publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
|---|---|---|---|
2020-12-24 | Backflow in simulated MHD accretion disks | We perform resistive MHD simulations of accretion disk with alpha-viscosity,
accreting onto a rotating star endowed with a magnetic dipole. We find backflow
in the presence of strong magnetic field and large resistivity, and probe for
the dependence on Prandtl number. We find that in the magnetic case the
distance from the star at which backflow begins, the stagnation radius, is
different than in the hydrodynamic case, and the backflow shows non-stationary
behavior. We compare the results with hydrodynamics simulations. | 2012.13194v1 |
2021-10-05 | Density-Driven Resistance Response in $MnS_{2}$: Theory | A colossal insulator-to-metal transition in high-spin pyrite phase of
$MnS_{2}$ has been experimentally observed \cite{colomns2}. There are two
possibilities behind this colossal insulator-to-metal transition: (1) migration
of $Mn$ electrons to unoccupied $S^{2-}_{2}$ antibonding states under pressure
which leads to conducting ligand states and hence metallic transition, and (2)
possibility of band crossing transition. We have analyzed this experimental
obervation theoretically using a toy statistical model and found that the
transition is due to the migration of electrons from the transition metal ions
to the ligand sites (i.e. the possibility (1)). The calculated resistivity
compares well with the experimental data within the fitting parameters of the
model. | 2110.01902v1 |
2022-07-25 | Superconductor--Insulator Transition in a non-Fermi Liquid | We present a model of a strongly correlated system with a non-Fermi liquid
high temperature phase. Its ground state undergoes an insulator to
superconductor quantum phase transition (QPT) as a function of a pairing
interaction strength. Both the insulator and the superconductor are originating
from the same interaction mechanism. The resistivity in the insulating phase
exhibits the activation behavior with the activation energy, which goes to zero
at the QPT. This leads to a wide quantum critical regime with an algebraic
temperature dependence of the resistivity. Upon raising the temperature in the
superconducting phase, the model exhibits a finite temperature phase transition
to a Bose metal phase, which separates the superconductor from the non-Fermi
liquid metal. | 2207.12307v1 |
2024-01-19 | Asymptotic behavior of solution of the non-resistive 2D MHD equations on the half space | In this paper, we obtain the global well-posedness and the asymptotic
behavior of solution of non-resistive 2D MHD problem on the half space. We
overcome the difficulty of zero spectrum gap by building the relationship
between half space and the whole space, and get the resolvent estimate for the
weak diffusion system. We use the two-tier energy method that couples the
boundedness of high-order $(H^3)$ energy to the decay of low-order energy, the
latter of which is necessary to control the growth of the highest energy. | 2401.10456v1 |
2005-03-22 | Theoretical current-voltage characteristics of ferroelectric tunnel junctions | We present the concept of ferroelectric tunnel junctions (FTJs). These
junctions consist of two metal electrodes separated by a nanometer-thick
ferroelectric barrier. The current-voltage characteristics of FTJs are analyzed
under the assumption that the direct electron tunneling represents the dominant
conduction mechanism. First, the influence of converse piezoelectric effect
inherent in ferroelectric materials on the tunnel current is described. The
calculations show that the lattice strains of piezoelectric origin modify the
current-voltage relationship owing to strain-induced changes of the barrier
thickness, electron effective mass, and position of the conduction-band edge.
Remarkably, the conductance minimum becomes shifted from zero voltage due to
the piezoelectric effect, and a strain-related resistive switching takes place
after the polarization reversal in a ferroelectric barrier. Second, we analyze
the influence of the internal electric field arising due to imperfect screening
of polarization charges by electrons in metal electrodes. It is shown that, for
asymmetric FTJs, this depolarizing-field effect also leads to a considerable
change of the barrier resistance after the polarization reversal. However, the
symmetry of the resulting current-voltage loop is different from that
characteristic of the strain-related resistive switching. The crossover from
one to another type of the hysteretic curve, which accompanies the increase of
FTJ asymmetry, is described taking into account both the strain and
depolarizing-field effects. It is noted that asymmetric FTJs with dissimilar
top and bottom electrodes are preferable for the non-volatile memory
applications because of a larger resistance on/off ratio. | 0503546v1 |
2013-04-09 | Active control of magnetoresistance of organic spin valves using ferroelectricity | Organic spintronic devices have been appealing because of the long spin life
time of the charge carriers in the organic materials and their low cost,
flexibility and chemical diversity. In previous studies, the control of
resistance of organic spin valves is generally achieved by the alignment of the
magnetization directions of the two ferromagnetic electrodes, generating
magnetoresistance.1 Here we employ a new knob to tune the resistance of organic
spin valves by adding a thin ferroelectric interfacial layer between the
ferromagnetic electrode and the organic spacer. We show that the resistance can
be controlled by not only the spin alignment of the two ferromagnetic
electrodes, but also by the electric polarization of the interfacial
ferroelectric layer: the MR of the spin valve depends strongly on the history
of the bias voltage which is correlated with the polarization of the
ferroelectric layer; the MR even changes sign when the electric polarization of
the ferroelectric layer is reversed. This new tunability can be understood in
terms of the change of relative energy level alignment between ferromagnetic
electrode and the organic spacer caused by the electric dipole moment of the
ferroelectric layer. These findings enable active control of resistance using
both electric and magnetic fields, opening up possibility for multi-state
organic spin valves and shed light on the mechanism of the spin transport in
organic spin valves. | 1304.2446v2 |
2017-12-22 | The Role of Oxygen in Ionic Liquid Gating on 2D Cr2Ge2Te6: a Non-Oxide Material | Ionic liquid gating can markedly modulate the materials' carrier density so
as to induce metallization, superconductivity, and quantum phase transitions.
One of the main issues is whether the mechanism of ionic liquid gating is an
electrostatic field effect or an electrochemical effect, especially for oxide
materials. Recent observation of the suppression of the ionic liquid
gate-induced metallization in the presence of oxygen for oxide materials
suggests the electrochemical effect. However, in more general scenarios, the
role of oxygen in ionic liquid gating effect is still unclear. Here, we perform
the ionic liquid gating experiments on a non-oxide material: two-dimensional
ferromagnetic Cr2Ge2Te6. Our results demonstrate that despite the large
increase of the gate leakage current in the presence of oxygen, the oxygen does
not affect the ionic liquid gating effect (< 5 % difference), which suggests
the electrostatic field effect as the mechanism on non-oxide materials.
Moreover, our results show that the ionic liquid gating is more effective on
the modulation of the channel resistances compared to the back gating across
the 300 nm thick SiO2. | 1712.08281v1 |
2022-11-30 | Anomalous magneto-thermoelectric behavior in massive Dirac materials | Extensive studies of electron transport in Dirac materials have shown
positive magneto-resistance (MR) and positive magneto-thermopower (MTP) in a
magnetic field perpendicular to the excitation current or thermal gradient. In
contrast, measurements of electron transport often show a negative longitudinal
MR and negative MTP for a magnetic field oriented along the excitation current
or thermal gradient; this is attributed to the chiral anomaly in Dirac
materials. Here, we report a very different magneto-thermoelectric transport
behavior in the massive Dirac material ZrTe5. Although thin flakes show a
commonly observed positive MR in a perpendicular magnetic field, distinct from
other Dirac materials, we observe a sharp negative MTP. In a parallel magnetic
field, we still observe a negative longitudinal MR, however, a remarkable
positive MTP is observed for the fields parallel to the thermal gradients. Our
theoretical calculations suggest that this anomalous magneto-thermoelectric
behavior can be attributed to the screened Coulomb scattering. This work
demonstrates the significance of impurity scattering in the electron transport
of topological materials and provides deep insight into the novel
magneto-transport phenomena in Dirac materials. | 2211.17027v1 |
2022-12-01 | Process parameter sensitivity of the energy absorbing properties of additively manufactured metallic cellular materials | Additive Manufacturing (AM) has enabled the fabrication of metallic cellular
materials that are of interest in the design of lightweight impact resistant
structures. However, there is a need to understand the interactions between:
(i) the material architecture, (ii) the AM process parameters, and (iii) the
as-built geometry, microstructure and energy absorbing properties. In this
work, we investigate the quasi-static and dynamic behaviour of cellular
materials manufactured from 316L stainless steel using laser powder bed fusion
(LPBF). Four cellular architectures are considered (octet lattice,
lattice-walled square honeycomb, origami and square honeycomb), as well as
three sets of AM process parameters, characterised by laser powers of 50, 125
and 200 W. The exposure time is adjusted to deliver the same total heat input.
The 125 W case leads to material with the highest strength and ductility. The
cellular materials with this process variant match their nominal densities most
closely, and have the highest strength and energy absorption. Either reducing
(50 W) or increasing (200 W) the power leads to a significant increase in
porosity, reducing strength and energy absorption. However, we find that
changes due to process-induced porosity have a smaller influence than those
resulting from the choice of cellular architecture. | 2212.00438v1 |
2023-09-11 | Button Shear Testing for Adhesion Measurements of 2D Materials | Two-dimensional (2D) materials are considered for numerous applications in
microelectronics, although several challenges remain when integrating them into
functional devices. Weak adhesion is one of them, caused by their chemical
inertness. Quantifying the adhesion of 2D materials on three-dimensional
surfaces is, therefore, an essential step toward reliable 2D device
integration. To this end, button shear testing is proposed and demonstrated as
a method for evaluating the adhesion of 2D materials with the examples of
graphene and hexagonal boron nitride (hBN), molybdenum disulfide, and tungsten
diselenide on silicon dioxide (SiO${_2}$) and silicon nitride substrates. We
propose a fabrication process flow for polymer buttons on the 2D materials and
establish suitable button dimensions and testing shear speeds. We show with our
quantitative data that low substrate roughness and oxygen plasma treatments on
the substrates before 2D material transfer result in higher shear strengths.
Thermal annealing increases the adhesion of hBN on SiO${_2}$ and correlates
with the thermal interface resistance between these materials. This establishes
button shear testing as a reliable and repeatable method for quantifying
adhesion of 2D materials. | 2309.05852v3 |
1997-05-09 | Small-q electron-phonon scattering and linear dc resistivity in high-T_c oxides | We examine the effect on the DC resistivity of small-q electron-phonon
scattering, in a system with the electronic topology of the high-T_c oxides.
Despite the fact that the scattering is dominantly forward, its contribution to
the transport can be significant due to ``ondulations'' of the bands in the
flat region and to the umpklapp process. When the extended van-Hove
singularities are sufficiently close to $E_F$ the acoustic branch of the
phonons contribute significantly to the transport. In that case one can obtain
linear $T$ dependent resistivity down to temperatures as low as 10 K, even if
electrons are scattered also by optical phonons of about 500 K as reported by
Raman measurements. | 9705085v1 |
1999-05-14 | Universal scaling of Hall resistivity in clean and moderately clean limits for Hg- and Tl-based superconductors | The mixed-state Hall resistivity and the longitudinal resistivity in
HgBa_{2}CaCu_{2}O_{6}, HgBa_{2}Ca_{2}Cu_{3}O_{8}, and Tl_{2}Ba_{2}CaCu_{2}O_{8}
thin films have been investigated as functions of the magnetic field up to 18
T. We observe the universal scaling behavior between \rho_{xy} and \rho_{xx} in
the regions of the clean and the moderately clean limit. The scaling exponent
\beta is 1.9 in the clean limit at high field and low temperature whereas \beta
is 1.0 in the moderately clean limit at low field and high temperature,
consistent with a theory based on the midgap states in the vortex cores. This
finding implies that the Hall conductivity is also universal in Hg- and
Tl-based superconductors. | 9905201v1 |
1999-10-04 | Normal State Resistivity of Underdoped YBa2Cu3Ox Thin Films and La2-xSrxCuO4 Ultra-Thin Films under Epitaxial Strain | The normal state resistivity of high temperature superconductors can be
probed in the region below Tc by suppressing the superconducting state in high
magnetic fields. Here we present the normal state properties of YBa2Cu3Ox thin
films in the underdoped regime and the normal state resistance of La2-xSrxCuO4
thin films under epitaxial strain, measured below Tc by applying pulsed fields
up to 60 T. A universal rho(T) behaviour is reported. We interpret these data
in terms of the recently proposed 1D quantum transport model with the 1D paths
corresponding to the charge stripes. | 9910033v1 |
2001-03-04 | Effect of the In-Plane Magnetic Field on Conduction of the Si-inversion Layer: Magnetic Field Driven Disorder | We compare the effects of temperature, disorder and parallel magnetic field
on the metallic-like temperature dependence of the resistivity. We found a
similarity between the effects of disorder and parallel field: the parallel
field weakens the metallic-like conduction in high mobility samples and make it
similar to that for low-mobility samples. We found a smooth continuous effect
of the in-plane field on conduction, without any threshold. While conduction
remains non-activated, the parallel magnetic field restores the same
resistivity value as the high temperature does. This matching sets substantial
constraints on the choice of the theoretical models developed to explain the
mechanism of the metallic conduction and parallel field magnetoresistance in 2D
carrier systems. We demonstrate that the data for magneto- and temperature
dependence of the resistivity of Si-MOS samples in parallel field may be well
described by a simple model of the magnetic field dependent disorder. | 0103087v2 |
2001-11-20 | High-pressure study on the superconducting pyrochlore oxide Cd2Re2O7 | Superconducting and structural phase transitions in a pyrochlore oxide
Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical
resistivity measurements. A rich P-T phase diagram is obtained, which contains
at least two phases with the ideal and slightly distorted pyrochlore
structures. It is found that the transition between them is suppressed with
increasing pressure and finally disappears at a critical pressure Pc = 3.5 GPa.
Remarkable enhancements in the residual resistivity as well as the coefficient
A of the AT 2 term in the resistivity are found around the critical pressure.
Superconductivity is detected only for the phase with the structural
distortion. It is suggested that the charge fluctuations of Re ions play a
crucial role in determining the electronic properties of Cd2Re2O7. | 0111388v2 |
2002-10-02 | Two-band effects in transport properties of MgB2 | We present resistivity and thermal conductivity measurements on bulk samples,
prepared either by a standard method or by a one-step technique. The latter
samples, due to their high density and purity, show residual resistivity values
as low as 0.5 mW cm and thermal conductivity values as high as 215 W/mK, higher
than the single crystal ones. Thermal and electrical data of all the samples
are analysed in the framework of the Bloch-Gruneisen equation giving reliable
parameter values. In particular the temperature resitivity coefficient,
obtained both from resistivity and thermal conductivity, in the dirty sample
comes out ten time larger than in the clean ones. This result supports the
hypothesis of ref. [1] that p and s bands conduct in parallel, prevailing p
conduction in clean samples and s conduction in dirty samples . | 0210047v2 |
2003-07-31 | Radiation-intensity and temperature dependence of microwave-induced magnetoresistance oscillations in high-mobility two-dimensional electron systems | We present a detailed theoretical investigation on the radiation induced
giant magnetoresistance oscillations recently discovered in high-mobility
two-dimensional electron gas. Electron interactions with impurities, transverse
and longitudinal acoustic phonons in GaAs-based heterosystems are considered
simultaneously. Multiphoton-assisted impurity scatterings are shown to be the
primary origin of the resistance oscillation. Based on the balance-equation
theory developed for magnetotransport in Faraday geometry, we are able not only
to reproduce the observed period, phase and the negative resistivity of the
main oscillations, but also to predict the secondary peak/valley structures
relating to two-photon and three-photon processes. The dependence of the
magnetoresistance oscillation on microwave intensity, the role of dc bias
current and the effect of elevated electron temperature are discussed.
Furthermore, we propose that the temperature-dependence of the resistance
oscillation stems from the growth of the Landau level broadening due to the
enhancement of acoustic phonon scattering with increasing lattice temperature.
The calculated temperature-variation of the oscillation agrees well with
experimental observations. | 0307757v1 |
2003-09-29 | Andreev reflection and enhanced subgap conductance in NbN/Au/InGaAs-InP junctions | We report on the fabrication of highly transparent superconductor/normal
metal/two-dimensional electron gas junctions formed by a superconducting NbN
electrode, a thin (10nm) Au interlayer, and a two-dimensional electron gas in a
InGaAs/InP heterostructure. High junction transparency has been achieved by
exploiting of a newly developed process of Au/NbN evaporation and rapid
annealing at 400C. This allowed us to observe for the first time a decrease in
the differential resistance with pronounced double-dip structure within the
superconducting energy gap in superconductor-2DEG proximity systems. The effect
of a magnetic field perpendicular to the plane of the 2DEG on the differential
resistance of the interface was studied. It has been found that the reduced
subgap resistance remains in high magnetic fields. Zero-field data are analyzed
within the previously established quasiclassical model for the proximity
effect. | 0309682v2 |
2004-01-07 | Large positive magneto-resistance in high mobility 2D electron gas : interplay of short and long range disorder | We have observed a large positive quasi-classical magneto-resistance (MR) in
a high mobility 2D electron gas in AlGaAs/GaAs heterostructure. The
magneto-resistance is non-saturating and increases with magnetic field as
$\rho_{xx}\sim B^{\alpha} (\alpha=0.9-1.2)$. In antidot lattices a
non-monotonic MR is observed. We show that in both cases this MR can be
qualitatively described in terms of the theory recently advanced by Polyakov et
al (PRB, 64, 205306 (2001)). Their prediction is that such behavior as we
observe may be the consequence of a concurrent existence of short and long
range scattering potentials. | 0401085v2 |
2004-03-01 | Electronic Phase Diagram of High-T_c Cuprate Superconductors from a Mapping of the In-Plane Resistivity Curvature | We propose that Resistivity Curvature Mapping (RCM) based on the in-plane
resistivity data is a useful way to objectively draw an electronic phase
diagrams of high-T_c cuprates, where various crossovers are important. In
particular, the pseudogap crossover line can be conveniently determined by RCM.
We show experimental phase diagrams obtained by RCM for
Bi_{2}Sr_{2-z}La_{z}CuO_{6+\delta}, La_{2-x}Sr_{x}CuO_{4}, and
YBa_{2}Cu_{3}O_{y}, and demonstrate the universal nature of the pseudogap
crossover. Intriguingly, the electronic crossover near optimum doping depicted
by RCM appears to occur rather abruptly, suggesting that the quantum critical
regime, if exists, must be very narrow. | 0403032v2 |
2004-12-15 | The resistive transition and Meissner effect in carbon nanotubes: Evidence for quasi-one-dimensional superconductivity above room temperature | It is well known that copper-based perovskite oxides rightly enjoy consensus
as high-temperature superconductors on the basis of two signatures: the
resistive transition and the Meissner effect. We show that the resistive
transitions in carbon nanotubes agree quantitatively with the
Langer-Ambegaokar-McCumber-Halperin (LAMH) theory for quasi-1D superconductors
although the superconducting transition temperatures can vary from 0.4 K to 750
K for different samples. We have also identified the Meissner effect in the
field parallel to the tube axis up to room temperature for aligned and
physically separated multi-walled nanotubes (MWNTs). The magnitude of the
Meissner effect is in quantitative agreement with the predicted penetration
depth from the measured carrier density. Furthermore, the bundling of
individual MWNTs into closely packed bundles leads to a large enhancement in
the diamagnetic susceptibility, which is the hallmark of the Josephson coupling
among the tubes in bundles. These results consistently indicate quasi-1D
high-temperature superconductivity in carbon nanotubes. | 0412382v2 |
2005-02-09 | Low-temperature nodal-quasiparticle transport in lightly doped YBa_{2}Cu_{3}O_{y} near the edge of the superconducting doping regime | In-plane transport properties of nonsuperconducting YBa_{2}Cu_{3}O_{y} (y =
6.35) are measured using high-quality untwinned single crystals. We find that
both the a- and b-axis resistivities show log(1/T) divergence down to 80 mK,
and accordingly the thermal conductivity data indicate that the nodal
quasiparticles are progressively localized with lowering temperature. Hence,
both the charge and heat transport data do not support the existence of a
"thermal metal" in nonsuperconducting YBa_{2}Cu_{3}O_{y}, as opposed to a
recent report by Sutherland {\it et al.} [Phys. Rev. Lett. {\bf 94}, 147004
(2005)]. Besides, the present data demonstrate that the peculiar log(1/T)
resistivity divergence of cuprate is {\it not} a property associated with
high-magnetic fields. | 0502223v2 |
2006-04-19 | Transport Properties of Granular High-TC Superconductors | We report on the application of the Resistively Shunted Junction (RSJ) model
to granular high-TC superconductors. Some derived predictions of the RSJ model
are applied to a set of superconducting granular samples which can be
considered as a network of Josephson junctions. The investigated samples belong
to both hole-doped Y1-xPrxBa2Cu3O7-d (x = 0.0, 0.35, and 0.45) and the
electron-doped Sm2-xCexCuO4-d (x = 0.18) systems which display the so-called
double resistive superconducting transition. We have performed several
transport measurements in these compounds including temperature and magnetic
field dependence of the electrical resistance, R(T,H), and I-V characteristics.
Several aspects of the I-V characteristics were quantitatively well described
by the RSJ model. The combined results strongly suggest that dissipation in
granular superconducting samples is a natural consequence of the normal current
flowing in parallel with the supercurrent current. | 0604460v1 |
2006-10-05 | Unconventional resistivity at the border of metallic antiferromagnetism in NiS2 | We report low-temperature and high-pressure measurements of the electrical
resistivity \rho(T) of the antiferromagnetic compound NiS_2 in its
high-pressure metallic state. The form of \rho(T) suggests that metallic
antiferromagnetism in NiS_2 is quenched at a critical pressure p_c=76+-5 kbar.
Near p_c the temperature variation of \rho(T) is similar to that observed in
NiS_{2-x}Se_x near the critical composition x=1 where the Neel temperature
vanishes at ambient pressure. In both cases \rho(T) varies approximately as
T^{1.5} over a wide range below 100 K. However, on closer analysis the
resistivity exponent in NiS_2 exhibits an undulating variation with temperature
not seen in NiSSe (x=1). This difference in behaviour may be due to the effects
of spin-fluctuation scattering of charge carriers on cold and hot spots of the
Fermi surface in the presence of quenched disorder, which is higher in NiSSe
than in stoichiometric NiS_2. | 0610166v1 |
2009-05-29 | Ferromagnetic quantum phase transition in Sr$_{1-x}$Ca$_x$RuO$_3$ thin films | The ferromagnetic quantum phase transition in the perovskite ruthenate
Sr$_{1-x}$Ca$_x$RuO$_3$ is studied by low-temperature magnetization and
electrical resistivity measurements on thin films. The films were grown
epitaxially on SrTiO$_3$ substrates using metalorganic aerosol deposition and
characterized by X-ray diffraction and room temperature scanning tunneling
microscopy. High residual resistivity ratios of 29 and 16 for $x=0$ and $x=1$,
respectively, prove the high quality of the investigated samples. We observe a
continuous suppression of the ferromagnetic Curie temperature from $T_C=160$ K
at $x=0$ towards $T_C\to 0$ at $x_c\approx 0.8$. The analysis of the electrical
resistivity between 2 and 10 K reveals $T^2$ and $T^{3/2}$ behavior at $x\leq
0.6$ and $x\geq 0.7$, respectively. For undoped CaRuO$_3$, the measurement has
been extended down to 60 mK, revealing a crossover to $T^2$ behavior around 2
K, which suggests a Fermi-liquid ground state in this system. | 0905.4885v1 |
2009-08-10 | Temperature Dependence of Magnetophonon Resistance Oscillations in GaAs/AlAs Heterostructures at High Filling Factors | The temperature dependence of phonon-induced resistance oscillations has been
investigated in two-dimensional electron system with moderate mobility at large
filling factors at temperature range T = 7.4 - 25.4 K. The amplitude of
phonon-induced oscillations has been found to be governed by quantum relaxation
time which is determined by electron-electron interaction effects. This is in
agreement with results recently obtained in ultra-high mobility two-dimensional
electron system with low electron density [A. T. Hatke et al., Phys. Rev. Lett.
102, 086808 (2009)]. The shift of the main maximum of the magnetophonon
resistance oscillations to higher magnetic fields with increasing temperature
is observed. | 0908.1293v2 |
2009-10-09 | Electromagnetic response of LaO_0.94F_0.06FeAs: AC susceptibility and microwave surface resistance | We discuss on the electromagnetic response of a polycrystalline sample of
LaO_0.94F_0.06FeAs exposed to DC magnetic fields up to 10 kOe. The low- and
high-frequency responses have been investigated by measuring the AC
susceptibility at 100 kHz and the microwave surface resistance at 9.6 GHz. At
low as well as high DC magnetic fields, the susceptibility strongly depends on
the amplitude of the AC driving field, highlighting enhanced nonlinear effects.
The field dependence of the AC susceptibility exhibits a magnetic hysteresis
that can be justified considering the intragrain-field-penetration effects on
the intergrain critical current density. The microwave surface resistance
exhibits a clockwise magnetic hysteresis, which cannot be justified in the
framework of the critical-state models of the Abrikosov-fluxon lattice; it may
have the same origin as that detected in the susceptibility. | 0910.1805v1 |
2010-08-04 | High-Pressure Electrical Resistivity Measurements of EuFe2As2 Single Crystals | High-pressure electrical resistivity measurements up to 3.0GPa have been
performed on EuFe2As2 single crystals with residual resistivity ratios RRR=7
and 15. At ambient pressure, a magnetic / structural transition related to
FeAs-layers is observed at T0 =190K and 194K for samples with RRR=7 and 15,
respectively. Application of hydrostatic pressure suppresses T0, and then
induces similar superconducting behavior in the samples with different RRR
values. However, the critical pressure 2.7GPa, where T0=0, for the samples with
RRR=15 is slightly but distinctly larger than 2.5GPa for the samples with
RRR=7. | 1008.0684v1 |
2010-12-26 | Superconductivity at 32 K in single crystal Rb$_{0.78}$Fe$_2$Se$_{1.78}$} | We successfully grew the high-quality single crystal of
Rb$_{0.78}$Fe$_2$Se$_{1.78}$, which shows sharp superconducting transition in
magnetic susceptibility and electrical resistivity. Resistivity measurements
show the onset superconducting transition ($T_{\rm c}$) at 32.1 K and zero
resistivity at 30 K. From the low-temperature iso-magnetic-field
magnetoresistance, large upper critical field $H_{\rm c2}$(0) has been
estimated as high as 180 T for in-plane field and 59 T for out-of-plane field.
The anisotropy $H^{ab}_{\rm c2}$(0)/$H^{c}_{\rm c2}$(0) is around 3.0, right
lying between those observed in K$_x$Fe$_2$Se$_2$ and Cs$_x$Fe$_2$Se$_2$. | 1012.5525v1 |
2012-07-23 | Quantum oscillations and high carrier mobility in the delafossite PdCoO$_2$ | We present de Haas-van Alphen and resistivity data on single crystals of the
delafossite PdCoO2. At 295 K we measure an in-plane resistivity of 2.6
\mu{\Omega}-cm, making PdCoO2 the most conductive oxide known. The
low-temperature in-plane resistivity has an activated rather than the usual T^5
temperature dependence, suggesting a gapping of effective scattering that is
consistent with phonon drag. Below 10 K, the transport mean free path is 20
\mum, approximately 10^5 lattice spacings and an astoundingly high value for
flux-grown crystals. We discuss the origin of these properties in light of our
data. | 1207.5402v1 |
2012-10-02 | Magnetotransport in graphene on silicon side of SiC | We have studied the transport properties of graphene grown on silicon side of
SiC. Samples under study have been prepared by two different growth methods in
two different laboratories. Magnetoresistance and Hall resistance have been
measured at temperatures between 4 and 100 K in resistive magnet in magnetic
fields up to 22 T. In spite of differences in sample preparation, the field
dependence of resistances measured on both sets of samples exhibits two periods
of magneto-oscillations indicating two different parallel conducting channels
with different concentrations of carriers. The semi-quantitative agreement with
the model calculation allows for conclusion that channels are formed by
high-density and low-density Dirac carriers. The coexistence of two different
groups of carriers on the silicon side of SiC was not reported before. | 1210.0744v2 |
2013-01-02 | Plasmoid Instability in High-Lundquist-Number Magnetic Reconnection | Our understanding of magnetic reconnection in resistive magnetohydrodynamics
has gone through a fundamental change in recent years. The conventional wisdom
is that magnetic reconnection mediated by resistivity is slow in laminar high
Lundquist ($S$) plasmas, constrained by the scaling of the reconnection rate
predicted by Sweet-Parker theory. However, recent studies have shown that when
$S$ exceeds a critical value $\sim10^{4}$, the Sweet-Parker current sheet is
unstable to a super-Alfv\'enic plasmoid instability, with a linear growth rate
that scales as $S^{1/4}$. In the fully developed statistical steady state of
two-dimensional resistive magnetohydrodynamic simulations, the normalized
average reconnection rate is approximately 0.01, nearly independent of $S$, and
the distribution function $f(\psi)$ of plasmoid magnetic flux $\psi$ follows a
power law $f(\psi)\sim\psi^{-1}$. When Hall effects are included, the plasmoid
instability may trigger onset of Hall reconnection even when the conventional
criterion for onset is not satisfied. The rich variety of possible reconnection
dynamics is organized in the framework of a phase diagram. | 1301.0331v2 |
2013-02-09 | mrPUF: A Memristive Device based Physical Unclonable Function | Physical unclonable functions (PUFs) exploit the intrinsic complexity and
irreproducibility of physical systems to generate secret information. PUFs have
the potential to provide fundamentally higher security than traditional
cryptographic methods by preventing the cloning of identities and the
extraction of secret keys. One unique and exciting opportunity is that of using
the super-high information content (SHIC) capability of nanocrossbar
architecture as well as the high resistance programming variation of resistive
memories to develop a highly secure on-chip PUFs for extremely resource
constrained devices characterized by limited power and area budgets such as
passive Radio Frequency Identification (RFID) devices. We show how to implement
PUF based on nano-scale memristive (resistive memory) devices (mrPUF). Our
proposed architecture significantly increased the number of possible
challenge-response pairs (CRPs), while also consuming relatively lesser power
(around 70 uW). The presented approach can be used in other silicon-based PUFs
as well. | 1302.2191v1 |
2013-04-24 | A highly resistive layer within the crust of X-ray pulsars limits their spin periods | The lack of X-ray pulsars with spin periods > 12 s raises the question of
where the population of evolved high magnetic field neutron stars has gone.
Unlike canonical radio pulsars, X-ray pulsars are not subject to physical
limits to the emission mechanism nor observational biases against the detection
of sources with longer periods. Here we show that a highly resistive layer in
the innermost part of the crust of neutron stars naturally limits the spin
period to a maximum value of about 10-20 s. This highly resistive layer is
expected if the inner crust is amorphous and heterogeneous in nuclear charge,
possibly due to the existence of a nuclear pasta phase. Our findings suggest
that the maximum period of isolated X-ray pulsars can be the first
observational evidence of an amorphous inner crust, which properties can be
further constrained by future X-ray timing missions combined with more detailed
models. | 1304.6546v2 |
2014-05-05 | Hall field-induced resistance oscillations in Ge/SiGe quantum wells | We report on a magnetotransport study in a high-mobility 2D hole gas hosted
in a pure Ge/SiGe quantum well subject to dc electric fields and high frequency
microwave radiation. We find that under applied dc bias the differential
resistivity exhibits a pronounced maximum at a magnetic field which increases
linearly with the applied current. We associate this maximum with the
fundamental peak of Hall field-induced resistance oscillations (HIRO) which are
known to occur in 2D electron gases in GaAs/AlGaAs systems. After taking into
account the Dingle factor correction, we find that the position of the HIRO
peak is well described by the hole effective mass $m^\star \approx 0.09\,m_0$,
obtained from microwave photoresistance in the same sample. | 1405.1093v1 |
2014-07-28 | An apparent metal insulator transition in high mobility 2D InAs heterostructures | We report on the first experimental observation of an apparent metal
insulator transition in a 2D electron gas confined in an InAs quantum well. At
high densities we find that the carrier mobility is limited by background
charged impurities and the temperature dependence of the resistivity shows a
metallic behavior with resistivity increasing with increasing temperature. At
low densities we find an insulating behavior below a critical density of $n_{c}
= 5 \times 10^{10}$ cm$^{-2}$ with the resistivity decreasing with increasing
temperature. We analyze this transition using a percolation model arising from
the failure of screening in random background charged impurities. We also
examine the percolation transition experimentally by introducing remote ionized
impurities at the surface. Using a bias during cool-down, we modify the
screening charge at the surface which strongly affects the critical density.
Our study shows that transition from a metallic to an insulating phase in our
system is due to percolation transition. | 1407.7541v3 |
2014-11-01 | Unusual resistance-voltage dependence of nanojunctions during electromigration in ultra-high vacuum | The electrical resistance R of metallic nanocontacts subjected to controlled
cyclic electromigration in ultra-high vacuum has been investigated in-situ as a
function of applied voltage V. For sufficiently small contacts, i.e., large
resistance, a decrease of R(V) while increasing V is observed. This effect is
tentatively attributed to the presence of contacts separated by thin vacuum
barriers in parallel to ohmic nanocontacts. Simple model calculations indicate
that both thermal activation or tunneling can lead to this unusual behavior. We
describe our data by a tunneling model whose key parameter, i.e., the tunneling
distance, changes because of thermal expansion due to Joule heating and/or
electrostatic strain arising from the applied voltage. Oxygen exposure during
electromigration prevents the formation of negative R(V) slopes, and at the
same time enhances the probability of uncontrolled melting, while other gases
show little effects. In addition, indication for field emission has been
observed in some samples | 1411.0105v1 |
2015-01-15 | High Pressure Measurements of the Resistivity of $β$-YbAlB$_4$ | The electric resistivity $\rho(T)$ under hydrostatic pressure up to 8 GPa was
measured above 2 K using a high-quality single crystal of the Yb-based heavy
fermion system $\beta$-YbAlB$_4$. We found pressure-induced magnetic ordering
above the critical pressure $P_{\rm c} \approx $ 2.4 GPa. This phase transition
temperature $T_M$ is enhanced with pressure and reaches 30 K at a pressure of 8
GPa, which is the highest transition temperature for the Yb-based heavy fermion
compounds. In contrast, the resistivity is insensitive to pressure below $P_c$
and exhibits the $T$-linear behavior in the temperature range between 2 and 20
K. Our results indicate that quantum criticality for $\beta$-YbAlB$_4$ is also
located near $P_{\rm c}$ in addition to the ambient pressure. | 1501.03852v1 |
2015-12-17 | Alfvén Wave Heating of the Solar Chromosphere: 1.5D models | Physical processes which may lead to solar chromospheric heating are analyzed
using high-resolution 1.5D non-ideal MHD modelling. We demonstrate that it is
possible to heat the chromospheric plasma by direct resistive dissipation of
high-frequency Alfv\'en waves through Pedersen resistivity. However this is
unlikely to be sufficient to balance radiative and conductive losses unless
unrealistic field strengths or photospheric velocities are used. The precise
heating profile is determined by the input driving spectrum since in 1.5D there
is no possibility of Alfv\'en wave turbulence. The inclusion of the Hall term
does not affect the heating rates. If plasma compressibility is taken into
account, shocks are produced through the ponderomotive coupling of Alfv\'en
waves to slow modes and shock heating dominates the resistive dissipation. In
1.5D shock coalescence amplifies the effects of shocks and for compressible
simulations with realistic driver spectra the heating rate exceeds that
required to match radiative and conductive losses. Thus while the heating rates
for these 1.5D simulations are an overestimate they do show that ponderomotive
coupling of Alfv\'en waves to sound waves is more important in chromospheric
heating than Pedersen dissipation through ion-neutral collisions. | 1512.05816v1 |
2016-02-14 | Ultra-sensitive nanoscale magnetic field sensors based on resonant spin filtering | Solid state magnetic field sensors based on magneto-resistance modulation
find direct applications in communication devices, specifically in proximity
detection, rotational reference detection and current sensing. In this work, we
propose sensor structures based on the magneto-resistance physics of resonant
spin-filtering and present device designs catered toward exceptional magnetic
field sensing capabilities. Using the non-equilibrium Green's function spin
transport formalism self consistently coupled to the Poisson's equation, we
present highly-tunable pentalayer magnetic tunnel junction structures that are
capable of exhibiting an ultra-high peak tunnel magneto resistance $(\approx
2500 \%$). We show how this translates to device designs featuring an
ultra-high current sensitivity enhancement of over 300\% in comparison with
typical trilayer MTJ sensors, and a wider tunable range of field sensitivity.
We also demonstrate that a dynamic variation in sensor functionalities with the
structural landscape enables a superior design flexibility over typical
trilayer sensors. An optimal design exhibiting close to a 700\% sensitivity
increase as a result of angle dependent spin filtering is then presented.This
work sets a stage to engineer spintronic building blocks via the design of
functional structures tailored to exhibit ultra-sensitive spin filtering. | 1602.04438v1 |
2016-04-10 | Terahertz-induced resistance oscillations in high mobility two-dimensional electron systems | We report on a theoretical work on magnetotransport under terahertz radiation
with high mobility two-dimensional electron systems. We focus on the
interaction between the obtained radiation-induced magnetoresistance
oscillations (RIRO) and the Shubnikov-de Haas (SdHO) oscillations. We study two
effects experimentally obtained with this radiation. First, the observed
disappearance of the SdHO oscillations simultaneously with the vanishing
resistance at the zero resistance states region. And secondly the strong
modulation of the SdHO oscillations at sufficient terahertz radiation power. We
conclude that both effects share the same physical origin, the interference
between the average advanced distance by the scattered electron between
irradiated Landau states, (RIRO), and the available initial density of states
at a certain magnetic field, (SdHO). Thus, from a physical standpoint, what the
terahertz experiments and theoretical simulations reveal is, on the one hand,
the oscillating nature of the Landau states subjected to radiation and, on the
other hand, how they behave in the presence of scattering. | 1604.02721v1 |
2016-05-12 | Improved Contacts to MoS2 Transistors by Ultra-High Vacuum Metal Deposition | The scaling of transistors to sub-10 nm dimensions is strongly limited by
their contact resistance (Rc). Here we present a systematic study of scaling
MoS2 devices and contacts with varying electrode metals and controlled
deposition conditions, over a wide range of temperatures (80 to 500 K), carrier
densities (10^12 to 10^13 1/cm^2), and contact dimensions (20 to 500 nm). We
uncover that Au deposited in ultra-high vacuum (~10^-9 Torr) yields three times
lower Rc than under normal conditions, reaching 740 Ohm-um and specific contact
resistivity 3x10^-7 Ohm.cm2, stable for over four months. Modeling reveals
separate Rc contributions from the Schottky barrier and the series access
resistance, providing key insights on how to further improve scaling of MoS2
contacts and transistor dimensions. The contact transfer length is ~35 nm at
300 K, which is verified experimentally using devices with 20 nm contacts and
70 nm contact pitch (CP), equivalent to the "14 nm" technology node. | 1605.03972v2 |
2016-10-03 | A variational approach to resistive relativistic plasmas | We develop an action principle to construct the field equations for a
multi-fluid system containing charge-neutral fluids, plasmas, and dissipation
(via resistive interactions), by combining the standard, Maxwell action and
minimal coupling of the electromagnetic field with a recently developed action
for relativistic dissipative fluids. We use a pull-back formalism from
spacetime to abstract matter spaces to build unconstrained variations for both
the charge-neutral fluids and currents making up the plasmas. Using basic
linear algebra techniques, we show that a general "relabeling" invariance
exists for the abstract matter spaces. With the field equations in place, a
phenomenological model for the resistivity is developed, using as constraints
charge conservation and the Second Law of Thermodynamics. A minimal model for a
system of electrons, protons, and heat is developed using the Onsager procedure
for incorporating dissipation. | 1610.00445v1 |
2017-02-06 | Semiempirical Modeling of Reset Transitions in Unipolar Resistive-Switching Based Memristors | We have measured the transition process from the high to low resistivity
states, i.e., the reset process of resistive switching based memristors based
on Ni/HfO2/Si-n+ structures, and have also developed an analytical model for
their electrical characteristics. When the characteristic curves are plotted in
the current-voltage (I-V) domain a high variability is observed. In spite of
that, when the same curves are plotted in the charge-flux domain (Q-f), they
can be described by a simple model containing only three parameters: the charge
(Qrst) and the flux (frst) at the reset point, and an exponent, n, relating the
charge and the flux before the reset transition. The three parameters can be
easily extracted from the Q-f plots. There is a strong correlation between
these three parameters, the origin of which is still under study. | 1702.01533v1 |
2017-02-28 | Evidence for conventional superconductivity in Sr0.1Bi2Se3 from high pressure studies | SrxBi2Se3 is recently reported to be a superconductor derived from
topological insulator Bi2Se3. It shows a maximum resistive Tc of 3.25 K at
ambient pressure. We report magnetic (upto 1 GPa) and transport properties
(upro 8 Gpa) under pressure for single crystalline Sr0.1Bi2Se3 superconductor.
Magnetic measurements show that Tc decreases from ~2.6 K (0 GPa) to ~1.9 K
(0.81 GPa). Similar behavior is observed in transport properties as well
without much change in the metallic characteristics in normal state
resistivity. No reentrant superconducting phase (Physical Review B 93, 144514
(2016)) is observed at high pressure. Normal state resistivity near Tc is
explained by Fermi liquid model. Above 100 K, a polaronic hopping conduction
mechanism with two parallel channels for current flow is indicated. Band
structure calculations indicate decreasing density of states at Fermi level
with pressure. In consonance with transition temperature suppression in
conventional BCS low Tc superconductors, the pressure effect in SrxBi2Se3 is
well accounted by pressure induced band broadening. | 1702.08829v1 |
2017-12-21 | DC resistivity of quantum critical, charge density wave states from gauge-gravity duality | In contrast to metals with weak disorder, the resistivity of weakly-pinned
charge density waves (CDWs) is not controlled by irrelevant processes relaxing
momentum. Instead, the leading contribution is governed by incoherent,
diffusive processes which do not drag momentum and can be evaluated in the
clean limit. We compute analytically the dc resistivity for a family of
holographic charge density wave quantum critical phases and discuss its
temperature scaling. Depending on the critical exponents, the ground state can
be conducting or insulating. We connect our results to dc electrical transport
in underdoped cuprate high $T_c$ superconductors. We conclude by speculating on
the possible relevance of unstable, semi-locally critical CDW states to the
strange metallic region. | 1712.07994v2 |
2018-09-27 | p-GaAs nanowire MESFETs with near-thermal limit gating | Difficulties in obtaining high-performance p-type transistors and gate
insulator charge-trapping effects present two major challenges for III-V
complementary metal-oxide semiconductor (CMOS) electronics. We report a p-GaAs
nanowire metal-semiconductor field-effect transistor (MESFET) that eliminates
the need for a gate insulator by exploiting the Schottky barrier at the
metal-GaAs interface. Our device beats the best-performing p-GaSb nanowire
metal-oxide-semiconductor field effect transistor (MOSFET), giving a typical
sub-threshold swing of 62 mV/dec, within 4% of the thermal limit, on-off ratio
$\sim 10^{5}$, on-resistance ~700 k$\Omega$, contact resistance ~30 k$\Omega$,
peak transconductance 1.2 $\mu$S/$\mu$m and high-fidelity ac operation at
frequencies up to 10 kHz. The device consists of a GaAs nanowire with an
undoped core and heavily Be-doped shell. We carefully etch back the nanowire at
the gate locations to obtain Schottky-barrier insulated gates whilst leaving
the doped shell intact at the contacts to obtain low contact resistance. Our
device opens a path to all-GaAs nanowire MESFET complementary circuits with
simplified fabrication and improved performance. | 1809.10479v1 |
2018-10-07 | High-resolution disruption halo current measurements using Langmuir probes in Alcator C-Mod | Halo currents generated during disruptions on Alcator C-Mod have been
measured with Langmuir "rail" probes. These rail probes are embedded in a lower
outboard divertor module in a closely-spaced vertical (poloidal) array. The
dense array provides detailed resolution of the spatial dependence (~1 cm
spacing) of the halo current distribution in the plasma scrape-off region with
high time resolution (400 kHz digitization rate). As the plasma limits on the
outboard divertor plate, the contact point is clearly discernible in the halo
current data (as an inversion of current) and moves vertically down the
divertor plate on many disruptions. These data are consistent with filament
reconstructions of the plasma boundary, from which the edge safety factor of
the disrupting plasma can be calculated. Additionally, the halo current
"footprint" on the divertor plate is obtained and related to the halo flux
width. The voltage driving halo current and the effective resistance of the
plasma region through which the halo current flows to reach the probes are also
investigated. Estimations of the sheath resistance and halo region resistivity
and temperature are given. This information could prove useful for modeling
halo current dynamics. | 1810.03207v1 |
2020-04-27 | The Resistivity of High-Tc Cuprates | We show that the resistivity in each phase of the High-Tc cuprates is a
special case of a general expression derived from the Kubo formula. We obtain,
in particular, the T-linear behavior in the strange metal (SM) and upper
pseudogap (PG) phases, the pure $T^2$, Fermi liquid (FL) behavior observed in
the strongly overdoped regime as well as the $T^{1+\delta}$ behavior that
interpolates both in the crossover. We calculate the coefficients: a) of $T$ in
the linear regime and show that it is proportional to the PG temperature
$T^*(x)$; b) of the $T^2$-term in the FL regime, without adjusting any
parameter; and c) of the $T^{1.6}$ term in the crossover regime, all in
excellent agreement with the experimental data. From our model, we are able to
infer that the resistivity in cuprates is caused by the scattering of holes by
excitons, which naturally form as holes are doped into the electron background. | 2004.12785v1 |
2012-01-05 | Phonon-limited transport coefficients in extrinsic graphene | The effect of electron-phonon scattering processes over the thermoelectric
properties of extrinsic graphene was studied. Electrical and thermal
resistivity, as well as the thermopower, were calculated within the Bloch
theory approximations. Analytical expressions for the different transport
coefficients were obtained from a variational solution of the Boltzmann
equation. The phonon-limited electrical resistivity \rho_{e-ph} shows a linear
dependence at high temperatures, and follows {\rho}_{e-ph} \sim T^{4} at low
temperatures, in agreement with experiments and theory previously reported in
the literature. The phonon-limited thermal resistivity at low temperatures
exhibits a \sim T dependence, and achieves a nearly constant value at high
temperatures. The predicted Seebeck coefficient at verylow temperatures is Q(T)
\sim -\pi 2 k_B T /(3 e E_F), which shows a n^{-1/2} dependence with the
density of carriers, in agreement with experimental evidence. Our results
suggest that thermoelectric properties can be controlled by adjusting the
Bloch-Gruneisen temperature through its dependence on the extrinsic carrier
density in graphene. | 1201.1057v1 |
2012-01-27 | Giant negative magnetoresistance in high-mobility 2D electron systems | We report on a giant negative magnetoresistance in very high mobility
GaAs/AlGaAs heterostructures and quantum wells. The effect is the strongest at
$B \simeq 1$ kG, where the magnetoresistivity develops a minimum emerging at $T
\lesssim 2$ K. Unlike the zero-field resistivity which saturates at $T \simeq 2
$ K, the resistivity at this minimum continues to drop at an accelerated rate
to much lower temperatures and becomes several times smaller than the
zero-field resistivity. Unexpectedly, we also find that the effect is destroyed
not only by increasing temperature but also by modest in-plane magnetic fields.
The analysis shows that giant negative magnetoresistance cannot be explained by
existing theories considering interaction-induced or disorder-induced
corrections. | 1201.5679v1 |
2019-03-12 | DEM simulation of soil-tool interaction under extraterrestrial environmental effects | In contrast to terrestrial environment, the harsh lunar environment
conditions include lower gravity acceleration, ultra-high vacuum and high (low)
temperature in the daytime (night-time). This paper focuses on the effects of
those mentioned features on soil cutting tests, a simplified excavation test,
to reduce the risk of lunar excavation missions. Soil behavior and blade
performance were analyzed under different environmental conditions. The results
show that: (1) the cutting resistance and the energy consumption increase
linearly with the gravity. The bending moment has a bigger increasing rate in
low gravity fields due to a decreasing moment arm; (2) the cutting
resistance,energy consumption and bending moment increase significantly because
of the raised soil strength on the lunar environment, especially in low gravity
fields. Under the lunar environment, the proportions of cutting resistance,
bending moment and energy consumption due to the effect of the van der Waals
forces are significant. Thus, they should be taken into consideration when
planning excavations on the Moon. Therefore, considering that the maximum
frictional force between the excavator and the lunar surface is proportional to
the gravity acceleration, the same excavator that works efficiently on the
Earth may not be able to work properly on the Moon. | 1903.04821v1 |
2019-04-05 | Superconductivity in the dilute single band limit in reduced Strontium Titanate | We report on superconductivity in single crystals of SrTiO$_{3-\delta}$ with
carrier densities $\textit{n} < 1.4 \times10^{18}cm^{-3}$, where only a single
band is occupied. For all samples in this regime, the resistive transition
occurs at $T_{c} \approx 65 \pm 25 \ mK$. We observe a zero resistance state
for $\textit{n}$ as low as $1.03 \times10^{17}cm^{-3}$, and a partial resistive
transition for $\textit{n} = 3.85 \times10^{16}cm^{-3}$. We observe low
critical current densities, relatively high and isotropic upper critical
fields, and an absence of diamagnetic screening in these samples. Our findings
suggest an inhomogeneous superconducting state, embedded within a homogeneous
high-mobility 3-dimensional electron gas. $T_{c}$ does not vary appreciably
when $\textit{n}$ changes by more than an order of magnitude, inconsistent with
conventional superconductivity. | 1904.03121v2 |
2012-06-25 | A Study of Ni-Substitution Effects on Heavy-Fermion CeCu2Si2 - Similarities between Ni Substitution and High-Pressure Effects - | The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by
specific heat and electrical resistivity measurements. The specific heat
measurement has revealed that the enhanced quantum fluctuations around an
antiferromagnetic quantum critical point are markedly suppressed by Ni
substitution, and that the Fermi liquid state recovers in the Nirich region (x
> 0.12). The characteristic T-linear dependence of the resistivity has been
observed at approximately x ~ 0.10 together with a sign of superconductivity.
The variation of n in the form of rho - rho0 = aT^n against Tmax^1, at which
the resistivity peaks, coincides with the case of high-pressure experiments on
pure CeCu2Si2. The anomalous T-linear behavior appears to occur in the
crossover region from the Kondo regime to the valence fluctuation regime rather
than in the conventional antiferromagnetic quantum critical region. | 1206.5747v1 |
2015-07-08 | Future Large-Scale Memristive Device Crossbar Arrays: Limits Imposed by Sneak-Path Currents on Read Operations | Passive crossbar arrays based upon memristive devices, at crosspoints, hold
great promise for the future high-density and non-volatile memories. The most
significant challenge facing memristive device based crossbars today is the
problem of sneak-path currents. In this paper, we investigate a memristive
device with intrinsic rectification behavior to suppress the sneak-path
currents in crossbar arrays. The device model is implemented in Verilog-A
language and is simulated to match device characteristics readily available in
the literature. Then, we systematically evaluate the read operation performance
of large-scale crossbar arrays utilizing our proposed model in terms of read
margin and power consumption while considering different crossbar sizes,
interconnect resistance values, HRS/LRS (High Resistance State/Low Resistance
State) values, rectification ratios and different read-schemes. The outcomes of
this study are understanding the trade-offs among read margin, power
consumption, read-schemes and most importantly providing a guideline for
circuit designers to improve the performance of a memory based crossbar
structure. In addition, read operation performance comparison of the intrinsic
rectifying memristive device model with other memristive device models are
studied. | 1507.02077v1 |
2020-01-31 | Dynamo in weakly collisional nonmagnetized plasmas impeded by Landau damping of magnetic fields | We perform fully kinetic simulations of flows known to produce dynamo in
magnetohydrodynamics (MHD), considering scenarios with low Reynolds number and
high magnetic Prandtl number, relevant for galaxy cluster scale fluctuation
dynamos. We find that Landau damping on the electrons leads to a rapid decay of
magnetic perturbations, impeding the dynamo. This collisionless damping process
operates on spatial scales where electrons are nonmagnetized, reducing the
range of scales where the magnetic field grows in high magnetic Prandtl number
fluctuation dynamos. When electrons are not magnetized down to the resistive
scale, the magnetic energy spectrum is expected to be limited by the scale
corresponding to magnetic Landau damping or, if smaller, the electron
gyroradius scale, instead of the resistive scale. In simulations we thus
observe decaying magnetic fields where resistive MHD would predict a dynamo. | 2001.11929v2 |
2020-07-24 | Strange Metallic Transport in the Antiferromagnetic Regime of Electron Doped Cuprates | We report magnetoresistance and Hall Effect results for electron-doped films
of the high-temperature superconductor La$_{2-x}$Ce$_x$CuO$_4$ (LCCO) for
temperatures from 0.7 to 45 K and magnetic fields up to 65 T. For x = 0.12 and
0.13, just below the Fermi surface reconstruction (FSR), the normal state
in-plane resistivity exhibits a well-known upturn at low temperature. Our new
results show that this resistivity upturn is eliminated at high magnetic field
and the resistivity becomes linear-in-temperature from $\sim$ 40 K down to 0.7
K. The magnitude of the linear coefficient scales with Tc and doping, as found
previously [1,2] for dopings above the FSR. In addition, the normal state Hall
coefficient has an unconventional field dependence for temperatures below 50K.
This anomalous transport data presents a new challenge to theory and suggests
that the strange metal normal state is also present in the antiferromagnetic
regime. | 2007.12765v1 |
2020-08-26 | An 8-bit In Resistive Memory Computing Core with Regulated Passive Neuron and Bit Line Weight Mapping | The rapid development of Artificial Intelligence (AI) and Internet of Things
(IoT) increases the requirement for edge computing with low power and
relatively high processing speed devices. The Computing-In-Memory(CIM) schemes
based on emerging resistive Non-Volatile Memory(NVM) show great potential in
reducing the power consumption for AI computing. However, the device
inconsistency of the non-volatile memory may significantly degenerate the
performance of the neural network. In this paper, we propose a low power
Resistive RAM (RRAM) based CIM core to not only achieve high computing
efficiency but also greatly enhance the robustness by bit line regulator and
bit line weight mapping algorithm. The simulation results show that the power
consumption of our proposed 8-bit CIM core is only 3.61mW (256*256). The SFDR
and SNDR of the CIM core achieve 59.13 dB and 46.13 dB, respectively. The
proposed bit line weight mapping scheme improves the top-1 accuracy by 2.46%
and 3.47% for AlexNet and VGG16 on ImageNet Large Scale Visual Recognition
Competition 2012 (ILSVRC 2012) in 8-bit mode, respectively. | 2008.11669v1 |
2022-04-29 | Nonlocal thermoelectric resistance in vortical viscous transport | The pursuit for clearly identifiable signatures of viscous electron flow in
the solid state systems has been a paramount task in the search of the
hydrodynamic electron transport behavior. In this work, we investigate
theoretically the nonlocal electric and thermal resistances for the generic
non-Galilean-invariant electron liquids in the multiterminal Hall-bar devices
in the hydrodynamic regime. The role of the device inhomogeneity is carefully
addressed in the model of the disorder potential with the long-range
correlation radius. We obtain analytic expressions for the thermoelectric
resistances that are applicable in the full crossover regime from charge
neutrality to high electron density. We show that the vortical component of the
electron flow manifests in the thermal transport mode close to the charge
neutrality where vorticity is already suppressed by the intrinsic conductivity
in the electric current. This behavior can be tested by the high-resolution
thermal imaging probes. | 2204.14104v2 |
2022-11-04 | In-plane anisotropy of electrical transport in Y$_{0.85}$Tb$_{0.15}$Ba$_2$Cu$_3$O$_{7-x}$ films | We fabricate high-quality c-axis oriented epitaxial YBa$_2$Cu$_3$O$_{7-x}$
films with 15% of yttrium atoms replaced by terbium (YTBCO) and study their
electrical properties. The Tb substitution reduces the charge carrier density
resulting in increased resistivity and decreased critical current density
compared to the pure YBa$_2$Cu$_3$O$_{7-x}$ films. The electrical properties of
the YTBCO films show an in-plane anisotropy in both the superconducting and
normal state providing evidence for the twin-free film. Unexpectedly, the
resistive transition of the bridges also demonstrates the in-plane anisotropy
that can be explained within the framework of Tinkham's model of the resistive
transition and the Berezinskii-Kosterlitz-Thouless (BKT) model depending on the
sample parameters. We consider YTBCO films to be a promising platform for both
the fundamental research on the BKT transition in the cuprate superconductors
and for the fabrication of devices with high kinetic inductance. | 2211.02564v2 |
2023-02-23 | Anomalous Electronic Transport in High Mobility Corbino Rings | We report low-temperature electronic transport measurements performed in two
multi-terminal Corbino samples formed in GaAs/Al-GaAs two-dimensional electron
gases (2DEG) with both ultra-high electron mobility ($\gtrsim 20\times 10^6$
$cm^2/Vs)$ and with distinct electron density of $1.7$ and $3.6\times
10^{11}~cm^{-2}$. In both Corbino samples, a non-monotonic behavior is observed
in the temperature dependence of the resistance below 1~$K$. Surprisingly, a
sharp {\it decrease} in resistance is observed with {\it increasing}
temperature in the sample with lower electron density, whereas an opposite
behavior is observed in the sample with higher density. To investigate further,
transport measurements were performed in large van der Pauw samples having
identical heterostructures, and as expected they exhibit resistivity that is
monotonic with temperature. Finally, we discuss the results in terms of various
lengthscales leading to ballistic and hydrodynamic electronic transport, as
well as a possible Gurzhi effect. | 2302.12147v2 |
2024-01-01 | Debye temperature, electron-phonon coupling constant, and microcrystalline strain in highly-compressed La$_3$Ni$_2$O$_{7-δ}$ | Recently Sun et al (Nature 621, 493 (2023)) reported on the discovery of
high-temperature superconductivity in highly-compressed
La$_3$Ni$_2$O$_{7-\delta}$. In addition to ongoing studies of the phase
structural transition, pairing mechanism, and other properties/parameters in
this highly-pressurized nickelate, here explore a possibility for the
electron-phonon pairing mechanism in the La$_3$Ni$_2$O$_{7-\delta}$. To do
this, we analyzed experimental data on temperature dependent resistance,
$R(T)$, and extracted pressure dependent Debye temperature, $\Theta_D$, for the
$Fmmm$-phase (high-pressure phase). Derived ballpark value is $\Theta_D(P = 25
GPa) = 550$ $K$. We also estimated the electron-phonon coupling constant,
$\lambda_{e-ph}(P=22.4 GPa) = 1.75$, for La$_3$Ni$_2$O$_{7-\delta}$ sample
exhibited zero-resistance transition. Performed analysis of XRD data showed
that the crystal lattice strain, $\epsilon(P)$, is higher in the $Fmmm$-phase
in comparison with the $Amam$-phase (low-pressure phase). Based on performed
$\epsilon(P)$ analysis, we proposed possible reason for the presence/absence of
the zero-resistance state in La$_3$Ni$_2$O$_{7-\delta}$. | 2401.00804v2 |
2024-01-15 | Comprehensive Joint Modeling of First-Line Therapeutics in Non-Small Cell Lung Cancer | First-line antiproliferatives for non-small cell lung cancer (NSCLC) have a
relatively high failure rate due to high intrinsic resistance rates and
acquired resistance rates to therapy. 57% patients are diagnosed in late-stage
disease due to the tendency of early-stage NSCLC to be asymptomatic. For
patients first diagnosed with metastatic disease the 5-year survival rate is
approximately 5%. To help accelerate the development of novel therapeutics and
computer-based tools for optimizing individual therapy, we have collated data
from 11 different clinical trials in NSCLC and developed a semi-mechanistic,
clinical model of NSCLC growth and pharmacodynamics relative to the various
therapeutics represented in the study. In this study, we have produced
extremely precise estimates of clinical parameters fundamental to cancer
modeling such as the rate of acquired resistance to various pharmaceuticals,
the relationship between drug concentration and rate of cancer cell death, as
well as the fine temporal dynamics of anti-VEGF therapy. In the simulation sets
documented in this study, we have used the model to make meaningful
descriptions of efficacy gain in making bevacizumab-antiproliferative
combination therapy sequential, over a series of days, rather than concurrent. | 2401.07719v1 |
2018-11-09 | A Detailed Model of the Irish High Voltage Power Network for Simulating GICs | Constructing a power network model for geomagnetically induced current (GIC)
calculations requires information on the DC resistances of elements within a
network. This information is often not known, and power network models are
simplified as a result, with assumptions used for network element resistances.
Ireland's relatively small, isolated network presents an opportunity to model a
complete power network in detail, using as much real-world information as
possible. A complete model of the Irish 400, 275, 220 and 110 kV network was
made for GIC calculations, with detailed information on the number, type and DC
resistances of transformers. The measured grounding resistances at a number of
substations were also included in the model, which represents a considerable
improvement on previous models of the Irish power network for GIC calculations.
Sensitivity tests were performed to show how calculated GIC amplitudes are
affected by different aspects of the model. These tests investigated: (1) How
the orientation of a uniform electric field affects GICs. (2) The effect of
including/omitting lower-voltage elements of the power network. (3) How the
substation grounding resistances assumptions affected GIC values. It was found
that changing the grounding resistance value had a considerable effect on
calculated GICs at some substations, and no discernible effect at others.
Finally, five recent geomagnetic storm events were simulated in the network. It
was found that heavy rainfall prior to the 26-28 August 2015 geomagnetic storm
event may have had a measurable impact on measured GIC amplitudes at a 400/220
kV transformer ground. | 1811.04128v1 |
2020-03-09 | Understanding the reduction of the edge safety factor during hot VDEs and fast edge cooling events | In the present work a simple analytical approach is presented in order to
clarify the physics behind the edge current density behaviour of a hot plasma
entering in contact with a resistive conductor. When a plasma enters in contact
with a highly resistive wall, large current densities appear at the edge of the
plasma. The model shows that this edge current originates from the plasma
response, which attempts to conserve the poloidal magnetic flux ($\Psi$) when
the outer current is being lost. The loss of outer current is caused by the
high resistance of the outer current path compared to the plasma core
resistance. The resistance of the outer path may be given by plasma contact
with a very resistive structure or by a sudden decrease of the outer plasma
temperature (e.g. due to a partial thermal quench or due to a cold front
penetration caused by massive gas injection). For general plasma geometries and
current density profiles the model shows that given a small change of minor
radius ($\delta a$) the plasma current is conserved to first order ($\delta I_p
= 0 + \mathcal{O}(\delta a^2)$). This conservation comes from the fact that
total inductance remains constant ($\delta L = 0$) due to an exact compensation
of the change of external inductance with the change of internal inductance
($\delta L_\text{ext}+\delta L_\text{int} = 0$). As the total current is
conserved and the plasma volume is reduced, the edge safety factor drops
according to $q_a \propto a^2/I_p$. Finally the consistency of the resulting
analytical predictions is checked with the help of free-boundary MHD
simulations. | 2003.04064v1 |
2019-07-24 | GR-MHD disk winds and jets from black holes and resistive accretion disks | We perform GR-MHD simulations of outflow launching from thin accretion disks.
As in the non-relativistic case, resistivity is essential for the mass loading
of the disk wind. We implemented resistivity in the ideal GR-MHD code HARM3D,
extending previous works (Qian et al. 2017, 2018) for larger physical grids,
higher spatial resolution, and longer simulation time. We consider an initially
thin, resistive disk orbiting the black hole, threaded by a large-scale
magnetic flux. As the system evolves, outflows are launched from the black hole
magnetosphere and the disk surface. We mainly focus on disk outflows,
investigating their MHD structure and energy output in comparison with the
Poynting-dominated black hole jet. The disk wind encloses two components -- a
fast component dominated by the toroidal magnetic field and a slower component
dominated by the poloidal field. The disk wind transitions from sub to
super-Alfv\'enic speed, reaching velocities $\simeq 0.1c$. We provide parameter
studies varying spin parameter and resistivity level, and measure the
respective mass and energy fluxes. A higher spin strengthens the
$B_{\phi}$-dominated disk wind along the inner jet. We disentangle a critical
resistivity level that leads to a maximum matter and energy output for both,
resulting from the interplay between re-connection and diffusion, which in
combination govern the magnetic flux and the mass loading. For counter-rotating
black holes the outflow structure shows a magnetic field reversal. We estimate
the opacity of the inner-most accretion stream and the outflow structure around
it. This stream may be critically opaque for a lensed signal, while the axial
jet funnel remains optically thin. | 1907.10622v1 |
2017-05-23 | The influence of outflow and global magnetic field on the structure and spectrum of resistive CDAFs | We examine the effects of a global magnetic field and outflow on radiatively
inefficient accretion flow (RIAF) in the presence of magnetic resistivity. We
find a self-similar solutions for the height integrated equations that govern
the behavior of the flow. We use the mixing length mechanism for studying the
convection parameter. We adopt a radius dependent mass accretion rate as
$\dot{M}=\dot{M}_{out}{(\frac{r}{r_{out}})^{s}}$ with $s> 0$ to investigate the
influence of outflow on the structure of inflow where $s$ is a constant and
indication the effect of wind. Also, we have studied the radiation spectrum and
temperature of CDAFs. The thermal bermsstrahlung emission as a radiation
mechanism is taken into account for calculating the spectra emitted by the
CDAFs. The energy that powers bremsstrahlung emission at large radii is
provided by convective transport from small radii and viscous and resistivity
dissipation. Our results indicate that the disc rotates slower and accretes
faster, it becomes hotter and thicker for stronger wind. By increasing all
component of magnetic field, the disc rotates faster and accretes slower while
it becomes hotter and thicker. We show that the outflow parameter and all
component of magnetic field have the same effects on the luminosity of the
disc. We compare the dynamical structure of the disc in two different solutions
(with and without resistivity parameter). We show that only the radial infall
velocity and the surface density could changed by resistivity parameter
obviously. Increasing the effect of wind increases the disc's temperature and
luminosity of the disc. The effect of magnetic field is similar to the effect
of wind in the disc's temperature and luminosity of the disc, but the influence
of resistivity on the observational properties is not evident. | 1705.08099v1 |
2020-01-21 | Particle acceleration with anomalous pitch angle scattering in 3D separator reconnection | Understanding how the release of stored magnetic energy contributes to the
generation of non-thermal high energy particles during solar flares is an
important open problem in solar physics. Magnetic reconnection plays a
fundamental role in the energy release and conversion processes taking place
during flares. A common approach for investigating particle acceleration is to
use test particles in fields derived from magnetohydrodynamic (MHD) simulations
of reconnection. These MHD simulations use anomalous resistivities that are
much larger than the Spitzer resistivity based on Coulomb collisions. The
processes leading to enhanced resistivity should also affect the test
particles. We explore the link between resistivity and particle orbits building
on a previous study using a 2D MHD simulation of magnetic reconnection. This
paper extends the previous investigation to a 3D magnetic reconnection
configuration and to study the effect on test particle orbits. We carried out
orbit calculations using a 3D MHD simulation of separator reconnection. We use
the relativistic guiding centre approximation including stochastic pitch angle
scattering. The effects of varying the resistivity and the models for pitch
angle scattering on particle orbit trajectories, final positions, energy
spectra, final pitch angle distribution, and orbit duration are all studied in
detail. Pitch angle scattering widens collimated beams of orbit trajectories,
allowing orbits to access previously unaccessible field lines; this causes
final positions to spread to topological structures that were previously
inaccessible. Scattered orbit energy spectra are found to be predominantly
affected by the level of anomalous resistivity, with the pitch angle scattering
model only playing a role in isolated cases. Scattering is found to play a
crucial role in determining the pitch angle and orbit duration distributions. | 2001.07548v1 |
2021-07-27 | Resistance distance distribution in large sparse random graphs | We consider an Erdos-Renyi random graph consisting of N vertices connected by
randomly and independently drawing an edge between every pair of them with
probability c/N so that at N->infinity one obtains a graph of finite mean
degree c. In this regime, we study the distribution of resistance distances
between the vertices of this graph and develop an auxiliary field
representation for this quantity in the spirit of statistical field theory.
Using this representation, a saddle point evaluation of the resistance distance
distribution is possible at N->infinity in terms of an 1/c expansion. The
leading order of this expansion captures the results of numerical simulations
very well down to rather small values of c; for example, it recovers the
empirical distribution at c=4 or 6 with an overlap of around 90%. At large
values of c, the distribution tends to a Gaussian of mean 2/c and standard
deviation sqrt{2/c^3}. At small values of c, the distribution is skewed toward
larger values, as captured by our saddle point analysis, and many fine features
appear in addition to the main peak, including subleading peaks that can be
traced back to resistance distances between vertices of specific low degrees
and the rest of the graph. We develop a more refined saddle point scheme that
extracts the corresponding degree-differentiated resistance distance
distributions. We then use this approach to recover analytically the most
apparent of the subleading peaks that originates from vertices of degree 1.
Rather intuitively, this subleading peak turns out to be a copy of the main
peak, shifted by one unit of resistance distance and scaled down by the
probability for a vertex to have degree 1. We comment on a possible lack of
smoothness in the true N->infinity distribution suggested by the numerics. | 2107.12561v2 |
2002-01-30 | Activity in Very Cool Stars: Magnetic Dissipation in late-M and L Dwarf Atmospheres | Recent observations show that chromospheric activity in late-M and L dwarfs
is much lower than in the earlier M types, in spite of comparatively rapid
rotation. We investigate the possibility that this drop-off in activity results
from the very high electrical resistivities in the dense, cool and
predominantly neutral atmospheres of late-M and L dwarfs. We calculate magnetic
field diffusivities in the atmospheres of objects with effective temperatures
in the range 3000-1500 (mid-M to L), using the atmospheric structure models of
Allard and Hauschildt. We find that the combination of very low ionization
fraction and high density in these atmospheres results in very large
resistivities due to neutral-charged particle collisions, and efficient field
diffusion. The resistivities are found to increase with both decreasing optical
depth, and decreasing effective temperature. As a result, any existing magnetic
fields are increasingly decoupled from atmospheric motions as one moves from
mid-M to L; we quantify this through a simple Reynolds number calculation.
This, coupled with the difficulty in transporting magnetic stresses through the
highly resistive atmosphere, can account for the observed drop in activity from
mid-M to L, assuming activity in these objects is magnetically driven. We also
examine the issue of acoustic heating, and find that this appears inadequate to
explain the observed H-alpha fluxes in mid-M to L dwarfs. Consequently,
magnetic heating does seem to be the most viable mechanism for generating
activity in these objects. Finally, we speculate on a possible flare mechanism
in these cool dwarfs. | 0201518v1 |
1996-11-14 | Vortex Quantum Nucleation and Tunneling in Superconducting Thin Films: Role of Dissipation and Periodic Pinning | We investigate the phenomenon of decay of a supercurrent in a superconducting
thin film in the absence of an applied magnetic field. The resulting
zero-temperature resistance derives from two equally possible mechanisms: 1)
quantum tunneling of vortices from the edges of the sample; and 2) homogeneous
quantum nucleation of vortex-antivortex pairs in the bulk of the sample,
arising from the instability of the Magnus field's ``vacuum''. We study both
situations in the case where quantum dissipation dominates over the inertia of
the vortices. We find that the vortex tunneling and nucleation rates have a
very rapid dependence on the current density driven through the sample.
Accordingly, whilst normally the superconductor is essentially resistance-free,
for the high current densities that can be reached in high-$T_c$ films a
measurable resistance might develop. We show that edge-tunneling appears
favoured, but the presence of pinning centres and of thermal fluctuations leads
to an enhancement of the nucleation rates. In the case where a periodic pinning
potential is artificially introduced in the sample, we show that
current-oscillations will develop indicating an effect specific to the
nucleation mechanism where the vortex pair-production rate, thus the
resistance, becomes sensitive to the corrugation of the pinning substrate. In
all situations, we give estimates for the observability of the studied
phenomena. | 9611112v1 |
1997-12-19 | C-axis resistivity and high Tc superconductivity | Recently we had proposed a mechanism for the normal-state C-axis resistivity
of the high-T$_c$ layered cuprates that involved blocking of the
single-particle tunneling between the weakly coupled planes by strong
intra-planar electron-electron scattering. This gave a C-axis resistivity that
tracks the ab-plane T-linear resistivity, as observed in the high-temperature
limit. In this work this mechanism is examined further for its implication for
the ground-state energy and superconductivity of the layered cuprates. It is
now argued that, unlike the single-particle tunneling, the tunneling of a
boson-like pair between the planes prepared in the BCS-type coherent trial
state remains unblocked inasmuch as the latter is by construction an eigenstate
of the pair annihilation operator. The resulting pair-delocalization along the
C-axis offers energetically a comparative advantage to the paired-up trial
state, and, thus stabilizes superconductivity. In this scheme the strongly
correlated nature of the layered system enters only through the blocking
effect, namely that a given electron is effectively repeatedly monitored
(intra-planarly scattered) by the other electrons acting as an environment, on
a time-scale shorter than the inter-planar tunneling time. Possible
relationship to other inter-layer pairing mechanisms proposed by several
workers in the field is also briefly discussed. | 9712247v2 |
2000-07-03 | Electron-Phonon Coupling Origin of the resistivity in YNi_{2}B_{2}C Single Crystals | Resistivity measurements from 4.2 K up to 300 K were made on YNi_{2}B_{2}C
single crystals with Tc=15.5 K. The resulting rho(T) curve shows a perfect
Bloch-Grueneisen (BG) behavior, with a very small residual resistivity which
indicates the low impurity content and the high cristallographic quality of the
samples. The value lambda_{tr}=0.53 for the transport electron-phonon coupling
constant was obtained by using the high-temperature constant value of d(rho)/dT
and the plasma frequency reported in literature. The BG expression for the
phononic part of the resistivity rho_{ph}(T) was then used to fit the data in
the whole temperature range, by approximating alpha^{2}_{tr}F(Omega) with the
experimental phonon spectral density G(Omega) multiplied by a two-step
weighting function to be determined by the fit. The resulting fitting curve
perfectly agrees with the experimental points. We also solved the real-axis
Eliashberg equations in both s- and d-wave symmetries under the approximation
alpha^{2}F(Omega)= alpha^{2}_{tr}F(Omega). We found that the value of
lambda_{tr} here determined in single-band approximation is quite compatible
with Tc and the gap Delta experimentally observed. Finally, we calculated the
normalized tunneling conductance, whose comparison with break-junction tunnel
data gives indication of the possible s-wave symmetry for the order parameter
in YNi_{2}B_{2}C. | 0007033v1 |
2010-12-10 | High pressure study of transport properties in Co$_{1/3}$NbS$_2$ | This is the first study of the effect of pressure on transition metal
dichalcogenides intercalated by atoms that order magnetically.
Co$_{1/3}$NbS$_2$ is a layered system where the intercalated Co atoms order
antiferromagnetically at T$_N$ = 26 K at ambient pressure. We have conducted a
detailed study of dc-resistivity ($\rho$), thermoelectric power (S) and thermal
conductivity ($\kappa$). We found that at ambient pressure the magnetic
transition corresponds to a well pronounced peak in dS/dT, as well as to a kink
in the dc-resistivity. The effect of ordering on the thermal conductivity is
rather small but, surprisingly, more pronounced in the lattice contribution
than in the electronic contribution to $\kappa$. Under pressure, the
resistivity increases in the high temperature range, contrary to all previous
measurements in other layered transition metal dichalcogenides (TMD). In the
low temperature range, the strong dependences of thermopower and resistivity on
pressure are observed below TN, which, in turn, also depends on pressure at
rate of dT$_N$/dp $\approx$ -1 K/kbar. Several possible microscopic
explanations of the reduction of the ordering temperature and the evolution of
the transport properties with pressure are discussed. | 1012.2408v1 |
2011-09-14 | Evidence for a fractional quantum Hall state with anisotropic longitudinal transport | At high magnetic fields, where the Fermi level lies in the N=0 lowest Landau
level (LL), a clean two-dimensional electron system (2DES) exhibits numerous
incompressible liquid phases which display the fractional quantized Hall effect
(FQHE) (Das Sarma and Pinczuk, 1997). These liquid phases do not break
rotational symmetry, exhibiting resistivities which are isotropic in the plane.
In contrast, at lower fields, when the Fermi level lies in the $N\ge2$ third
and several higher LLs, the 2DES displays a distinctly different class of
collective states. In particular, near half filling of these high LLs the 2DES
exhibits a strongly anisotropic longitudinal resistance at low temperatures
(Lilly et al., 1999; Du et al., 1999). These "stripe" phases, which do not
exhibit the quantized Hall effect, resemble nematic liquid crystals, possessing
broken rotational symmetry and orientational order (Koulakov et al., 1996;
Fogler et al., 1996; Moessner and Chalker, 1996; Fradkin and Kivelson, 1999;
Fradkin et al, 2010). Here we report a surprising new observation: An
electronic configuration in the N=1 second LL whose resistivity tensor
simultaneously displays a robust fractionally quantized Hall plateau and a
strongly anisotropic longitudinal resistance resembling that of the stripe
phases. | 1109.3219v3 |
2011-10-18 | A numerical model of resistive generation of intergalactic magnetic field at cosmic dawn | Miniati and Bell (2011) proposed a mechanism for the generation of magnetic
seeds that is based the finite resistivity of the low temperature IGM in the
high redshift universe. In this model, cosmic-ray protons generated by the
first generation of galaxies, escape into the intergalactic medium carrying an
electric current that induces return currents, $j_t$, and associated electric
fields, $\vec E=\eta\vec j_t$ there. Because the resistivity, $\eta$, depends
on the IGM temperature, which is highly inhomogeneous due to adiabatic
contraction and shocks produced by structure formation, a non-vanishing curl of
the electric field exists which sustains the growth of magnetic field. In this
contribution we have developed an approximate numerical model for this process
by implementing the source terms of the resistive mechanism in the cosmological
code CHARM. Our numerical estimates substantiate the earlier analysis in
Miniati and Bell (2011) which found magnetic seeds between 10$^{-18}$ and
10$^{-16}$ Gauss throughout cosmic space at redshift z~6, consistent with
conservative estimates of magnetic fields in voids at z~0 from recent gamma-ray
experiments. | 1110.4115v1 |
2017-02-18 | Soft-proton exchange on Magnesium-oxide-doped substrates a route toward efficient and power-resistant nonlinear converters | Despite its attractive features, Congruent-melted Lithium Niobate (CLN)
suffers from Photo-Refractive Damage (PRD). This light-induced refractive-index
change hampers the use of CLN when high-power densities are in play, a typical
regime in integrated optics. The resistance to PRD can be largely improved by
doping the lithium-niobate substrates with magnesium oxide. However, the
fabrication of waveguides on MgO-doped substrates is not as effective as for
CLN: either the resistance to PRD is strongly reduced by the waveguide
fabrication process (as it happens in Ti-indiffused waveguides) or the
nonlinear conversion efficiency is lowered (as it occurs in annealed-proton
exchange). Here we fabricate, for the first time, waveguides starting from
MgO-doped substrates using the Soft-Proton Exchange (SPE) technique and we show
that this third way represents a promising alternative. We demonstrate that SPE
allows to produce refractive-index profiles almost identical to those produced
on CLN without reducing the nonlinearity in the substrate. We also prove that
the SPE does not affect substantially the resistance to PRD. Since the
fabrication recipe is identical between CLN and MgO-doped substrates, we
believe that SPE might outperform standard techniques to fabricate robust and
efficient waveguides for high-intensity-beam confinement. | 1702.05590v1 |
2019-04-11 | Novel Resistive-Plate WELL sampling element for (S)DHCAL | Digital and Semi-Digital Hadronic Calorimeters (S)DHCAL were suggested for
future Colliders as part of the particle-flow concept. Though studied mostly
with RPC-based techniques, investigations have shown that MPGD-based sampling
elements could outperform. An attractive, industry-produced, robust,
particle-tracking detector for large-area coverage, e.g. in (S)DHCAL, could be
the novel single-stage Resistive Plate WELL (RPWELL). It is a single-sided
THGEM coupled to the segmented readout electrode through a sheet of large bulk
resistivity. We summarize here the preliminary test-beam results obtained with
6.5 mm thick (incl. electronics) {$48 \times 48\,\mathrm{cm^2}$}~RPWELL
detectors. Two configurations are considered: a standalone RPWELL detector
studied with 150 GeV muons and high-rate pions beams and RPWELL sampling
element investigated within a small-(S)DHCAL prototype consisting of 7
resistive MICROMEGAS sampling elements followed by 5 RPWELL ones. The sampling
elements were equipped with a Semi-Digital readout electronics based on the
MICROROC chip. | 1904.05545v2 |
2020-05-22 | Accelerating Antimicrobial Discovery with Controllable Deep Generative Models and Molecular Dynamics | De novo therapeutic design is challenged by a vast chemical repertoire and
multiple constraints, e.g., high broad-spectrum potency and low toxicity. We
propose CLaSS (Controlled Latent attribute Space Sampling) - an efficient
computational method for attribute-controlled generation of molecules, which
leverages guidance from classifiers trained on an informative latent space of
molecules modeled using a deep generative autoencoder. We screen the generated
molecules for additional key attributes by using deep learning classifiers in
conjunction with novel features derived from atomistic simulations. The
proposed approach is demonstrated for designing non-toxic antimicrobial
peptides (AMPs) with strong broad-spectrum potency, which are emerging drug
candidates for tackling antibiotic resistance. Synthesis and testing of only
twenty designed sequences identified two novel and minimalist AMPs with high
potency against diverse Gram-positive and Gram-negative pathogens, including
one multidrug-resistant and one antibiotic-resistant K. pneumoniae, via
membrane pore formation. Both antimicrobials exhibit low in vitro and in vivo
toxicity and mitigate the onset of drug resistance. The proposed approach thus
presents a viable path for faster and efficient discovery of potent and
selective broad-spectrum antimicrobials. | 2005.11248v2 |
2020-10-22 | Projecting the optimal control strategy on invasive plants combining effects of herbivores and native plants resistance | Understanding how to limit biological invasion is critical, especially in the
context of accelerating anthropogenic ecological changes. Although biological
invasion success could be explained by the lack of natural enemies in new
regions, recent studies have revealed that resident herbivores often do have a
substantial effect on both native and invasive plants. Very few studies have
included consideration of native plant resistance while estimating methods of
controlling invasion; hence, it is unclear to what extent the interactive
effects of controlling approaches and native plants' resistance could slow down
or even inhibit biological invasion. We developed a spatial modeling framework,
using a paired logistic equation model, with considerations of the dispersal
processes, to capture the dynamics change of native and invasive plants under
various strategies of control. We found that when biocontrol agents could have
a strong effect on invasive plant, that could almost completely limit the
invasion, together with a high native plant resistance. However, a high
application frequency is needed make an efficient impact, whereas, a low
frequency treatment leads to nearly the same outcome as the no treatment case.
Lastly, we showed that evenly controlling a larger area with a weaker effect
still lead to a better outcome than focusing on small patches with a stronger
effect. Overall, this study has some management implications, such as how to
determine the optimal allocation strategy. | 2010.14944v1 |
2021-10-14 | Mitigation of parasitic losses in the quadrupole resonator enabling direct measurements of low residual resistances of SRF samples | The quadrupole resonator (QPR) is a dedicated sample-test cavity for the RF
characterization of superconducting samples in a wide temperature, RF field and
frequency range. Its main purpose are high resolution measurements of the
surface resistance with direct access to the residual resistance thanks to the
low frequency of the first operating quadrupole mode. Besides the well-known
high resolution of the QPR, a bias of measurement data towards higher values
has been observed, especially at higher harmonic quadrupole modes. Numerical
studies show that this can be explained by parasitic RF losses on the adapter
flange used to mount samples into the QPR. Coating several micrometer of
niobium on those surfaces of the stainless steel flange that are exposed to the
RF fields significantly reduced this bias, enabling a direct measurement of a
residual resistance smaller than 5 n$\Omega$ at 2 K and 413 MHz. A constant
correction based on simulations was not feasible due to deviations from one
measurement to another. However, this issue is resolved given these new
results. | 2110.07236v2 |
2022-01-27 | On the Mitigation of Read Disturbances in Neuromorphic Inference Hardware | Non-Volatile Memory (NVM) cells are used in neuromorphic hardware to store
model parameters, which are programmed as resistance states. NVMs suffer from
the read disturb issue, where the programmed resistance state drifts upon
repeated access of a cell during inference. Resistance drifts can lower the
inference accuracy. To address this, it is necessary to periodically reprogram
model parameters (a high overhead operation). We study read disturb failures of
an NVM cell. Our analysis show both a strong dependency on model
characteristics such as synaptic activation and criticality, and on the voltage
used to read resistance states during inference. We propose a system software
framework to incorporate such dependencies in programming model parameters on
NVM cells of a neuromorphic hardware. Our framework consists of a convex
optimization formulation which aims to implement synaptic weights that have
more activations and are critical, i.e., those that have high impact on
accuracy on NVM cells that are exposed to lower voltages during inference. In
this way, we increase the time interval between two consecutive reprogramming
of model parameters. We evaluate our system software with many emerging
inference models on a neuromorphic hardware simulator and show a significant
reduction in the system overhead. | 2201.11527v1 |
2024-03-20 | Picosecond Femtojoule Resistive Switching in Nanoscale VO$_{2}$ Memristors | Beyond-Moore computing technologies are expected to provide a sustainable
alternative to the von Neumann approach not only due to their down-scaling
potential but also via exploiting device-level functional complexity at the
lowest possible energy consumption. The dynamics of the Mott transition in
correlated electron oxides, such as vanadium dioxide, has been identified as a
rich and reliable source of such functional complexity. However, its full
potential in high-speed and low-power operation has been largely unexplored. We
fabricated nanoscale VO$_{2}$ devices embedded in a broad-band test circuit to
study the speed and energy limitations of their resistive switching operation.
Our picosecond time-resolution, real-time resistive switching experiments and
numerical simulations demonstrate that tunable low-resistance states can be set
by the application of 20~ps long, $<$1.7~V amplitude voltage pulses at 15~ps
incubation times and switching energies starting from a few femtojoule.
Moreover, we demonstrate that at nanometer-scale device sizes not only the
electric field induced insulator-to-metal transition, but also the thermal
conduction limited metal-to-insulator transition can take place at timescales
of 100's of picoseconds. These orders of magnitude breakthroughs open the route
to the design of high-speed and low-power dynamical circuits for a plethora of
neuromorphic computing applications from pattern recognition to numerical
optimization. | 2403.13530v1 |
2024-05-21 | A lightweight PUF-based authentication protocol | Lightweight authentication is essential for resource-constrained
Internet-of-Things (IoT). Implementable with low resource and operable with low
power, Physical Unclonable Functions (PUFs) have the potential as hardware
primitives for implementing lightweight authentication protocols. The arbiter
PUF (APUF) is probably the most lightweight strong PUF capable of generating
exponentially many challenge-response pairs (CRPs), a desirable property for
authentication protocols, but APUF is severely weak against modeling attacks.
Efforts on PUF design have led to many PUFs of higher resistance to modeling
attacks and also higher area overhead. There are also substantial efforts on
protocol development, some leverage PUFs' strength in fighting modeling
attacks, and some others employ carefully designed protocol techniques to
obfuscate either the challenges or the responses with modest increase of area
overhead for some or increased operations for some others. To attain both low
resource footprint and high modeling attack resistance, in this paper we
propose a co-design of PUF and protocol, where the PUF consists of an APUF and
a zero-transistor interface that obfuscates the true challenge bits fed to the
PUF. The obfuscated PUF possesses rigorously proven potential and
experimentally supported performance against modeling attacks when a condition
is met, and the protocol provides the condition required by the PUF and
leverages the PUF's modeling resistance to arrive at low resource overhead and
high operational simplicity, enabling lightweight authentications while
resisting modeling attacks. | 2405.13146v1 |
2008-04-14 | Phase Diagram and Quantum Critical Point in Newly Discovered Superconductors: SmO_{1-x}F_xFeAs | The magnetic fluctuations associated with a quantum critical point (QCP) are
widely believed to cause the non-Fermi liquid behaviors and unconventional
superconductivities, for example, in heavy fermion systems and high temperature
cuprate superconductors. Recently, superconductivity has been discovered in
iron-based layered compound $LaO_{1-x}F_xFeAs$ with $T_c$=26 K\cite{yoichi},
and it competes with spin-density-wave (SDW) order\cite{dong}. Neutron
diffraction shows a long-rang SDW-type antiferromagnetic (AF) order at $\sim
134$ K in LaOFeAs\cite{cruz,mcguire}. Therefore, a possible QCP and its role in
this system are of great interests. Here we report the detailed phase diagram
and anomalous transport properties of the new high-Tc superconductors
$SmO_{1-x}F_xFeAs$ discovered by us\cite{chenxh}. It is found that
superconductivity emerges at $x\sim$0.07, and optimal doping takes place in the
$x\sim$0.20 sample with highest $T_c \sim $54 K. While $T_c$ increases
monotonically with doping, the SDW order is rapidly suppressed, suggesting a
QCP around $x \sim$0.14. As manifestations, a linear temperature dependence of
the resistivity shows up at high temperatures in the $x<0.14$ regime, but at
low temperatures just above $T_c$ in the $x>0.14$ regime; a drop in carrier
density evidenced by a pronounced rise in Hall coefficient are observed, which
mimic the high-$T_c$ cuprates. The simultaneous occurrence of order, carrier
density change and criticality makes a compelling case for a quantum critical
point in this system. | 0804.2105v3 |
2008-07-07 | Magnetoresistance and collective Coulomb blockade in super-lattices of ferromagnetic CoFe nanoparticles | We report on transport properties of millimetric super-lattices of CoFe
nanoparticles surrounded by organic ligands. R(T)s follow R(T) =
R_0.exp(T/T_0)^0.5 with T_0 ranging from 13 to 256 K. At low temperature I(V)s
follow I=K[(V-V_T)/V_T]^ksi with ksi ranging 3.5 to 5.2. I(V) superpose on a
universal curve when shifted by a voltage proportional to the temperature.
Between 1.8 and 10 K a high-field magnetoresistance with large amplitude and a
strong voltage-dependence is observed. Its amplitude only depends on the
magnetic field/temperature ratio. Its origin is attributed to the presence of
paramagnetic states present at the surface or between the nanoparticles. Below
1.8 K, this high-field magnetoresistance abruptly disappears and inverse
tunnelling magnetoresistance is observed, the amplitude of which does not
exceed 1%. At this low temperature, some samples display in their I(V)
characteristics abrupt and hysteretic transitions between the Coulomb blockade
regime and the conductive regime. The increase of the current during these
transitions can be as high as a factor 30. The electrical noise increases when
the sample is near the transition. The application of a magnetic field
decreases the voltage at which these transitions occur so magnetic-field
induced transitions are also observed. Depending on the applied voltage, the
temperature and the amplitude of the magnetic field, the magnetic-field induced
transitions are either reversible or irreversible. These abrupt and hysteretic
transitions are also observed in resistance-temperature measurements. They
could be the soliton avalanches predicted by Sverdlov et al. [Phys. Rev. B 64,
041302 (R), 2001] or could also be interpreted as a true phase transition
between a Coulomb glass phase to a liquid phase of electrons. | 0807.1060v3 |
2015-09-29 | Simulation of radiation-induced defects | Mainly due to their outstanding performance the position sensitive silicon
detectors are widely used in the tracking systems of High Energy Physics
experiments such as the ALICE, ATLAS, CMS and LHCb at LHC, the world's largest
particle physics accelerator at CERN, Geneva. The foreseen upgrade of the LHC
to its high luminosity (HL) phase (HL-LHC scheduled for 2023), will enable the
use of maximal physics potential of the facility. After 10 years of operation
the expected fluence will expose the tracking systems at HL-LHC to a radiation
environment that is beyond the capacity of the present system design. Thus, for
the required upgrade of the all-silicon central trackers extensive measurements
and simulation studies for silicon sensors of different designs and materials
with sufficient radiation tolerance have been initiated within the RD50
Collaboration.
Supplementing measurements, simulations are in vital role for e.g. device
structure optimization or predicting the electric fields and trapping in the
silicon sensors. The main objective of the device simulations in the RD50
Collaboration is to develop an approach to model and predict the performance of
the irradiated silicon detectors using professional software. The first
successfully developed quantitative models for radiation damage, based on two
effective midgap levels, are able to reproduce the experimentally observed
detector characteristics like leakage current, full depletion voltage and
charge collection efficiency (CCE). Recent implementations of additional traps
at the SiO$_2$/Si interface or close to it have expanded the scope of the
experimentally agreeing simulations to such surface properties as the
interstrip resistance and capacitance, and the position dependency of CCE for
strip sensors irradiated up to $\sim$$1.5\times10^{15}$
n$_{\textrm{eq}}\textrm{cm}^{-2}$. | 1509.08657v1 |
2015-10-14 | Elastic Composite, Reinforced Lightweight Concrete as a Type of Resilient Composite Systems | . A kind of "Elastic Composite, Reinforced Lightweight Concrete (ECRLC)" with
the mentioned specifics is a type of "Resilient Composite Systems (RCS)" in
which, contrary to the basic geometrical assumption of flexure theory in Solid
Mechanics, "the strain changes in the beam height during bending" is typically
"Non-linear". . Through employing this integrated structure, with significant
high strain capability and modulus of resilience in bending, we could
constructively achieve high bearing capacities in beams with secure fracture
pattern, in less weight. . Due to the system particulars and its behavior in
bending, the usual calculation of the equilibrium steel amount to attain the
low-steel bending sections with secure fracture pattern in the beams and its
related limitations do not become propounded. Thereby, the strategic deadlock
of high possibility of brittle fracture pattern in the bending elements made of
the usual reinforced lightweight concretes, especially about the low-thickness
bending elements as slabs, is being unlocked. . This simple, applied technology
and the related components and systems can have several applications in "the
Road and Building Industries" too. . Regarding the "strategic importance of the
Lightweight & Integrated Construction in practical increase of the resistance
and safety against earthquake" and considering the appropriate behavior of this
resilient structure against the dynamic loads, shakes, impacts and shocks and
capability of making some lightweight and insulating, non-brittle, reinforced
sandwich panels and pieces, this system and its components could be also useful
in "seismic areas". . This system could be also employed in constructing the
vibration and impact absorber bearing pieces and slabs, which can be used in
"the Railroad & Subway Structures" too. . Here, the "RCS" and "ECRLC" (as a
type of RCS) have been concisely presented. | 1510.03933v1 |
2018-01-26 | Enhanced moments of Eu in single crystals of the metallic helical antiferromagnet EuCo{2-y}As2 | The compound EuCo{2-y}As2 with the tetragonal ThCr2Si2 structure is known to
contain Eu{+2} ions with spin S = 7/2 that order below a temperature TN = 47 K
into an antiferromagnetic (AFM) proper helical structure with the ordered
moments aligned in the tetragonal ab plane, perpendicular to the helix axis
along the c axis, with no contribution from the Co atoms. Here we carry out a
detailed investigation of the properties of single crystals. Enhanced ordered
and effective moments of the Eu spins are found in most of our crystals.
Electronic structure calculations indicate that the enhanced moments arise from
polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical
resistivity measurements indicate metallic behavior. The low-field in-plane
magnetic susceptibilities chi{ab}(T < TN) for several crystals are reported
that are fitted well by unified molecular field theory (MFT), and the Eu-Eu
exchange interactions Jij are extracted from the fits. High-field magnetization
M data for magnetic fields H||ab reveal what appears to be a first-order
spin-flop transition followed at higher field by a second-order metamagnetic
transition of unknown origin, and then by another second-order transition to
the paramagnetic (PM) state. For H||c, the magnetization shows only a
second-order transition from the canted AFM to the PM state, as expected. The
critical fields for the AFM to PM transition are in approximate agreement with
the predictions of MFT. Heat capacity Cp measurements in zero and high H are
reported. Phase diagrams for H||c and H||ab versus T are constructed from the
high-field M(H,T) and Cp(H,T) measurements. The magnetic part Cmag(T, H = 0) of
Cp(T, H = 0) is extracted and is fitted rather well below TN by MFT, although
dynamic short-range AFM order is apparent in Cmag(T) up to about 70 K, where
the molar entropy attains its high-T limit of R ln8. | 1801.08941v1 |
2018-09-10 | High-performance InSe Transistors with Ohmic Contact Enabled by Nonrectifying-barrier-type Indium Electrodes | The electrical contact to two-dimensional (2D)-semiconductor materials are
decisive to the electronic performance of 2D-semiconductor field-effect devices
(FEDs). The presence of a Schottky barrier often leads to a large contact
resistance, which seriously limits the channel conductance and carrier mobility
measured in a two-terminal geometry. In contrast, ohmic contact is desirable
and can be achieved by the presence of a nonrectifying or tunneling barrier.
Here, we demonstrate that an nonrectifying barrier can be realized by
contacting indium (In), a low work function metal, with layered InSe because of
a favorable band alignment at the In-InSe interface. The nonrectifying barrier
is manifested by ohmic contact behavior at T=2 K and a low barrier height,
{\Phi}$_B$=50 meV. This ohmic contact enables demonstration of an ON-current as
large as 410 {\mu}A/{\mu}m, which is among the highest values achieved in FEDs
based on layered semiconductors. A high electron mobility of 3,700 and 1,000
cm$^2$/Vs is achieved with the two-terminal In-InSe FEDs at T=2 K and room
temperature, respectively, which can be attributed to enhanced quality of both
conduction channel and the contacts. The improvement in the contact quality is
further proven by an X-ray photoelectron spectroscopy study, which suggests
that a reduction effect occurs at the In-InSe interface. The demonstration of
high-performance In-InSe FEDs indicates a viable interface engineering method
for next-generation, 2D-semiconductor-based electronics. | 1809.03181v1 |
2018-11-19 | Characterisation of AMS H35 HV-CMOS monolithic active pixel sensor prototypes for HEP applications | Monolithic active pixel sensors produced in High Voltage CMOS (HV-CMOS)
technology are being considered for High Energy Physics applications due to the
ease of production and the reduced costs. Such technology is especially
appealing when large areas to be covered and material budget are concerned.
This is the case of the outermost pixel layers of the future ATLAS tracking
detector for the HL-LHC. For experiments at hadron colliders, radiation
hardness is a key requirement which is not fulfilled by standard CMOS sensor
designs that collect charge by diffusion. This issue has been addressed by
depleted active pixel sensors in which electronics are embedded into a large
deep implantation ensuring uniform charge collection by drift. Very first small
prototypes of hybrid depleted active pixel sensors have already shown a
radiation hardness compatible with the ATLAS requirements. Nevertheless, to
compete with the present hybrid solutions a further reduction in costs
achievable by a fully monolithic design is desirable. The H35DEMO is a large
electrode full reticle demonstrator chip produced in AMS 350 nm HV-CMOS
technology by the collaboration of Karlsruher Institut f\"ur Technologie (KIT),
Institut de F\'isica d'Altes Energies (IFAE), University of Liverpool and
University of Geneva. It includes two large monolithic pixel matrices which can
be operated standalone. One of these two matrices has been characterised at
beam test before and after irradiation with protons and neutrons. Results
demonstrated the feasibility of producing radiation hard large area fully
monolithic pixel sensors in HV-CMOS technology. H35DEMO chips with a substrate
resistivity of 200$\Omega$ cm irradiated with neutrons showed a radiation
hardness up to a fluence of $10^{15}$n$_{eq}$cm$^{-2}$ with a hit efficiency of
about 99% and a noise occupancy lower than $10^{-6}$ hits in a LHC bunch
crossing of 25ns at 150V. | 1811.07817v3 |
2019-05-10 | Vacuum electrical breakdown conditioning study in a parallel plate electrode pulsed DC system | Conditioning of a metal structure in a high-voltage system is the progressive
development of resistance to vacuum arcing over the operational life of the
system. This is, for instance, seen during the initial operation of radio
frequency (rf) cavities in particle accelerators. It is a relevant topic for
any technology where breakdown limits performance, and where conditioning
continues for a significant duration of system runtime. Projected future linear
accelerators require structures with accelerating gradients of up to 100 MV/m.
Currently, this performance level is only achievable after a multi-month
conditioning period. In this work, a pulsed DC system applying voltage pulses
over parallel disk electrodes was used to study the conditioning process, with
the objective of obtaining insight into its underlying mechanics, and
ultimately, to find ways to shorten the conditioning process. Two kinds of
copper electrodes were tested: As-prepared machine-turned electrodes ("hard"
copper), and electrodes that additionally had been subjected to high
temperature treatments ("soft" copper). The conditioning behaviour of the soft
electrodes was found to be similar to that of comparably treated accelerating
structures, indicating a similar conditioning process. The hard electrodes
reached the same ultimate performance as the soft electrodes much faster, with
a difference of more than an order of magnitude in the number of applied
voltage pulses. Two distinctly different distributions of breakdown locations
were observed on the two types of electrodes. Considered together, our results
support the crystal structure dislocation theory of breakdown, and suggest that
the conditioning of copper in high field systems such as rf accelerating
structures is dominated by material hardening. | 1905.03996v1 |
2019-07-18 | High-performance silicon-graphene hybrid plasmonic waveguide photodetectors beyond 1.55 μm | A fast silicon-graphene hybrid plasmonic waveguide photodetectors beyond 1.55
{\mu}m is proposed and realized by introducing an ultra-thin wide
silicon-on-insulator ridge core region with a narrow metal cap. With this novel
design, the light absorption in graphene is enhanced while the metal absorption
loss is reduced simultaneously, which helps greatly improve the responsivity as
well as shorten the absorption region for achieving fast responses.
Furthermore, metal-graphene-metal sandwiched electrodes are introduced to
reduce the metal-graphene contact resistance, which is also helpful for
improving the response speed. When the photodetector operates at 2 {\mu}m, the
measured 3dB-bandwidth is >20 GHz (which is limited by the experimental setup)
while the 3dB-bandwith calculated from the equivalent circuit with the
parameters extracted from the measured S11 is as high as ~100 GHz. To the best
of our knowledge, it is the first time to report the waveguide photodetector at
2 {\mu}m with a 3dB-bandwidth over 20 GHz. Besides, the present photodetectors
also work very well at 1.55 {\mu}m. The measured responsivity is about 0.4 A/W
under a bias voltage of -0.3 V for an optical power of 0.16 mW, while the
measured 3dB-bandwidth is over 40 GHz (limited by the test setup) and the 3
dB-bandwidth estimated from the equivalent circuit is also as high as ~100 GHz,
which is one of the best results reported for silicon-graphene photodetectors
at 1.55 {\mu}m. | 1907.12498v1 |
2020-07-01 | Predicting Oxidation and Spin States by High-Dimensional Neural Networks: Applications to Lithium Manganese Oxide Spinels | Lithium ion batteries often contain transition metal oxides like
Li$_{x}$Mn$_2$O$_4$ ($0\leq x\leq2$). Depending on the Li content different
ratios of Mn$^\text{III}$ to Mn$^\text{IV}$ ions are present. In combination
with electron hopping the Jahn-Teller distortions of the Mn$^\text{III}$O$_6$
octahedra can give rise to complex phenomena like structural transitions and
conductance. While for small model systems oxidation and spin states can be
determined using density functional theory (DFT), the investigation of
dynamical phenomena by DFT is too demanding. Previously, we have shown that a
high-dimensional neural network potential can extend molecular dynamics (MD)
simulations of Li$_{x}$Mn$_2$O$_4$ to nanosecond time scales, but these
simulations did not provide information about the electronic structure. Here we
extend the use of neural networks to the prediction of atomic oxidation and
spin states. The resulting high-dimensional neural network is able to predict
the spins of the Mn ions with an error of only 0.03 $\hbar$. We find that the
Mn e$_\text{g}$ electrons are correctly conserved and that the number of
Jahn-Teller distorted Mn$^\text{III}$O$_6$ octahedra is predicted precisely for
different Li loadings. A charge ordering transition is observed between 280 and
300 K, which matches resistivity measurements. Moreover, the activation energy
of the electron hopping conduction above the phase transition is predicted to
be 0.18 eV deviating only 0.02 eV from experiment. This work demonstrates that
machine learning is able to provide an accurate representation of both, the
geometric and the electronic structure dynamics of Li$_x$Mn$_2$O$_4$, on time
and length scales that are not accessible by ab initio MD. | 2007.00335v2 |
2022-08-19 | Superconductivity of Cs$_3$C$_{60}$ at atmosphere pressure | Pressure as a clean and efficient tool can bring about unexpected
extraordinary physical and chemical properties of matters. The recent
discoveries of superconductivity at nearly room temperature in hydrides
highlight the power of pressure in this aspect. Capturing such Tc
superconductivity at atmosphere pressure for the technological applications is
highly desired. The large-scale growth of diamond through the chemical vapor
deposition away from the usual high-pressure and high-temperature conditions
fuels such a hope. Similar to hydrides, Cs-doped C$_{60}$ was also found to
exhibit superconductivity by the application of pressure with a comparable Tc
of 40 K as MgB$_2$. Here, we report the successful realization of
superconductivity in Cs-doped C$_{60}$ at atmosphere pressure. The phase is
characterized to have the primitive cubic structure in the space group of Pa-3
with the stoichiometry of Cs$_3$C$_{60}$. The superconductivity is evidenced
from the observations of both the Meissner effect and zero-resistance state.
Although the pressure effects on superconductivity are different for the newly
discovered Cs$_{3}$C$_{60}$ compared to the known two phases with fcc and A15
structure, the evolution of Tc with the volume for all these superconductors
follows the same universal trend, suggesting the same pairing mechanism of the
superconductivity. Such a trend together with the nearly linear Tc vs the
lattice constant in the structure with smaller unit-cell volumes and the
neighbouring antiferromagnetic state in the structure with larger unit-cell
volumes invites the electron-phonon coupling and the electron correlations
together to account for the superconductivity in Cs$_3$C$_{60}$. The present
results and findings suggest a new route to capturing the superconductivity
which takes place at high pressures to atmosphere pressure environment. | 2208.09429v1 |
2022-11-02 | High Temperature Ferromagnetism in Cr$_{1+x}$Pt$_{5-x}$P | We present the growth and basic magnetic and transport properties of
Cr$_{1+x}$Pt$_{5-x}$P. We show that single crystals can readily be grown from a
high-temperature solution created by adding dilute quantities of Cr to Pt-P
based melts. Like other 1-5-1 compounds, Cr$_{1+x}$Pt$_{5-x}$P adopts a
tetragonal P4/mmm structure composed face-sharing CrPt$_3$ like slabs that are
broken up along the c-axis by sheets of P atoms. EDS and X-ray diffraction
measurements both suggest Cr$_{1+x}$Pt$_{5-x}$P has mixed occupancy between Cr
and Pt atoms, similar to what is found in the closely related compound
CrPt$_3$, giving real compositions of Cr$_{1.5}$Pt$_{4.5}$P (x = 0.5). We
report that Cr$_{1.5}$Pt$_{4.5}$P orders ferromagnetically at T$_C$ = 464.5 K
with a saturated moment of $\approx$ 2.1 $\mu_{\textit{B}}$/Cr at 1.8 K. Likely
owing to the strong spin-orbit coupling associated with the large quantity of
high Z Pt atoms, Cr$_{1.5}$Pt$_{4.5}$P has exceptionally strong planar
anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and
300 K respectively. The resistance of Cr$_{1.5}$Pt$_{4.5}$P has a metallic
temperature dependence with relatively weak magnetoresistance. Electronic band
structure calculations show that CrPt$_5$P has a large peak in the density of
states near the Fermi level which is split into spin majority and minority
bands in the ferromagnetic state. Furthermore, the calculations suggest
substantial hybridization between Cr-3d and Pt-5d states near the Fermi level,
in agreement with the experimentally measured anisotropy. | 2211.01491v1 |
2020-01-22 | Spintronic superconductor in a bulk layered material with natural spin-valve structure | Multi-layered materials provide fascinating platforms to realize various
functional properties, possibly leading to future electronic devices controlled
by external fields. In particular, layered magnets coupled with conducting
layers have been extensively studied recently for possible control of their
transport properties via the spin structure. Successful control of
quantum-transport properties in the materials with antiferromagnetic (AFM)
layers, so-called natural spin-valve structure, has been reported for the Dirac
Fermion and topological/axion materials. However, a bulk crystal in which
magnetic and superconducting layers are alternately stacked has not been
realized until now, and the search for functional properties in it is an
interesting yet unexplored field in material science. Here, we discover
superconductivity providing such an ideal platform in EuSn2As2 with the van der
Waals stacking of magnetic Eu layers and superconducting Sn-As layers, and
present the first demonstration of a natural spin-valve effect on the
superconducting current. Below the superconducting transition temperature (Tc),
the electrical resistivity becomes zero in the in-plane direction. In contrast,
it, surprisingly, remains finite down to the lowest temperature in the
out-of-plane direction, mostly due to the structure of intrinsic magnetic
Josephson junctions in EuSn2As2. The magnetic order of the Eu layers (or
natural spin-valve) is observed to be extremely soft, allowing one to easy
control of the out-of-plane to in-plane resistivities ratio from 1 to infinity
by weak external magnetic fields. The concept of multi-functional materials
with stacked magnetic-superconducting layers will open a new pathway to develop
novel spintronic devices with magnetically controllable superconductivity. | 2001.07991v1 |
1997-02-26 | Stripes, Non-Fermi-Liquid Behavior, and High-Tc Superconductivity | The electronic structure of the high-Tc cuprates is studied in terms of
"large-U" and "small-U" orbitals. A striped structure and three types of
quasiparticles are obtained, polaron-like "stripons" carrying charge, "svivons"
carrying spin, and "quasielectrons" carrying both. The anomalous properties are
explained, and specifically the behavior of the resistivity, Hall constant, and
thermoelectric power. High-temperature superconductivity results from
transitions between pair states of quasielectrons and stripons. | 9702232v1 |
2014-12-09 | Materials Cartography: Representing and Mining Material Space Using Structural and Electronic Fingerprints | As the proliferation of high-throughput approaches in materials science is
increasing the wealth of data in the field, the gap between
accumulated-information and derived-knowledge widens. We address the issue of
scientific discovery in materials databases by introducing novel analytical
approaches based on structural and electronic materials fingerprints. The
framework is employed to (i) query large databases of materials using
similarity concepts, (ii) map the connectivity of the materials space (i.e., as
a materials cartogram) for rapidly identifying regions with unique
organizations/properties, and (iii) develop predictive Quantitative Materials
Structure-Property Relation- ships (QMSPR) models for guiding materials design.
In this study, we test these fingerprints by seeking target material
properties. As a quantitative example, we model the critical temperatures of
known superconductors. Our novel materials fingerprinting and materials
cartography approaches contribute to the emerging field of materials
informatics by enabling effective computational tools to analyze, visualize,
model, and design new materials. | 1412.4096v3 |
2013-10-14 | High Pressure Effects on the Superconductivity in Rare-Earth Doped CaFe2As2 | High-pressure superconductivity in a rare-earth doped Ca0.86Pr0.14Fe2As2
single crystalline sample has been studied up to 12 GPa and temperatures down
to 11 K using designer diamond anvil cell under a quasi-hydrostatic pressure
medium. The electrical resistance measurements were complemented by high
pressure and low temperature x-ray diffraction studies at a synchrotron source.
The electrical resistance measurements show an intriguing observation of
superconductivity under pressure, with Tc as high as ~51 K at 1.9 GPa,
presenting the highest Tc reported in the intermetallic class of 1-2-2
iron-based superconductors. The resistive transition observed suggests a
possible existence of two superconducting phases at low pressures of 0.5 GPa:
one phase starting at Tc1 ~48 K, and the other starting at Tc2~16 K. The two
superconducting transitions show distinct variations with increasing pressure.
High pressure low temperature structural studies indicate that the
superconducting phase is a collapsed tetragonal ThCr2Si2-type (122) crystal
structure. Our high pressure studies indicate that high Tc state attributed to
non-bulk superconductivity in rare-earth doped 1-2-2 iron-based superconductors
is stable under compression over a broad pressure range. | 1310.3842v2 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.