publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2018-03-05 | Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds | Newly emerged materials from the family of Heuslers and complex oxides
exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much
higher than even room temperature. In this work, using the semiclassical
top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that
utilizes such ferromagnetic semiconductors as channel materials, in addition to
ferromagnetic source/drain contacts. Such a device could retain the spin
polarization of injected electrons in the channel, the loss of which limits the
operation of traditional spin transistors with non-ferromagnetic channels. We
examine the operation of four material systems that are currently considered
some of the most prominent known ferromagnetic semiconductors, three
Heusler-type alloys (Mn2CoAl, CrVZrAl, CoVZrAl) and one from the oxide family
(NiFe2O4). We describe their bandstructures by using data from DFT
calculations. We investigate under which conditions high spin polarization and
significant ION/IOFF ratio, two essential requirements for the spin-MOSFET
operation, are both achieved. We show that these particular Heusler channels,
in their bulk form, do not have adequate bandgap to provide high ION/IOFF
ratios, and have small magnetoconductance compared to state-of-the-art devices.
However, with confinement into ultra-narrow sizes down to a few nanometers, and
by engineering their spin dependent contact resistances, they could prove
promising channel materials for the realization of spin-MOSFET transistor
devices that offer combined logic and memory functionalities. Although the main
compounds of interest in this paper are Mn2CoAl, CrVZrAl, CoVZrAl, and NiFe2O4
alone, we expect that the insight we provide is relevant to other classes of
such materials as well. | 1803.01789v1 |
2022-03-14 | HDPView: Differentially Private Materialized View for Exploring High Dimensional Relational Data | How can we explore the unknown properties of high-dimensional sensitive
relational data while preserving privacy? We study how to construct an
explorable privacy-preserving materialized view under differential privacy. No
existing state-of-the-art methods simultaneously satisfy the following
essential properties in data exploration: workload independence, analytical
reliability (i.e., providing error bound for each search query), applicability
to high-dimensional data, and space efficiency. To solve the above issues, we
propose HDPView, which creates a differentially private materialized view by
well-designed recursive bisected partitioning on an original data cube, i.e.,
count tensor. Our method searches for block partitioning to minimize the error
for the counting query, in addition to randomizing the convergence, by choosing
the effective cutting points in a differentially private way, resulting in a
less noisy and compact view. Furthermore, we ensure formal privacy guarantee
and analytical reliability by providing the error bound for arbitrary counting
queries on the materialized views. HDPView has the following desirable
properties: (a) Workload independence, (b) Analytical reliability, (c) Noise
resistance on high-dimensional data, (d) Space efficiency. To demonstrate the
above properties and the suitability for data exploration, we conduct extensive
experiments with eight types of range counting queries on eight real datasets.
HDPView outperforms the state-of-the-art methods in these evaluations. | 2203.06791v3 |
2024-01-23 | Integration of High-Tc Superconductors with High Q Factor Oxide Mechanical Resonators | Micro-mechanical resonators are building blocks of a variety of applications
in basic science and applied electronics. This device technology is mainly
based on well-established and reproducible silicon-based fabrication processes
with outstanding performances in term of mechanical Q factor and sensitivity to
external perturbations. Broadening the functionalities of MEMS by the
integration of functional materials is a key step for both applied and
fundamental science. However, combining functional materials and silicon-based
compounds is challenging. An alternative approach is fabricating MEMS based on
complex heterostructures made of materials inherently showing a variety of
physical properties such as transition metal oxides. Here, we report on the
integration of a high-Tc superconductor YBa2Cu3O7 (YBCO) with high Q factor
micro-bridge resonator made of a single-crystal LaAlO3 (LAO) thin film. LAO
resonators are tensile strained, with a stress of 345 MPa, show Q factor in the
range of tens of thousands, and have low roughness. The topmost YBCO layer
deposited by Pulse Laser Deposition shows a superconducting transition starting
at 90 K with zero resistance below 78 K. This result opens new possibilities
towards the development of advanced transducers, such as bolometers or magnetic
field detectors, as well as basic science experiments in solid state physics,
material science, and quantum opto-mechanics. | 2401.12758v1 |
2004-06-25 | Resistance Noise Near to Electrical Breakdown: Steady State of Random Networks as a Function of the Bias | A short review is presented of a recently developed computational approach
which allows the study of the resistance noise over the full range of bias
values, from the linear regime up to electrical breakdown. Resistance noise is
described in terms of two competing processes in a random resistor network. The
two processes are thermally activated and driven by an electrical bias. In the
linear regime, a scaling relation has been found between the relative variance
of resistance fluctuations and the average resistance. The value of the
critical exponent is significantly higher than that associated with 1/f noise.
In the nonlinear regime, occurring when the bias overcomes the threshold value,
the relative variance of resistance fluctuations scales with the bias. Two
regions can be identified in this regime: a moderate bias region and a
pre-breakdown one. In the first region, the scaling exponent has been found
independent of the values of the model parameters and of the bias conditions. A
strong nonlinearity emerges in the pre-breakdown region which is also
characterized by non-Gaussian noise. The results compare well with measurements
of electrical breakdown in composites and with electromigration experiments in
metallic lines. | 0406648v1 |
2010-11-29 | Contact effects on transport in magnetite, an archetypal correlated transition metal oxide | Multiterminal measurements have typically been employed to examine electronic
properties of strongly correlated electronic materials such as transition metal
oxides without the influence of contact effects. In contrast, in this work we
investigate the interface properties of Fe$_3$O$_4$ with different metals, with
the contact effects providing a window on the physics at work in the correlated
oxide. Contact resistances are determined by means of four-terminal electrical
measurements as a function of source voltage and temperature. Contact
resistances vary systematically with the work function of the electrode metal,
$\phi(M)$, $M=$Cu, Au and Pt, with higher work function yielding lower contact
resistance. This trend and the observation that contact resistances are
directly proportional to the Fe$_3$O$_4$ resistivity are consistent with
modeling the oxide as an effective $p$-type semiconductor with hopping
transport. The jumps in contact resistance values at the bias-driven
insulator-metal transition have a similar trend with $\phi$($M$), consistent
with the transition mechanism of charge gap closure by electric field. | 1011.6407v1 |
2012-10-01 | Thermal Contact Resistance Across Nanoscale Silicon Dioxide and Silicon Interface | Silicon dioxide and silicon (SiO$_{2}$/Si) interface plays a very important
role in semiconductor industry. However, at nanoscale, its interfacial thermal
properties haven't been well understood so far. In this paper, we
systematically study the interfacial thermal resistance (Kapitza resistance) of
a heterojunction composed of amorphous silicon dioxide and crystalline silicon
by using molecular dynamics simulations. Numerical results have shown that
Kapitza resistance at SiO$_{2}$/Si interface depends on the interfacial
coupling strength remarkably. In the weak interfacial coupling limit, Kapitza
resistance depends on both the detailed interfacial structure and the length of
the heterojunction, showing large fluctuation among different samples. In
contrast, it is almost insensitive to the detailed interfacial structure or the
length of the heterojunction in the strong interfacial coupling limit, giving
rise to a nearly constant value around 0.9 $\times10^{-9}$ m$^{2}$KW$^{-1}$ at
room temperature. Moreover, the temperature dependent Kapitza resistance in the
strong interfacial coupling limit has also been examined. Our study provides
useful guidance to the thermal management and heat dissipation across nanoscale
SiO$_{2}$/Si interface, in particular for the design of silicon nanowire based
nano electronics and photonics devices. | 1210.0354v1 |
2013-02-19 | Local breakdown of the quantum Hall effect in narrow single layer graphene Hall devices | We have analyzed the breakdown of the quantum Hall effect in 1 micrometer
wide Hall devices fabricated from an exfoliated monolayer graphene transferred
on SiOx. We have observed that the deviation of the Hall resistance from its
quantized value is weakly dependent on the longitudinal resistivity up to
current density of 5 A/m, where the Hall resistance remains quantized even when
the longitudinal resistance increases monotonously with the current. Then a
collapse in the quantized resistance occurs while longitudinal resistance keeps
its gradual increase. The exponential increase of the conductivity with respect
to the current suggests impurity mediated inter-Landau level scattering as the
mechanism of the breakdown. The results are interpreted as the strong variation
of the breakdown behavior throughout the sample due to the randomly distributed
scattering centers that mediates the breakdown. | 1302.4729v1 |
2016-01-17 | Low-resistance GaN tunnel homojunctions with 150 kA/cm^2 current and repeatable negative differential resistance | We report GaN n++/p++ interband tunnel junctions with repeatable negative
differential resistance and low resistance. Reverse and forward tunneling
current densities were observed to increase as Si and Mg doping concentrations
were increased. Hysteresis-free, bidirectional negative differential resistance
was observed at room temperature from these junctions at a forward voltage of
~1.6-2 V. Thermionic PN junctions with tunnel contact to the p-layer exhibited
forward current density of 150 kA/cm^2 at 7.6 V, with a low series device
resistance of 1 x 10^-5 ohm.cm^2. | 1601.04353v2 |
2017-02-13 | Deconstructing temperature gradients across fluid interfaces: the structural origin of the thermal resistance of liquid-vapor interfaces | The interfacial thermal resistance determines condensation-evaporation
processes and thermal transport across material-fluid interfaces. Despite its
importance in transport processes, the interfacial structure responsible for
the thermal resistance is still unknown. By combining non-equilibrium molecular
dynamics simulations and interfacial analyses that remove the interfacial
thermal fluctuations we show that the thermal resistance of liquid-vapor
interfaces is connected to a low density fluid layer that is adsorbed at the
liquid surface. This thermal resistance layer (TRL) defines the boundary where
the thermal transport mechanism changes from that of gases (ballistic) to that
characteristic of dense liquids, dominated by frequent particle collisions
involving very short mean free paths. We show that the thermal conductance is
proportional to the number of atoms adsorbed in the TRL, and hence we explain
the structural origin of the thermal resistance in liquid-vapor interfaces. | 1702.03896v2 |
2018-03-21 | Measuring the thermal conductivity and interfacial thermal resistance of suspended MoS2 using electron beam self-heating technique | Establishment of a new technique or extension of an existing technique for
thermal and thermoelectric measurements to a more challenging system is an
important task to explore the thermal and thermoelectric properties of various
materials and systems. The bottleneck lies in the challenges in measuring the
thermal contact resistance. In this work, we applied electron beam self-heating
technique to derive the intrinsic thermal conductivity of suspended Molybdenum
Disulfide (MoS2) ribbons and the thermal contact resistance, with which the
interfacial thermal resistance between few-layer MoS2 and Pt electrodes was
calculated. The measured room temperature thermal conductivity of MoS2 is
around 30 W/mK, while the estimated interfacial thermal resistance is around
2*10-6 m2K/W. Our experiments extend a useful branch in application of this
technique for studying thermal properties of suspended layered ribbons and have
potential application in investigating the interfacial thermal resistance of
different 2D heterojunctions. | 1803.07757v1 |
2019-09-16 | An experimental proof that resistance-switching memories are not memristors | It has been suggested that all resistive-switching memory cells are
memristors. The latter are hypothetical, ideal devices whose resistance, as
originally formulated, depends only on the net charge that traverses them.
Recently, an unambiguous test has been proposed [J. Phys. D: Appl. Phys. {\bf
52}, 01LT01 (2019)] to determine whether a given physical system is indeed a
memristor or not. Here, we experimentally apply such a test to both in-house
fabricated Cu-SiO2 and commercially available electrochemical metallization
cells. Our results unambiguously show that electrochemical metallization memory
cells are not memristors. Since the particular resistance-switching memories
employed in our study share similar features with many other memory cells, our
findings refute the claim that all resistance-switching memories are
memristors. They also cast doubts on the existence of ideal memristors as
actual physical devices that can be fabricated experimentally. Our results then
lead us to formulate two memristor impossibility conjectures regarding the
impossibility of building a model of physical resistance-switching memories
based on the memristor model. | 1909.07238v2 |
2014-08-22 | Resistance and lifetime measurements of polymer solar cells using glycerol doped poly[3,4-ethylenedioxythiophene]: poly[styrenesulfonate] hole injection layers | We have performed resistivity measurements of
poly[3,4-ethylenedioxythiophene]: poly[styrenesulfonate] (PEDOT:PSS) films with
varying concentrations of glycerol. Resistivity is seen to decrease
exponentially from roughly 3 ohm-cm for pure PEDOT:PSS to 3x10-2 ohm-cm for 35
mg/cm3 glycerol in PEDOT:PSS. Beyond this concentration adding glycerol does
not significantly change resistivity. Bulk heterojunction polymer solar cells
using these variously doped PEDOT:PSS layers as electrodes were studied to
characterize the effects on efficiency and lifetime. Although our data display
significant scatter, lowering the resistance of the PEDOT:PSS layers results in
lower device resistance and higher efficiency as expected. We also note that
the lifetime of the devices tends to be reduced as the glycerol content of
PEDOT:PSS is increased. Many devices show an initial increase in efficiency
followed by a roughly exponential decay. This effect is explained based on
concomitant changes in the zero bias conductance of the samples under dark
conditions. | 1408.5199v2 |
2017-01-17 | Grain Boundary Resistance in Copper Interconnects from an Atomistic Model to a Neural Network | Orientation effects on the resistivity of copper grain boundaries are studied
systematically with two different atomistic tight binding methods. A
methodology is developed to model the resistivity of grain boundaries using the
Embedded Atom Model, tight binding methods and non-equilibrum Green's functions
(NEGF). The methodology is validated against first principles calculations for
small, ultra-thin body grain boundaries (<5nm) with 6.4% deviation in the
resistivity. A statistical ensemble of 600 large, random structures with grains
is studied. For structures with three grains, it is found that the distribution
of resistivities is close to normal. Finally, a compact model for grain
boundary resistivity is constructed based on a neural network. | 1701.04897v3 |
2015-07-20 | Effect of Covalent Functionalisation on Thermal Transport Across Graphene-Polymer Interfaces | This paper is concerned with the interfacial thermal resistance for polymer
composites reinforced by various covalently functionalised graphene. By using
molecular dynamics simulations, the obtained results show that the covalent
functionalisation in graphene plays a significant role in reducing the
graphene-paraffin interfacial thermal resistance. This reduction is dependent
on the coverage and type of functional groups. Among the various functional
groups, butyl is found to be the most effective in reducing the interfacial
thermal resistance, followed by methyl, phenyl and formyl. The other functional
groups under consideration such as carboxyl, hydroxyl and amines are found to
produce negligible reduction in the interfacial thermal resistance. For
multilayer graphene with a layer number up to four, the interfacial thermal
resistance is insensitive to the layer number. The effects of the different
functional groups and the layer number on the interfacial thermal resistance
are also elaborated using the vibrational density of states of the graphene and
the paraffin matrix. The present findings provide useful guidelines in the
application of functionalised graphene for practical thermal management. | 1507.05397v1 |
2020-12-05 | Machine Learning and Data Analytics for Design and Manufacturing of High-Entropy Materials Exhibiting Mechanical or Fatigue Properties of Interest | This chapter presents an innovative framework for the application of machine
learning and data analytics for the identification of alloys or composites
exhibiting certain desired properties of interest. The main focus is on alloys
and composites with large composition spaces for structural materials. Such
alloys or composites are referred to as high-entropy materials (HEMs) and are
here presented primarily in context of structural applications. For each output
property of interest, the corresponding driving (input) factors are identified.
These input factors may include the material composition, heat treatment,
manufacturing process, microstructure, temperature, strain rate, environment,
or testing mode. The framework assumes the selection of an optimization
technique suitable for the application at hand and the data available.
Physics-based models are presented, such as for predicting the ultimate tensile
strength (UTS) or fatigue resistance. We devise models capable of accounting
for physics-based dependencies. We factor such dependencies into the models as
a priori information. In case that an artificial neural network (ANN) is deemed
suitable for the applications at hand, it is suggested to employ custom kernel
functions consistent with the underlying physics, for the purpose of attaining
tighter coupling, better prediction, and for extracting the most out of the -
usually limited - input data available. | 2012.07583v1 |
2000-11-10 | The origin of high transport spin polarization in La$_{0.7}$Sr$_{0.3} $MnO$_{3}$: direct evidence for minority spin states | Using the point contact Andreev reflection technique, we have carried out a
systematic study of the spin polarization in the colossal magnetoresistive
manganite, La$_{0.7}$Sr$_{0.3}$MnO$_{3}$} (LSMO). Surprisingly, we observed a
significant increase in the current spin polarization with the residual
resistivity. This counterintuitive trend can be understood as a transition from
ballistic to diffusive transport in the contact. Our results strongly suggest
that LSMO does have minority spin states at the Fermi level. However, since its
current spin polarization is much higher than that of the density of states,
this material can mimic the behavior of a true half-metal in transport
experiments. Based on our results we call this material a {\it transport}
half-metal. | 0011198v1 |
2006-05-30 | Complex Precipitation Pathways in Multi-Component Alloys | One usual way to strengthen a metal is to add alloying elements and to
control the size and the density of the precipitates obtained. However,
precipitation in multicomponent alloys can take complex pathways depending on
the relative diffusivity of solute atoms and on the relative driving forces
involved. In Al-Zr-Sc alloys, atomic simulations based on first-principle
calculations combined with various complementary experimental approaches
working at different scales reveal a strongly inhomogeneous structure of the
precipitates: owing to the much faster diffusivity of Sc compared with Zr in
the solid solution, and to the absence of Zr and Sc diffusion inside the
precipitates, the precipitate core is mostly Sc-rich, whereas the external
shell is Zr-rich. This explains previous observations of an enhanced nucleation
rate in Al-Zr-Sc alloys compared with binary Al-Sc alloys, along with much
higher resistance to Ostwald ripening, two features of the utmost importance in
the field of light high-strength materials. | 0605738v1 |
2006-11-06 | Coexisting tuneable fractions of glassy and equilibrium long-range-order phases in manganites | Antiferromagnetic-insulating(AF-I) and the ferromagnetic-metallic(FM-M)
phases coexist in various half-doped manganites over a range of temperature and
magnetic field, and this is often believed to be an essential ingredient to
their colossal magnetoresistence. We present magnetization and resistivity
measurements on Pr(0.5)Ca(0.5)Mn(0.975)Al(0.025)O(3) and Pr(0.5)Sr(0.5)MnO(3)
showing that the fraction of the two coexisting phases at low-temperature in
any specified measuring field H, can be continuously controlled by following
designed protocols traversing field-temperature space; for both materials the
FM-M fraction rises under similar cooling paths. Constant-field temperature
variations however show that the former sample undergoes a 1st order transition
from AF-I to FM-M with decreasing T, while the latter undergoes the reverse
transition. We suggest that the observed path-dependent phase-separated states
result from the low-T equilibrium phase coexisting with supercooled glass-like
high temperature phase, where the low-T equilibrium phases are actually
homogeneous FM-M and AF-I phases respectively for the two materials. | 0611152v1 |
2008-05-27 | Colossal electroresistance effect around room temperature in LuFe2O4 | A colossal electroresistance effect is observed around room temperature in a
transition metal oxide LuFe2O4. The measurements of resistance under various
applied voltages as well as the highly nonlinear current-voltage
characteristics reveal that a small electric field is able to drive the
material from the insulating state to a metallic state. The threshold field at
which the insulating-metallic transition occurs, decreases exponentially with
increasing temperature. We interpret this transition as a consequence of the
breakdown of the charge-ordered state triggered by applied electric field,
which is supported by the dramatic dielectric response in a small electric
field. This colossal electroresistance effect as well as the high dielectric
tunability around room temperature in low applied fields makes LuFe2O4 a very
promising material for many applications. | 0805.4042v1 |
2008-07-21 | Superconducting and thermal properties of ex-situ Glidcop sheathed multifilamentary MgB2 wires | In DC and AC practical applications of MgB2 superconducting wires an
important role is represented by the material sheath which has to provide,
among other things, a suitable electrical and thermal stabilization. A way to
obtain a large enough amount of low resistivity material in to the conductor
architecture is to use it as external sheath. In this paper we study ex-situ
multifilamentary MgB2 wires using oxide-dispersion-strengthened copper
(GlidCop) as external sheath in order to reach a good compromise between
critical current density and thermal properties. We prepared three GlidCop
samples differing by the content of dispersed sub-microscopic Al2O3 particles.
We characterized the superconducting and thermal properties and we showed that
the good thermal conductivity together the good mechanical properties and a
reasonable critical current density make of GlidCop composite wire a useful
conductor for applications where high thermal conductivity is request at
temperature above 30K, such as Superconducting-FCL. | 0807.3259v1 |
2012-12-14 | Using metallic photonic crystals as visible light sources | In this paper we study numerically and experimentally the possibility of
using metallic photonic crystals (PCs) of different geometries (log-piles,
direct and inverse opals) as visible light sources. It is found that by tuning
geometrical parameters of a direct opal PC one can achieve substantial
reduction of the emissivity in the infrared along with its increase in the
visible. We take into account disorder of the PC elements in their sizes and
positions, and get quantitative agreement between the numerical and
experimental results. We analyze the influence of known temperature-resistant
refractory host materials necessary for fixing the PC elements, and find that
PC effects become completely destroyed at high temperatures due to the host
absorption. Therefore, creating PC-based visible light sources requires that
low-absorbing refractory materials for embedding medium be found. | 1212.3451v1 |
2013-01-10 | Weak antilocalization in topological insulator Bi$_{2}$Te$_{3}$ microflakes | We have studied the carrier transport in two topological insulator (TI)
Bi$_{2}$Te$_{3}$ microflakes between 0.3 and 10 K and under applied backgate
voltages ($V_{\rm BG}$). Logarithmic temperature dependent resistance
corrections due to the two-dimensional electron-electron interaction effect in
the presence of weak disorder were observed. The extracted Coulomb screening
parameter is negative, which is in accord with the situation of strong
spin-orbit scattering as is inherited in the TI materials. In particular,
positive magnetoresistances (MRs) in the two-dimensional weak-antilocalization
(WAL) effect were measured in low magnetic fields, which can be satisfactorily
described by a multichannel-conduction model. Both at low temperatures of $T <
1$ K and under high positive $V_{\rm BG}$, signatures of the presence of two
coherent conduction channels were observed, as indicated by an increase by a
factor of $\approx$ 2 in the prefactor which characterizes the WAL MR
magnitude. Our results are discussed in terms of the (likely) existence of the
Dirac fermion surface states, in addition to the bulk states, in the
three-dimensional TI Bi$_2$Te$_3$ material. | 1301.2023v1 |
2013-12-12 | Niobium Silicon alloys for Kinetic Inductance Detectors | We are studying the properties of Niobium Silicon amorphous alloys as a
candidate material for the fabrication of highly sensitive Kinetic Inductance
Detectors (KID), optimized for very low optical loads. As in the case of other
composite materials, the NbSi properties can be changed by varying the relative
amounts of its components. Using a NbSi film with T_c around 1 K we have been
able to obtain the first NbSi resonators, observe an optical response and
acquire a spectrum in the band 50 to 300 GHz. The data taken show that this
material has very high kinetic inductance and normal state surface resistivity.
These properties are ideal for the development of KID. More measurements are
planned to further characterize the NbSi alloy and fully investigate its
potential. | 1312.3588v1 |
2014-07-05 | Approaching the Limits of Transparency and Conductivity in Graphitic Materials through Lithium Intercalation | Various bandstructure engineering methods have been studied to improve the
performance of graphitic transparent conductors; however none demonstrated an
increase of optical transmittance in the visible range. Here we measure in situ
optical transmittance spectra and electrical transport properties of
ultrathin-graphite (3-60 graphene layers) simultaneously via electrochemical
lithiation/delithiation. Upon intercalation we observe an increase of both
optical transmittance (up to twofold) and electrical conductivity (up to two
orders of magnitude), strikingly different from other materials. Transmission
as high as 91.7% with a sheet resistance of 3.0 {\Omega} per square is achieved
for 19-layer LiC6, which corresponds to a figure of merit
{\sigma}_dc/{\sigma}_opt = 1400, significantly higher than any other continuous
transparent electrodes. The unconventional modification of ultrathin-graphite
optoelectronic properties is explained by the suppression of interband optical
transitions and a small intraband Drude conductivity near the interband edge.
Our techniques enable the investigation of other aspects of intercalation in
nanostructures. | 1407.1416v1 |
2014-10-02 | Absence of the Ordinary and Extraordinary Hall effects scaling in granular ferromagnets at metal-insulator transition | Universality of the extraordinary Hall effect scaling was tested in granular
three-dimensional Ni-SiO2 films across the metal-insulator transition. Three
types of magnetotransport behavior have been identified: metallic, weakly
insulating and strongly insulating. Scaling between both the ordinary and
extraordinary Hall effects and material resistivity is absent in the weakly
insulating range characterized by logarithmic temperature dependence of
conductivity. The results provide compelling experimental confirmation to
recent models of granular metals predicting transition from logarithmic to
exponential conductivity temperature dependence when inter-granular conductance
drops below the quantum conductance value and loss of Hall effect scaling when
inter-granular conductance is higher than the quantum one. The effect was found
at high temperatures and reflects the granular structure of material rather
than low temperature quantum corrections. | 1410.0491v1 |
2014-11-04 | Self-consistent modelling of nonlinear dynamic ESM microscopy in mixed ionic-electronic conductors | Dynamic Electrochemical Strain Microscopy (ESM) response of mixed
ionic-electronic conductors is analysed in the framework of the Thomas-Fermi
screening theory and Vegard law with accounting of the steric effects. The
emergence of dynamic charge waves and nonlinear deformation of the surface as
result of applying probing voltage is numerically explored. 2D maps of the
strain and concentration distribution across the mixed ionic-electronic
conductor and bias-induced surface displacements for ESM microscopy were
calculated. Obtained numerical results can be of applied to quantify ESM
response of Li-based solid electroytes, materials with resistive switching and
electroactive ferroelectric polymers, which are of potential interest for
flexible and high-density non-volatile memory devices. | 1411.0966v1 |
2015-06-03 | Stable room-temperature ferromagnetic phase at the FeRh(100) surface | Interfaces and low dimensionality are sources of strong modifications of
electronic, structural, and magnetic properties of materials. FeRh alloys are
an excellent example because of the first-order phase transition taking place
at $\sim$400 K from an antiferromagnetic phase at room temperature to a high
temperature ferromagnetic one. It is accompanied by a resistance change and
volume expansion of about 1\%. We have investigated the electronic and magnetic
properties of FeRh(100) epitaxially grown on MgO by combining spectroscopies
characterized by different probing depths, namely X-ray magnetic circular
dichroism and photoelectron spectroscopy. We thus reveal that the symmetry
breaking induced at the Rh-terminated surface stabilizes a surface
ferromagnetic layer involving five planes of Fe and Rh atoms in the nominally
antiferromagnetic phase at room temperature. First-principles calculations
provide a microscopic description of the structural relaxation and the electron
spin-density distribution that fully support the experimental findings. | 1508.01777v1 |
2015-09-10 | Three-Dimensional Stateful Material Implication Logic | Monolithic three-dimensional integration of memory and logic circuits could
dramatically improve performance and energy efficiency of computing systems.
Some conventional and emerging memories are suitable for vertical integration,
including highly scalable metal-oxide resistive switching devices (memristors),
yet integration of logic circuits proves to be much more challenging. Here we
demonstrate memory and logic functionality in a monolithic three-dimensional
circuit by adapting recently proposed memristor-based stateful material
implication logic. Though such logic has been already implemented with a
variety of memory devices, prohibitively large device variability in the most
prospective memristor-based circuits has limited experimental demonstrations to
simple gates and just a few cycles of operations. By developing a
low-temperature, low-variability fabrication process, and modifying the
original circuit to increase its robustness to device imperfections, we
experimentally show, for the first time, reliable multi-cycle multi-gate
material implication logic operation within a three-dimensional stack of
monolithically integrated memristors. The direct data manipulation in three
dimensions enables extremely compact and high-throughput logic-in-memory
computing and, remarkably, presents a viable solution for the Feynman grand
challenge of implementing an 8-bit adder at the nanoscale. | 1509.02986v1 |
2018-01-19 | Superconductivity in potassium-doped 2,2$'$-bipyridine | Organic compounds are always promising candidates of superconductors with
high transition temperatures. We examine this proposal by choosing
2,2$'$-bipyridine solely composed by C, H, and N atoms. The presence of
Meissner effect with a transition temperature of 7.2 K in this material upon
potassium doping is demonstrated by the $dc$ magnetic susceptibility
measurements. The real part of the $ac$ susceptibility exhibits the same
transition temperature as that in $dc$ magnetization, and a sharp peak appeared
in the imaginary part indicates the formation of the weakly linked
superconducting vortex current. The occurence of superconductivity is further
supported by the resistance drop at the transition together with its
suppression by the applied magnetic fields. The superconducting phase is
identified to be K$_3$-2,2$'$-bipyridine from the analysis of Raman scattering
spectra. This work not only opens an encouraging window for finding
superconductivity after optoelectronics in 2,2$'$-bipyridine-based materials
but also offers an example to realize superconductivity from conducting
polymers and their derivatives. | 1801.06320v2 |
2018-05-07 | The Role of Grain Boundaries under Long-Time Radiation | Materials containing a high proportion of grain boundaries offer significant
potential for the development of radiation-resistent structural materials.
However, a proper understanding of the connection between the radiation-induced
microstructural behaviour of grain boundary and its impact at long natural time
scales is still missing. In this letter, point defect absorption at interfaces
is summarised by a jump Robin-type condition at a coarse-grained level, wherein
the role of interface microstructure is effectively taken into account. Then a
concise formula linking the sink strength of a polycrystalline aggregate with
its grain size is introduced, and is well compared with experimental
observation. Based on the derived model, a coarse-grained formulation
incorporating the coupled evolution of grain boundaries and point defects is
proposed, so as to underpin the study of long-time morphological evolution of
grains induced by irradiation. Our simulation results suggest that the presence
of point defect sources within a grain further accelerates its shrinking
process, and radiation tends to trigger the extension of twin boundary
sections. | 1805.02360v1 |
2019-09-19 | Low compressible BP$_3$N$_6$ | Using first principles calculation, the structural and mechanical properties
of BP$_3$N$_6$ which adopts an orthorhombic structure with space group Pna2$_1$
(no. 33), were determined at three different pressure values (0, 20 and
42.4~GPa). The nine independent elastic constants meet all necessary and
sufficient conditions for mechanical stability criteria for an orthorhombic
crystal. BP$_3$N$_6$ show strong resistance to volume change hence a potential
low compressible material. The Vicker's hardness of BP$_3$N$_6$ was found to
range between 49-51~GPa for different external pressures imposed on the
crystal. These high values of Vicker's hardness implies that BP$_3$N$_6$ is a
potential superhard material. | 1909.08879v2 |
2014-08-06 | Crystal structure and electronic structure of CePt2In7 | We report a corrected crystal structure for the CePt2In7 superconductor,
refined from single crystal x-ray diffraction data. The corrected crystal
structure shows a different Pt-In stacking along the c-direction in this
layered material than was previously reported. In addition, all the atomic
sites are fully occupied with no evidence of atom site mixing, resolving a
discrepancy between the observed high resistivity ratio of the material and the
atomic disorder present in the previous structural model The Ce-Pt distance and
coordination is typical of that seen in all other reported Ce_nM_mIn_3n+2m
compounds. Our band structure calculations based on the correct structure
reveal three bands at the Fermi level that are more three dimensional than
those previously proposed, and Density functional theory (DFT) calculations
show that the new structure has a significantly lower energy. | 1408.1246v1 |
2017-01-30 | Pressure-induced superconductivity and topological quantum phase transitions in a quasi-one-dimensional topological insulator: Bi4I4 | Superconductivity and topological quantum states are two frontier fields of
research in modern condensed matter physics. The realization of
superconductivity in topological materials is highly desired, however,
superconductivity in such materials is typically limited to two- or
three-dimensional materials and is far from being thoroughly investigated. In
this work, we boost the electronic properties of the quasi-one-dimensional
topological insulator bismuth iodide \b{eta}-Bi4I4 by applying high pressure.
Superconductivity is observed in \b{eta}-Bi4I4 for pressures where the
temperature dependence of the resistivity changes from a semiconducting-like
behavior to that of a normal metal. The superconducting transition temperature
Tc increases with applied pressure and reaches a maximum value of 6 K at 23
GPa, followed by a slow decrease. Our theoretical calculations suggest the
presence of multiple pressure-induced topological quantum phase transitions as
well as a structural-electronic instability. | 1701.08860v1 |
2019-03-12 | Structural and electronic properties of the spin-filter material CrVTiAl with disorder | The effects of chemical disorder on the transport properties of the
spin-filter material CrVTiAl are investigated experimentally and theoretically.
Synchrotron X-ray diffraction experiments on bulk CrVTiAl and the associated
Rietveld analysis indicate that the crystal structure consists primarily of a
mixture of a partially ordered B2 phase, a fully disordered A2 phase and a
small component of an ordered L2\textsubscript{1} or Y phase. High temperature
resistivity measurements confirm the existence of a band gap. First-principles,
all-electron, self-consistent electronic structure computations show that the
chemically disordered A2 and B2 phases are metallic, while the spin-filter
properties of the ideal Y-type phase are preserved in the presence of
L2\textsubscript{1} disorder. The Hall coefficient is found to decrease with
increasing temperature, similar to the measured increase in the conductivity,
indicating the presence of thermally activated semiconductor-like carriers. | 1903.05004v1 |
2019-01-28 | Effect of Bi Substitution on Thermoelectric Properties of SbSe2-based Layered Compounds NdO$_{0.8}$F$_{0.2}$Sb$_{1-x}$Bi$_x$Se$_2$ | Although SbSe2-based layered compounds have been predicted to be
high-performance thermoelectric materials and topological materials, most of
these compounds obtained experimentally have been insulators so far. Here, we
present the effect of Bi substitution on the thermoelectric properties of
SbSe2-based layered compounds NdO0.8F0.2Sb1-xBixSe2 (x = 0-0.4). The room
temperature electrical resistivity is decreased to 8.0 * 10^-5 ohmm for x =
0.4. The electrical power factor is calculated to be 1.4 * 10^-4 W/mK^2 at 660
K, which is in reasonable agreement with combined Jonker and Ioffe analysis.
The room-temperature lattice thermal conductivity of less than 1 W/mK is almost
independent of x, in contrast to the point-defect scattering model for
conventional alloys. The present work provides an avenue for exploring
SbSe2-based insulating and BiSe2-based conducting systems. | 1901.09909v1 |
2020-08-21 | An unexplored MBE growth mode reveals new properties of superconducting NbN | Accessing unexplored conditions in crystal growth often reveals remarkable
surprises and new regimes of physical behavior. In this work, performing
molecular beam epitaxy of the technologically important superconductor NbN at
temperatures greater than 1000$^\circ$C, higher than in the past, is found to
reveal persistent RHEED oscillations throughout the growth, atomically smooth
surfaces, normal metal resistivities as low as 37$\mu\Omega$-cm and
superconducting critical temperatures in excess of 15 K. Most remarkably, a
reversal of the sign of the Hall coefficient is observed as the NbN films are
cooled, and the high material quality allows the first imaging of Abrikosov
vortex lattices in this superconductor. | 2008.09596v3 |
2020-09-25 | A Possible Method of Carbon Deposit Mapping on Plasma Facing Components Using Infrared Thermography | The material eroded from the surface of plasma facing components is
redeposited partly close to high heat flux areas. At these locations, the
deposit is heated by the plasma and the deposition pattern evolves depending on
the operation parameters. The mapping of the deposit is still a matter of
intense scientific activity, especially during the course of experimental
campaigns. A method based on the comparison of surface temperature maps,
obtained in situ by infrared cameras and by theoretical modelling is proposed.
The difference between the two is attributed to the thermal resistance added by
deposited material, and expressed as a deposit thickness. The method benefits
of elaborated imaging techniques such as possibility theory and fuzzy logics.
The results are consistent with deposit maps obtained by visual inspection
during shutdowns. | 2010.06374v1 |
2020-10-29 | Nature of native atomic defects in ZrTe$_5$ and their impact on the low-energy electronic structure | Over the past decades, investigations of the anomalous low-energy electronic
properties of ZrTe$_5$ have reached a wide array of conclusions. An open
question is the growth method's impact on the stoichiometry of ZrTe$_5$
samples, especially given the very small density of states near its chemical
potential. Here we report on high resolution scanning tunneling microscopy and
spectroscopy measurements performed on samples grown via different methods.
Using density functional theory calculations, we identify the most prevalent
types of atomic defects on the surface of ZrTe$_5$, namely Te vacancies and
intercalated Zr atoms. Finally, we precisely quantify their density and outline
their role as ionized defects in the anomalous resistivity of this material. | 2010.15513v1 |
2021-11-17 | Anisotropic superconductivity and unusually robust electronic critical field in single crystal La$_{7}$Ir$_{3}$ | Polycrystalline La$_{7}$Ir$_{3}$ is reported to show superconductivity
breaking time-reversal symmetry while also having an isotropic $s$-wave gap.
Single crystals of this noncentrosymmetric superconductor are highly desirable
to understand the nature of the electron pairing mechanism in this system. Here
we report the growth of high-quality single crystals of La$_{7}$Ir$_{3}$ by the
Czochralski method. The structural and superconducting properties of these
large crystals have been investigated using x-rays, magnetization, resistivity
and heat capacity measurements. We observe a clear anisotropy in the lower and
upper critical fields for magnetic fields applied parallel and perpendicular to
the hexagonal $c$ axis. We also report the presence of a robust electronic
critical field, that diverges from the upper critical field derived from heat
capacity, which is the hallmark of surface superconductivity. | 2111.09239v2 |
2022-01-09 | Phase field fracture predictions of microscopic bridging behaviour of composite materials | We investigate the role of microstructural bridging on the fracture toughness
of composite materials. To achieve this, a new computational framework is
presented that integrates phase field fracture and cohesive zone models to
simulate fibre breakage, matrix cracking and fibre-matrix debonding. The
composite microstructure is represented by an embedded cell at the vicinity of
the crack tip, whilst the rest of the sample is modelled as an anisotropic
elastic solid. The model is first validated against experimental data of
transverse matrix cracking from single-notched three-point bending tests. Then,
the model is extended to predict the influence of grain bridging,
brick-and-mortar microstructure and 3D fibre bridging on crack growth
resistance. The results show that these microstructures are very efficient in
enhancing the fracture toughness via fibre-matrix debonding, fibre breakage and
crack deflection. In particular, the 3D fibre bridging effect can increase the
energy dissipated at failure by more than three orders of magnitude, relative
to that of the bulk matrix; well in excess of the predictions obtained from the
rule of mixtures. These results shed light on microscopic bridging mechanisms
and provide a virtual tool for developing high fracture toughness composites. | 2201.03066v1 |
2022-10-30 | Linear nonsaturating magnetoresistance in kagome superconductor CsV3Sb5 thin flakes | Linear nonsaturating magnetoresistance (LMR) represents a class of anomalous
resistivity response to external magnetic field that has been observed in a
variety of materials including but not limited to topological semi-metals,
high-Tc superconductors and materials with charge/spin density wave (CDW/SDW)
orders. Here we report the observation of LMR in layered kagome superconductor
and CDW material CsV3Sb5 thin flakes, as well as the dimensional crossover and
temperature (T) crossover of such LMR. Specifically, in ultrathin CsV3Sb5
crystals, the magnetoresistance (MR) exhibits a crossover from LMR at low T to
quadratic B dependence above the CDW transition temperature; the MR also
exhibits a crossover from LMR to sublinear MR for sample thickness at around
~20 nm at low T. We discuss several possible origins of the LMR and attribute
the effect to two-dimensional (2D) CDW fluctuations. Our results may provide a
new perspective for understanding the interactions between competing orders in
kagome superconductors. | 2210.16890v1 |
2023-08-09 | Superionic phase transition of copper(I) sulfide and its implication for purported superconductivity of LK-99 | Lee, Kim, and coworkers have recently claimed room-temperature and
ambient-pressure superconductivity in a copper-doped lead apatite material
named LK-99. However, the polycrystalline material synthesized has a
significant fraction of copper(I) sulfide. Copper(I) sulfide has a known phase
transition at 104 degrees C from an ordered low-temperature phase to a
high-temperature superionic phase. As a result of this phase transition,
copper(I) sulfide exhibits sharp transitions in electrical resistivity and heat
capacity, which are expected to coincide with the temperature-induced
transitions reported for LK-99. This implies that LK-99 must be synthesized
without any copper(I) sulfide to allow unambiguous validation of the
superconducting properties of LK-99. | 2308.05222v3 |
2023-11-15 | Strongly pinned skyrmionic bubbles and higher-order nonlinear Hall resistances at the interface of Pt/FeSi bilayer | Engineering of magnetic heterostructures for spintronic applications has
entered a new phase, driven by the recent discoveries of topological materials
and exfoliated van der Waals materials. Their low-dimensional properties can be
dramatically modulated in designer heterostructures via proximity effects from
adjacent materials, thus enabling the realization of diverse quantum states and
functionalities. Here we investigate spin-orbit coupling (SOC) proximity
effects of Pt on the recently discovered quasi-two-dimensional ferromagnetic
state at FeSi surface. Skyrmionic bubbles (SkBs) are formed as a result of the
enhanced interfacial Dzyloshinskii-Moriya interaction. The strong pinning
effects on the SkBs are evidenced from the significant dispersion in size and
shape of the SkBs and are further identified as a greatly enhanced threshold
current density required for depinning of the SkBs. The robust integrity of the
SkB assembly leads to the emergence of higher-order nonlinear Hall effects in
the high current density regime, which originate from nontrivial Hall effects
due to the noncollinearity of the spin texture, as well as from the
current-induced magnetization dynamics via the augmented spin-orbit torque. | 2311.08730v1 |
2023-11-21 | Reliable lift-off patterning of graphene dispersions for humidity sensors | Dispersion-based graphene materials are promising candidates for various
sensing applications. They offer the advantage of relatively simple and fast
deposition via spin-coating, Langmuir-Blodgett deposition, or inkjet printing.
Film uniformity and reproducibility remain challenging in all of these
deposition methods. Here, we demonstrate, characterize, and successfully apply
a scalable structuring method for graphene dispersions. The method is based on
a standard lift-off process, is simple to implement, and increases the film
uniformity of graphene devices. It is also compatible with standard
semiconductor manufacturing methods. We investigate two different graphene
dispersions via Raman spectroscopy and Atomic Force Microscopy and observe no
degradation of the material properties by the structuring process. Furthermore,
we achieve high uniformity of the structured patterns and homogeneous graphene
flake distribution. Electrical characterizations show reproducible sheet
resistance values correlating with material quantity and uniformity. Finally,
repeatable humidity sensing is demonstrated with van der Pauw devices, with
sensing limits of less than 1% relative humidity. | 2311.12650v2 |
2024-04-10 | Optimal Matching of Thermal Vibrations into Carbon Nanotubes | Carbon nanotubes (CNTs) are promising candidates to improve the thermal
conductivity of nano-composites. The main obstacle to these applications is the
extremely high thermal boundary (Kapitza) resistance between the CNTs and their
matrix. In this theoretical work our goal is to maximize the heat flux through
the CNT by functionalizing the CNT ends. We use a Landauer approach to
calculate and optimize the energy flux from a soft to a hard material in one
dimension through a connecting continuous medium of varying elasticity and
density. The transmission probability of phonons through the system is
calculated both numerically and analytically. We find that over 90% of the
maximum heat flux into CNT is possible for 1nm length of the intermediate
material at room temperature (300K). | 2404.06938v1 |
2010-11-12 | Suspension and Measurement of Graphene and Bi2Se3 Atomic Membranes | Coupling high quality, suspended atomic membranes to specialized electrodes
enables investigation of many novel phenomena, such as spin or Cooper pair
transport in these two dimensional systems. However, many electrode materials
are not stable in acids that are used to dissolve underlying substrates. Here
we present a versatile and powerful multi-level lithographical technique to
suspend atomic membranes, which can be applied to the vast majority of
substrate, membrane and electrode materials. Using this technique, we
fabricated suspended graphene devices with Al electrodes and mobility of 5500
cm^2/Vs. We also demonstrate, for the first time, fabrication and measurement
of a free-standing thin Bi2Se3 membrane, which has low contact resistance to
electrodes and a mobility of >~500 cm^2/Vs. | 1011.2837v1 |
2011-11-04 | Dual-gated bilayer graphene hot electron bolometer | Detection of infrared light is central to diverse applications in security,
medicine, astronomy, materials science, and biology. Often different materials
and detection mechanisms are employed to optimize performance in different
spectral ranges. Graphene is a unique material with strong, nearly
frequency-independent light-matter interaction from far infrared to
ultraviolet, with potential for broadband photonics applications. Moreover,
graphene's small electron-phonon coupling suggests that hot-electron effects
may be exploited at relatively high temperatures for fast and highly sensitive
detectors in which light energy heats only the small-specific-heat electronic
system. Here we demonstrate such a hot-electron bolometer using bilayer
graphene that is dual-gated to create a tunable bandgap and
electron-temperature-dependent conductivity. The measured large electron-phonon
heat resistance is in good agreement with theoretical estimates in magnitude
and temperature dependence, and enables our graphene bolometer operating at a
temperature of 5 K to have a low noise equivalent power (33 fW/Hz1/2). We
employ a pump-probe technique to directly measure the intrinsic speed of our
device, >1 GHz at 10 K. | 1111.1202v1 |
2012-11-08 | Structural phase transformations in metallic grain boundaries | Structural transformations at interfaces are of profound fundamental interest
as complex examples of phase transitions in low-dimensional systems. Despite
decades of extensive research, no compelling evidence exists for structural
transformations in high-angle grain boundaries in elemental systems. Here we
show that the critical impediment to observations of such phase transformations
in atomistic modeling has been rooted in inadequate simulation methodology. The
proposed new methodology allows variations in atomic density inside the grain
boundary and reveals multiple grain boundary phases with different atomic
structures. Reversible first-order transformations between such phases are
observed by varying temperature or injecting point defects into the boundary
region. Due to the presence of multiple metastable phases, grain boundaries can
absorb significant amounts of point defects created inside the material by
processes such as irradiation. We propose a novel mechanism of radiation damage
healing in metals which may guide further improvements in radiation resistance
of metallic materials through grain boundary engineering. | 1211.1756v2 |
2014-10-10 | Topological Origin of Fracture Toughening in Complex Solids: the Viewpoint of Rigidity Theory | In order to design tougher materials, it is crucial to understand the
relationship between their composition and their resistance to fracture. To
this end, we investigate the fracture toughness of usual sodium silicate
glasses (NS) and complex calcium--silicate--hydrates (CSH), the binding phase
of cement. Their atomistic structure is described in the framework of the
topological constraints theory, or rigidity theory. We report an analogous
rigidity transition, driven by pressure in NS and by composition in CSH.
Relying both on simulated and available experimental results, we show that
optimally constrained isostatic systems show improved fracture toughness. The
flexible to stressed--rigid transition is shown to be correlated to a
ductile-to-brittle transition, with a local minimum of the brittleness for
isostatic system. This fracture toughening arises from a reversible molecular
network, allowing optimal stress relaxation and crack blunting behaviors. This
opens the way to the discovery of high-performance materials, designed at the
molecular scale. | 1410.2916v1 |
2015-02-09 | Pressure-induced superconductivity in the three-dimensional Dirac semimetal Cd3As2 | The recently discovered Dirac and Weyl semimetals are new members of
topological materials. Starting from them, topological superconductivity may be
achieved, e.g. by carrier doping or applying pressure. Here we report
high-pressure resistance and X-ray diffraction study of the three-dimensional
topological Dirac semimetal Cd3As2. Superconductivity with Tc ~ 2.0 K is
observed at 8.5 GPa. The Tc keeps increasing to about 4.0 K at 21.3 GPa, then
shows a nearly constant pressure dependence up to the highest pressure 50.9
GPa. The X-ray diffraction measurements reveal a structure phase transition
around 3.5 GPa. Our observation of superconductivity in pressurized topological
Dirac semimetal Cd3As2 provides a new candidate for topological superconductor,
as argued in a recent point contact study and a theoretical work. | 1502.02509v2 |
2017-06-19 | Electrical and Thermal Transport at the Planckian Bound of Dissipation in the Hydrodynamic Electron Fluid of WP2 | Materials with strongly-correlated electrons exhibit interesting phenomena
such as metal-insulator transitions and high-temperature superconductivity. In
stark contrast to ordinary metals, electron transport in these materials is
thought to resemble the flow of viscous fluids. Despite their differences, it
is predicted that transport in both, conventional and correlated materials, is
fundamentally limited by the uncertainty principle applied to energy
dissipation. Here we discover hydrodynamic electron flow in the Weyl-semimetal
tungsten phosphide (WP2). Using thermal and magneto-electric transport
experiments, we observe the transition from a conventional metallic state, at
higher temperatures, to a hydrodynamic electron fluid below 20 K. The
hydrodynamic regime is characterized by a viscosity-induced dependence of the
electrical resistivity on the square of the channel width, and by the
observation of a strong violation of the Wiedemann-Franz law. From
magneto-hydrodynamic experiments and complementary Hall measurements, the
relaxation times for momentum and thermal energy dissipating processes are
extracted. Following the uncertainty principle, both are limited by the
Planckian bound of dissipation, independent of the underlying transport regime. | 1706.05925v2 |
2017-09-22 | On Extracting Mechanical Properties from Nanoindentation at Temperatures up to 1000$^{\circ}$C | Alloyed MCrAlY bond coats, where M is usually cobalt and/or nickel, are
essential parts of modern turbine blades, imparting environmental resistance
while mediating thermal expansivity differences. Nanoindentation allows the
determination of their properties without the complexities of traditional
mechanical tests, but was not previously possible near turbine operating
temperatures.
Here, we determine the hardness and modulus of CMSX-4 and an Amdry-386 bond
coat by nanoindentation up to 1000$^{\circ}$C. Both materials exhibit a
constant hardness until 400$^{\circ}$C followed by considerable softening,
which in CMSX-4 is attributed to the multiple slip systems operating underneath
a Berkovich indenter.
The creep behaviour has been investigated via the nanoindentation hold
segments. Above 700$^{\circ}$C, the observed creep exponents match the
temperature-dependence of literature values in CMSX-4. In Amdry-386,
nanoindentation produces creep exponents very close to literature data,
implying high-temperature nanoindentation may be powerful in characterising
these coatings and providing inputs for material, model and process
optimisations. | 1709.07714v1 |
2017-03-16 | Equivalence of Effective Medium and Random Resistor Network models for disorder-induced unsaturating linear magnetoresistance | A linear unsaturating magnetoresistance at high perpendicular magnetic
fields, together with a quadratic positive magnetoresistance at low fields, has
been seen in many different experimental materials, ranging from silver
chalcogenides and thin films of InSb to topological materials like graphene and
Dirac semimetals. In the literature, two very different theoretical approaches
have been used to explain this classical magnetoresistance as a consequence of
sample disorder. The phenomenological Random Resistor Network model constructs
a grid of four-terminal resistors, each with a varying random resistance. The
Effective Medium Theory model imagines a smoothly varying disorder potential
that causes a continuous variation of the local conductivity. Here, we
demonstrate numerically that both models belong to the same universality class
and that a restricted class of the Random Resistor Network is actually
equivalent to the Effective Medium Theory. Both models are also in good
agreement with experiments on a diverse range of materials. Moreover, we show
that in both cases, a single parameter, i.e. the ratio of the fluctuations in
the carrier density to the average carrier density, completely determines the
magnetoresistance profile. | 1703.05478v1 |
2017-08-24 | Probing the Fermi surface and magnetotransport properties in MoAs$_{2}$ | Transition metal dipnictides (TMDs) have recently been identified as possible
candidates to host topology protected electronic band structure. These
materials belong to an isostructural family and show several exotic transport
properties. Especially, the large values of magnetoresistance (MR) and carrier
mobility have drawn significant attention from the perspective of technological
applications. In this report, we have investigated the magnetotransport and
Fermi surface properties of single crystalline MoAs$_{2}$, another member of
this group of compounds. Field induced resistivity plateau and a large MR have
been observed, which are comparable to several topological systems.
Interestingly, in contrast to other isostructural materials, the carrier
density in MoAs$_{2}$ is quite high and shows single-band dominated transport.
The Fermi pockets, which have been identified from the quantum oscillation, are
largest among the members of this group and have significant anisotropy with
crystallographic direction. Our first-principles calculations reveal a
substantial difference between the band structures of MoAs$_{2}$ and other
TMDs. The calculated Fermi surface consists of one electron pocket and another
'open-orbit' hole pocket, which has not been observed in TMDs so far. | 1708.07294v1 |
2019-03-18 | Zirconia UV-curable colloids for additive manufacturing via hybrid inkjet printing-stereolithography | Currently, additive manufacturing of ceramics by stereolithography (SLA) is
limited to single materials and by a poor thickness resolution that strongly
depends on the ceramic particles-UV light interaction. Combining selective
laser curing with inkjet printing represents a novel strategy to overcome these
constrains. Nonetheless, this approach requires UV-curable inks that allow
hardening of the printed material and sintering to high density. In this work,
we report how to design an ink for inkjet printing of yttria stabilized
zirconia (YSZ) which can be impressed by addition of UV-curable monomers. We
especially show how the formulation of the inks and particularly the UV-monomer
concentration impacts the printability and the UV-curing. This leads to prints
that are resistant to solvent washing first and densify to 96% dense YSZ layers
after sintering. | 1903.07731v1 |
2019-12-23 | Large $d_{33}$ Piezoelectric-Polymer Composites For RF Acoustic Resonators | While piezoelectric transduction enables designing acoustic resonators
operating at multi-GHz frequencies, the deposition of piezoelectric materials
typically requires high temperature processes and specific crystallographic
orientation of substrates, thus imposing a limitation on materials that could
be used. In this paper we present a piezoelectrically transduced thickness mode
acoustic resonator that employs piezoelectric (PMNPT) nanoparticles embedded in
a polymer (SU8) matrix. This composite material is deposited using standard
resist-spin coaters and is thus compatible with a variety of substrates. The
device presented here uses a double side polished single crystal silicon wafer
as the low loss acoustic substrate for the resonator and $1.7\mu m$ thick
SU8-PMNPT composite film as the actuator, and exhibits large effective
piezoelectric coefficient $(d_{33})$ of $216pm/V$, and we experimentally
demonstrate efficient transduction of acoustic resonances at frequencies up to
$1.5GHz$. | 1912.10713v1 |
2021-01-25 | Polycaprolactone/graphite nanoplates composite nanopapers | Nanopapers based on graphene and related materials were recently proposed for
application in heat spreader applications. To overcome typical limitations in
brittleness of such materials, this work addressed the combination of graphite
nanoplatelets (GNP) with a soft, tough and crystalline polymer, acting as an
efficient binder between nanoplates. With this aim, polycaprolactone (PCL) was
selected and exploited in this paper. The crystalline organization of PCL
within the nanopaper was studied to investigate the effect of polymer
confinement between GNP. Thermomechanical properties were studied by dynamic
mechanical analyses at variable temperature and creep measurements at high
temperature, demonstrating superior resistance at temperatures well above PCL
melting. Finally, the heat conduction properties on the nanopapers were
evaluated, resulting in outstanding values above 150 Wm-1K-1. | 2101.10283v1 |
2019-11-13 | Portable and wireless signal transducer for field testing of environmental sensors based on 2D materials | In this paper we present the design and fabrication of a portable device for
environmental monitoring applications. This novel hand-held apparatus monitors
the changes in the resistance of a sensing surface with a high accuracy and
resolution and transmits the recorded data wirelessly to a cellphone. Such a
design offers a solution for field testing of environmental sensors. The tested
sensing surface in this study is based on an ultrathin material: graphene,
which is placed on the surface of a Si/SiO2 wafer. This signal transducer and
wireless communication system form together an ideal platform to harvest the
sensitivity and selectivity of 2D materials for gas sensing applications. | 1911.05764v2 |
2022-01-08 | Dynamical Mean Field Studies of Infinite Layer Nickelates: Physics Results and Methodological Implications | This article summarizes recent work on the many-body (beyond density
functional theory) electronic structure of layered rare-earth nickelates, both
in the context of the materials themselves and in comparison to the
high-temperature superconducting (high-$T_c$) layered copper-oxide compounds.
It aims to outline the current state of our understanding of layered nickelates
and to show how the analysis of these fascinating materials can shed light on
fundamental questions in modern electronic structure theory. A prime focus is
determining how the interacting physics defined over a wide energy range can be
estimated and "downfolded" into a low energy theory that would describe the
relevant degrees of freedom on the $\sim 0.5$ eV scale and that could be solved
to determine superconducting and spin and charge density wave phase boundaries,
temperature-dependent resistivities, and dynamical susceptibilities. | 2201.02852v1 |
2022-03-04 | Broadband Cross-Circular Polarization Carpet Cloaking based on a Phase Change Material Metasurface in the Mid-infrared Region | In view of the fact that most invisibility devices focus on linear
polarization cloaking and that the characteristics of mid infrared cloaking are
rarely studied, we propose a cross circularly polarized invisibility carpet
cloaking device in the mid infrared band. Based on the Pancharatnam Berry phase
principle, the unit cells with the cross circular polarization gradient phase
were carefully designed and constructed into a metasurface. In order to achieve
tunable cross circular polarization carpet cloaks, a phase change material is
introduced into the design of the unit structure. When the phase change
material is in amorphous and crystalline states, the proposed metasurface unit
cells can achieve high efficiency cross polarization conversion and reflection
intensity can be tuned. According to the phase compensation principle of carpet
cloaking, we construct a metasurface cloaking device with a phase gradient
using the designed unit structure. From the near and far field distributions,
the cross circular polarization cloaking property is confirmed in the broadband
wavelength range. The proposed cloaking device can effectively resist detection
of cross-circular polarization. | 2203.02222v1 |
2022-03-06 | Scaled indium oxide transistors fabricated using atomic layer deposition | In order to continue to improve integrated circuit performance and
functionality, scaled transistors with short channel lengths and low thickness
are needed. But the further scaling of silicon-based devices and the
development of alternative semiconductor channel materials that are compatible
with current fabrication processes is challenging. Here we report
atomic-layer-deposited indium oxide transistors with channel lengths down to 8
nm, channel thicknesses down to 0.5 nm and equivalent dielectric oxide
thickness down to 0.84 nm. Due to the scaled device dimensions and low contact
resistance, the devices exhibit high on-state currents of 3.1 A/mm at a drain
voltage of 0.5 V and a transconductance of 1.5 S/mm at a drain voltage 1 V. Our
devices are a promising alternative channel material for scaled transistors
with back-end-of-line processing compatibility. | 2203.02869v1 |
2022-10-18 | Nanoscale friction controlled by top layer thickness in [LaMnO$_{3}$]$_{m}$/[SrMnO$_{3}$]$_{n}$ superlattices | We conducted lateral force microscopy measurements on seven
[LaMnO$_{3}$]$_{m}$/[SrMnO$_{3}$]$_{n}$ superlattices with varied layer
thicknesses. We observe that the friction forces and the friction coefficients
initially increase with increasing LaMnO3 top layer thickness, followed by
saturation when the top layer thickness exceeds a few nanometers. These
observations clearly demonstrate that sliding friction is affected by
sub-surface material properties to a depth of several nanometers and is not
just determined by dynamics in the contact interface. We argue that the
sub-surface dissipated energy is governed by damping in the elastically
strained volume below the AFM tip, an effect which we estimate via
thermoelasticity. The absence of a correlation between friction and the thermal
resistivity of our superlattices shows furthermore that high-frequency phonons
and heat conduction do not play a role in determining friction. Our
observations thus demonstrate that friction can be tailored by sub-surface
material properties. | 2210.09677v1 |
2023-05-15 | Superconductivity at epitaxial LaTiO3-KTaO3 interfaces | Design of epitaxial interfaces is a pivotal way to engineer artificial
structures where new electronic phases can emerge. Here we report a systematic
emergence of interfacial superconducting state in epitaxial heterostructures of
LaTiO3 and KTaO3. The superconductivity transition temperature increases with
decreasing the thickness of LaTiO3. Such behavior is observed for both (110)
and (111) crystal oriented structures. For thick samples, the finite resistance
developing below the superconducting transition temperature increases with
increasing LaTiO3 thickness. Consistent with previous reports, the (001)
oriented heterointerface features high electron mobility of 250 cm2/Vs and
shows no superconducting transition down to 40 mK. Our results imply a
non-trivial impact of LaTiO3 on the superconducting state and indicate how
superconducting KTaO3 interfaces can be integrated with other oxide materials. | 2305.08304v1 |
2024-02-16 | Erosion Study of Tungsten Carbide films under 100 keV Kr+ ion irradiation | Tungsten carbide (WC) stands out as a crucial material for exploration in
extreme environments due to its resistance to radiation and impressive
mechanical strength. Widely utilized in cutting tools, high-wear components,
and as a potential contender for plasma-facing material in nuclear reactors,
WC's erosion behavior under surrogate irradiations is a subject of
investigation. In the present work, WC films were synthesized at two different
substrate temperatures of 400 K and 600 K using RF sputtering and were then
irradiated with 100 keV Kr1+ ions at a fluence of 1x1017 ions/cm2. The
crystalline phases of as deposited WC films were confirmed by glancing
incidence X-ray diffraction (GIXRD) measurements. Rutherford Backscattering
Spectrometry (RBS) was employed to determine the thicknesses of pristine
samples and the sputtering rate by measuring the difference in the areal
densities of the pristine and irradiated films. The erosion rate of both types
of films was found to be ~ 1.6 atoms per incident Kr+ ion. These findings
contribute to a foundational comprehension of the radiation tolerance behavior
of WC thin films, crucial for their performance in the demanding conditions of
extreme radiation. | 2402.10461v1 |
2001-05-22 | Infrared optical properties of Pr2CuO4 | The ab-plane reflectance of a Pr2CuO4 single crystal has been measured over a
wide frequency range at a variety of temperatures, and the optical properties
determined from a Kramers-Kronig analysis. Above ~ 250 K, the low frequency
conductivity increases quickly with temperature; the resistivity follows the
form e^(E_a/k_BT), where E_a ~ 0.17 eV is much less than the inferred optical
gap of ~ 1.2 eV. Transport measurements show that at low temperature the
resistivity deviates from activated behavior and follows the form
e^[(T_0/T)^1/4], indicating that the dc transport in this material is due to
variable-range hopping between localized states in the gap. The four
infrared-active Eu modes dominate the infrared optical properties. Below ~ 200
K, a striking new feature appears near the low-frequency Eu mode, and there is
additional new fine structure at high frequency. A normal coordinate analysis
has been performed and the detailed nature of the zone-center vibrations
determined. Only the low-frequency Eu mode has a significant Pr-Cu interaction.
Several possible mechanisms related to the antiferromagnetism in this material
are proposed to explain the sudden appearance of this and other new spectral
features at low temperature. | 0105445v2 |
2006-11-29 | What is the valence of a correlated solid? The double life of delta-plutonium | Plutonium displays phase transitions with enormous volume differences among
its phases and both its Pauli like magnetic susceptibility and resistivity are
an order of magnitude larger than those of simple metals. Curium is also highly
resistive but its susceptibility is Curie-like at high temperatures and orders
antiferromagnetically at low temperatures. The anomalous properties of the late
actinides stem from the competition between the itinerancy and localization of
its f electrons, which makes the late actinides elemental strongly correlated
materials. A central problem in this field is to understand the mechanism by
which these materials resolve these conflicting tendencies. In this letter we
identify the electronic mechanisms responsible for the anomalous behaviour of
late actinides. We revisit the concept of valence using theoretical approach
that treats magnetism, Kondo screening, atomic multiplet effects, spin orbit
coupling and crystal field splitting on the same footing. Plutonium is found to
be in a rare mixed valent state, namely its ground state is a superposition of
two distinct valencies. Curium settles in a single valence magnetically ordered
state at low temperatures. The f7 atomic configuration of Curium is contrasted
with the multiple configuration manifolds present in Plutonium ground state
which we characterize by a valence histogram. The balance between the Kondo
screening and magnetism is determined by the competition between spin orbit
coupling and the strength of atomic multiplets which is in turn regulated by
the degree of itinerancy. The approach presented here, highlights the
electronic origin of the bonding anomalies in plutonium and can be applied to
predict generalized valences and the presence or absence of magnetism in other
compounds starting from first principles. | 0611760v1 |
2009-05-08 | Magnetotransport in polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ thin films of controlled granularity | Polycrystalline La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO) thin films were
synthesized by pulsed laser ablation on single crystal (100) yttria-stabilized
zirconia (YSZ) substrates to investigate the mechanism of magneto-transport in
a granular manganite. Different degrees of granularity is achieved by using the
deposition temperature (T$_{D}$) of 700 and 800 $^{0}$C. Although no
significant change in magnetic order temperature (T$_C$) and saturation
magnetization is seen for these two types of films, the temperature and
magnetic field dependence of their resistivity ($\rho$(T, H)) is strikingly
dissimilar. While the $\rho$(T,H) of the 800 $^{0}$C film is comparable to that
of epitaxial samples, the lower growth temperature leads to a material which
undergoes insulator-to-metal transition at a temperature (T$_{P}$ $\approx$ 170
K) much lower than T$_C$. At T $\ll$ T$_P$, the resistivity is characterized by
a minimum followed by ln $\emph{T}$ divergence at still lower temperatures. The
high negative magnetoresistance ($\approx$ 20$%$) and ln $\emph{T}$ dependence
below the minimum are explained on the basis of Kondo-type scattering from
blocked Mn-spins in the intergranular material. Further, a striking feature of
the T$_D$ = 700 $^{0}$C film is its two orders of magnitude larger anisotropic
magnetoresistance (AMR) as compared to the AMR of epitaxial films. We attribute
it to unquenching of the orbital angular momentum of 3d electrons of Mn ions in
the intergranular region where crystal field is poorly defined. | 0905.1306v1 |
2009-12-27 | Topological Insulator Nanowires and Nanoribbons | Recent theoretical calculations and photoemission spectroscopy measurements
on the bulk Bi2Se3 material show that it is a three-dimensional topological
insulator possessing conductive surface states with nondegenerate spins,
attractive for dissipationless electronics and spintronics applications.
Nanoscale topological insulator materials have a large surface-to-volume ratio
that can manifest the conductive surface states and are promising candidates
for devices. Here we report the synthesis and characterization of high quality
single crystalline Bi2Se3 nanomaterials with a variety of morphologies. The
synthesis of Bi2Se3 nanowires and nanoribbons employs Au-catalyzed
vapor-liquid-solid (VLS) mechanism. Nanowires, which exhibit rough surfaces,
are formed by stacking nanoplatelets along the axial direction of the wires.
Nanoribbons are grown along [11-20] direction with a rectangular cross-section
and have diverse morphologies, including quasi-one-dimensional, sheetlike,
zigzag and sawtooth shapes. Scanning tunneling microscopy (STM) studies on
nanoribbons show atomically smooth surfaces with ~ 1 nm step edges, indicating
single Se-Bi-Se-Bi-Se quintuple layers. STM measurements reveal a honeycomb
atomic lattice, suggesting that the STM tip couples not only to the top Se
atomic layer, but also to the Bi atomic layer underneath, which opens up the
possibility to investigate the contribution of different atomic orbitals to the
topological surface states. Transport measurements of a single nanoribbon
device (four terminal resistance and Hall resistance) show great promise for
nanoribbons as candidates to study topological surface states. | 0912.5045v1 |
2010-06-02 | Antiferromagnetic Mott insulating state in single crystals of the hexagonal lattice material Na2IrO3 | We have synthesized single crystals of Na_2IrO_3 and studied their structure,
transport, magnetic, and thermal properties using powder x-ray diffraction
(PXRD), electrical resistivity, isothermal magnetization M versus magnetic
field H, magnetic susceptibility \chi versus temperature T, and heat capacity C
versus T measurements. Na_2IrO_3 crystallizes in the monoclinic \emph{C2/c}
(No. 15) type structure which is made up of Na and NaIr_2O_6 layers alternately
stacked along the c axis. The \chi(T) data show Curie-Weiss behavior at high T
> 200K 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 large Weiss temperature \theta = -
116(3)K indicates substantial antiferromagnetic interactions between these
S_eff = 1/2, Ir^4+ moments. Sharp anomalies in \chi(T) and C(T) data indicate
that Na_2IrO_3 undergoes a transition into a long-range antiferromagnetically
ordered state below T_N = 15 K. The magnetic entropy at T_N is only about 20%
of what is expected for S_eff = 1/2 moment ordering. The reduced entropy and
the small ratio T_N/\theta \approx 0.13 suggest geometrical magnetic
frustration and/or low-dimensional magnetic interactions in Na_2IrO_3. In plane
resistivity measurements show insulating behavior. This together with the local
moment magnetism indicates that bulk Na_2IrO_3 is a Mott insulator. | 1006.0437v1 |
2010-11-02 | Graphene: from materials science to particle physics | Since its discovery in 2004, graphene, a two-dimensional hexagonal carbon
allotrope, has generated great interest and spurred research activity from
materials science to particle physics and vice versa. In particular, graphene
has been found to exhibit outstanding electronic and mechanical properties, as
well as an unusual low-energy spectrum of Dirac quasiparticles giving rise to a
fractional quantum Hall effect when freely suspended and immersed in a magnetic
field. One of the most intriguing puzzles of graphene involves the
low-temperature conductivity at zero density, a central issue in the design of
graphene-based nanoelectronic components. While suspended graphene experiments
have shown a trend reminiscent of semiconductors, with rising resistivity at
low temperatures, most theories predict a constant or even decreasing
resistivity. However, lattice field theory calculations have revealed that
suspended graphene is at or near the critical coupling for excitonic gap
formation due to strong Coulomb interactions, which suggests a simple and
straightforward explanation for the experimental data. In this contribution we
review the current status of the field with emphasis on the issue of gap
formation, and outline recent progress and future points of contact between
condensed matter physics and Lattice QCD. | 1011.0643v1 |
2013-03-04 | Statistical Study of Deep Sub-Micron Dual-Gated Field-Effect Transistors on Monolayer CVD Molybdenum Disulfide Films | Monolayer Molybdenum Disulfide (MoS2) with a direct band gap of 1.8 eV is a
promising two-dimensional material with a potential to surpass graphene in next
generation nanoelectronic applications. In this letter, we synthesize monolayer
MoS2 on Si/SiO2 substrate via chemical vapor deposition (CVD) method and
comprehensively study the device performance based on dual-gated MoS2
field-effect transistors. Over 100 devices are studied to obtain a statistical
description of device performance in CVD MoS2. We examine and scale down the
channel length of the transistors to 100 nm and achieve record high drain
current of 62.5 mA/mm in CVD monolayer MoS2 film ever reported. We further
extract the intrinsic contact resistance of low work function metal Ti on
monolayer CVD MoS2 with an expectation value of 175 {\Omega}.mm, which can be
significantly decreased to 10 {\Omega}.mm by appropriate gating. Finally,
field-effect mobilities ({\mu}FE) of the carriers at various channel lengths
are obtained. By taking the impact of contact resistance into account, an
average and maximum intrinsic {\mu}FE is estimated to be 13.0 and 21.6 cm2/Vs
in monolayer CVD MoS2 films, respectively. | 1303.0776v1 |
2014-10-17 | Anisotropic strain in SmSe and SmTe: implications for electronic transport | Mixed valence rare-earth samarium compounds SmX (X=Se,Te) have been recently
proposed as candidate materials for use in high-speed, low-power digital
switches driven by stress induced changes of resistivity. At room temperature
these materials exhibit a pressure driven insulator-to-metal transition with
resistivity decreasing by up to 7 orders of magnitude over a small pressure
range. Thus, the application of only a few GPa's to the piezoresistor (SmX)
allows the switching device to perform complex logic. Here we study from first
principles the electronic properties of these compounds under uniaxial strain
and discuss the consequences on carrier transport. The changes in the band
structure show that the piezoresistive response is mostly governed by the
reduction of band gap with strain. Furthermore, it becomes optimal when the
Fermi level is pinned near the localized valence band. The piezoresistive
effect under uniaxial strain which must be taken into account in thin films and
other systems with reduced dimensionality is also quantified. Under uniaxial
strain we find that the piezoresistive response can be substantially larger
than in the isotropic case. Analysis of complex band structure of SmSe yields a
tunneling length of the order of 1 nm. The results suggest that the conduction
mechanism governing the piezoresistive effect in bulk, i.e.~thermal promotion
of electrons, should still be dominant in few-nanometer-thick films. | 1410.4740v1 |
2015-08-19 | Independent tuning of electronic properties and induced ferromagnetism in topological insulators with heterostructure approach | The quantum anomalous Hall effect (QAHE) has been recently demonstrated in
Cr- and V-doped three-dimensional topological insulators (TIs) at temperatures
below 100 mK. In those materials, the spins of unfilled d-electrons in the
transition metal dopants are exchange coupled to develop a long-range
ferromagnetic order, which is essential for realizing QAHE. However, the
addition of random dopants does not only introduce excess charge carriers that
require readjusting the Bi/Sb ratio, but also unavoidably introduces
paramagnetic spins that can adversely affect the chiral edge transport in QAHE.
In this work, we show a heterostructure approach to independently tune the
electronic and magnetic properties of the topological surface states in
(BixSb1-x)2Te3 without resorting to random doping of transition metal elements.
In heterostructures consisting of a thin (BixSb1-x)2Te3 TI film and yttrium
iron garnet (YIG), a high Curie temperature (~ 550 K) magnetic insulator, we
find that the TI surface in contact with YIG becomes ferromagnetic via
proximity coupling which is revealed by the anomalous Hall effect (AHE). The
Curie temperature of the magnetized TI surface ranges from 20 to 150 K but is
uncorrelated with the Bi fraction x in (BixSb1-x)2Te3. In contrast, as x is
varied, the AHE resistivity scales with the longitudinal resistivity. In this
approach, we decouple the electronic properties from the induced ferromagnetism
in TI. The independent optimization provides a pathway for realizing QAHE at
higher temperatures, which is important for novel spintronic device
applications. | 1508.04719v1 |
2016-11-08 | Superconductivity Induced by High Pressure in Weyl Semimetal TaP | Weyl semimetal defines a material with three dimensional Dirac cones which
appear in pair due to the breaking of spatial inversion or time reversal
symmetry. Superconductivity is the state of quantum condensation of paired
electrons. Turning a Weyl semimetal into superconducting state is very
important in having some unprecedented discoveries. In this work, by doing
resistive measurements on a recently recognized Weyl semimetal TaP under
pressure up to about 100 GPa, we observe superconductivity at about 70 GPa. The
superconductivity retains when the pressure is released. The systematic
evolutions of resistivity and magnetoresistance with pressure are well
interpreted by the relative shift between the chemical potential and paired
Weyl points. Calculations based on the density functional theory also
illustrate the structure transition at about 70GPa, the phase at higher
pressure may host superconductivity. Our discovery of superconductivity in TaP
by pressure will stimulate further study on superconductivity in Weyl
semimetals. | 1611.02548v1 |
2017-02-15 | On Ni-Sb-Sn based skutterudites | Novel filled skutterudites EpyNi4Sb12-xSnx (Ep = Ba and La) have been
prepared by arc melting followed by annealing at 250C, 350C and 450C up to 30
days in sealed quartz vials. A maximum filling level of y = 0.93 and y = 0.65
was achieved for the Ba and La filled skutterudite, respectively. Single-phase
samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and
Ba0.92Ni4Sb6.7Sn5.3 were employed for measurements of the physical properties
i.e. temperature dependent electrical resistivity, Seebeck coefficient and
thermal conductivity.
Resistivity data showed a crossover from metallic to semiconducting
behaviour. The corresponding gap width was extracted from maxima in the Seebeck
coefficient data as a function of temperature. Temperature dependent single
crystal X-ray structure analyses (at 100 K, 200 K and 300 K) revealed the
thermal expansion coefficients, Einstein and Debye temperatures for two
selected samples Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data
compare well with Debye temperatures from measurements of specific heat (4.4 K
< T < 200 K).
Several mechanical properties were measured and evaluated. Thermal expansion
coefficients are 11.8.10-6 K-1 for Ni4Sb8.2Sn3.8 to 13.8.10-6 K-1 for
Ba0.92Ni4Sb6.7Sn5.3. Room temperature Vicker's hardness values (up to a load of
24.5 mN) vary within the range of 2.6 GPa to 4.7 GPa. Severe plastic
deformation (SPD) via high-pressure torsion (HPT) was used to introduce
nanostructuring. Physical properties before and after HPT were compared,
showing no significant effect on the material's thermoelectric behaviour. | 1702.04654v1 |
2018-04-13 | Tuning spin one channel to exotic orbital two-channel Kondo effect in ferrimagnetic composites of LaNiO3 and CoFe2O4 | We report the tuning from spin one channel (1CK) to orbital two-channel Kondo
(2CK) effect by varying CoFe2O4 (CFO) content in the composites with LaNiO3
(LNO) along with the presence of ferrimagnetism. Although there is no signature
of resistivity upturn in case of pure LNO, all the composites exhibit a
distinct upturn in the temperature range 30-80 K. For composite with lower
percentage of CFO (10 %), the electron spin plays the key role in the emergence
of resistivity upturn which is affected by external magnetic field. On the
other hand, when the CFO content is increased (15%), the upturn shows strong
robustness against high magnetic field (14 T) and a crossover in temperature
variation from lnT to T^1/2 at the Kondo temperature, indicating the appearance
of orbital 2CK effect. The orbital 2CK effect is originated due to the
scattering of conduction electrons from the structural two-level systems which
is created at the interfaces between the two phases (LNO and CFO) of different
crystal structures as well as inside the crystal planes. A negative
magnetoresistance (MR) is observed at low temperature (< 30 K) for composites
containing both lower (10 %) and higher percentage (15 %) of CFO. We have
analyzed the negative MR using Khosla and Fisher semi-empirical model based on
spin dependent scattering of conduction electrons from localized spins. | 1804.04796v1 |
2018-06-20 | Tunable disorder and localization in the rare-earth nickelates | The rare-earth nickelates are a rich playground for transport properties,
known to host non-Fermi liquid character, resistance saturation and
metal-insulator transitions. We report a study of transport in LaNiO3 in the
presence of tunable disorder induced by irradiation. While pristine LaNiO3
samples are metallic, highly irradiated samples show insulating behaviour at
all temperatures. Using irradiation fluence as a tuning handle, we uncover an
intermediate region hosting a metal-insulator transition. This transition falls
within the Mott-Ioffe-Regel regime wherein the mean free path is comparable to
lattice spacing. In the high temperature metallic regime, we find a transition
from non-Fermi liquid to a Fermi-liquid-like character. On the insulating side
of the metal-insulator transition, we find behaviour that is consistent with
weak localization. This is reflected in magnetoresistance that scales with the
square of the field and in resistivity. In the highly irradiated insulating
samples, we find good agreement with variable range hopping, consistent with
Anderson localization. We find qualitatively similar behaviour in thick PrNiO3
films as well. Our results demonstrate that ion irradiation can be used to
tailor transport, serving as an excellent tool to study the physics of
localization. | 1806.07986v1 |
2019-09-04 | Exploring Disorder in the Spin Gapless Semiconductor Mn$_2$CoAl | Since the prediction of spin-gapless semiconducting behaviour in the Heusler
compound Mn$_2$CoAl, evidence of spin-gapless behaviour in thin films has
typically been inferred from magnetotransport measurements. The spin gapless
state is however fragile, and further, band structure calculations indicate
that even a small amount of atomic disorder may destroy it. To explore the
impact of disorder on the properties of Mn$_2$CoAl, we have undertaken an
experimental study of the structural, magnetotransport and optical properties
from the far infrared to the UV, on DC magnetron sputtered Mn$_2$CoAl thin
films. A very short mean free path, of the order of a lattice spacing, is
extracted from the DC transport data. A room temperature resistivity of 200
$\mu$$\Omega$cm along with a small and negative temperature coefficient of
resistance between 4 and 400 K was measured. We note that parameters of this
magnitude are often observed in disordered metals. We find this behaviour is
well described by a weak localisation model, a result that is supported by a
large Drude contribution to the optical response, where a high scattering rate
is derived, which is equal to the value derived from the DC conductivity and
Hall effect data. We also note the strong similarities between the
magnetotransport behaviour reported for Mn$_2$CoAl films in the literature,
including ours. We conclude that, based on comparisons between the experimental
data, and recent band structure calculations that explicitly include disorder,
as-prepared Mn$_2$CoAl films are best described as a disordered metal, rather
than a spin gapless semiconductor. | 1909.02153v1 |
2019-07-10 | Electronic Transport Evidence for Topological Nodal-Line Semimetals of ZrGeSe single crystals | Although the band topology of ZrGeSe has been studied via magnetic torque
technique, the electronic transport behaviors related to the relativistic
Fermions in ZrGeSe are still unknown. Here, we first report systematic
electronic transport properties of high-quality ZrGeSe single crystals under
magnetic fields up to 14 T. Resistivity plateaus of temperature dependent
resistivity curves both in the presence and absence of magnetic fields as well
as large, non-saturating magnetoresistance in low-temperature region were
observed. By analyzing the temperature- and angular-dependent Shubnikov-de Haas
oscillations and fitting it via the Lifshitz-Kosevich (LK) formula with the
Berry phase being taken into account, we proved that Dirac fermions dominate
the electronic transport behaviors of ZrGeSe and the presence of non-trivial
Berry phase. First principles calculations demonstrate that ZrGeSe possesses
Dirac bands and normal bands near Fermi surface, resulting in the observed
magnetotransport phenomena. These results demonstrate that ZrGeSe is a
topological nodal-line semimetal, which provides a fundamentally important
platform to study the quantum physics of topological semimetals. | 1907.04762v1 |
2019-12-06 | Correlated Insulating States and Transport Signature of Superconductivity in Twisted Trilayer Graphene Moiré of Moiré Superlattices | Layers of two-dimensional materials stacked with a small twist-angle give
rise to beating periodic patterns on a scale much larger than the original
lattice, referred to as a moir\'e superlattice. When the stacking involves more
than two layers with independent twist angles between adjacent layers, it
generates moir\'e of moir\'e superlattices, with multiple length scales that
control the system's behavior. Here we demonstrate these effects of a
high-order moir\'e superlattice in twisted trilayer graphene with two
consecutive small twist angles. We report correlated insulating states near the
half filling of the moir\'e of moir\'e superlattice at an extremely low carrier
density (~1010 cm-2), near which we also report a zero-resistance transport
behavior typically expected in a 2D superconductor. Moreover, the temperature
dependence of the measured resistances at full-occupancy (v = -4 and v = 4)
states are semi-metallic, distinct from the insulating behavior of twisted
bilayer systems, providing the first demonstration of emergent correlated
transport behaviors from continuous, non-isolated higher-order moir\'e flat
bands. Our findings shed new insights into the microscopic mechanisms of
moir\'e correlated states and provide the impetus for future studies on this
material platform, such as the demonstration of phase coherence and
Meissner-like effect. | 1912.03375v2 |
2020-01-14 | Heavy non-degenerate electrons in doped strontium titanate | Room-temperature metallicity of lightly doped SrTiO$_3$ is puzzling, because
the combination of mobility and the effective mass would imply a mean-free-path
(mfp) below the Mott Ioffe Regel (MIR) limit and a scattering time shorter than
the Planckian time ($\tau_P=\hbar/k_BT$). We present a study of electric
resistivity, Seebeck coefficient and inelastic neutron scattering extended to
very high temperatures, which deepens the puzzle. Metallic resistivity persists
up to 900 K and is accompanied by a large Seebeck coefficient whose magnitude
(as well as its temperature and doping dependence) indicates that carriers are
becoming heavier with rising temperature. Combining this with neutron
scattering data, we find that between 500 K and 900 K, the Bohr radius and the
electron wave-length become comparable to each other and twice the lattice
parameter. According to our results, between 100 K and 500 K, metallicity is
partially driven by temperature-induced amplification of the carrier mass. We
contrast this mass amplification of non-degenerate electrons with the
better-known case of heavy degenerate electrons. Above 500 K, the
mean-free-path continues to shrink with warming in spite of becoming shorter
than both the interatomic distance and the thermal wavelength of the electrons.
The latter saturates to twice the lattice parameter. Available theories of
polaronic quasi-particles do not provide satisfactory explanation for our
observations. | 2001.04668v4 |
2021-06-21 | Three-dimensional quasi-quantized Hall insulator phase in SrSi2 | In insulators, the longitudinal resistivity becomes infinitely large at zero
temperature. For classic insulators, the Hall conductivity becomes zero at the
same time. However, there are special systems, such as two-dimensional quantum
Hall isolators, in which a more complex scenario is observed at high magnetic
fields. Here, we report experimental evidence for a quasi-quantized Hall
insulator in the quantum limit of the three-dimensional semimetal SrSi2. Our
measurements reveal a magnetic field-range, in which the longitudinal
resistivity diverges with decreasing temperature, while the Hall conductivity
approaches a quasi-quantized value that is given only by the conductance
quantum and the Fermi wave vector in the field-direction. The quasi-quantized
Hall insulator appears in a magnetic-field induced insulating ground state of
three-dimensional materials and is deeply rooted in quantum Hall physics. | 2106.11329v1 |
2021-07-05 | Quantum anomalous Hall effect from intertwined moiré bands | Electron correlation and topology are two central threads of modern condensed
matter physics. Semiconductor moir\'e materials provide a highly tunable
platform for studies of electron correlation. Correlation-driven phenomena,
including the Mott insulator, generalized Wigner crystals, stripe phases and
continuous Mott transition, have been demonstrated. However, nontrivial band
topology has remained elusive. Here we report the observation of a quantum
anomalous Hall (QAH) effect in AB-stacked MoTe2/WSe2 moir\'e heterobilayers.
Unlike in the AA-stacked structures, an out-of-plane electric field controls
not only the bandwidth but also the band topology by intertwining moir\'e bands
centered at different high-symmetry stacking sites. At half band filling,
corresponding to one particle per moir\'e unit cell, we observe quantized Hall
resistance, h/e2 (with h and e denoting the Planck's constant and electron
charge, respectively), and vanishing longitudinal resistance at zero magnetic
field. The electric-field-induced topological phase transition from a Mott
insulator to a QAH insulator precedes an insulator-to-metal transition;
contrary to most known topological phase transitions, it is not accompanied by
a bulk charge gap closure. Our study paves the path for discovery of a wealth
of emergent phenomena arising from the combined influence of strong correlation
and topology in semiconductor moir\'e materials. | 2107.01796v1 |
2021-10-01 | Gate-tunable Intrinsic Anomalous Hall Effect in Epitaxial MnBi2Te4 Films | Anomalous Hall effect (AHE) is an important transport signature revealing
topological properties of magnetic materials and their spin textures. Recently,
antiferromagnetic MnBi2Te4 has been demonstrated to be an intrinsic magnetic
topological insulator that exhibits quantum AHE in exfoliated nanoflakes.
However, its complicated AHE behaviors may offer an opportunity for the
unexplored correlation between magnetism and band structure. Here, we show the
Berry curvature dominated intrinsic AHE in wafer-scale MnBi2Te4 thin films. By
utilizing a high-dielectric SrTiO3 as the back-gate, we unveil an ambipolar
conduction and electron-hole carrier (n-p) transition in ~7 septuple layer
MnBi2Te4. A quadratic relation between the saturated AHE resistance and
longitudinal resistance suggests its intrinsic AHE mechanism. For ~3 septuple
layer MnBi2Te4, however, the AHE reverses its sign from pristine negative to
positive under the electric-gating. The first-principles calculations
demonstrate that such behavior is due to the competing Berry curvature between
polarized spin-minority-dominated surface states and spin-majority-dominated
inner-bands. Our results shed light on the physical mechanism of the
gate-tunable intrinsic AHE in MnBi2Te4 thin films and provide a feasible
approach to engineering its AHE. | 2110.00540v1 |
2021-12-23 | Impact of the superconductors properties on the measurement sensitivity of resonant-based axion detectors | Axions, hypothetical particles theorized to solve the strong CP-problem, are
presently being considered as strong candidates as cold dark matter
constituents. The signal power of resonant-based axion detectors, known as
haloscopes, is directly proportional to their quality factor $Q$. In this
paper, the impact of the use of superconductors in the performances of the
haloscopes is studied by evaluating the obtainable $Q$. In particular, the
surface resistance $R_s$ of NbTi, Nb$_3$Sn, YBa$_2$Cu$_3$O$_{7-\delta}$ and
FeSe$_{0.5}$Te$_{0.5}$ is computed in the frequency, magnetic field and
temperature ranges of interest, starting from the measured vortex motion
complex resistivity and screening lengths of these materials. From $R_s$ the
quality factor $Q$ of a cylindrical haloscope with copper conical bases and
superconductive lateral wall, operating with the TM$_{010}$ mode, is evaluated
and used to perform a comparison of the performances of the different
materials. Both YBa$_2$Cu$_3$O$_{7-\delta}$ and FeSe$_{0.5}$Te$_{0.5}$ are
shown to improve the measurement sensitivity by almost an order of magnitude
with respect to a whole Cu cavity, while NbTi is shown to be suitable only at
lower frequencies (<10 GHz). Nb$_3$Sn can give an intermediate improvement in
the whole spectrum of interest. | 2112.12775v1 |
2022-01-28 | Substitutional Doped GeSe: Tunable Oxidative States with Strain Engineering | Layered chalcogenide materials have a wealth of nanoelectronics applications
like resistive switching and energy-harvesting such as photocatalyst owing to
rich electronic, orbital, and lattice excitations. In this work, we explore
monochalcogenide germanium selenide GeSe with respect to substitutional doping
with 13 metallic cations by using first-principles calculations. Typical
dopants including s-shell (alkali elements Li and Na), p-shell (Al, Pb and Bi),
3d (Fe, Cu, Co and Ni), 4d (Pd and Ag) and 5d (Au and Pt) elements are
systematically examined. Amongst all the cationic dopants, Al with the highest
oxidation states, implying a high mobility driven by electric field, and
Al-doped GeSe may be a promising candidate for novel resistive switching
devices. We show that there exist many localized induced states in the band gap
of GeSe upon doping Fe, Co, or Ni, while for Cu, Ag, and Au cases there is no
such states in the gap. The Ag and Cu are + 0.27 and + 0.35 charged
respectively and the positive charges are beneficial for field-driven motion in
GeSe. In contrast, Au is slightly negatively charged renders Au-doped GeSe a
promising photocatalyst and enhanced surface plasmon. Moreover, we explore the
coexistence of dopant and strain in GeSe and find dynamical adjustments of
localized states in GeSe with levels successive shifting upward/downward with
strain. This induces dynamic oxidative states of the dopants under strain which
should be quite popular in composites where motion of metal adatoms causes
significant deformation. | 2201.11890v1 |
2022-05-24 | Quantum hybridization negative differential resistance from non-toxic halide perovskite nanowire heterojunctions and its strain control | While low-dimensional organometal halide perovskites are expected to open up
new opportunities for a diverse range of device applications, like in their
bulk counterparts, the toxicity of Pb-based halide perovskite materials is a
significant concern that hinders their practical use. We recently predicted
that lead triiodide (PbI$_3$) columns de-rived from trimethylsulfonium (TMS)
lead triiodide (CH$_3$)$_3$SPbI$_3$ (TMSPbI$_3$) by stripping off TMS ligands
should be semimetallic, and additionally ultrahigh negative differential
resistance (NDR) can arise from the heterojunction composed of a TMSPbI$_3$
channel sandwiched by PbI$_3$ electrodes. Herein, we computationally explore
whether similar material and device characteristics can be obtained from other
one-dimensional halide perovskites based on non-Pb metal elements, and in doing
so deepen the understanding of their mechanistic origins. First, scanning
through several candidate metal halide inorganic frameworks as well as their
parental form halide perovskites, we find that the germanium triiodide
(GeI$_3$) column also assumes a semimetallic character by avoiding the Peierls
distortion. Next, adopting the bundled nanowire GeI$_3$-TMSGeI$_3$-GeI$_3$
junction configuration, we obtain a drastically high peak current density and
ultrahigh NDR at room temperature. Furthermore, the robustness and
controllability of NDR signals under strain are revealed, establishing its
potential for flexible electronics applications. It will be emphasized that,
despite the performance metrics notably enhanced over those from the
PbI$_3$-TMSPbI$_3$-PbI$_3$ case, these device characteristics still arise from
the identical quantum hybridization NDR mechanism. | 2205.11689v1 |
2022-06-06 | Anisotropic magnetic property of single crystals $R$V$_6$Sn$_6$ ($R$ = Y, Gd - Tm, Lu) | $R$V${_6}$Sn${_6}$ ($R$ = Y, Gd - Tm, Lu) single crystals are synthesized by
Sn-flux method and their physical properties are characterized by
magnetization, resistivity, and specific heat measurements. Powder X-ray
diffraction patterns of all samples can be well indexed with the hexagonal
HfFe$_6$Ge$_6$-type structure, where rare-earth atoms form hexagonal layers and
vanadium atoms form Kagome layers. At high temperatures, magnetic
susceptibility measurements of moment bearing rare-earths ($R$ = Gd - Tm)
follow Curie-Weiss behavior. Effective moments estimated from the
polycrystalline average of magnetic susceptibility curves are consistent with
the values for free $R^{3+}$ ion. Strong magnetic anisotropy due to crystalline
electric field effects is observed for moment bearing rare-earths, except
GdV$_6$Sn$_6$. The easy magnetization direction is determined to be $c$-axis
for $R$ = Tb - Ho and $ab$-plane for $R$ = Er, and Tm. The vanadium ions in
$R$V${_6}$Sn${_6}$ possess no magnetic moment. The compounds for $R$ = Y and Lu
exhibit typical characteristics of paramagnetic metals. At low temperatures,
the magnetic ordering is confirmed from magnetization, specific heat, and
resistivity: the highest $T_{N} = 4.9$~K for GdV$_6$Sn$_6$ and the lowest
$T_{N} = 2.3$~K for HoV$_6$Sn$_6$. No magnetic ordering is observed down to
1.8~K for $R$ = Er and Tm. A slight deviation of the magnetic ordering
temperature from the de Gennes scaling suggests the dominant
Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between rare-earth
moments in metallic $R$V${_6}$Sn${_6}$ compounds. | 2206.02924v1 |
2022-09-21 | Optical properties and carrier localization in the layered phosphide EuCd$_\mathbf{2}$P$_\mathbf{2}$ | The temperature dependence of the complex optical properties of the layered
phosphide material EuCd$_2$P$_2$ have been measured over a wide frequency range
above and below $T_{\rm N} \simeq 11.5$ K for light polarized in the $a-b$
planes. At room temperature, the optical conductivity is well described by a
weak free-carrier component with a Drude plasma frequency of $\simeq 1100$
cm$^{-1}$ and a scattering rate of $1/\tau_D\simeq 700$ cm$^{-1}$, with the
onset of interband absorptions above $\simeq 2000$ cm$^{-1}$. Two
infrared-active $E_u$ modes are observed at $\simeq\,$89 and 239 cm$^{-1}$. As
the temperature is reduced the scattering rate decreases and the low-frequency
conductivity increases slightly; however, below $\simeq 50$ K the conductivity
decreases until at the resistivity maximum at $\simeq 18$ K (just below
$2T_{\rm N}$) the spectral weight associated with free carriers is transferred
to a localized excitation at $\simeq 500$ cm$^{-1}$. Below $T_{\rm N}$,
metallic behavior is recovered. Interestingly, the $E_u$ modes are largely
unaffected by these changes, with only the position of the high-frequency mode
showing any signs of anomalous behavior. While several scenarios are
considered, the prevailing view is that the resistivity maximum and subsequent
carrier localization is due to the formation of ferromagnetic domains below
$\simeq 2T_{\rm N}$ that result in spin-polarized clusters due to spin-carrier
coupling [1]. | 2209.10606v2 |
2022-10-14 | Anti-site disorder and Berry curvature driven anomalous Hall effect in spin gapless semiconducting Mn2CoAl Heusler compound | Spin gapless semiconductors exhibit a finite band gap for one spin channel
and closed gap for other spin channel, emerged as a new state of magnetic
materials with a great potential for spintronic applications. The first
experimental evidence for the spin gapless semiconducting behavior was observed
in an inverse Heusler compound Mn2CoAl. Here, we report a detailed
investigation of the crystal structure and anomalous Hall effect in the Mn2CoAl
using experimental and theoretical studies. The analysis of the high-resolution
synchrotron x-ray diffraction data shows anti-site disorder between Mn and Al
atoms within the inverse Heusler structure. The temperature-dependent
resistivity shows semiconducting behavior and follows Mooijs criteria for
disordered metal. Scaling behavior of the anomalous Hall resistivity suggests
that the anomalous Hall effect in the Mn2CoAl is primarily governed by
intrinsic mechanism due to the Berry curvature in momentum space. The
experimental intrinsic anomalous Hall conductivity (AHC) is found to be 35
S/cm, which is considerably larger than the theoretically predicted value for
ordered Mn2CoAl. Our first-principle calculations conclude that the anti-site
disorder between Mn and Al atoms enhances the Berry curvature and hence the
value of intrinsic AHC, which is in a very well agreement with the experiment. | 2210.07668v1 |
2022-12-02 | FeRhCrSi: A new spin semimetal with room temperature spin-valve behavior | Spin semimetals are a recently discovered new class of spintronic materials,
which exhibit a band gap in one spin channel while a semimetallic feature in
the other and thus allows for tunable spin transport. Here, we present
experimental verification of spin semimetallic behavior in FeRhCrSi, a
quaternary Heusler alloy with saturation moment 2 $\mu_B$ and Curie temperature
$>$ 400 K. It crystallises in the L2$_1$ structure with 50$\%$ antisite
disorder between Fe and Rh. Below 300 K, it shows a weakly temperature
dependent electrical resistivity with negative temperature coefficient,
indicating the normal semimetal or spin semimetal behavior. Anomalous
magnetoresistance data reveals dominant contribution from asymmetric part, a
clear signature of spin-valve nature, which is retained even at room
temperature. \textcolor{black}{The asymmetric part of magneto-resistance shows
an unusual increase with increasing temperature.} Hall measurements confirm the
anomalous nature of conductivity originating from the intrinsic Berry
curvature, with holes being the majority carriers. Ab-initio simulation
confirms a unique long-range ferrimagnetic ordering to be the ground state,
explaining the origin behind the unexpected low saturation moment. The
ferrimagnetic disordered structure confirms the spin semimetallic feature of
FeRhCrSi, as observed experimentally. | 2212.00924v2 |
2023-01-11 | Domain Wall-Magnetic Tunnel Junction Analog Content Addressable Memory Using Current and Projected Data | With the rise in in-memory computing architectures to reduce the
compute-memory bottleneck, a new bottleneck is present between analog and
digital conversion. Analog content-addressable memories (ACAM) are being
recently studied for in-memory computing to efficiently convert between analog
and digital signals. Magnetic memory elements such as magnetic tunnel junctions
(MTJs) could be useful for ACAM due to their low read/write energy and high
endurance, but MTJs are usually restricted to digital values. The spin orbit
torque-driven domain wall-magnetic tunnel junction (DW-MTJ) has been recently
shown to have multi-bit function. Here, an ACAM circuit is studied that uses
two domain wall-magnetic tunnel junctions (DW-MTJs) as the analog storage
elements. Prototype DW-MTJ data is input into the magnetic ACAM (MACAM) circuit
simulation, showing ternary CAM function. Device-circuit co-design is carried
out, showing that 8-10 weight bits are achievable, and that designing
asymmetrical spacing of the available DW positions in the device leads to
evenly spaced ACAM search bounds. Analyzing available spin orbit torque
materials shows platinum provides the largest MACAM search bound while still
allowing spin orbit torque domain wall motion, and that the circuit is
optimized with minimized MTJ resistance, minimized spin orbit torque material
resistance, and maximized tunnel magnetoresistance. These results show the
feasibility of using DW-MTJs for MACAM and provide design parameters. | 2301.04598v1 |
2023-04-26 | Microbial Corrosion Prevention by Citrobacter sp. Biofilms | Microbiologically influenced corrosion (MIC) compromises the integrity of
many technologically relevant metals. Protective coatings based on synthetic
materials pose potential environmental impacts. Here, we report a MIC resistant
coating based on a biofilm matrix of Citrobacter sp. strain MIC21 on underlying
copper (Cu) surfaces. Three identical corrosion cells varying in the type of
working electrode (annealed Cu, 29.5% coldworked, and 56.2% coldworked Cu) were
used. Graphite plate and Ag/AgCl served as counter and reference electrodes,
respectively. The working electrolyte was based on lactate-C media along with
an inocula consisting of Oleidesulfovibrio alaskensis strain G20 and
Citrobacter sp. strain MIC21. Passivating effect of the co-cultured biofilm
matrix was observed in the form of an ennoblement effect. Tests based on
sequencing, microscopy, and spectroscopy revealed the formation of a compact
biofilm matrix dominated by strain MIC21 cells, exopolymers, and insoluble
precipitates. This matrix displayed elastic modulus (a measure of rigidity) as
high as 0.8 Gpa and increased corrosion resistance by ~10-fold. Interestingly,
strain MIC21 has the capacity to inhibit the undesirable growth of aggressive
strain G20. Additional corrosion tests also substantiated the passivation
effects of strain MIC21. We provide mechanistic insight into the underlying
reasons responsible for corrosion prevention behavior of the biofilm matrix. | 2304.13862v1 |
2023-06-01 | Bulk conducting states of intrinsically doped Bi$_2$Se$_3$ | With a large band gap and a single Dirac cone responsible for the topological
surface states, Bi2Se3 is widely regarded as a prototypical 3D topological
insulator. Further applications of the bulk material has, however, been
hindered by inherent structural defects that donate electrons and make the bulk
conductive. Consequently, controlling these defects is of great interest for
future technological applications, and while past literature has focused on
adding external doping elements to the mixture, a complete study on undoped
Bi2Se3 was still lacking. In this work, we use the self-flux method to obtain
high-quality Bi2Se3 single-crystals in the entire concentration range available
on the phase-diagram for the technique. By combining basic structural
characterization with measurements of the resistivity, Hall effect and
Shubnikov-de Haas (SdH) quantum oscillations, the effects of these impurities
on the bulk transport are investigated in samples with electron densities
ranging from 10^17 cm^-3 to 10^19 cm^-3, from Se-rich to Bi-rich mixtures,
respectively, evidencing the transition into a degenerate semiconductor regime.
We find that electron-donor impurities, likely Se vacancies, unavoidably shift
the Fermi level up to 200 meV inside the conduction band. Other impurities,
like interstitial Bi and Se, are shown to play a significant role as scattering
centres, specially at low temperatures and in the decoherence of the SdH
oscillations. Previous open questions on Bi2Se3, such as the upturn in
resistivity below 30 K, the different scattering times in transport and quantum
oscillations, and the presence of additional low mobility bands, are addressed.
The results outlined here provide a concise picture on the bulk conducting
states in flux-grown Bi2Se3 single crystals, enabling better control of the
structural defects and electronic properties. | 2306.00827v1 |
2023-07-06 | Tunable magnetism and electron correlation in Titanium-based Kagome metals RETi3Bi4 (RE = Yb, Pr, and Nd) by rare-earth engineering | Rare-earth engineering is an effective way to introduce and tune the
magnetism in topological Kagome magnets, which has been acting as a fertile
platform to investigate the quantum interactions between geometry, topology,
spin, and correlation. Here we report the structure and properties of three
newly discovered Titanium-based Kagome metals RETi3Bi4 (RE = Yb, Pr, and Nd)
with various magnetic states. They crystalize in the orthogonal space group
Fmmm (No.69), where slightly distorted Ti Kagome lattice, RE triangular
lattice, Bi honeycomb and triangular lattices stack along the a axis. By
changing the rare earth atoms on RE zag-zig chains, the magnetism can be tuned
from nonmagnetic YbTi3Bi4 to short-range ordered PrTi3Bi4 (Tanomaly ~ 8.2 K),
and finally to ferromagnetic NdTi3Bi4 (Tc ~ 8.5 K). The measurements of
resistivity and specific heat capacity demonstrate an evolution of electron
correlation and density of states near the Fermi level with different rare
earth atoms. In-situ resistance measurements of NdTi3Bi4 under high pressure
further reveal a potential relationship between the electron correlation and
ferromagnetic ordering temperature. These results highlight RETi3Bi4 as another
family of topological Kagome magnets to explore nontrivial band topology and
exotic phases in Kagome materials. | 2307.02942v1 |
2023-09-23 | Three-dimensional graphene on a nano-porous 4H-SiC backbone: a novel material for food sensing applications | Sensors which are sensitive to volatile organic compounds and thus able to
monitor the conservation state of food, are precious because they work
non-destructively and allow to avoid direct contact with the food, ensuring
hygienic conditions. In particular, the monitoring of rancidity would solve a
widespread issue in food storage. The sensor discussed here is produced
utilizing a novel three-dimensional arrangement of graphene, which is grown on
a crystalline silicon carbide (SiC) wafer previously porousified by chemical
etching. This approach allows a very high surface-to.volume ratio. Furthermore,
the structure of the sensor surface features a large amount of edges, dangling
bounds, and active sites, which make the sensor, on a chemically robust
skeleton, chemically active, particularly to hydrogenated molecules. The
interaction of the sensor with such compounds is read out by measuring the
sensor resistance in a four wire configuration. The sensor performance has been
assessed on three hazelnut samples: sound hazelnuts, spoiled hazelnuts, and
stink bug hazelnuts. A resistance variation of about DeltaR = 0.13 (0.02) Ohm
between sound and damaged hazelnuts has been detected. Our measurements confirm
the ability of the sensor to discriminate between sound and damaged hazelnuts.
The sensor signal is stable for days, providing the possibility to use this
sensor for the monitoring of the storage state of fats and foods in general. | 2309.13431v1 |
2023-09-26 | On Hyperelastic Crease | We present analyses of crease-formation and stability criteria for
incompressible hyperelastic solids. A generic singular perturbation over a
laterally compressed half-space creates a far-field eigenmode of three
energy-release angular sectors separated by two energy-elevating sectors of
incremental deformation. The far-field eigenmode braces the energy-release
field of the surface flaw against the transition to a self-similar crease
field, and the braced-incremental-deformation (bid) field has a unique shape
factor that determines the creasing stability. The shape factor, which is
identified by two conservation integrals that represent a subsurface
dislocation in the tangential manifold, is a monotonically increasing function
of compressive strain. For Neo-Hookean material, when the shape factor is below
unity, the bid field is configurationally stable. When the compressive strain
is 0.356, the shape factor becomes unity, and the bid field undergoes a
higher-order transition to a crease field. At the crease-limit point, we have
two asymptotic solutions of the crease-tip folding field and the leading-order
far field with two scaling parameters, the ratio of which is determined by
matched asymptotes. Our analyses show that the surface is stable against
singular perturbation up to the crease limit point and becomes unstable beyond
the limit. However, the flat state is metastable against a regular perturbation
between the crease limit point and wrinkle critical point, which is a
first-order instability point. We introduced a novel finite element method for
simulating the bid field with a finite domain size. For Gent model, the
strain-stiffening alters the shape factor dependence on the compressive strain,
raising crease resistance. The new findings in crease mechanisms will help
study ruga mechanics of self-organization and design soft-material structures
for high crease resistance. | 2309.14626v1 |
2024-02-15 | Quantum Linear Magnetoresistance and Fermi Liquid Behavior in Kagome Metal Ni3In2S2 | Kagome metals gain attention as they manifest a spectrum of quantum
phenomena, including superconductivity, charge order, frustrated magnetism, and
intertwined correlated states of condensed matter. With regard to electronic
band structure, several of the them exhibit non-trivial topological
characteristics. Here, we present a thorough investigation on the growth and
the physical properties of single crystals of Ni3In2S2 which is established to
be a Dirac nodal line Kagome metal. Extensive characterization is attained
through temperature and field-dependent resistivity, angle-dependent
magnetoresistance and specific heat measurements. In most metals, the Fermi
liquid behaviour is mostly restricted to a narrow range of temperature. In
Ni3In2S2, this characteristic feature has been observed for an extensive
temperature range of 82 K. This is attributed to the strong electron-electron
correlation in the material. Specific heat measurements reveal a high
Kadowaki-Woods ratio which is in good agreement with strongly correlated
systems. Almost linear positive magnetoresistance follows the conventional
Kohler scaling which depicts the applicability of semi-classical theories. The
angle-dependent magneto-resistance been explained using the Voigt-Thomson
formula. Furthermore, de-Haas van Alphen oscillations are observed in
magnetization vs. magnetic field measurement which shed light on the
topological features in the Shandite Ni3In2S2. | 2402.10096v1 |
2022-11-28 | On the energy conversion efficiency of the bulk photovoltaic effect | The bulk photovoltaic effect (BPVE) leads to directed photo-currents and
photo-voltages in bulk materials. Unlike photo-voltages in p-n junction solar
cells that are limited by carrier recombination to values below the bandgap
energy of the absorbing material, the BPVE photo-voltages have been shown to
greatly exceed the bandgap energy. Therefore the BPVE is not subject to the
Shockley-Queisser limit for sunlight to electricity conversion in single
junction solar cells and experimental claims of efficiencies beyond this limit
have been made. Here, we show that BPVE energy conversion efficiencies are, in
practice, orders of magnitude below the Shockley-Queisser limit of single
junction solar cells and are subject to different, more stringent limits. The
name BPVE stands for two different fundamental effects, the shift current and
the injection current. In both of these, the voltage bias necessary to produce
electrical energy, accelerates both, intrinsic and photo-generated, carriers.
We discuss how energy conservation alone fundamentally limits the BPVE to a
bandgap-dependent value that exceeds the Shockley Queisser limit only for very
small bandgaps. Yet, small bandgap materials have a large number of intrinsic
carriers, leading to high conductivity which suppresses the photo-voltage. We
discuss further how slightly more stringent fundamental limits for injection
(ballistic) currents may be derived from the trade-off between high
resistivity, needed for a high voltage, and long ballistic transport length,
needed for a high current. We also explain how erroneous experimental and
theoretical claims of high efficiency have arisen. Finally, we calculate the
energy conversion efficiency for an example 2D material that has been suggested
as candidate material for high efficiency BPVE based solar cells and show that
the efficiency is very similar to the efficiency of known 3D materials. | 2211.15124v2 |
2016-07-06 | Thermal Resistances of Thin-Films of Small Molecule Organic Semiconductors | We have measured the thermal resistances of thin films of the small molecule
organic semiconductors bis(triisopropylsilylethynyl) pentacene (TIPS-pn),
bis(triethylsilylethynyl) anthradithiophene (TES-ADT) and difluoro
bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT). For each material,
several films of different thicknesses have been measured to separate the
effects of intrinsic thermal conductivity from interface thermal resistance.
For non-crystalline films of all three materials, with thicknesses ranging from
< 100 nm to > 4 microns, the thermal conductivities are similar to that of
polymers and over an order of magnitude smaller than that of the crystals,
reflecting the large reduction in phonon mean-free path in the films. Thin (<
205 nm) crystalline films of TES-ADT, prepared by vapor-annealing spin-cast
films, have also been measured, but for these the thermal resistances are
dominated by interface scattering. | 1607.01712v2 |
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