publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2012-04-24 | Microstructural analysis of phase separation in iron chalcogenide superconductors | The interplay between superconductivity, magnetism and crystal structure in
iron-based superconductors is a topic of great interest amongst the condensed
matter physics community as it is thought to be the key to understanding the
mechanisms responsible for high temperature superconductivity. Alkali metal
doped iron chalcogenide superconductors exhibit several unique characteristics
which are not found in other iron-based superconducting materials such as
antiferromagnetic ordering at room temperature, the presence of ordered iron
vacancies and high resistivity normal state properties. Detailed
microstructural analysis is essential in order to understand the origin of
these unusual properties. Here we have used a range of complementary scanning
electron microscope based techniques, including high-resolution electron
backscatter di raction mapping, to assess local variations in composition and
lattice parameter with high precision and sub-micron spatial resolution. Phase
separation is observed in the Csx Fe2-ySe2 crystals, with the minor phase
distributed in a plate-like morphology throughout the crystal. Our results are
consistent with superconductivity occurring only in the minority phase. | 1204.5472v4 |
2017-08-16 | Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage | Compared to traditional pn-junction photovoltaics, hot carrier solar cells
offer potentially higher efficiency by extracting work from the kinetic energy
of photogenerated "hot carriers" before they cool to the lattice temperature.
Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric
insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap
materials, where the potential efficiency gain is highest. Recently, a high
open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire
with a low bandgap of 0.39 eV, and was interpreted in terms of a
photothermoelectric effect. Here, we point out that this device is a hot
carrier solar cell and discuss its performance in those terms. In the
demonstrated devices, InP heterostructures are used as energy filters in order
to thermoelectrically harvest the energy of hot electrons photogenerated in
InAs absorber segments. The obtained photovoltage depends on the
heterostructure design of the energy filter and is therefore tunable. By using
a high-resistance, thermionic barrier an open-circuit voltage is obtained that
is in excess of the Shockley-Queisser limit. These results provide
generalizable insight into how to realize high voltage hot carrier solar cells
in low-bandgap materials, and therefore are a step towards the demonstration of
higher efficiency hot carrier solar cells. | 1708.04848v1 |
2019-11-11 | Mechanical properties of VMoNO as a function of oxygen concentration: toward development of hard and tough refractory oxynitrides | Improved toughness is a central goal in the development of wear-resistant
refractory ceramic coatings. Extensive theoretical and experimental research
has revealed that NaCl structure VMoN alloys exhibit surprisingly high
ductility combined with high hardness and toughness. However, during operation,
protective coatings inevitably oxidize, a problem which may compromise material
properties and performance. Here, we explore the role of oxidation in altering
VMoN properties. Density functional theory and theoretical intrinsic hardness
models are used to investigate the mechanical behavior of cubic V0.5Mo0.5N1-xOx
solid solutions as a function of the oxygen concentration x. Elastic-constant
and intrinsic hardness calculations show that oxidation does not degrade the
mechanical properties of V0.5Mo0.5N. Electronic structure analyses indicate
that the presence of oxygen reduces the covalent bond character, which slightly
lowers the alloy strength and intrinsic hardness. Nevertheless, the character
of metallic d-d states, which are crucial for allowing plastic deformation and
enhancing toughness, remains unaffected. Overall, our results suggest that
VMoNO oxynitrides, with oxygen concentrations as high as 50%, possess high
intrinsic hardness, while still being ductile. | 1911.04165v1 |
2020-12-25 | Superconductivity to 262 kelvin via catalyzed hydrogenation of yttrium at high pressures | Room temperature superconductivity has been achieved under high pressure in
an organically derived carbonaceous sulfur hydride with a critical
superconducting transition temperature (Tc) of 288 kelvin. This development is
part of a new class of dense, hydrogen rich materials with remarkably high
critical temperatures. Metal superhydrides are a subclass of these materials
that provide a different and potentially more promising route to very high Tc
superconductivity. The most promising binary metal superhydrides contain
alkaline or rare earth elements, and recent experimental observations of LaH10
have shown them capable of Tc s up to 250 to 260 kelvin. Predictions have shown
yttrium superhydrides to be the most promising with an estimated Tc in excess
of 300 kelvin for YH10. Here we report the synthesis of an yttrium superhydride
that exhibits superconductivity at a critical temperature of 262 kelvin at 182
gigapascal. A palladium thin film assists the synthesis by protecting the
sputtered yttrium from oxidation and promoting subsequent hydrogenation. Phonon
mediated superconductivity is established by the observation of zero
resistance, an isotope effect and the reduction of Tc under an external
magnetic field. The upper critical magnetic field is 103 tesla at zero
temperature. We suggest YH9 is the synthesized product based on comparison of
the measured Raman spectra and Tc to calculated Raman results. | 2012.13627v1 |
2021-08-25 | A Stable High-Capacity Lithium-Ion Battery Using a Biomass-Derived Sulfur-Carbon Cathode and Lithiated Silicon Anode | A full lithium-ion-sulfur cell with a remarkable cycle life was achieved by
combining an environmentally sustainable biomass-derived sulfur-carbon cathode
and a pre-lithiated silicon oxide anode. X-ray diffraction, Raman spectroscopy,
energy dispersive spectroscopy, and thermogravimetry of the cathode evidenced
the disordered nature of the carbon matrix in which sulfur was uniformly
distributed with a weight content as high as 75%, while scanning and
transmission electron microscopy revealed the micrometric morphology of the
composite. The sulfur-carbon electrode in the lithium half-cell exhibited a
maximum capacity higher than 1200 mAhgS-1, reversible electrochemical process,
limited electrode/electrolyte interphase resistance, and a rate capability up
to C/2. The material showed a capacity decay of about 40% with respect to the
steady-state value over 100 cycles, likely due to the reaction with the lithium
metal of dissolved polysulfides or impurities including P detected in the
carbon precursor. Therefore, the replacement of the lithium metal with a less
challenging anode was suggested, and the sulfur-carbon composite was
subsequently investigated in the full lithium-ion-sulfur battery employing a
Li-alloying silicon oxide anode. The full-cell revealed an initial capacity as
high as 1200 mAhgS-1, a retention increased to more than 79% for 100
galvanostatic cycles, and 56% over 500 cycles. The data reported herein well
indicated the reliability of energy storage devices with extended cycle life
employing high-energy, green, and safe electrode materials. | 2108.11284v1 |
2023-09-07 | Enhanced strength-ductility combination by introducing bimodal grains structures in high-density oxide dispersion strengthened FeCrAl alloys fabricated by spark plasma sintering technology | Oxide dispersion strengthened FeCrAl alloys dispersed high-density
nano-oxides in the matrix show outstanding corrosion resistance and mechanical
properties. However, ODS FeCrAl alloys achieve the high strength generally at
the expense of ductility in some way. Here, a method by introducing a bimodal
grain structure was designed to overcome the strength-ductility tradeoff. In
this work, ODS FeCrAl alloys were successfully fabricated through various
mechanical alloying time, combined with spark plasma sintering under the vacuum
of less than 4Pa. Microstructural characterization showed that the average
grains size and nano-oxides size decrease gradually, and the density of
nano-oxides increases, as the milling time increases. Mechanical properties
revealed that both the strength and ductility were significantly synergistic
enhanced with increasing milling time. The bimodal grain distribution
characterized by electron backscatter diffraction (EBSD) (vacuum degree was
less than 5E-5pa) was beneficial for the activation of the back stress
strengthening and the annihilation of these microcracks, thus achieving the
excellent ductility (27.65%). In addition, transmission electron microscope
(TEM) characterization under the vacuum degree of less than 10-6pa illustrated
that ultra-high-density nano-oxides (9.61E22/m3) was crucial for enhancing the
strength of ODS FeCrAl alloys (993MPa). The strengthening mechanism
superposition, based on the model of nano-oxides interrelated with the
dislocation, illustrated an excellent agreement with experimental results from
yield strength strengthening mechanisms. To our best knowledge, H40 (milled for
40h, and sintered at 1100C) alloy presents the outstanding strength with the
exceptional ductility among all studied ODS FeCrAl alloys, which makes it the
promising cladding materials for the accident tolerant fuel cladding. | 2309.03703v1 |
2017-11-14 | The Dominant Role of Critical Valence Fluctuations on High $T_{\rm c}$ Superconductivity in Heavy Fermions | Despite almost 40 years of research, the origin of heavy-fermion
superconductivity is still strongly debated. Especially, the pressure-induced
enhancement of superconductivity in CeCu$_2$Si$_2$ away from the magnetic
breakdown is not sufficiently taken into consideration. As recently reported in
CeCu$_2$Si$_2$ and several related compounds, optimal superconductivity occurs
at the pressure of a valence crossover, which arises from a virtual critical
end point at negative temperature $T_{\rm cr}$. In this context, we did a
meticulous analysis of a vast set of top-quality high-pressure electrical
resistivity data of several Ce-based heavy fermion compounds. The key novelty
is the salient correlation between the superconducting transition temperature
$T_{\rm c}$ and the valence instability parameter $T_{\rm cr}$, which is in
line with theory of enhanced valence fluctuations. Moreover, it is found that,
in the pressure region of superconductivity, electrical resistivity is governed
by the valence crossover, which most often manifests in scaling behavior. We
develop the new idea that the optimum superconducting $T_{\rm c}$ of a given
sample is mainly controlled by the compound's $T_{\rm cr}$ and limited by
non-magnetic disorder. In this regard, the present study provides compelling
evidence for the crucial role of critical valence fluctuations in the formation
of Cooper pairs in Ce-based heavy fermion superconductors besides the
contribution of spin fluctuations near magnetic quantum critical points, and
corroborates a plausible superconducting mechanism in strongly correlated
electron systems in general. | 1711.05145v2 |
2017-05-09 | Universal experimental test for the role of free charge carriers in thermal Casimir effect within a micrometer separation range | We propose a universal experiment to measure the differential Casimir force
between a Au-coated sphere and two halves of a structured plate covered with a
P-doped Si overlayer. The concentration of free charge carriers in the
overlayer is chosen slightly below the critical one, f or which the phase
transition from dielectric to metal occurs. One ha f of the structured plate is
insulating, while its second half is made of gold. For the former we consider
two different structures, one consisting of bulk high-resistivity Si and the
other of a layer of silica followed by bulk high-resistivity Si. The
differential Casimir force is computed within the Lifshitz theory using four
approaches that have been proposed in the literature to account for the role of
free charge carriers in metallic and dielectric materials interacting with
quantum fluctuations. According to these approaches, Au at low frequencies is
described by either the Drude or the plasma model, whereas the free charge
carriers in dielectric materials at room temperature are either taken into
account or disregarded. It is shown that the values of differential Casimir
forces, computed in the micrometer separation range using these four
approaches, are widely distinct from each other and can be easily discriminated
experimentally. It is shown that for all approaches the thermal component of
the differential Casimir force is sufficiently large for direct observation.
The possible errors and uncertainties in the proposed experiment are estimated
and its importance for the theory of quantum fluctuations is discussed. | 1705.03223v2 |
2021-03-10 | Solid phase epitaxial growth of the correlated-electron transparent conducting oxide SrVO3 | SrVO3 thin films with a high figure of merit for applications as transparent
conductors were crystallized from amorphous layers using solid phase epitaxy
(SPE). Epitaxial SrVO3 films crystallized on SrTiO3 using SPE exhibit a room
temperature resistivity of 2.5 x 10-5 Ohms cm, a residual resistivity ratio of
3.8, and visible light transmission above 0.5 for a 60 nm-thick film. SrVO3
layers were deposited at room temperature using radio-frequency sputtering in
an amorphous form and subsequently crystallized by heating in controlled gas
environment. The lattice parameters and mosaic angular width of x-ray
reflections from the crystallized films are consistent with partial relaxation
of the strain resulting from the epitaxial mismatch between SrVO3 and SrTiO3. A
reflection high-energy electron diffraction study of the kinetics of SPE
indicates that crystallization occurs via the thermally activated propagation
of the crystalline/amorphous interface, similar to SPE phenomena in other
perovskite oxides. Thermodynamic calculations based on density functional
theory predict the temperature and oxygen partial pressure conditions required
to produce the SrVO3 phase and are consistent with the experiments. The
separate control of deposition and crystallization conditions in SPE presents
new possibilities for the crystallization of transparent conductors in complex
geometries and over large areas. | 2103.05797v2 |
2023-11-13 | Superconductivity in trilayer nickelate La$_4$Ni$_3$O$_{10}$ single crystals | The pursuit of discovering new high-temperature superconductors that diverge
from the copper-based paradigm carries profound implications for elucidating
mechanisms behind superconductivity and may also enable new applications. Here,
our investigation reveals that application of pressure effectively suppresses
the spin and charge order in trilayer nickelate La$_4$Ni$_3$O$_{10}$ single
crystals, leading to the emergence of superconductivity with a maximum critical
temperature (Tc) of around 30 K. In the normal state, we observe a "strange
metal" behavior, characterized by a linear temperature-dependent resistance
extending up to 300 K. These results could be interpreted as the pressure's
influence, inducing damping on the density-wave gap and spin order, while
promoting spin fluctuations and bringing the associated flat dz2 band into
close proximity with the Fermi surface. This, in turn, fosters strong
correlations and "strange metal" behavior, thus setting the stage for the
eventual emergence of superconductivity. Furthermore, the layer-dependent
superconductivity observed hints at a unique interlayer coupling mechanism
specific to nickelates, setting them apart from cuprates in this regard. Our
findings provide crucial insights into the fundamental mechanisms underpinning
superconductivity, while also introducing a new material platform to explore
the intricate interplay between the spin/charge order, flat band structures,
interlayer coupling, strange metal behavior and high-temperature
superconductivity. | 2311.07353v2 |
2019-02-28 | 3D quench modeling based on T-A formulation for high temperature superconductor CORC cables | High temperature superconductor (HTS) (RE)Ba2Cu3Ox (REBCO) conductor on round
core cable (CORC) has high current carrying capacity for high field magnet and
power applications. In REBCO CORC cables, current redistribution occurs among
tapes through terminal contact resistances when a local quench occurs.
Therefore, the quench behaviour of CORC cable is different from single tape
situation, for it is significantly affected by terminal contact resistances. To
better understand the underlying physical process of local quenches in CORC
cables, a new 3D multi-physics modelling tool for CORC cables is developed and
presented in this paper. In this model, the REBCO tape is treated as a thin
shell without thickness, and four models are coupled: T-formulation model,
A-formulation model, a heat transfer model and an equivalent circuit model. The
current redistribution, temperature and tape voltage of CORC cable during hot
spot induced quenches are analysed using this model. The results show that the
thermal stability of CORC cable can be considerably improved by reducing
terminal contact resistance. The minimum quench energy (MQE) increases rapidly
with the reduction of terminal contact resistance when the resistance is in a
middle range. When the terminal contact resistance is too low or too high, the
MQE shows no obvious variation with terminal contact resistances. With a low
terminal contact resistance, a hot spot in one tape may induce an over-current
quench on the other tapes without hot spots. This will not happen in a cable
with high terminal contact resistance. In this case, the tape with hot spot
will quench and burn out before inducing a quench on other tapes. The modelling
tool developed can be used to design CORC cables with improved thermal
stability. | 1902.11055v1 |
2001-06-20 | Saturation of electrical resistivity in metals at large temperatures | We present a microscopic model for systems showing resistivity saturation. An
essentially exact quantum Monte-Carlo calculation demonstrates that the model
describes saturation. We give a simple explanation for saturation, using charge
conservation and considering the limit where thermally excited phonons have
destroyed the periodicity. Crucial model features are phonons coupling to the
hopping matrix elements and a unit cell with several atoms. We demonstrate the
difference to a model of alkali-doped C60 with coupling to the level positions,
for which there is no saturation. | 0106397v2 |
2002-05-13 | Pseudogap effects on the charge dynamics in the underdoped copper oxide materials | Within the t-J model, the charge dynamics of copper oxide materials in the
underdoped regime is studied based on the fermion-spin theory. It is shown that
both in-plane charge dynamics and c-axis charge dynamics are mainly governed by
the scattering from the in-plane fluctuation, which would be suppressed when
the holon pseudogap opens at low temperatures, leading to the temperature
linear to the nonlinear range in the in-plane resistivity and crossovers to the
semiconducting-like range in the c-axis resistivity. | 0205248v1 |
2004-05-26 | An Inhomogeneous Josephson Phase Near the (Super) Conductor-Insulator Transition | In many cases inhomogeneities are known to exist near the metal (or
superconductor)- insulator transition, as follows from well-known domain-wall
arguments. If the conducting regions are large enough, and if they have
superconducting correlations, it becomes energetically favorable for the system
to go into a Josephson- coupled zero-resistance state before (i.e. at higher
resistance than) the material becomes a real metal. We show that this is
plausible by a simple comparison of the relevant coupling constants. We also
illustrate using data in the literature on oxide materials as well as
ultra-thin films, that when this proposed Josephson state is quenched by a
magnetic field, an insulating, rather then a metallic, state indeed appears. | 0405625v1 |
2005-08-15 | Electronic structure and anisotropic transport properties in hexagonal YPtIn and LuAgGe ternary compounds | We present anisotropic, zero applied magnetic field, temperature dependent
resistivity measurements on hexagonal, non-magnetic, YPtIn and LuAgGe single
crystals. For these materials the in-plane resistivity, $\rho_{ab}$, is
significantly higher than the $c$ - axis one, $\rho_c$, with $\rho_{ab}/\rho_c
\approx 1.4$ for YPtIn and $\approx 4.2 - 4.7$ for LuAgGe. The connection
between the electronic structure and the anisotropic transport properties is
discussed using density functional calculations that link the observed
anisotropy with a specific shape of Fermi surface and anisotropy of the Fermi
velocities. | 0508346v1 |
2010-11-12 | Microwave inductance of thin metal strips | We have measured the frequency-dependent, complex impedance of thin metal
strips in a broad range of microwave frequencies (45~MHz to 20~GHz). The
spectra are in good agreement with theoretical predictions of an RCL model. The
resistance, inductance, and capacitance, which govern the microwave response,
depend on the strip width and thickness as well as on the strip and substrate
materials. While the strip resistance scales inversely with the cross section,
the inductance depends on the width of the strip, but not on the thickness (in
the limit of small thickness). | 1011.2913v1 |
2011-01-24 | Graded anharmonic crystals as genuine thermal diodes: Analytical description of rectification and negative differential thermal resistance | We address the heat flow study starting from microscopic models of matter: we
develop an approach and investigate some anharmonic graded mass crystals, with
weak interparticle interactions. We calculate the thermal conductivity, and
show the existence of rectification and negative differential thermal
resistance. Our formalism allows us to understand the mechanism behind the
phenomena, and shows that the properties of graded materials make them genuine
thermal diodes. | 1101.4589v1 |
2011-07-15 | Enhanced Gas-Flow-Induced Voltage in Graphene | We show by systemically experimental investigation that gas-flow-induced
voltage in monolayer graphene is more than twenty times of that in bulk
graphite. Examination over samples with sheet resistances ranging from 307 to
1600 {\Omega}/sq shows that the induced voltage increase with the resistance
and can be further improved by controlling the quality and doping level of
graphene. The induced voltage is nearly independent of the substrate materials
and can be well explained by the interplay of Bernoulli's principle and the
carrier density dependent Seebeck coefficient. The results demonstrate that
graphene has great potential for flow sensors and energy conversion devices. | 1107.3049v1 |
2016-02-17 | On the analysis of stage I in the resistivity recovery of electron irradiated iron | The experimental results of Takaki et al. [1] on the stage I resistivity
recovery of electron irradiated iron are analyzed using the analytical theory
of diffusion annealing formulated by Simpson & Sossin [2] and Schroeder [3]
taking into account the recent first-principles calculations of Fu et al. [4]
regarding the mobility of interstitials. Excellent agreement between theory and
experiment is obtained by a minimal set of adjustable parameters. The results
show that the diffusion annealing equations can be successfully employed for
the analysis of recovery experiments in iron. | 1602.05449v2 |
2016-04-18 | Large thermopower in the antiferromagnetic semiconductor BaMn$_2$Bi$_2$ | We report electrical and thermal transport properties of Mn-based material
BaMn$_2$Bi$_2$ with ThCr$_2$Si$_2$ structure. The resistivity of the
antiferromagnetic BaMn$_2$Bi$_2$ shows a metal-semiconductor transition at
$\sim 80$ K with decreasing temperature. Correspondingly, the thermopower $S$
shows a peak at the same temperature, approaching ~150 $\mu$V/K. With
increasing temperature $S$ decreases to about 125 $\mu$V/K at the room
temperature. The magnetic field enhances the peak value to 210 $\mu$V/K. The
Hall resistivity reveals an abrupt change of the carrier density close to the
metal-semiconductor transition temperature. | 1604.05296v1 |
2016-06-20 | Resistivity scaling in metallic thin films and nanowires due to grain boundary and surface roughness scattering | A modeling approach, based on an analytical solution of the semiclassical
multi-subband Boltzmann transport equation, is presented to study resistivity
scaling in metallic thin films and nanowires due to grain boundary and surface
roughness scattering. While taking into account the detailed statistical
properties of grains, roughness and barrier material as well as the metallic
band structure and quantum mechanical aspects of scattering and confinement,
the model does not rely on phenomenological fitting parameters. | 1606.05972v2 |
2016-07-27 | Alloy-like behaviour of the thermal conductivity of non-symmetric superlattices | In this work, we show a phenomenological alloy-like fit of the thermal
conductivity of (A)d1:(B)d2 superlattices with d1 /= d2, i.e. non-symmetric
structure. The presented method is a generalization of the Norbury rule of the
summation of thermal resistivities in alloy compounds. Namely, we show that
this approach can be also extended to describe the thermal properties of
crystalline and ordered-system composed by two or more elements, and, has a
potentially much wider application range. Using this approximation we estimate
that the interface thermal resistance depends on the period and the ratio of
materials that form the superlattice structure | 1607.08017v2 |
2018-03-30 | Nanostructured Ceramic Oxides with a Slow Crack Growth Resistance Close to Covalent Materials | Oxide ceramics are sensitive to slow crack growth because adsorption of water
can take place at the crack tip, leading to a strong decrease of the surface
energy in humid (or air) conditions. This is a major drawback concerning
demanding, long-term applications such as orthopaedic implants. Here we show
that a specific nanostructuration of ceramic oxides can lead to a crack
resistance never reached before, similar to that of covalent ceramics. | 1804.01393v1 |
2018-05-30 | Interface thermal behavior in nanomaterials by thermal grating relaxation | We study the relaxation of a thermal grating in multilayer materials with
interface thermal resistances. The analytical development allows for the nu-
merical determination of this thermal property in Approach to Equilibrium
Molecular Dynamics and suggests an experimental setup for its measurement.
Possible non-diffusive effects at the nanoscale are take into consideration by
a non-local formulation of the heat equation. As a case study, we numerically
apply the present approach to silicon grain boundary thermal resistance | 1805.12086v1 |
2019-07-04 | Pressure-induced superconductivity in SnSb2Te4 | We report the discovery of a new superconductor from phase change materials
SnSb2Te4. Single crystals of SnSb2Te4 were grown using a conventional
melting-growth method. The sample resistance under pressure was measured using
an originally designed diamond anvil cell with boron-doped diamond electrodes.
The pressure dependence of the resistance has been measured up to 32.6 GPa. The
superconducting transition of SnSb2Te4 appeared at 2.1 K(Tconset) under 8.1
GPa, which was further increased with applied pressure to a maximum onset
transition temperature 7.4K under 32.6 GPa. | 1907.02381v1 |
2019-04-13 | Giant Interfacial Thermal Resistance Arising From Materials With Mismatched Phonon Structures | Previous researches only reported very small interfacial thermal resistances
at room temperature due to limitations in sample combinations and methods.
Taking cognizance of the importance of mismatched phonon structures, we report
values up to $2*10^{-4}W^{-1}m^{2}K$, thousand times larger than highest values
reported to date. This enables substantial tuning of the thermal conductivity
in composites, and does not constrain other characteristics. Our findings
inspire new design strategies, for heat control in integrated circuits and
thermoelectric composites, that harness thermal transport at interfaces. | 1904.06540v2 |
2020-01-26 | Pulse percolation conduction and multi-value memory | We develop a theory of pulse conduction in percolation type of materials such
as noncrystalline semiconductors and nano-metal compounds. For short voltage
pulses, the corresponding electric currents are inversely proportional to the
pulse length and exhibit significant nonohmicity due to strong local fields in
resistive regions of the percolation bonds. These fields can trigger local
switching events incrementally changing bond resistances in response to pulse
trains. Our prediction opens a venue to a class of multi-value nonvolatile
memory implementable with a variety of materials. | 2001.09512v3 |
2020-08-27 | Nitrobenzene as Additive to Improve Reproducibility and Degradation Resistance of Highly Efficient Methylammonium-Free Inverted Perovskite Solar Cells | We show that the addition of 1 % (v/v) nitrobenzene within the perovskite
formulation can be used as a method to improve the power conversion efficiency
and reliability performance of methylammonium-free (CsFA) inverted perovskite
solar cells. Addition of nitrobenzene increased PCE due to defect passivation
and provides smoother films resulting in PVSCs with narrower PCE distribution.
Moreover, the nitrobenzene additive methylammonium-free hybrid PVSCs exhibit
prolonged lifetime compare to additive free PVSCs due to enhanced air and
moisture degradation resistance. | 2008.12041v1 |
2021-10-27 | Planar Hall effect in Cu intercalated PdTe$_2$ | We present the Planar Hall effect studies on the Cu intercalated type-II
Dirac semimetal PdTe$_{2}$. The electrical resistivity exhibits a positive
field dependence both in perpendicular and parallel field directions, causing
non-zero anisotropy. The longitudinal magnetoresistance shows almost linear
field dependence at low temperatures. A tilted prolate spheroid shaped orbits
are observed in parametric plot between transverse and longitudinal
resistivities. Our study suggest that for the type-II Dirac semimetal materials
with positive longitudinal magnetoresistance, the origin of Planar Hall effect
cannot be asserted with certainty to the topological or non-topological without
taking into account the anisotropy of Fermi surface. | 2110.14251v1 |
2023-10-04 | Anisotropic transport and Negative Resistance in a polycrystalline metal-semiconductor (Ni-TiO2) hybrid | We investigate anomalous electrical transport properties of a Ni-TiO2 hybrid
system displaying a unique nanostructured morphology. The system undergoes an
insulator to metal transition below 150 K with a low temperature metallic phase
that shows negative resistance in a four-probe configuration. Temperature
dependent transport measurements and numerical modelling show that the
anomalies originate from the dendritic architecture of the TiO2 backbone
interspersed with Ni nanoparticles that paradoxically renders this
polycrystalline, heterogeneous system highly anisotropic. The study critiques
inferences that may be drawn from four-probe transport measurements and offers
valuable insights into modelling conductivity of anisotropic hybrid materials. | 2310.02976v1 |
2024-02-21 | Nonlinear longitudinal current of band-geometric origin in wires of finite thickness | The miniaturization of integrated circuits is facing an obstruction due to
the escalating electrical resistivity of conventional copper interconnects. The
underlying reason for this problem was unveiled by Fuchs and Sondheimer, who
showed that thinner wires are more resistive because current-carrying electrons
encounter the rough surfaces of the wire more frequently therein. Here, we
present a generalization of the Fuchs-Sondheimer theory to Dirac and Weyl
materials, which are candidates for next-generation interconnects. We predict a
nonlinear longitudinal electric current originating from the combined action of
the Berry curvature and non-specular surface-scattering. | 2402.14112v1 |
2007-09-25 | Quantum to Classical Transition of the Charge Relaxation Resistance of a Mesoscopic Capacitor | We present an analysis of the effect of dephasing on the single channel
charge relaxation resistance of a mesoscopic capacitor in the linear low
frequency regime. The capacitor consists of a cavity which is via a quantum
point contact connected to an electron reservoir and Coulomb coupled to a gate.
The capacitor is in a perpendicular high magnetic field such that only one
(spin polarized) edge state is (partially) transmitted through the contact. In
the coherent limit the charge relaxation resistance for a single channel
contact is independent of the transmission probability of the contact and given
by half a resistance quantum. The loss of coherence in the conductor is modeled
by attaching to it a fictitious probe, which draws no net current. In the
incoherent limit one could expect a charge relaxation resistance that is
inversely proportional to the transmission probability of the quantum point
contact. However, such a two terminal result requires that scattering is
between two electron reservoirs which provide full inelastic relaxation. We
find that dephasing of a single edge state in the cavity is not sufficient to
generate an interface resistance. As a consequence the charge relaxation
resistance is given by the sum of one constant interface resistance and the
(original) Landauer resistance. The same result is obtained in the high
temperature regime due to energy averaging over many occupied states in the
cavity. Only for a large number of open dephasing channels, describing
spatially homogenous dephasing in the cavity, do we recover the two terminal
resistance, which is inversely proportional to the transmission probability of
the QPC. We compare different dephasing models and discuss the relation of our
results to a recent experiment. | 0709.3956v1 |
2007-01-23 | Silicon Sensors implemented on p-type substrates for high radiation resistance applications | Silicon based micropattern detectors are essential elements of modern high
energy physics experiments. Cost effectiveness and high radiation resistance
are two important requirements for technologies to be used in inner tracking
devices. Processes based on p-type substrates have very strong appeal for these
applications. Recent results and prototype efforts under way are reviewed. | 0701270v1 |
2021-05-01 | Ultra-stable shear jammed granular material | Dry granular materials such as sand, gravel, pills, or agricultural grains,
can become rigid when compressed or sheared. At low density, one can distort
the shape of a container of granular material without encountering any
resistance. Under isotropic compression, the material will reach a certain {\it
jamming} density and then resist further compression. {\em Shear jamming}
occurs when resistance to shear emerges in a system at a density lower than the
jamming density, and the elastic properties of such states have important
implications for industrial and geophysical processes. We report on
experimental observations of changes in the mechanical properties of a
shear-jammed granular material subjected to small-amplitude, quasi-static
cyclic shear. We study a layer of plastic discs confined to a shear cell, using
photoelasticimetry to measure all inter-particle vector forces. For
sufficiently small cyclic shear amplitudes and large enough initial shear, the
material evolves to an unexpected "ultra-stable" state in which all the
particle positions and inter-particle contact forces remain unchanged after
each complete shear cycle for thousands of cycles. The stress response of these
states to small imposed shear is nearly elastic, in contrast to the original
shear jammed state. | 2105.00313v3 |
2014-09-05 | Thermalization and possible quantum relaxation times in "classical" fluids: theory and experiment | Quantum effects in material systems are often pronounced at low energies and
become insignificant at high temperatures. We find that, perhaps
counterintuitively, certain quantum effects may follow the opposite route and
become sharp when extrapolated to high temperature within a "classical" liquid
phase. In the current work, we suggest basic quantum bounds on relaxation (and
thermalization) times, examine kinetic theory by taking into account such
possible fundamental quantum time scales, find new general equalities
connecting semi-classical dynamics and thermodynamics to Planck's constant, and
compute current correlation functions. Our analysis suggests that, on average,
the extrapolated high temperature dynamical viscosity of general liquids may
tend to a value set by the product of the particle number density ${\sf n}$ and
Planck's constant $h$. We compare this theoretical result with experimental
measurements of an ensemble of 23 metallic fluids where this seems to indeed be
the case. The extrapolated high temperature viscosity of each of these liquids
$\eta$ divided (for each respective fluid by its value of ${\sf n} h$) veers
towards a Gaussian with an ensemble average value that is close to unity up to
an error of size $0.6 \%$. Inspired by the Eigenstate Thermalization
Hypothesis, we suggest a relation between the lowest equilibration temperature
to the melting or liquidus temperature and discuss a possible corollary
concerning the absence of finite temperature "ideal glass" transitions. We
suggest a general quantum mechanical derivation for the viscosity of glasses at
general temperatures. We invoke similar ideas to discuss other transport
properties and demonstrate how simple behaviors including resistivity
saturation and linear $T$ resistivity may appear very naturally. Our approach
suggests that minimal time lags may be present in fluid dynamics. | 1409.1915v14 |
2002-02-15 | Resistance and Resistance Fluctuations in Random Resistor Networks Under Biased Percolation | We consider a two-dimensional random resistor network (RRN) in the presence
of two competing biased percolations consisting of the breaking and recovering
of elementary resistors. These two processes are driven by the joint effects of
an electrical bias and of the heat exchange with a thermal bath. The electrical
bias is set up by applying a constant voltage or, alternatively, a constant
current. Monte Carlo simulations are performed to analyze the network evolution
in the full range of bias values. Depending on the bias strength, electrical
failure or steady state are achieved. Here we investigate the steady-state of
the RRN focusing on the properties of the non-Ohmic regime. In constant voltage
conditions, a scaling relation is found between $<R>/<R>_0$ and $V/V_0$, where
$<R>$ is the average network resistance, $<R>_0$ the linear regime resistance
and $V_0$ the threshold value for the onset of nonlinearity. A similar relation
is found in constant current conditions. The relative variance of resistance
fluctuations also exhibits a strong nonlinearity whose properties are
investigated. The power spectral density of resistance fluctuations presents a
Lorentzian spectrum and the amplitude of fluctuations shows a significant
non-Gaussian behavior in the pre-breakdown region. These results compare well
with electrical breakdown measurements in thin films of composites and of other
conducting materials. | 0202268v1 |
2007-03-29 | Magnetic-field cycling induced anomalous irreversibility in resistivity of charge-ordered manganites | The rare-earth ions (RE = Eu, Dy Ho, Tm, Y) substituted charge-ordered
antiferromagnetic manganites, Pr0.45RE0.05Ca0.5MnO3, were studied for the
magnetic and the transport properties in the presence of external
magnetic-fields of up to 14 Tesla. Regardless of the intrinsic magnetic
property of RE ions, all the compounds exhibit successive step-like
metamagnetic transitions at low temperatures, which are strongly correlated to
their electronic transitions. At any fixed temperature in two different
temperature-regimes, we observed contrary effects of the magnetic-field cycling
on the resistivity of these manganites, namely, i) in the low temperature
regime (<70 K), the resistivity was irreversible showing lower values than
initial after a magnetic-field cycle was over, which is consistent with the
irreversible magnetization, and ii) in a temperature regime above 70 K, the
resistivity is irreversible with noticeably higher values than initial, whereas
the magnetization was found to be reversible. For the latter case, we further
show that this irreversibility of resistivity systematically depends on the
temperature and the magnitude of applied magnetic-field. These results suggest
that the observed resistivity behavior originated from the magnetic-field
induced metamagnetic transitions and training effect. | 0703771v1 |
2011-06-02 | Anisotropic resistivity in underdoped single crystals (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$, $0 \leq x<0.35$ | Temperature-dependent in-plane, $\rho_a(T)$, and inter-plane, $\rho_c(T)$,
resistivities were measured for the iron-arsenide superconductor
(Ba$_{1-x}$K$_x$)Fe $_2$As$_2$ over a broad doping range from parent compound
to optimal doping $T_c\approx 38 K$, $0\leq x \leq 0.35$. The coupled
magnetic/structural transition at $T_{SM}$ is clearly observed for samples with
$T_c <$26 K ($x <0.25$), however its effect on resistivity is much weaker than
in the electron-doped Ba(Fe$_{1-x}$Co$_x$)Fe $_2$As$_2$, and the transition
leads only to a decrease of resistivity. In addition to the feature at
$T_{SM}$, the inter-plane resistivity shows a maximum at $T^*\sim$200 K, which
moves slightly to higher temperature with doping, revealing a trend opposite to
the electron-doped materials. A smeared feature at about the same temperature
is seen in $\rho_a(T)$. For $T<T^*$, the temperature dependence of resistivity
shows systematic evolution and is close to linear at optimal doping. This
feature, being most pronounced for $\rho_c(T)$, suggests the existence of a
quantum critical point close to optimal doping. | 1106.0533v1 |
2012-02-15 | Noise studies of magnetization dynamics in dilute magnetic semiconductor heterostructures | We study theoretically and experimentally the frequency and temperature
dependence of resistivity noise in semiconductor heterostructures delta-doped
by Mn. The resistivity noise is observed to be non-monotonous as a function of
frequency. As a function of temperature, the noise increases by two orders of
magnitude for a resistivity increase of about 50%. We study two possible
sources of resistivity noise -- dynamic spin fluctuations and charge
fluctuations, and find that dynamic spin fluctuations are more relevant for the
observed noise data. The frequency and temperature dependence of resistivity
noise provide important information on the nature of the magnetic interactions.
In particular, we show how noise measurements can help resolve a long standing
debate on whether the Mn-doped GaAs is an p-d Zener/RKKY or double exchange
ferromagnet. Our analysis includes the effect of different kinds of disorder
such as spin-glass type of interactions and a site-dilution type of disorder.
We find that the resistivity noise in these structures is well described by a
disordered RKKY ferromagnet model dynamics with a conserved order parameter. | 1202.3207v2 |
2016-12-02 | Structural, Morphological and Electrical Properties of Porous Silicon Prepared Under Laser Illumination | Porous silicon (PSi) layers has been prepared in this work via
photoelectrochemical (PEC) etching process of an n type silicon wafers of two
resistivities (3.5 ohm.cm and 0.02 ohm.cm) in hydrofluoric (HF) acid of 24.5
precent concentration at different etching times (5 to 25 min). The irradiation
has been achieved using laser beam of 2W power and 810 nm wavelength. We have
studied the morphological and structural properties of PSi layers using the
techniques of Xray Diffraction (XRD) and Scanning Electron Microscopy (SEM) and
Gravimetric method. The Xray Diffraction data shows that the structure aspect
of PSi layers remains crystalline as well as the decreasing of diffraction
angle (thetaB) of Xray from PSi layers (29 to 26 degree) and increasing of the
lattice parameter values of PSi structures with increasing of etching times
from 5 to 25 min., and the resistivity of silicon substrates from 0.02 to 3.5
ohm.cm. The nanocrystallite size is decreasing from (20.72 to 5.13 nm) with
increasing of etching times, and the resistivity of silicon substrates. The SEM
images shows that the values of pore width and PSi layer thickness increases
from (0.5 to 6.25 micrometer) and (6.7 to 47 micrometer) respectively with
increasing of etching times and silicon substrates resistivities, while the
values of the thickness of walls between pores has been varied from (1.25 to
0.03 micrometer) with increasing of etching times and silicon substrates
resistivities. The pore shape of pores has been varied from Cylindrical to
Rectangular and to Starful with varied of etching conditions. Further the
measured specific surface area of PSi layers has been increased from (7.43 to
235.35 m2/cm3) with increasing of etching times and silicon substrates
resistivities. | 1612.04865v1 |
2017-11-20 | Anomalous transport properties in Nb/Bi1.95Sb0.05Se3 hybrid structure | We report the proximity induced anomalous transport behavior in a Nb
Bi1.95Sb0.05Se3 heterostructure. Mechanically Exfoliated single crystal of
Bi1.95Sb0.05Se3 topological insulator (TI) is partially covered with a 100 nm
thick Niobium superconductor using DC magnetron sputtering by shadow masking
technique. The magnetotransport (MR) measurements have been performed
simultaneously on the TI sample with and without Nb top layer in the
temperature,T, range of 3 to 8 K, and a magnetic field B up to 15 T. MR on TI
region shows Subnikov de Haas oscillation at fields greater than 5 T. Anomalous
linear change in resistance is observed in the field range of negative 4T to
positive 4T at which Nb is superconducting. At 0 T field, the temperature
dependence of resistance on the Nb covered region revealed a superconducting
transition (TC) at 8.2 K, whereas TI area showed similar TC with the absence of
zero resistance states due to the additional resistance from superconductor
(SC) TI interface. Interestingly below the TC the R vs T measured on TI showed
an enhancement in resistance for positive field and prominent fall in
resistance for negative field direction. This indicates the directional
dependent scattering of the Cooper pairs on the surface of the TI due to the
superposition of spin singlet and triplet states in the superconductor and TI
respectively. | 1711.07147v1 |
2017-03-02 | Nature of carrier injection in metal/2D semiconductor interface and its implications to the limits of contact resistance | Monolayers of transition metal dichalcogenides (TMDCs) exhibit excellent
electronic and optical properties. However, the performance of these
two-dimensional (2D) devices are often limited by the large resistance offered
by the metal contact interface. Till date, the carrier injection mechanism from
metal to 2D TMDC layers remains unclear, with widely varying reports of
Schottky barrier height (SBH) and contact resistance (Rc), particularly in the
monolayer limit. In this work, we use a combination of theory and experiments
in Au and Ni contacted monolayer MoS2 device to conclude the following points:
(i) the carriers are injected at the source contact through a cascade of two
potential barriers - the barrier heights being determined by the degree of
interaction between the metal and the TMDC layer; (ii) the conventional
Richardson equation becomes invalid due to the multi-dimensional nature of the
injection barriers, and using Bardeen-Tersoff theory, we derive the appropriate
form of the Richardson equation that describes such composite barrier; (iii) we
propose a novel transfer length method (TLM) based SBH extraction methodology,
to reliably extract SBH by eliminating any confounding effect of temperature
dependent channel resistance variation; (iv) we derive the Landauer limit of
the contact resistance achievable in such devices. A comparison of the limits
with the experimentally achieved contact resistance reveals plenty of room for
technological improvements. | 1703.00671v2 |
2017-05-08 | The influence of magnetic order on the magnetoresistance anisotropy of Fe$_{1+δ-x}$Cu$_{x}$Te | We performed resistance measurements on Fe$_{1+\delta-x}$Cu$_{x}$Te with
$x_{EDX}\leq 0.06$ in the presence of in-plane applied magnetic fields,
revealing a resistance anisotropy that can be induced at a temperature far
below the structural and magnetic zero-field transition temperatures. The
observed resistance anisotropy strongly depends on the field orientation with
respect to the crystallographic axes, as well as on the field-cooling history.
Our results imply a correlation between the observed features and the
low-temperature magnetic order. Hysteresis in the angle-dependence indicates a
strong pinning of the magnetic order within a temperature range that varies
with the Cu content. The resistance anisotropy vanishes at different
temperatures depending on whether an external magnetic field or a remnant field
is present: the closing temperature is higher in the presence of an external
field. For $x_{EDX} = 0.06$ the resistance anisotropy closes above the
structural transition, at the same temperature at which the zero-field
short-range magnetic order disappears and the sample becomes paramagnetic. Thus
we suggest that under an external magnetic field the resistance anisotropy
mirrors the magnetic order parameter. We discuss similarities to nematic order
observed in other iron pnictide materials. | 1705.02849v1 |
2019-06-21 | A Two Dimensional Tunneling Resistance Transmission Line Model for Nanoscale Parallel Electrical Contacts | Contact resistance and current crowding are important to nanoscale electrical
contacts. In this paper, we present a self-consistent model to characterize
partially overlapped parallel contacts with varying specific contact
resistivity along the contact length. For parallel tunneling contacts formed
between contacting members separated by a thin insulating gap, we examine the
local voltage-dependent variation of potential barrier height and tunneling
current along the contact length, by solving the lumped circuit transmission
line model (TLM) equations coupled with the tunneling current self
consistently. The current and voltage distribution along the parallel tunneling
contacts and their overall contact resistance are analyzed in detail, for
various input voltage, electrical contact dimension, and material properties
(i.e. work function, sheet resistance of the contact members, and permittivity
of the insulating layer). It is found the existing one-dimensional (1D)
tunneling junction models become less reliable when the tunneling layer
thickness becomes smaller or the applied voltage becomes larger. In these
regimes, the proposed self-consistent model may provide a more accurate
evaluation of the parallel tunneling contacts. This work provides insights on
the design, and potential engineering, of nanoscale electrical contacts with
controlled current distribution and contact resistance via engineered spatially
varying contact layer properties and geometry. | 1906.09188v2 |
2020-11-25 | Linear-in temperature resistivity from an isotropic Planckian scattering rate | A variety of "strange metals" exhibit resistivity that decreases linearly
with temperature as $T\rightarrow 0$, in contrast with conventional metals
where resistivity decreases as $T^2$. This $T$-linear resistivity has been
attributed to charge carriers scattering at a rate given by $\hbar/\tau=\alpha
k_{\rm B} T$, where $\alpha$ is a constant of order unity. This simple
relationship between the scattering rate and temperature is observed across a
wide variety of materials, suggesting a fundamental upper limit on
scattering---the "Planckian limit"---but little is known about the underlying
origins of this limit. Here we report a measurement of the angle-dependent
magnetoresistance (ADMR) of Nd-LSCO---a hole-doped cuprate that displays
$T$-linear resistivity down to the lowest measured temperatures. The ADMR
unveils a well-defined Fermi surface that agrees quantitatively with
angle-resolved photoemission spectroscopy (ARPES) measurements and reveals a
$T$-linear scattering rate that saturates the Planckian limit, namely $\alpha =
1.2 \pm 0.4$. Remarkably, we find that this Planckian scattering rate is
isotropic, i.e. it is independent of direction, in contrast with expectations
from "hot-spot" models. Our findings suggest that $T$-linear resistivity in
strange metals emerges from a momentum-independent inelastic scattering rate
that reaches the Planckian limit. | 2011.13054v2 |
2023-05-10 | Voltage-tunable giant nonvolatile multiple-state resistance in sliding-interlayer ferroelectric h-BN van der Waals multiferroic tunnel junction | Multiferroic tunnel junctions (MFTJs) based on two-dimensional (2D) van der
Waals heterostructures with sharp and clean interfaces at the atomic scale are
crucial for applications in nanoscale multi-resistive logic memory devices. The
recently discovered sliding ferroelectricity in 2D van der Waals materials has
opened new avenues for ferroelectric-based devices. Here, we theoretically
investigate the spin-dependent electronic transport properties of
Fe$_3$GeTe$_2$/graphene/bilayer-$h$-BN/graphene/CrI$_3$ (FGT/Gr-BBN-Gr/CrI)
all-vdW MFTJs by employing the nonequilibrium Green's function combined with
density functional theory. We demonstrate that such FGT/Gr-BBN-Gr/CrI MFTJs
exhibit four non-volatile resistance states associated with different staking
orders of sliding ferroelectric BBN and magnetization alignment of
ferromagnetic free layer CrI$_3$, with a maximum tunnel magnetoresistance
(electroresistance) ratio, i.e., TMR (TER) up to $\sim$$3.36\times10^{4}$\%
($\sim$$6.68\times10^{3}$\%) at a specific bias voltage. Furthermore, the
perfect spin filtering and remarkable negative differential resistance effects
are evident in our MFTJs. We further discover that the TMR, TER, and spin
polarization ratio under an equilibrium state can be enhanced by the
application of in-plane biaxial strain. This work shows that the giant
tunneling resistance ratio, multiple resistance states, and excellent
spin-polarized transport properties of sliding ferroelectric BBN-based MFTJs
indicate its significant potential in nonvolatile memories. | 2305.06126v2 |
1999-08-17 | Experiments on Ladders Reveal a Complex Interplay between a Spin-Gapped Normal State and Superconductivity | In recent years, the study of ladder materials has developed into a
well-established area of research within the general context of Strongly
Correlated Electrons. This effort has been triggered by an unusual
cross-fertilization between theory and experiments. In this paper, the main
experimental results obtained in the context of ladders are reviewed from the
perspective of a theorist. Emphasis is given to the many similarities between
the two-dimensional high-$\rm T_c$ cuprates and the two-leg ladder compounds,
including Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (14-24-41) which has a
superconducting phase at high pressure and a small hole density. Examples of
these similarities include regimes of linear resistivity vs temperature in
metallic ladders and a normal state with spin-gap or pseudogap characteristics.
Some controversial results in this context are also discussed. It is remarked
that the ladder 14-24-41 is the first superconducting copper-oxide material
with a non-square-lattice layered arrangement, and certainly much can be
learned from a careful analysis of this compound. A short summary of the main
theoretical developments in this field is also included, as well as a brief
description of the properties of non-copper-oxide ladders. Suggestions by the
author on possible experiments are described in the text. Overall, it is
concluded that the enormous experimental effort carried out on ladders has
already unveiled quite challenging and interesting physics that adds to the
rich behavior of electrons in transition-metal-oxides, and in addition
contributes to the understanding of the two-dimensional cuprates. However,
still considerable work needs to be carried out to fully understand the
interplay between charge and spin degrees of freedom in these materials. | 9908250v1 |
2001-03-03 | Magnetic properties of magnetically textured Bi-2212 ceramics | This paper aims at reporting magnetic properties of bulk polycrystalline
Bi2Sr2Ca0.8Dy0.2Cu2O8-y samples textured under a magnetic field. The
microstructure of these materials is highly anisotropic and exhibits particular
features needed to be taken into account in order to interpret their magnetic
and electrical properties. First the AC magnetic susceptibility c = c ' - j c"
has been measured for several magnetic fields (H // ab and H // c) and compared
to the electrical resistivity data. The structure of the c" peak is shown to be
related to the chemical content distribution of the superconducting grains.
Next, the magnetic flux profiles have been extracted from the magnetic
measurements using the Campbell - Rollins procedure. The anisotropy of the flux
profiles and their peculiar curvature behaviour for H // c point out the role
of both grain platelet structure and the presence of secondary phases. From
these results, we conclude that the magnetic properties of such magnetically
textured materials do not allow for a reliable extraction of the critical
current density Jc but essentially probe geometric effects. Such effects have
to be taken into account for improving the manufacture of attractive high-Tc
materials. | 0103081v2 |
2005-02-16 | Abrupt metal-insulator transition observed in VO2 thin films induced by a switching voltage pulse | An abrupt metal-insulator transition (MIT) was observed in VO2 thin films
during the application of a switching voltage pulse to two-terminal devices.
Any switching pulse over a threshold voltage for the MIT of 7.1 V enabled the
device material to transform efficiently from an insulator to a metal. The
characteristics of the transformation were analyzed by considering both the
delay time and rise time of the measured current response. The extrapolated
switching time of the MIT decreased down to 9 ns as the external load
resistance decreased to zero. Observation of the intrinsic switching time of
the MIT in the correlated oxide films is impossible because of the
inhomogeneity of the material; both the metallic state and an insulating state
co-exist in the measurement volume. This indicates that the intrinsic switching
time is in the order of less than a nanosecond. The high switching speed might
arise from a strong correlation effect (Coulomb repulsion) between the
electrons in the material. | 0502375v4 |
2006-05-19 | Magnetic unipolar features in con- ductivity of point contacts between normal and ferromagnetic d-metals (Co, Ni, Fe) | In nanocontacts between normal and ferromagnetic metals (N--F) abrupt changes
of the order of 1% are detected in differential resistance, dV/dI(V), versus
bias voltage, V, on achieving of high current densities, ~10^9 A/cm^2. These
features in dV/dI(V) are observed when the electron flow is directed from the
nonmagnetic metal into the ferromagnet and connected with magnetization
excitations in the ferromagnet induced by the current. Applying an external
magnetic field leads to a shift of the observed features to higher biasing
current, confirming the magnetic nature of the effect. Such effects are
observed for the non-ballistic (not spectral) regime of current flow in the
nanocontacts. Thus, the current induced magneto-conductance effects in
multilayered N--F structures (nanopillars) extensively studied in the recent
literature have much more general character and can be stimulated by elastic
electron scattering at single N--F interfaces. | 0605485v1 |
2007-08-14 | Landscape phage, phage display, stripped phage, biosensors, detection, affinity reagent, nanotechnology, Salmonella typhimurium, Bacillus anthracis | Filamentous phage, such as fd used in this study, are thread-shaped bacterial
viruses. Their outer coat is a tube formed by thousands equal copies of the
major coat protein pVIII. We constructed libraries of random peptides fused to
all pVIII domains and selected phages that act as probes specific for a panel
of test antigens and biological threat agents. Because the viral carrier is
infective, phage borne bio-selective probes can be cloned individually and
propagated indefinitely without needs of their chemical synthesis or
reconstructing. We demonstrated the feasibility of using landscape phages and
their stripped fusion proteins as new bioselective materials that combine
unique characteristics of affinity reagents and self assembling membrane
proteins. Biorecognition layers fabricated from phage-derived probes bind
biological agents and generate detectable signals. The performance of
phage-derived materials as biorecognition films was illustrated by detection of
streptavidin-coated beads, Bacillus anthracis spores and Salmonella typhimurium
cells. With further refinement, the phage-derived analytical platforms for
detecting and monitoring of numerous threat agents may be developed, since the
biodetector films may be obtained from landscape phages selected against any
bacteria, virus or toxin. As elements of field-use detectors, they are superior
to antibodies, since they are inexpensive, highly specific and strong binders,
resistant to high temperatures and environmental stresses. | 0708.1823v1 |
2010-01-28 | A simple kinetic sensor to structural transitions | Driven non-equilibrium structural phase transformation has been probed using
time varying resistance fluctuations or noise. We demonstrate that the
non-Gaussian component (NGC) of noise obtained by evaluating the higher order
statistics of fluctuations, serves as a simple kinetic detector of these phase
transitions. Using the martensite transformation in free-standing wires of
nickel-titanium binary alloys as a prototype, we observe clear deviations from
the Gaussian background in the transformation zone, indicative of the long
range correlations in the system as the phase transforms. The viability of non-
Gaussian statistics as a robust probe to structural phase transition was also
confirmed by comparing the results from differential scanning calorimetry
measurements. We further studied the response of the NGC to the modifications
in the microstructure on repeated thermal cycling, as well as the variations in
the temperature drive rate, and explained the results using established
simplistic models based on the different competing time scales. Our experiments
(i) suggest an alternative method to estimate the transformation temperature
scales with high accuracy, and (ii) establish a connection between the
material-specific evolution of microstructure to the statistics of its linear
response. Since the method depends on an in-built long-range correlation during
transformation, it could be portable to other structural transitions, as well
as to materials of different physical origin and size. | 1001.5137v1 |
2010-03-04 | Spin glass like behavior in the novel layered material Na_2IrO_3 | We have synthesized the novel material Na_2IrO_3 and studied its structure,
transport, magnetic, and thermal properties using powder x-ray diffraction
(PXRD), electrical resistivity, isothermal magnetization M versus magnetic
field H, static \chi and dynamic \chi_ac magnetic susceptibility versus
temperature T, and heat capacity C versus T measurements. Na_2IrO_3
crystallizes in the monoclinic C2/c (No. 15) structure which is made up of Na
and NaIr_2O_6 layers alternately stacked along the c axis. From a Rietveld
refinement of the PXRD pattern we identify atomic disorder arising from a
mixing of Ir and Na sites within the NaIr_2O_6 layers. The \chi data in H = 1 T
shows Curie-Weiss behavior at high T > 100 K with an effective moment \mu_eff =
1.82(1) \mu_B indicating an effective spin S_eff = 1/2 on the Ir^{4+} moments.
A Weiss temperature \theta = - 62(1) K indicates substantial antiferromagnetic
interactions between these S_eff = 1/2, Ir^{4+} moments. The \chi data in low
field show a sharp cusp at T_g = 5.5 K and there is a bifurcation between
zero-field-cooled (ZFC) and field-cooled (FC) data below this T. The \chi_ac
data also show a sharp cusp at T_g = 5.5 K at a frequency f = 1 Hz which moves
to higher temperatures with increasing f. We did not observe any anomaly at T_g
in our C measurements and only a broad shoulder was observed at a much higher T
= 12 K. Our results indicate that in Na_2IrO_3, a spin-glass like state occurs
below the freezing temperature T_g = 5.5 K and this freezing most likely arises
either from structural disorder or geometrical magnetic frustration. | 1003.0973v2 |
2013-01-10 | Micro-branching in mode-I fracture in a randomly perturbed lattice | We study mode-I fracture in lattices with noisy bonds. In contrast to
previous attempts, by using a small parameter that perturbs the force-law
between the atoms in perfect lattices and using a 3-body force law, simulations
reproduce the qualitative behavior of the beyond steady-state cracks in the
high velocity regime, including reasonable micro-branching. As far as the
physical properties such as the structure factor $g(r)$, the radial or angular
distributions, these lattices share the physical properties of perfect lattices
rather than that of an amorphous material (e.g., the continuous random network
model). A clear transition can be seen between steady-state cracks, where a
single crack propagates in the midline of the sample and the regime of unstable
cracks, where micro-branches start to appear near the main crack, in line with
previous experimental results. This is seen both in a honeycomb lattice and a
fully hexagonal lattice. This model reproduces the main physical features of
propagating cracks in brittle materials, including the behavior of velocity as
a function of driving displacement and the increasing amplitude of oscillations
of the electrical resistance. In addition, preliminary indications of power-law
behavior of the micro-branch shapes can be seen, potentially reproducing one of
the most intriguing experimental results of brittle fracture. | 1301.2143v1 |
2013-04-24 | Supramolecular Spin Valves | Magnetic molecules possess a high potential as building blocks for the design
of spintronic devices. Moreover, the use of molecular materials opens the way
for the controlled use of bottom-up, e.g. supramolecular, processing techniques
combining massively parallel self-fabrication with conventional top-down
nanostructuring techniques. The development of solid state spintronic devices
based on the giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), and
spin valve effects has revolutionized the field of magnetic memory
applications. Recently, organic semiconductors were inserted into nanometer
sized tunnel junctions allowing enhancement of spin reversal, giant
magneto-resistance behaviour was observed in single non-magnetic molecules
coupled to magnetic electrodes, and the use of the quantum tunnelling
properties of single-molecule magnets (SMMs) in hybrid devices was proposed.
Herein, we present an original device in which a non-magnetic molecular quantum
dot, made of a single-wall carbon nanotube (SWCNT) contacted with non-magnetic
electrodes, is laterally coupled via supramolecular interactions to a TbPc2-SMM
(Pc = phthalocyanine), which provides a localized magnetic moment. The
conductance through the SWCNT is modulated by sweeping the magnetic field,
exhibiting magnetoresistance ratios up to 300% between fully polarized and
non-polarized SMMs below 1 K. We thus demonstrate the functionality of a
supramolecular spin valve without magnetic leads. Our results open up prospects
of circuit-integration and implementation of new device capabilities. | 1304.6543v1 |
2014-09-10 | Controlling and distinguishing electronic transport of topological and trivial surface states in a topological insulator | Topological insulators (TI), with characteristic Dirac-fermion topological
surface states (TSS), have emerged as a new class of electronic materials with
rich potentials for both novel physics and device applications. However, a
major challenge with realistic TI materials is to access, distinguish and
manipulate the electronic transport of TSS often obscured by other possible
parallel conduction channels that include the bulk as well as a two-dimensional
electron gas (2DEG) formed near the surface due to bending of the bulk bands.
Such a (Schrodinger-fermion) 2DEG represents topologically-trivial surface
states, whose coexistence with the TSS has been revealed by angle resolved
photoemission spectroscopy. Here we show that simple manipulations of surface
conditions can be used to access and control both types of surface states and
their coexistence in bulk-insulating Bi2Te2Se, whose surface conduction is
prominently manifested in temperature dependent resistance and nonlocal
transport. The trivial 2DEG and TSS can both exhibit clear Shubnikov-de Haas
oscillations in magnetoresistance, with different Berry phases ~0 and ~pi that
distinguish their different topological characters. We also report a deviation
from the typical weak antilocalization behavior, possibly due to high mobility
TSS. Our study enables distinguishing, controlling and harnessing electronic
transport of TI surface carriers with different topological natures. | 1409.3217v1 |
2014-09-12 | Fast non-thermal switching between macroscopic charge-ordered quantum states induced by charge injection | The functionality of logic and memory elements in current electronics is
based on multi-stability, driven either by manipulating local concentrations of
electrons in transistors, or by switching between equivalent states of a
material with a degener- ate ground state in magnetic or ferroelectric
materials. Another possibility is offered by phase transitions with switching
between metallic and insulating phases, but classical phase transitions are
limited in speed by slow nucleation, proliferation of domains and hysteresis.
We can in principle avoid these problems by using quantum states for switching,
but microscopic systems suffer from decoherence which prohibits their use in
everyday devices. Macroscopic quantum states, such as the superconducting
ground state have the advantage that on a fundamental level they do not suffer
from decoherence plaguing microscopic systems. Here we demonstrate for the
first time ultrafast non-thermal switching between different metastable
electronically ordered states by pulsed electrical charge injection. The
macroscopic nature of the many-body quantum states(1-4) - which are not part of
the equilibrium phase diagram - gives rise to unprecedented stability and
remarka- bly sharp switching thresholds. Fast sub-50 ps switching, large
associated re- sistance changes, 2-terminal operation and demonstrable high
fidelity of bi-stability control suggest new opportunities for the use of
macroscopic quantum states in electronics, particularly for an ultrafast
non-volatile quantum charge-order resistive random access memory (QCOR-RAM). | 1409.3794v1 |
2014-10-19 | Enabling microstructural changes of FCC/BCC alloys in 2D dislocation dynamics | Dimension reduction procedure is the recipe to represent defects in two
dimensional dislocation dynamics according to the changes in the geometrical
properties of the defects triggered by different conditions such as radiation,
high temperature, or pressure. In the present study, this procedure is extended
to incorporate further features related to the presence of defects with a
special focus on face-centered cubic/body-centered cubic alloys used for
diverse engineering purposes. In order to reflect the microstructural state of
the alloy on the computational cell of two dimensional dislocation dynamics,
the distribution of the multi-type defects over slip lines is implemented by
using corresponding strength and line spacing for each type of defect.
Additionally, a simple recursive incremental relation is set to count the loop
accumulation on the precipitates. In the case of continuous resistance against
the motion of edge dislocations on the slip lines, an expression of friction is
introduced to see its contribution on the yield strength. Each new property is
applied independently on a different material by using experimental information
about defect properties and grain sizes under the condition of plain strain
deformation: both constant and dynamically increasing obstacle strength for
precipitate coarsening in prime-aged and heat-treated
copper-chromium-zirconium, internal friction in tantalum-2.5tungsten, and mixed
hardening due to the presence of precipitates and prismatic loops in irradiated
oxide dispersion strengthened EUROFER with 0.3% yttria. | 1410.5094v2 |
2015-10-22 | Thermal conductivity of III-V semiconductor superlattices | This paper presents a semiclassical model for the anisotropic thermal
transport in III-V semiconductor superlattices (SLs). An effective interface
rms roughness is the only adjustable parameter. Thermal transport inside a
layer is described by the Boltzmann transport equation in the relaxation time
approximation and is affected by the relevant scattering mechanisms
(three-phonon, mass-difference, and dopant and electron scattering of phonons),
as well as by diffuse scattering from the interfaces captured via an effective
interface scattering rate. The in-plane thermal conductivity is obtained from
the layer conductivities connected in parallel. The cross-plane thermal
conductivity is calculated from the layer thermal conductivities in series with
one another and with thermal boundary resistances (TBRs) associated with each
interface; the TBRs dominate cross-plane transport. The TBR of each interface
is calculated from the transmission coefficient obtained by interpolating
between the acoustic mismatch model (AMM) and the diffuse mismatch model (DMM),
where the weight of the AMM transmission coefficient is the same
wavelength-dependent specularity parameter related to the effective interface
rms roughness that is commonly used to describe diffuse interface scattering.
The model is applied to multiple III-arsenide superlattices, and the results
are in very good agreement with experimental findings. The method is both
simple and accurate, easy to implement, and applicable to complicated SL
systems, such as the active regions of quantum cascade lasers. It is also valid
for other SL material systems with high-quality interfaces and predominantly
incoherent phonon transport. | 1510.06725v1 |
2016-08-22 | Superconducting Order from Disorder in 2H-TaSe$_{2-x}$S$_{x}$ (0$\leq$x$\leq$2) | We report on the emergence of robust superconducting order in single crystal
alloys of 2H-TaSe$_{2-x}$S$_{x}$ (0$\leq$x$\leq$2) . The critical temperature
of the alloy is surprisingly higher than that of the two end compounds
TaSe$_{2}$ and TaS$_{2}$. The evolution of superconducting critical temperature
T$_{c} (x)$ correlates with the full width at half maximum of the Bragg peaks
and with the linear term of the high temperature resistivity. The conductivity
of the crystals near the middle of the alloy series is higher or similar than
that of either one of the end members 2H-TaSe$_{2}$ and/or 2H-TaS$_{2}$. It is
known that in these materials superconductivity (SC) is in close competition
with charge density wave (CDW) order. We interpret our experimental findings in
a picture where disorder tilts this balance in favor of superconductivity by
destroying the CDW order. | 1608.06275v2 |
2017-02-07 | Quantitative Nanoscale Mapping of Three-Phase Thermal Conductivities in Filled Skutterudites via Scanning Thermal Microscopy | In the last two decades, a nanostructuring paradigm has been successfully
applied in a wide range of thermoelectric materials, resulting in significant
reduction in thermal conductivity and superior thermoelectric performance.
These advances, however, have been accomplished without directly investigating
the local thermoelectric properties, even though local electric current can be
mapped with high spatial resolution. In fact, there still lacks an effective
method that links the macroscopic thermoelectric performance to the local
microstructures and properties. Here, we show that local thermal conductivity
can be mapped quantitatively with good accuracy, nanometer resolution, and
one-to-one correspondence to the microstructure using a three-phase
skutterudite as a model system. Scanning thermal microscopy combined with
finite element simulations demonstrate close correlation between sample
conductivity and probe resistance, enabling us to distinguish thermal
conductivities spanning orders of magnitude, yet resolving thermal variation
across a phase interface with small contrast. The technique thus provides a
powerful tool to correlate local thermal conductivities, microstructures, and
macroscopic properties for nanostructured materials in general, and
nanostructured thermoelectrics in particular. | 1702.01895v3 |
2017-06-24 | Probing nanocrystalline grain dynamics in nanodevices | Dynamical structural defects exist naturally in a wide variety of solids.
They fluctuate temporally, and hence can deteriorate the performance of many
electronic devices. Thus far, the entities of such dynamic objects have been
identified to be individual atoms. On the other hand, it is a long-standing
question whether a nanocrystalline grain constituted of a large number of atoms
can switch, as a whole, reversibly like a dynamical atomic defect (i.e., a
two-level system). This is an emergent issue considering the current
development of nanodevices with ultralow electrical noise, qubits with long
quantum coherence time, and nanoelectromechanical system (NEMS) sensors with
ultrahigh resolution. Here we demonstrate experimental observations of dynamic
nanocrystalline grains which repeatedly switch between two or more metastable
coordinate states. We study temporal resistance fluctuations in thin ruthenium
dioxide (RuO2) metal nanowires and extract microscopic parameters including
relaxation time scales, mobile grain sizes, and the bonding strengths of
nanograin boundaries. Such material parameters are not obtainable by other
experimental approaches. When combined with previous in-situ high-resolution
transmission electron microscopy (HRTEM), our electrical method can be used to
infer rich information about the structural dynamics of a wide variety of
nanodevices and new 2D materials. | 1706.07887v1 |
2017-12-27 | Controlled synthesis of the antiperovskite oxide superconductor Sr$_{3-x}$SnO | A large variety of perovskite oxide superconductors are known, including some
of the most prominent high-temperature and unconventional superconductors.
However, superconductivity among the oxidation state inverted material class,
the antiperovskite oxides, was reported just recently for the first time. In
this superconductor, Sr$_{3-x}$SnO, the unconventional ionic state Sn$^{4-}$ is
realized and possible unconventional superconductivity due to a band inversion
has been discussed. Here, we discuss an improved facile synthesis method,
making it possible to control the strontium deficiency in Sr$_{3-x}$SnO.
Additionally, a synthesis method above the melting point of Sr$_{3}$SnO is
presented. We show temperature dependence of magnetization and electrical
resistivity for superconducting strontium deficient Sr$_{3-x}$SnO
($T_{\mathrm{c}}$ ~ 5 K) and for Sr$_{3}$SnO without a superconducting
transition down to 0.15 K. Further, we reveal a significant effect of strontium
raw material purity on the superconductivity and achieve 40% increased
superconducting volume fraction (~100%) compared to the highest value reported
so far. More detailed characterisation utilising powder X-ray diffraction and
energy-dispersive X-ray spectroscopy show that a minor cubic phase, previously
suggested to be a Sr$_{3-x}$SnO, is SrO. The improved characterization and
controlled synthesis reported herein enable detailed investigations on the
superconducting nature and its dependency on the strontium deficiency in
Sr$_{3-x}$SnO. | 1712.09484v1 |
2018-04-11 | NMR and the antiferromagnetic crystal phase regions in rapidly quenched ribbons and in alloys of the type $Cu-Mn-Al$ | It was shown that anomalous resistivity behavior of the $Cu-Mn-Al$ ribbons is
explained by the s-d interaction between conduction electrons and the clustered
Mn atoms. While nuclear magnetic resonance measurements show the
antiferromagnetic and ferromagnetic clusters of Mn atom coexisting without
long-range order, it is an interesting problem to study magnetic resonance
properties also for the antiferromagnetic crystal phase regions (which have
long-range order for larger regions) and which may also occur in these ribbons.
The Heusler Type $Cu-Mn-Al$ Alloy has a composition half way between
$Cu_{2}MnAl$ and $Cu_{3}Al$. Electron microscopy of the premartensitic $\beta
Cu-Zn-Al$ alloy has shown that the $\beta Cu-Zn-Al$ alloy quenched from high
temperature has the electron diffraction patterns of this alloy well explained
by the model with the existence of small particles with an orthorhombic
structure. It was noted that an important aspect of improvement in the material
properties is to create a nanostructured state in matrix, which has significant
advantages in magnetic and mechanical characteristics in contrast to the bulk
materials in crystalline or amorphous state. It is an interesting problem to
study magnetic resonance properties not only for the Mn atoms and clusters
without long-range order but also for the antiferromagnetic crystal phase
regions (which have long-range order for larger regions) which may also occur
in ribbons. This is the aim of our paper. | 1804.04196v1 |
2020-03-25 | Magnetic-field-induced FM-AFM metamagnetic transition and strong negative magnetoresistance in Mn$_{1/4}$NbS$_2$ under pressure | Transition metal dichalcogenides (TMDC) stand out with their high chemical
stability and the possibility to incorporate a wide range of magnetic species
between the layers. The behavior of conduction electrons in such materials
intercalated by 3d-elements is closely related to their magnetic properties and
can be sensitively controlled by external magnetic fields. Here, we study the
magnetotransport properties of NbS$_2$ intercalated with Mn, Mn$_{1/4}$NbS$_2$,
demonstrating a complex behavior of the magnetoresistance and of the ordinary
and anomalous Hall resistivities. Application of pressure as tuning parameter
leads to the drastic changes of the magnetotransport properties of
Mn$_{1/4}$NbS$_2$ exhibiting large negative magnetoresistance up to $65 \%$ at
7.1 GPa. First-principles electronic structure calculations indicates
pressure-induced transition from ferromagnetic to antiferromagnetic state.
Theoretical calculations accounting for the finite temperature magnetic
properties of Mn$_{1/4}$NbS$_2$ suggest a field-induced metamagnetic
ferromagnetic-antiferromagnetic transition as an origin of the large negative
magentoresistance. These results inspire the development of materials for
spintronic applications based on intercalated TMDC with a well controllable
metamagnetic transition. | 2003.11678v1 |
2017-03-16 | Elemental Phosphorus: structural and superconducting phase diagram under pressure | Pressure-induced superconductivity and structural phase transitions in
phosphorous (P) are studied by resistivity measurements under pressures up to
170 GPa and fully $ab-initio$ crystal structure and superconductivity
calculations up to 350 GPa. Two distinct superconducting transition temperature
(T$_{c}$) vs. pressure ($P$) trends at low pressure have been reported more
than 30 years ago, and for the first time we are able to reproduce them and
devise a consistent explanation founded on thermodynamically metastable phases
of black-phosphorous. Our experimental and theoretical results form a single,
consistent picture which not only provides a clear understanding of elemental P
under pressure but also sheds light on the long-standing and unsolved
$anomalous$ superconductivity trend. Moreover, at higher pressures we predict a
similar scenario of multiple metastable structures which coexist beyond their
thermodynamical stability range. Metastable phases of P experimentally
accessible at pressures above 240 GPa should exhibit T$_{c}$'s as high as 15 K,
i.e. three times larger than the predicted value for the ground-state crystal
structure. We observe that all the metastable structures systematically exhibit
larger transition temperatures than the ground-state ones, indicating that the
exploration of metastable phases represents a promising route to design
materials with improved superconducting properties. | 1703.05694v1 |
2018-10-08 | Monte Carlo phonon transport simulations in hierarchically disordered silicon nanostructures | Hierarchical material nanostructuring is considered to be a very promising
direction for high performance thermoelectric materials. In this work we
investigate thermal transport in hierarchically nanostructured silicon. We
consider the combined presence of nanocrystallinity and nanopores, arranged
under both ordered and randomized positions and sizes, by solving the Boltzmann
transport equation using the Monte Carlo method. We show that nanocrystalline
boundaries degrade the thermal conductivity more drastically when the average
grain size becomes smaller than the average phonon mean free path. The
introduction of pores degrades the thermal conductivity even further. Its
effect, however, is significantly more severe when the pore sizes and positions
are randomized, as randomization results in regions of higher porosity along
the phonon transport direction, which introduce significant thermal resistance.
We show that randomization acts as a large increase in the overall effective
porosity. Using our simulations, we show that existing compact nanocrystalline
and nanoporous theoretical models describe thermal conductivity accurately
under uniform nanostructured conditions, but overestimate it in randomized
geometries. We propose extensions to these models that accurately predict the
thermal conductivity of randomized nanoporous materials based solely on a few
geometrical features. Finally, we show that the new compact models introduced
can be used within Matthiessens rule to combine scattering from different
geometrical features within approximately 10 per cent accuracy. | 1810.03334v1 |
2020-09-22 | A cracking oxygen story: a new view of stress corrosion cracking in titanium alloys | Titanium alloys can suffer from halide-associated stress corrosion cracking
at elevated temperatures e.g., in jet engines, where chlorides and Ti-oxide
promote the cracking of water vapour in the gas stream, depositing embrittling
species at the crack tip. Here we report, using isotopically-labelled
experiments, that crack tips in an industrial Ti-6Al-2Sn-4Zr-6Mo alloy are
strongly enriched (>5 at.%) in oxygen from the water vapour, far greater than
the amounts (0.25 at.%) required to embrittle the material. Surprisingly,
relatively little hydrogen (deuterium) is measured, despite careful preparation
and analysis. Therefore, we suggest that a combined effect of O and H leads to
cracking, with O playing a vital role, since it is well-known to cause
embrittlement of the alloy. In contrast it appears that in alpha+beta Ti
alloys, it may be that H may drain away into the bulk owing to its high
solubility in beta-Ti, rather than being retained in the stress field of the
crack tip. Therefore, whilst hydrides may form on the fracture surface,
hydrogen ingress might not be the only plausible mechanism of embrittlement of
the underlying matrix. This possibility challenges decades of understanding of
stress-corrosion cracking as being related solely to the hydrogen enhanced
localised plasticity (HELP) mechanism, which explains why H-doped Ti alloys are
embrittled. This would change the perspective on stress corrosion embrittlement
away from a focus purely on hydrogen to also consider the ingress of O
originating from the water vapour, insights critical for designing corrosion
resistant materials. | 2009.10567v2 |
2017-05-08 | Casimir free energy of dielectric films: Classical limit, low-temperature behavior and control | The Casimir free energy of dielectric films, both free-standing in vacuum and
deposited on metallic or dielectric plates, is investigated. It is shown that
the values of the free energy depend considerably on whether the calculation
approach used neglects or takes into account the dc conductivity of film
material. We demonstrate that there are the material-dependent and universal
classical limits in the former and latter cases, respectively. The analytic
behavior of the Casimir free energy and entropy for a free-standing dielectric
film at low temperature in found. According to our results, the Casimir entropy
goes to zero when the temperature vanishes if the calculation approach with
neglected dc conductivity of a film is employed. If the dc conductivity is
taken into account, the Casimir entropy takes the positive value at zero
temperature, depending on the parameters of a film, i.e., the Nernst heat
theorem is violated. By considering the Casimir free energy of silica and
sapphire films deposited on a Au plate in the framework of two calculation
approaches, we argue that physically correct values are obtained by
disregarding the role of dc conductivity. A comparison with the well known
results for the configuration of two parallel plates is made. Finally, we
compute the Casimir free energy of silica, sapphire and Ge films deposited on
high-resistivity Si plates of different thicknesses and demonstrate that it can
be positive, negative and equal to zero. Possible applications of the obtained
results to thin films used in microelectronics are discussed. | 1705.02897v1 |
2017-07-17 | Realizing Thermoelectric and Thermistor Bi-functionalities via Triggering Electron Correlations with Lattice-dipole | Establishing strong electron-correlations not only shed lights on overcoming
the trade-off limitations for optimizing thermoelectric materials, but can also
introduce new functionalities that extend the vision of conventional
thermoelectric applications. Here, we demonstrate that the high thermoelectric
and thermistor functionalities coexist in lattice distorted SrNbxTi1-xO3 films
with electron correlations between carriers and ordering aligned lattice
dipoles. As-grown SrNbxTi1-xO3/SrTiO3 with effectively preserved interfacial
strains exhibits cross-plane charge ordering and orbital anisotropy, as
indicated by the polarization dependent near edge X-ray absorption fine
structures. The resultant coulomb-correlations regulate the carrier transport
and enhance the Seebeck coefficient more independently via enlarging the system
vibration entropy. As-achieved maximum thermoelectric power factor exceeds 100
uWcm-1K-2 measured in the bulk performance of SrNb0.2Ti0.8O3 (2.2 um)/SrTiO3
(100 um), which is comparable to the best thermoelectric materials for low
temperature applications. In addition, the strong temperature dependence of the
carrier scattering aroused by the lattice dipoles introduces a positive
temperature dependent thermistor transportation behavior with large temperature
coefficient of resistance ranging from 30 to 300 K, which is rarely seen in
conventional thermistors. Combining both functionalities largely extend the
horizon in exploring new Joule sensors for detection of temperature and thermal
perturbations across a broad temperature range. | 1707.04988v2 |
2017-08-17 | Tailoring tricolor structure of magnetic topological insulator for robust axion insulator | Exploration of novel electromagnetic phenomena is a subject of great interest
in topological quantum materials. One of the unprecedented effects to be
experimentally verified is topological magnetoelectric (TME) effect originating
from an unusual coupling of electric and magnetic fields in materials. A
magnetic heterostructure of topological insulator (TI) hosts such an exotic
magnetoelectric coupling and can be expected to realize the TME effect as an
axion insulator. Here we designed a magnetic TI with tricolor structure where a
non-magnetic layer of (Bi, Sb)2Te3 is sandwiched by a soft ferromagnetic
Cr-doped (Bi, Sb)2Te3 and a hard ferromagnetic V-doped (Bi, Sb)2Te3.
Accompanied by the quantum anomalous Hall (QAH) effect, we observe zero Hall
conductivity plateaus, which are a hallmark of the axion insulator state, in a
wide range of magnetic field between the coercive fields of Cr- and V-doped
layers. The resistance of the axion insulator state reaches as high as 10^9
ohm, leading to a gigantic magnetoresistance ratio exceeding 10,000,000% upon
the transition from the QAH state. The tricolor structure of TI may not only be
an ideal arena for the topologically distinct phenomena, but also provide
magnetoresistive applications for advancing dissipationless topological
electronics. | 1708.05387v1 |
2019-03-02 | AC Elastocaloric effect as a probe for thermodynamic signatures of continuous phase transitions | Studying the response of materials to strain can elucidate subtle properties
of electronic structure in strongly correlated materials. So far, mostly the
relation between strain and resistivity, the so called elastoresistivity, has
been investigated. The elastocaloric effect is a second rank tensor quantity
describing the relation between entropy and strain. In contrast to the
elastoresistivity, the elastocaloric effect is a thermodynamic quantity.
Experimentally, elastocaloric effect measurements are demanding since the
thermodynamic conditions during the measurement have to be well controlled.
Here we present a technique to measure the elastocaloric effect under quasi
adiabatic conditions. The technique is based on oscillating strain, which
allows for increasing the frequency of the elastocaloric effect above the
thermal relaxation rate of the sample. We apply the technique to Co-doped iron
pnictide superconductors and show that the thermodynamic signatures of second
order phase transitions in the elastocaloric effect closely follow those
observed in calorimetry experiments. In contrast to the heat capacity, the
electronic signatures in the elastocaloric effect are measured against a small
phononic background even at high temperatures, establishing this technique as a
powerful complimentary tool for extracting the entropy landscape proximate to a
continuous phase transition. | 1903.00791v1 |
2019-03-27 | Investigation of Room Temperature Ferroelectricity and Ferrimagnetism in Multiferroic AlxFe2-xO3 Epitaxial Thin Films | Multiferroic materials open up the possibility to design novel functionality
in electronic devices, with low energy consumption. However, there are very few
materials that show multiferroicity at room temperature, which is essential to
be practically useful. AlxFe2-xO3 (x-AFO) thin films, belonging to the k-Al2O3
family are interesting because they show room temperature ferrimagnetism and
have a polar crystal structure. However, it is difficult to realise its
ferroelectric properties at room temperature, due to low resistivity of the
films. In this work, we have deposited x-AFO (0.5 <= x <= 1) epitaxial thin
films with low leakage, on SrTiO3<111> substrates by Pulsed Laser Deposition.
Magnetic measurements confirmed room temperature ferrimagnetism of the films,
however the Curie temperature was found to be influenced by deposition
conditions. First principle calculations suggested that ferroelectric domain
switching occurs through shearing of in-plane oxygen layers, and predicted a
high polarization value of 24 uC/cm2. However, actual ferroelectric
measurements showed the polarization to be two order less. Presence of multiple
in-plane domains which oppose polarization switching of adjacent domains, was
found to be the cause for the small observed polarization. Comparing dielectric
relaxation studies and ferroelectric characterization showed that
oxygen-vacancy defects assist domain wall motion, which in turn facilitates
polarization switching. | 1903.11422v1 |
2016-09-09 | Extremely large magnetoresistance in a topological semimetal candidate pyrite PtBi2 | While pyrite-type PtBi2 with face-centered cubic structure has been predicted
to be a three-dimensional (3D) Dirac semimetal, experimental study on its
physical properties remains absent. Here we report the angular-dependent
magnetoresistance (MR) measurements of PtBi2 single-crystal under high magnetic
fields. We observed extreme large unsaturated magnetoresistance (XMR) up to
11.2 million percent at T = 1.8 K in a magnetic field of 33 T, which surpasses
the previously reported Dirac materials, such as WTe2, LaSb and NbP. The
crystals exhibit an ultrahigh mobility and significant Shubnikov-de Hass (SdH)
quantum oscillations with nontrivial Berry's phase. Analysis of Hall
resistivity indicates that the XMR can be ascribed to the nearly compensated
electron and hole. Our experimental results associated with the ab initio
calculations suggest that pyrite PtBi2 is a topological semimetal candidate
which might provide a platform for exploring topological materials with XMR in
noble metal alloys. | 1609.02626v2 |
2019-06-19 | Apparatus for Seebeck coefficient measurement of wire, thin film and bulk materials in the wide temperature range (80-650K) | A Seebeck coefficient measurement apparatus has been designed and developed,
which is very effective for accurate characterization of different type of
samples in a wide temperature range (80 - 650K) simultaneously covering low as
well as the high-temperature regime. Reducing the complexity of the technical
design of sample holder and data collections has always been challenging to
implement in a single instrument when samples are in different geometrical
shape and electronic structure. Our unique design of sample holder with
pressure probes covers measurements of different samples shapes (wires, thin
films and pellets) as well as different resistivity ranges (metals,
semiconductors and insulators). It is suitable for characterization of
different samples sizes (3-12 mm). A double heater configuration powered by a
dual channel source meter is employed for maintaining a desired constant
temperature difference across the sample for the whole temperature range. Two
K-type thermocouples are used for simultaneously reading of temperatures and
Seebeck voltages by utilizing different channels of a multichannel digital
multimeter. Calibration of the system has been carried out using constantan,
chromel and alumel materials and recorded data is found to be very accurate and
consistent with earlier reports. The Seebeck coefficients of standard samples
of constantan (wire) and GaN (thin film) have been reported, which shows the
measurement capability of designed setup with versatile samples. | 1906.08023v2 |
2019-11-20 | Piezoelectricity in monolayer hexagonal boron nitride | Two-dimensional (2D) hexagonal boron nitride (hBN) is a wide-bandgap van der
Waals crystal with a unique combination of properties, including exceptional
strength, large oxidation resistance at high temperatures and optical
functionalities. Furthermore, in recent years hBN crystals have become the
material of choice for encapsulating other 2D crystals in a variety of
technological applications, from optoelectronic and tunnelling devices to
composites. Monolayer hBN, which has no center of symmetry, has been predicted
to exhibit piezoelectric properties, yet experimental evidence is lacking.
Here, by using electrostatic force microscopy, we observed this effect as a
strain-induced change in the local electric field around bubbles and creases,
in agreement with theoretical calculations. No piezoelectricity was found in
bilayer and bulk hBN, where the centre of symmetry is restored. These results
add piezoelectricity to the known properties of monolayer hBN, which makes it a
desirable candidate for novel electromechanical and stretchable optoelectronic
devices, and pave a way to control the local electric field and carrier
concentration in van der Waals heterostructures via strain. The experimental
approach used here also shows a way to investigate the piezoelectric properties
of other materials on the nanoscale by using electrostatic scanning probe
techniques. | 1911.09134v1 |
2020-07-16 | The influence of material properties and process parameters on the spreading process in additive manufacturing | Laser powder bed fusion (LPBF) is an additive manufacturing (AM) technology.
To achieve high product quality, the powder is best spread as a uniform, dense
layer. The challenge for LPBF manufacturers is to develop a spreading process
that can produce a consistent layer quality for the many powders used, which
show considerable differences in spreadability. Therefore, we investigate the
influence of material properties, process parameters and the type of spreading
tool on the layer quality. The discrete particle method is used to simulate the
spreading process and to define metrics to evaluate the powder layer
characteristics. We found that particle shape and surface roughness in terms of
rolling resistance and interparticle sliding friction as well as particle
cohesion all have a major (sometimes surprising) influence on the powder layer
quality: more irregular shaped particles, rougher particle surfaces and/or
higher interfacial cohesion usually, but not always, lead to worse
spreadability. Our findings illustrate that there is a trade-off between
material properties and process parameters. Increasing the spreading speed
decreases layer quality for non- and weakly cohesive powders, but improves it
for strongly cohesive ones. Using a counter-clockwise rotating roller as a
spreading tool improves the powder layer quality compared to spreading with a
blade. Finally, for both geometries, a unique correlation between the quality
criteria uniformity and mass fraction is reported and some of the findings are
related to size-segregation during spreading. | 2007.10125v1 |
2021-03-12 | Nanodevices engineering and spin transport properties of MnBi2Te4 monolayer | Two-dimensional (2D) magnetic materials are essential for the development of
the next-generation spintronic technologies. Recently, layered van der Waals
(vdW) compound MnBi2Te4 (MBT) has attracted great interest, and its 2D
structure has been reported to host coexisting magnetism and topology. Here, we
design several conceptual nanodevices based on MBT monolayer (MBT-ML) and
reveal their spin-dependent transport properties by means of the
first-principles calculations. The pn-junction diodes and sub-3-nm pin-junction
field-effect transistors (FETs) show a strong rectifying effect and a spin
filtering effect, with an ideality factor n close to 1 even at a reasonably
high temperature. In addition, the pip- and nin-junction FETs give an
interesting negative differential resistive (NDR) effect. The gate voltages can
tune currents through these FETs in a large range. Furthermore, the MBT-ML has
a strong response to light. Our results uncover the multifunctional nature of
MBT-ML, pave the road for its applications in diverse next-generation
semiconductor spin electric devices. | 2103.07025v1 |
2021-04-12 | Fiber Packing and Morphology Driven Moisture Diffusion Mechanics in Reinforced Composites | Fiber reinforced polymer composite (FRPC) materials are extensively used in
lightweight applications due to their high specific strength and other
favorable properties including enhanced endurance and corrosion resistance.
However, these materials are inevitably exposed to moisture, which is known to
drastically reduce their mechanical properties caused by moisture absorption
and often accompanied with plasticization, weight gain, hygrothermal swelling,
and de-bonding between fiber and matrix. Hence, it is vital to understand
moisture diffusion mechanics into FRPCs. The presence of fibers, especially
impermeable like Carbon fibers, introduce tortuous moisture diffusion pathways
through polymer matrix. In this paper, we elucidate the impact of fiber packing
and morphology on moisture diffusion in FRPC materials. Computational models
are developed within a finite element framework to evaluate moisture kinetics
in impermeable FRPCs. We introduce a tortuosity factor for measuring the extent
of deviation in moisture diffusion pathways due to impermeable fiber
reinforcements. Two-dimensional micromechanical models are analyzed with
varying fiber volume fractions, spatial distributions and morphology to
elucidate the influence of internal micromechanical fiber architectures on
tortuous diffusion pathways and corresponding diffusivities. Finally, a
relationship between tortuosity and diffusivity is established such that
diffusivity can be calculated using tortuosity for a given micro-architecture.
Tortuosity can be easily calculated for a given architecture by solving steady
state diffusion governing equations, whereas time-dependent transient diffusion
equations need to be solved for calculating moisture diffusivity. Hence,
tortuosity, instead of diffusivity, can be used in future composites designs,
multi-scale analyses, and optimization for enabling robust structures in
moisture environments. | 2104.05180v2 |
2021-05-01 | Anisotropy and Current Control of Magnetization in SrRuO$_3$ SrTiO$_3$ Heterostructures for Spin-Memristors | Spintronics-based nonvolatile components in neuromorphic circuits offer the
possibility of realizing novel functionalities at low power. Current-controlled
electrical switching of magnetization is actively researched in this context.
Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA),
consisting of SrRuO$_3$ (SRO) grown on SrTiO$_3$ (STO) are strong material
contenders. Utilizing the crystal orientation, magnetic anisotropy in such
simple heterostructures can be tuned to either exhibit a perfect or slightly
tilted PMA. Here, we investigate current-induced magnetization modulation in
such tailored ferromagnetic layers with a material with strong spin-orbit
coupling (Pt), exploiting the spin Hall effect. We find significant differences
in the magnetic anisotropy between the SRO/STO heterostructures, as manifested
in the first and second harmonic magnetoresistance measurements.
Current-induced magnetization switching can be realized with spin-orbit
torques, but for systems with perfect PMA this switching is probabilistic as a
result of the high symmetry. Slight tilting of the PMA can break this symmetry
and allow the realization of deterministic switching. Control over the magnetic
anisotropy of our heterostructures therefore provides control over the manner
of switching. Based on our findings, we propose a three-terminal spintronic
memristor, with a magnetic tunnel junction design, that shows several resistive
states controlled by electric charge. Non-volatile states can be written
through SOT by applying an in-plane current, and read out as a tunnel current
by applying a small out-of-plane current. Depending on the anisotropy of the
SRO layer, the writing mechanism is either deterministic or probabilistic
allowing for different functionalities to emerge. We envisage that the
probabilistic MTJs could be used as synapses while the deterministic devices
can emulate neurons | 2105.00269v1 |
2021-05-05 | Ni$_{80}$Fe$_{20}$ Nanotubes with Optimized Spintronic Functionalities Prepared by Atomic Layer Deposition | Permalloy Ni$_{80}$Fe$_{20}$ is one of the key magnetic materials in the
field of magnonics. Its potential would be further unveiled if it could be
deposited in three dimensional (3D) architectures of sizes down to the
nanometer. Atomic Layer Deposition, ALD, is the technique of choice for
covering arbitrary shapes with homogeneous thin films. Early successes with
ferromagnetic materials include nickel and cobalt. Still, challenges in
depositing ferromagnetic alloys reside in the synthesis via decomposing the
consituent elements at the same temperature and homogeneously. We report
plasma-enhanced ALD to prepare permalloy Ni$_{80}$Fe$_{20}$ thin films and
nanotubes using nickelocene and iron(III) tert-butoxide as metal precursors,
water as the oxidant agent and an in-cycle plasma enhanced reduction step with
hydrogen. We have optimized the ALD cycle in terms of Ni:Fe atomic ratio and
functional properties. We obtained a Gilbert damping of 0.013, a resistivity of
28 $\mu\Omega$cm and an anisotropic magnetoresistance effect of 5.6 $\%$ in the
planar thin film geometry. We demonstrate that the process also works for
covering GaAs nanowires, resulting in permalloy nanotubes with high aspect
ratios and diameters of about 150 nm. Individual nanotubes were investigated in
terms of crystal phase, composition and spin-dynamic response by microfocused
Brillouin Light Scattering. Our results enable NiFe-based 3D spintronics and
magnonic devices in curved and complex topology operated in the GHz frequency
regime. | 2105.01969v1 |
2021-09-17 | Towards replacing physical testing of granular materials with a Topology-based Model | In the study of packed granular materials, the performance of a sample (e.g.,
the detonation of a high-energy explosive) often correlates to measurements of
a fluid flowing through it. The "effective surface area," the surface area
accessible to the airflow, is typically measured using a permeametry apparatus
that relates the flow conductance to the permeable surface area via the
Carman-Kozeny equation. This equation allows calculating the flow rate of a
fluid flowing through the granules packed in the sample for a given pressure
drop. However, Carman-Kozeny makes inherent assumptions about tunnel shapes and
flow paths that may not accurately hold in situations where the particles
possess a wide distribution in shapes, sizes, and aspect ratios, as is true
with many powdered systems of technological and commercial interest. To address
this challenge, we replicate these measurements virtually on micro-CT images of
the powdered material, introducing a new Pore Network Model based on the
skeleton of the Morse-Smale complex. Pores are identified as basins of the
complex, their incidence encodes adjacency, and the conductivity of the
capillary between them is computed from the cross-section at their interface.
We build and solve a resistive network to compute an approximate laminar fluid
flow through the pore structure. We provide two means of estimating
flow-permeable surface area: (i) by direct computation of conductivity, and
(ii) by identifying dead-ends in the flow coupled with isosurface extraction
and the application of the Carman-Kozeny equation, with the aim of establishing
consistency over a range of particle shapes, sizes, porosity levels, and void
distribution patterns. | 2109.08777v1 |
2021-11-11 | Tuning the Room Temperature Ferromagnetism in Fe5GeTe2 by Arsenic Substitution | In order to tune the magnetic properties of the cleavable high-Curie
temperature ferromagnet Fe$_{5-x}$GeTe$_2$, the effect of increasing the
electron count through arsenic substitution has been investigated. Small
additions of arsenic (2.5 and 5%) seemingly enhance ferromagnetic order in
polycrystalline samples by quenching fluctuations on one of the three magnetic
sublattices, whereas larger As concentrations decrease the ferromagnetic Curie
temperature ($T_{\rm C}$) and saturation magnetization. This work also
describes the growth and characterization of Fe$_{4.8}$AsTe$_2$ single crystals
that are structurally analogous to Fe$_{5-x}$GeTe$_2$ but with some phase
stability complications. Magnetization measurements reveal dominant
antiferromagnetic behavior in Fe$_{4.8}$AsTe$_2$ with a N\'{e}el temperature of
$T_{\rm N}$ $\approx$42K. A field-induced spin-flop below $T_{\rm N}$ results
in a switch from negative to positive magnetoresistance, with significant
hysteresis causing butterfly-shaped resistance loops. In addition to reporting
the properties of Fe$_{4.8}$AsTe$_2$, this work shows the importance of
manipulating the individual magnetic sublattices in Fe$_{5-x}$GeTe$_2$ and
motivates further efforts to control the magnetic properties in related
materials by fine tuning of the Fermi energy or crystal chemistry. | 2111.06439v1 |
2022-01-11 | Antiferromagnetic Excitonic Insulator State in Sr3Ir2O7 | Excitonic insulators are usually considered to form via the condensation of a
soft charge mode of bound electron-hole pairs. This, however, presumes that the
soft exciton is of spin-singlet character. Early theoretical considerations
have also predicted a very distinct scenario, in which the condensation of
magnetic excitons results in an antiferromagnetic excitonic insulator state.
Here we report resonant inelastic x-ray scattering (RIXS) measurements of
Sr3Ir2O7. By isolating the longitudinal component of the spectra, we identify a
magnetic mode that is well-defined at the magnetic and structural Brillouin
zone centers, but which merges with the electronic continuum in between these
high-symmetry points and which decays upon heating concurrent with a decrease
in the material's resistivity. We show that a bilayer Hubbard model, in which
electron-hole pairs are bound by exchange interactions, consistently explains
all the electronic and magnetic properties of Sr3Ir2O7 indicating that this
material is a realization of the long-predicted antiferromagnetic excitonic
insulators phase. | 2201.04030v1 |
2022-03-18 | Surface temperature and emissivity measurement for materials exposed to a flame through two-color IR-thermography | Two-color (2C) pyrometry has long been used for flame temperature and soot
concentration studies and is now becoming more widely used to measure surface
temperatures of burning materials. With the obvious advantage of being a
contact-free method that requires only minimal optical access, 2C pyrometry
combined with high-speed acquisition is a promising diagnostic tool to obtain
exceptional temporal and spatial resolution of thermally degrading samples.
However, its conceptual simplicity relies on a set of basic assumptions that
when violated can result in large errors. In this work, we use an experimental
configuration representative for fire resistance testing for aerospace and
naval applications to analyze the impact of camera parameters and test setup on
the accuracy of the surface temperature results obtained. Two types of fibre
reinforced polymer composites and a steel plate are used to investigate
material specific aspects that effect the measurements. An improved workflow
for camera calibration is presented that takes the actual experimental setup
into account. The temperature and emissivity mapping obtained trough in-situ IR
measurements is compared against data acquired trough thermocouples and
post-fire hemispherical directional reflectance measurements at room
temperature. This comparison illustrates the necessity for proper
post-processing and demonstrates that emissivity values obtained from pristine
or burnt samples are not well suited to obtain accurate surface temperatures
through conventional (single color) IR thermography. We also present a detailed
error budget and suggestions for calibration measurements to keep the overall
error well below 50 K in a temperature range from 673 K - 1473 K. | 2203.09689v1 |
2022-04-11 | A-type antiferromagnetic order in semiconducting EuMg$_2$Sb$_2$ single crystals | Eu-based Zintl-phase materials EuA$_2$Pn$_2$ (A = Mg, In, Cd, Zn; Pn = Bi,
Sb, As, P) have generated significant recent interest owing to the complex
interplay of magnetism and band topology. Here, we investigated the electronic,
magnetic, and electronic properties of the layered Zintl-phase single crystals
of EuMg$_2$Sb$_2$ with the trigonal CaAl$_2$Si$_2$ crystal structure (space
group $P\bar{3}m1$). Electrical resistivity measurements complemented with
angle-resolved photoemission spectroscopy (ARPES) studies find an activated
behavior with the intrinsic conductivity at high temperatures indicating a
semiconducting electronic ground state with a narrow energy gap of 370 meV.
Magnetic susceptibility and zero-field heat-capacity measurements indicate that
the compound undergoes antiferromagnetic (AFM) ordering at the Neel temperature
$T_{\rm N}$ = 8.0(2) K. Zero-field neutron-diffraction measurements reveal that
the AFM ordering is A-type where the Eu ordered moments (Eu$^{2+}$, S= 7/2)
arranged in ab-plane layers are aligned ferromagnetically in the ab plane with
the Eu moments in adjacent layers aligned antiferromagnetically. We also find
that Eu-moment reorientation in the trigonal AFM domains within the ab planes
occurs below $T_{\rm N}$ at low fields < 0.05 T due to very small in-plane
anisotropy. Although isostructural semimetallic EuMg$_2$Bi$_2$ is reported to
host Dirac surface states, the observation of narrow-gap semiconducting
behavior in EuMg$_2$Sb$_2$ implies a strong role of spin-orbit coupling in
tuning the electronic states of these materials. | 2204.05261v1 |
2022-05-11 | Tunable photochemical deposition of silver nanostructures on layered ferroelectric CuInP$_2$S6 | 2D layered ferroelectric materials such as CuInP$_2$S6 (CIPS) are promising
candidates for novel and high-performance photocatalysts, owning to their
ultrathin layer thickness, strong interlayer coupling, and intrinsic
spontaneous polarization, while how to control the photocatalytic activity in
layered CIPS remains unexplored. In this work, we report for the first time the
photocatalytic activity of ferroelectric CIPS for the chemical deposition of
silver nanostructures (AgNSs). The results show that the shape and spatial
distribution of AgNSs on CIPS are tunable by controlling layer thickness,
environmental temperature, and light wavelength. The ferroelectric polarization
in CIPS plays a critical role in tunable AgNS photodeposition, as evidenced by
layer thickness and temperature dependence experiments. We further reveal that
AgNS photodeposition process starts from the active site creation, selective
nanoparticle nucleation/aggregation, to the continuous film formation.
Moreover, AgNS/CIPS heterostructures prepared by photodeposition exhibit
excellent resistance switching behavior and good surface enhancement Raman
Scattering activity. Our findings provide new insight into the photocatalytic
activity of layered ferroelectrics and offer a new material platform for
advanced functional device applications in smart memristors and enhanced
chemical sensors. | 2205.05385v2 |
2022-06-23 | Superconductivity in the crystallogenide LaFeSiO$_{1-δ}$ with squeezed FeSi layers | Pnictogens and chalcogens are both viable anions for promoting Fe-based
superconductivity and intense research activity in the related families has
established systematic correlation between the Fe-anion height and the
superconducting critical temperature $T_c$, with an optimum Fe-anion height of
$\sim$ 1.38 \r{A}. Here, we report the discovery of superconductivity in a
novel compound LaFeSiO$_{1-\delta}$ that incorporates a crystallogen element,
Si, and challenges the above picture: considering the strongly squeezed Fe-Si
height of 0.94 \r{A}, the superconducting transition at $T_{c}$ = 10 K is
unusually high. In the normal state, the resistivity displays non-Fermi-liquid
behavior while NMR experiments evidence weak antiferromagnetic fluctuations.
According to first-principles calculations, the Fermi surface of this material
is dominated by hole pockets without nesting properties, which explains the
strongly suppressed tendency towards magnetic order and suggests that the
emergence of superconductivity materializes in a distinct set-up, as compared
to the standard $s_\pm$- and $d$-wave electron-pocket-based situations. These
properties and its simple-to-implement synthesis make LaFeSiO$_{1-\delta}$ a
particularly promising platform to study the interplay between structure,
electron correlations and superconductivity. | 2206.11690v1 |
2022-10-18 | All-electrical spin-to-charge conversion in sputtered Bi$_x$Se$_{1-x}$ | One of the major obstacles to realizing spintronic devices such as MESO logic
devices is the small signal magnitude used for magnetization readout, making it
important to find materials with high spin-to-charge conversion efficiency.
Although intermixing at the junction of two materials is a widely occurring
phenomenon, its influence on material characterization and the estimation of
spin-to-charge conversion efficiencies is easily neglected or underestimated.
Here, we demonstrate all electrical spin-to-charge conversion in
Bi$_x$Se$_{1-x}$ nanodevices and show how the conversion efficiency can be
overestimated by tens of times depending on the adjacent metal used as a
contact. We attribute this to the intermixing-induced compositional change and
the properties of a polycrystal that lead to drastic changes in resistivity and
spin Hall angle. Strategies to improve the spin-to-charge conversion signal in
similar structures for functional devices are discussed. | 2210.09792v1 |
2023-09-09 | Intrinsic magnetic properties of the layered antiferromagnet CrSBr | Van der Waals magnetic materials are an ideal platform to study
low-dimensional magnetism. Opposed to other members of this family, the
magnetic semiconductor CrSBr is highly resistant to degradation in air, which,
besides its exceptional optical, electronic, and magnetic properties, is the
reason the compound is receiving considerable attention at the moment. For many
years, its magnetic phase diagram seemed to be well-understood. Recently,
however, several groups observed a magnetic transition in magnetometry
measurements at temperatures of around 40 K that is not expected from
theoretical considerations, causing a debate about the intrinsic magnetic
properties of the material. In this letter, we report the absence of this
particular transition in magnetization measurements conducted on high-quality
CrSBr crystals, attesting to the extrinsic nature of the low-temperature
magnetic phase observed in other works. Our magnetometry results obtained from
large bulk crystals are in very good agreement with the magnetic phase diagram
of CrSBr previously predicted by the mean-field theory; A-type
antiferromagnetic order is the only phase observed below the N\'eel temperature
at TN = 131 K. Moreover, numerical fits based on the Curie-Weiss law confirm
that strong ferromagnetic correlations are present within individual layers
even at temperatures much larger than TN. | 2309.04778v1 |
2024-01-25 | Threshold displacement energy map of Frenkel pair generation in $\rm Ga_2O_3$ from machine-learning-driven molecular dynamics simulations | $\beta$ phase gallium oxide ($\beta$-$\rm Ga_2O_3$) demonstrates tremendous
potential for electronics applications and offers promising prospects for
integration into future space systems with the necessity of high radiation
resistance. Therefore, a comprehensive understanding of the threshold
displacement energy (TDE) and the radiation-induced formation of Frenkel pairs
(FPs) in this material is vital but has not yet been thoroughly studied. In
this work, we performed over 5,000 molecular dynamics simulations using our
machine-learning potentials to determine the TDE and investigate the formation
of FPs. The average TDEs for the two Ga sites, Ga1 (tetrahedral site) and Ga2
(octahedral site), are 22.9 and 20.0 eV, respectively. While the average TDEs
for the three O sites are nearly uniform, ranging from 17.0 to 17.4 eV. The
generated TDE maps reveal significant differences in displacement behavior
between these five atomic sites. Our developed defect identification methods
successfully categorize various types of FPs in this material, with more than
ten types of Ga FPs being produced during our simulations. O atoms are found to
form two main types of FPs and the O split interstitial site on O1 site is most
common. Finally, the recombination behavior and barriers of Ga and O FPs
indicate that the O FP has a higher possibility of recovery upon annealing. Our
findings provide important insights into the studies of radiation damage and
defects in $\rm Ga_2O_3$ and can contribute to the design and development of
$\rm Ga_2O_3$-based devices | 2401.14039v2 |
2024-03-06 | Collision Cascade-Driven Evolution of Vacancy Defects in Ni-Based Concentrated Solid-Solution Alloys | Concentrated solid--solution alloys (CSAs) in single--phase form have
recently garnered considerable attention owing to their potential for
exceptional irradiation resistance. This computational study delves into the
intricate interplay of alloying elements on the generation, recombination, and
evolution of irradiation-induced defects. Molecular dynamics simulations were
conducted for collision cascades at room temperature, spanning a range of
primary knock-on atom energies from 1 to 10 keV. The investigation encompasses
a series of model crystals, progressing from pure Ni to binary CSAs such as
NiFe$_{20}$, NiFe, NiCr$_{20}$, and culminating in the more intricate
NiFeCr$_{20}$ CSA. We observe that materials rich in chromium actively
facilitate dislocation emissions and induce the nucleation of stacking fault
tetrahedra in the proximity of nanovoids, owing to Shockley partial
interactions. This result is validated by molecular static simulations, which
calculate the surface, vacancy, and defect formation energies. Among various
shapes considered, the spherical void proves to be the most stable, followed by
the truncated octahedron and octahedron shapes. On the other hand, the
tetrahedron cubic shape is identified as the most unstable, and stacking fault
tetrahedra exhibit the highest formation energy. Notably, among the materials
studied, NiCr$_{20}$ and NiFeCr$_{20}$ CSAs stood out as the sole alloys
capable of manifesting this mechanism, mainly observed at high impact energies. | 2403.03922v1 |
2024-05-08 | Pressure induced metallization and loss of surface magnetism in FeSi | Single crystalline FeSi samples with a conducting surface state (CSS) were
studied under high pressure ($\textit{P}$) and magnetic field ($\textit{B}$) by
means of electrical resistance ($\textit{R}$) measurements to explore how the
bulk semiconducting state and the surface state are tuned by the application of
pressure. We found that the energy gap ($\Delta$) associated with the
semiconducting bulk phase begins to close abruptly at a critical pressure
($P_{cr}$) of ~10 GPa and the bulk material becomes metallic with no obvious
sign of any emergent phases or non-Fermi liquid behavior in
$\textit{R}$($\textit{T}$) in the neighborhood of $P_{cr}$ above 3 K. Moreover,
the metallic phase appears to remain at near-ambient pressure upon release of
the pressure. Interestingly, the hysteresis in the $\textit{R}$($\textit{T}$)
curve associated with the magnetically ordered CSS decreases with pressure and
vanishes at $P_{cr}$, while the slope of the $\textit{R}$($\textit{B}$) curve,
d$\textit{R}$/d$\textit{B}$, which has a negative value for $\textit{P}$ <
$P_{cr}$, decreases in magnitude with $\textit{P}$ and changes sign at
$P_{cr}$. Thus, the CSS and the corresponding two-dimensional magnetic order
collapse at $P_{cr}$ where the energy gap $\Delta$ of the bulk material starts
to close abruptly, revealing the connection between the CSS and the
semiconducting bulk state in FeSi. | 2405.04739v1 |
2024-05-09 | Controlled Fabrication of Native Ultra-Thin Amorphous Gallium Oxide from 2D Gallium Sulfide for Emerging Electronic Applications | Oxidation of two-dimensional (2D) layered materials has proven advantageous
in creating oxide/2D material heterostructures, opening the door for a new
paradigm of low-power electronic devices. Gallium (II) sulfide ($\beta$-GaS), a
hexagonal phase group III monochalcogenide, is a wide bandgap semiconductor
with a bandgap exceeding 3 eV in single and few layer form. Its oxide, gallium
oxide (Ga$_2$O$_3$), combines large bandgap (4.4-5.3 eV) with high dielectric
constant (~10). Despite the technological potential of both materials,
controlled oxidation of atomically-thin $\beta$-GaS remains under-explored.
This study focuses into the controlled oxidation of $\beta$-GaS using oxygen
plasma treatment, achieving ultrathin native oxide (GaS$_x$O$_y$, ~4 nm) and
GaS$_x$O$_y$/GaS heterostructures where the GaS layer beneath remains intact.
By integrating such structures between metal electrodes and applying electric
stresses as voltage ramps or pulses, we investigate their use for resistive
random-access memory (ReRAM). The ultrathin nature of the produced oxide
enables low operation power with energy use as low as 0.22 nJ per operation
while maintaining endurance and retention of 350 cycles and 10$^4$ s,
respectively. These results show the significant potential of the
oxidation-based GaS$_x$O$_y$/GaS heterostructure for electronic applications
and, in particular, low-power memory devices. | 2405.05632v1 |
2013-06-04 | Constitutive Model for Material Comminuting at High Shear Rate | The modeling of high velocity impact into brittle or quasibrittle solids is
hampered by the unavailability of a constitutive model capturing the effects of
material comminution into very fine particles. The present objective is to
develop such a model, usable in finite element programs. The comminution at
very high strain rates can dissipate a large portion of the kinetic energy of
an impacting missile. The spatial derivative of the energy dissipated by
comminution gives a force resisting the penetration, which is superposed on the
nodal forces obtained from the static constitutive model in a finite element
program. The present theory is inspired partly by Grady's model for comminution
due to explosion inside a hollow sphere, and partly by analogy with turbulence.
In high velocity turbulent flow, the energy dissipation rate is enhanced by the
formation of micro-vortices (eddies) which dissipate energy by viscous shear
stress. Similarly, here it is assumed that the energy dissipation at fast
deformation of a confined solid gets enhanced by the release of kinetic energy
of the motion associated with a high-rate shear strain of forming particles.
For simplicity, the shape of these particles in the plane of maximum shear rate
is considered to be regular hexagons. The rate of release of free energy
density consisting of the sum of this energy and the fracture energy of the
interface between the forming particle is minimized. The particle sizes are
assumed to be distributed according to Schuhmann's power law. It is concluded
that the minimum particle size is inversely proportional to the (2/3)-power of
the shear strain rate, that the kinetic energy release is to proportional to
the (2/3)-power, and that the dynamic comminution creates an apparent material
viscosity inversely proportional to the (1/3)-power of the shear strain rate. | 1306.1120v1 |
2005-10-03 | A Study of Apparent Symmetry Breakdown in Perovskite Oxide-based Symmetric RRAM Devices | A new model of a symmetric two-terminal non-volatile RRAM device based on
Perovskite oxide thin film materials, specifically Pr1-xCaxMnO3 (PCMO), is
proposed and analyzed. The model consists of two identical half-parts, which
are completely characterized by the same resistance verses pulse voltage
hysteresis loop, connected together in series. Even though the modeled device
is physically symmetric with respect to the direction of current, it is found
to exhibit switching of the resistance with the application of voltage pulses
of sufficient amplitude and of different polarities. The apparent breakdown of
parity conservation of the device is attributed to changes in resistance of the
active material layer near the electrodes during switching. Thus the switching
is history dependent, a feature that can be very useful for the construction of
real non-volatile memory devices. An actual symmetric device, not previously
reported in the literature and based on the proposed model, is fabricated in
the PCMO material system. Measurements of the resistance of this new device
generated an experimental hysteresis curve that matches well the calculated
hysteresis curve of the model, thus confirming the features predicated by the
new symmetric model. | 0510059v1 |
2009-02-20 | Lattice Resistance to Dislocation Motion : Singularity Distribution Approach | This paper has been withdrawn. | 0902.3505v3 |
2015-03-03 | Negative differential resistance and characteristic nonlinear electromagnetic response of a Topological Insulator | Materials exhibiting negative differential resistance have important
applications in technologies involving microwave generation, which range from
motion sensing to radio astronomy. Despite their usefulness, there has been few
physical mechanisms giving rise to materials with such properties, i.e. GaAs
employed in the Gunn diode. In this work, we show that negative differential
resistance also generically arise in Dirac ring systems, an example of which
has been experimentally observed in the surface states of Topological
Insulators. This novel realization of negative differential resistance is based
on a completely different physical mechanism from that of the Gunn effect,
relying on the characteristic non-monotonicity of the response curve that
remains robust in the presence of nonzero temperature, chemical potential, mass
gap and impurity scattering. As such, it opens up new possibilities for
engineering applications, such as frequency upconversion devices which are
highly sought for terahertz signal generation. Our results may be tested with
thin films of Bi2Se3 Topological Insulators, and are expected to hold
qualitatively even in the absence of a strictly linear Dirac dispersion, as
will be the case in more generic samples of Bi2Se3 and other materials with
topologically nontrivial Fermi sea regions. | 1503.01097v4 |
2016-01-09 | Flux trapping in superconducting accelerating cavities during cooling down with a spatial temperature gradient | During the cool-down of a superconducting accelerating cavity, a magnetic
flux is trapped as quantized vortices, which yield additional dissipation and
contribute to the residual resistance. Recently, cooling down with a large
spatial temperature gradient attracts much attention for successful reductions
of trapped vortices. The purpose of the present paper is to propose a model to
explain the observed efficient flux expulsions and the role of spatial
temperature gradient during the cool-down of cavity. In the vicinity of a
region with a temperature close to the critical temperature Tc,the critical
fields are strongly suppressed and can be smaller than the ambient magnetic
field. A region with a lower critical field smaller than the ambient field is
in the vortex state. As a material is cooled down, a region with a temperature
close Tc associating the vortex state domain sweeps and passes through the
material. In this process, vortices contained in the vortex state domain are
trapped by pinning centers that randomly distribute in the material. A number
of trapped vortices can be naively estimated by using the analogy with the
beam-target collision event. Based on this result, the residual resistance is
evaluated. We find that a number of trapped vortices and the residual
resistance are proportional to the strength of the ambient magnetic field and
the inverse of the temperature gradient. The obtained residual resistance
agrees well with experimental results. A material property dependence of a
number of trapped vortices is also discussed. | 1601.02118v2 |
2018-01-08 | Magnetoresistance when Spin Effects on Conduction are Weak | This paper considers certain materials, including topological insulators,
where spin rotation symmetry is broken much more strongly than time reversal
symmetry. When these materials are in the diffusive regime, i.e. when they have
disorder that is strong enough to cause an electron to scatter many times while
crossing a sample, electrons and holes move in pairs that have zero spin and
are insensitive to spin physics. Working within this spinless scenario, we show
that Fourier transforming the magnetoconductance with respect to external
magnetic field obtains a curve describing the area distribution of loops traced
by electrons and holes within the sample. We present loop area distributions of
Landau levels, weak (anti)localization, conduction governed by Levy flights,
and linear-in-field resistance. Of these four the last two are new results.
Comparing these distributions, we argue that the linear-in-field resistance
seen in some topological insulators is caused by the same diffusive scattering
that causes weak antilocalization. The difference is that linear-in-field
resistance materials retain a level of quantum coherence that is usually seen
only on the surface of 2-D wires or in ring geometries. In an appendix we
include some speculative material about linear-in-temperature resistance. | 1801.02663v6 |
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