publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
|---|---|---|---|
1999-04-01 | Radio-frequency impedance measurements using a tunnel-diode oscillator (TDO) technique | A resonant method based on a tunnel-diode oscillator (TDO) for precision
measurements of relative impedance changes in materials, is described. The
system consists of an effective self-resonant LC-tank circuit driven by a
forward-biased tunnel diode operating in its negative resistance region.
Samples under investigation are placed in the core of an inductive coil and
impedance changes are determined directly from the measured shift in resonance
frequency. A customized low temperature insert is used to integrate this
experiment with a commercial Model 6000 Physical Property Measurement System
(Quantum Design). Test measurements on a manganese-based perovskite sample
exhibiting colossal magneto-resistance (CMR) indicate that this method is well
suited to study the magneto-impedance in these materials. | 9904026v1 |
2000-01-19 | Pseudogap effects on the c-axis charge dynamics in copper oxide materials | The c-axis charge dynamics of copper oxide materials in the underdoped and
optimally doped regimes has been studied by considering the incoherent
interlayer hopping. It is shown that the c-axis charge dynamics for the chain
copper oxide materials is mainly governed by the scattering from the in-plane
fluctuation, and the c-axis charge dynamics for the no-chain copper oxide
materials is dominated by the scattering from the in-plane fluctuation
incorporating with the interlayer disorder, which would be suppressed when the
holon pseudogap opens at low temperatures and lower doping levels, leading to
the crossovers to the semiconducting-like range in the c-axis resistivity and
the temperature linear to the nonlinear range in the in-plane resistivity. | 0001260v1 |
2002-02-27 | Anisotropic Magnetoresistance in Ga$_{1-x}$Mn$_x$As | We have measured the magnetoresistance in a series of Ga$_{1-x}$Mn$_x$As
samples with 0.033$\le x \le$ 0.053 for three mutually orthogonal orientations
of the applied magnetic field. The spontaneous resistivity anisotropy (SRA) in
these materials is negative (i.e. the sample resistance is higher when its
magnetization is perpendicular to the measuring current than when the two are
parallel) and has a magnitude on the order of 5% at temperatures near 10K and
below. This stands in contrast to the results for most conventional magnetic
materials where the SRA is considerably smaller in magnitude for those few
cases in which a negative sign is observed. The magnitude of the SRA drops from
its maximum at low temperatures to zero at T$_C$ in a manner that is consistent
with mean field theory. These results should provide a significant test for
emerging theories of transport in this new class of materials. | 0202508v1 |
2008-05-28 | Unified explanation of the Kadowaki-Woods ratio in strongly correlated materials | Discoveries of ratios whose values are constant within broad classes of
materials have led to many deep physical insights. The Kadowaki-Woods ratio
(KWR) compares the temperature dependence of a metal's resistivity to that of
its heat capacity; thereby probing the relationship between the
electron-electron scattering rate and the renormalisation of the electron mass.
However, the KWR takes very different values in different materials. Here we
introduce a ratio, closely related to the KWR, that includes the effects of
carrier density and spatial dimensionality and takes the same (predicted) value
in organic charge transfer salts, transition metal oxides, heavy fermions and
transition metals - despite the numerator and denominator varying by ten orders
of magnitude. Hence, in these materials, the same emergent physics is
responsible for the mass enhancement and the quadratic temperature dependence
of the resistivity and no exotic explanations of their KWRs are required. | 0805.4275v4 |
2016-06-15 | Suppression of lattice thermal conductivity by mass-conserving cation mutation in multi-component semiconductors | In semiconductors almost all heat is conducted by phonons (lattice
vibrations), which is limited by their quasi-particle lifetimes. Phonon-phonon
interactions represent scattering mechanisms that produce thermal resistance.
In thermoelectric materials, this resistance due to anharmonicity should be
maximised for optimal performance. We use a first-principles lattice-dynamics
approach to explore the changes in lattice dynamics across an isostructural
series where the average atomic mass is conserved: ZnS to CuGaS$_2$ to
Cu$_2$ZnGeS$_4$. Our results demonstrate an enhancement of phonon interactions
in the multernary materials, and confirm that lattice thermal conductivity can
be controlled independently of the average mass and local coordination
environments. | 1606.04914v1 |
2018-06-12 | Determination of the BCS material parameters of the HIE-ISOLDE superconducting resonator | Superconducting material parameters of the Nb film coating on the
Quarter-Wave Resonator (QWR) for the HIE-ISOLDE project were studied by fitting
experimental results with the Mattis-Bardeen theory. We pointed out a strong
correlation among fitted estimators of material parameters in the BCS theory,
and proposed a procedure to remove the correlation by simultaneously fitting
the surface resistance and effective penetration depth. Unlike previous
studies, no literature values were assumed in the fitting. As surface
resistance and penetration depth had a similar dependence on coherence length
and mean free path, the correlation between these two parameters could not be
eliminated by this fitting. The upper critical field measured by SQUID
magnetometry showed complementary constraint to the RF result, and this allowed
all the material parameters to be determined. | 1806.04443v1 |
2018-09-19 | Electrical Parameters for Planar Transport in Graphene and 2-D Materials | Classical electrodynamics has been revisited with a view to recast the
electrical parameters for planar transport in 2-dimensional (2-D) materials
like graphene. In this attempt a new line integral, named transverse line
integral, with extensive applications in 2-D, is defined. Since the existing
divergence theorem in not applicable in 2-D, we introduced a new divergence
theorem. A new definition for the in-plane flux of any 2-D vector is
introduced. A new vector named electric vector potential is defined and Gauss
law is modified in terms of the 2-D flux of the new vector. The new Gauss law
in presence of dielectric is obtained and a new electric displacement vector is
defined for the 2-D materials. The conduction and displacement current
densities in 2-D are defined. Resistance and resistivity in 2-D materials are
discussed. The continuity equation for planar transport is derived. | 1809.07319v1 |
2020-09-04 | Fracture mechanics of micro samples: Fundamental considerations | In this review article we consider the crack growth resistance ofmicrometer
and submicrometer sized samples from the fracture mechanics point of view.
Standard fracture mechanics test procedures were developed for macroscale
samples, and reduction of the specimen dimensions by three to five orders of
magnitude has severe consequences. This concerns the interpretation of results
obtained by micro and nanomechanics, as well as the life time and failure
prediction of micro and nano devices. We discuss the relevant fracture
mechanics length scales and their relation to the material specific structural
lengths in order to conduct rigorous fracture mechanics experiments. To ensure
general validity and applicability of evaluation concepts, these scaling
considerations are detailed for ideally brittle, semi brittle and micro ductile
crack propagation, subject to both monotonic and cyclic loading. Special
attention is devoted to the requirements for determining specimen size for
various loading types to measure material characteristic crack propagation
resistance at small scales. Finally, we discuss novel possibilities of micron
and submicron fracture mechanics tests to improve the basic understanding of
specific crack propagation processes. | 2009.05386v1 |
2015-07-23 | Ba{0.4}Rb{0.6}Mn2As2: A Prototype Half-Metallic Ferromagnet | Half-metallic ferromagnetism (FM) in single-crystal
Ba{0.39(1)}Rb{0.61(1)}Mn2As2 below its Curie temperature TC = 103(2) K is
reported. The magnetization M versus applied magnetic field H isotherm data at
1.8 K show complete polarization of the itinerant doped-hole magnetic moments
that are introduced by substituting Rb for Ba. The material exhibits extremely
soft FM, with unobservably small remanent magnetization and coercive field.
Surprisingly, and contrary to typical itinerant FMs, the M(H) data follow the
Arrott-plot paradigm that is based on a mean-field theory of local-moment FMs.
The in-plane electrical resistivity data are fitted well by an activated-T^2
expression for T < TC, whereas the data sharply deviate from this model for T >
TC. Hence the activated-T^2 resistivity model is an excellent diagnostic for
determining the onset of half-metallic FM in this compound, which in turn
demonstrates the presence of a strong correlation between the electronic
transport and magnetic properties of the material. Together with previous data
on 40% hole-doped Ba{0.6}K{0.4}Mn2As2, these measurements establish 61%-doped
Ba{0.39}Rb{0.61}Mn2As2 as a prototype for a new class of half-metallic
ferromagnets in which all the itinerant carriers in the material are
ferromagnetic. | 1507.06679v1 |
2018-12-18 | Atomistic study of an ideal metal/thermoelectric contact: the full-Heusler/half-Heusler interface | Half-Heusler alloys such as the (Zr,Hf)NiSn intermetallic compounds are
important thermoelectric materials for converting waste heat into electricity.
Reduced electrical resistivity at the hot interface between the half-Heusler
material and a metal contact is critical for device performance, however this
has yet to be achieved in practice. Recent experimental work suggests that a
coherent interface between half-Heusler and full-Heusler compounds can form due
to diffusion of transition metal atoms into the vacant sublattice of the
half-Heusler lattice. We study theoretically the structural and electronic
properties of such an interface using a first-principles based approach that
combines {\it ab initio} calculations with macroscopic modeling. We find that
the prototypical interface HfNi$_2$Sn/HfNiSn provides very low contact
resistivity and almost ohmic behavior over a wide range of temperatures and
doping levels. Given the potential of these interfaces to remain stable over a
wide range of temperatures, our study suggests that full-Heuslers might provide
nearly ideal electrical contacts to half-Heuslers that can be harnessed for
efficient thermoelectric generator devices. | 1812.07189v1 |
2020-11-21 | All-Materials-Inclusive Flash Spark Plasma Sintering | A new flash (ultra-rapid) spark plasma sintering method applicable to various
materials systems, regardless of their electrical resistivity, is developed. A
number of powders ranging from metals to electrically insulative ceramics have
been successfully densified resulting in homogeneous microstructures within
sintering times of 8-35 s. A finite element simulation reveals that the
developed method, providing an extraordinary fast and homogeneous heating
concentrated in the sample's volume and punches, is applicable to all the
different samples tested. The utilized uniquely controllable flash phenomenon
is enabled by the combination of the electric current concentration around the
sample and the confinement of the heat generated in this area by the lateral
thermal contact resistance. The presented new method allows: extending flash
sintering to nearly all materials, controlling sample shape by an added
graphite die, and an energy efficient mass production of small and intermediate
size objects. This approach represents also a potential venue for future
investigations of flash sintering of complex shapes. | 2011.14012v1 |
2021-03-26 | A micropolar continuum model of diffusion creep | Solid polycrystalline materials undergoing diffusion creep are usually
described by Cauchy continuum models with a Newtonian viscous rheology
dependent on the grain size. Such a continuum lacks the rotational degrees of
freedom needed to describe grain rotation. Here we provide a more general
continuum description of diffusion creep that includes grain rotation, and
identifies the deformation of the material with that of a micropolar (Cosserat)
fluid. We derive expressions for the micropolar constitutive tensors by a
homogenisation of the physics describing a discrete collection of rigid grains,
demanding an equivalent dissipation between the discrete and continuum
descriptions. General constitutive laws are derived for both Coble
(grain-boundary diffusion) and Nabarro-Herring (volume diffusion) creep.
Detailed calculations are performed for a two-dimensional tiling of irregular
hexagonal grains, which illustrates a potential coupling between the rotational
and translational degrees of freedom. If only the plating out or removal of
material at grain boundaries is considered, the constitutive laws are
degenerate: modes of deformation that involve pure tangential motion at the
grain boundaries are not resisted. This degeneracy can be removed by including
the resistance to grain-boundary sliding, or by imposing additional constraints
on the deformation. | 2103.14458v3 |
2021-04-30 | Material surface -- analyte interactions with similar energy rates vary as univariate quadratic function of topological polar surface area of analytes | Material surface - analyte interactions play important roles in numerous
processes including gas sensing. However, the effects of topological polar
surface area (TPSA) of analytes on surface interactions during gas sensing have
been so far largely disregarded. In this work, based on experimental
observations on changes in electrical resistance of cadmium sulphide (CdS) due
to surface interactions during gas sensing, we found that unexpected univariate
quadratic correlation exists between changes in resistance of CdS and TPSA of
analytes. Further experiments on four other material systems showed the same
trend, revealing a generalized picture of TPSA dependence of surface
interactions. | 2104.14867v1 |
2022-06-08 | Scalable fabrication of edge contacts to 2D materials | We present a fabrication method for reliably and reproducibly forming
electrical contacts to 2D materials, based on the tri-layer resist system. We
demonstrate the applicability of this method for epitaxial graphene on silicon
carbide (epigraphene) and the transition metal dichalcogenides (TMDCs)
molybdenum disulfide ($MoS_2$). For epigraphene, the specific contact
resistances are of the order of $\rho_c$ ~ $50$ $\Omega\mu m$, and follow the
Landauer quantum limit, $\rho_c \propto n^{-1/2}$, with $n$ being the carrier
density of graphene. For $MoS_2$ flakes, our edge contacts enable field effect
transistors (FET) with ON/OFF ratio of $> 10^6$ at room temperature ( $> 10^9$
at cryogenic temperatures). The fabrication route here demonstrated allows for
contact metallization using thermal evaporation and also by sputtering, giving
an additional flexibility when designing electrical interfaces, which is key in
practical devices and when exploring the electrical properties of emerging
materials. | 2206.03839v2 |
2022-07-04 | An Important Structural Requirement for the Superconductor Material: A Hypothesis | On a microscopic scale, resistivity during electric conduction is caused by
collisions of the free conduction electrons with the obstructing atoms or
molecules of the conductor material, resulting in heat production. Based on
this fundamental understanding, a hypothesis concerning a physical requirement
of the superconductor material is proposed, which suggests that for
superconductivity (i.e., with zero resistivity) to occur, the conductor
material must have nano-sized, continuous and straight vacuum tunnels inside
with effective radius size large enough to allow collision-free conduction of
free electrons. Besides, some of the composite atoms of the conductor should be
able to readily release electrons to form the conduction band; in fact, this
basic requirement is for all forms of electrical conductors, not just for
superconductors. The proposed hypothesis is supported by experimental
observations in the literature, and also offers a plausible explanation for
some of the poorly-understood experimental phenomena observed in the past. In
addition, the hypothesis offers practical strategies for the rational design of
electrical conductors with (quasi-)superconductivity. Lastly, the proposed new
hypothesis also suggests a novel mechanism for neural microtubule-mediated
electrical quasi-superconductance in the nervous system. | 2207.01226v2 |
1994-06-03 | Localization Effects in Bi2Sr2Ca(Cu,Co)2O8+y High Temperature Superconductors | Doping Bi2Sr2Ca1Cu2O8+y with Co causes a superconductor-insulator transition.
We study correlations between changes in the electrical resistivity RHOab(T)
and the electronic bandstructure using identical single crystalline samples.
For undoped samples the resistivity is linear in temperature and has a
vanishing residual resistivity. In angle resolved photoemission these samples
show dispersing band-like states. Co-doping decreases TC and causes and
increase in the residual resistivity. Above a threshold Co-concentration the
resistivity is metallic (drab/dT >0) at room temperature, turns insulating
below a characteristic temperature Tmin and becomes super- conducting at even
lower temperature. These changes in the resistivity correlate with the
disappearance of the dispersing band-like states in angle resolved
photoemission. We show that Anderson localization caused by the impurity
potential of the doped Co-atoms provides a consistent explanation of all
experimental features. Therefore the TC reduction in 3d-metal doped high-
temperature superconductors is not caused by Abrikosov Gor'kov pair- breaking
but by spatial localization of the carriers. The observed suppression of TC
indicates that the system is in the homogenous limit of the
superconductor-insulator transition. The coexistance of insulating (dRHOab/dT
<0) normal state behavior and super- conductivity indicates that the
superconducting ground state is formed out of spatially almost localized
carriers. | 9406021v1 |
2011-11-17 | Stability of a self-gravitating homogeneous resistive plasma | In this paper, we analyze the stability of a homogeneous self-gravitating
plasma, having a non-zero resistivity. This study provides a generalization of
the Jeans paradigm for determining the critical scale above which gravitational
collapse is allowed. We start by discussing the stability of an ideal
self-gravitating plasma embedded in a constant magnetic field. We outline the
existence of an anisotropic feature of the gravitational collapse. In fact,
while in the plane orthogonal to the magnetic field the Jeans length is
enhanced by the contribution of the magnetic pressure, outside this plane
perturbations are governed by the usual Jeans criterium. The anisotropic
collapse of a density contrast is sketched in details, suggesting that the
linear evolution provides anisotropic initial conditions for the non-linear
stage, where this effect could be strongly enforced. The same problem is then
faced in the presence of non-zero resistivity and the conditions for the
gravitational collapse are correspondingly extended. The relevant feature
emerging in this resistive scenario is the cancellation of the collapse
anisotropy in weakly conducting plasmas. In this case, the instability of a
self-gravitating resistive plasma is characterized by the standard isotropic
Jeans length in any directions. The limit of very small resistivity coefficient
is finally addressed, elucidating how reminiscence of the collapse anisotropy
can be found in the different value of the perturbation frequency inside and
outside the plane orthogonal to the magnetic field. | 1111.4051v1 |
2013-02-26 | Inter-plane resistivity of isovalent doped BaFe$_2$(As$_{1-x}$P$_x$)$_2$ | Temperature-dependent inter-plane resistivity, $\rho_c(T)$, was measured for
the iron-based superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ over a broad
isoelectron phosphorus substitution range from $x$=0 to $x$=0.60, from
non-superconducting parent compound to heavily overdoped superconducting
composition with $T_c\approx 10 K$. The features due to structural and magnetic
transitions are clearly resolved in $\rho_c(T)$ of the underdoped crystals. A
characteristic maximum in $\rho_c(T)$, found in the parent BaFe$_2$As$_2$ at
around 200 K, moves rapidly with phosphorus substitution to high temperatures.
At the optimal doping, the inter-plane resistivity shows $T$-linear temperature
dependence without any cross-over anomalies, similar to the previously reported
in-plane resistivity. This observation is in stark contrast with dissimilar
temperature dependences found at optimal doping in electron-doped
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$. Our finding suggests that despite similar
values of the resistivity and its anisotropy, the temperature dependent
transport in the normal state is very different in electron and isoelectron
doped compounds. Similar temperature dependence of both in-plane and
inter-plane resistivities, in which the dominant contributions are coming from
different parts of the Fermi surface, suggests that scattering is the same on
the whole Fermi surface. Since magnetic fluctuations are expected to be much
stronger on the quasi-nested sheets, this observation may point to the
importance of the inter-orbital scattering between different sheets. | 1302.6440v1 |
2013-05-16 | Effect of doping on the magnetostructural ordered phase of iron arsenides: A comparative study of the resistivity anisotropy in the doped BaFe$_2$As$_2$ with doping into three different sites | In order to unravel a role of doping in the iron-based superconductors, we
investigated the in-plane resistivity for BaFe$_2$As$_2$ doped at either of the
three different lattice sites, Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$,
BaFe$_2$(As$_{1-x}$P$_x$)$_2$, and Ba$_{1-x}$K$_x$Fe$_2$As$_2$, focusing on the
doping effect in the low-temperature antiferromagnetic/orthorhombic (AFO)
phase. A major role of doping in the high-temperature paramagnetic/tetragonal
(PT) phase is known to change the Fermi surface by supplying charge carriers or
by exerting chemical pressure. In the AFO phase, we found a clear correlation
between the magnitude of residual resistivity and resistivity anisotropy. This
indicates that the resistivity anisotropy originates from the anisotropic
impurity scattering from dopant atoms. The magnitude of residual resistivity is
also found to be a parameter controlling the suppression rate of AFO ordering
temperature $T_s$. Therefore, the dominant role of doping in the AFO phase is
to introduce disorder to the system, distinct from that in the PT phase. | 1305.3744v1 |
2016-01-13 | Limiting the Development of Anti-Cancer Drug Resistance in a Spatial Model of Micrometastases | While chemoresistance in primary tumors is well-studied, much less is known
about the influence of systemic chemotherapy on the development of drug
resistance at metastatic sites. In this work, we use a hybrid spatial model of
tumor response to a DNA damaging drug to study how the development of
chemoresistance in micrometastases depends on the drug dosing schedule. We
separately consider cell populations that harbor pre-existing resistance to the
drug, and those that acquire resistance during the course of treatment. For
each of these independent scenarios, we consider one hypothetical cell line
that is responsive to metronomic chemotherapy, and another that with high
probability cannot be eradicated by a metronomic protocol. Motivated by
experimental work on ovarian cancer xenografts, we consider all possible
combinations of a one week treatment protocol, repeated for three weeks, and
constrained by the total weekly drug dose. Simulations reveal a small number of
fractionated-dose protocols that are at least as effective as metronomic
therapy in eradicating micrometastases with acquired resistance (weak or
strong), while also being at least as effective on those that harbor weakly
pre-existing resistant cells. Given the responsiveness of very different
theoretical cell lines to these few fractionated-dose protocols, these may
represent more effective ways to schedule chemotherapy with the goal of
limiting metastatic tumor progression. | 1601.03412v2 |
2014-01-08 | Angular and Polarization Response of Multimode Sensors with Resistive-Grid Absorbers | High sensitivity receiver systems with near ideal polarization sensitivity
are highly desirable for development of millimeter and sub-millimeter radio
astronomy. Multimoded bolometers provide a unique solution to achieve such
sensitivity, for which hundreds of single-mode sensors would otherwise be
required. The primary concern in employing such multimoded sensors for
polarimetery is the control of the polarization systematics. In this paper, we
examine the angular- and polarization- dependent absorption pattern of a thin
resistive grid or membrane, which models an absorber used for a multimoded
bolometer. The result shows that a freestanding thin resistive absorber with a
surface resistivity of \eta/2, where \eta\ is the impedance of free space,
attains a beam pattern with equal E- and H-plane responses, leading to zero
cross polarization. For a resistive-grid absorber, the condition is met when a
pair of grids is positioned orthogonal to each other and both have a
resistivity of \eta/2. When a reflective backshort termination is employed to
improve absorption efficiency, the cross-polar level can be suppressed below
-30 dB if acceptance angle of the sensor is limited to <60degrees. The small
cross-polar systematics have even-parity patterns and do not contaminate the
measurements of odd-parity polarization patterns, for which many of recent
instruments for cosmic microwave background are designed. Underlying symmetry
that suppresses these cross-polar systematics is discussed in detail. The
estimates and formalism provided in this paper offer key tools in the design
consideration of the instruments using the multimoded polarimeters. | 1401.1859v1 |
2021-08-30 | Clonal Diversity at Cancer Recurrence | Despite initial success, cancer therapies often fail due to the emergence of
drug-resistant cells. In this study, we use a mathematical model to investigate
how cancer evolves over time, specifically focusing on the state of the tumor
when it recurs after treatment. We use a two-type branching process to capture
the dynamics of both drug-sensitive and drug-resistant cells. We analyze the
clonal diversity of drug-resistant cells at the time of cancer recurrence,
which is defined as the first time the population size of drug-resistant cells
exceeds a specified proportion of the initial population size of drug-sensitive
cells. We examine two clonal diversity indices: the number of clones and the
Simpson's Index. We calculate the expected values of these indices and utilize
them to develop statistical methods for estimating model parameters.
Additionally, we examine these two indices conditioned on early recurrence in
the special case of a deterministically decaying sensitive population, with the
aim of addressing the question of whether early recurrence is driven by a
single mutation that generates an unusually large family of drug-resistant
cells (corresponding to a low clonal diversity), or if it is due to the
presence of an unusually large number of mutations causing drug resistance
(corresponding to a high clonal diversity). Our findings, based on both
indices, support the latter possibility. Furthermore, we demonstrate that the
time of cancer recurrence can serve as a valuable indicator of clonal
diversity, offering new insights for the treatment of recurrent cancers. | 2108.13472v3 |
2022-03-23 | A Fast Diagnostic to Inform Screening of Discarded or Retired Batteries | With the increased pervasiveness of Lithium-ion batteries, there is growing
concern for the amount of retired batteries that will be entering the waste
stream. Although these batteries no longer meet the demands of their first
application, many still have a significant portion of their initial capacity
remaining for use in secondary applications. Yet, direct repurposing is
generally not possible and each cell in a battery must be evaluated, increasing
the cost of the repurposed packs due to the time intensive screening process.
In this paper, a rapid assessment of the internal resistance of a cell is
proposed. First, this method of measuring the resistance is completed on cells
from twelve retired battery packs and one fresh pack using a hybrid pulse power
characterization (HPPC) test as a benchmark for the analysis. Results from
these tests show relatively constant resistance measurements across mid to high
terminal voltages, allowing this metric to be independent of state of charge
(SOC). Then, the relation between internal resistance and capacity across the
various packs is discussed. Initial experimental results from this study show a
correlation between internal resistance and capacity which can be approximated
with a linear fit, suggesting internal resistance measurements taken above a
threshold cell terminal voltage may be a suitable initial screening metric for
the capacity of retired cells without knowledge of the SOC. | 2203.12376v1 |
2023-01-15 | Effects of quantum recoil forces in resistive switching in memristors | Memristive devices, whose resistance can be controlled by applying a voltage
and further retained, are attractive as possible circuit elements for
neuromorphic computing. This new type of devices poses a number of both
technological and theoretical challenges. Even the physics of the key process
of resistive switching, usually associated with formation or breakage of
conductive filaments in the memristor, is not completely understood yet. This
work proposes a new resistive switching mechanism, which should be important in
the thin-filament regime and take place due to the back reaction, or recoil, of
quantum charge carriers -- independently of the conventional
electrostatically-driven ion migration. Since thinnest conductive filaments are
in question, which are only several atoms thick and allow for a
quasi-ballistic, quantized conductance, we use a mean-field theory and the
framework of nonequilibrium Green's functions to discuss the electron recoil
effect for a quantum current through a nanofilament on its geometry and compare
it with the transmission probability of charge carriers. Namely, we first study
an analytically tractable toy model of a 1D atomic chain, to qualitatively
demonstrate the importance of the charge-carrier recoil, and further proceed
with a realistic molecular-dynamics simulation of the recoil-driven ion
migration along a copper filament and the resulting resistive switching. The
results obtained are expected to add to the understanding of resistive
switching mechanisms at the nanoscale and to help downscale high-retention
memristive devices. | 2301.06066v2 |
2024-01-16 | Resistively controlled primordial magnetic turbulence decay | Magnetic fields generated in the early Universe undergo turbulent decay
during the radiation-dominated era. The decay is governed by a decay exponent
and a decay time. It has been argued that the latter is prolonged by magnetic
reconnection, which depends on the microphysical resistivity and viscosity.
Turbulence, on the other hand, is not usually expected to be sensitive to
microphysical dissipation, which affects only very small scales. We want to
test and quantify the reconnection hypothesis in decaying hydromagnetic
turbulence. We performed high-resolution numerical simulations with zero net
magnetic helicity using the Pencil Code with up to $2048^3$ mesh points and
relate the decay time to the Alfv\'en time for different resistivities and
viscosities. The decay time is found to be longer than the Alfv\'en time by a
factor that increases with increasing Lundquist number to the 1/4 power. The
decay exponent is as expected from the conservation of the Hosking integral,
but a timescale dependence on resistivity is unusual for developed turbulence
and not found for hydrodynamic turbulence. In two dimensions, the Lundquist
number dependence is shown to be leveling off above values of $\approx25,000$,
independently of the value of the viscosity. Our numerical results suggest that
resistivity effects have been overestimated in earlier work. Instead of
reconnection, it may be the magnetic helicity density in smaller patches that
is responsible for the resistively slow decay. The leveling off at large
Lundquist number cannot currently be confirmed in three dimensions. | 2401.08569v3 |
2015-09-11 | Model of Flux Trapping in Cooling Down Process | The flux trapping that occurs in the process of cooling down of the
superconducting cavity is studied. The critical fields $B_{c2}$ and $B_{c1}$
depend on a position when a material temperature is not uniform. In a region
with $T\simeq T_c$, $B_{c2}$ and $B_{c1}$ are strongly suppressed and can be
smaller than the ambient magnetic field, $B_a$. A region with $B_{c2}\le B_a$
is normal conducting, that with $B_{c1}\le B_a < B_{c2}$ is in the vortex
state, and that with $B_{c1}> B_a$ is in the Meissner state. As a material is
cooled down, these three domains including the vortex state domain sweep and
pass through the material. In this process, vortices contained in the vortex
state domain are trapped by pinning centers distributing in the material. A
number of trapped fluxes can be evaluated by using the analogy with the
beam-target collision event, where beams and a target correspond to pinning
centers and the vortex state domain, respectively. We find a number of trapped
fluxes and thus the residual resistance are proportional to the ambient
magnetic field and the inverse of the temperature gradient. The obtained
formula for the residual resistance is consistent with experimental results.
The present model focuses on what happens at the phase transition fronts during
a cooling down, reveals why and how the residual resistance depends on the
temperature gradient, and naturally explains how the fast cooling works. | 1509.03369v1 |
2020-06-21 | A Novel Magnetic Material by Design: Observation of Yb3+ with Spin-1/2 and Possible Superconducting Trace in YbxPt5P | The localized f-electrons enrich the magnetic properties in rare-earth-based
intermetallics. Among those, compounds with heavier 4d and 5d transition metals
are even more fascinating because anomalous electronic properties may be
induced by the hybridization of 4f and itinerant conduction electrons primarily
from the d orbitals. Here, we describe the observation of trivalent Yb3+ with S
= 1/2 at low temperatures in YbxPt5P, the first of a new family of materials.
YbxPt5P (0.20< x <1) phases were synthesized and structurally characterized.
They exhibit a large homogeneity width with the Yb ratio exclusively occupying
the 1a site in the anti-CeCoIn5 structure. Moreover, the resistivity
measurement of a sample analyzed as Yb0.25Pt5P shows it to exist a complete
zero-resistance transition with a critical transition temperature of ~0.6 K,
possible superconductivity. However, the zero-resistivity transition was not
observed in YbPt5P with antiferromagnetic ordering existing solely.
First-principles electronic structure calculations substantiate the
antiferromagnetic ground state and indicate that 2D nesting around the Fermi
level may give rise to exotic physical properties, such as superconductivity.
YbxPt5P appears to be a unique case among materials. | 2006.11891v1 |
2024-03-19 | Giant electrode effect on tunneling magnetoresistance and electroresistance in van der Waals intrinsic multiferroic tunnel junctions using VS2 | Van der Waals multiferroic tunnel junctions (vdW-MFTJs) with multiple
nonvolatile resistive states are highly suitable for new physics and
next-generation storage electronics. However, currently reported vdW-MFTJs are
based on two types of materials, i.e., vdW ferromagnetic and ferroelectric
materials, forming a multiferroic system. This undoubtedly introduces
additional interfaces, increasing the complexity of experimental preparation.
Herein, we engineer vdW intrinsic MFTJs utilizing bilayer VS$_2$. By employing
the nonequilibrium Green's function combined with density functional theory, we
systematically investigate the influence of three types of electrodes
(including non-vdW pure metal Ag/Au, vdW metallic 1T-MoS$_2$/2H-PtTe$_2$, and
vdW ferromagnetic metallic Fe$_3$GaTe$_2$/Fe$_3$GeTe$_2$) on the electronic
transport properties of VS$_2$-based intrinsic MFTJs. We demonstrate that these
MFTJs manifest a giant electrode-dependent electronic transport characteristic
effect. Comprehensively comparing these electrode pairs, the
Fe$_3$GaTe$_2$/Fe$_3$GeTe$_2$ electrode combination exhibits optimal transport
properties, the maximum TMR (TER) can reach 10949\% (69\%) and the minimum
resistance-area product (RA) is 0.45 $\Omega$$\mu$m$^{2}$, as well as the
perfect spin filtering and negative differential resistance effects. More
intriguingly, TMR (TER) can be further enhanced to 34000\% (380\%) by applying
an external bias voltage (0.1 V), while RA can be reduced to 0.16
$\Omega$$\mu$m$^{2}$ under the influence of biaxial stress (-3\%). Our proposed
concept of designing vdW-MFTJs using intrinsic multiferroic materials points
towards new avenues in experimental exploration. | 2403.12845v2 |
2001-05-15 | Current-Driven Magnetic Memory with Tunable Magnetization Switching | Co(x nm, x=10nm or 40nm)/Cu(5nm)/Co(2.5nm) layers were deposited between
copper electrodes in SiO2 vias. Magnetic states, and the corresponding
resistance states, of these devices were switched by electric currents
perpendicular to the layers. The I-V loops show asymmetric behavior with
hysteresis. When electrons flow in the direction from thick to thin Co layer
(positive current), multiple switches were observed on increasing current up to
a chosen maximum positive I(write). On decreasing current from I(write), the
I-V curve was smooth and characterized by considerably lower resistance. Under
reverse current, an abrupt switch to the high resistance state occurred at the
current value I(erase)~ -0.9*I(write). Resistance had a maximum at zero current
in both states, where the ratio R(high)/R(low) could be as high as factor of
four. | 0105290v1 |
2005-12-19 | Multiphoton processes in microwave photoresistance of 2D electron system | We extend our studies of microwave photoresistance of ultra-high mobility
two-dimensional electron system (2DES) into the high-intensity, non-linear
regime employing both monochromatic and bichromatic radiation. Under
high-intensity monochromatic radiation $\omega$ we observe new zero-resistance
states (ZRS) which correspond to rational values of $\epsilon=\omega/\omega_C$
($\omega_C$ is the cyclotron frequency) and can be associated with multiphoton
processes. %Formation of these rational ZRS is accompanied by a dramatic
reconstruction of the photoresistance spectrum which reveals diminishing,
narrowing, and phase reduction of the resistance peaks, as well as overall
suppression of resistance at $\epsilon<1/2$. Under bichromatic radiation
$\omega_1,\omega_2$ we discover new resistance minimum, possibly a precursor of
bichromatic ZRS, which seems to originate from a frequency mixing process,
$\omega_1+\omega_2$. These findings indicate that multiphoton processes play
important roles in the physics of non-equilibrium transport of microwave-driven
2DES, and suggest new directions for theoretical and experimental studies. | 0512479v1 |
2007-08-17 | Developments and the preliminary tests of Resistive GEMs manufactured by a screen printing technology | We report promising initial results obtained with new resistive-electrode GEM
(RETGEM) detectors manufactured, for the first time, using screen printing
technology. These new detectors allow one to reach gas gains nearly as high as
with ordinary GEM-like detectors with metallic electrodes; however, due to the
high resistivity of its electrodes the RETGEM, in contrast to ordinary
hole-type detectors, has the advantage of being fully spark protected. We
discovered that RETGEMs can operate stably and at high gains in noble gases and
in other badly quenched gases, such as mixtures of noble gases with air and in
pure air; therefore, a wide range of practical applications, including
dosimetry and detection of dangerous gases, is foreseeable. To promote a better
understanding of RETGEM technology some comparative studies were completed with
metallic-electrode thick GEMs. A primary benefit of these new RETGEMs is that
the screen printing technology is easily accessible to many research
laboratories. This accessibility encourages the possibility to manufacture
these GEM-like detectors with the electrode resistivity easily optimized for
particular experimental or practical applications. | 0708.2344v1 |
2016-03-15 | Thermo Activated Hysteresis on High Quality Graphene/h-BN Devices | We report on gate hysteresis in resistance on high quality graphene/h-BN
devices. We observe a thermal activated hysteretic behavior in resistance as a
function of the applied gate voltage at temperatures above 375K. In order to
investigate the origin of the hysteretic phenomenon, we design heterostructures
involving graphene/h-BN devices with different underlying substrates such as:
SiO2/Si and graphite; where heavily doped silicon and graphite are used as a
back gate electrodes, respectively. The gate hysteretic behavior of the
resistance shows to be present only in devices with an h-BN/SiO2 interface and
is dependent on the orientation of the applied gate electric field and sweep
rate. Finally, we suggest a phenomenological model, which captures all of our
findings based on charges trapped at the h-BN/SiO2. Certainly, such hysteretic
behavior in graphene resistance represents a technological problem for the
application of graphene devices at high temperatures, but conversely, it can
open new routes for applications on digital electronics and graphene memory
devices. | 1603.04872v1 |
2021-09-29 | Magnetotransport patterns of collective localization near $ν=1$ in a high-mobility two-dimensional electron gas | We report complex magnetotransport patterns of the $\nu=1$ integer quantum
Hall state in a GaAs/AlGaAs sample from the newest generation with a record
high electron mobility. The reentrant integer quantum Hall effect in the flanks
of the $\nu=1$ plateau indicates the formation of the integer quantum Hall
Wigner solid, a collective insulator. Moreover, at a fixed filling factor, the
longitudinal resistance versus temperature in the region of the integer quantum
Hall Wigner solid exhibits a sharp peak. Such sharp peaks in the longitudinal
resistance versus temperature so far were only detected for bubble phases
forming in high Landau levels but were absent in the region of the Anderson
insulator. We suggest that in samples of sufficiently low disorder sharp peaks
in the longitudinal resistance versus temperature traces are universal
transport signatures of all isotropic electron solids that form in the flanks
of integer quantum Hall plateaus. We discuss possible origins of these sharp
resistance peaks and we draw a stability diagram for the insulating phases in
the $\nu$-$T$ phase space. | 2109.14649v1 |
2024-04-29 | Mobility and Threshold Voltage Extraction in Transistors with Gate-Voltage-Dependent Contact Resistance | The mobility of emerging (e.g., two-dimensional, oxide, organic)
semiconductors is commonly estimated from transistor current-voltage
measurements. However, such devices often experience contact gating, i.e.,
electric fields from the gate modulate the contact resistance during
measurements, which can lead conventional extraction techniques to estimate
mobility incorrectly even by a factor >2. This error can be minimized by
measuring transistors at high gate-source bias, |$V_\mathrm{gs}$|, but this
regime is often inaccessible in emerging devices that suffer from high contact
resistance or early gate dielectric breakdown. Here, we propose a method of
extracting mobility in transistors with gate-dependent contact resistance that
does not require operation at high |$V_\mathrm{gs}$|, enabling accurate
mobility extraction even in emerging transistors with strong contact gating.
Our approach relies on updating the transfer length method (TLM) and can
achieve <10% error even in regimes where conventional techniques overestimate
mobility by >2$\times$. | 2404.19022v1 |
2004-09-11 | Magnetic and electron transport properties of the rare-earth cobaltates, La0.7-xLnxCa0.3CoO3 (Ln = Pr, Nd, Gd and Dy) : A case of phase separation | Magnetic and electrical properties of four series of rare earth cobaltates of
the formula La0.7-xLnxCa0.3CoO3 with Ln = Pr, Nd, Gd and Dy have been
investigated. Compositions close to x = 0.0 contain large ferromagnetic
clusters or domains, and show Brillouin-like behaviour of the field-cooled DC
magnetization data with fairly high ferromagnetic Tc values, besides low
electrical resistivities with near-zero temperature coefficients. The
zero-field-cooled data generally show a non-monotonic behaviour with a peak at
a temperatures slightly lower than Tc. The near x = 0.0 compositions show a
prominent peak corresponding to the Tc in the AC-susceptibility data. The
ferromagnetic Tc varies linearly with x or the average radius of the A-site
cations, (rA). With increase in x or decrease in (rA), the magnetization value
at any given temperature decreases markedly and the AC-susceptibility
measurements show a prominent transition arising from small magnetic clusters
with some characteristics of a spin-glass. Electrical resistivity increases
with increase in x, showed a significant increase around a critical value of x
or (rA), at which composition the small clusters also begin to dominate. These
properties can be understood in terms of a phase separation scenario wherein
large magnetic clusters give way to smaller ones with increase in x, with both
types of clusters being present in certain compositions. The changes in
magnetic and electrical properties occur parallely since the large
ferromagnetic clusters are hole-rich and the small clusters are hole-poor.
Variable-range hopping seems to occur at low temperatures in these cobaltates. | 0409288v2 |
2004-11-17 | Al substitution in MgB2 crystals: influence on superconducting and structural properties | Single crystals of Mg1-xAlxB2 have been grown at a pressure of 30 kbar using
the cubic anvil technique. Precipitation free crystals with x < 0.1 were
obtained as a result of optimization of already developed MgB2 crystal growth
procedure. Systematic decrease of the c-axis lattice constant with increasing
Al content, when the a-axis lattice constant is practically unchanged, was
observed. Variation of the critical temperature on Al content in Mg1-xAlxB2
crystals was found to be slightly different than that one observed for
polycrystalline samples since, even a very small substitution of 1-2% of Al
leads to the decrease of Tc by about 2-3 K. X-ray and high resolution
transmission electron microscopy investigations indicate on the appearance of
second precipitation phase in the crystals with x > 0.1. This is in a form of
non-superconducting MgAlB4 domains in the structure of superconducting
Mg1-xAlxB2 matrix. Resistivity and magnetic investigations show the slight
increase of the upper critical field, Hc2, for H//c for the samples with small
x, significant reduction of the Hc2 anisotropy at lower temperatures, and
decrease of the residual resistance ratio value for Al substituted samples as
compared to those of unsubstituted crystals. Superconducting gaps variation as
a function of Al content, investigated with point contact spectroscopy for the
series of the crystals with Tc in the range from 20 to 37 K, does not indicate
on the merging of the gaps with decreasing Tc down to 20 K. It may be related
to an appearance of the precipitation phase in the Mg1-xAlxB2 structure. | 0411449v2 |
2007-08-01 | Structural and transport properties of GaAs/delta<Mn>/GaAs/InxGa1-xAs/GaAs quantum wells | We report results of investigations of structural and transport properties of
GaAs/Ga(1-x)In(x)As/GaAs quantum wells (QWs) having a 0.5-1.8 ML thick Mn
layer, separated from the QW by a 3 nm thick spacer. The structure has hole
mobility of about 2000 cm2/(V*s) being by several orders of magnitude higher
than in known ferromagnetic two-dimensional structures. The analysis of the
electro-physical properties of these systems is based on detailed study of
their structure by means of high-resolution X-ray diffractometry and
glancing-incidence reflection, which allow us to restore the depth profiles of
structural characteristics of the QWs and thin Mn containing layers. These
investigations show absence of Mn atoms inside the QWs. The quality of the
structures was also characterized by photoluminescence spectra from the QWs.
Transport properties reveal features inherent to ferromagnetic systems: a
specific maximum in the temperature dependence of the resistance and the
anomalous Hall effect (AHE) observed in samples with both "metallic" and
activated types of conductivity up to ~100 K. AHE is most pronounced in the
temperature range where the resistance maximum is observed, and decreases with
decreasing temperature. The results are discussed in terms of interaction of
2D-holes and magnetic Mn ions in presence of large-scale potential fluctuations
related to random distribution of Mn atoms. The AHE values are compared with
calculations taking into account its "intrinsic" mechanism in ferromagnetic
systems. | 0708.0056v1 |
2009-08-03 | Fabrication of Diamond Nanowires for Quantum Information Processing Applications | We present a design and a top-down fabrication method for realizing diamond
nanowires in both bulk single crystal and polycrystalline diamond. Numerical
modeling was used to study coupling between a Nitrogen Vacancy (NV) color
center and optical modes of a nanowire, and to find an optimal range of
nanowire diameters that allows for large collection efficiency of emitted
photons. Inductively coupled plasma (ICP) reactive ion etching (RIE) with
oxygen is used to fabricate the nanowires. Drop-casted nanoparticles (including
$\mathrm{Au}$, $\mathrm{SiO_{2}}$ and $\mathrm{Al_2O_3}$) as well as electron
beam lithography defined spin-on glass and evaporated $\mathrm{Au}$ have been
used as an etch mask. We found $\mathrm{Al_2O_3}$ nanoparticles to be the most
etch resistant. At the same time FOx e-beam resist (spin-on glass) proved to be
a suitable etch mask for fabrication of ordered arrays of diamond nanowires. We
were able to obtain nanowires with near vertical sidewalls in both
polycrystalline and single crystal diamond. The heights and diameters of the
polycrystalline nanowires presented in this paper are $\unit[\approx1]{\mu m}$
and $\unit[120-340]{nm}$, respectively, having a $\unit[200]{nm/min}$ etch
rate. In the case of single crystal diamond (types Ib and IIa) nanowires the
height and diameter for different diamonds and masks shown in this paper were
$\unit[1-2.4]{\mu m}$ and $\unit[120-490]{nm}$ with etch rates between
$\unit[190-240]{nm/min}$. | 0908.0352v2 |
2015-08-25 | Central Acceptance Testing for Camera Technologies for CTA | The Cherenkov Telescope Array (CTA) is an international initiative to build
the next generation ground based very-high energy gamma-ray observatory. It
will consist of telescopes of three different sizes, employing several
different technologies for the cameras that detect the Cherenkov light from the
observed air showers. In order to ensure the compliance of each camera
technology with CTA requirements, CTA will perform central acceptance testing
of each camera technology. To assist with this, the Camera Test Facilities
(CTF) work package is developing a detailed test program covering the most
important performance, stability, and durability requirements, including
setting up the necessary equipment. Performance testing will include a wide
range of tests like signal amplitude, time resolution, dead-time determination,
trigger efficiency, performance testing under temperature and humidity
variations and several others. These tests can be performed on fully-integrated
cameras using a portable setup at the camera construction sites. In addition,
two different setups for performance tests on camera sub-units are being built,
which can provide early feedback for camera development. Stability and
durability tests will include the long-term functionality of movable parts,
water tightness of the camera housing, temperature and humidity cycling,
resistance to vibrations during transport or due to possible earthquakes,
UV-resistance of materials and several others. Some durability tests will need
to be contracted out because they will need dedicated equipment not currently
available within CTA. The planned test procedures and the current status of the
test facilities will be presented. | 1508.06074v1 |
2016-08-28 | Magnetic order and spin-orbit coupled Mott state in double perovskite (La$_{1-x}$Sr$_x$)$_2$CuIrO$_6$ | Double-perovskite oxides that contain both 3d and 5d transition metal
elements have attracted growing interest as they provide a model system to
study the interplay of strong electron interaction and large spin-orbit
coupling (SOC). Here, we report on experimental and theoretical studies of the
magnetic and electronic properties of double-perovskites
(La$_{1-x}$Sr$_x$)$_2$CuIrO$_6$ ($x$ = 0.0, 0.1, 0.2, and 0.3). The undoped
La$_2$CuIrO$_6$ undergoes a magnetic phase transition from paramagnetism to
antiferromagnetism at T$_N$ $\sim$ 74 K and exhibits a weak ferromagnetic
behavior below $T_C$ $\sim$ 52 K. Two-dimensional magnetism that was observed
in many other Cu-based double-perovskites is absent in our samples, which may
be due to the existence of weak Cu-Ir exchange interaction. First-principle
density-functional theory (DFT) calculations show canted antiferromagnetic
(AFM) order in both Cu$^{2+}$ and Ir$^{4+}$ sublattices, which gives rise to
weak ferromagnetism. Electronic structure calculations suggest that
La$_2$CuIrO$_6$ is an SOC-driven Mott insulator with an energy gap of $\sim$
0.3 eV. Sr-doping decreases the magnetic ordering temperatures ($T_N$ and
$T_C$) and suppresses the electrical resistivity. The high temperatures
resistivity can be fitted using a variable-range-hopping model, consistent with
the existence of disorders in these double-pervoskite compounds. | 1608.07763v2 |
2017-10-11 | Fermi surface with Dirac fermions in CaFeAsF determined via quantum oscillation measurements | Despite the fact that 1111-type iron arsenides hold the record transition
temperature of iron-based superconductors, their electronic structures have not
been studied much because of the lack of high-quality single crystals. In this
study, we completely determine the Fermi surface in the antiferromagnetic state
of CaFeAsF, a 1111 iron-arsenide parent compound, by performing quantum
oscillation measurements and band-structure calculations. The determined Fermi
surface consists of a symmetry-related pair of Dirac electron cylinders and a
normal hole cylinder. From analyses of quantum-oscillation phases, we
demonstrate that the electron cylinders carry a nontrivial Berry phase $\pi$.
The carrier density is of the order of 10$^{-3}$ per Fe. This unusual metallic
state with the extremely small carrier density is a consequence of the
previously discussed topological feature of the band structure which prevents
the antiferromagnetic gap from being a full gap. We also report a nearly
linear-in-$B$ magnetoresistance and an anomalous resistivity increase above
about 30 T for $B \parallel c$, the latter of which is likely related to the
quantum limit of the electron orbit. Intriguingly, the electrical resistivity
exhibits a nonmetallic temperature dependence in the paramagnetic tetragonal
phase ($T >$ 118 K), which may suggest an incoherent state. Our study provides
a detailed knowledge of the Fermi surface in the antiferromagnetic state of
1111 parent compounds and moreover opens up a new possibility to explore
Dirac-fermion physics in those compounds. | 1710.03938v3 |
2020-04-23 | Ultralow Schottky Barriers in hBN-Encapsulated Monolayer WSe$_2$ Tunnel Field-Effect Transistors | To explore the potential of field-effect transistors (FETs) based on
monolayers of the two-dimensional semiconducting channel(SC) for spintronics,
the two most important issues are to ensure the formation of variable low
resistive tunnel ferromagnetic contacts(FC), and to preserve intrinsic
properties of the SC during fabrication. Large Schottky barriers lead to the
formation of high resistive contacts and methods adopted to control the
barriers often alter the intrinsic properties of the SC. This work aims at
addressing both issues in fully encapsulated monolayer WSe$_2$ FETs by using
bi-layer h-BN as a tunnel barrier at the FC/SC interface. We investigate the
electrical transport in monolayer WSe$_2$ FETs with current-in-plane geometry
that yields hole mobilities $\sim$ 38.3 $cm^{2}V^{-1}s^{-1}$ at 240 K and
On/Off ratios of the order of 10$^7$, limited by the contact regions. We have
achieved ultralow effective Schottky barrier ($\sim$ 5.34 meV) with
encapsulated tunneling device as opposed to a non-encapsulated device in which
the barrier heights are considerably higher. These observations provide an
insight into the electrical behavior of the FC/h-BN/SC/h-BN heterostructures
and such control over the barrier heights opens up the possibilities for
WSe$_2$-based spintronic devices. | 2004.10962v1 |
2015-04-23 | Fowler-Nordheim Plot Analysis: a Progress Report | The commonest method of characterizing a cold field electron emitter is to
measure its current-voltage characteristics, and the commonest method of
analysing these characteristics is by means of a Fowler-Nordheim (FN) plot.
This tutorial/review-type paper outlines a more systematic method of setting
out the Fowler-Nordheim-type theory of cold field electron emission, and brings
together and summarises the current state of work by the authors on developing
the theory and methodology of FN plot analysis. This has turned out to be far
more complicated than originally expected. Emphasis is placed in this paper on:
(a) the interpretation of FN-plot slopes, which is currently both easier and of
more experimental interest than the analysis of FN-plot intercepts; and (b)
preliminary explorations into developing methodology for interpreting
current-voltage characteristics when there is series resistance in the
conduction path from the high-voltage generator to the emitter's emitting
regions. This work reinforces our view that FN-plot analysis is best carried
out on the raw measured current-voltage data, without pre-conversion into
another data format, particularly if series resistance is present in the
measuring circuit. Relevant formulae are given for extracting
field-enhancement-factor values from such an analysis. | 1504.06134v7 |
2018-07-07 | Three-dimensional quantum Hall effect and metal-insulator transition in ZrTe5 | Symmetry, dimensionality, and interaction are crucial ingredients for phase
transitions and quantum states of matter. As a prominent example, the integer
quantum Hall effect (QHE) represents a topological phase generally regarded as
characteristic for two-dimensional (2D) electronic systems, and its many
aspects can be understood without invoking electron-electron interaction. The
intriguing possibility of generalizing QHE to three-dimensional (3D) systems
was proposed decades ago, yet it remains elusive experimentally. Here, we
report clear experimental evidence for the 3D QHE observed in bulk ZrTe5
crystals. Owing to the extremely high sample quality, the extreme quantum limit
with only the lowest Landau level occupied can be achieved by an applied
magnetic field as low as 1.5 T. Remarkably, in this regime, we observe a
dissipationless longitudinal resistivity rho_xx=0 accompanied with a
well-developed Hall resistivity plateau rho_xy=(1\pm0.1) h/e^2
(\lambda_(F,z)/2), where \lambda_(F,z) is the Fermi wavelength along the field
direction (z axis). This striking result strongly suggests a Fermi surface
instability driven by the enhanced interaction effects in the extreme quantum
limit. In addition, with further increasing magnetic field, both rho_xx and
rho_xy increase dramatically and display an interesting metal-insulator
transition, representing another magnetic field driven quantum phase
transition. Our findings not only unambiguously reveal a novel quantum state of
matter resulting from an intricate interplay among dimensionality, interaction,
and symmetry breaking, but also provide a promising platform for further
exploration of more exotic quantum phases and transitions in 3D systems. | 1807.02678v2 |
2019-01-14 | Detailed physical property characterization of FeTe1-xSex x = 0.0 to 0.50 single crystals | Here, we report self flux single crystal growth of FeTe1-xSex for x = 0 to
0.50 series via solid state reaction route,the resulted crystals as seen are
shiny. X Ray diffraction performed on the surface of crystals elucidated the
growth in 00l plane, i.e. orientation in c direction only. Scanning electron
microscopy (SEM) images showed slab like morphology and EDX (Energy dispersive
X ray analyzer) confirmed that the crystals are closed to their designed
compositions. Rietveld analysis of the XRD patterns of crushed crystal powders
showed that the cell parameters decrease with Se content increase. Coupled
magnetic and structural phase transition temperature, seen as a step in
resistivity for the lower Se concentration and it is not detected for higher x
values. Superconductivity is observed by resistivity measurement for higher Se
concentration with a maximum temperature of 14K at x = 0.50. Thermally
Activated Flux Flow (TAFF) analysis based on high field transport measurements
in superconducting region done for x = 0.20 crystal. Raman spectroscopy at room
temperature of synthesized samples exhibits all the allowed phonon modes with
slight shift to higher frequency with Se content. Mossbauer spectra of
FeTe1-xSex crystals series were recorded at 300 and 5K. At 5K, the average
hyperfine field decreases systematically with Se content increase from 10.6 to
6.1Tesla for x = 0.0 to x = 0.20 samples. This indicates a possibility of
co-existing magnetism and superconductivity in x = 0.07 to 0.20 crystals. For x
= 0.50 sample, no hyperfine field related to magnetic ordering is seen. Based
on above results, detailed phase diagram of the FeTe1-xSex compounds is defined
in the present study. | 1901.04224v1 |
2019-01-24 | Fascinating interplay between Charge Density Wave Order and magnetic field in Non-magnetic Rare-Earth Tritelluride LaTe$_{3}$ | Charge density wave (CDW) states in solids bear an intimate connection to
underlying fermiology. Modification of the latter by a suitable perturbation
provides an attractive handle to unearth novel CDW states. Here, we combine
extensive magnetotransport experiments and first-principles electronic
structure calculations on a non-magnetic tritelluride LaTe$_{3}$ single crystal
to uncover phenomena rare in CDW systems: $(i)$ hump-like feature in the
temperature dependence of resistivity at low temperature under application of
magnetic field, which moves to higher temperature with increasing field
strength, $(ii)$ highly anisotropic large transverse magnetoresistance (MR)
upon rotation of magnetic field about current parallel to crystallographic
c-axis, (iii) anomalously large positive MR with spike-like peaks at
characteristic angles when the angle between current and field is varied in the
bc-plane, (iv) extreme sensitivity of the angular variation of MR on field and
temperature. Moreover, our Hall measurement reveals remarkably high carrier
mobility $\sim$ 33000 cm$^{2}$/Vs, which is comparable to that observed in some
topological semimetals. These novel observations find a comprehensive
explication in our density functional theory (DFT) and dynamical mean field
theory (DMFT) calculations that capture field-induced electronic structure
modification in LaTe$_{3}$. The band structure theory together with transport
calculations suggest the possibility of a second field-induced CDW transition
from the field-reconstructed Fermi surface, which qualitatively explains the
hump in temperature dependence of resistivity at low temperature. Thus, our
study exposes the novel manifestations of the interplay between CDW order and
field-induced electronic structure modifications in LaTe$_{3}$, and establishes
a new route to tune CDW states by perturbations like magnetic field. | 1901.08267v2 |
2019-06-09 | Spin dynamics and unconventional magnetism in insulating La$_{(1-2x)}$Sr$_{2x}$Co$_{(1-x)}$Nb$_{x}$O$_3$ | We study the structural, magnetic, transport and electronic properties of
LaCoO$_3$ with Sr/Nb co-substitution, i.e.,
La$_{(1-2x)}$Sr$_{2x}$Co$_{(1-x)}$Nb$_{x}$O$_3$ using x-ray and neutron
diffraction, dc and ac-magnetization, neutron depolarization, dc-resistivity
and photoemission measurements. The powder x-ray and neutron diffraction data
were fitted well with the rhombohedral crystal symmetry (space group
\textit{R$\bar{3}$c}) in Rietveld refinement analysis. The calculated effective
magnetic moment ($\approx$3.85~$\mu_B$) and average spin ($\approx$1.5) of Co
ions from the analysis of magnetic susceptibility data are consistent with 3+
state of Co ions in intermediate-spin (IS) and high-spin (HS) states in the
ratio of $\approx$50:50, i.e., spin-state of Co$^{3+}$ is preserved at least up
to $x=$ 0.1 sample. Interestingly, the magnetization values were significantly
increased with respect to the $x=$ 0 sample, and the M-H curves show
non-saturated behavior up to an applied maximum magnetic field of $\pm$70 kOe.
The ac-susceptibility data show a shift in the freezing temperature with
excitation frequency and the detailed analysis confirm the slower dynamics and
a non-zero value of the Vogel-Fulcher temperature T$_0$, which suggests for the
cluster spin glass. The unusual magnetic behavior indicates the presence of
complex magnetic interactions at low temperatures. The dc-resistivity
measurements show the insulating nature in all the samples. However, relatively
large density of states $\approx$10$^{22}$ eV$^{-1}$cm$^{-3}$ and low
activation energy $\approx$130~meV are found in $x=$ 0.05 sample. Using x-ray
photoemission spectroscopy, we study the core-level spectra of La 3$d$, Co
2$p$, Sr 3$d$, and Nb 3$d$ to confirm the valence state. | 1906.03659v1 |
2019-10-14 | First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade | First simulations of deuterium shattered pellet injection (SPI) into an ASDEX
Upgrade H-Mode plasma with the JOREK MHD code are presented. Resistivity is
increased by one order of magnitude in most simulations to reduce computational
costs and allow for extensive parameter scans. The effect of various physical
parameters onto MHD activity and thermal quench (TQ) dynamics is studied and
the influence of MHD onto ablation is shown. TQs are obtained quickly after
injection in most simulations with a typical duration of 100 microseconds,
which slows down at lower resistivity. Although the n=1 magnetic perturbation
dominates in the simulations, toroidal harmonics up to n=10 contribute to
stochastization and stochastic transport in the plasma core. The post-TQ
density profile remains hollow for a few hundred microseconds. However, when
flux surfaces re-form around the magnetic axis, the density has become
monotonic again suggesting a beneficial behaviour for runaway electron
avoidance/mitigation. With $10^{21}$ atoms injected, the TQ is typically
incomplete and triggered when the shards reach the q=2 rational surface. At a
larger number of injected atoms, the TQ can set in even before the shards reach
this surface. For low field side injection considered here, repeated formation
of outward convection cells is observed in the ablation region reducing
material assimilation. Responsible is a sudden rise of pressure in the high
density cloud when the stochastic region expands further releasing heat from
the hot core. After the TQ, strong sheared poloidal rotation is created by
Maxwell stress, which contributes to re-formation of flux surfaces. | 1910.06095v4 |
2020-08-25 | Isospin Pomeranchuk effect and the entropy of collective excitations in twisted bilayer graphene | In condensed matter systems, higher temperatures typically disfavors ordered
phases leading to an upper critical temperature for magnetism,
superconductivity, and other phenomena. A notable exception is the Pomeranchuk
effect in 3He, in which the liquid ground state freezes upon increasing the
temperature due to the large entropy of the paramagnetic solid phase. Here we
show that a similar mechanism describes the finite temperature dynamics of spin
and valley-isospins in magic-angle twisted bilayer graphene. Most strikingly a
resistivity peak appears at high temperatures near superlattice filling factor
nu = -1, despite no signs of a commensurate correlated phase appearing in the
low-temperature limit. Tilted field magnetotransport and thermodynamic
measurements of the inplane magnetic moment show that the resistivity peak is
adiabatically connected to a finite-field magnetic phase transition at which
the system develops finite isospin polarization. These data are suggestive of a
Pomeranchuk-type mechanism, in which the entropy of disordered isospin moments
in the ferromagnetic phase stabilizes it relative to an isospin unpolarized
Fermi liquid phase at elevated temperatures. Measurements of the entropy, S/kB
indeed find it to be of order unity per unit cell area, with a measurable
fraction that is suppressed by an in-plane magnetic field consistent with a
contribution from disordered physical spins. In contrast to 3He, however, no
discontinuities are observed in the thermodynamic quantities across this
transition. Our findings imply a small isospin stiffness, with implications for
the nature of finite temperature transport as well as the mechanisms underlying
isospin ordering and superconductivity in twisted bilayer graphene and related
systems. | 2008.10830v4 |
2021-05-18 | One-reactor vacuum and plasma synthesis of transparent conducting oxide nanotubes and nanotrees: from single wire conductivity to ultra-broadband perfect absorbers in the NIR | The eventual exploitation of one-dimensional nanomaterials yet needs the
development of scalable, high yield, homogeneous, and environmentally friendly
methods able to meet the requirements for the fabrication of under design
functional nanomaterials. In this article, we demonstrate a vacuum and plasma
one-reactor approach for the synthesis of the fundamental common element in
solar energy and optoelectronics, i.e. the transparent conducting electrode but
in the form of nanotubes and nanotrees architectures. Although the process is
generic and can be used for a variety of TCOs and wide-bandgap semiconductors,
we focus herein on Indium Doped Tin Oxide (ITO) as the most extended in the
previous applications. This protocol combines widely applied deposition
techniques such as thermal evaporation for the formation of organic nanowires
serving as 1D and 3D soft templates, deposition of polycrystalline layers by
magnetron sputtering, and removal of the template by simply annealing under
mild vacuum conditions. The process variables are tuned to control the
stoichiometry, morphology, and alignment of the ITO nanotubes and nanotrees.
Four-probe characterization reveals the improved lateral connectivity of the
ITO nanotrees and applied on individual nanotubes shows resistivities as low as
3.5 +/- 0.9 x 10-4 {\Omega}.cm, a value comparable to single-crystalline
counterparts. The assessment of diffuse reflectance and transmittance in the
UV-VIS range confirms the viability of the supported ITO nanotubes as a random
optical media working as strong scattering layers. Further ability to form ITO
nanotrees opens the path for practical applications as ultra-broadband
absorbers in the NIR. The demonstrated low resistivity and optical properties
of these ITO nanostructures open the way for their use in LEDs, IR shield,
energy harvesting, nanosensors, and photoelectrochemical applications | 2105.08751v1 |
2021-09-01 | Interaction driven giant thermopower in magic-angle twisted bilayer graphene | Magic-angle twisted bilayer graphene (MtBLG) has proven to be an extremely
promising new platform to realize and study a host of emergent quantum phases
arising from the strong correlations in its narrow bandwidth flat band. In this
regard, thermal transport phenomena like thermopower, in addition to being
coveted technologically, is also sensitive to the particle-hole (PH) asymmetry,
making it a crucial tool to probe the underlying electronic structure of this
material. We have carried out thermopower measurements of MtBLG as a function
of carrier density, temperature and magnetic field, and report the observation
of an unusually large thermopower reaching up to a value as high as $\sim
\bf{100\mu V/K}$ at a low temperature of 1K. Surprisingly, our observed
thermopower exhibiting peak-like features in close correspondence to the
resistance peaks around the integer Moire fillings, including the Dirac Point,
violating the Mott formula. %Surprisingly, our observed thermopower exhibits
peak-like features in close correspondence to the resistance peaks around the
integer Moire fillings, including the Dirac Point, which completely violates
the Mott formula. We show that the large thermopower peaks and their
%non-monotonic dependence with temperature and magnetic field associated
behaviour arise from the emergent highly PH asymmetric electronic structure due
to the cascade of Dirac revivals. Furthermore, the thermopower shows an
anomalous peak around the superconducting transition on the hole side and
points towards the possible role of enhanced superconducting fluctuations in
MtBLG. | 2109.00361v2 |
2022-06-13 | Long-range magnetic order in the anisotropic triangular lattice system CeCd3As3 | We report the physical properties of $R$Cd$_{3}$As$_{3}$ ($R$ = La and Ce)
compounds, crystallized into a hexagonal ScAl$_{3}$C$_{3}$-type structure
($P$6$_{3}$/mmc) such that the $R$ sublattice forms a spin-orbit coupled
triangular lattice. Magnetic susceptibility measurements indicate the 4$f$
electrons of Ce$^{3+}$ ions are well localized and reveal a large magnetic
anisotropy. The electrical resistivity and specific heat measurement for
$R$Cd$_{3}$As$_{3}$ exhibit an anomaly at high temperatures ($T_{0}$ $\sim$ 63
K for $R$ = La and $T_{0}$ $\sim$ 136 K for $R$ = Ce), most likely due to a
structural transition. Specific heat measurements for CeCd$_{3}$As$_{3}$
clearly indicate a long range magnetic order below $T_{N}$ = 0.42 K. Although
the magnetic contribution to the specific heat $C_{m}/T$ increases
significantly below $\sim$ 10 K, the electrical resistivity for
CeCd$_{3}$As$_{3}$ follows typical, metallic behavior inconsistent with Kondo
lattice systems. In CeCd$_3$As$_3$ only $\sim$ 40 $\%$ of the $R \ln(2)$
magnetic entropy is recovered by $T_N$ and the $R$ln(2) entropy is fully
achieved at about the Curie-Weiss temperature $|\theta_{p}|$. Unusually, based
on our current investigations, the magnetic specific heat below $|\theta_{p}|$
is not attributed to a Kondo contribution, but rather associated with the
magnetic ordering and frustration on the triangular lattice. Specific heat
measurements in applied magnetic field show a negligible variation of $T_{N}$
for $H \parallel c$, whereas a suppression of $T_{N}$ is observed above 40 kOe
for $H \parallel ab$. Such behavior is consistent with the application a
magnetic field within the $ab$-plane breaking the triangular symmetry and
partially relieving the magnetic frustration in this system. | 2206.06403v1 |
2022-11-05 | Effect of various electron and hole transport layers on the performance of CsPbI3-based perovskite solar cells: A numerical investigation in DFT, SCAPS-1D, and wxAMPS frameworks | CsPbI3 has recently received tremendous attention as a possible absorber of
perovskite solar cells (PSCs). However, CsPbI3-based PSCs have yet to achieve
the high performance of the hybrid PSCs. In this work, we performed a density
functional theory (DFT) study using the Cambridge Serial Total Energy Package
(CASTEP) code for the cubic CsPbI3 absorber to compare and evaluate its
structural, electronic, and optical properties. The calculated electronic band
gap (Eg) using the GGA-PBE approach of CASTEP was 1.483 eV for this CsPbI3
absorber. Moreover, the computed density of states (DOS) exhibited the dominant
contribution from the Pb-5d orbital, and most charge also accumulated for the
Pb atom as seen from the electronic charge density map. Fermi surface
calculation showed multiband character, and optical properties were computed to
investigate the optical response of CsPbI3. Furthermore, we used IGZO, SnO2,
WS2, CeO2, PCBM, TiO2, ZnO, and C60 as the electron transport layers (ETLs),
and Cu2O, CuSCN, CuSbS2, Spiro-MeOTAD, V2O5, CBTS, CFTS, P3HT, PEDOT: PSS, NiO,
CuO, and CuI as the hole transport layers (HTLs) to identify the best
HTL/CsPbI3/ETL combinations using the SCAPS-1D solar cell simulation software.
Among 96 device structures, the best-optimized device structure,
ITO/TiO2/CsPbI3/CBTS/Au was identified, which exhibited an efficiency of 17.9%.
The effect of absorber and ETL thickness, series resistance, shunt resistance,
and operating temperature was also evaluated for the six best devices along
with their corresponding generation rate, recombination rate,
capacitance-voltage, current density-voltage, and quantum efficiency
characteristics. The obtained results from SCAPS-1D were also compared with
wxAMPS simulation software. | 2211.02968v1 |
2023-01-30 | Infrared ellipsometry study of the charge dynamics in K3p-terphenyl | We report an infrared ellipsometry study of the charge carrier dynamics in
polycrystalline Kxp-terphenyl samples with nominal $x=3$, for which signatures
of high-temperature superconductivity were previously reported. The infrared
spectra are dominated by two Lorentzian bands with maxima around 4 000
cm$^{-1}$ and 12 000 cm$^{-1}$ which, from a comparison with calculations based
on a H\"uckel model are assigned to intra-molecular excitations of $\pi$
electrons of the anionic p-terphenyl molecules. The inter-molecular electronic
excitations are much weaker and give rise to a Drude peak and a similarly weak
Lorentzian band around 220 cm$^{-1}$. A dc resistivity of about 0.3 $\Omega$ cm
at 300 K is deduced from the IR data, comparable to values measured by
electrical resistivity on a twin sample. The analysis of the temperature
dependence of the low-frequency response reveals a gradual decrease of the
plasma frequency and the scattering rate of the Drude peak below 300 K that
gets anomalously enhanced below 90 K. The corresponding missing spectral weight
of the Drude peak appears blue-shifted towards the Lorentz-band at 220
cm$^{-1}$. This characteristic blue-shift signifies an enhanced localization of
the charge carriers at low temperatures and contrasts the behavior expected for
a bulk superconducting state for which the missing spectral weight would be
redshifted to a delta-function at zero frequency that accounts for the
loss-free response of the superconducting condensate. Our data might still be
compatible with a filamentary superconducting state with a volume fraction well
below the percolation limit for which the spatial confinement of the condensate
can result in a plasmonic resonance at finite frequency. | 2302.10097v2 |
2023-08-04 | Observation of Fractionally Quantized Anomalous Hall Effect | The integer quantum anomalous Hall (QAH) effect is a lattice analog of the
quantum Hall effect at zero magnetic field. This striking transport phenomenon
occurs in electronic systems with topologically nontrivial bands and
spontaneous time-reversal symmetry breaking. Discovery of its putative
fractional counterpart in the presence of strong electron correlations, i.e.,
the fractional quantum anomalous Hall (FQAH) effect, would open a new chapter
in condensed matter physics. Here, we report the direct observation of both
integer and fractional QAH effects in electrical measurements on twisted
bilayer MoTe$_2$. At zero magnetic field, near filling factor $\nu = -1$ (one
hole per moir\'e unit cell) we see an extended integer QAH plateau in the Hall
resistance $R_\text{xy}$ that is quantized to $h/e^2 \pm 0.1 \%$ while the
longitudinal resistance $R_\text{xx}$ vanishes. Remarkably, at $\nu=-2/3$ and
$-3/5$ we see plateau features in $R_\text{xy}$ at $3h/2e^2 \pm 1\%$ and
$5h/3e^2 \pm 3\%$, respectively, while $R_\text{xx}$ remains small. All these
features shift linearly in an applied magnetic field with slopes matching the
corresponding Chern numbers $-1$, $-2/3$, and $-3/5$, precisely as expected for
integer and fractional QAH states. In addition, at zero magnetic field,
$R_\text{xy}$ is approximately $2h/e^2$ near half filling ($\nu = -1/2$) and
varies linearly as $\nu$ is tuned. This behavior resembles that of the
composite Fermi liquid in the half-filled lowest Landau level of a
two-dimensional electron gas at high magnetic field. Direct observation of the
FQAH and associated effects paves the way for researching charge
fractionalization and anyonic statistics at zero magnetic field. | 2308.02657v1 |
2023-09-29 | Fractional Quantum Anomalous Hall Effect in a Graphene Moire Superlattice | The fractional quantum anomalous Hall effect (FQAHE), the analog of the
fractional quantum Hall effect1 at zero magnetic field, is predicted to exist
in topological flat bands under spontaneous time-reversal-symmetry breaking.
The demonstration of FQAHE could lead to non-Abelian anyons which form the
basis of topological quantum computation. So far, FQAHE has been observed only
in twisted MoTe2 (t-MoTe2) at moire filling factor v > 1/2. Graphene-based
moire superlattices are believed to host FQAHE with the potential advantage of
superior material quality and higher electron mobility. Here we report the
observation of integer and fractional QAH effects in a rhombohedral pentalayer
graphene/hBN moire superlattice. At zero magnetic field, we observed plateaus
of quantized Hall resistance Rxy = h/(ve^2) at filling factors v = 1, 2/3, 3/5,
4/7, 4/9, 3/7 and 2/5 of the moire superlattice respectively. These features
are accompanied by clear dips in the longitudinal resistance Rxx. In addition,
at zero magnetic field, Rxy equals 2h/e^2 at v = 1/2 and varies linearly with
the filling factor-similar to the composite Fermi liquid (CFL) in the
half-filled lowest Landau level at high magnetic fields. By tuning the gate
displacement field D and v, we observed phase transitions from CFL and FQAH
states to other correlated electron states. Our graphene system provides an
ideal platform for exploring charge fractionalization and (non-Abelian) anyonic
braiding at zero magnetic field, especially considering a lateral junction
between FQAHE and superconducting regions in the same device. | 2309.17436v4 |
2024-03-20 | Effect of annealing on the hot salt corrosion resistance of the fine-grained titanium alpha-alloy Ti-2.5Al-2.6Zr obtained via cold Rotary Swaging | A hot salt corrosion (HSC) test was performed on the fine-grained titanium
alpha-alloy Ti-2.5Al-2.6Zr (Russian industrial alloy PT-7M). The
ultrafine-grained (UFG) microstructure in the titanium alpha-alloy was formed
via cold Rotary Swaging. The grain size and volume fraction of the
recrystallized microstructure in the alloy were varied by choosing appropriate
annealing temperatures and times. The microstructure and corrosion resistance
of UFG alloys were studied after 30 min of annealing at 500-700C and after 1000
h of annealing at 250C. Metallographic studies were carried out to investigate
the effects of annealing on the nature and extent of corrosive damage in the
titanium alpha-alloy Ti-2.5Al-2.6Zr. After HSC tests, surface analyses of the
titanium alpha-alloy samples were conducted using X-ray diffraction and
electron microscopy. During the HSC testing of the titanium alpha-alloy
Ti-2.5Al-2.6Zr, a competitive interaction between intergranular corrosion (IGC)
and pitting corrosion was observed. To the best of our knowledge, it was shown
for the first time that annealing affects the relationship among the IGC,
pitting corrosion and uniform corrosion rates of the titanium alloy. Prolonged
low-temperature annealing at 250C resulted in a more pronounced increase in the
uniform corrosion rate than short-term high-temperature annealing for 30 min at
500-700C. An in-depth analysis of the effect of the structure and phase
composition of the grain boundaries on the susceptibility of the alpha-alloy
Ti-2.5Al-2.6Zr to HSC was conducted. | 2403.13587v1 |
2024-04-23 | Magnetic anisotropy in single-crystalline antiferromagnetic Mn$_2$Au | Multiple recent studies have identified the metallic antiferromagnet Mn$_2$Au
to be a candidate for spintronic applications due to apparent in-plane
anisotropy, preserved magnetic properties above room temperature, and
current-induced N\'eel vector switching. Crystal growth is complicated by the
fact that Mn$_2$Au melts incongruently. We present a bismuth flux method to
grow millimeter-scale bulk single crystals of Mn$_2$Au in order to examine the
intrinsic anisotropic electrical and magnetic properties. Flux quenching
experiments reveal that the Mn$_2$Au crystals precipitate below 550{\deg}C,
about 100{\deg}C below the decomposition temperature of Mn$_2$Au. Bulk Mn$_2$Au
crystals have a room-temperature resistivity of 16-19 $\mu\Omega$-cm and a
residual resistivity ratio of 41. Mn$_2$Au crystals have a dimensionless
susceptibility on the order of 10$^{-4}$, comparable to calculated and
experimental reports on powder samples. Single-crystal neutron diffraction
confirms the in-plane magnetic structure. The tetragonal symmetry of Mn$_2$Au
constrains the $ab$-plane magnetic susceptibility to be constant, meaning that
$\chi_{100}=\chi_{110}$ in the low-field limit, below any spin-flop transition.
We find that three measured magnetic susceptibilities $\chi_{100}$,
$\chi_{110}$, and $\chi_{001}$ are the same order of magnitude and agree with
the calculated prediction, meaning the low-field susceptibility of Mn$_2$Au is
quite isotropic, despite clear differences in $ab$-plane and $ac$-plane
magnetocrystalline anisotropy. Mn$_2$Au is calculated to have an extremely high
in-plane spin-flop field above 30 T, which is much larger than that of another
in-plane antiferromagnet Fe$_2$As (less than 1 T). The subtle anisotropy of
intrinsic susceptibilities may lead to dominating effects from shape,
crystalline texture, strain, and defects in devices that attempt spin readout
in Mn$_2$Au. | 2404.15525v1 |
2006-05-06 | Three-dimensionality of field-induced magnetism in a high-temperature superconductor | Many physical properties of high-temperature (high-Tc) superconductors are
two-dimensional phenomena derived from their square planar CuO2 building
blocks. This is especially true of the magnetism from the copper ions. As
mobile charge carriers enter the CuO2 layers, the antiferromagnetism of the
parent insulators, where each copper spin is antiparallel to its nearest
neighbours1, evolves into a fluctuating state where the spins show tendencies
towards magnetic order of a longer periodicity. For certain charge carrier
densities, quantum fluctuations are sufficiently suppressed to yield static
long-period order2,3,4,5,6, and external magnetic fields also induce such
order7,8,9,10,11,12. Here we show that in contrast to the chemically-controlled
order in superconducting samples, the field-induced order in these same samples
is actually three-dimensional, implying significant magnetic linkage between
the CuO2 planes. The results are important because they show that there are
three-dimensional magnetic couplings which survive into the superconducting
state, and coexist with the crucial inter-layer couplings responsible for
three-dimensional superconductivity. Both types of coupling will straighten the
vortex lines, implying that we have finally established a direct link between
technical superconductivity, which requires zero electrical resistance in an
applied magnetic field and depends on vortex dynamics, and the underlying
antiferromagnetism of the cuprates. | 0605164v1 |
2008-06-24 | Crystal structure and phase transitions across the metal-superconductor boundary in the SmFeAsO1-xFx (0 < x < 0.20) family | The fluorine-doped rare-earth iron oxyarsenides, REFeAsO1-xFx (RE =rare
earth) have recently emerged as a new family of high-temperature
superconductors with transition temperatures (Tc) as high as 55 K (refs 1-4).
Early work has provided compelling evidence that the undoped parent materials
exhibit spin-density-wave (SDW) antiferromagnetic order and undergo a
structural phase transition from tetragonal to orthorhombic crystal symmetry
upon cooling.5 Both the magnetic and structural instabilities are suppressed
upon doping with fluoride ions before the appearance of superconductivity.6,7
Here we use high-resolution synchrotron X-ray diffraction to study the
structural properties of SmFeAsO1-xFx (0 < x < 0.20) in which superconductivity
emerges near x ~ 0.07 and Tc increases monotonically with doping up to x ~
0.20.8 We find that orthorhombic symmetry survives through the
metal-superconductor boundary well into the superconducting regime 2 and the
structural distortion is only suppressed at doping levels, x > 0.15 when the
superconducting phase becomes metrically tetragonal. Remarkably this crystal
symmetry crossover coincides with reported drastic anomalies in the resistivity
and the Hall coefficient8 and a switch of the pressure coefficient of Tc from
positive to negative,9 thereby implying that the low-temperature structure
plays a key role in defining the electronic properties of these
superconductors. | 0806.3962v1 |
2012-04-23 | Integrating Functional Oxides with Graphene | Graphene-oxide hybrid structures offer the opportunity to combine the
versatile functionalities of oxides with the excellent electronic transport in
graphene. Understanding and controlling how the dielectric environment affects
the intrinsic properties of graphene is also critical to fundamental studies
and technological development of graphene. Here we review our recent effort on
understanding the transport properties of graphene interfaced with
ferroelectric Pb(Zr,Ti)O_3 (PZT) and high-k HfO_2. Graphene field effect
devices prepared on high-quality single crystal PZT substrates exhibit up to
tenfold increases in mobility compared to SiO_2-gated devices. An unusual and
robust resistance hysteresis is observed in these samples, which is attributed
to the complex surface chemistry of the ferroelectric. Surface polar optical
phonons of oxides in graphene transistors play an important role in the device
performance. We review their effects on mobility and the high source-drain bias
saturation current of graphene, which are crucial for developing graphene-based
room temperature high-speed amplifiers. Oxides also introduce scattering
sources that limit the low temperature electron mobility in graphene. We
present a comprehensive study of the transport and quantum scattering times to
differentiate various scattering scenarios and quantitatively evaluate the
density and distribution of charged impurities and the effect of dielectric
screening. Our results can facilitate the design of multifunctional
nano-devices utilizing graphene-oxide hybrid structures. | 1204.5161v1 |
2012-08-30 | High-pressure flux growth, structural, and superconducting properties of LnFeAsO (Ln = Pr, Nd, Sm) single crystals | Single crystals of the LnFeAsO (Ln1111, Ln = Pr, Nd, and Sm) family with
lateral dimensions up to 1 mm were grown from NaAs and KAs flux at high
pressure. The crystals are of good structural quality and become
superconducting when O is partially substituted by F (PrFeAsO1-xFx and
NdFeAsO1-xFx) or when Fe is substituted by Co (SmFe1-xCoxAsO). From
magnetization measurements, we estimate the temperature dependence and
anisotropy of the upper critical field and the critical current density of
underdoped PrFeAsO0.7F0.3 crystal with Tc = 25 K. Single crystals of
SmFe1-xCoxAsO with maximal Tc up to 16.3 K for x = 0.08 were grown for the
first time. From transport and magnetic measurements we estimate the critical
fields and their anisotropy, and find these superconducting properties to be
quite comparable to the ones in SmFeAsO1-xFx with a much higher Tc of = 50 K.
The magnetically measured critical current densities are as high as 109 A/m2 at
2 K up to 7 T, with indication of the usual fishtail effect. The upper critical
field estimated from resistivity measurements is anisotropic with slopes of
-8.7 T/K (H // ab-plane) and -1.7 T/K (H // c-axis). This anisotropy (= 5) is
similar to that in other Ln1111 crystals with various higher Tc s. | 1208.6207v2 |
2013-09-06 | MgB2 nonlinear properties investigated under localized high rf magnetic field excitation-report 2 | The high transition temperature and low surface resistance of MgB2 attracts
interest in its potential application in superconducting radio frequency
accelerating cavities. However, compared to traditional Nb cavities, the
viability of MgB2 at high rf fields is still open to question. Our approach is
to study the nonlinear electrodynamics of the material under localized rf
magnetic fields. Because of the presence of the small superconducting gap in
the $\pi$ band, the nonlinear response of MgB2 at low temperature is
potentially complicated compared to a single-gap s-wave superconductor such as
Nb. Understanding the mechanisms of nonlinearity coming from the two-band
structure of MgB2, as well as extrinsic sources of nonlinearity, is an urgent
requirement. A localized and strong rf magnetic field, created by a magnetic
write head, is integrated into our nonlinear-Meissner-effect scanning microwave
microscope [Tamin Tai, X. X. Xi, C. G. Zhuang, D. I. Mircea, and S. M. Anlage,
IEEE Trans. Appl. Supercond. 21, 2615 (2011)]. MgB2 films with thickness 50 nm,
fabricated by a hybrid physical-chemical vapor deposition technique on
dielectric substrates, are measured at a fixed location and show a strongly
temperature-dependent third harmonic response. We propose that several possible
mechanisms are responsible for this nonlinear response. | 1309.1706v1 |
2013-12-26 | A Novel High-Pressure Monoclinic Metallic Phase of V2O3 | Vanadium sesquioxide, V2O3, is a prototypical metal-to-insulator system
where, in temperature-dependent studies, the transition always coincides with a
corundum-to-monoclinic structural transition. As a function of pressure, V2O3
follows the expected behavior of increased metallicity due to a larger
bandwidth for pressures up to 12.5 GPa. Surprisingly, for higher pressures when
the structure becomes unstable, the resistance starts to increase. Around 32.5
GPa at 300 K, we observe a novel pressure-induced corundum-to-monoclinic
transition between two metallic phases, showing that the structural phase
transition can be decoupled from the metal-insulator transition. Using X-ray
Raman scattering, we find that screening effects, which are strong in the
corundum phase, become weakened at high pressures. Theoretical calculations
indicate that this can be related to a decrease in coherent quasiparticle
strength, suggesting that the high-pressure phase is likely a critical
correlated metal, on the verge of Mott-insulating behavior. | 1312.7063v1 |
2014-06-19 | Synthesis of SnTe Nanoplates with {100} and {111} Surfaces | SnTe is a topological crystalline insulator that possesses spin-polarized,
Dirac-dispersive surface states protected by crystal symmetry. Multiple surface
states exist on the {100}, {110}, and {111} surfaces of SnTe, with the band
structure of surface states depending on the mirror symmetry of a particular
surface. Thus, to access surface states selectively, it is critical to control
the morphology of SnTe such that only desired crystallographic surfaces are
present. Here, we grow SnTe nanostructures using vapor-liquid-solid and
vapor-solid growth mechanisms. Previously, SnTe nanowires and nanocrystals have
been grown.1-4 In this report, we demonstrate synthesis of SnTe nanoplates with
lateral dimensions spanning tens of microns and thicknesses of a hundred
nanometers. The top and bottom surfaces are either (100) or (111), maximizing
topological surface states on these surfaces. Magnetotransport on these SnTe
nanoplates shows high bulk carrier density, consistent with bulk SnTe crystals
arising due to defects such as Sn vacancies. In addition, we observe a
structural phase transition in these nanoplates from the high temperature rock
salt to low temperature rhombohedral structure. For nanoplates with very high
carrier density, we observe a slight upturn in resistance at low temperatures,
indicating electron-electron interactions. | 1406.5227v1 |
2017-12-13 | High Field (up to 140kOe) Angle Dependent Magneto Transport of Bi2Te3 Single Crystals | We report the angle dependent high field (up to 140kOe) magneto transport of
Bi2Te3 single crystals, a well-known topological insulator. The crystals were
grown from melt of constituent elements via solid state reaction route by
self-flux method. Details of crystal growth along with their brief
characterization up to 5 Tesla applied field was reported by some of us
recently [J. Magn. Mag. Mater. 428, 213 (2017)]. The angle dependence of the
magneto-resistance (MR) of Bi2Te3 follows the cos Theta function i.e., MR is
responsive, when the applied field is perpendicular (tilt angle Theta = o
and/or 180) to the transport current. The low field (10 kOe) MR showed the
signatures of weak anti localization (WAL) character with typical cusp near
origin at 5 K. Further, the MR is linear right up to highest applied field of
140 kOe. The large positive MR are observed up to high temperatures and are
above 250 and 150 percent at 140 kOe in perpendicular fields at 50 K and 100 K
respectively. Heat capacity CP(T) measurements revealed the value of Debye
temperature to be 135 K. ARPES (angle resolved photoemission spectroscopy) data
clearly showed that the bulk Bi2Te3 single crystal consists of a single Dirac
cone. | 1712.04632v1 |
2018-05-14 | Structural Dependence of Chemical Durability in Modified Aluminoborate Glasses | Alkali and alkaline earth aluminoborate glasses feature high resistance to
cracking under sharp contact loading compared to other oxide glasses. However,
due to the high content of hygroscopic B2O3, it is expected that applications
of these glasses could be hindered by poor chemical durability in aqueous
solutions. Indeed, the compositional and structural dependence of their
dissolution kinetics remains unexplored. In this work, we correlate the
dissolution rates of aluminoborate glasses in acidic, neutral, and basic
solutions with the structural changes induced by varying the aluminum-to-boron
ratio. In detail, we investigate a total of seventeen magnesium, lithium, and
sodium aluminoborate glasses with fixed modifier content of 25 mol%. We show
that the structural changes induced by alumina depend on the network modifier.
We also demonstrate a correlation between the chemical durability at various pH
values and the structural changes in Mg-, Li- and Na- aluminoborate glasses.
The substitution of alumina by boron oxide leads to a general decrease of
chemical corrosion in neutral and acidic solutions. The lowest dissolution rate
value is observed in Mg-aluminoborate glasses, as a consequence of the
intermediate character of magnesium which can increase the network
cross-linking. For basic solutions, the chemical durability is almost constant
for the different amount of alumina in the three series, likely because B2O3 is
susceptible to nucleophilic attack, which is favored in high-OH- solutions. | 1805.05191v1 |
2018-06-12 | Characterization of a depleted monolithic pixel sensors in 150 nm CMOS technology for the ATLAS Inner Tracker upgrade | This work presents a depleted monolithic active pixel sensor (DMAPS)
prototype manufactured in the LFoundry 150\,nm CMOS process. DMAPS exploit high
voltage and/or high resistivity inclusion of modern CMOS technologies to
achieve substantial depletion in the sensing volume. The described device,
named LF-Monopix, was designed as a proof of concept of a fully monolithic
sensor capable of operating in the environment of outer layers of the ATLAS
Inner Tracker upgrade in 2025 for the High Luminosity Large Hadron Collider
(HL-LHC). This type of devices has a lower production cost and lower material
budget compared to presently used hybrid designs. In this work, the chip
architecture will be described followed by the characterization of the
different pre-amplifier and discriminator flavors with an external injection
signal and an iron source (5.9\,keV x-rays). | 1806.04400v1 |
2018-06-14 | Demonstration of nonpolar m-plane vertical GaN-on-GaN p-n power diodes grown on free-standing GaN substrates | This work demonstrates the first nonpolar vertical GaN on GaN pn power diodes
grown on m-plane free standing substrates by MOCVD. The SEM and HRXRD results
showed the good crystal quality of the homoepitaxial nonpolar structure with
low defect densities. The CL result confirmed the nonpolar p GaN was of high
quality with considerably reduced deep level states. At forward bias, the
device showed good rectifying behaviors with a turn-on voltage of 4.0 V, an
on-resistance of 2.3 mohmcm2, and a high on off ratio of 1e10. At reverse bias,
the current leakage and breakdown were described by the trap assisted space
charge limited current conduction mechanism, where I was proportional to V
power 4.5. The critical electrical field was calculated to be 2.0 MV per cm
without field plates or edge termination, which is the highest value reported
on nonpolar power devices. The high performance m-plane p-n diodes can serve as
key building blocks to further develop nonpolar GaN power electronics and
polarization-engineering-related advanced power device structures for power
conversion applications. | 1806.05308v1 |
2019-09-23 | Superconductivity up to 243 K in yttrium hydrides under high pressure | The discovery of high-temperature conventional superconductivity in H3S with
a critical temperature of Tc=203 K was followed by the recent record of Tc ~250
K in the face-centered cubic (fcc) lanthanum hydride LaH10 compound. It was
realized in a new class of hydrogen-dominated compounds having a clathrate-like
crystal structure in which hydrogen atoms form a 3D framework and surround a
host atom of rare earth elements. Yttrium hydrides are predicted to have even
higher Tc exceeding room temperature. In this paper, we synthesized and refined
the crystal structure of new hydrides: YH4, YH6, and YH9 at pressures up to 237
GPa finding that YH4 crystalizes in the I4/mmm lattice, YH6 in Im-3m lattice
and YH9 in P63/mmc lattice in excellent agreement with the calculations. The
observed very high-temperature superconductivity is comparable to that found in
fcc-LaH10: the pressure dependence of Tc for YH9 also displays a "dome like
shape" with the highest Tc of 243 K at 201 GPa. We also observed a Tc of 227 K
at 237 GPa for the YH6 phase. However, the measured Tcs are notably lower by
~30 K than predicted. Evidence for superconductivity includes the observation
of zero electrical resistance, a decrease of Tc under an external magnetic
field and an isotope effect. The theoretically predicted fcc YH10 with the
promising highest Tc>300 K was not stabilized in our experiments under
pressures up to 237 GPa. | 1909.10482v1 |
2019-02-26 | Modelling a Transition-Edge Sensor X-ray Microcalorimeter Linear Array for Compton Profile Measurements and Energy Dispersive Diffraction | Transition-edge sensors are a type of superconducting detector that offers
high energy resolution based on their sharp resistance-temperature feature in
the superconducting-to-normal transition. TES X-ray microcalorimeters have
typically been designed and used for spectroscopic applications. In this work,
we present a design optimization for a TES X-ray microcalorimeter array for
high-energy scattering and diffraction measurements. In particular, Compton
scattering provides information about the electron momentum distribution, while
energy dispersive diffraction provides structural information about dense
engineering materials. Compton scattering and energy dispersive diffraction
experiments must be conducted in the very hard X-ray regime (~ 100 keV),
demanding a high X-ray stopping power in the detector; therefore, an absorber
with a large heat capacity is needed in conjunction with the TES. In addition,
both applications would benefit from an array composed of parallel strips. We
present a design for a TES X-ray microcalorimeter optimized for such
applications. In particular, we model the longitudinal position dependence due
to the finite thermal diffusion time in the absorber. | 1902.10047v2 |
2019-07-14 | Current-Induced magnetization switching by the high spin Hall conductivity $α$-W | The spin Hall effect originating from 5d heavy transition metal thin films
such as Pt, Ta, and W is able to generate efficient spin-orbit torques that can
switch adjacent magnetic layers. This mechanism can serve as an alternative to
conventional spin-transfer torque for controlling next-generation magnetic
memories. Among all 5d transition metals, W in its resistive amorphous phase
typically shows the largest spin-orbit torque efficiency ~ 0.20-0.50. In
contrast, its conductive and crystalline $\alpha$ phase possesses a
significantly smaller efficiency ~ 0.03 and no spin-orbit torque switching has
yet been realized using $\alpha$-W thin films as the spin Hall source. In this
work, through a comprehensive study of high quality W/CoFeB/MgO and the
reversed MgO/CoFeB/W magnetic heterostructures, we show that although
amorphous-W has a greater spin-orbit torque efficiency, the spin Hall
conductivity of $\alpha$-W
($|\sigma_{\operatorname{SH}}^{\alpha\operatorname{-W}}|=3.71\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$)
is ~3.5 times larger than that of amorphous-W
($|\sigma_{\operatorname{SH}}^{\operatorname{amorphous-W}}|=1.05\times10^{5}\operatorname{\Omega}^{-1}\operatorname{m}^{-1}$).
Moreover, we demonstrate spin-orbit torque driven magnetization switching using
a MgO/CoFeB/$\alpha$-W heterostructure. Our findings suggest that the
conductive and high spin Hall conductivity $\alpha$-W can be a potential
candidate for future low power consumption spin-orbit torque memory
applications. | 1907.06192v1 |
2020-02-22 | Electron irradiation on multilayer PdSe$_2$ field effect transistors | Palladium diselenide (PdSe2) is a recently isolated layered material that has
attracted a lot of interest for the pentagonal structure, the air stability and
the electrical properties largely tunable by the number of layers. In this
work, PdSe2 is used in the form of multilayer as the channel of back-gate
field-effect transistors, which are studied under repeated electron
irradiations. Source-drain Pd leads enable contacts with resistance below 350
kOhm um. The transistors exhibit a prevailing n-type conduction in high vacuum,
which reversibly turns into ambipolar electric transport at atmospheric
pressure. Irradiation by 10 keV electrons suppresses the channel conductance
and promptly transforms the device from n-type to p-type. An electron fluence
as low as 160 e-/nm2 dramatically change the transistor behavior demonstrating
a high sensitivity of PdSe2 to electron irradiation. The sensitivity is lost
after few exposures, that is a saturation condition is reached for fluence
higher than 4000 e-/nm2. The damage induced by high electron fluence is
irreversible as the device persist in the radiation-modified state for several
hours, if kept in vacuum and at room temperature. With the support of numerical
simulation, we explain such a behavior by electron-induced Se atom vacancy
formation and charge trapping in slow trap states at the Si/SiO_2 interface. | 2002.09785v1 |
2020-04-27 | Recent advancements of the NEWS-G experiment | NEWS-G (New Experiments With Spheres-Gas) is an experiment aiming to shine a
light on the dark matter conundrum with a novel gaseous detector, the spherical
proportional counter. It uses light gases, such as hydrogen, helium, and neon,
as targets to expand dark matter searches to the sub-GeV/c$^{2}$ mass region.
NEWS-G produced its first results with a 60 cm in diameter detector installed
at LSM (France), excluding at 90% C.L. cross-sections above $4.4\cdot{10}^{37}$
cm$^{2}$ for dark matter candidates of 0.5 GeV/c$^{2}$ mass. Currently, a 140
cm in diameter detector is being built at LSM and a commissioning run is
underway, prior to its installation at SNOLAB (Canada) at the end of the year.
Presented here are developments incorporated in this new detector: a) sensor
technologies using resistive materials and multi-anode read-out that allow high
gain and high pressure operation; b) gas purification techniques to remove
contaminants (H$_{2}$O, O$_{2}$); c) reduction of ${}^{210}$Pb induced
background through copper electroforming methods; d) utilisation of UV-lasers
for detector calibration, detector response monitoring and estimation of gas
related fundamental properties. This next phase of NEWS-G will allow searches
for low mass dark matter with unprecedented sensitivity. | 2004.12795v1 |
2016-03-02 | Conformal Titanium Nitride in a Porous Silicon Matrix: a Nanomaterial for In-Chip Supercapacitors | Today's supercapacitor energy storages are typically discrete devices aimed
for printed boards and power applications. The development of autonomous sensor
networks and wearable electronics and the miniaturisation of mobile devices
would benefit substantially from solutions in which the energy storage is
integrated with the active device. Nanostructures based on porous silicon (PS)
provide a route towards integration due to the very high inherent surface area
to volume ratio and compatibility with microelectronics fabrication processes.
Unfortunately, pristine PS has limited wettability and poor chemical stability
in electrolytes and the high resistance of the PS matrix severely limits the
power efficiency. In this work, we demonstrate that excellent wettability and
electro-chemical properties in aqueous and organic electrolytes can be obtained
by coating the PS matrix with an ultra-thin layer of titanium nitride by atomic
layer deposition. Our approach leads to very high specific capacitance (15
F/cm$^3$), energy density (1.3 mWh/cm$^3$), power density (up to 214 W/cm$^3$)
and excellent stability (more than 13,000 cycles). Furthermore, we show that
the PS-TiN nanomaterial can be integrated inside a silicon chip monolithically
by combining MEMS and nanofabrication techniques. This leads to realisation of
in-chip supercapacitor, i.e., it opens a new way to exploit the otherwise
inactive volume of a silicon chip to store energy. | 1603.00798v1 |
2019-02-28 | Effect of atomic ordering on the magnetic anisotropy of single crystal Ni80Fe20 | We investigate the effect of atomic ordering on the magnetic anisotropy of
Ni80Fe20 at.% (Py). To this end, Py films were grown epitaxially on MgO (001)
using dc magnetron sputtering (dcMS) and high power impulse magnetron
sputtering (HiPIMS). Aside from twin boundaries observed in the latter case,
both methods present high quality single crystals with cube-on-cube epitaxial
relationship as verified by the polar mapping of important crystal planes.
However, X-ray diffraction results indicate higher order for the dcMS deposited
film towards L12 Ni3Fe superlattice. This difference can be understood by the
very high deposition rate of HiPIMS during each pulse which suppresses adatom
mobility and ordering. We show that the dcMS deposited film presents biaxial
anisotropy while HiPIMS deposition gives well defined uniaxial anisotropy.
Thus, higher order achieved in the dcMS deposition behaves as predicted by
magnetocrystalline anisotropy i.e. easy axis along the [111] direction that
forced in the plane along the [110] direction due to shape anisotropy. The
uniaxial behaviour in HiPIMS deposited film then can be explained by pair
ordering or more recent localized composition non-uniformity theories. Further,
we studied magnetoresistance of the films along the [100] directions using an
extended van der Pauw method. We find that the electrical resistivities of the
dcMS deposited film are lower than in their HiPIMS counterparts verifying the
higher order in the dcMS case. | 1903.00105v1 |
2019-03-29 | Multi-contact Phase Change Toggle Logic Device Utilizing Thermal Crosstalk | Phase change memory (PCM) is an emerging high speed, high density, high
endurance, and scalable non-volatile memory technology which utilizes the large
resistivity contrast between the amorphous and crystalline phases of
chalcogenide materials such as Ge2Sb2Te5 (GST). In addition to being used as a
standalone memory, there has been a growing interest in integration of PCM
devices on top of the CMOS layer for computation in memory and neuromorphic
computing. The large CMOS overhead for memory controllers is a limiting factor
for this purpose. Transferring functionality like routing, multiplexing, and
logic to the memory layer can substantially reduce the CMOS overhead, making it
possible to integrate 100s of GB of PCM storage on top of a conventional CPU.
In this work, we present computational analysis of a phase change device
concept that can perform toggle operations. The toggle functionality is
achieved using two physical mechanisms: (i) isolation of different read
contacts due to amorphization between different write contact pairs, and (ii)
thermal cross-talk between a molten region and a previously amorphized region.
Phase-change devices with six contacts can be implemented as toggle flip-flops,
multiplexer, or demultiplexer when interfaced with CMOS transistors. Here, we
demonstrate the operation of the device as a toggle flip-flop with 5
transistors, requiring ~50% of the footprint compared to conventional CMOS
alternatives, with the added advantage of non-volatility. | 1904.00836v1 |
2021-01-05 | High-Temperature Superconductivity in Cerium Superhydrides | The discoveries of high-temperature superconductivity in H3S and LaH10 have
excited the search for superconductivity in compressed hydrides. In contrast to
rapidly expanding theoretical studies, high-pressure experiments on hydride
superconductors are expensive and technically challenging. Here we
experimentally discover superconductivity in two new phases,Fm-3m-CeH10 (SC-I
phase) and P63/mmc-CeH9 (SC-II phase) at pressures that are much lower (<100
GPa) than those needed to stabilize other polyhydride superconductors.
Superconductivity was evidenced by a sharp drop of the electrical resistance to
zero, and by the decrease of the critical temperature in deuterated samples and
in an external magnetic field. SC-I has Tc=115 K at 95 GPa, showing expected
decrease on further compression due to decrease of the electron-phonon coupling
(EPC) coefficient {\lambda} (from 2.0 at 100 GPa to 0.8 at 200 GPa). SC-II has
Tc = 57 K at 88 GPa, rapidly increasing to a maximum Tc ~100 K at 130 GPa, and
then decreasing on further compression. This maximum of Tc is due to a maximum
of {\lambda} at the phase transition from P63/mmc-CeH9 into a symmetry-broken
modification C2/c-CeH9. The pressure-temperature conditions of synthesis affect
the actual hydrogen content, and the actual value of Tc. Anomalously low
pressures of stability of cerium superhydrides make them appealing for studies
of superhydrides and for designing new superhydrides with even lower pressures
of stability. | 2101.01315v2 |
2015-07-30 | Likelihood-free inference in high-dimensional models | Methods that bypass analytical evaluations of the likelihood function have
become an indispensable tool for statistical inference in many fields of
science. These so-called likelihood-free methods rely on accepting and
rejecting simulations based on summary statistics, which limits them to low
dimensional models for which the absolute likelihood is large enough to result
in manageable acceptance rates. To get around these issues, we introduce a
novel, likelihood-free Markov-Chain Monte Carlo (MCMC) method combining two key
innovations: updating only one parameter per iteration and accepting or
rejecting this update based on subsets of statistics sufficient for this
parameter. This increases acceptance rates dramatically, rendering this
approach suitable even for models of very high dimensionality. We further
derive that for linear models, a one dimensional combination of statistics per
parameter is sufficient and can be found empirically with simulations. Finally,
we demonstrate that our method readily scales to models of very high
dimensionality using both toy models as well as by jointly inferring the
effective population size, the distribution of fitness effects of new mutations
(DFE) and selection coefficients for each locus from data of a recent
experiment on the evolution of drug-resistance in Influenza. | 1507.08612v2 |
2019-06-19 | Scalable, green fabrication of single-crystal noble metal films and nanostructures for low-loss nanotechnology applications | High quality metal thin films and nanostructures are critical building blocks
for next generation nanotechnologies. They comprise low-loss circuit elements
in nanodevices, provide new catalytic pathways for water splitting and $CO_2$
reduction technologies, and enable the confinement of spatially extended
electromagnetic waves to be harnessed for application in information
processing, energy harvesting, engineered metamaterials, and new technologies
that will operate in the quantum plasmonics limit. However, the controlled
fabrication of high-definition single-crystal subwavelength metal
nanostructures remains a significant hurdle, due to the tendency for
polycrystalline metal growth using conventional physical vapor deposition
methods, and the challenges associated with placing solution-grown nanocrystals
in desired orientations and locations on a surface to fabricate functional
devices. Here, we introduce a new scalable, green, wet chemical approach to
monocrystalline noble metals that enables the fabrication of ultrasmooth,
epitaxial, single-crystal films of controllable thickness. They are ideal for
the subtractive manufacture of nanostructure through ion beam milling, and
additive crystalline nanostructure via lithographic patterning to enable large
area, single-crystal metamaterials and high aspect ratio nanowires. Our
single-crystal nanostructures demonstrate improved feature quality and pattern
transfer yield, reduced optical and resistive losses, tailored local fields,
and greatly improved stability compared to polycrystalline structures,
supporting greater local field enhancements and enabling new practical advances
at the nanoscale. | 1906.07879v1 |
2019-10-23 | Implications for Dark Matter Direct Detection in the Presence of LIGO-Motivated Primordial Black Holes | We discuss formation of dark matter (DM) mini-halos around primordial black
holes (PBHs) and its implication on DM direct detection experiments, including
axion searches. Motivated by LIGO observations, we consider $f_{\textrm{DM}}
\simeq 0.01$ as the fraction of DM in PBHs with masses $10 M_{\odot} - 70
M_{\odot}$. In this case, we expect the presence of dressed PBHs after Milky
Way halo formation with mini-halo masses peaked around $M_{\textrm{halo}} \sim
(50-55) M_{\textrm{PBH}}$. We analyze the effect of tidal forces acting on
dressed PBHs within the Milky Way galaxy. In the solar neighborhood, the
mini-halos are resistant against tidal disruption from the mean-field potential
of the galaxy and encounters with stars, but they undergo a small level of
disruption caused by disk shocking. The presence of mini-halos around
LIGO-motivated PBHs today could reduce by half the local dark matter
background. High-resolution simulations are encouraged. If the proposed
scenario is realized, chances of direct detection of DM would decrease. | 1910.10575v3 |
2020-06-24 | Predicting the propensity for thermally activated $β$ events in metallic glasses via interpretable machine learning | The elementary excitations in metallic glasses (MGs), i.e., $\beta$ processes
that involve hopping between nearby sub-basins, underlie many unusual
properties of the amorphous alloys. A high-efficacy prediction of the
propensity for those activated processes from solely the atomic positions,
however, has remained a daunting challenge. Recently, employing well-designed
site environment descriptors and machine learning (ML), notable progress has
been made in predicting the propensity for stress-activated $\beta$ processes
(i.e., shear transformations) from the static structure. However, the complex
tensorial stress field and direction-dependent activation would induce
non-trivial noises in the data, limiting the accuracy of the structure-property
mapping learned. Here, we focus on the thermally activated elementary
excitations and generate high-quality data in several Cu-Zr MGs, allowing
quantitative mapping of the potential energy landscape. After fingerprinting
the atomic environment with short- and medium-range interstice distribution, ML
can identify the atoms with strong resistance or high compliance to thermal
activation, at an unprecedented accuracy over ML models for stress-driven
activation events. Interestingly, a quantitative "between-task" transferring
test reveals that our learnt model can also generalize to predict the
propensity of shear transformation. Our dataset is potentially useful for
benchmarking future ML models on structure-property relationships in MGs. | 2006.13552v1 |
2020-10-07 | Physical properties and electronic structure of single-crystal KCo$_2$As$_2$ | We present a method for producing high quality KCo2As2 crystals, stable in
air and suitable for a variety of measurements. X-ray diffraction, magnetic
susceptibility, electrical transport and heat capacity measurements confirm the
high quality and an absence of long range magnetic order down to at least 2 K.
Residual resistivity values approaching 0.25 $\mu\Omega$~cm are representative
of the high quality and low impurity content, and a Sommerfeld coefficient
$\gamma$ = 7.3 mJ/mol K$^2$ signifies weaker correlations than the Fe-based
counterparts. Together with Hall effect measurements, angle-resolved
photoemission experiments reveal a Fermi surface consisting of electron pockets
at the center and corner of the Brillouin zone, in line with theoretical
predictions and in contrast to the mixed carrier types of other pnictides with
the ThCr2Si2 structure. A large, linear magnetoresistance of 200\% at 14~T,
together with an observed linear and hyperbolic, rather than parabolic, band
dispersions are unusual characteristics of this metallic compound and may
indicate more complex underlying behavior. | 2010.03447v2 |
2020-10-16 | Investigation of n-type dilute magnetic semiconductor property observed in amorphous AlNO alloy thin film incorporated with dilute nitrogen at 300K | In the present work, a thin film was deposited on quartz substrate by
reactive RF magnetron sputtering of high purity (99.999%) aluminium target
using ultra-high pure (Ar + N2) gas mixture. The percentage ratio of Ar and N2
in the gas mixture was 95% and 5%, respectively. Chemical characterization
using x-ray photoelectron spectroscopy (XPS) and energy-dispersive xray (EDX)
spectroscopy reveals that in the presence of dilute nitrogen, Al prefers to
react with residual oxygen to form Al2O3 while the nitrogen is incorporated in
it. The stoichiometry of bulk film is Al2N0.38O3.1. Magnetic and electrical
properties measurement shows that the film exhibits ntype dilute magnetic
semiconductor (DMS) property at 300K. The film has low electrical resistivity
of 6.3 {\Omega}-cm and high carrier mobility of 5.7*106 cm2V-1s-1 at 300K. A
density functional theory (DFT) calculation was performed to investigate the
origin of observed magnetism in the film. From first-principles calculation
based on DFT, it is found that for thermodynamic stability dilute nitrogen
incorporated in Al2O3 preferred to sit at the interstitial site, which is
responsible for observed magnetic property. Present study reported here
provides a new insight to prepare rarely observed n-type DMS at room
temperature by incorporating nitrogen interstitials in Al2O3, which is
desirable for potential application in the field of spintronics. | 2010.08361v1 |
2020-11-03 | In situ mechanical testing of an Al matrix composite to investigate compressive plasticity and failure on multiple length scales | SiC particle-reinforced Al matrix composites exhibit high strength, high wear
resistance, and excellent high-temperature performance, but can also have low
plasticity and fracture toughness, which limits their use in structural
applications. This study investigates the plasticity and failure of such a
composite on multiple length scales, from strain localization through a complex
microstructure to the debonding of individual microparticles from the matrix.
Three microscale pillars containing microstructures with different complexities
and sizes/volume fraction of SiC particles were used to study the effect of
these features on deformation. For the matrix, nanoscale intermetallic
precipitates within the Al grains contribute most to the strengthening effect,
and the Al grain boundaries are shown to be effective obstacles for preventing
strain localization by dominant shear bands and, therefore, catastrophic
failure. When shear localization occurs, SiC particles can then debond from the
matrix if the shear band and interface are aligned. To investigate whether the
interface is a weak point during catastrophic failure, a number of SiC
particles were separated from the matrix with direct debonding tests, which
yield an interface strength that is much higher than the critical resolved
shear stress for a pillar exhibiting both shear localization and interface
debonding. Therefore, the matrix-particle interface is ruled out as a possible
weak point, and instead shear localization is identified as the mechanism that
can drive subsequent interface debonding. | 2011.01390v3 |
2020-12-04 | Revealing the Nanostructure of Mesoporous Fuel Cell Catalyst Supports for Durable, High-Power Performance | Achieving high power performance and durability with low Pt loadings are
critical challenges for proton exchange membrane fuel cells. PtCo catalysts
developed on new carbon black supports show promise by simultaneously providing
good oxygen reduction kinetics and local oxygen transport. We investigate the
role of nanoscale morphology in the performance of these catalysts supported on
accessible (HSC-e and HSC-f) and conventional (Ketjen Black) porous carbons
using 3D electron tomography, nitrogen sorption, and electrochemical
performance measurements. We find that the accessible porous carbons have
hollow interiors with mesopores that are larger and more numerous than
conventional porous carbons. However, mesopore-sized openings (>2nm width) are
too rare to account for significant oxygen transport. Instead we propose the
primary oxygen transport pathway into the interior is through 1-2nm microporous
channels permeating the carbon. The increased mesoporosity in the accessible
porous carbons results in a shorter diffusion pathlength through constrictive,
tortuous micropores in the support shell leading to lower local oxygen
transport resistance. In durability testing, the accessible porous carbons show
faster rates of electrochemical surface area loss, likely from fewer
constrictive pores that would mitigate coarsening, but maintain superior high
current density performance at end of life from the improved local oxygen
transport. | 2012.02879v1 |
2020-12-08 | Complex impedance and Raman spectroscopy of Na$_{0.5}$(Bi$_{1-x}$Dy$_x$)$_{0.5}$TiO$_3$ ceramics | In this work structural refinement, complex impedance spectroscopy, and Raman
spectroscopy have been investigated on
Na$_{0.5}$(Bi$_{1-x}$Dy$_x$)$_{0.5}$TiO$_3$ (xDyNBT) ceramic systems. The pure
NBT, 2DyNBT and 5DyNBT compounds crystallize in a rhombohedral structure while
the 15DyNBT composition crystallizes in an orthorhombic Pnma structure. We
reported that dysprosium addition affects the phase transition temperatures as
well as the dielectric losses. The electrical transport at high temperatures
was investigated using the CIS over a wide frequency range. The studied samples
showed a non-Debye type process, with a short-range relaxation for the pure NBT
and a coexistence of both localized and long-range relaxations of charge
carriers for the 2DyNBT and 5DyNBT compounds. For the high concentration,
15DyNBT, a short-range relaxation is observed. Moreover, using a brick-layer
model we discuss the resistance and capacitance of the different contributors
(grain and grain boundaries) in our samples. High temperature Raman
spectroscopy investigation was performed in order to follow the temperature
evolution of the structural transformations on ferroelectric compounds.
Anomalies in the temperature evolution of the vibrational modes are seen to
correlate well with the temperature transitions observed from dielectric
measurements. | 2012.04325v1 |
2021-02-18 | Characterization of high aspect ratio TiAu TES X-ray microcalorimeters array using the X-IFU Frequency Domain Multiplexing readout | We are developing X-ray microcalorimeters as a backup option for the baseline
detectors in the X-IFU instrument on board the ATHENA space mission led by ESA
and to be launched in the early 2030s.5$\times$5 mixed arrays with TiAu
transition-edge sensor (TES), which have different high aspect ratios and thus
high resistances, have been designed and fabricated to meet the energy
resolution requirement of the X-IFU instrument. Such arrays can also be used to
optimise the performance of the Frequency Domain Multiplexing (FDM) readout and
lead to the final steps for the fabrication of a large detector array. In this
work we present the experimental results from tens of the devices with an
aspect ratio (length-to-width) ranging from 1-to-1 up to 6-to-1, measured in a
single-pixel mode with a FDM readout system developed at SRON/VTT. We observed
a nominal energy resolution of about 2.5 eV at 5.9 keV at bias frequencies
ranging from 1 to 5 MHz. These detectors are proving to be the best TES
microcalorimeters ever reported in Europe, being able to meet not only the
requirements of the X-IFU instrument, but also those of other future
challenging X-ray space missions, fundamental physics experiments, plasma
characterization and material analysis. | 2102.09378v1 |
2021-07-19 | Miniaturization of Josephson junction for digital superconducting circuits | In this work, we briefly overview various options for Josephson junctions
which should be scalable down to nanometer range for utilization in nanoscale
digital superconducting technology. Such junctions should possess high values
of critical current, $I_c$, and normal state resistance, $R_n$. Another
requirement is the high reproducibility of the junction parameters across a
wafer in a fabrication process. We argue that Superconductor - Normal metal -
Superconductor (SN-N-NS) Josephson junction of "variable thickness bridge"
geometry is a promising choice to meet these requirements. Theoretical analysis
of SN-N-NS junction is performed in the case where the distance between the
S-electrodes is comparable to the coherence length of the N-material. The
restriction on the junction geometrical parameters providing the existence of
superconductivity in the S-electrodes is derived for the current flowing
through the junction of an order of $I_c$. The junction heating, as well as
available mechanisms for the heat removal, is analyzed. The obtained results
show that an SN-N-NS junction with a high (sub-millivolt) value of $I_cR_n$
product can be fabricated from a broadly utilized combination of materials like
Nb/Cu using well-established technological processes. The junction area can be
scaled down to that of semiconductor transistors fabricated in the frame of a
40-nm process. | 2107.08711v1 |
2021-11-18 | Searching for Superconductivity in High Entropy Oxide Ruddlesden-Popper Cuprate Films | In this work, the high entropy oxide A2CuO4 Ruddlesden-Popper
(La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 is explored by charge doping with Ce+4 and
Sr+2 at concentrations known to induce superconductivity in the simple parent
compounds, Nd2CuO4 and La2CuO4. Electron doped
(La0.185Pr0.185Nd0.185Sm0.185Eu0.185Ce0.075)2CuO4 and hole doped
(La0.18Pr0.18Nd0.18Sm0.18Eu0.18Sr0.1)2CuO4 are synthesized and shown to be
single crystal, epitaxially strained, and highly uniform. Transport
measurements demonstrate that all as-grown films are insulating regardless of
doping. Annealing studies show that resistivity can be tuned by modifying
oxygen stoichiometry and inducing metallicity but without superconductivity.
These results in turn are connected to extended x-ray absorption fine structure
(EXAFS) results indicating that the lack of superconductivity in the high
entropy cuprates likely originates from a large distortion within the Cu-O
plane ({\sigma}2>0.015 {\AA}2) due to A-site cation size variance, which drives
localization of charge carriers. These findings describe new opportunities for
controlling charge- and orbital-mediated functional responses in
Ruddlesden-Popper crystal structures, driven by balancing of cation size and
charge variances that may be exploited for functionally important behaviors
such as superconductivity, antiferromagnetism, and metal-insulator transitions,
while opening less understood phase spaces hosting doped Mott insulators,
strange metals, quantum criticality, pseudogaps, and ordered charge density
waves. | 2111.09767v1 |
2022-01-03 | Phase Diagram of Infinite-layer Nickelate Compounds from First- and Second-principles Calculations | The fundamental properties of infinite-layer rare-earth nickelates (RNiO2)
are carefully revisited and compared with those of CaCuO2 and RNiO3
perovskites. Combining first-principles and finite-temperature
second-principles calculations, we highlight that bulk NdNiO2 compound are far
from equivalent to CaCuO2, together at the structural, electronic, and magnetic
levels. Structurally, it is shown to be prone to spin-phonon coupling induced
oxygen square rotation motion, which might be responsible for the intriguing
upturn of the resistivity. At the electronic and magnetic levels, we point out
orbital-selective Mott localization with strong out-of-plane band dispersion,
which should result in the isotropic upper critical fields and weakly
three-dimensional magnetic interactions with in-plane local moment and
out-of-plane itinerant moment. We further demonstrate that as in RNiO3
perovskites, oxygen rotation motion and rare-earth ion controlled electronic
and magnetic properties can give rise in RNiO2 compounds to a rich phase
diagram and high tunability of various appealing properties. In line with that,
we reveal that key ingredients of high-Tc superconductor such as orbital
polarization, Fermi surface, and antiferromagnetic interactions can be
deliberately controlled in NdNiO2 through epitaxial strain. Exploiting
strain-orbital engineering, a crossover from three- to two-dimensional magnetic
transition can be established, making then NdNiO2 thin film a true analog of
high-Tc cuprates. | 2201.00709v1 |
2022-03-20 | Deposition temperature dependence of thermo-spin and magneto-thermoelectric conversion in Co$_2$MnGa films on Y$_3$Fe$_5$O$_{12}$ and Gd$_3$Ga$_5$O$_{12}$ | We have characterized Co$_2$MnGa (CMG) Heusler alloy films grown on
Y$_3$Fe$_5$O$_{12}$ (YIG) and Gd$_3$Ga$_5$O$_{12}$ (GGG) substrates at
different deposition temperatures and investigated thermo-spin and
magneto-thermoelectric conversion properties by means of a lock-in thermography
technique. X-ray diffraction, magnetization, and electrical transport
measurements show that the deposition at high substrate temperatures induces
the crystallized structures of CMG while the resistivity of the CMG films on
YIG (GGG) prepared at and above 500 {\deg}C (550 {\deg}C) becomes too high to
measure the thermo-spin and magneto-thermoelectric effects due to large
roughness, highlighting the difficulty of fabricating highly ordered continuous
CMG films on garnet structures. Our lock-in thermography measurements show that
the deposition at high substrate temperatures results in an increase in the
current-induced temperature change for CMG/GGG and a decrease in that for
CMG/YIG. The former indicates the enhancement of the anomalous Ettingshausen
effect in CMG through crystallization. The latter can be explained by the
superposition of the anomalous Ettingshausen effect and the spin Peltier effect
induced by the positive (negative) charge-to-spin conversion for the amorphous
(crystallized) CMG films. These results provide a hint to construct
spin-caloritronic devices based on Heusler alloys. | 2203.10566v2 |
2022-04-10 | Efficient route to achieve superconductivity improvement via substitutional La-Ce alloy superhydride at high pressure | The discovery of clathrate superhydrides has approached the long-standing
dream of room-temperature superconductivity and thus inspired their prosperous
research under high pressure. However, how to experimentally optimize these
compelling superhydrides is still a formidable challenge. Here, we find that
half of the Ce atoms in the recently discovered hexagonal close packed (hcp)
CeH9 structure can be randomly replaced by adjacent La, resulting in the
formation of LaH9 unit that is impossible in a binary system. Our experiments
show that hcp (La, Ce)H9 can be synthesized at ~110 GPa and possesses a maximum
Tc of 178 K at higher pressure, which is evidenced by in-situ X-ray diffraction
and electronic transport measurement where a sharp drop of resistivity to zero
and a characteristic decrease of Tc under a magnetic field up to 9 T. More
importantly, the Tc of (La, Ce)H9 is significantly increased by ~50-80 K
compared to CeH9, showing the hitherto highest Tc at megabar pressure. Our
experimental results not only verify the feasibility of improving the
superconductivity of hydrides by introducing other suitable metals, but also
provide important inspiration for finding high-Tc superconductors in various
multinary superhydrides. | 2204.04623v1 |
2022-06-16 | A Lateral AlGaN/GaN Schottky Barrier Diode with 0.36 V Turn-on Voltage and 10 kV Breakdown Voltage by Using Double Barrier Anode Structure | In this letter, we demonstrate a lateral AlGaN/GaN Schottky barrier diode
(SBD) on sapphire substrate with low turn-on voltage (Von) and high breakdown
voltage (VBK). By using a double barrier anode (DBA) structure formed by the
mixture of Platinum (Pt) and Tantalum (Ta), the Von of the SBD can be as low as
0.36 V with a leakage current of 2.5E-6 A/mm. Supported by the high-quality
carbon-doped GaN buffer on sapphire, the VBK can reach more than 10 kV with the
anode-to-cathode spacing of 85 {\mu}m. Combining the VBK and the specific
on-resistance (Ron,sp) of 25.1 m{\Omega}.cm^2, the power figure of merit of the
SBD can reach 4.0 GW/cm^2, demonstrating a great potential for the application
in ultra-high-voltage electronics. | 2206.07881v1 |
2022-07-08 | Synthesis and Superconductivity in yttrium superhydrides under high pressure | The flourishing rare earth superhydrides are a class of recently discovered
materials that possess near-room-temperature superconductivity at high
pressures, opening a new era of superconductivity research at high pressures.
Among these superhydrides, yttrium superhydrides attracted great interest owing
to their abundance of stoichiometries and excellent superconductivities. Here,
we carried out a comprehensive study of yttrium superhydrides in a wide
pressure range of 145-300 GPa. We successfully synthesized a series of
superhydrides with the compositions of YH4, YH6, YH7, and YH9, and reported
their superconducting transition temperatures of 82 K at 167 GPa, 218 K at 165
GPa, 29 K at 162 GPa, and 230 K at 300 GPa, respectively, which were evidenced
by a sharp drop of resistivity. The structure and superconductivity of YH4,
which was taken as a representative example, were also examined by X-ray
diffraction measurements and the suppression of the superconductivity under
external magnetic fields, respectively. Clathrate YH10 as a candidate of
room-temperature superconductor was not synthesized within the studied pressure
and temperature ranges of up to 300 GPa and 2000 K, respectively. The current
work created a detailed platform for further searching room-temperature
superconductors in polynary yttrium-based superhydrides. | 2207.03918v1 |
2022-08-31 | Pouch cells with 15% silicon calendar-aged for 4 years | Small amounts of high-capacity silicon-based materials are already used in
the anode of commercial Li-ion batteries, helping increase their energy
density. Despite their remarkable storage capability, silicon continuously
reacts with the electrolyte, accelerating time-dependent cell performance fade.
Nevertheless, very limited information is available on the specific
consequences of this reactivity for the calendar aging of Li-ion cells. Here,
we analyze aging effects on 450 mAh pouch cells containing 15 wt% of Si (and 73
wt% graphite) after storage at 21 oC for four years. We show that severe losses
of Si capacity occurred due to particle isolation when cells were stored at
high states of charge (SOC), but not when cells were fully discharged prior to
storage. Impedance rise was also significantly higher when cells were kept at
high SOCs and was mostly due to phenomena taking place at the cathode; the
continuous electrolyte reduction at the anode did not lead to a major increase
in bulk electrode resistance. A series of post-test characterization provided
additional information on the effects of time and SOC on the calendar aging of
Si-containing cells. Our study highlights the many challenges posed by Si
during calendar aging and can inform future studies in the field. | 2209.00138v1 |
2022-10-13 | Diffusion mechanism and electrochemical investigation of 1T phase Al-MoS$_{2}$@rGO nano-composite as a high-performance anode for sodium-ion batteries | We report the electrochemical investigation of 5% Al doped MoS$_2$@rGO
composite as a high-performance anode for sodium (Na)-ion batteries. The x-ray
diffraction (XRD), Raman spectroscopy and high-resolution transmission electron
microscopy characterizations reveal that the Al doping increase the interlayer
spacing of (002) plane of MoS$_2$ nanosheets and form a stable 1T phase. The
galvanostatic charge-discharge measurements show the specific capacity stable
around 450, 400, 350, 300 and 200 mAhg$^{-1}$ at current densities of 0.05,
0.1, 0.3, 0.5 and 1~Ag$^{-1}$, respectively. Also, we observe the capacity
retentions of 86% and 66% at 0.1 and 0.3 Ag$^{-1}$, respectively, over 200
cycles with a consistent Coulombic efficiency of nearly 100%. The cyclic
voltammetry, galvanostatic intermittent titration technique, and
electrochemical impedance spectroscopy are used to find the kinetic behavior
and the obtained value of diffusion coefficient falls in the range of
10$^{-10}$ to 10$^{-12}$ cm$^2$s$^{-1}$. Intriguingly, the in-situ EIS also
explains the electrochemical kinetics of the electrode at different
charge-discharge states with the variation of charge transfer resistance.
Moreover, the post cycling investigation using ex-situ XRD and photoemission
spectroscopy indicate the coexistence of 1T/2H phase and field-emission
scanning electron microscopy confirm the stable morphology after 500 cycles.
Also, the Na-ion transport properties are calculated for 1T Al--MoS$_2$@rGO
interface and Al--MoS$_2$--MoS$_2$ interlayer host structure by theoretical
calculations using density functional theory. | 2210.06735v1 |
2022-11-02 | Discovery of a high-temperature antiferromagnetic state and transport signatures of exchange interactions in a Bi2Se3/EuSe heterostructure | Spatial confinement of electronic topological surface states (TSS) in
topological insulators poses a formidable challenge because TSS are protected
by time-reversal symmetry. In previous works formation of a gap in the
electronic spectrum of TSS has been successfully demonstrated in topological
insulator/magnetic material heterostructures, where ferromagnetic exchange
interactions locally lifts the time-reversal symmetry. Here we report an
experimental evidence of exchange interaction between a topological insulator
Bi2Se3 and a magnetic insulator EuSe. Spin-polarized neutron reflectometry
reveals a reduction of the in-plane magnetic susceptibility within a 2 nm
interfacial layer of EuSe, and the combination of SQUID magnetometry and Hall
measurements points to the formation of an antiferromagnetic layer with at
least five-fold enhancement of N\'eel's temperature. Abrupt resistance changes
in high magnetic fields indicate interfacial exchange coupling that affects
transport in a TSS. High temperature local control of TSS with zero net
magnetization unlocks new opportunities for the design of electronic,
spintronic and quantum computation devices, ranging from quantization of Hall
conductance in zero fields to spatial localization of non-Abelian excitations
in superconducting topological qubits. | 2211.01211v1 |
2022-11-09 | Evolution of the strange-metal scattering in momentum space of electron-doped ${\rm La}_{2-x}{\rm Ce}_x{\rm CuO}_4$ | The linear-in-temperature resistivity is one of the important mysteries in
the strange metal state of high-temperature cuprate superconductors. To uncover
this anomalous property, the energy-momentum-dependent imaginary part of the
self-energy Im ${\rm \Sigma}(k, \omega)$ holds the key information. Here we
perform systematic doping, momentum, and temperature-dependent angle-resolved
photoemission spectroscopy measurements of electron-doped cuprate ${\rm
La}_{2-x}{\rm Ce}_x{\rm CuO}_4$ and extract the evolution of the strange metal
scattering in momentum space. At low doping levels and low temperatures, Im
${\rm\Sigma} \propto \omega$ dependence dominates the whole momentum space. For
high doping levels and high temperatures, Im ${\rm\Sigma} \propto \omega^2$
shows up, starting from the antinodal region. By comparing with the hole-doped
cuprates ${\rm La}_{2-x}{\rm Sr}_x{\rm CuO}_4$ and ${\rm Bi}_2{\rm Sr}_2{\rm
CaCu}_2{\rm O}_8$, we find a dichotomy of the scattering rate exists along the
nodal and antinodal direction, which is ubiquitous in the cuprate family. Our
work provides new insight into the strange metal state in cuprates. | 2211.04833v1 |
2023-03-30 | Physics-based bias-dependent compact modeling of 1/f noise in single- to few- layer 2D-FETs | 1/f noise is a critical figure of merit for the performance of transistors
and circuits. For two-dimensional devices (2D-FETs), and especially for
applications in the GHz range where short-channel FETs are required, velocity
saturation (VS) effect can result in the reduction of 1/f noise at high
longitudinal electric fields. A new physics-based compact model is for the
first time introduced for single- to few- layer 2D-FETs in this study,
precisely validating 1/f noise experiments for various types of devices. The
proposed model mainly accounts for the measured 1/f noise bias dependence as
the latter is defined by different physical mechanisms. Thus, analytical
expressions are derived, valid in all regions of operation in contrast to
conventional approaches available in literature so far, accounting for carrier
number fluctuation (DN), mobility fluctuation (Dmu}) and contact resistance
(DR) effects based on the underlying physics that rules these devices. DN
mechanism due to trapping/detrapping together with an intense Coulomb
scattering effect, dominates 1/f noise from medium to strong accumulation
region while Dmu, is also demonstrated to modestly contribute in subthreshold
region. DR can also be significant in very high carrier density. The VS induced
reduction of 1/f noise measurements at high electric fields, is also remarkably
captured by the model. The physical validity of the model can also assist in
extracting credible conclusions when conducting comparisons between
experimental data from devices with different materials or dielectrics. | 2303.17162v1 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.