
multiscale strategy. In the macroscale model, flow in and poroelastic
deformation of the matrix are coupled with the flow in the fractures and
fracture contact mechanics, allowing fractures to frictionally slide. Fracture
propagation is handled at the microscale, where the maximum tangential stress
criterion triggers the propagation of fractures, and Paris' law governs the
fracture growth processes. Simulations show how the shearing of a fracture due
to fluid injection is linked to fracture propagation, including cases with
hydraulically and mechanically interacting fractures. | 2112.01811v2 |
2022-04-05 | Tunable Energy Level Alignment in the Multilayers of Carboxylic Acids on Silver | The precise energy level alignment between a metal electrode and an organic
semiconductor is required to reduce contact resistance and enhance the
efficiency of organic-semiconductor-based devices. One of the ways is to
include interlayers that mediate the energy level alignment, i.e., charge
injection layers (CILs). Here we introduce the monolayer thick CILs based on
the aromatic carboxylic acids that can induce the energy level shift in the
subsequent layers by up to 0.8 eV. By gradual chemical transformation of the
as-deposited molecules, we achieve a highly tunable energy level shift in the
range of 0.5 eV. We reveal that the position of both the work function and
energy-level position in the CIL increases linearly with the density of induced
dipoles. The energy level position of subsequent layers changes in the same way
as the CIL. Our results thus connect the energy alignment quantities, i.e.,
energy level positions of both CIL and subsequent layers and sample work
function. The high tunability would allow precise tuning of the active layers
deposited on the CIL, which marks the path towards efficient charge injection
layers on metal electrodes. | 2204.02141v2 |
2022-05-11 | Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene | Twisted bilayer graphene (TBG) near the magic twist angle of $\sim1.1^{o}$
exhibits a rich phase diagram. However, the interplay between different phases
and their dependence on twist angle is still elusive. Here, we explore the
stability of various TBG phases and demonstrate that superconductivity near
filling of two electrons per moir\'e unit cell alongside Fermi surface
reconstructions, as well as entropy-driven high-temperature phase transitions
and linear-in-T resistance occur over a range of twist angles which extends far
beyond those exhibiting correlated insulating phases. In the vicinity of the
magic angle, we also find a metallic phase that displays a hysteretic anomalous
Hall effect and incipient Chern insulating behaviour. Such a metallic phase can
be rationalized in terms of the interplay between interaction-driven
deformations of TBG bands leading to Berry curvature redistribution and Fermi
surface reconstruction. Our results provide an extensive perspective on the
hierarchy of correlated phases in TBG as classified by their robustness against
deviations from the magic angle or, equivalently, their electronic interaction
requirements. | 2205.05225v1 |
2022-06-16 | Origin of Hole-Trapping States in Solution-Processed Copper(I) Thiocyanate (CuSCN) and Defect-Healing by I$_2$ Doping | Solution-processed copper(I) thiocyanate (CuSCN) typically exhibits low
crystallinity with short-range order; the defects result in a high density of
trap states that limit the device performance. Despite the extensive electronic
applications of CuSCN, its defect properties have not been studied in detail.
Through X-ray absorption spectroscopy, pristine CuSCN prepared from the
standard diethyl sulfide-based recipe is found to contain under-coordinated Cu
atoms, pointing to the presence of SCN vacancies. A defect passivation strategy
is introduced by adding solid I$_2$ to the processing solution. At small
concentrations, the iodine is found to exist as I$^-$ which can substitute for
the missing SCN$^-$ ligand, effectively healing the defective sites and
restoring the coordination around Cu. Applying I$_2$-doped CuSCN as a p-channel
in thin-film transistors shows that the hole mobility increases by more than
five times at the optimal doping concentration of 0.5 mol%. Importantly, the
on/off current ratio and the subthreshold characteristics also improve as the
I$_2$ doping method leads to the defect healing effect while avoiding the
creation of detrimental impurity states. An analysis of the capacitance-voltage
characteristics corroborates that the trap state density is reduced upon I$_2$
addition. The contact resistance and bias-stress stability of the devices also
improve. This work shows a simple and effective route to improve hole transport
properties of CuSCN which is applicable to wide-ranging electronic and
optoelectronic applications. | 2206.08040v1 |
2022-07-09 | Diffusion-aware voltage source: An equivalent circuit network to resolve lithium concentration gradients in active particles | Traditional equivalent circuit models (ECMs) have difficulties in estimating
battery internal states due to the lack of relevant physics, such as the
lithium diffusion in active particles. Here we configure a circuit network to
describe the lithium diffusion and define it as a new high-level circuit
element called diffusion-aware voltage source. The circuit representation is
proven equivalent to the discretized diffusion equation. The new voltage source
gives the electrode potential as a function of the surface concentration and
thus automatically incorporates the diffusion overpotential. We show that an
ECM with the proposed diffusion-aware voltage sources (called "shell ECM") can
reproduce the single particle model simulation results, making it a trustworthy
easy-to-implement substitute. Furthermore, the simplest shell ECM consisting of
a single diffusion-aware voltage source and a resistor is validated against
experimental constant-current discharges at various rates. The diffusion-aware
voltage source can be used to measure diffusivity by fitting the diffusion
resistance against experimental data. The viability of the shell ECM for
onboard usage is confirmed by implementation into a battery management system
of WAE Technologies. By tracking the internal concentration states, the shell
ECM demonstrates robustness to dynamic applied-current profiles. | 2207.04249v2 |
2022-07-27 | Effect on the Electronic and Magnetic Properties of Antiferromagnetic Topological Insulator MnBi$_2$Te$_4$ with Sn Doping | We thoroughly investigate the effect of nonmagnetic Sn doping on the
electronic and magnetic properties of antiferromagnetic topological insulator
MnBi$_2$Te$_4$. We observe that Sn doping reduces the out-of-plane
antiferromagnetic (AFM) interactions in MnBi$_2$Te$_4$ up to 68\% of Sn
concentration and above the system is found to be paramagnetic. In this way,
the anomalous Hall effect observed at a very high field of 7.8 T in
MnBi$_2$Te$_4$ is reduced to 2 T with 68\% of Sn doping. Electrical transport
measurements suggest that all compositions are metallic in nature, while the
low-temperature resistivity is sensitive to the AFM ordering and to the
doping-induced disorder. Hall effect study demonstrates that Sn actually dopes
electrons into the system, thus, enhancing the electron carrier density almost
by two orders at 68\% of Sn. In contrast, SnBi$_2$Te$_4$ is found to be a
p-type system. Angle-resolved photoemission spectroscopy (ARPES) studies show
that the topological properties are intact at least up to 55\% of Sn as the
Dirac surface states are present in the valance band, but in SnBi$_2$Te$_4$ we
are unable to detect the topological states due to heavy hole doping. Overall,
Sn doping significantly affects the electronic and magnetic properties of
MnBi$_2$Te$_4$. | 2207.13595v1 |
2022-08-01 | Morphological Evolution of NMC Secondary Particles Through in situ electrochemical FIB/SEM experiment | Microstructural evolution of NMC secondary particles during the battery
operation drives the electrochemical performance and impacts the Li-ion battery
lifetime. In this work, we develop an in situ methodology using the FIB/SEM
instrument to cycle single secondary particles of NMC active materials while
following the modifications of their 3D morphology. Two types of secondary
particles, i.e. low and high gradient NMC, were studied alongside morphological
investigations in both pristine state and different number of cycles. The
quantification of initial inner porosity and cracking evolution upon
electrochemical cycling reveals a clear divergence depending on the type of
gradient particles. An unexpected enhancement of the discharge capacity is
observed during the first cycles concurrently to the appearance of inner
cracks. At the first stages, impedance spectroscopy shows a charge transfer
resistance reduction that suggests a widening of the crack network connected to
the surface, which leads to an increase of contact area between liquid
electrolyte and NMC particle. 3D microstructure of individual secondary
particles after in situ cycles were investigated using FIB/SEM and nano-XCT.
The results suggest a strong impact of the initial porosity shape on the
degradation rate. | 2208.00878v1 |
2022-10-06 | Even-Denominator Fractional Quantum Hall State at Filling Factor ν = 3/4 | Fractional quantum Hall states (FQHSs) exemplify exotic phases of
low-disorder two-dimensional (2D) electron systems when electron-electron
interaction dominates over the thermal and kinetic energies. Particularly
intriguing among the FQHSs are those observed at even-denominator Landau level
filling factors, as their quasi-particles are generally believed to obey
non-Abelian statistics and be of potential use in topological quantum
computing. Such states, however, are very rare and fragile, and are typically
observed in the excited Landau level of 2D electron systems with the lowest
amount of disorder. Here we report the observation of a new and unexpected
even-denominator FQHS at filling factor {\nu} = 3/4 in a GaAs 2D hole system
with an exceptionally high quality (mobility). Our magneto-transport
measurements reveal a strong minimum in the longitudinal resistance at {\nu} =
3/4, accompanied by a developing Hall plateau centered at (h/e2)/(3/4). This
even-denominator FQHS is very unusual as it is observed in the lowest Landau
level and in a 2D hole system. While its origin is unclear, it is likely a
non-Abelian state, emerging from the residual interaction between composite
fermions. | 2210.03226v1 |
2023-02-07 | Towards Flexible Biolaboratory Automation: Container Taxonomy-Based, 3D-Printed Gripper Fingers | Automation in the life science research laboratory is a paradigm that has
gained increasing relevance in recent years. Current robotic solutions often
have a limited scope, which reduces their acceptance and prevents the
realization of complex workflows. The transport and manipulation of laboratory
supplies with a robot is a particular case where this limitation manifests. In
this paper, we deduce a taxonomy of biolaboratory liquid containers that
clarifies the need for a flexible grasping solution. Using the taxonomy as a
guideline, we design fingers for a parallel robotic gripper which are developed
with a monolithic dual-extrusion 3D print that integrates rigid and soft
materials to optimize gripping properties. We design fine-tuned fingertips that
provide stable grasps of the containers in question. A simple actuation system
and a low weight are maintained by adopting a passive compliant mechanism. The
ability to resist chemicals and high temperatures and the integration with a
tool exchange system render the fingers usable for daily laboratory use and
complex workflows. We present the task suitability of the fingers in
experiments that show the wide range of vessels that can be handled as well as
their tolerance against displacements and their grasp stability. | 2302.03644v2 |
2023-04-21 | Revealing the higher-order spin nature of the Hall effect in non-collinear antiferromagnet $\mathrm{Mn_3Ni_{0.35}Cu_{0.65}N}$ | Ferromagnets generate an anomalous Hall effect even without the presence of a
magnetic field, something that conventional antiferromagnets cannot replicate
but noncollinear antiferromagnets can. The anomalous Hall effect governed by
the resistivity tensor plays a crucial role in determining the presence of time
reversal symmetry and the topology present in the system. In this work we
reveal the complex origin of the anomalous Hall effect arising in noncollinear
antiferromagnets by performing Hall measurements with fields applied in
selected directions in space with respect to the crystalline axes. Our coplanar
magnetic field geometry goes beyond the conventional perpendicular field
geometry used for ferromagnets and allows us to suppress any magnetic dipole
contribution. It allows us to map the in-plane anomalous Hall contribution and
we demonstrate a 120$^\circ$ symmetry which we find to be governed by the
octupole moment at high fields. At low fields we subsequently discover a
surprising topological Hall-like signature and, from a combination of
theoretical techniques, we show that the spins can be recast into dipole,
emergent octupole and noncoplanar effective magnetic moments. These co-existing
orders enable magnetization dynamics unachievable in either ferromagnetic or
conventional collinear antiferromagnetic materials. | 2304.10747v1 |
2023-04-25 | Effects of Oxidation on the Tribological Properties of Diamond Sliding Against Silica. Insights from Ab initio Molecular Dynamics | Tribological phenomena such as adhesion, friction, and wear can undermine the
functionality of devices and applications based on the diamond-silica
interface. Controlling these phenomena is highly desirable, but difficult since
extrinsic factors, such as the surface termination by adsorbed species, can
deeply affect the reactivity of diamond and its resistance to wear. In this
work, we investigate the effects of diamond oxidation by massive ab initio
molecular dynamics simulations of silica sliding against diamond surfaces
considering different surface orientations, O-coverages, and tribological
conditions. Our findings reveal a dual role of oxygen that depends on coverage.
At full coverage, the adsorbed oxygen is very effective in friction and wear
reduction because the repulsion with the silica counter-surface prevents the
formation of chemical bonds across the interface. At reduced coverage and high
pressure, Si-O-C bonds are anyway established. In this situation the presence
of oxygen results detrimental as it weakens the surface C-C bonds making the
surface more vulnerable to wear. Indeed we observed atomic wear on the C(110)
surface at 50% O-coverage under harsh tribological conditions. The mechanisms
of friction reduction and atomistic wear are explained through the analysis of
the electronic properties and surface-surface interactions. Overall, our
accurate in silico experiments shed light into the effects of adsorbed oxygen
on the tribological behavior of diamond and show how oxidized diamond can be
worn by silica. | 2304.12511v1 |
2023-05-03 | Correlated Insulator and Chern Insulators in Pentalayer Rhombohedral Stacked Graphene | Rhombohedral stacked multilayer graphene is an ideal platform to search for
correlated electron phenomena, due to its pair of flat bands touching at zero
energy and further tunability by an electric field. Furthermore, its
valley-dependent Berry phase at zero energy points to possible topological
states when the pseudospin symmetry is broken by electron correlation. However,
experimental explorations of these opportunities are very limited so far, due
to a lack of devices with optimized layer numbers and configurations. Here we
present electron transport measurements of hBN-encapsulated pentalayer graphene
at down to 100 milli-Kelvin. We observed a correlated insulating state with
>MOhm resistance at zero charge density and zero displacement field, where the
tight-binding calculation predicts a metallic ground state. By increasing the
displacement field, we observed a Chern insulator state with C = -5 and two
other states with C = -3 at a low magnetic field of ~1 Tesla. At high
displacement fields and charge densities, we observed isospin-polarized
quarter- and half-metals. Therefore, rhombohedral-stacked pentalayer graphene
is the first graphene system to exhibit two different types of Fermi-surface
instabilities: driven by a pair of flat bands touching at zero energy, and by
the Stoner mechanism in a single flat band. Our results demonstrate a new
direction to explore intertwined electron correlation and topology phenomena in
natural graphitic materials without the need of moir\'e superlattice
engineering. | 2305.03151v2 |
2023-05-10 | Strange metallicity in an antiferromagnetic quantum critical model: A sign-problem-free quantum Monte-Carlo study | We compute transport and thermodynamic properties of a two-band spin-fermion
model describing itinerant fermions in two dimensions interacting via $Z_2$
antiferromagnetic quantum critical fluctuations by means of a sign-problem-free
quantum Monte-Carlo approach. We show that the phase diagram of this model
indeed contains a $d$-wave superconducting phase at low enough temperatures.
However, a crucial question that arises is whether a non-Fermi-liquid metallic
regime exists above $T_c$ exhibiting hallmark strange-metal transport
phenomenology. Interestingly, we find that this version of the model describes
a non-Fermi-liquid metallic regime that displays an approximately $T$-linear
resistivity above $T_c$ for a strong fermion-boson interaction. Using
Nernst-Einstein relation, our QMC results also show that this strange metal
phase exhibits a crossover from being characterized by a charge compressibility
given approximately by $\chi_{c}\sim 1/T$ at high temperatures to being
described by a charge diffusivity consistent with the scaling $D_{c}\sim 1/T$
at low temperatures. Therefore, our work adds support to the view that the
$Z_2$ antiferromagnetic spin-fermion model at strong coupling can be considered
a minimal model that describes both unconventional superconductivity and
strange metallicity, which are fundamentally interconnected in many important
strongly-correlated quantum materials. | 2305.06421v2 |
2023-06-09 | Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator | Topological insulators (TI) and magnetic topological insulators (MTI) can
apply highly efficient spin-orbit torque (SOT) and manipulate the magnetization
with their unique topological surface states with ultra-high efficiency. Here,
we demonstrate efficient SOT switching of a hard MTI, V-doped (Bi,Sb)2Te3
(VBST) with a large coercive field that can prevent the influence of an
external magnetic field. A giant switched anomalous Hall resistance of 9.2
$k\Omega$ is realized, among the largest of all SOT systems. The SOT switching
current density can be reduced to $2.8\times10^5 A/cm^2$. Moreover, as the
Fermi level is moved away from the Dirac point by both gate and composition
tuning, VBST exhibits a transition from edge-state-mediated to
surface-state-mediated transport, thus enhancing the SOT effective field to
$1.56\pm 0.12 T/ (10^6 A/cm^2)$ and the interfacial charge-to-spin conversion
efficiency to $3.9\pm 0.3 nm^{-1}$. The findings establish VBST as an
extraordinary candidate for energy-efficient magnetic memory devices. | 2306.05603v3 |
2023-06-26 | CIMulator: A Comprehensive Simulation Platform for Computing-In-Memory Circuit Macros with Low Bit-Width and Real Memory Materials | This paper presents a simulation platform, namely CIMulator, for quantifying
the efficacy of various synaptic devices in neuromorphic accelerators for
different neural network architectures. Nonvolatile memory devices, such as
resistive random-access memory, ferroelectric field-effect transistor, and
volatile static random-access memory devices, can be selected as synaptic
devices. A multilayer perceptron and convolutional neural networks (CNNs), such
as LeNet-5, VGG-16, and a custom CNN named C4W-1, are simulated to evaluate the
effects of these synaptic devices on the training and inference outcomes. The
dataset used in the simulations are MNIST, CIFAR-10, and a white blood cell
dataset. By applying batch normalization and appropriate optimizers in the
training phase, neuromorphic systems with very low-bit-width or binary weights
could achieve high pattern recognition rates that approach software-based CNN
accuracy. We also introduce spiking neural networks with RRAM-based synaptic
devices for the recognition of MNIST handwritten digits. | 2306.14649v1 |
2023-07-03 | Designing impact-resistant bio-inspired low-porosity structures using neural networks | Biological structural designs in nature, like hoof walls, horns, and antlers,
can be used as inspiration for generating structures with excellent mechanical
properties. A common theme in these designs is the small percent porosity in
the structure ranging from 1 - 5\%. In this work, the sheep horn was used as an
inspiration due to its higher toughness when loaded in the radial direction
compared to the longitudinal direction. Under dynamic transverse compression,
we investigated the structure-property relations in low porosity structures
characterized by their two-dimensional (2D) cross-sections. A diverse design
space was created by combining polygonal tubules with different numbers of
sides placed on a grid with varying numbers of rows and columns. The volume
fraction and the orientation angle of the tubules were also varied. The finite
element (FE) method was used with a rate-dependent elastoplastic material model
to generate the stress-strain curves under plane strain conditions. A gated
recurrent unit (GRU) model was trained to predict the structures' stress-strain
response and energy absorption under different strain rates and applied
strains. The parameter-based model uses eight discrete parameters to
characterize the design space and as inputs to the model. The trained GRU model
can efficiently predict the response of a new design in as little as 0.16 ms
and allows rapid performance evaluation of 128000 designs in the design space.
The GRU predictions identified high-performance structures, and four design
trends that affect the specific energy absorption were extracted and discussed. | 2307.00986v2 |
2023-07-07 | Using electrical impedance spectroscopy to identify equivalent circuit models of lubricated contacts with complex geometry: in-situ application to mini traction machine | Electrical contact resistance or capacitance as measured between a lubricated
contact has been used in tribometers, partially reflecting the lubrication
condition. In contrast, the electrical impedance provides rich information of
magnitude and phase, which can be interpreted using equivalent circuit models,
enabling more comprehensive measurements, including the variation of lubricant
film thickness and the asperity (metal to metal) contact area. An accurate
circuit model of the lubricated contact is critical as needed for the
electrical impedance analysis. However, existing circuit models are hand
derived and suited to interfaces with simple geometry, such as parallel plates,
concentric and eccentric cylinders. Circuit model identification of lubricated
contacts with complex geometry is challenging. This work takes the ball-on-disc
lubricated contact in a Mini Traction Machine (MTM) as an example, where screws
on the ball, grooves on the disc, and contact close to the disc edge make the
overall interface geometry complicated. The electrical impedance spectroscopy
(EIS) is used to capture its frequency response, with a group of load, speed,
and temperature varied and tested separately. The results enable an
identification of equivalent circuit models by fitting parallel
resistor-capacitor models, the dependence on the oil film thickness is further
calibrated using a high-accuracy optical interferometry, which is operated
under the same lubrication condition as in the MTM. Overall, the proposed
method is applicable to general lubricated interfaces for the identification of
equivalent circuit models, which in turn facilitates in-situ tribo-contacts
with electric impedance measurement of oil film thickness. It does not need
transparent materials as optical techniques do, or structural modifications for
piezoelectric sensor mounting as ultrasound techniques do. | 2307.03668v1 |
2023-08-22 | Magnetic Skyrmion: From Fundamental Physics to Pioneering Applications | Skyrmionic devices exhibit energy-efficient and high-integration data storage
and computing capabilities due to their small size, topological protection, and
low drive current requirements. So, to realize these devices, an extensive
study, from fundamental physics to practical applications, becomes essential.
In this article, we present an exhaustive review of the advancements in
understanding the fundamental physics behind magnetic skyrmions and the novel
data storage and computing technologies based on them. We begin with an
in-depth discussion of fundamental concepts such as topological protection,
stability, statics and dynamics essential for understanding skyrmions,
henceforth the foundation of skyrmion technologies. For the realization of
CMOS-compatible skyrmion functional devices, the writing and reading of the
skyrmions are crucial. We discuss the developments in different writing schemes
such as STT, SOT, and VCMA. The reading of skyrmions is predominantly achieved
via two mechanisms: the Magnetoresistive Tunnel Junction (MTJ) TMR effect and
topological resistivity (THE). So, a thorough investigation into the Skyrmion
Hall Effect, topological properties, and emergent fields is also provided,
concluding the discussion on skyrmion reading developments. Based on the
writing and reading schemes, we discuss the applications of the skyrmions in
conventional logic, unconventional logic, memory applications, and neuromorphic
computing in particular. Subsequently, we present an overview of the potential
of skyrmion-hosting Majorana Zero Modes (MZMs) in the emerging Topological
Quantum Computation and helicity-dependent skyrmion qubits. | 2308.11811v2 |
2023-09-11 | Ultrafast optical properties of stoichiometric and non-stoichiometric refractory metal nitrides TiNx, ZrNx, and HfNx | Refractory metal nitrides have recently gained attention in various fields of
modern photonics due to their cheap and robust production technology,
silicon-technology compatibility, high thermal and mechanical resistance, and
competitive optical characteristics in comparison to typical plasmonic
materials like gold and silver. In this work, we demonstrate that by varying
the stoichiometry of sputtered nitride films, both static and ultrafast optical
responses of refractory metal nitrides can efficiently be controlled. We
further prove that the spectral changes in ultrafast transient response are
directly related to the position of the epsilon-near-zero region. At the same
time, the analysis of the temporal dynamics allows us to identify three time
components - the "fast" femtosecond one, the "moderate" picosecond one, and the
"slow" at the nanosecond time scale. We also find out that the
non-stoichiometry does not significantly decrease the recovery time of the
reflectance value. Our results show the strong electron-phonon coupling and
reveal the importance of both the electron and lattice temperature-induced
changes in the permittivity near the ENZ region and the thermal origin of the
long tail in the transient optical response of refractory nitrides. | 2309.05593v1 |
2023-10-01 | Effect of Spin Fluctuations on Magnetoresistance and Anomalous Hall Effect in the Chiral Magnet Co8Zn8Mn4 | The beta Mn type Co-Zn-Mn alloys have seized significant attention due to
their ability to host skyrmions at room temperature. Here we analyse the
unconventional magneto-transport properties of Co8Zn8Mn4 single crystals with a
Curie temperature of 275 K. A negative magnetoresistance is obtained over a
wide temperature range of 50K to 300K. The deviation of the isothermal
magnetoresistance (MR) curves from linearity to non-linearity as one approaches
higher temperatures points towards the transition from the dominance of magnons
to spin fluctuations. In the paramagnetic phase, the change in the shape of the
MR curve has been explained using the Khosla and Fischer model. The
relationship between the anomalous Hall effect (AHE) and longitudinal
resistivity reveals the dominance of the skew-scattering mechanism, which is
inexplicable based on the theories of semi-classical magneto-transport. We
experimentally determine that the spin fluctuation is the source of the
skew-scattering mechanism in Co8Zn8Mn4. In general skew-scattering mechanisms
predominate in compounds with high conductivity, but our findings demonstrate
that this is not always the case and that other aspects also require equal
consideration. Our work throws new light on the predominant scattering
mechanism in chiral magnets with skyrmionics phase at low conductivity. | 2310.00739v1 |
2023-11-01 | Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies | In magnetic tunnel junctions based on iron oxide nanoparticles the disorder
and the oxidation state of the surface spin as well as the nanoparticles
functionalization play a crucial role in the magnetotransport properties. In
this work, we report a systematic study of the effects of vacuum annealing on
the structural, magnetic and transport properties of self-assembled ~10 nm
Fe3O4 nanoparticles. The high temperature treatment (from 573 to 873 K)
decomposes the organic coating into amorphous carbon, reducing the electrical
resistivity of the assemblies by 4 orders of magnitude. At the same time, the
3Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing
temperature of the sample increases from 573 to 873 K, indicating an important
surface oxidation. Although the 2 nm physical gap remains unchanged with the
thermal treatment, a monotonous decrease of tunnel barrier width was obtained
from the electron transport measurements when the annealing temperature
increases, indicating an increment in the number of defects and hot-spots in
the gap between the nanoparticles. This is reflected in the reduction of the
spin dependent tunneling, which reduces the interparticle magnetoresistance.
This work shows new insights about influence of the nanoparticle interfacial
composition, as well their the spatial arrangement, on the tunnel transport of
self-assemblies, and evidence the importance of optimizing the nanostructure
fabrication for increasing the tunneling current without degrading the spin
polarized current. | 2311.00700v1 |
2023-11-08 | Incorporating temporal dynamics of mutations to enhance the prediction capability of antiretroviral therapy's outcome for HIV-1 | Motivation: In predicting HIV therapy outcomes, a critical clinical question
is whether using historical information can enhance predictive capabilities
compared with current or latest available data analysis. This study analyses
whether historical knowledge, which includes viral mutations detected in all
genotypic tests before therapy, their temporal occurrence, and concomitant
viral load measurements, can bring improvements. We introduce a method to weigh
mutations, considering the previously enumerated factors and the reference
mutation-drug Stanford resistance tables. We compare a model encompassing
history (H) with one not using it (NH). Results: The H-model demonstrates
superior discriminative ability, with a higher ROC-AUC score (76.34%) than the
NH-model (74.98%). Significant Wilcoxon test results confirm that incorporating
historical information improves consistently predictive accuracy for treatment
outcomes. The better performance of the H-model might be attributed to its
consideration of latent HIV reservoirs, probably obtained when leveraging
historical information. The findings emphasize the importance of temporal
dynamics in mutations, offering insights into HIV infection complexities.
However, our result also shows that prediction accuracy remains relatively high
even when no historical information is available. Supplementary information:
Supplementary material is available. | 2311.04846v1 |
2024-03-12 | Fragmentation of Dense Rotation-Dominated Structures Fed by Collapsing Gravomagneto-Sheetlets and Origin of Misaligned 100 au-Scale Binaries and Multiple Systems | The majority of stars are in binary/multiple systems. How such systems form
in turbulent, magnetized cores of molecular clouds in the presence of non-ideal
MHD effects remains relatively under-explored. Through ATHENA++-based non-ideal
MHD AMR simulations with ambipolar diffusion, we show that the collapsing
protostellar envelope is dominated by dense gravomagneto-sheetlets, a
turbulence-warped version of the classic pseuodisk produced by anisotropic
magnetic resistance to the gravitational collapse, in agreement with previous
simulations of turbulent, magnetized single-star formation. The sheetlets feed
mass, magnetic fields, and angular momentum to a Dense ROtation-Dominated
(DROD) structure, which fragments into binary/multiple systems. This DROD
fragmentation scenario is a more dynamic variant of the traditional disk
fragmentation scenario for binary/multiple formation, with dense spiral
filaments created by inhomogeneous feeding from the highly structured
larger-scale sheetlets rather than the need for angular momentum transport,
which is dominated by magnetic braking. Collisions between the dense spiraling
filaments play a key role in pushing the local magnetic Toomre parameter
$Q_\mathrm{m}$ below unity, leading to gravitational collapse and stellar
companion formation provided that the local material is sufficiently
demagnetized, with a plasma-$\beta$ of order unity or more. This mechanism can
naturally produce {\it in situ} misaligned systems on the 100-au scale, often
detected with high-resolution ALMA observations. Our simulations also highlight
the importance of non-ideal MHD effects, which affect whether fragmentation
occurs and, if so, the masses and orbital parameters of the stellar companions
formed. | 2403.07777v1 |
2024-03-17 | Thickness effect on superconducting properties of niobium films for radio-frequency cavity applications | Niobium-coated copper radio-frequency cavities are cost-effective
alternatives to bulk niobium cavities, given the lower material costs of copper
substrates and their operation in liquid helium at around 4.2 K. However, these
cavities historically exhibited a gradual degradation in performance with the
accelerating field. This phenomenon, not yet fully understood, limits the
application of niobium thin film cavities in accelerators where the real-estate
gradient needs to be maximized. Recent studies on niobium films deposited on
copper using high power impulse magnetron sputtering (HiPIMS) technique show
promising results in mitigating the performance degradation of niobium thin
film radio-frequency cavities. This paper examines the effect of film thickness
on the superconducting properties of niobium films deposited on copper using
HiPIMS. The study provides insights into how the critical temperature,
transition width, lower and upper critical fields, and critical current density
vary with the film thickness. Increasing the thickness of niobium films
deposited through HiPIMS is found to enhance superconducting properties and
reduce densities of defects and structural irregularities in the crystalline
lattice. This shows potential for enhancing overall performance and potentially
mitigating the observed performance degradation in niobium thin film
radio-frequency cavities. Additionally, the Ivry's scaling relation among
critical temperature, thickness, and sheet resistance at the normal state
appears applicable to niobium films up to approximately 4 $\mu$m. This extends
the previously confirmed validity for niobium films, which was limited to
around 300 nm thickness. | 2403.11245v1 |
2024-04-15 | Stiffness-Tuneable Limb Segment with Flexible Spine for Malleable Robots | Robotic arms built from stiffness-adjustable, continuously bending segments
serially connected with revolute joints have the ability to change their
mechanical architecture and workspace, thus allowing high flexibility and
adaptation to different tasks with less than six degrees of freedom, a concept
that we call malleable robots. Known stiffening mechanisms may be used to
implement suitable links for these novel robotic manipulators; however, these
solutions usually show a reduced performance when bending due to structural
deformation. By including an inner support structure this deformation can be
minimised, resulting in an increased stiffening performance. This paper
presents a new multi-material spine-inspired flexible structure for providing
support in stiffness-controllable layer-jamming-based robotic links of large
diameter. The proposed spine mechanism is highly movable with type and range of
motions that match those of a robotic link using solely layer jamming, whilst
maintaining a hollow and light structure. The mechanics and design of the
flexible spine are explored, and a prototype of a link utilising it is
developed and compared with limb segments based on granular jamming and layer
jamming without support structure. Results of experiments verify the advantages
of the proposed design, demonstrating that it maintains a constant central
diameter across bending angles and presents an improvement of more than 203% of
resisting force at 180 degrees. | 2404.09653v1 |
2024-04-23 | Ultrafast nanocomposite scintillators based on Cd-enhanced CsPbCl3 nanocrystals in polymer matrix | Lead halide perovskite nanocrystals (LHP-NCs) embedded in polymer matrices
are gaining traction for next-generation radiation detectors. While progress
has been made on green-emitting CsPbBr3 NCs, scant attention has been given to
the scintillation properties of CsPbCl3 NCs, which emit size-tunable UV-blue
light matching the peak efficiency of ultrafast photodetectors. In this study,
we explore the scintillation characteristics of CsPbCl3 NCs produced through a
scalable method and treated with CdCl2. Spectroscopic, radiometric and
theoretical analysis on both untreated and treated NCs uncover deep hole trap
states due to surface undercoordinated chloride ions, eliminated by Pb to Cd
substitution. This yields near-perfect efficiency and resistance to
polyacrylate mass-polymerization. Radiation hardness tests demonstrate
stability to high gamma doses while time-resolved experiments reveal ultrafast
radioluminescence with an average lifetime as short as 210 ps. These findings
enhance our comprehension of LHP NCs' scintillation properties, positioning
CsPbCl3 as a promising alternative to conventional fast scintillators. | 2404.14813v1 |
1994-10-19 | $Pb_{0.4}Bi_{1.6}Sr_{2}Ca_{1}Cu_{2}O_{8+x}$ and Oxygen Stoichiometry: Structure, Resistivity, Fermi Surface Topology and Normal State Properties | $Pb_{0.4}Bi_{1.6}Sr_2CaCu_2O_{8+x}$ ($Bi(Pb)-$2212) single crystal samples
were studied using transmission electron microscopy (TEM), $ab-$plane
($\rho_{ab}$) and $c-$axis ($\rho_c$) resistivity, and high resolution
angle-resolved ultraviolet photoemission spectroscopy (ARUPS). TEM reveals that
the modulation in the $b-$axis for $Pb(0.4)-$doped $Bi(Pb)-$2212 is dominantly
of $Pb-$type that is not sensitive to the oxygen content of the system, and the
system clearly shows a structure of orthorhombic symmetry. Oxygen annealed
samples exhibit a much lower $c-$axis resistivity and a resistivity minimum at
$80-130$K. He-annealed samples exhibit a much higher $c-$axis resistivity and
$d\rho_c/dT<0$ behavior below 300K. The Fermi surface (FS) of oxygen annealed
$Bi(Pb)-$2212 mapped out by ARUPS has a pocket in the FS around the $\bar{M}$
point and exhibits orthorhombic symmetry. There are flat, parallel sections of
the FS, about 60\% of the maximum possible along $k_x = k_y$, and about 30\%
along $k_x = - k_y$. The wavevectors connecting the flat sections are about
$0.72(\pi, \pi)$ along $k_x = k_y$, and about $0.80(\pi, \pi)$ along $k_x = -
k_y$, rather than $(\pi,\pi)$. The symmetry of the near-Fermi-energy dispersing
states in the normal state changes between oxygen-annealed and He-annealed
samples. | 9410069v1 |
2003-05-30 | General expressions for the electrical resistivity and thermal conductivity of twinned crystals | General expressions are derived for the electrical resisitivity and thermal
conductivity of a twinned single crystal. Particular attention is paid to the
effect of the structure of the twin domains on these transport coefficients.
Edge effects are also considered. The expression for the thermal conductivity
is used to fit data for a twinned single crystal of 0.8% Zn-doped YBa2Cu3O6.98.
The expression for the electrical resistivity is used to fit previously
published electrical resistivity data for a twinned single crystal of
YBa2Cu3O6.9. It is found that twin boundaries are not a significant source of
electron scattering in high-quality single crystals of Y-123. We cannot rule
out scattering of phonons by twin boundaries in these crystals, with up to 12%
suppression of the phonon component of the thermal conductivity. The related
problem of determining the electrical resistivity and thermal conductivity of a
crystal with oblique and alternating isotropic regions of different
conductivities is also solved. | 0305698v5 |
2003-06-13 | Behavior of the contacts of Quantum Hall Effect devices at high currents : an electronic thermometer | This paper reports on an experimental study of the contact resistance of Hall
bars in the Quantum Hall Effect regime while increasing the current through the
sample. These measurements involve also the longitudinal resistance and they
have been always performed before the breakdown of the Quantum Hall Effect. Our
investigations are restricted to the $i=2$ plateau which is used in all
metrological measurements of the von Klitzing constant $R_K$. A particular care
has been taken concerning the configuration of the measurement. Four
configurations were used for each Hall bar by reversing the current and the
magnetic field polarities. Several samples with different width have been
studied and we observed that the critical current for the contact resistance
increases with the width of the Hall bar as previously observed for the
critical current of the longitudinal resistance. The critical currents exhibit
either a linear or a sublinear increase. All our observations are interpreted
in the current understanding of the Quantum hall effect brekdown. Our analysis
suggests that a heated region appears at the current contact, develops and then
extends in the whole sample while increasing the current. Consequently, we
propose to use the contact resistance as an electronic thermometer for the Hall
fluid. | 0306368v3 |
2004-07-19 | Resistivity studies under hydrostatic pressure on a low-resistance variant of the quasi-2D organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br: quest for intrinsic scattering contributions | Resistivity measurements have been performed on a low (LR)- and high
(HR)-resistance variant of the kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br superconductor.
While the HR sample was synthesized following the standard procedure, the LR
crystal is a result of a somewhat modified synthesis route. According to their
residual resistivities and residual resistivity ratios, the LR crystal is of
distinctly superior quality. He-gas pressure was used to study the effect of
hydrostatic pressure on the different transport regimes for both variants. The
main results of these comparative investigations are (i) a significant part of
the inelastic-scattering contribution, which causes the anomalous rho(T)
maximum in standard HR crystals around 90 K, is sample dependent, i.e.
extrinsic in nature, (ii) the abrupt change in rho(T) at T* approx. 40 K from a
strongly temperature-dependent behavior at T > T* to an only weakly T-dependent
rho(T) at T < T* is unaffected by this scattering contribution and thus marks
an independent property, most likely a second-order phase transition, (iii)
both variants reveal a rho(T) proportional to AT^2 dependence at low
temperatures, i.e. for T_c < T < T_0, although with strongly sample-dependent
coefficients A and upper bounds for the T^2 behavior measured by T_0. The
latter result is inconsistent with the T^2 dependence originating from coherent
Fermi-liquid excitations. | 0407478v1 |
2004-10-28 | Transport properties in manganite thin films | The resistivity of thin $La_{0.7}A_{0.3}MnO_{3}$ films ($A=Ca, Sr$) is
investigated in a wide temperature range. The comparison of the resistivities
is made among films grown by different techniques and on several substrates
allowing to analyze samples with different amounts of disorder. In the
low-temperature nearly half-metallic ferromagnetic state the prominent
contribution to the resistivity scales as $T^{\alpha}$ with $\alpha \simeq 2.5$
for intermediate strengths of disorder supporting the theoretical proposal of
single magnon scattering in presence of minority spin states localized by the
disorder. For large values of disorder the low-temperature behavior of the
resistivity is well described by the law $T^{3}$ characteristic of anomalous
single magnon scattering processes, while in the regime of low disorder the
$\alpha$ exponent tends to a value near 2. In the high temperature insulating
paramagnetic phase the resistivity shows the activated behavior characteristic
of polaronic carriers. Finally in the whole range of temperatures the
experimental data are found to be consistent with a phase separation scenario
also in films doped with strontium ($A=Sr$). | 0410743v1 |
2008-12-22 | Joule Heating and Anomalous Resistivity in the Solar Corona | Recent radioastronomical observations of Faraday rotation in the solar corona
can be interpreted as evidence for coronal currents, with values as large as
$2.5 \times 10^9$ Amperes (Spangler 2007). These estimates of currents are used
to develop a model for Joule heating in the corona. It is assumed that the
currents are concentrated in thin current sheets, as suggested by theories of
two dimensional magnetohydrodynamic turbulence. The Spitzer result for the
resistivity is adopted as a lower limit to the true resistivity. The calculated
volumetric heating rate is compared with an independent theoretical estimate by
Cranmer et al (2007). This latter estimate accounts for the dynamic and
thermodynamic properties of the corona at a heliocentric distance of several
solar radii. Our calculated Joule heating rate is less than the Cranmer et al
estimate by at least a factor of $3 \times 10^5$. The currents inferred from
the observations of Spangler (2007) are not relevant to coronal heating unless
the true resistivity is enormously increased relative to the Spitzer value.
However, the same model for turbulent current sheets used to calculate the
heating rate also gives an electron drift speed which can be comparable to the
electron thermal speed, and larger than the ion acoustic speed. It is therefore
possible that the coronal current sheets are unstable to current-driven
instabilities which produce high levels of waves, enhance the resistivity and
thus the heating rate. | 0812.4220v1 |
2009-06-24 | Turbulent resistivity driven by the magnetorotational instability | We measure the turbulent resistivity in the nonlinear regime of the MRI, and
evaluate the turbulent magnetic Prandtl number. We perform a set of numerical
simulations with the Eulerian finite volume codes Athena and Ramses in the
framework of the shearing box model. We consider models including explicit
dissipation coefficients and magnetic field topologies such that the net
magnetic flux threading the box in both the vertical and azimuthal directions
vanishes. We first demonstrate good agreement between the two codes by
comparing the properties of the turbulent states in simulations having
identical microscopic diffusion coefficients (viscosity and resistivity). We
find the properties of the turbulence do not change when the box size is
increased in the radial direction, provided it is elongated in the azimuthal
direction. To measure the turbulent resistivity in the disk, we impose a fixed
electromotive force on the flow and measure the amplitude of the saturated
magnetic field that results. We obtain a turbulent resistivity that is in rough
agreement with mean field theories like the Second Order Smoothing
Approximation. The numerical value translates into a turbulent magnetic Prandtl
number Pm_t of order unity. Pm_t appears to be an increasing function of the
forcing we impose. It also becomes smaller as the box size is increased in the
radial direction, in good agreement with previous results obtained in very
large boxes. Our results are in general agreement with other recently published
papers studying the same problem but using different methodology. Thus, our
conclusion that Pm_t is of order unity appears robust. | 0906.4422v2 |
2009-07-08 | Turbulent resistivity evaluation in MRI generated turbulence | (abriged) MRI turbulence is a leading mechanism for the generation of an
efficient turbulent transport of angular momentum in an accretion disk through
a turbulent viscosity effect. It is believed that the same process could also
transport large-scale magnetic fields in disks, reshaping the magnetic
structures in these objects. This process, known as turbulent resistivity, has
been suggested and used in several accretion-ejection models and simulations to
produce jets. Still, the efficiency of MRI-driven turbulence to transport
large-scale magnetic fields is largely unknown.
We investigate this problem both analytically and numerically. We introduce a
linear calculation of the MRI in the presence of a spatially inhomogeneous mean
magnetic field. We show that, in this configuration, MRI modes lead to an
efficient magnetic field transport, on the order of the angular momentum
transport. We next use fully non linear simulations of MRI turbulence to
compute the turbulent resistivity in several magnetic configurations.
We find that the turbulent resistivity is on the order of the turbulent
viscosity in all our simulations, although somewhat lower. The turbulent
resistivity tensor is found to be highly anisotropic with a diffusion
coefficient 3 times greater in the radial direction than in the vertical
direction.
These results support the possibility of driving jets from turbulent disks;
the resulting jets may not be steady. | 0907.1393v1 |
2009-07-15 | Transport properties and the anisotropy of Ba_{1-x}K_xFe_2As_2 single crystals in normal and superconducting states | The transport and superconducting properties of Ba_{1-x}K_xFe_2As_2 single
crystals with T_c = 31 K were studied. Both in-plane and out-of plane
resistivity was measured by modified Montgomery method. The in-plane
resistivity for all studied samples, obtained in the course of the same
synthesis, is almost the same, unlike to the out-of plane resistivity, which
differ considerably. We have found that the resistivity anisotropy
\gamma=\rho_c /\rho_{ab} is almost temperature independent and lies in the
range 10-30 for different samples. This, probably, indicates on the extrinsic
nature of high out-of-plane resistivity, which may appear due to the presence
of the flat defects along Fe-As layers in the samples. This statement is
supported by comparatively small effective mass anisotropy, obtained from the
upper critical field measurements, and from the observation of the so-called
"Friedel transition", which indicates on the existence of some disorder in the
samples in c-direction. | 0907.2598v1 |
2010-12-31 | In-plane anisotropy of electrical resistivity in the strain-detwinned SrFe2As2 | Intrinsic, in-plane anisotropy of electrical resistivity was studied on
mechanically detwinned single crystals of SrFe$_2$As$_2$ above and below the
temperature of the coupled structural/magnetic transition, $T_{\textrm{TO}}$.
Resistivity is smaller for electrical current flow along the orthorhombic $a_o$
direction (direction of antiferromagnetically alternating magnetic moments) and
is larger for transport along the $b_o$ direction (direction of ferromagnetic
chains), which is similar to CaFe$_2$As$_2$ and BaFe$_2$As$_2$ compounds. A
strongly first order structural transition in SrFe$_2$As$_2$ was confirmed by
high-energy x-ray measurements, with the transition temperature, and character
unaffected by moderate strain. For small strain levels, which are just
sufficient to detwin the sample, we find a negligible effect on the resistivity
above $T_{\textrm{TO}}$. With the increase of strain, the resistivity
anisotropy starts to develop above $T_{\textrm{TO}}$, clearly showing the
relation of anisotropy to an anomalously strong response to strain. Our study
suggests that electronic nematicity cannot be observed in the FeAs based
compounds in which the structural transition is strongly first order. | 1101.0274v1 |
2012-12-05 | Electric field driven destabilization of the insulating state in nominally pure LaMnO3 | We report an electric field driven destabilization of the insulating state in
nominally pure LaMnO3 single crystal with a moderate field which leads to a
resistive state transition below 300 K. The transition is between the
insulating state in LaMnO3 and a high resistance bad metallic state that has a
temperature independent resistivity. The transition occurs at a threshold field
(Eth) which shows a steep enhancement on cooling. While at lower temperatures
the transition is sharp and involves large change in resistance but it softens
on heating and eventually absent above 280K. When the Mn4+ content is increased
by Sr substitution up to x=0.1, the observed transition though observable in
certain temperature range, softens considerably. The observation has been
explained as bias driven percolation type transition between two coexisting
phases, where the majority phase is a charge and orbitally ordered polaronic
insulating phase and the minority phase is a bad metallic phase. The mobile
fraction f of the bad metallic phase deduced from the experimental data follows
an activated kinetics with the activation energy nearly equal to 200 meV and
the prefactor fo is a strong function of the field that leads to a rapid
enhancement of f on application of field leading to the resistive state
transition. We suggest likely scenarios for such co-existing phases in
nominally pure LaMnO3 that can lead to the bias driven percolation type
transition. | 1212.1001v2 |
2013-09-21 | A switch to reduce resistivity in smoothed particle magnetohydrodynamics | Artificial resistivity is included in Smoothed Particle Magnetohydrodynamics
simulations to capture shocks and discontinuities in the magnetic field. Here
we present a new method for adapting the strength of the applied resistivity so
that shocks are captured but the dissipation of the magnetic field away from
shocks is minimised. Our scheme utilises the gradient of the magnetic field as
a shock indicator, setting {\alpha}_B = h|gradB|/|B|, such that resistivity is
switched on only where strong discontinuities are present. The advantage to
this approach is that the resistivity parameter does not depend on the absolute
field strength. The new switch is benchmarked on a series of shock tube tests
demonstrating its ability to capture shocks correctly. It is compared against a
previous switch proposed by Price & Monaghan (2005), showing that it leads to
lower dissipation of the field, and in particular, that it succeeds at
capturing shocks in the regime where the Alfv\'en speed is much less than the
sound speed (i.e., when the magnetic field is very weak). It is also simpler.
We also demonstrate that our recent constrained divergence cleaning algorithm
has no difficulty with shock tube tests, in contrast to other implementations. | 1309.5437v1 |
2013-10-04 | Piggyback resistive Micromegas | Piggyback Micromegas consists in a novel readout architecture where the anode
element is made of a resistive layer on a ceramic substrate. The resistive
layer is deposited on the thin ceramic substrate by an industrial process which
provides large dynamic range of resistivity (10$^6$ to
10$^{10}$\,M$\Omega$/square). The particularity of this new structure is that
the active part is entirely dissociated from the read-out element. This gives a
large flexibility on the design of the anode structure and the readout scheme.
Without significant loss, signals are transmitted by capacitive coupling to the
read-out pads. The detector provides high gas gain, good energy resolution and
the resistive layer assures spark protection for the electronics. This assembly
could be combined with modern pixel array electronic ASICs. First tests with
different Piggyback detectors and configurations will be presented. This
structure is adequate for cost effective fabrication and low outgassing
detectors. It was designed to perform in sealed mode and its long term
stability has been extensively studied. In addition perspectives on the future
developments will be evoked. | 1310.1242v1 |
2013-10-15 | Recent advances with THGEM detectors | The Thick Gaseous Electron Multiplier (THGEM) is a simple and robust
electrode suitable for large area detectors. In this work the results of
extensive comparative studies of the physical properties of different
THGEM-based structures are reviewed. The focus is on newly suggested THGEM-like
WELL configurations as well as on recently developed characterization methods.
The WELL structures are single-sided THGEM electrodes directly coupled to
different anode readout electrodes. The structures differ by the coupling
concept of the bottom THGEM electrode to the metallic readout pads: a Thick
WELL (THWELL) with direct coupling; the Resistive WELL (RWELL) and the
Segmented Resistive WELL (SRWELL) coupled through thin resistive films
deposited on insulating sheets and a Resistive-Plate WELL (RPWELL) coupled
through a plate of high bulk resistivity. The results are compared to that of
traditional double-sided THGEM electrodes followed by induction gaps - in some
cases with moderate additional multiplication within the gap. We compare the
different configurations in terms of gain, avalanche extension, discharge-rate
and magnitude as well as rate capabilities over a broad dynamic range -
exploiting a method that mimics highly ionizing particles in the laboratory. We
report on recent studies of avalanche distribution in THGEM holes using optical
readout. | 1310.3912v1 |
2014-10-10 | On the bad metallicity and phase diagrams of Fe$_{1+δ}X$ ($X$ =Te, Se, S, solid solutions): an electrical resistivity study | Based on a systematic analysis of the thermal evolution of the resistivities
of Fe-based chalcogenides Fe$_{1+\delta }$Te$_{1-x}X_{x}$ ($X$= Se, S), it is
inferred that their often observed nonmetallic resistivities are related to a
presence of two resistive channels: one is a high-temperature
thermally-activated process while the other is a low-temperature log-in-$T$
process. On lowering temperature, there are often two metal-to-nonmetall
crossover events: one from the high-$T$ thermally-activated nonmetallic regime
into a metal-like phase and the other from the log-in-$T$ regime into a second
metal-like phase. Based on these events, together with the magnetic and
superconducting transitions, a phase diagram is constructed for each series. We
discuss the origin of both processes as well as the associated crossover
events. We also discuss how these resistive processes are being influenced by
pressure, intercalation, disorder, doping, or sample condition and, in turn,
how these modifications are shaping the associated phase diagrams. | 1410.2676v1 |
2016-11-17 | On the measurements of numerical viscosity and resistivity in Eulerian MHD codes | We propose a simple ansatz for estimating the value of the numerical
resistivity and the numerical viscosity of any Eulerian MHD code. We test this
ansatz with the help of simulations of the propagation of (magneto)sonic waves,
Alfven waves, and the tearing mode instability using the MHD code Aenus. By
comparing the simu- lation results with analytical solutions of the
resistive-viscous MHD equations and an empirical ansatz for the growth rate of
tearing modes we measure the numerical viscosity and resistivity of Aenus. The
comparison shows that the fast-magnetosonic speed and wavelength are the
characteristic velocity and length, respectively, of the aforementioned
(relatively simple) systems. We also determine the dependance of the numerical
viscosity and resistivity on the time integration method, the spatial
reconstruction scheme and (to a lesser extent) the Riemann solver employed in
the simulations. From the measured results we infer the numerical resolution
(as a function of the spatial reconstruction method) required to properly
resolve the growth and saturation level of the magnetic field amplified by the
magnetorotational instability in the post-collapsed core of massive stars. Our
results show that it is to the best advantage to resort to ultra-high order
methods (e.g., 9th-order Monotonicity Preserving method) to tackle this problem
properly, in particular in three dimensional simulations. | 1611.05858v2 |
2017-02-06 | Rings and gaps produced by variable magnetic disk winds and avalanche accretion streams: I. Axisymmetric resistive MHD simulations | Rings and gaps are being observed in an increasing number of disks around
young stellar objects. We illustrate the formation of such radial structures
through idealized, 2D (axisymmetric) resistive MHD simulations of coupled
disk-wind systems threaded by a relatively weak poloidal magnetic field
(plasma-$\beta \sim 10^3$). We find two distinct modes of accretion depending
on the resistivity and field strength. A small resistivity or high field
strength promotes the development of rapidly infalling `avalanche accretion
streams' in a vertically extended disk envelope that dominates the dynamics of
the system, especially the mass accretion. The streams are suppressed in
simulations with larger resistivities or lower field strengths, where most of
the accretion instead occurs through a laminar disk. In these simulations, the
disk accretion is driven mainly by a slow wind that is typically accelerated by
the pressure gradient from a predominantly toroidal magnetic field. Both
wind-dominated and stream-dominated modes of accretion create prominent
features in the surface density distribution of the disk, including rings and
gaps, with a strong spatial variation of the magnetic flux relative to the
mass. Regions with low mass-to-flux ratios accrete quickly, leading to the
development of gaps, whereas regions with higher mass-to-flux ratios tend to
accrete more slowly, allowing matter to accumulate and form dense rings. In
some cases, avalanche accretion streams are observed to produce dense rings
directly through continuous feeding. We discuss the implications of ring and
gap formation driven by winds and streams on grain growth and planet formation. | 1702.01565v2 |
2017-09-18 | Log-rise of the Resistivity in the Holographic Kondo Model | We study a single-channel Kondo effect using a recently developed holographic
large-$N$ technique. In order to obtain resistivity of this model, we introduce
a probe field. The gravity dual of a localized fermionic impurity in
1+1-dimensional host matter is constructed by embedding a localized
2-dimensional Anti-de Sitter (\ads{2})-brane in the bulk of \ads{3}. This helps
us construct an impurity charge density which acts as a source to the bulk
equation of motion of the probe gauge field. The functional form of the charge
density is obtained independently by solving the equations of motion for the
fields confined to the \ads{2}-brane. The asymptotic solution of the probe
field is dictated by the impurity charge density, which in turn, affects the
current-current correlation functions, and hence the resistivity. Our choice of
parameters tunes the near-boundary impurity current to be marginal, resulting
in a $\log T$ behavior in the UV resistivity, as is expected for the Kondo
problem. The resistivity at the IR fixed point turns out to be zero, signaling
a complete screening of the impurity. | 1709.06086v2 |
2019-07-11 | First results of Resistive-Plate Well (RPWELL) detector operation at 163 K | We present for the first time, discharge-free operation at cryogenic
conditions of a Resistive-Plate WELL (RPWELL) detector. It is a single-sided
Thick Gaseous Electron Multiplier (THGEM) coupled to a readout anode via a
plate of high bulk resistivity. The results of single- and double-stage RPWELL
detectors operated in stable conditions in Ne/5$\%$CH$_{4}$ at 163 K are
summarized. The RPWELL comprised a ferric-based (Fe$^{3+}$) ceramic composite
("Fe-ceramic") as the resistive plate, of volume resistivity $\sim$$10^{11}$
$\Omega$$\cdot$cm at this temperature. Gains of $\sim$$10^{4}$ and
$\sim$$10^{5}$ were reached with the single-stage RPWELL, with 6 keV X-rays and
single UV-photons, respectively. The double-stage detector, a THGEM followed by
the RPWELL, reached gains $\sim$$10^{5}$ and $\sim$$10^{6}$ with X-rays and
single UV-photons, respectively. The results were obtained with and without a
CsI photocathode on the first multiplying element. Potential applications at
these cryogenic conditions are discussed. | 1907.05057v1 |
2020-04-10 | Linear in temperature resistivity in the limit of zero temperature from the time reparameterization soft mode | The most puzzling aspect of the 'strange metal' behavior of correlated
electron compounds is that the linear in temperature resistivity often extends
down to low temperatures, lower than natural microscopic energy scales. We
consider recently proposed deconfined critical points (or phases) in models of
electrons in large dimension lattices with random nearest-neighbor exchange
interactions. The criticality is in the class of Sachdev-Ye-Kitaev models, and
exhibits a time reparameterization soft mode representing gravity in dual
holographic theories. We compute the low temperature resistivity in a large $M$
limit of models with SU($M$) spin symmetry, and find that the dominant
temperature dependence arises from this soft mode. The resistivity is linear in
temperature down to zero temperature at the critical point, with a co-efficient
universally proportional to the product of the residual resistivity and the
co-efficient of the linear in temperature specific heat. We argue that the time
reparameterization soft mode offers a promising and generic mechanism for
resolving the strange metal puzzle. | 2004.05182v4 |
2017-07-31 | Universal linear-temperature resistivity: possible quantum diffusion transport in strongly correlated superconductors | The strongly correlated electron fluids in high temperature cuprate
superconductors demonstrate an anomalous linear temperature ($T$) dependent
resistivity behavior, which persists to a wide temperature range without
exhibiting saturation. As cooling down, those electron fluids lose the
resistivity and condense into the superfluid. However, the origin of the
linear-$T$ resistivity behavior and its relationship to the strongly correlated
superconductivity remain a mystery. Here we report a universal relation
$d\rho/dT=(\mu_0k_B/\hbar)\lambda^2_L$, which bridges the slope of the
linear-$T$-dependent resistivity ($d\rho/dT$) to the London penetration depth
$\lambda_L$ at zero temperature among cuprate superconductor
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and heavy fermion superconductors
CeCoIn$_5$, where $\mu_0$ is vacuum permeability, $k_B$ is the Boltzmann
constant and $\hbar$ is the reduced Planck constant. We extend this scaling
relation to different systems and found that it holds for other cuprate,
pnictide and heavy fermion superconductors as well, regardless of the
significant differences in the strength of electronic correlations, transport
directions, and doping levels. Our analysis suggests that the scaling relation
in strongly correlated superconductors could be described as a hydrodynamic
diffusive transport, with the diffusion coefficient ($D$) approaching the
quantum limit $D\sim\hbar/m^*$, where $m^*$ is the quasi-particle effective
mass. | 1707.09782v1 |
2019-03-28 | Faster Spectral Sparsification in Dynamic Streams | Graph sketching has emerged as a powerful technique for processing massive
graphs that change over time (i.e., are presented as a dynamic stream of edge
updates) over the past few years, starting with the work of Ahn, Guha and
McGregor (SODA'12) on graph connectivity via sketching. In this paper we
consider the problem of designing spectral approximations to graphs, or
spectral sparsifiers, using a small number of linear measurements, with the
additional constraint that the sketches admit an efficient recovery scheme.
Prior to our work, sketching algorithms were known with near optimal $\tilde
O(n)$ space complexity, but $\Omega(n^2)$ time decoding (brute-force over all
potential edges of the input graph), or with subquadratic time, but rather
large $\Omega(n^{5/3})$ space complexity (due to their reliance on a rather
weak relation between connectivity and effective resistances). In this paper we
first show how a simple relation between effective resistances and edge
connectivity leads to an improved $\widetilde O(n^{3/2})$ space and time
algorithm, which we show is a natural barrier for connectivity based
approaches. Our main result then gives the first algorithm that achieves
subquadratic recovery time, i.e. avoids brute-force decoding, and at the same
time nontrivially uses the effective resistance metric, achieving
$n^{1.4+o(1)}$ space and recovery time.
Our main technical contribution is a novel method for `bucketing' vertices of
the input graph into clusters that allows fast recovery of edges of high
effective resistance: the buckets are formed by performing ball-carving on the
input graph using (an approximation to) its effective resistance metric. We
feel that this technique is likely to be of independent interest. | 1903.12165v1 |
2012-06-13 | Current Challenges and Perspectives in Resistive Gaseous Detectors: a manifesto from RPC 2012 | Resistive gaseous detectors can be broadly defined as those operated in
conditions where virtually no field lines exist that connect any two metallic
electrodes sitting at different potential. This condition can be operationally
recognized as 'no gas gap being delimited by two metallic electrodes'. Since
early 70's, Resistive Plate Chambers (RPCs) are the most successful
implementation of this idea, that leads to fully spark-protected gaseous
detectors, with solid state-like reliability at working fields beyond 100kV/cm,
yet enjoying the general characteristics of gaseous detectors in terms of
flexibility, optimization and customization. We present a summary of the status
of the field of resistive gaseous detectors as discussed in a dedicated closing
session that took place during the XI Workshop for Resistive Plate Chambers and
Related Detectors celebrated in Frascati, and especially we review the
perspectives and ambitions towards the XII Workshop to be celebrated in Beijing
in year 2014. Due to the existence of two specific reviews ([1,2]) also at this
workshop, a minimum amount of overlap was found to be unavoidable. We have
realized, however, that the three works provide a look at the field from
different optics, so they can be largely considered to be complementary.
Contrary to the initial concerns, the overall appearance seems to be fairly
round, in our opinion. | 1206.2735v2 |
2018-12-03 | Resistive evolution of toroidal field configurations and their relation to magnetic clouds | We study the resistive evolution of a localized self-organizing
magnetohydrodynamic equilibrium. In this configuration the magnetic forces are
balanced by a pressure force caused by a toroidal depression in the pressure.
Equilibrium is attained when this low pressure region prevents further
expansion into the higher-pressure external plasma. We find that, for the
parameters investigated, the resistive evolution of the structures follows a
universal pattern when rescaled to resistive time. The finite resistivity
causes both a decrease in the magnetic field strength and a finite slip of the
plasma fluid against the static equilibrium. This slip is caused by a
Pfirsch-Schl\"uter type diffusion, similar to what is seen in tokamak
equilibria. The net effect is that the configuration remains in Magnetostatic
equilibrium whilst it slowly grows in size. The rotational transform of the
structure becomes nearly constant throughout the entire structure, and
decreases according to a power law. In simulations this equilibrium is observed
when highly tangled field lines relax in a high-pressure (relative to the
magnetic field strength) environment, a situation that occurs when the twisted
field of a coronal loop is ejected into the interplanetary solar wind. In this
paper we relate this localized MHD equilibrium to magnetic clouds in the solar
wind. | 1812.00005v1 |
2019-01-24 | Parylene Based Memristive Devices with Multilevel Resistive Switching for Neuromorphic Applications | In this paper, the resistive switching and neuromorphic behavior of
memristive devices based on parylene, a polymer both low-cost and safe for the
human body, is comprehensively studied. The Metal/Parylene/ITO sandwich
structures were prepared by means of the standard gas phase surface
polymerization method with different top active metal electrodes (Ag, Al, Cu or
Ti of about 500 nm thickness). These organic memristive devices exhibit
excellent performance: low switching voltage (down to 1 V), large OFF/ON
resistance ratio (about 10^3), retention (> 10^4 s) and high multilevel
resistance switching (at least 16 stable resistive states in the case of Cu
electrodes). We have experimentally shown that parylene-based memristive
elements can be trained by a biologically inspired spike-timing-dependent
plasticity (STDP) mechanism. The obtained results have been used to implement a
simple neuromorphic network model of classical conditioning. The described
advantages allow considering parylene-based organic memristors as prospective
devices for hardware realization of spiking artificial neuron networks capable
of supervised and unsupervised learning and suitable for biomedical
applications. | 1901.08667v2 |
2020-01-24 | Metal-to-metal transition and heavy-electron state in Nd$_4$Ni$_3$O$_{10-δ}$ | The trilayer nickelate Nd$_4$Ni$_3$O$_{10-\delta}$ ($\delta \approx$ 0.15)
was investigated by the measurements of x-ray diffraction, electrical
resistivity, magnetic susceptibility, and heat capacity. The crystal structure
data suggest a higher Ni valence in the inner perovskite-like layer. At ambient
pressure the resistivity shows a jump at 162 K, indicating a metal-to-metal
transition (MMT). The MMT is also characterized by a magnetic susceptibility
drop, a sharp specific-heat peak, and an isotropic lattice contraction. Below
$\sim$ 50 K, a resistivity upturn with a log$T$ dependence shows up,
accompanying with a negative thermal expansion. External hydrostatic pressure
suppresses the resistivity jump progressively, coincident with the diminution
of the log$T$ behavior. The low-temperature electronic specific-heat
coefficient is extracted to be $\sim$ 150 mJ K$^{-2}$ mol-fu$^{-1}$, equivalent
to $\sim$ 50 mJ K$^{-2}$ mol-Ni$^{-1}$, indicating an unusual heavy-electron
correlated state. The novel heavy-electron state as well as the logarithmic
temperature dependence of resistivity is explained in terms of the Ni$^{3+}$
centered Kondo effect in the inner layer of the (NdNiO$_3$)$_3$ trilayers. | 2001.09059v2 |
2021-04-07 | Functional annotation of creeping bentgrass protein sequences based on convolutional neural network | Background: Creeping bentgrass (Agrostis soionifera) is a perennial grass of
Gramineae, belonging to cold season turfgrass, but has poor disease resistance.
Up to now, little is known about the induced systemic resistance (ISR)
mechanism, especially the relevant functional proteins, which is important to
disease resistance of turfgrass. Achieving more information of proteins of
infected creeping bentgrass is helpful to understand the ISR mechanism.
Results: With BDO treatment, creeping bentgrass seedlings were grown, and the
ISR response was induced by infecting Rhizoctonia solani. High-quality protein
sequences of creeping bentgrass seedlings were obtained. Some of protein
sequences were functionally annotated according to the database alignment while
a large part of the obtained protein sequences was left non-annotated. To treat
the non-annotated sequences, a prediction model based on convolutional neural
network was established with the dataset from Uniport database in three domains
to acquire good performance, especially the higher false positive control rate.
With established model, the non-annotated protein sequences of creeping
bentgrass were analyzed to annotate proteins relevant to disease-resistance
response and signal transduction. Conclusions: The prediction model based on
convolutional neural network was successfully applied to select good candidates
of the proteins with functions relevant to the ISR mechanism from the protein
sequences which cannot be annotated by database alignment. The waste of
sequence data can be avoided, and research time and labor will be saved in
further research of protein of creeping bentgrass by molecular biology
technology. It also provides reference for other sequence analysis of turfgrass
disease-resistance research. | 2104.03139v2 |
2021-08-19 | Resistive Hot Accretion Flows with Anisotropic Pressure | Since the collisional mean free path of charged particles in hot accretion
flows can be significantly larger than the typical length-scale of the
accretion flows, the gas pressure is anisotropic to magnetic field lines. For
such a large collisional mean free path, the resistive dissipation can also
play a key role in hot accretion flows. In this paper, we study the dynamics of
resistive hot accretion flows in the presence of anisotropic pressure. We
present a set of self-similar solutions where the flow variables are assumed to
be a function only of radius. Our results show that the radial and rotational
velocities and the sound speed increase considerably with the strength of
anisotropic pressure. The increase in infall velocity and in sound speed are
more significant if the resistive dissipation is taken into account. We find
that such changes depend on the field strength. Our results indicate that the
resistive heating is $10\%$ of the heating by the work done by anisotropic
pressure when the strength of anisotropic pressure is 0.1. This value becomes
higher when the strength of anisotropic pressure reduces. The increase in disk
temperature can lead to heating and acceleration of the electrons in such
flows. It helps us to explain the origin of phenomena such as the flares in
Galactic Center Sgr A*. | 2108.09829v1 |
2022-05-22 | First Report of Susceptibility Status of the Invasive Vector: Aedes albopictus to insecticides used in vector control in Morocco | Aedes albopictus has been newly recorded in Agdal district at Rabat in
Morocco. The establishment of this invasive mosquito could affect the public
health by causing serious epidemics despite of its high nuisance in urban and
sub-urban areas. Vector control is mainly based on environmental management but
chemical insecticides can be used to reduce adult mosquito densities during
peak periods. However, the level of susceptibility of this mosquito to
insecticides has not been studied yet in Morocco. This paper reports the
results of the first study conducted to monitor the insecticide resistance of
adult and larva Ae. albopictus to the insecticides currently used in the vector
control. The study was carried out during May-June 2018 at Rabat from the
north-west of the country. Adult susceptibility tests were performed following
the WHO test procedures. One organochlorate (DDT 4%), one pyrethroids
(cyfluthrin 0.15%), one carbamate (bendiocarb 0.1%) and one organophosphate
(fenithrothion 1%) were tested at diagnostic doses (DD). The five-fold DD of
bendiocarb were also used to yield information on the intensity of mosquito
adult resistance. The results of the performed susceptibility bioassay showed
that the vector is susceptible to cyfluthrin and resistant to DDT, bendiocarb
and fenithrothion. Larval bioassays to temephos were conducted according to WHO
standard operating protocol to establish the dose-mortality relationship and
deduct the LC50 and LC90 then resistance ratios. We show that larval
populations of Ae. albopictus are still sensible to this insecticide. This
information could help policy-makers to plan insecticide resistance management. | 2205.11994v1 |
2023-09-15 | Greedy Optimization of Resistance-based Graph Robustness with Global and Local Edge Insertions | The total effective resistance, also called the Kirchhoff index, provides a
robustness measure for a graph $G$. We consider two optimization problems of
adding $k$ new edges to $G$ such that the resulting graph has minimal total
effective resistance (i.e., is most robust) -- one where the new edges can be
anywhere in the graph and one where the new edges need to be incident to a
specified focus node. The total effective resistance and effective resistances
between nodes can be computed using the pseudoinverse of the graph Laplacian.
The pseudoinverse may be computed explicitly via pseudoinversion; yet, this
takes cubic time in practice and quadratic space. We instead exploit
combinatorial and algebraic connections to speed up gain computations in an
established generic greedy heuristic. Moreover, we leverage existing randomized
techniques to boost the performance of our approaches by introducing a
sub-sampling step. Our different graph- and matrix-based approaches are indeed
significantly faster than the state-of-the-art greedy algorithm, while their
quality remains reasonably high and is often quite close. Our experiments show
that we can now process larger graphs for which the application of the
state-of-the-art greedy approach was impractical before. | 2309.08271v1 |
2024-05-28 | Differential Voltage Analysis and Patterns in Parallel-Connected Pairs of Imbalanced Cells | Diagnosing imbalances in capacity and resistance within parallel-connected
cells in battery packs is critical for battery management and fault detection,
but it is challenging given that individual currents flowing into each cell are
often unmeasured. This work introduces a novel method useful for identifying
imbalances in capacity and resistance within a pair of parallel-connected cells
using only voltage and current measurements from the pair. Our method utilizes
differential voltage analysis (DVA) when the pair is under constant current
discharge and demonstrates that features of the pair's differential voltage
curve (dV/dQ), namely its mid-to-high SOC dV/dQ peak's height and skewness, are
sensitive to imbalances in capacity and resistance. We analyze and explain how
and why these dV/dQ peak shape features change in response to these imbalances,
highlighting that the underlying current imbalance dynamics resulting from
these imbalances contribute to these changes. Ultimately, we demonstrate that
dV/dQ peak shape features can identify the product of capacity imbalance and
resistance imbalance, but cannot uniquely identify the imbalances. This work
lays the groundwork for identifying imbalances in capacity and resistance in
parallel-connected cell groups in battery packs, where commonly only a single
current sensor is placed for each parallel cell group. | 2405.17754v1 |
2018-02-05 | Electrical-current-induced magnetic hysteresis in self-assembled vertically aligned La_{2/3}Sr_{1/3}MnO_3:ZnO-nanopillar composites | Magnetoresistive random-access memory (MRAM) is poised to become a
next-generation information storage device. Yet, many materials challenges
remain unsolved before it can become a widely used memory storage solution.
Among them, an urgent need is to identify a material system that is suitable
for downscaling and is compatible with low-power logic applications.
Self-assembled, vertically-aligned La_{2/3}Sr_{1/3}MnO_3:ZnO nanocomposites, in
which La_{2/3}Sr_{1/3}MnO_3 (LSMO) matrix and ZnO nanopillars form an
intertwined structure with coincident-site-matched growth occurring between the
LSMO and ZnO vertical interfaces, may offer new MRAM applications by combining
their superior electric, magnetic (B), and optical properties. In this paper,
we show the results of electrical current induced magnetic hysteresis in
magneto-resistance measurements in these nano-pillar composites. We observe
that when the current level is low, for example, 1 uA, the magneto-resistance
displays a linear, negative, non-hysteretic B field dependence. Surprisingly,
when a large current is used, I > 10 uA, a hysteretic behavior is observed when
the B field is swept in the up and down directions. This hysteresis weakens as
the sample temperature is increased. A possible spin-valve mechanism related to
this electrical current induced magnetic hysteresis is proposed and discussed. | 1802.01632v1 |
2018-03-05 | Measurement of Elastoresistivity at Finite Frequency by Amplitude Demodulation | Elastoresistivity, the relation between resistivity and strain, can elucidate
subtle properties of the electronic structure of a material and is an
increasingly important tool for the study of strongly correlated materials. To
date, elastoresistivity measurements have been predominantly performed with
quasi-static (DC) strain. In this work, we demonstrate a method for using AC
strain in elastoresistivity measurements. A sample experiencing AC strain has a
time-dependent resistivity, which modulates the voltage produced by an AC
current; this effect produces time-dependent variations in resisitivity that
are directly proportional to the elastoresistivity, and which can be measured
more quickly, with less strain on the sample, and with less stringent
requirements for temperature stability than the previous DC technique. Example
measurements between 10 Hz and 3 kHz are performed on a material with a large,
well-characterized and temperature dependent elastoresistivity: the
representative iron-based superconductor BaFe$_{1.975}$Co$_{0.025}$As$_2$.
These measurements yield a frequency independent elastoresistivity and
reproduce results from previous DC elastoresistivity methods to within
experimental accuracy. We emphasize that the dynamic (AC) elastoresistivity is
a distinct material-specific property that has not previously been considered. | 1803.01909v2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.