publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2023-10-27 | Practical application of quantum neural network to materials informatics: prediction of the melting points of metal oxides | Quantum neural network (QNN) models have received increasing attention owing
to their strong expressibility and resistance to overfitting. It is
particularly useful when the size of the training data is small, making it a
good fit for materials informatics (MI) problems. However, there are only a few
examples of the application of QNN to multivariate regression models, and
little is known about how these models are constructed. This study aims to
construct a QNN model to predict the melting points of metal oxides as an
example of a multivariate regression task for the MI problem. Different
architectures (encoding methods and entangler arrangements) are explored to
create an effective QNN model. Shallow-depth ansatzs could achieve sufficient
expressibility using sufficiently entangled circuits. The "linear" entangler
was adequate for providing the necessary entanglement. The expressibility of
the QNN model could be further improved by increasing the circuit width. The
generalization performance could also be improved, outperforming the classical
NN model. No overfitting was observed in the QNN models with a well-designed
encoder. These findings suggest that QNN can be a useful tool for MI. | 2310.17935v1 |
2023-11-01 | Giant anomalous Hall effect in epitaxial Mn$_{3.2}$Ge films with a cubic kagome structure | We report on the first example of epitaxial Mn$_{3 + \delta}$Ge thin films
with a cubic $L1_2$ structure. The films are found to exhibit frustrated
ferromagnetism with an average magnetization corresponding to
0.98$~\pm~$0.06$~\mu_B$/Mn, far larger than the parasitic ferromagnetism in
hexagonal Mn$_3$Ge and the partially compensated ferrimagnetism in tetragonal
Mn$_3$Ge. The Hall conductivity is the largest reported for the kagome magnets
with a low temperature value of $\sigma_{xy} = 1587~$S/cm. Density functional
calculations predict that a chiral antiferromagnetic structure is lower in
energy than a ferromagnetic configuration in an ordered stoichiometric crystal.
However, chemical disorder driven by the excess Mn in our films explains why a
frustrated 120$^\circ$ spin structure is not observed. Comparisons between the
magnetization and the Hall resistivity indicate that a non-coplanar spin
structure contributes the Hall signal. Anisotropic magnetoresistance and planar
Hall effect with hysteresis up to 14 T provides further insights into this
material. | 2311.00683v1 |
2023-11-06 | Current-induced spin polarization in chiral Tellurium: a first-principles quantum transport study | Te is a naturally p-doped semiconductor with a chiral structure, where an
electrical current causes the conduction electrons to become spin polarized
parallel to the transport direction. In this paper, we present a comprehensive
theoretical study of this effect by employing density functional theory (DFT)
combined with the non-equilibrium Green's functions (NEGF) technique for
quantum transport. We suggest that the spin polarization can quantitatively be
estimated in terms of two complementary quantities, namely the non-equilibrium
magnetic moments and the spin current density. The calculated magnetic moments
are directly compared with the values from previous theoretical studies
obtaining overall consistent results. On the other hand, the inspection of the
spin current density provides insights of the magnetotransport properties of
the material. Specifically, we predict that the resistance along a Te wire
changes when an external magnetic field is applied parallel or antiparallel to
the charge current direction. The computed magnetoresistance is however quite
small (~ 0.025%). Finally, we show that the description of the current-induced
spin polarization in terms of the spin current establishes a straightforward
connection with the phenomenon called chiral-induced spin selectivity, recently
observed in several nano-junctions. | 2311.03219v2 |
2023-12-11 | Superconductivity in Ternary Germanide ScPdGe and Silicide ScPdSi | The electronic properties of ScPdGe and ScPdSi, crystallizing in the
hexagonal ZrNiAl and orthorhombic TiNiSi structures, respectively, are
investigated. ScPdGe and ScPdSi are found to show bulk superconductivity below
0.9 and 1.7 K, respectively, based on electrical resistivity and heat capacity
data measured using synthesized polycrystalline samples. First principles
calculations indicate the presence of large contributions of Sc 3d and Pd 4d
electrons at the Fermi energy in both materials. The electronic properties and
electronic states of these materials are discussed in comparison with those of
several superconductors containing scandium and a 4d transition metal element. | 2312.06045v1 |
2024-01-12 | Direction dependent switching of carrier-type enabled by Fermi surface geometry | While charge carriers can typically be designated as either electron- or
hole- type, depending on the sign of the Hall coefficient, some materials defy
this straightforward classification. Here we find that LaRh$_6$Ge$_4$ goes
beyond this dichotomy, where the Hall resistivity is electron-like for magnetic
fields along the $c$-axis but hole-like in the basal plane. Together with
first-principles calculations, we show that this direction-dependent switching
of the carrier type arises within a single band, where the special geometry
leads to charge carriers on the same Fermi surface orbiting as electrons along
some directions, but holes along others. The relationship between the Fermi
surface geometry and occurrence of a Hall sign reversal is further generalized
by considering tight-binding model calculations, which show that this type of
Fermi surface corresponds to a more robust means of realizing this phenomenon,
suggesting an important route for tailoring direction dependent properties for
advanced electronic device applications. | 2401.06333v1 |
2024-01-13 | Synthesis of thin film infinite-layer nickelates by atomic hydrogen reduction: clarifying the role of the capping layer | We present an integrated procedure for the synthesis of infinite-layer
nickelates using molecular-beam epitaxy with gas-phase reduction by atomic
hydrogen. We first discuss challenges in the growth and characterization of
perovskite NdNiO$_3$/SrTiO$_3$, arising from post growth crack formation in
stoichiometric films. We then detail a procedure for fully reducing NdNiO$_3$
films to the infinite-layer phase, NdNiO$_2$, using atomic hydrogen; the
resulting films display excellent structural quality, smooth surfaces, and
lower residual resistivities than films reduced by other methods. We utilize
the in situ nature of this technique to investigate of the role that SrTiO$_3$
capping layers play in the reduction process, illustrating their importance in
preventing the formation of secondary phases at the exposed nickelate surface.
A comparative bulk- and surface-sensitive study indicates formation of a
polycrystalline crust on the film surface serves to limit the reduction
process. | 2401.07129v1 |
2024-02-01 | A mechanism for electrostatically generated magnetoresistance in chiral systems without spin-dependent transport | Significant attention has been drawn to electronic transport in chiral
materials coupled to ferromagnets in the chirality induced spin selectivity
(CISS) effect. A large magnetoresistance (MR) is usually observed which is
widely interpreted to originate from spin (dependent) transport. However, there
are severe discrepancies between the experimental results and theoretical
interpretations, most notably the apparent failure of the Onsager reciprocity
relation in the linear response regime. We provide an alternative explanation
for the mechanism of the two terminal MR in chiral systems coupled to a
ferromagnet. For this we point out that it was observed that the electrostatic
contact potential of chiral materials on a ferromagnet depends on the
magnetization direction and chirality. In our explanation this causes the
transport barrier to be modified by the magnetization direction, already in
equilibrium, in the absence of a bias current. This strongly alters the charge
transport through/over the barrier, not requiring spin transport. This provides
a mechanism that allows the linear response resistance to be sensitive to the
magnetization direction and also explains the failure of the Onsager
reciprocity relations. We propose experimental configurations to confirm our
alternative mechanism for MR. | 2402.00472v1 |
2024-02-28 | Optimizing Beer Glass Shapes to Minimize Heat Transfer During Consumption | This paper addresses the problem of determining the optimum shape for a beer
glass that minimizes the heat transfer while the liquid is consumed, thereby
keeping it cold for as long as possible. The proposed solution avoids the use
of insulating materials. The glass is modelled as a body of revolution
generated by a smooth curve S, constructed from a material with negligible
thermal resistance at the revolution surface but insulated at the bottom. The
ordinary differential equation describing the problem is derived from the first
law of Thermodynamics applied to a control volume encompassing the liquid. This
is an inverse optimization problem, aiming to find the shape of the glass
(represented by curve S) that minimizes the heat transfer rate. In contrast,
the direct problem aims to determine the heat transfer rate for a given
geometry. The solution obtained is analytic, and the resulting expression for S
is in closed form, providing a family of optimal glass shapes that can be
manufactured using conventional methods. | 2402.18544v1 |
2024-03-03 | Defect-Induced Strain-Tunable Photoluminescence in AgScP$_2$S$_6$ | Metal thiophosphates (MTPs) are a large family of 2D materials that exhibit
large structural and chemical diversity. They also show promise for
applications in energy harvesting and photodetection. Strain and defect
engineering have previously been demonstrated as useful mechanisms to tune
several properties of MTPs such as resistivity, magnetic state, and electronic
band gap. However, the effect of these stimuli on engineering tunable light
emission in MTPs remains unexplored. Here, we show experimentally that
structural defects in metal thiophosphate AgScP$_2$S$_6$ are prominent in
exhibiting photoluminescence, which is likely driven by the
defect-state-to-conduction-band transitions and can be further tuned by
temperature-induced strain gradients. | 2403.01581v1 |
2024-03-29 | Gate-tunable quantum acoustoelectric transport in graphene | Transport probes the motion of quasiparticles in response to external
excitations. Apart from the well-known electric and thermoelectric transport,
acoustoelectric transport induced by traveling acoustic waves has been rarely
explored. Here, by adopting a hybrid nanodevices integrated with piezoelectric
substrates, we establish a simple design of acoustoelectric transport with gate
tunability. We fabricate dual-gated acoustoelectric devices based on
BN-encapsuled graphene on LiNbO3. Longitudinal and transverse acoustoelectric
voltages are generated by launching pulsed surface acoustic wave. The gate
dependence of zero-field longitudinal acoustoelectric signal presents
strikingly similar profiles as that of Hall resistivity, providing a valid
approach for extracting carrier density without magnetic field. In magnetic
fields, acoustoelectric quantum oscillations appear due to Landau quantization,
which are more robust and pronounced than Shubnikov-de Haas oscillations. Our
work demonstrates a feasible acoustoelectric setup with gate tunability, which
can be extended to the broad scope of various Van der Waals materials. | 2403.20248v1 |
2024-04-02 | Accurate determination of thermoelectric figure of merit using ac Harman method with a four-probe configuration | The ac Harman method has been used for the direct estimation of dimensionless
thermoelectric figure of merit (zT) through ac/dc resistance measurements.
However, accurate zT estimation with a four-probe configuration is difficult
owing to the occurrence of a thermal phase-delay in the heat flow with a low
frequency current. This study reports an exact solution for zT estimation by
solving the heat conduction equation. The analysis can explain the reverse heat
flow, which is the main source of the error in the four-probe configuration,
and the experimentally obtained behavior of the frequency dependence of zT of
(Bi,Sb)$_2$Te$_3$. Approximately 20 % of the error is caused by a thermal
phase-delay, unless an appropriate current frequency and voltage-terminal
position are chosen. Thus, an accurate zT evaluation using a four-probe
configuration at any voltage terminal position is achieved. These findings can
lead to interesting thermoelectric metrology and could serve as a powerful tool
to search for promising thermoelectric materials. | 2404.01565v1 |
2024-04-02 | From Seaweed to Security: The Emergence of Alginate in Compromising IoT Fingerprint Sensors | The increasing integration of capacitive fingerprint recognition sensors in
IoT devices presents new challenges in digital forensics, particularly in the
context of advanced fingerprint spoofing. Previous research has highlighted the
effectiveness of materials such as latex and silicone in deceiving biometric
systems. In this study, we introduce Alginate, a biopolymer derived from brown
seaweed, as a novel material with the potential for spoofing IoT-specific
capacitive fingerprint sensors. Our research uses Alginate and cutting-edge
image recognition techniques to unveil a nuanced IoT vulnerability that raises
significant security and privacy concerns. Our proof-of-concept experiments
employed authentic fingerprint molds to create Alginate replicas, which
exhibited remarkable visual and tactile similarities to real fingerprints. The
conductivity and resistivity properties of Alginate, closely resembling human
skin, make it a subject of interest in the digital forensics field, especially
regarding its ability to spoof IoT device sensors. This study calls upon the
digital forensics community to develop advanced anti-spoofing strategies to
protect the evolving IoT infrastructure against such sophisticated threats. | 2404.02150v1 |
2024-04-19 | Perspective on descriptors of mechanical behavior of cubic transition-metal carbides and nitrides | Cubic rocksalt structured transition-metal carbides, nitrides, and related
alloys (TMC/Ns) are attractive for a wide variety of applications, notably as
hard, wear-resistant material. To-date, valence electron concentration (VEC) is
used as a good indicator of stability and mechanical properties of these
refractory compounds. In this perspective, we argue for the need for electronic
descriptors beyond VEC to explain and predict the mechanical behavior of the
cubic TMC/Ns. As such, we point out that descriptors that highlight differences
between constituent have been underused, along with semi-empirical models of
mechanical properties. Additionally, it appears promising to partition VEC into
contribution to ionic, covalent, and metallic bonds and we suggest that such
partition could provide more insight into predicting mechanical properties in
the future. | 2404.12853v2 |
2024-04-25 | Anisotropic magnetoresistance in altermagnetic MnTe | Recently, MnTe was established as an altermagnetic material that hosts
spin-polarized electronic bands as well as anomalous transport effects like the
anomalous Hall effect. In addition to these effects arising from
altermagnetism, MnTe also hosts other magnetoresistance effects. Here, we study
the manipulation of the magnetic order by an applied magnetic field and its
impact on the electrical resistivity. In particular, we establish which
components of anisotropic magnetoresistance are present when the magnetic order
is rotated within the hexagonal basal plane. Our experimental results, which
are in agreement with our symmetry analysis of the magnetotransport components,
showcase the existence of an anisotropic magnetoresistance linked to both the
relative orientation of current and magnetic order, as well as crystal and
magnetic order. | 2404.16516v1 |
2024-05-26 | Observation of in-plane anomalous Hall effect associated with orbital magnetization | For over a century, the Hall effect, a transverse effect under out-of-plane
magnetic field or magnetization, has been a cornerstone for magnetotransport
studies and applications. Modern theoretical formulation based on the Berry
curvature has revealed the potential that even in-plane magnetic field can
induce anomalous Hall effect, but its experimental demonstration has remained
difficult due to its potentially small magnitude and strict symmetry
requirements. Here we report observation of the in-plane anomalous Hall effect
by measuring low-carrier density films of magnetic Weyl semimetal
EuCd$_2$Sb$_2$. Anomalous Hall resistance exhibits distinct three-fold
rotational symmetry for changes in the in-plane field component, and this can
be understood in terms of out-of-plane Weyl points splitting or orbital
magnetization induced by in-plane field, as also confirmed by model
calculation. Our findings demonstrate the importance of in-plane field to
control the Hall effect, accelerating materials development and further
exploration of various in-plane field induced phenomena. | 2405.16722v1 |
2024-05-28 | Exchange Splitting Mechanism of Negative Magnetoresistance in Layered Antiferromagnetic Semimetals | Layered topologically non-trivial and trivial semimetals with AFM-type
ordering of magnetic sublattice are known to exhibit a negative
magnetoresistance that is well correlated with AFM magnetization changes in a
magnetic field. This effect is reported in several experimental studies with
EuFe$_2$As$_2$, EuSn$_2$As$_2$, EuSn$_2$P$_2$, etc., where the resistance
decreases quadratically with field by about $\delta\rho/\rho \sim 4-6\%$ up to
the spin-polarization field. Despite the fact that this effect is well
documented experimentally, its theoretical explanation is missing up to date.
In this paper we propose a novel theoretical mechanism describing the observed
magnetoresistance that does not imply either topological origin of the
materials, surface roughness, their potential defect structure, or
electron-magnon scattering. We believe, the proposed intrinsic mechanism of
magnetoresistance is applicable to a wide class of the layered AFM- ordered
semimetals. The theoretically calculated magnetoresistance is qualitatively
consistent with experimental data for crystals of various composition. | 2405.18046v1 |
2005-04-07 | Design of HIV-1-PR inhibitors which do not create resistance: blocking the folding of single monomers | One of the main problems of drug design is that of optimizing the
drug--target interaction. In the case in which the target is a viral protein
displaying a high mutation rate, a second problem arises, namely the eventual
development of resistance. We wish to suggest a scheme for the design of
non--conventional drugs which do not face any of these problems and apply it to
the case of HIV--1 protease. It is based on the knowledge that the folding of
single--domain proteins, like e.g. each of the monomers forming the HIV--1--PR
homodimer, is controlled by local elementary structures (LES), stabilized by
local contacts among hydrophobic, strongly interacting and highly conserved
amino acids which play a central role in the folding process. Because LES have
evolved over myriads of generations to recognize and strongly interact with
each other so as to make the protein fold fast as well as to avoid aggregation
with other proteins, highly specific (and thus little toxic) as well as
effective folding--inhibitor drugs suggest themselves: short peptides (or
eventually their mimetic molecules), displaying the same amino acid sequence of
that of LES (p--LES). Aside from being specific and efficient, these inhibitors
are expected not to induce resistance: in fact, mutations which successfully
avoid their action imply the destabilization of one or more LES and thus should
lead to protein denaturation. Making use of Monte Carlo simulations within the
framework of a simple although not oversimplified model, which is able to
reproduce the main thermodynamic as well as dynamic properties of monoglobular
proteins, we first identify the LES of the HIV--1--PR and then show that the
corresponding p--LES peptides act as effective inhibitors of the folding of the
protease which do not create resistance. | 0504011v1 |
2012-04-25 | Rossby wave instability at dead zone boundaries in 3D resistive magnetohydrodynamical global models of protoplanetary disks | It has been suggested that the transition between magnetorotationally active
and dead zones in protoplanetary disks should be prone to the excitation of
vortices via Rossby wave instability (RWI). However, the only numerical
evidence for this has come from alpha disk models, where the magnetic field
evolution is not followed, and the effect of turbulence is parametrized by
Laplacian viscosity. We aim to establish the phenomenology of the flow in the
transition in 3D resistive-magnetohydrodynamical models. We model the
transition by a sharp jump in resistivity, as expected in the inner dead zone
boundary, using the Pencil Code to simulate the flow. We find that vortices are
readily excited in the dead side of the transition. We measure the mass
accretion rate finding similar levels of Reynolds stress at the dead and active
zones, at the $\alpha\approx 10^{-2}$ level. The vortex sits in a pressure
maximum and does not migrate, surviving until the end of the simulation. A
pressure maximum in the active zone also triggers the RWI. The magnetized
vortex that results should be disrupted by parasitical magneto-elliptic
instabilities, yet it subsists in high resolution. This suggests that either
the parasitic modes are still numerically damped, or that the RWI supplies
vorticity faster than they can destroy it. We conclude that the resistive
transition between the active and dead zones in the inner regions of
protoplanetary disks, if sharp enough, can indeed excite vortices via RWI. Our
results lend credence to previous works that relied on the alpha-disk
approximation, and caution against the use of overly reduced azimuthal coverage
on modeling this transition. | 1204.5711v2 |
2014-12-18 | Field topologies in ideal and near ideal magnetohydrodynamics and vortex dynamics | Magnetic field topology frozen in ideal magnetohydrodynamics (MHD) and its
breakage in near ideal MHD are reviewed in two parts. The first part gives a
physically complete description of the frozen in field topology, taking
magnetic flux conservation as fundamental and treating four topics, Eulerian
and Lagrangian descriptions of MHD, Chandrasekhar-Kendall and Euler-potential
field representations, magnetic helicity, and inviscid vortex dynamics in
comparison to ideal MHD. A corollary clarifies the challenge of achieving a
high degree of the frozen in condition in numerical MHD. The second part treats
field topology breakage centered on the Parker Magnetostatic Theorem on a
general incompatibility of a continuous magnetic field with the dual demand of
force free equilibrium and an arbitrarily prescribed, 3D field topology.
Preserving field topology as a global constraint readily results in formation
of tangential magnetic discontinuities, i.e., electric current sheets of zero
thickness. A similar incompatibility is present in the steady, force and
thermal balance of a heated radiating fluid subject to an anisotropic thermal
flux conducted strictly along the frozen in magnetic field in the low beta
limit. In a weakly resistive fluid the thinning of current sheets by these
incompatibilities inevitably results in sheet dissipation, resistive heating
and topological changes in the field despite the small resistivity. Faraday
induction drives but also macroscopically limits this mode of energy
dissipation, storing free energy in self organized, ideal MHD structures. This
property of MHD turbulence captured by the Taylor hypothesis is reviewed in
relation to the Sun's corona, calling for a basic quantitative description of
the breakdown of flux conservation in the low resistivity limit. A cylindrical,
initial boundary value problem provides specificity in the review. | 1412.6158v1 |
2015-01-27 | Unconventional Strong Spin-Fluctuation Effects around the Critical Pressure of the Itinerant Ising-Type Ferromagnet URhAl | Resistivity measurements were performed for the itinerant Ising-type
ferromagnet URhAl at temperatures down to 40 mK under high pressure up to 7.5
GPa, using single crystals. We found that the critical pressure of the Curie
temperature exists at around $P_c$ ~ 5.2 GPa. Near $P_c$, the $A$-coefficient
of the $AT^{2}$ Fermi-liquid resistivity term below $T^*$ is largely enhanced
with a maximum around 5.2-5.5 GPa. Above $P_c$, the exponent of the resistivity
$\rho(T)$ deviates from 2. At $P_c$, it is close to $n = 5/3$, which is
expected by the theory of three-dimensional ferromagnetic spin fluctuations for
a 2nd-order quantum-critical point (QCP). However, $T_C(P)$ disappears as a
1st-order phase transition, and the critical behavior of resistivity in URhAl
cannot be explained by the theory of a 2nd-order QCP. The 1st-order nature of
the phase transition is weak, and the critical behavior is still dominated by
the spin fluctuation at low temperature. With increasing pressure, the
non-Fermi-liquid behavior is observed in higher fields. Magnetic field studies
point out a ferromagnetic wing structure with a tri-critical point (TCP) at ~
4.8-4.9 GPa in URhAl. One open possibility is that the switch from the
ferromagnetic to the paramagnetic states does not occur simply but an
intermediate state arises below the TCP as suggested theoretically recently.
Quite generally, if a drastic Fermi-surface change occurs through $P_c$, the
nature of the interaction itself may change and lead to the observed
unconventional behavior. | 1501.06701v2 |
2015-02-06 | General-relativistic resistive-magnetohydrodynamic simulations of binary neutron stars | We have studied the dynamics of an equal-mass magnetized neutron-star binary
within a resistive magnetohydrodynamic (RMHD) approach in which the highly
conducting stellar interior is matched to an electrovacuum exterior. Because
our analysis is aimed at assessing the modifications introduced by resistive
effects on the dynamics of the binary after the merger and through to collapse,
we have carried out a close comparison with an equivalent simulation performed
within the traditional ideal magnetohydrodynamic approximation. We have found
that there are many similarities between the two evolutions but also one
important difference: the survival time of the hyper massive neutron star
increases in a RMHD simulation. This difference is due to a less efficient
magnetic-braking mechanism in the resistive regime, in which matter can move
across magnetic-field lines, thus reducing the outward transport of angular
momentum. Both the RMHD and the ideal magnetohydrodynamic simulations carried
here have been performed at higher resolutions and with a different grid
structure than those in previous work of ours [L. Rezzolla, B. Giacomazzo, L.
Baiotti, J. Granot, C. Kouveliotou, and M. A. Aloy, Astrophys. J. Letters 732,
L6 (2011)], but confirm the formation of a low-density funnel with an ordered
magnetic field produced by the black hole--torus system. In both regimes the
magnetic field is predominantly toroidal in the highly conducting torus and
predominantly poloidal in the nearly evacuated funnel. Reconnection processes
or neutrino annihilation occurring in the funnel, none of which we model, could
potentially increase the internal energy in the funnel and launch a
relativistic outflow, which, however, is not produced in these simulations. | 1502.02021v2 |
2016-04-19 | A chemical solver to compute molecule and grain abundances and non-ideal MHD resistivities in prestellar core collapse calculations | We develop a detailed chemical network relevant to the conditions
characteristic of prestellar core collapse. We solve the system of
time-dependent differential equations to calculate the equilibrium abundances
of molecules and dust grains, with a size distribution given by size-bins for
these latter. These abundances are used to compute the different non-ideal
magneto-hydrodynamics resistivities (ambipolar, Ohmic and Hall), needed to
carry out simulations of protostellar collapse. For the first time in this
context, we take into account the evaporation of the grains, the thermal
ionisation of Potassium, Sodium and Hydrogen at high temperature, and the
thermionic emission of grains in the chemical network, and we explore the
impact of various cosmic ray ionisation rates. All these processes
significantly affect the non-ideal magneto-hydrodynamics resistivities, which
will modify the dynamics of the collapse. Ambipolar diffusion and Hall effect
dominate at low densities, up to n_H = 10^12 cm^-3, after which Ohmic diffusion
takes over. We find that the time-scale needed to reach chemical equilibrium is
always shorter than the typical dynamical (free fall) one. This allows us to
build a large, multi-dimensional multi-species equilibrium abundance table over
a large temperature, density and ionisation rate ranges. This table, which we
make accessible to the community, is used during first and second prestellar
core collapse calculations to compute the non-ideal magneto-hydrodynamics
resistivities, yielding a consistent dynamical-chemical description of this
process. | 1604.05613v6 |
2017-03-06 | Mutation supply and the repeatability of selection for antibiotic resistance | Whether evolution can be predicted is a key question in evolutionary biology.
Here we set out to better understand the repeatability of evolution. We
explored experimentally the effect of mutation supply and the strength of
selective pressure on the repeatability of selection from standing genetic
variation. Different sizes of mutant libraries of an antibiotic resistance
gene, TEM-1 $\beta$-lactamase in Escherichia coli, were subjected to different
antibiotic concentrations. We determined whether populations went extinct or
survived, and sequenced the TEM gene of the surviving populations. The
distribution of mutations per allele in our mutant libraries- generated by
error-prone PCR- followed a Poisson distribution. Extinction patterns could be
explained by a simple stochastic model that assumed the sampling of beneficial
mutations was key for survival. In most surviving populations, alleles
containing at least one known large-effect beneficial mutation were present.
These genotype data also support a model which only invokes sampling effects to
describe the occurrence of alleles containing large-effect driver mutations.
Hence, evolution is largely predictable given cursory knowledge of mutational
fitness effects, the mutation rate and population size. There were no clear
trends in the repeatability of selected mutants when we considered all
mutations present. However, when only known large-effect mutations were
considered, the outcome of selection is less repeatable for large libraries, in
contrast to expectations. Furthermore, we show experimentally that alleles
carrying multiple mutations selected from large libraries confer higher
resistance levels relative to alleles with only a known large-effect mutation,
suggesting that the scarcity of high-resistance alleles carrying multiple
mutations may contribute to the decrease in repeatability at large library
sizes. | 1703.01896v1 |
2020-03-16 | Effect of cytosol viscosity on the flow behavior of red blood cell suspensions in microvessels | The flow behavior of blood in microvessels is directly associated with tissue
perfusion and oxygen delivery. Current efforts on modeling blood flow have
primarily focused on the flow properties of blood with red blood cells (RBCs)
having a viscosity ratio $C$ of unity between the cytosol and suspending
medium, while under physiological conditions the cytosol viscosity is about
five times larger than the plasma viscosity (i.e., $C\approx 5$). The
importance of $C$ for the behavior of single RBCs in fluid flow has already
been demonstrated, while the effect of $C$ on blood flow has only been sparsely
studied. We employ mesoscopic hydrodynamic simulations to perform a systematic
investigation of flow properties of RBC suspensions with different cytosol
viscosities for various flow conditions in cylindrical microchannels. Our main
aim is to link macroscopic flow properties such as flow resistance to single
cell deformation and dynamics as a function of $C$. Starting from a dispersed
cell configuration, we find that the flow convergence and the development of a
RBC-free layer (RBC-FL) depend only weakly on $C$, and require a convergence
length in the range of $25D-50D$, where $D$ is the channel diameter. The flow
resistance for $C=5$ is nearly the same as that for $C=1$, which is facilitated
by a slightly larger RBC-FL thickness for $C=5$. This effect is due to the
suppression of membrane motion and dynamic shape deformations by a more viscous
cytosol for $C=5$, resulting in a more compact cellular core of the flow in
comparison to $C=1$. The weak effect of cytosol viscosity on the flow
resistance and RBC-FL explains why cells can have a high concentration of
hemoglobin for efficient oxygen delivery, without a pronounced increase in the
flow resistance. | 2003.09217v1 |
2019-12-24 | DC resistivity near a nematic quantum critical point: Effects of weak disorder and acoustic phonons | We calculate the resistivity associated with an Ising-nematic quantum
critical point in the presence of disorder and acoustic phonons in the lattice
model. We use the memory-matrix transport theory, which has a crucial advantage
compared to other methods of not relying on the existence of well-defined
quasiparticles in the low-energy effective theory. As a result, we obtain that
by including an inevitable interaction between the nematic fluctuations and the
elastic degrees of freedom of the lattice (parametrized by the nemato-elastic
coupling $\kappa_{\text{latt}}$), the resistivity $\rho(T)$ of the system as a
function of temperature obeys a universal scaling form described by
$\rho(T)\sim T\ln (1/T)$ at high temperatures, reminiscent of the paradigmatic
strange metal regime observed in many strongly correlated compounds. For a
window of temperatures comparable with
$\kappa^{3/2}_{\text{latt}}\varepsilon_F$ (where $\varepsilon_F$ is the Fermi
energy of the microscopic model), the system displays another regime in which
the resistivity is consistent with a description in terms of $\rho(T)\sim
T^{\alpha}$, where the effective exponent roughly satisfies the inequality
$1\lesssim\alpha\lesssim 2$. However, in the low-temperature limit (i.e.,
$T\ll\kappa^{3/2}_{\text{latt}}\varepsilon_F$), the properties of the quantum
critical state change in an important way depending on the types of disorder
present in the system: It can either recover a conventional Fermi liquid
described by $\rho(T)\sim T^2$ or it could exhibit yet another non-Fermi liquid
regime characterized by the scaling form $\rho(T)-\rho_0\sim T^2\ln T$. Our
results emphasize the key role played by both phonon and disorder effects in
the scenario of nematic quantum criticality and might be fundamental for
addressing recent transport experiments in some iron-based superconductors. | 1912.11558v3 |
2016-08-16 | Universal Fragment Descriptors for Predicting Electronic Properties of Inorganic Crystals | Historically, materials discovery has been driven by a laborious
trial-and-error process. The growth of materials databases and emerging
informatics approaches finally offer the opportunity to transform this practice
into data- and knowledge-driven rational design. By using data from the AFLOW
repository for high-throughput ab-initio calculations, we have generated
Quantitative Materials Structure-Property Relationship (QMSPR) models to
predict eight critical electronic and thermomechanical materials properties,
such as the metal/insulator classification, band gap energy, bulk and shear
moduli, Debye temperature, and heat capacity. The prediction accuracy obtained
with these QMSPR models approaches training data for virtually any
stoichiometric inorganic crystalline material. The success and universality of
these models is attributed to the construction of new materials
descriptors---referred to as the universal Property-Labeled Materials Fragments
(PLMF). The representation requires only minimal structural input and affords
straightforward model interpretation in terms of simple heuristic design rules
that guide rational materials design. This study demonstrates the power of
materials informatics to dramatically accelerate the search for new materials. | 1608.04782v3 |
2019-05-30 | Surface waves with negative phase velocity supported by temperature-dependent hyperbolic materials | A numerical investigation was undertaken to elucidate the propagation of
electromagnetic surface waves guided by the planar interface of two
temperature-sensitive materials. One partnering material was chosen to be
isotropic and the other to be anisotropic. Both partnering materials were
engineered composite materials, based on the temperature-sensitive
semiconductor InSb. At low temperatures the anisotropic partnering material is
a non-hyperbolic uniaxial material; as the temperature is raised this material
becomes a hyperbolic uniaxial material. At low temperatures, a solitary
Dyakonov wave propagates along any specific direction in a range of directions
parallel to the planar interface. At high temperatures, up to three different
surface waves can propagate in certain directions parallel to the planar
interface; one of these surface waves propagates with negative phase velocity
(NPV). At a fixed temperature, the range of directions for NPV propagation
decreases uniformly in extent as the volume fraction of InSb in the isotropic
partnering material decreases. At a fixed volume fraction of InSb in the
isotropic partnering material, the angular range for NPV propagation varies
substantially as the temperature varies. | 1905.13092v2 |
2015-06-13 | Predicting Fracture Energies and Crack-Tip Fields of Soft Tough Materials | Soft materials including elastomers and gels are pervasive in biological
systems and technological applications. Whereas it is known that intrinsic
fracture energies of soft materials are relatively low, how the intrinsic
fracture energy cooperates with mechanical dissipation in process zone to give
high fracture toughness of soft materials is not well understood. In addition,
it is still challenging to predict fracture energies and crack-tip strain
fields of soft tough materials. Here, we report a scaling theory that accounts
for synergistic effects of intrinsic fracture energies and dissipation on the
toughening of soft materials. We then develop a coupled cohesive-zone and
Mullins-effect model capable of quantitatively predicting fracture energies of
soft tough materials and strain fields around crack tips in soft materials
under large deformation. The theory and model are quantitatively validated by
experiments on fracture of soft tough materials under large deformations. We
further provide a general toughening diagram that can guide the design of new
soft tough materials. | 1506.04271v1 |
2023-04-19 | Towards a muon scattering tomography system for both low-Z and high-Z materials | Muon scattering tomography (MST) is a non-destructive technique to image
various materials by utilizing cosmic ray muons as probes. A typical MST system
with a two-fold track detectors is particularly effective in detecting high-$Z$
materials (e.g. nuclear materials), but difficult to recognize low-$Z$
materials (e.g. explosive materials). In this work, we present a concept of MST
system to discriminate both low-$Z$ and high-$Z$ materials by extra measuring
momentum of low-energy muons with a Cherenkov detector. A toy Monte Carlo
simulation to describe detector responses and multiple scatterings of a muon
tracking through materials is developed for statistical tests. Based on
momentum-dependent track reconstruction and image reconstruction algorithm, we
evaluate separation powers of different materials in the system. The results
show that momentum measurement of low-energy muons and accurate track
reconstruction can improve separation power of low-$Z$ materials significantly.
This may enable the MST system to detect both low-$Z$ and high-$Z$ materials
with cosmic ray muons in the whole energy range. | 2304.09489v2 |
2024-05-08 | 2D ferroelectrics and ferroelectrics with 2D: materials and device prospects | Ferroelectric and two-dimensional materials are both heavily investigated
classes of electronic materials. This is unsurprising since they both have
superlative fundamental properties and high-value applications in computing,
sensing etc. In this Perspective, we investigate the research topics where 2D
semiconductors and ferroelectric materials both in 2D or 3D form come together.
2D semiconductors have unique attributes due to their van der Waals nature that
permits their facile integration with any other electronic or optical
materials. In addition, the emergence of ferroelectricity in 2D monolayers,
multilayers, and artificial structures offers further advantages since
traditionally ferroelectricity has been difficult to achieve in extremely
thickness scaled materials. In this perspective, we elaborate on the
applications of 2D materials + ferroelectricity in non-volatile memory devices
highlighting their potential for in-memory computing, neuromorphic computing,
optoelectronics, and spintronics. We also suggest the challenges posed by both
ferroelectrics and 2D materials, including material/device preparation, and
reliable characterizations to drive further investigations at the interface of
these important classes of electronic materials. | 2405.05432v1 |
2019-08-14 | Substrate effects on charged defects in two-dimensional materials | Two-dimensional (2D) materials are strongly affected by the dielectric
environment including substrates, making it an important factor in designing
materials for quantum and electronic technologies. Yet, first-principles
evaluation of charged defect energetics in 2D materials typically do not
include substrates due to the high computational cost. We present a general
continuum model approach to incorporate substrate effects directly in
density-functional theory calculations of charged defects in the 2D material
alone. We show that this technique accurately predicts charge defect energies
compared to much more expensive explicit substrate calculations, but with the
computational expediency of calculating defects in free-standing 2D materials.
Using this technique, we rapidly predict the substantial modification of charge
transition levels of two defects in MoS$_2$ and ten defects promising for
quantum technologies in hBN, due to SiO$_2$ and diamond substrates. This
establishes a foundation for high-throughput computational screening of new
quantum defects in 2D materials that critically accounts for substrate effects. | 1908.05208v1 |
2019-12-05 | Do 2D material-based battery electrodes have inherently poor rate-performance? | Two dimensional materials show great potential for use in battery electrodes
and are believed to be particularly promising for high-rate applications.
However, there does not seem to be much hard evidence for the superior
rate-performance of 2D materials compared to non-2D materials. To examine this
point, we have analyzed published rate-performance data for a wide range of 2D
materials as well as non-2D materials for comparison. For each capacity-rate
curve we extract parameters which quantify performance which can then be
analyzed using a simple mechanistic model. Contrary to expectations, by
comparing a previously-proposed figure of merit, we find 2D-based electrodes to
be on average ~40 times poorer in terms of rate performance than non-2D
materials. This is not due to differences in solid-state diffusion times which
were similarly distributed for 2D and non-2D materials. In fact, we found the
main difference between 2D and non-2D materials to be that ion mobility within
the electrolyte-filled pores of the electrodes to be significantly lower for 2D
materials, a situation which we attribute to their high aspect ratios. | 1912.02482v1 |
2023-08-18 | MATLABER: Material-Aware Text-to-3D via LAtent BRDF auto-EncodeR | Based on powerful text-to-image diffusion models, text-to-3D generation has
made significant progress in generating compelling geometry and appearance.
However, existing methods still struggle to recover high-fidelity object
materials, either only considering Lambertian reflectance, or failing to
disentangle BRDF materials from the environment lights. In this work, we
propose Material-Aware Text-to-3D via LAtent BRDF auto-EncodeR
(\textbf{MATLABER}) that leverages a novel latent BRDF auto-encoder for
material generation. We train this auto-encoder with large-scale real-world
BRDF collections and ensure the smoothness of its latent space, which
implicitly acts as a natural distribution of materials. During appearance
modeling in text-to-3D generation, the latent BRDF embeddings, rather than BRDF
parameters, are predicted via a material network. Through exhaustive
experiments, our approach demonstrates the superiority over existing ones in
generating realistic and coherent object materials. Moreover, high-quality
materials naturally enable multiple downstream tasks such as relighting and
material editing. Code and model will be publicly available at
\url{https://sheldontsui.github.io/projects/Matlaber}. | 2308.09278v1 |
2023-08-23 | Energy landscape and phase competition of CsV3Sb5-, CsV6Sb6-, and TbMn6Sn6-type Kagome materials | Finding viable Kagome lattices is vital for materializing novel phenomena in
quantum materials. In this work, we performed element substitutions on CsV3Sb5
with space group P6/mmm, TbMn6Sn6 with space group P6/mmm, and CsV6Sb6 with
space group R-3 m, respectively, as the parent compounds. A total of 4158
materials were obtained through element substitutions, and these materials were
then calculated via density function theory in high-throughput mode. Afterward,
48 materials were identified with high thermodynamic stability
(E_hull<5meV/atom). Furthermore, we compared the thermodynamic stability of
three different phases with the same elemental composition and predicted some
competing phases that may arise during material synthesis. Finally, by
calculating the electronic structures of these materials, we attempted to
identify patterns in the electronic structure variations as the elements
change. This work provides guidance for discovering promising AM3X5/AM6X6
Kagome materials from a vast phase space. | 2308.11930v1 |
2019-11-26 | A hunt for ultrahard materials | Recent results on search (theoretical prediction, high-pressure synthesis,
etc.) for novel superhard and ultrahard materials are briefly reviewed. | 1911.11731v1 |
2021-12-17 | High-throughput Discovery and Intelligent Design of 2D Functional Materials for Various Applications | Novel technologies and new materials are in high demand for future
energy-efficient electronic devices to overcome the fundamental limitations of
miniaturization of current silicon-based devices. Two-dimensional (2D)
materials show promising applications in the next generation devices because
they can be tailored on the specific property that a technology is based on,
and be compatible with other technologies, such as the silicon-based
(opto)electronics. Although the number of experimentally discovered 2D
materials is growing, the speed is very slow and only a few dozen 2D materials
have been synthesized or exfoliated since the discovery of graphene. Recently,
a novel computational technique, dubbed "high-throughput computational
materials design", becomes a burgeoning area of materials science, which is the
combination of the quantum-mechanical theory, materials genome, and database
construction with intelligent data mining. This new and powerful tool can
greatly accelerate the discovery, design and application of 2D materials by
creating database containing a large amount of 2D materials with calculated
fundamental properties, and then intelligently mining (via high-throughput
automation or machine learning) the database in the search of 2D materials with
the desired properties for particular applications, such as energy conversion,
electronics, spintronics, and optoelectronics. | 2112.09347v1 |
2006-05-25 | High-Pressure Synthesized Materials: a Chest of Treasure and Hints | The present review covers the production of new materials under high
pressures. A primary limitation on the use of pressures higher than 1 GPa is a
small volume and mass of a produced material. Therefore, despite an extremely
wide range of new high-pressure synthesized substances with unique properties,
synthesis on an commercial scale is applied up to now only to obtain superhard
materials, this real treasure of today's industry. At the same time,
high-pressure experiments often give material scientists a hint at what new
intriguing substances can exist in principle. This is true for new superhard,
semiconducting, magnetic, superconducting and optical materials already
synthesized under pressure, and as well as for a large number of hypothetic new
polymers from low-Z elements. Many of new materials, including the above
polymers, may exist in the metastable form at normal pressure at sufficiently
high temperatures. | 0605626v1 |
2020-02-13 | First-principles discovery of stable two-dimensional materials with high-level piezoelectric response | The rational design of two-dimensional piezoelectric materials has recently
garnered great interest due to their increasing use in technological
applications, including sensor technology, actuating devices, energy
harvesting, and medical applications. Several materials possessing high
piezoelectric response have been reported so far, but a high-throughput
first-principles approach to estimate the piezoelectric potential of layered
materials has not been performed yet. In this study, we systematically
investigated the piezoelectric ($e_{11}$, $d_{11}$) and elastic (C$_{11}$ and
C$_{12}$) properties of 128 thermodynamically stable two-dimensional (2D)
semiconductor materials by employing first-principle methods. Our
high-throughput approach demonstrates that the materials containing
Group-\textrm{V} elements produce significantly high piezoelectric strain
constants, $d_{11}$ $>$ 40 pmV$^{-1}$, and 49 of the materials considered have
the $e_{11}$ coefficient higher than MoS$_{2}$ insomuch as BrSSb has one of the
largest $d_{11}$ with a value of 373.0 pmV$^{-1}$. Moreover, we established a
simple empirical model in order to estimate the $d_{11}$ coefficients by
utilizing the relative ionic motion in the unit cell and the polarizability of
the individual elements in the compounds. | 2002.05803v2 |
2022-03-08 | Recent Progress of Heterostructures Based on Two Dimensional Materials and Wide Bandgap Semiconductors | Recent progress in the synthesis and assembly of two-dimensional (2D)
materials has laid the foundation for various applications of atomically thin
layer films. These 2D materials possess rich and diverse properties such as
layer-dependent band gaps, interesting spin degrees of freedom, and variable
crystal structures. They exhibit broad application prospects in micro-nano
devices. In the meantime, the wide bandgap semiconductors (WBS) with an
elevated breakdown voltage, high mobility, and high thermal conductivity have
shown important applications in high-frequency microwave devices,
high-temperature and high-power electronic devices. Beyond the study on single
2D materials or WBS materials, the multi-functional 2D/WBS heterostructures can
promote the carrier transport at the interface, potentially providing novel
physical phenomena and applications, and improving the performance of
electronic and optoelectronic devices. In this review, we overview the
advantages of the heterostructures of 2D materials and WBS materials, and
introduce the construction methods of 2D/WBS heterostructures. Then, we present
the diversity and recent progress in the applications of 2D/WBS
heterostructures, including photodetectors, photocatalysis, sensors, and energy
related devices. Finally, we put forward the current challenges of 2D/WBS
heterostructures and propose the promising research directions in the future. | 2203.03895v1 |
1998-11-17 | Stripes, Electron-Like and Polaron-Like Carriers, and High-T_c in the Cuprates | Both "large-U" and "small-U" orbitals are used to study the electronic
structure of the high-T_c cuprates. A striped structure with three types of
carriers are induced, polaron-like "stripons" which carry charge,
"quasielectrons" which carry both charge and spin, and "svivons" which carry
spin and lattice distortion. Anomalous physical properties of the cuprates are
derived, and specifically the systematic behavior of the resistivity, Hall
constant, and thermoelectric power. Transitions between pair states of
quasielectrons and stripons drive high-temperature superconductivity. | 9811261v1 |
1999-05-12 | Stripes, Carriers, and High Tc in the Cuprates | Considering both "large-U" and "small-U" orbitals it is found that the
high-Tc cuprates are characterized by a striped structure, and three types of
carriers: polaron-like "stripons" carrying charge, "quasielectrons" carrying
charge and spin, and "svivons" carrying spin and lattice distortion. It is
shown that this electronic structure leads to the anomalous physical properties
of the cuprates, and specifically the systematic behavior of the resistivity,
Hall constant, and thermoelectric power. High-Tc pairing results from
transitions between pair states of quasielectrons and stripons through the
exchange of svivons. A pseudogap phase occurs when pairing takes place above
the temperature where stripons become coherent, and this temperature determines
the Uemura limit. | 9905172v1 |
1999-11-12 | High-Field Electrical Transport in Single-Wall Carbon Nanotubes | Using low-resistance electrical contacts, we have measured the intrinsic
high-field transport properties of metallic single-wall carbon nanotubes.
Individual nanotubes appear to be able to carry currents with a density
exceeding 10^9 A/cm^2. As the bias voltage is increased, the conductance drops
dramatically due to scattering of electrons. We show that the current-voltage
characteristics can be explained by considering optical or zone-boundary phonon
emission as the dominant scattering mechanism at high field. | 9911186v1 |
2003-06-12 | Magnetoresistance of Si(001) MOSFETs with high concentration of electrons | We present an experimental study of electron transport in inversion layers of
high-mobility Si(001) samples with occupied excited subbands. The second series
of oscillations, observed in addition to the main series of Shubnikov-de Hass
oscillations, is tentatively attributed to the occupation of a subband
associated with the $E_{0'}$ level. Besides, a strong negative
magnetoresistance and nonlinear field dependence of the Hall resistance
accompany the novel oscillations at high carrier concentrations. The heating of
the 2D electron layers leads to suppression of the observed anomalies. | 0306330v1 |
2005-02-18 | High pressure synthesis of a new superconductor Sr2CuO2+xCl2-y induced by apical oxygen doping | Using the apical oxygen doping mechanism, i.e. a partial substitution of
divalence O for the monovalence Cl, a p-type oxychloride cuprate
superconductor, Sr2CuO2+xCl2-y, was synthesized at high pressure high
temperature. The x-ray diffraction refinement suggests the superconductor
crystallizes into a 0201 structure with space group I4/mmm and lattice
parameters being a=3.92A, c=15.6 A. The magnetic susceptibility as well as
resistance measurements indicated that the bulk superconductivity with
transition temperature 30K was achieved in the sample. | 0502449v1 |
2006-04-28 | Evidence for Carrier-Induced High-Tc Ferromagnetism in Mn-doped GaN film | A GaN film doped with 8.2 % Mn was grown by the molecular-beam-epitaxy
technique. Magnetization measurements show that this highly Mn-doped GaN film
exhibits ferromagnetism above room temperature. It is also revealed that the
high-temperature ferromagnetic state is significantly suppressed below 10 K,
accompanied by an increase of the electrical resistivity with decreasing
temperature. This observation clearly demonstrates a close relation between the
ferromagnetism with extremely high-Tc and the carrier transport in the Mn-doped
GaN film. | 0604647v1 |
2006-10-05 | Robust charge stripe order under high electric fields in Nd1.67Sr0.33NiO4 | The influence of high electric fields on the charge stripe order in
Nd1.67Sr0.33NiO4 was studied by means of simultaneous hard x-ray diffraction
and electrical transport experiments. Direct measurements of the charge stripe
satellite peaks in zero and high electric fields provide no evidence for a
deformation or a sliding of the stripe lattice, which contradicts previous
indications from non-linear conductance effects. By using the order parameter
of a structural phase transition for instant sample temperature measurements,
non-linear transport effects can be attributed to resistive heating.
Implications for the pinning of stripes in the nickelates are discussed. | 0610132v1 |
2005-04-26 | Flux profile scanners for scattered high-energy electrons | The paper describes the design and performance of flux integrating Cherenkov
scanners with air-core reflecting light guides used in a high-energy, high-flux
electron scattering experiment at the Stanford Linear Accelerator Center. The
scanners were highly radiation resistant and provided a good signal to
background ratio leading to very good spatial resolution of the scattered
electron flux profile scans. | 0504029v1 |
2001-06-05 | Bell inequalities for arbitrarily high dimensional systems | We develop a novel approach to Bell inequalities based on a constraint that
the correlations exhibited by local realistic theories must satisfy. This is
used to construct a family of Bell inequalities for bipartite quantum systems
of arbitrarily high dimensionality which are strongly resistant to noise. In
particular our work gives an analytic description of numerical results of D.
Kaszlikowski, P. Gnacinski, M. Zukowski, W. Miklaszewski, A. Zeilinger, Phys.
Rev. Lett. {\bf 85}, 4418 (2000) and T. Durt, D. Kaszlikowski, M. Zukowski,
quant-ph/0101084, and generalises them to arbitrarily high dimensionality. | 0106024v2 |
2008-04-07 | Hg-Based Superconducting Cuprates: High Tc and Pseudo Spin-Gap | A brief review of microscopic studies of high-Tc superconductors HgBa2CuO4+d
and HgBa2CaCu2O6+d is presented. The topics concerned are the pseudo spin-gap,
the antiferromagnetic spin fluctuations near the quantum critical point, and
the mechanism of the high Tc via NMR. The crystal structure with the flat CuO2
plane, two-dimensional electrical resistivity, Cu NQR, NMR experimental results
are discussed. | 0804.0911v2 |
2008-09-12 | Effect of oxygen incorporation on normal and superconducting properties of MgB2 films | Oxygen was systematically incorporated in MBE grown MgB2 films using in-situ
post-growth anneals in an oxygen environment. Connectivity analysis in
combination with measurements of the critical temperature and resistivity
indicate that oxygen is distributed both within and between the grains. High
values of critical current densities in field (~4x10^5 A/cm^2 at 8 T and 4.2
K), extrabolated critical fields (>45 T) and slopes of critical field versus
temperature (1.4 T/K) are observed. Our results suggest that low growth
temperatures (300oC) and oxygen doping (>0.65%) can produce MgB2 with high Jc
values in field and Hc2 for high-field magnet applications. | 0809.2297v1 |
2009-07-20 | Electrical Transport in High Quality Graphene pnp Junctions | We fabricate and investigate high quality graphene devices with contactless,
suspended top gates, and demonstrate formation of graphene pnp junctions with
tunable polarity and doping levels. The device resistance displays distinct
oscillations in the npn regime, arising from the Fabry-Perot interference of
holes between the two pn interfaces. At high magnetic fields, we observe
well-defined quantum Hall plateaus, which can be satisfactorily fit to
theoretical calculations based on the aspect ratio of the device. | 0907.3366v1 |
2009-11-11 | Enhanced superconductivity of YBCO interfaces: origin of high critical temperature in layered superconductors | Superconducting transition temperatures Tc of the YBCO film surface and of
the YBCO film/substrate interface were measured inductively. It was observed
that the interface- Tc is always higher then the surface - Tc. However
deposition of silver over-layer enhances the superconducting transition
temperatures. This observation was confirmed by four-point resistance
measurements. In the annealed YBCO/Ag bilayers magnetic properties of the
interface were observed. We believe that such phenomena are a common feature of
layered systems. This two dimensional structure reminds the layered
microstructure of the high-temperature superconductors and one can suppose that
covering of the superconducting layer by non-superconducting layer is a
condition for obtaining high critical temperatures in general. | 0911.2107v1 |
2010-12-22 | Transport properties of the new Fe-based superconductor KxFe2Se2 (Tc = 33 K) | We synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystals.
The obtained single crystal exhibited a sharp superconducting transition, and
the onset and zero-resistivity temperature was estimated to be 33 and 31.8 K,
respectively. A high upper critical field of 192 T was obtained. Anisotropy of
superconductivity of K0.8Fe2Se2 was ~3.6. Both the high upper critical field
and comparably low anisotropy are advantageous for the application under high
magnetic field. | 1012.4950v1 |
2011-12-13 | High-frequency performance of graphene field effect transistors with saturating IV-characteristics | High-frequency performance of graphene field-effect transistors (GFETs) with
boron-nitride gate dielectrics is investigated. Devices show saturating IV
characteristics and fmax values as high as 34 GHz at 600-nm channel length.
Bias dependence of fT and fmax and the effect of the ambipolar channel on
transconductance and output resistance are also examined. | 1112.2777v1 |
2018-02-02 | Ultra-high Q terahertz whispering-gallery modes in a silicon resonator | We report on the first experimental demonstration of terahertz (THz)
whispering-gallery modes (WGMs) with an ultra high quality (Q) factor of $1.5
\times {10}^{4}$ at 0.62THz. The WGMs are observed in a high resistivity float
zone silicon (HRFZ-Si) spherical resonator coupled to a sub-wavelength silica
waveguide. A detailed analysis of the coherent continuous wave (CW) THz
spectroscopy measurements combined with a numerical model based on
Mie-Debye-Aden-Kerker (MDAK) theory allows to unambiguously identify the
observed higher order radial THz WGMs. | 1802.00549v1 |
2022-06-09 | Characterisation of a new RPC prototype using conventional gas mixture | Resistive Plate Chamber (RPC) is a well-known gaseous detector in the field
of High Energy Physics (HEP) experiments for its good tracking capability, high
efficiency, good time resolution, and low cost of fabrication. The main issue
in RPC is its limitation in the rate handling capability. Several experimental
groups have developed sophisticated techniques to increase the particle rate
capability and reduce the noise rate of this detector. In this article, we
discussed a new method for linseed oil coating in case of bakelite RPC detector
to achieve good efficiency and the results obtained using a conventional gas
mixture. | 2206.04259v1 |
2023-04-05 | STRV -- A radiation hard RISC-V microprocessor for high-energy physics applications | While microprocessors are used in various applications, they are precluded
from the use in high-energy physics applications due to the harsh radiation
present. To overcome this limitation a microprocessor design must withstand
high doses of radiation and mitigate radiation induced soft errors. A TMR
protection scheme is applied to protect a RISC-V microprocessor core against
these faults. The protection of the integrated SRAM by an independent scrubbing
algorithm is discussed. Initial irradiation results and power consumption
measurements of the radiation-resistant RISC-V microprocessor implemented in 65
nm CMOS technology are presented. | 2304.02410v1 |
2023-05-02 | Robust and Adaptive Functional Logistic Regression | We introduce and study a family of robust estimators for the functional
logistic regression model whose robustness automatically adapts to the data
thereby leading to estimators with high efficiency in clean data and a high
degree of resistance towards atypical observations. The estimators are based on
the concept of density power divergence between densities and may be formed
with any combination of lower rank approximations and penalties, as the need
arises. For these estimators we prove uniform convergence and high rates of
convergence with respect to the commonly used prediction error under fairly
general assumptions. The highly competitive practical performance of our
proposal is illustrated on a simulation study and a real data example which
includes atypical observations. | 2305.01350v1 |
2014-10-07 | Decoding Spatial Complexity in Strongly Correlated Electronic Systems | Inside the metals, semiconductors, and magnets of our everyday experience,
electrons are uniformly distributed throughout the material. By contrast,
electrons often form clumpy patterns inside of strongly correlated electronic
systems (SCES) such as colossal magnetoresistance materials and high
temperature superconductors. In copper-oxide based high temperature
superconductors, scanning tunneling microscopy (STM) has detected an electron
nematic on the surface of the material, in which the electrons form nanoscale
structures which break the rotational symmetry of the host crystal. These
structures may hold the key to unlocking the mystery of high temperature
superconductivity in these materials, but only if the nematic also exists
throughout the entire bulk of the material. Using newly developed methods for
decoding these surface structures, we find that the nematic indeed persists
throughout the bulk of the material. We furthermore find that the intricate
pattern formation is set by a delicate balance among disorder, interactions,
and material anisotropy, leading to a fractal nature of the cluster pattern.
The methods we have developed can be extended to many other surface probes and
materials, enabling surface probes to determine whether surface structures are
confined only to the surface, or whether they extend throughout the material. | 1410.1787v1 |
2021-04-13 | Multiscale modeling of materials: Computing, data science,uncertainty and goal-oriented optimization | The recent decades have seen various attempts at accelerating the process of
developing materials targeted towards specific applications. The performance
required for a particular application leads to the choice of a particular
material system whose properties are optimized by manipulating its underlying
microstructure through processing. The specific configuration of the structure
is then designed by characterizing the material in detail, and using this
characterization along with physical principles in system level simulations and
optimization. These have been advanced by multiscale modeling of materials,
high-throughput experimentations, materials data-bases, topology optimization
and other ideas. Still, developing materials for extreme applications involving
large deformation, high strain rates and high temperatures remains a challenge.
This article reviews a number of recent methods that advance the goal of
designing materials targeted by specific applications. | 2104.05918v1 |
2021-09-05 | Discovery and Engineering of Low Work Function Perovskite Materials | Materials with low work functions are critical for an array of applications
requiring the facile removal or efficient transport of electrons through a
device. Perovskite oxides are a promising class of materials for finding low
work functions, and here we target applications in thermionic and field
electron emission. Perovskites have highly malleable compositions which enable
tunable work function values over a wide range, robust stability at high
temperatures, and high electronic conductivities. In this work, we screened
over 2900 perovskite oxides in search of stable, conductive, low-work-function
materials using Density Functional Theory (DFT) methods. Our work provides
insight into the materials chemistry governing the work function value of a
perovskite, where materials with barely filled d bands possess the lowest work
functions. Our screening has resulted in a total of seven promising compounds,
such as BaMoO3 and SrNb0.75Co0.25O3 with work functions of 1.1 eV and 1.5 eV,
respectively. These promising materials and others presented in this study may
find use as low work function electron emitters in high power vacuum electronic
and thermionic energy conversion devices. Moreover, the database of calculated
work functions and materials chemistry trends governing the value of the work
function may aid in the engineering of perovskite heterojunction devices. | 2109.02005v1 |
2003-05-20 | Very high upper critical fields in MgB2 produced by selective tuning of impurity scattering | We report a significant enhancement of the upper critical field $H_{c2}$ of
different $MgB_2$ samples alloyed with nonmagnetic impurities. By studying
films and bulk polycrystals with different resistivities $\rho$, we show a
clear trend of $H_{c2}$ increase as $\rho$ increases. One particular high
resistivity film had zero-temperature $H_{c2}(0)$ well above the $H_{c2}$
values of competing non-cuprate superconductors such as $Nb_3Sn$ and Nb-Ti. Our
high-field transport measurements give record values $H_{c2}^\perp (0) \approx
34T$ and $H_{c2}\|(0) \approx 49 T$ for high resistivity films and
$H_{c2}(0)\approx 29 T$ for untextured bulk polycrystals. The highest $H_{c2}$
film also exhibits a significant upward curvature of $H_{c2}(T)$, and
temperature dependence of the anisotropy parameter $\gamma(T) = H_{c2}\|/
H_{c2}^\perp$ opposite to that of single crystals: $\gamma(T)$ decreases as the
temperature decreases, from $\gamma(T_c) \approx 2$ to $\gamma(0) \approx 1.5$.
This remarkable $H_{c2}$ enhancement and its anomalous temperature dependence
are a consequence of the two-gap superconductivity in $MgB_2$, which offers
special opportunities for further $H_{c2}$ increase by tuning of the impurity
scattering by selective alloying on Mg and B sites. Our experimental results
can be explained by a theory of two-gap superconductivity in the dirty limit.
The very high values of $H_{c2}(T)$ observed suggest that $MgB_2$ can be made
into a versatile, competitive high-field superconductor. | 0305474v2 |
2021-08-30 | Machine Learning for Predicting Thermal Transport Properties of Solids | Quantitative descriptions of the structure-thermal property correlation have
been a bottleneck in designing materials with superb thermal properties. In the
past decade, the first-principles phonon calculations using density functional
theory and the Boltzmann transport equation have become a common practice for
predicting the thermal conductivity of new materials. However, first-principles
calculations are too costly for high-throughput material screening and
multi-scale structural design. First-principles calculations also face several
fundamental challenges in modeling thermal transport properties, e.g., of
crystalline materials with defects, of amorphous materials, and for materials
at high temperatures. In the past five years, machine learning started to play
a role in solving these challenges. This review provides a comprehensive
summary and discussion on the state-of-the-art, future opportunities, and the
remaining challenges in implementing machine learning for studying thermal
conductivity. After an introduction to the working principles of machine
learning and descriptors of material structures, recent research using machine
learning to study thermal transport is discussed. Three major applications of
machine learning for predicting thermal properties are discussed. First,
machine learning is applied to solve the challenges in modeling phonon
transport of crystals with defects, in amorphous materials, and at high
temperatures. Machine learning is used to build high-fidelity interatomic
potentials to bridge the gap between first-principles calculations and
molecular dynamics simulations. Second, machine learning can be used to study
the correlation between thermal conductivity and other properties for
high-throughput materials screening. Finally, machine learning is a powerful
tool for structural design to achieve target thermal conductance or thermal
conductivity. | 2108.12945v2 |
2020-12-02 | An Improved Iterative Neural Network for High-Quality Image-Domain Material Decomposition in Dual-Energy CT | Dual-energy computed tomography (DECT) has been widely used in many
applications that need material decomposition. Image-domain methods directly
decompose material images from high- and low-energy attenuation images, and
thus, are susceptible to noise and artifacts on attenuation images. The purpose
of this study is to develop an improved iterative neural network (INN) for
high-quality image-domain material decomposition in DECT, and to study its
properties. We propose a new INN architecture for DECT material decomposition.
The proposed INN architecture uses distinct cross-material convolutional neural
network (CNN) in image refining modules, and uses image decomposition physics
in image reconstruction modules. The distinct cross-material CNN refiners
incorporate distinct encoding-decoding filters and cross-material model that
captures correlations between different materials. We study the distinct
cross-material CNN refiner with patch-based reformulation and tight-frame
condition. Numerical experiments with extended cardiactorso (XCAT) phantom and
clinical data show that the proposed INN significantly improves the image
quality over several image-domain material decomposition methods, including a
conventional model-based image decomposition (MBID) method using an
edge-preserving regularizer, a recent MBID method using pre-learned
material-wise sparsifying transforms, and a noniterative deep CNN method. Our
study with patch-based reformulations reveals that learned filters of distinct
cross-material CNN refiners can approximately satisfy the tight-frame
condition. | 2012.01986v4 |
2023-10-03 | Estimating viscoelastic, soft material properties using a modified Rayleigh cavitation bubble collapse time | Accurate determination of high strain rate (> 10^3 1/s) constitutive
properties of soft materials remains a formidable challenge. Albeit recent
advancements among experimental techniques, in particular inertial
microcavitation rheometry (IMR), the intrinsic requirement to visualize the
bubble cavitation dynamics has limited its application to nominally transparent
materials. Here, in an effort to address this challenge and to expand the
experimental capability of IMR to optically opaque materials, we investigated
whether one could use the acoustic signature of the time interval between
bubble nucleation and collapse, characterized as the bubble collapse time, to
infer the viscoelastic material properties without being able to image the
bubble directly in the tissue. By introducing a modified Rayleigh collapse time
for soft materials, which is strongly dependent on the stiffness of the
material at hand, we show that, in principle, one can obtain an order of
magnitude or better estimate of the viscoelastic material properties of the
soft material under investigation. Using a newly developed energy-based
theoretical framework, we show that for materials stiffer than 10 kPa the
bubble collapse time during a single bubble cavitation event can provide
quantitative and meaningful information about the constitutive properties of
the material at hand. For very soft materials (i.e., shear modulus less than 10
kPa) our theory shows that unless the collapse time measurement has very high
precision and low uncertainties, the material property estimates based on the
bubble collapse time only will not be accurate and require visual resolution of
the full cavitation kinematics. | 2310.02475v1 |
2012-08-31 | Ionization by bulk heating of electrons in capacitive radio frequency atmospheric pressure microplasmas | Electron heating and ionization dynamics in capacitively coupled radio
frequency (RF) atmospheric pressure microplasmas operated in helium are
investigated by Particle in Cell simulations and semi-analytical modeling. A
strong heating of electrons and ionization in the plasma bulk due to high bulk
electric fields are observed at distinct times within the RF period. Based on
the model the electric field is identified to be a drift field caused by a low
electrical conductivity due to the high electron-neutral collision frequency at
atmospheric pressure. Thus, the ionization is mainly caused by ohmic heating in
this "Omega-mode". The phase of strongest bulk electric field and ionization is
affected by the driving voltage amplitude. At high amplitudes, the plasma
density is high, so that the sheath impedance is comparable to the bulk
resistance. Thus, voltage and current are about 45{\deg} out of phase and
maximum ionization is observed during sheath expansion with local maxima at the
sheath edges. At low driving voltages, the plasma density is low and the
discharge becomes more resistive resulting in a smaller phase shift of about
4{\deg}. Thus, maximum ionization occurs later within the RF period with a
maximum in the discharge center. Significant analogies to electronegative low
pressure macroscopic discharges operated in the Drift-Ambipolar mode are found,
where similar mechanisms induced by a high electronegativity instead of a high
collision frequency have been identified. | 1208.6519v2 |
2022-01-13 | High-temperature superconductivity in hydrides: experimental evidence and details | Since the discovery of superconductivity at 200 K in H3S [1] similar or
higher transition temperatures, Tcs, have been reported for various
hydrogen-rich compounds under ultra-high pressures [2]. Superconductivity was
experimentally proved by different methods, including electrical resistance,
magnetic susceptibility, optical infrared, and nuclear resonant scattering
measurements. The crystal structures of superconducting phases were determined
by X-ray diffraction. Numerous electrical transport measurements demonstrate
the typical behaviour of a conventional phonon-mediated superconductor: zero
resistance below Tc, the shift of Tc to lower temperatures under external
magnetic fields, and pronounced isotope effect. Remarkably, the results are in
good agreement with the theoretical predictions, which describe
superconductivity in hydrides within the framework of the conventional BCS
theory. However, despite this acknowledgment, experimental evidence for the
superconducting state in these compounds has recently been treated with
criticism [3, 4], which apparently stems from misunderstanding and
misinterpretation of complicated experiments performed under very high
pressures. Here, we describe in greater detail the experiments revealing
high-temperature superconductivity in hydrides under high pressures. We show
that the arguments against superconductivity [3, 4] can be either refuted or
explained. The experiments on the high-temperature superconductivity in
hydrides clearly contradict the theory of hole superconductivity [4] and
eliminate it [3]. | 2201.05137v1 |
2024-01-15 | High Frequency Response of Volatile Memristors | In this theoretical study, we focus on the high-frequency response of the
electrothermal NbO2-Mott threshold switch, a real-world electronic device,
which has been proved to be relevant in several applications and is classified
as a volatile memristor. Memristors of this kind, have been shown to exhibit
distinctive non-linear behaviors crucial for cutting-edge neuromorphic
circuits. In accordance with well-established models for these devices, their
resistances depend on their body temperatures, which evolve over time following
Newton's Law of Cooling. Here, we demonstrate that HP's NbO2-Mott memristor can
manifest up to three distinct steady-state oscillatory behaviors under a
suitable high-frequency periodic voltage input, showcasing increased
versatility despite its volatile nature. Additionally, when subjected to a
high-frequency periodic voltage signal, the device body temperature oscillates
with a negligible peak-to-peak amplitude. Since, the temperature remains almost
constant over an input cycle, the devices under study behave as linear
resistors during each input cycle. Based on these insights, this paper presents
analytical equations characterizing the response of the NbO2-Mott memristor to
high-frequency voltage inputs, demarcating regions in the state space where
distinct initial conditions lead to various asymptotic oscillatory behaviors.
Importantly, the mathematical methods introduced in this manuscript are
applicable to any volatile electrothermal resistive switch. Additionally, this
paper presents analytical equations that accurately reproduce the temperature
time-waveform of the studied device during both its transient and steady-state
phases when subjected to a zero-mean sinusoidal voltage input oscillating in
the high-frequency limit. | 2401.10924v1 |
2022-12-05 | Unveiling the complex structure-property correlation of defects in 2D materials based on high throughput datasets | Modification of physical properties of materials and design of materials with
on-demand characteristics is at the heart of modern technology. Rare
application relies on pure materials--most devices and technologies require
careful design of materials properties through alloying, creating
heterostructures of composites or controllable introduction of defects. At the
same time, such designer materials are notoriously difficult for modelling.
Thus, it is very tempting to apply machine learning methods for such systems.
Unfortunately, there is only a handful of machine learning-friendly material
databases available these days. We develop a platform for easy implementation
of machine learning techniques to materials design and populate it with
datasets on pristine and defected materials. Here we describe datasets of
defects in represented 2D materials such as MoS2, WSe2, hBN, GaSe, InSe, and
black phosphorous, calculated using DFT. Our study provides a data-driven
physical understanding of complex behaviors of defect properties in 2D
materials, holding promise for a guide to the development of efficient machine
learning models. In addition, with the increasing enrollment of datasets, our
database could provide a platform for designing of materials with predetermined
properties. | 2212.02110v1 |
2023-02-16 | GAASP: Genetic Algorithm Based Atomistic Sampling Protocol for High-Entropy Materials | High-Entropy Materials are composed of multiple elements on comparatively
simpler lattices. Due to the multicomponent nature of such materials, the
atomic scale sampling is computationally expensive due to the combinatorial
complexity. We propose a genetic algorithm based methodology for sampling such
complex chemically-disordered materials. Genetic Algorithm based Atomistic
Sampling Protocol (GAASP) variants can generate low and well as high-energy
structures. GAASP low-energy variant in conjugation with metropolis criteria
avoids the premature convergence as well as ensures the detailed balance
condition. GAASP can be employed to generate the low-energy structures for
thermodynamic predictions as well as diverse structures can be generated for
machine learning applications. | 2302.08101v1 |
2022-10-24 | Quantifying the performance of machine learning models in materials discovery | The predictive capabilities of machine learning (ML) models used in materials
discovery are typically measured using simple statistics such as the
root-mean-square error (RMSE) or the coefficient of determination ($r^2$)
between ML-predicted materials property values and their known values. A
tempting assumption is that models with low error should be effective at
guiding materials discovery, and conversely, models with high error should give
poor discovery performance. However, we observe that no clear connection exists
between a "static" quantity averaged across an entire training set, such as
RMSE, and an ML property model's ability to dynamically guide the iterative
(and often extrapolative) discovery of novel materials with targeted
properties. In this work, we simulate a sequential learning (SL)-guided
materials discovery process and demonstrate a decoupling between traditional
model error metrics and model performance in guiding materials discoveries. We
show that model performance in materials discovery depends strongly on (1) the
target range within the property distribution (e.g., whether a 1st or 10th
decile material is desired); (2) the incorporation of uncertainty estimates in
the SL acquisition function; (3) whether the scientist is interested in one
discovery or many targets; and (4) how many SL iterations are allowed. To
overcome the limitations of static metrics and robustly capture SL performance,
we recommend metrics such as Discovery Yield ($DY$), a measure of how many
high-performing materials were discovered during SL, and Discovery Probability
($DP$), a measure of likelihood of discovering high-performing materials at any
point in the SL process. | 2210.13587v1 |
2024-05-14 | An Interoperable Multi Objective Batch Bayesian Optimization Framework for High Throughput Materials Discovery | In this study, we introduce a groundbreaking framework for materials
discovery, we efficiently navigate a vast phase space of material compositions
by leveraging Batch Bayesian statistics in order to achieve specific
performance objectives. This approach addresses the challenge of identifying
optimal materials from an untenably large array of possibilities in a
reasonable timeframe with high confidence. Crucially, our batchwise methods
align seamlessly with existing material processing infrastructure for
synthesizing and characterizing materials. By applying this framework to a
specific high entropy alloy system, we demonstrate its versatility and
robustness in optimizing properties like strain hardening, hardness, and strain
rate sensitivity. The fact that the Bayesian model is adept in refining and
expanding the property Pareto front highlights its broad applicability across
various materials, including steels, shape memory alloys, ceramics, and
composites. This study advances the field of materials science and sets a new
benchmark for material discovery methodologies. By proving the effectiveness of
Bayesian optimization, we showcase its potential to redefine the landscape of
materials discovery. | 2405.08900v1 |
2023-02-19 | Resistance Maintained in Digital Organisms despite Guanine/Cytosine-Based Fitness Cost and Extended De-Selection: Implications to Microbial Antibiotics Resistance | Antibiotics resistance has caused much complication in the treatment of
diseases, where the pathogen is no longer susceptible to specific antibiotics
and the use of such antibiotics are no longer effective for treatment. A recent
study that utilizes digital organisms suggests that complete elimination of
specific antibiotic resistance is unlikely after the disuse of antibiotics,
assuming that there are no fitness costs for maintaining resistance once
resistance are established. Fitness cost are referred to as reaction to change
in environment, where organism improves its' abilities in one area at the
expense of the other. Our goal in this study is to use digital organisms to
examine the rate of gain and loss of resistance where fitness costs have
incurred in maintaining resistance. Our results showed that GC-content based
fitness cost during de-selection by removal of antibiotic-induced selective
pressure portrayed similar trends in resistance compared to that of no fitness
cost, at all stages of initial selection, repeated de-selection and
re-introduction of selective pressure. Paired t-test suggested that prolonged
stabilization of resistance after initial loss is not statistically significant
for its difference to that of no fitness cost. This suggests that complete
elimination of specific antibiotics resistance is unlikely after the disuse of
antibiotics despite presence of fitness cost in maintaining antibiotic
resistance during the disuse of antibiotics, once a resistant pool of
micro-organism has been established. | 2302.13897v1 |
1998-04-16 | Reconnection via the Tearing Instability | We discuss the role of tearing instabilities in magnetic reconnection. In
three dimensions this instability leads to the formation of strong Alfvenic
waves that remove plasma efficiently from the reconnection layer. As a result
the instability proceeds at high rates while staying close to the linear
regime. Our calculations show that for a resistive fluid the reconnection speed
scales as the product of the Alfven speed V_A over the magnetic Reynolds number
to the power -0.3. In the limit of vanishing resistivity, tearing modes proceed
at a non-zero rate, driven by the electron inertia term, giving rise to a
reconnection speed V_A (c/\omega_p L_x)^{3/5}, where \omega_p is the plasma
frequency and L_x is the transverse scale of the reconnection layer. Formally
this solves the problem of fast reconnection, but in practice this reconnection
speed is small. | 9804166v1 |
2006-06-15 | Tearing instability in relativistic magnetically dominated plasmas | Many astrophysical sources of high energy emission, such as black hole
magnetospheres, superstrongly magnetized neutron stars (magnetars), and
probably relativistic jets in Active Galactic Nuclei and Gamma Ray Bursts
involve relativistically magnetically dominated plasma. In such plasma the
energy density of magnetic field greatly exceeds the thermal and the rest mass
energy density of particles. Therefore the magnetic field is the main reservoir
of energy and its dissipation may power the bursting emission from these
sources, in close analogy to Solar flares. One of the principal dissipative
instabilities that may lead to release of magnetic energy is the tearing
instability. In this paper we study, both analytically and numerically, the
development of tearing instability in relativistically magnetically-dominated
plasma using the framework of resistive magnetodynamics. We confirm and
elucidate the previously obtained result on the growth rate of the tearing
mode: the shortest growth time is the same as in the case of classical
non-relativistic MHD, namely $\tau =\sqrt{\tau_a \tau_d}$ where $\tau_a$ is the
\Alfven crossing time and $\tau_d$ is the resistive time of a current layer. | 0606375v2 |
1994-11-17 | Hydrodynamic electron flow in high-mobility wires | Hydrodynamic electron flow is experimentally observed in the differential
resistance of electrostatically defined wires in the two-dimensional electron
gas in (Al,Ga)As heterostructures. In these experiments current heating is used
to induce a controlled increase in the number of electron-electron collisions
in the wire. The interplay between the partly diffusive wire-boundary
scattering and the electron-electron scattering leads first to an increase and
then to a decrease of the resistance of the wire with increasing current. These
effects are the electronic analog of Knudsen and Poiseuille flow in gas
transport, respectively. The electron flow is studied theoretically through a
Boltzmann transport equation, which includes impurity, electron-electron, and
boundary scattering. A solution is obtained for arbitrary scattering
parameters. By calculation of flow profiles inside the wire it is demonstrated
how normal flow evolves into Poiseuille flow. The boundary-scattering
parameters for the gate-defined wires can be deduced from the magnitude of the
Knudsen effect. Good agreement between experiment and theory is obtained. | 9411067v1 |
1995-12-15 | Nonlocal conductivity in the vortex-liquid regime | We investigate the nonlocal conductivity calculated from the time-dependent
Ginzburg-Landau equation. When the fluctuations of the vector potential are
negligible, the high-temperature (Gaussian) and low-temperature (flux-flow)
forms of the uniform conductivity withan an ab plane (sigma_yy) are essentially
identical. We find to what extent the nonlocal conductivity shares this
feature. The results suggest that for pure samples in theses regimes the length
scales of the nonlocal resistivity, rho_yy(y-y',z-z'), remain short-ranged in
the y and z directions in contrast to the assumptions made by the hydrodynamic
modelling of the multiterminal transport measurements. On the other hand, the
resistivity is seen to have a long length scale in the x direction
rho_yy(x-x'). The implications for the interpretation of recent experiments are
discussed. | 9512121v1 |
1996-02-13 | Giant Magneto-Resistance in Nd$_{0.7}$Sr$_{0.3}$MnO$_3$ at Optical Frequencies | The optical properties of Nd$_{0.7}$Sr$_{0.3}$MnO$_3$ thin films have been
studied from 5 meV to 25 meV and from 0.25 eV to 3 eV, at temperatures from 15
K to 300 K and magnetic fields up to 8.9 T. A large transfer of spectral weight
from high energy to low energy occurs as the temperature is decreased below 180
K, where the dc resistivity peaks, or as the magnetic field is increased. The
optical data are found to be consistent with models that include both the
double exchange interaction and the dynamic Jahn-Teller effect on the Mn$^{3+}$
e$_g$ levels. | 9602075v1 |
1997-09-01 | Superconductor-Insulator Transitions and Insulators with Localized Pairs | Two experiments are described which are related to the problem of localized
Cooper pairs. Magnetic-field-tuned superconductor-insulator transition was
studied in amorphous In--O films with onset of the superconducting transition
in zero field near 2 K. Experiments performed in the temperature range T>0.3 K
indicate that at the critical field, B=B_c, the first derivative of the
resistance dR/dT is non-zero at T=0 and hence the scaling relations should be
written in more general form. Study of the magnetotransport of high-resistance
metastable alloy Cd-Sb on the insulating side of the superconductor-insulator
transition revealed below 0.1 K a shunting condiction mechanism in addition to
usual one-particle hopping. Possibility of pair hopping is discussed. | 9709017v1 |
1997-09-02 | Spontaneous DC Current Generation in a Resistively Shunted Semiconductor Superlattice Driven by a TeraHertz Field | We study a resistively shunted semiconductor superlattice subject to a
high-frequency electric field. Using a balance equation approach that
incorporates the influence of the electric circuit, we determine numerically a
range of amplitude and frequency of the ac field for which a dc bias and
current are generated spontaneously and show that this region is likely
accessible to current experiments. Our simulations reveal that the Bloch
frequency corresponding to the spontaneous dc bias is approximately an integer
multiple of the ac field frequency. | 9709026v1 |
1997-10-15 | Normal-State Hall Effect and the Insulating Resistivity of High-T_c Cuprates at Low Temperatures | The normal-state Hall coefficient R_H and the in-plane resistivity \rho_{ab}
are measured in La-doped Bi_{2}Sr_{2}CuO_{y} (T_c \simeq 13 K) single crystals
and La_{2-x}Sr_{x}CuO_{4} thin films by suppressing superconductivity with 61-T
pulsed magnetic fields. In contrast to data above T_c, the R_H below \sim 10 K
shows little temperature dependence in all the samples measured, irrespective
of whether \rho_{ab} exhibits insulating or metallic behavior. Thus, whatever
physical mechanism gives rise to insulating behavior in the low-temperature
normal state, it leaves the Hall conductivity relatively unchanged. | 9710155v1 |
1997-12-19 | Nature of the Low Field Transition in the Mixed State of High Temperature Superconductors | We have numerically studied the statics and dynamics of a model
three-dimensional vortex lattice at low magnetic fields. For the statics we use
a frustrated 3D XY model on a stacked triangular lattice. We model the dynamics
as a coupled network of overdamped resistively-shunted Josephson junctions with
Langevin noise. At low fields, there is a weakly first-order phase transition,
at which the vortex lattice melts into a line liquid. Phase coherence parallel
to the field persists until a sharp crossover, conceivably a phase transition,
near $T_{\ell} > T_m$ which develops at the same temperature as an infinite
vortex tangle. The calculated flux flow resistivity in various geometries near
$T=T_{\ell}$ closely resembles experiment. The local density of field induced
vortices increases sharply near $T_\ell$, corresponding to the experimentally
observed magnetization jump. We discuss the nature of a possible transition or
crossover at $T_\ell$(B) which is distinct from flux lattice melting. | 9712246v2 |
1998-06-19 | Resistance behavior near the magnetic-field-tuned quantum transition in superconducting amorphous In-O films | We have studied the magnetic-field-tuned superconductivity destroying quantum
transition in amorphous In-O films with the onset of superconductivity in zero
field at about 2 K. At temperatures down to 30 mK the critical resistance
R_c=R(T,B_c) has been found to change approximately linearly with temperature,
which is in contradiction to a standard description where zero slope dR_c/dT =
0 is assumed near T=0. To make the data R(T,B) collapse in the vicinity of
transition against scaling variable (B-B_c)/T^{1/y}, one has either to allow
for the intrinsic temperature dependence of R_c or to postulate the critical
field B_c to be temperature-dependent B_c(T)-B_c(0)~T^{1+1/y}. We find that the
state on the high-field side of the transition can be both insulating and
metallic and we determine the critical index y=1.2. | 9806244v2 |
1998-11-19 | Nonlocal Effects on the Surface Resistance of High Temperature Superconductors with (100) and (110) Surfaces | The low temperature surface resistance R_s of d-wave superconductors is
calculated as function of frequency assuming normal state quasiparticle mean
free paths l in excess of the penetration depth. Results depend strongly on the
geometric configuration. In the clean limit, two contributions to R_s with
different temperature dependencies are identified: photon absorption by
quasiparticles and pair breaking. The size of nonlocal corrections, which can
be positive or negative depending on frequency decreases for given l as the
scattering phase shift \delta_N is increased. However, except in the unitarity
limit \delta_N = 0.5 \pi, nonlocal effects should be observable. | 9811291v2 |
1998-12-03 | Residual resistivity ratio and its relation to the positive magnetoresistance behavior in natural multilayer LaMn2Ge2; relevance to artificial multilayer physics | Results of low temperature magnetoresistance ($\Delta\rho/\rho$) and
isothermal magnetization (M) measurements on polycrystalline ferromagnetic (T_C
close to 300 K) natural multilayers, LaMn_{2+x}Ge_{2-y}Si_y, are reported. It
is found that the samples with large residual resistivity ratio,
$\rho(300K)/\rho(4.2K)$, exhibit large positive magnetoresistance at high
magnetic fields. The Kohler's rule is not obeyed in these alloys. In addition,
at 4.5 K, there is a tendency towards linear variation of $\Delta\rho/\rho$
with magnetic field with increasing $\rho(300K)/\rho(4.2K$); however, the field
dependence of $\Delta\rho/\rho$ does not track that of M, thereby suggesting
that the magnetoresistance originates from non-magnetic layers. It is
interesting that these experimental findings on bulk polycrystals are
qualitatively similar to what is seen in artificially grown multilayer systems
recently. | 9812052v1 |
1998-12-21 | Non-Universal Power Law of the "Hall Scattering Rate" in a Single-Layer Cuprate Bi_{2}Sr_{2-x}La_{x}CuO_{6} | In-plane resistivity \rho_{ab}, Hall coefficient, and magnetoresistance (MR)
are measured in a series of high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6} crystals
with various carrier concentrations, from underdope to overdope. Our crystals
show the highest T_c (33 K) and the smallest residual resistivity ever reported
for Bi-2201 at optimum doping. It is found that the temperature dependence of
the Hall angle obeys a power law T^n with n systematically decreasing with
increasing doping, which questions the universality of the Fermi-liquid-like
T^2 dependence of the "Hall scattering rate". In particular, the Hall angle of
the optimally-doped sample changes as T^{1.7}, not as T^2, while \rho_{ab}
shows a good T-linear behavior. The systematics of the MR indicates an
increasing role of spin scattering in underdoped samples. | 9812334v1 |
1999-08-30 | From an antiferromagnet to a heavy-fermion system: CeCu5Au under pressure | The electrical resistivity rho(T) of single crystalline CeCu_5Au under
pressure was measured in the temperature range 30mK<T<300K. Pressure suppresses
the antiferromagnetic order (T_N=2.35K at ambient pressure) and drives the
system into a non-magnetic heavy-fermion state above P_c=4.1(3)GPa. The
electrical resistivity shows a deviation from a T^2 dependence of a
Fermi-liquid in the pressure range 1.8GPa<=P<=5.15GPa. The rho(T)-curves can be
compared with those of CeCu_{6-x}Au_x at different Au concentrations. Just
before the long-range magnetic order vanishes, a possibly superconducting phase
(at T_c=0.1K and P=3.84GPa) occurs, pointing to a coexistence of
antiferromagnetic order and superconductivity. This new phase is only seen in a
narrow pressure interval Delta P=0.4GPa. | 9908442v1 |
1999-09-01 | Tunneling measurements of the coulomb pseudogap in a two-dimensional electron system in a quantizing magnetic field | We study the Coulomb pseudogap for tunneling into the two-dimensional
electron system of high-mobility (Al,Ga)As/GaAs heterojunctions subjected to a
quantizing magnetic field at filling factor $\nu \leq 1$.
Tunnel current-voltage characteristics show that for the double maximum
observed in the tunnel resistance at $\nu \approx 1$ the pseudogap is linear in
energy with a slope that depends on filling factor, magnetic field, and
temperature. We give a qualitative account of the filling factor dependence of
the pseudogap slope and we confirm the recently reported appearance of another
relaxation time for tunneling at $\nu \approx 1$. For the tunnel resistance
peaks at $\nu=1/3$ and 2/3 a completely different behaviour of the
current-voltage curves is found and interpreted as manifestation of the
fractional gap. | 9909011v2 |
1999-09-02 | Transport properties of strongly correlated metals:a dynamical mean-field approach | The temperature dependence of the transport properties of the metallic phase
of a frustrated Hubbard model on the hypercubic lattice at half-filling are
calculated. Dynamical mean-field theory, which maps the Hubbard model onto a
single impurity Anderson model that is solved self-consistently, and becomes
exact in the limit of large dimensionality, is used. As the temperature
increases there is a smooth crossover from coherent Fermi liquid excitations at
low temperatures to incoherent excitations at high temperatures. This crossover
leads to a non-monotonic temperature dependence for the resistance,
thermopower, and Hall coefficient, unlike in conventional metals. The
resistance smoothly increases from a quadratic temperature dependence at low
temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar
a/e^2 (where "a" is a lattice constant) associated with mean-free paths less
than a lattice constant. Further signatures of the thermal destruction of
quasiparticle excitations are a peak in the thermopower and the absence of a
Drude peak in the optical conductivity. The results presented here are relevant
to a wide range of strongly correlated metals, including transition metal
oxides, strontium ruthenates, and organic metals. | 9909041v1 |
1999-09-24 | Weak Localization Effect in Superconductors by Radiation Damage | Large reductions of the superconducting transition temperature $T_{c}$ and
the accompanying loss of the thermal electrical resistivity (electron-phonon
interaction) due to radiation damage have been observed for several A15
compounds, Chevrel phase and Ternary superconductors, and $\rm{NbSe_{2}}$ in
the high fluence regime. We examine these behaviors based on the recent theory
of weak localization effect in superconductors. We find a good fitting to the
experimental data. In particular, weak localization correction to the
phonon-mediated interaction is derived from the density correlation function.
It is shown that weak localization has a strong influence on both the
phonon-mediated interaction and the electron-phonon interaction, which leads to
the universal correlation of $T_{c}$ and resistance ratio. | 9909358v1 |
2000-01-26 | Antiferromagnetic Alignment and Relaxation Rate of Gd Spins in the High Temperature Superconductor GdBa_2Cu_3O_(7-delta) | The complex surface impedance of a number of GdBa$_2$Cu$_3$O$_{7-\delta}$
single crystals has been measured at 10, 15 and 21 GHz using a cavity
perturbation technique. At low temperatures a marked increase in the effective
penetration depth and surface resistance is observed associated with the
paramagnetic and antiferromagnetic alignment of the Gd spins. The effective
penetration depth has a sharp change in slope at the N\'eel temperature, $T_N$,
and the surface resistance peaks at a frequency dependent temperature below 3K.
The observed temperature and frequency dependence can be described by a model
which assumes a negligibly small interaction between the Gd spins and the
electrons in the superconducting state, with a frequency dependent magnetic
susceptibility and a Gd spin relaxation time $\tau_s $ being a strong function
of temperature. Above $T_N$, $\tau_s$ has a component varying as $1 / (T -
T_N)$, while below $T_N$ it increases $\sim T^{-5}$. | 0001379v1 |
2000-11-20 | Theory of the Hall Coefficient and the Resistivity on the Layered Organic Superconductors κ-(BEDT-TTF) | In the organic superconducting \kappa-(BEDT-TTF) compounds, various transport
phenomena exhibit striking non-Fermi liquid behaviors, which should be the
important clues to understanding the electronic state of this system.
Especially, the Hall coefficient ($R_H$) shows Curie-Weiss type temperature
dependence, which is similar to that of high-Tc cuprates. In this paper, we
study a Hubbard model on an anisotropic triangular lattice at half filling,
which is an effective model of \kappa-(BEDT-TTF) compounds. Based on the
fluctuation-exchange (FLEX) approximation, we calculate the resistivity
($\rho$) and $R_H$ by taking account of the vertex corrections for the current,
which is necessary for satisfying the conservation laws. Our theoretical
results of $R_H$ and $cot(\theta_H)$ explain the experimental behaviors well,
which are unable to be reproduced by the conventional Boltzmann transport
approximation. Moreover, we extend the standard Eliashberg's transport theory
and derive the more precise formula for the conductivity, which becomes
important at higher temperatures. | 0011324v2 |
2000-12-07 | Quantum Tunneling of the Order Parameter in Superconducting Nanowires | Quantum tunneling of the superconducting order parameter gives rise to the
phase slippage process which controls the resistance of ultra-thin
superconducting wires at sufficiently low temperatures. If the quantum phase
slip rate is high, superconductivity is completely destroyed by quantum
fluctuations and the wire resistance never decreases below its normal state
value. We present a detailed microscopic theory of quantum phase slips in
homogeneous superconducting nanowires. Focusing our attention on relatively
short wires we evaluate the quantum tunneling rate for phase slips, both the
quasiclassical exponent and the pre-exponential factor. In very thin and dirty
metallic wires the effect is shown to be clearly observable even at $T \to 0$.
Our results are fully consistent with recent experimental findings [A.
Bezryadin, C.N. Lau, and M. Tinkham, Nature {\bf 404}, 971 (2000)] which
provide direct evidence for the effect of quantum phase slips. | 0012104v1 |
2001-02-20 | Unusual Properties of Anisotropic Hall Gas: Implication to Metrology of the Integer Quantum Hall Effect | Physical properties of anisotropic compressible quantum Hall states and their
implications to integer quantum Hall effect are studied based on a mean field
theory on the von Neumann lattice. It is found that the Hall gas has unusual
thermodynamic properties such as negative pressure and negative compressibility
and unusual transport properties. Transport properties and density profile of
Hall gas states at half fillings agree with those of anisotropic states
discovered experimentally in higher Landau levels. Hall gas formed in the bulk
does not spread but shrinks, owing to negative pressure, and a strip of Hall
gas gives abnormal electric transport at finite temperature. Conductances at
finite temperature and finite injected current agree with recent experiments on
collapse and breakdown phenomena of the integer quantum Hall effect. As a
byproduct, existence of new quantum Hall regime, dissipative quantum Hall
regime, in which Hall resistance is quantized exactly even in the system of
small longitudinal resistance is derived. | 0102347v3 |
2001-08-03 | Electrical Resistivity Anisotropy from Self-Organized One-Dimensionality in High-Temperature Superconductors | We investigate the manifestation of the stripes in the in-plane resistivity
anisotropy in untwinned single crystals of La_{2-x}Sr_{x}CuO_{4} (x = 0.02 -
0.04) and YBa_{2}Cu_{3}O_{y} (y = 6.35 - 7.0). It is found that both systems
show strongly temperature-dependent in-plane anisotropy in the lightly
hole-doped region and that the anisotropy in YBa_{2}Cu_{3}O_{y} grows with
decreasing y below about 6.60 despite the decreasing orthorhombicity, which
gives most direct evidence that electrons self-organize into a macroscopically
anisotropic state. The transport is found to be easier along the direction of
the spin stripes already reported, demonstrating that the stripes are
intrinsically conducting in cuprates. | 0108053v2 |
2001-09-21 | Microwave Power, DC Magnetic Field, Frequency and Temperature Dependence of the Surface Resistance of MgB2 | The microwave power, dc magnetic field, frequency and temperature dependence
of the surface resistance of MgB2 films and powder samples were studied. Sample
quality is relatively easy to identify by a number of characteristics, the most
clear being the breakdown in the omega squared law for poor quality samples.
Analysis of the experimental data suggests the most attractive procedure for
high quality film growth for technical applications. | 0109397v1 |
2002-01-01 | Memory Effects in Electron Transport in Si Inversion Layers in the Dilute Regime: Individuality versus Universality | In order to separate the universal and sample-specific effects in the
conductivity of high-mobility Si inversion layers, we studied the electron
transport in the same device after cooling it down to 4K at different fixed
values of the gate voltage V^{cool}. Different V^{cool} did not modify
significantly either the momentum relaxation rate or the strength of
electron-electron interactions. However, the temperature dependences of the
resistance and the magnetoresistance in parallel magnetic fields, measured in
the vicinity of the metal-insulator transition in 2D, carry a strong imprint of
individuality of the quenched disorder determined by V^{cool}. This
demonstrates that the observed transition between ``metallic'' and insulating
regimes involves both, universal effects of electron-electron interaction and
sample-specific effects. Far away from the transition, at lower carrier
densities and lower resistivities < 0.1 h/e^2, the transport and
magnetotransport become nearly universal. | 0201001v1 |
2002-02-08 | Anisotropic Superconducting Properties of MgB2 Single Crystals | In-plane electrical transport properties of MgB2 single crystals grown under
high pressure of 4-6 GPa and temperature of 1400-1700oC in Mg-B-N system have
been measured. For all specimens we found sharp superconducting transition
around 38.1-38.3K with transition width within 0.2-0.3K. Estimated resistivity
value at 40K is about 1 mkOhmcm and resistivity ratio R(273K)/R(40K) of about
4.9. Results of measurements in magnetic field up to 5.5T perpendicular to Mg
and B planes and up to 9T in parallel orientation show temperature dependent
anisotropy of the upper critical field with anisotropy ratio increasing from
2.2 close to Tc up to about 3 below 30K. Strong deviation of the angular
dependence of Hc2 from anisotropic mass model has been also found. | 0202133v1 |
2002-03-27 | Transport critical current, anisotropy, irreversibility fields and exponential n factors in Fe sheathed MgB2 tapes | The influence of the initial MgB2 grain size on critical current density,
upper critical fields and irreversibility has been studied on Fe sheathed
monofilamentary MgB2 tapes prepared by the Powder-In-Tube technique. The effect
of the reduction of MgB2 grain size by ball milling was mainly to enhance both
the critical current density, jc, and the irreversibility field, while the
upper critical field remained unchanged. The anisotropy ratio of the upper
critical field between magnetic fields parallel and perpendicular the tape
surface was determined to 1.3, reflecting a deformation induced texture. A good
agreement has been found between resistive and inductive jc values, measured at
various temperatures. At 25K and 1 T, jc values close to 105 A/cm2 were
measured. The exponential n factor of the resistive transition was found to be
quite high at low fields, and decrease linearly from 60 at 4T to 10 at 8.5T. | 0203551v1 |
2002-05-10 | Universal Behavior of the Resistance Noise across the Metal-Insulator Transition in Silicon Inversion Layers | Studies of low-frequency resistance noise show that the glassy freezing of
the two-dimensional (2D) electron system in the vicinity of the metal-insulator
transition occurs in all Si inversion layers. The size of the metallic glass
phase, which separates the 2D metal and the (glassy) insulator, depends
strongly on disorder, becoming extremely small in high-mobility samples. The
behavior of the second spectrum, an important fourth-order noise statistic,
indicates the presence of long-range correlations between fluctuators in the
glassy phase, consistent with the hierarchical picture of glassy dynamics. | 0205226v2 |
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