publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2019-11-18 | Comparison of screening for methicillin-resistant Staphylococcus aureus (MRSA) at hospital admission and discharge | Methicillin-resistant Staphylococcus aureus (MRSA) is a significant
contributor to the growing concern of antibiotic resistant bacteria, especially
given its stubborn persistence in hospitals and other health care facility
settings. In combination with this characteristic of S. aureus (colloquially
referred to as staph), MRSA presents an additional barrier to treatment and is
now believed to have colonized two of every 100 people worldwide. According to
the CDC, MRSA prevalence sits as high as 25-50% in countries such as the United
Kingdom and the United States. Given the resistant nature of staph as well as
its capability of evolving to compensate antibiotic treatment, controlling MRSA
levels is more a matter of precautionary and defensive measures. This study
examines the method of "search and isolation," which seeks to isolate MRSA
positive patients in a hospital so as to decrease infection potential. Although
this strategy is straightforward, the question of just whom to screen is of
practical importance. We compare screening at admission to screening at
discharge. To do this, we develop a mathematical model and use simulations to
determine MRSA endemic levels in a hospital with either control measure
implemented. We found that screening at discharge was the more effective method
in controlling MRSA endemicity, but at the cost of a greater number of isolated
patients. | 1911.07711v1 |
2020-07-02 | Bloch-Grüneisen temperature and universal scaling of normalized resistivity in doped graphene revisited | In this work, we resolved some controversial issues on the
Bloch-Gr\"{u}neisen (BG) temperature in doped graphene via analytical and
numerical calculations based on full inelastic electron-acoustic-phonon (EAP)
scattering rate and various approximation schemes. Analytic results for BG
temperature obtained by semi-inelastic (SI) approximation (which gives
scattering rates in excellent agreement with the full inelastic scattering
rates) are compared with those obtained by quasi-elastic (QE) approximation and
the commonly adopted value of $\Theta^{LA}_{F} = 2\hbar v_{LA} k_F/k_B$. It is
found that the commonly adopted BG temperature in graphene ($\Theta^{LA}_{F}$)
is about 5 times larger than the value obtained by the QE approximation and
about 2.5 times larger than that by the SI approximation, when using the
crossing-point temperature where low-temperature and high-temperature limits of
the resistivity meet. The corrected analytic relation based on SI approximation
agrees extremely well with the transition temperatures determined by fitting
the the low- and high-$T$ behavior of available experimental data of graphene's
resistivity. We also introduce a way to determine the BG temperature including
the full inelastic EAP scattering rate and the deviation of electron energy
from the chemical potential ($\mu$) numerically by finding the maximum of
$\partial \rho(\mu,T)/\partial T$. Using the analytic expression of
$\Theta_{BG,1}$ we can prove that the normalized resistivity defined as
$R_{1}=\rho(\mu,T)/\rho(\mu,\Theta_{BG,1})$ plotted as a function of
$(T/\Theta_{BG,1})$ is independent of the carrier density. Applying our results
to previous experimental data extracted shows a universal scaling behavior,
which is different from previous studies. | 2007.00839v1 |
2020-11-16 | Transition region from turbulent to dead zone in protoplanetary disks: local shearing box simulations | The dynamical evolution of protoplanetary disks is of key interest for
building a comprehensive theory of planet formation and to explain the
observational properties of these objects. Using the magnetohydrodynamics code
Athena++, with an isothermal shearing box setup, we study the boundary between
the active and dead zone, where the accretion rate changes and mass can
accumulate. We quantify how the turbulence level is affected by the presence of
a non uniform ohmic resistivity in the radial-x direction that leads to a
region of inhibited turbulence (or dead zone). Comparing the turbulent activity
to that of ideal simulations, the turbulence inhibited area shows density
fluctuations and magnetic activity at its boundaries, driven by energy
injection from the active (ideal) zone boundaries. We find magnetic dissipation
to be significantly stronger in the ideal regions, and the turbulence
penetration through the boundary of the dead zone is determined by the value of
the resistivity itself, through the ohmic dissipation process, though the
thickness of the transition does not play a significant role in changing the
dissipation. We investigate the 1D spectra along the shearing direction:
magnetic spectra appear flat at large scales both in ideal as well as resistive
simulations, though a Kolmogorov scaling over more than one decade persists in
the dead zone, suggesting the turbulent cascade is determined by the
hydrodynamics of the system: MRI dynamo action is inhibited where sufficiently
high resistivity is present. | 2011.08219v1 |
2021-10-21 | E-DPNCT: An Enhanced Attack Resilient Differential Privacy Model For Smart Grids Using Split Noise Cancellation | High frequency reporting of energy consumption data in smart grids can be
used to infer sensitive information regarding the consumer's life style and
poses serious security and privacy threats. Differential privacy (DP) based
privacy models for smart grids ensure privacy when analysing energy consumption
data for billing and load monitoring. However, DP models for smart grids are
vulnerable to collusion attack where an adversary colludes with malicious smart
meters and un-trusted aggregator in order to get private information from other
smart meters. We first show the vulnerability of DP based privacy model for
smart grids against collusion attacks to establish the need of a collusion
resistant model privacy model. Then, we propose an Enhanced Differential
Private Noise Cancellation Model for Load Monitoring and Billing for Smart
Meters (E-DPNCT) which not only provides resistance against collusion attacks
but also protects the privacy of the smart grid data while providing accurate
billing and load monitoring. We use differential privacy with a split noise
cancellation protocol with multiple master smart meters (MSMs) to achieve
colluison resistance. We did extensive comparison of our E-DPNCT model with
state of the art attack resistant privacy preserving models such as EPIC for
collusion attack. We simulate our E-DPNCT model with real time data which shows
significant improvement in privacy attack scenarios. Further, we analyze the
impact of selecting different sensitivity parameters for calibrating DP noise
over the privacy of customer electricity profile and accuracy of electricity
data aggregation such as load monitoring and billing. | 2110.11091v4 |
2022-05-10 | Disorder-enhanced effective masses and deviations from Matthiessen's rule in PdCoO$_2$ thin films | The observation of hydrodynamic transport in the metallic delafossite
PdCoO$_2$ has increased interest in this family of highly conductive oxides,
but experimental studies so far have mostly been confined to bulk crystals. In
this work, the development of high-quality thin films of PdCoO$_2$ has enabled
a thorough study of the conductivity as a function of film thickness using both
dc transport and time-domain THz spectroscopy. With increasing film thickness
from 12 nm to 102 nm, the residual resistivity decreases and we observe a large
deviation from Matthiessen's rule (DMR) in the temperature dependence of the
resistivity. We find that the complex THz conductivity is well fit by a single
Drude term. We fit the data to extract the spectral weight and scattering rate
simultaneously. The temperature dependence of the Drude scattering rate is
found to be nearly independent of the residual resistivity and cannot be the
primary mechanism for the observed DMR. Rather, we observe large changes in the
spectral weight as a function of disorder, changing by a factor of 1.5 from the
most disordered to least disordered films. We believe this corresponds to a
mass enhancement of $\geq 2$ times the value of the bulk effective mass which
increases with residual disorder. This suggests that the mechanism behind the
DMR observed in dc resistivity is primarily driven by changes in the electron
mass. We discuss the possible origins of this behavior including the
possibility of disorder-enhanced electron-phonon scattering, which can be
systematically tuned by film thickness. | 2205.05006v2 |
2022-08-05 | Hall effect in Poiseuille flow of two-dimensional electron fluid | The hydrodynamic regime of charge transport has been recently realized in
high-quality conductors. In the hydrodynamic as well as in the Ohmic regimes
the main part of the Hall resistance of a long sample is determined by the
balance between the Lorentz force and the electric force, acting on conduction
electrons. Experimentally observed deviations of the Hall resistance in
hydrodynamic samples from such the ''standard'' value are usually associated
with the Hall viscosity term in the Navier-Stokes equation. In this work we
theoretically study the Hall effect in a Poiseuille flow of a two-dimensional
electron fluid. We show that the near-edge semiballistic layers with the width
of the order of the inter-particle mean free path, which inevitably appear near
sample edges, give the contribution to the Hall resistance which is comparable
with the bulk contribution from the Hall viscosity. In this way, the measured
deviations of the Hall resistance from the ''standard'' one in hydrodynamic
samples by the usual contact techniques should be associated with both the Hall
viscosity in the bulk and the semiballistic effects in the near-edge layers | 2208.03032v1 |
2022-10-28 | Lattice effects on the physical properties of half doped perovskite ruthenates | We investigate the unusual phase transitions in SrRuO$_{3}$ and
Sr$_{0.5}$Ca$_{0.5}$Ru$_{1-x}$Cr$_{x}$O$_{3}$ (x=0,0.05 and 0.1) employing
x-ray diffraction, resistivity, magnetic studies and x-ray photoemission
spectroscopy. Our results show the compounds undergo crossover from $itinerant$
ferromagnetism to $localised$ ferromagnetism. The combined studies suggests Ru
and Cr to be in 4+ valence state. A Griffith phase and an enhancement in Curie
temperature (Tc) from 38 K to 107 K is observed with Cr doping. A shift in the
chemical potential towards the valence band is observed with Cr doping. In the
metallic samples, interestingly, a direct link between the resistivity and
orthorhombic strain is observed. Detailed studies in this direction will be
helpful to understand the nature of interactions and hence manoeuvre its
properties. In the non metallic samples, the resistivity is mainly governed by
disorder and electron-electron correlation effects. The value of the
resistivity for the 5% Cr doped sample suggests semi metallic behaviour.
Understanding its nature in detail using electron spectroscopic techniques
could unravel the possibility of its utility in high mobility transistors at
room temperature and its combined property with ferromagnetism will be helpful
in making spintronic devices. | 2210.16036v1 |
2022-12-05 | DeAR: A Deep-learning-based Audio Re-recording Resilient Watermarking | Audio watermarking is widely used for leaking source tracing. The robustness
of the watermark determines the traceability of the algorithm. With the
development of digital technology, audio re-recording (AR) has become an
efficient and covert means to steal secrets. AR process could drastically
destroy the watermark signal while preserving the original information. This
puts forward a new requirement for audio watermarking at this stage, that is,
to be robust to AR distortions. Unfortunately, none of the existing algorithms
can effectively resist AR attacks due to the complexity of the AR process. To
address this limitation, this paper proposes DeAR, a deep-learning-based audio
re-recording resistant watermarking. Inspired by DNN-based image watermarking,
we pioneer a deep learning framework for audio carriers, based on which the
watermark signal can be effectively embedded and extracted. Meanwhile, in order
to resist the AR attack, we delicately analyze the distortions that occurred in
the AR process and design the corresponding distortion layer to cooperate with
the proposed watermarking framework. Extensive experiments show that the
proposed algorithm can resist not only common electronic channel distortions
but also AR distortions. Under the premise of high-quality embedding
(SNR=25.86dB), in the case of a common re-recording distance (20cm), the
algorithm can effectively achieve an average bit recovery accuracy of 98.55%. | 2212.02339v4 |
2023-04-18 | Characterization of a Superconducting Microstrip Single-Photon Detector Shunted with an External Resistor | A superconducting microstrip single-photon detector (SMSPD) generally
requires a shunt resistor to avoid latching, caused by its high
current-carrying capacity and low kinetic inductance. Here, the effect of the
shunt resistor on the behaviors of microbridge SMSPDs was investigated. We
analyzed the change in equivalent switching current at different shunt
resistances in two ways and determined the operating current range using
intrinsic dark count rate (iDCR) curves. We observed that the reduction in
shunt resistance can increase the operating current range, which helps to
improve the internal detection efficiency (IDE) and reduce the iDCR. However,
the reduction in the shunt resistance can reduce the pulse amplitude and
increase the pulse decay time, which can degrade the timing jitter and count
rate performance of the SMSPD. The trends of the experimental results can be
qualitatively reproduced using a circuit model for an SMSPD with a shunt
resistor, which provides useful information for the selection of shunt
resistors. Furthermore, we report the improved detection performance of a
helium-ion-irradiated SMSPD shunted with a small resistance of 5.2 {\Omega}. We
observed a weak IDE saturation with a bias current at a wavelength up to 2000
nm and a nonlinear relation between detection current and photon energy. | 2304.08762v1 |
2023-05-18 | Fabrication of Al/AlOx/Al junctions with high uniformity and stability on sapphire substrates | Tantalum and aluminum on sapphire are widely used platforms for qubits of
long coherent time. As quantum chips scale up, the number of Josephson
junctions on Sapphire increases. Thus, both the uniformity and stability of the
junctions are crucial to quantum devices, such as scalable superconducting
quantum computer circuit, and quantum-limited amplifiers. By optimizing the
fabrication process, especially, the conductive layer during the electron beam
lithography process, Al/AlOx/Al junctions of sizes ranging from 0.0169 to 0.04
{\mu}m2 on sapphire substrates were prepared. The relative standard deviation
of room temperature resistances (RN) of these junctions is better than 1.7% on
15 mmx15 mm chips, and better than 2.66% on 2 inch wafers, which is the highest
uniformity on sapphire substrates has been reported. The junctions are robust
and stable in resistances as temperature changes. The resistances increase by
the ratio of 9.73% relative to RN as the temperature ramp down to 4K, and
restore their initial values in the reverse process as the temperature ramps
back to RT. After being stored in a nitrogen cabinet for 100 days, the
resistance of the junctions changed by1.16% in average. The demonstration of
uniform and stable Josephson junctions in large area paves the way for the
fabrication of superconducting chip of hundreds of qubits on sapphire
substrates. | 2305.10956v2 |
2023-06-21 | Coherent states and their superpositions (cat states) in microwave-induced resistance oscillations | We report a novel theoretical approach on the microwave-induced resistance
oscillations based on the coherent states of the quantum harmonic oscillator.
We first obtain an expression for the coherent states of driven-quantum
harmonic oscillators that are used, in the model of microwaveinduced electron
orbits, to calculate magnetoresistance under radiation. Thus, we find that the
principle of minimum uncertainty of coherent states, involving time and energy,
is at the heart of photo-oscillations and zero resistance states. Accordingly,
we are able to explain important experimental evidence of this remarkable
effect. Such as the physical origin of oscillations, their periodicity with the
inverse of the magnetic field, their peculiar minima and maxima positions and
the existence of zero resistance states. We apply our theory to the case of
ultra-high mobility samples where we appeal to the principle of quantum
superposition of coherent states and obtain that Schrodinger cat states (even
and odd coherent states) are key to explain magnetoresistance at these extreme
mobilities. With them we explain the, experimentally obtained,
magnetoresistance resonance peak shift to a magnetic field where the cyclotron
frequency equals half the radiation frequency. This effect is similar to the
one described in quantum optics as a second harmonic generation process. We
also explain the magnetoresistance collapse, that take place in the dark and
with light. This effect is known as giant negative magnetoresistance. We
generalize our results to study the case of a three-component or triangular
Schrodinger cat state. | 2306.12160v1 |
2023-08-28 | Research on the Influence of Underwater Environment on the Dynamic Performance of the Mechanical Leg of a Deep-sea Crawling and Swimming Robot | The performance of underwater crawling and adjustment of the body posture for
underwater manipulating of the deep-sea crawling and swimming robot (DCSR) is
directly influenced by the dynamic performance of the underwater mechanical
legs (UWML), as it serves as the executive mechanism of the DCSR. Compared with
the mechanical legs of legged robots working on land, the UWML of the DCSR not
only possesses the characteristics of the land used mechanical legs, but is
also affected by the influence of the deep-sea underwater working environment
(i.e., the hydrodynamic force, viscous resistance and dynamic seal resistance).
To reduce these influence, firstly, the hydrodynamic force of the UWML were
researched based on theory and experiment, and the hydrodynamic model was
established with the fitted hydrodynamic parameters. Secondly, the oil viscous
resistance and the dynamic seal resistance were studied experimentally, and the
change laws of both with respect to the joint speed and the ambient pressure
(depth of operation) were obtained. The results provide a basis for the
subsequent research on the structure optimization and high performance control
of the UWML and DCSR. | 2308.14393v1 |
2023-11-17 | Current manipulation of Giant tunneling altermagnetic resistance in collinear Antiferromagnetic RuO2/MgO/RuO2 sandwich structure | As an emerging non-volatile memory technology, magnetic random access memory
(MRAM) has key features and advantages including non-volatility, high speed,
endurance, low power consumption and radiation tolerance. Conventional MRAM
utilizes magnetic tunnel junctions (MTJs), which consist of two ferromagnetic
layers separated by an insulating tunnel barrier. The orientation of the
magnetic layers represents the binary data (0 or 1), and electrical resistance
changes depending on the relative orientation of these magnetic layers. Despite
these advancements, the quest for a swifter, more stable magneto-resistive
random-access memory paradigm persists. In this vein, we present a
groundbreaking development: room-temperature antiferromagnetic tunnel junctions
devoid of any net magnetic moment. Over 200% tunneling altermagnetic resistance
(TAR) ratio was measured at RuO2 (110)/MgO/RuO2 (110)/W structure, which is
achieved by changing the antiferromagnetic Neel vector of RuO2 with an ultralow
current density 2 MA*cm-2. | 2311.10288v2 |
2024-02-09 | Wellposedness of the electron MHD without resistivity for large perturbations of the uniform magnetic field | We prove the local wellposedness of the Cauchy problems for the electron
magnetohydrodynamics equations (E-MHD) without resistivity for possibly large
perturbations of nonzero uniform magnetic fields. While the local wellposedness
problem for (E-MHD) has been extensively studied in the presence of resistivity
(which provides dissipative effects), this seems to be the first such result
without resistivity. (E-MHD) is a fluid description of plasma in small scales
where the motion of electrons relative to ions is significant. Mathematically,
it is a quasilinear dispersive equation with nondegenerate but nonelliptic
second-order principal term. Our result significantly improves upon the
straightforward adaptation of the classical work of Kenig--Ponce--Rolvung--Vega
on the quasilinear ultrahyperbolic Schr\"odinger equations, as the regularity
and decay assumptions on the initial data are greatly weakened to the level
analogous to the recent work of Marzuola--Metcalfe--Tataru in the case of
elliptic principal term.
A key ingredient of our proof is a simple observation about the relationship
between the size of a symbol and the operator norm of its quantization as a
pseudodifferential operator when restricted to high frequencies. This allows us
to localize the (non-classical) pseudodifferential renormalization operator
considered by Kenig--Ponce--Rolvung--Vega, and produce instead a classical
pseudodifferential renormalization operator. We furthermore incorporate the
function space framework of Marzuola--Metcalfe--Tataru to the present case of
nonelliptic principal term. | 2402.06278v1 |
2024-03-21 | Aging suppression in Multistrip Multigap Resistive Plate Chambers for high counting rate experiments | A long term operation of Multi-Strip Multi-Gap Resistive Plate Chambers
(MSMGRPC) with gas mixtures based on C2H2F4 and SF6 leads to aging effects,
observed as depositions on the surface of the resistive electrodes. Moreover,
enhanced depositions and higher noise rates were evidenced around the nylon
spacers used for defining the gas gaps between the resistive electrodes. The
aging effects are reflected in an increase of the dark current and dark
counting rate, with negative impact on the long term performance of the chamber
and data volume in a free running readout mode operation. MSMGRPC prototypes
designed with a direct gas flow through the gas gaps and minimization of the
number of spacers in the active area were developed as mitigation solution.
Prototypes with this new design and different granularities were assembled
using fishing line as spacers and investigated for aging effects. Although a
significant reduction in the dark current and dark counting rate was evidenced,
dark counting rate localized around the fishing line spacers remains. In this
paper, a new generation of direct flow chambers based on discrete spacers is
presented. The results of their aging investigations show that, even at lower
gas flows, the aging effects become negligible. | 2403.14190v1 |
2006-03-20 | Unusual metamagnetism in CeIrIn$_5$ | We report a high field investigation (up to 45 T) of the metamagnetic
transition in CeIrIn$_5$ with resistivity and de-Haas-van-Alphen (dHvA) effect
measurements in the temperature range 0.03-1 K. As the magnetic field is
increased the resistivity increases, reaches a maximum at the metamagnetic
critical field, and falls precipitously for fields just above the transition,
while the amplitude of all measurable dHvA frequencies are significantly
attenuated near the metamagnetic critical field. However, the dHvA frequencies
and cyclotron masses are not substantially altered by the transition. In the
low field state, the resistivity is observed to increase toward low
temperatures in a singular fashion, a behavior that is rapidly suppressed above
the transition. Instead, in the high field state, the resistivity monotonically
increases with temperature with a dependence that is more singular than the
iconic Fermi-liquid, temperature-squared, behavior. Both the damping of the
dHvA amplitudes and the increased resistivity near the metamagnetic critical
field indicate an increased scattering rate for charge carriers consistent with
critical fluctuation scattering in proximity to a phase transition. The dHvA
amplitudes do not uniformly recover above the critical field, with some
hole-like orbits being entirely suppressed at high fields. These changes, taken
as a whole, suggest that the metamagnetic transition in CeIrIn$_5$ is
associated with the polarization and localization of the heaviest of
quasiparticles on the hole-like Fermi surface. | 0603490v2 |
2022-11-10 | T-linear resistivity, optical conductivity and Planckian transport for a holographic local quantum critical metal in a periodic potential | High $T_c$ cuprate strange metals are noted for a DC-resistivity that scales
linearly with $T$ from the onset of superconductivity to the crystal melting
temperature, indicative of a Planckian dissipation life time
$\tau_{\hbar}\simeq \hbar /(k_B T)$. At the same time, the optical conductivity
ceases to be of Drude form at high temperatures, suggesting a change of the
underlying dynamics that surprisingly leaves the $T$-linear DC-resistivity
unaffected. We use the AdS/CFT correspondence that describes strongly coupled,
densely entangled metals to study DC thermo-electrical transport and the
optical conductivities of the local quantum critical Gubser-Rocha holographic
strange metal in the presence of a lattice potential, a prime candidate to
compare with experiment. We find that the DC-resistivity is linear in $T$ at
low temperatures for a range of lattice strengths and wavevectors, even as it
transitions between different dissipative regimes. At weak lattice potential
the optical conductivity evolves with increasing temperature from a Drude form
to a bad-metal characterized by a mid-IR resonance without changing the DC
transport, similar to that seen in cuprate strange metals. This mid-IR peak and
its temperature evolution can be understood as a consequence of Umklapp
hydrodynamics: hydrodynamic perturbations are Bloch modes in the presence of a
lattice. At strong lattice potential an incoherent metal is realized instead
where momentum conservation no longer plays a role in transport. In this regime
the thermal diffusivity can be explained by Planckian dissipation originating
in universal microscopic chaos, similar to holographic metals with strong
homogeneous momentum relaxation. The charge diffusivity does not submit to this
chaos explanation, even though the continuing linear-in-$T$ DC resistivity
saturates to an apparent universal slope, numerically equal to a Planckian
rate. | 2211.05492v2 |
1998-05-20 | A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries | It has been observed that in bulk and polycrystalline thin films of collossal
magnetoresistive (CMR) materials the magnetoresistance follows a different
behaviour compared to single crystals or single crystalline films below the
ferromagnetic transition temperature Tc. In this paper we develop a
phenomenological model to explain the magnetic field dependence of resistance
in granular CMR materials taking into account the spin polarised tunnelling at
the grain boundaries. The model has been fitted to two systems, namely,
La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have
separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the
intergranular contribution to the magnetoresistance coming from spin polarised
tunnelling at the grain boundaries. It is observed that the temperature
dependence of the intrinsic contribution to the magnetoresistance in
La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all
values of field. | 9805258v1 |
2000-11-21 | Anomalous NMR Spin-Lattice Relaxation in SrB_{6} and Ca_{1-x}La_{x}B_{6} | We report the results of {11}B nuclear magnetic resonance (NMR) measurements
of SrB_{6} and Ca_{0.995}La_{0.05}B_{6} below room temperature. Although the
electrical resistivities of these two materials differ substantially, their
{11}B-NMR responses exhibit some strikingly common features. Both materials
exhibit ferromagnetic order, but their {11}B-NMR spectra reveal very small
hyperfine fields at the Boron sites. The spin lattice relaxation T_{1}^{-1}
varies considerably with external field but changes with temperature only below
a few K. We discuss these unusual results by considering various different
scenarios for the electronic structure of these materials. | 0011352v2 |
2004-07-17 | Magneto - transport characterization of Dy123 monodomain superconductors | The following report considers textured materials of the DyBa2Cu3O7 type
seeded with a Nd123 seed as initiator. They are grown with an excess 20% Dy211
phase on a Dy2O3 substrate. We report chemical characterizations, electrical
resistivity, thermoelectric power and thermal conductivity over a broad
temperature range as a function of an applied magnetic field up to 6 T. We show
that specific features appear on the magneto thermal transport properties
different in these materials from those found in single crystals and
polycrystalline samples. We propose that two vortex regimes can be
distinguished in the mixed phase, - due to the intrinsic microstructure. We
calculate the viscosity, entropy and figure of merit of the samples. | 0407463v1 |
2007-01-09 | Pressure Study of Superconductivity and Magnetism in Pure and Rh-Doped RuSr2GdCu2O8 Materials | A hydrostatic pressure study was made on pure and Rh-doped specimens of the
superconducting ferromagnetic compounds Ru1-xRhxSr2GdCu2O8 (x = 0-0.15) by
means of measurement of electrical resistivity vs temperature, in pressures up
to 2 GPa. Partial substitution of Rh for Ru decreases the magnetization of the
material, lowers both the magnetic ordering temperature Tm, and the
superconducting transition temperature Tc, and promotes granularity. The effect
of pressure for all compositions is an increase in both the intra- and
intergranular superconductivity transition temperatures, Tc and Tp
respectively, as well as Tm. The rate of change of each transition temperature
with pressure first drops for Rh concentrations near 5%, increasing latter for
higher concentrations. While the rate of increase of Tc with pressure for all
compositions is 2-3 times lower than in YBCO materials, the simultaneous
increase of Tc and Tm with pressure could support the notion of competition
between superconductivity and ferromagnetism in these materials. The effect of
pressure on the weak-links was a significant improvement of inter-granular
connectivity. | 0701183v1 |
2007-04-25 | Studies of the temperature and frequency dependent impedance of an electroceramic functional oxide thermistor | The charge transport mechanism and the macroscopic dielectric constant in
polycrystalline device materials commonly exhibit several components such as
electrode-sample interface, grain boundary and bulk contributions. In order to
gain precise understanding of the functionality of polycrystalline
electroceramic device materials it is essential to deconvolute these
contributions. The paradigm of functional thermistor ceramics based on thick
film spinel manganates has been studied by temperature dependent alternating
current impedance spectroscopy. Three typical relaxation phenomena were
detected, which all showed a separated temperature dependence of resistivity
consistent with thermally activated charge transport. The dominating grain
boundary and the interface contributions exhibited distinctively different
capacitance allowing clear identification. The composite nature of the
dielectric properties in polycrystalline functional ceramics was emphasized,
and impedance spectroscopy was shown to be a powerful tool to account for and
model such behaviour. | 0704.3378v1 |
2007-07-17 | Gate-induced insulating state in bilayer graphene devices | The potential of graphene-based materials consisting of one or a few layers
of graphite for integrated electronics originates from the large
room-temperature carrier mobility in these systems (approx. 10,000 cm2/Vs).
However, the realization of electronic devices such as field-effect transistors
will require controlling and even switching off the electrical conductivity by
means of gate electrodes, which is made difficult by the absence of a bandgap
in the intrinsic material. Here, we demonstrate the controlled induction of an
insulating state - with large suppression of the conductivity - in bilayer
graphene, by using a double-gate device configuration that allows an electric
field to be applied perpendicular to the plane. The dependence of the
resistance on temperature and electric field, and the absence of any effect in
a single-layer device, strongly suggest that the gate-induced insulating state
originates from the recently predicted opening of a bandgap between valence and
conduction bands. | 0707.2487v2 |
2009-05-12 | Large magnetic entropy change near room temperature in antipervoskite SnCMn3 | We report the observation of large magnetocaloric effect near room
temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at
the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is
about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48
kOe, respectively. These values are close to those of typical magnetocaloric
materials. The large magnetocaloric effect is associated with the sharp change
of lattice, resistivity and magnetization in the vicinity of TC. Through the
measurements of Seebeck coefficient and normal Hall effect, the title system is
found to undergo a reconstruction of electronic structure at TC. Considering
its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are
suggested to be appropriate for pursuing new materials with larger
magnetocaloric effect. | 0905.1773v1 |
2009-06-28 | Partial Kekule Ordering of Adatoms on Graphene | Electronic and transport properties of Graphene, a one-atom thick crystalline
material, are sensitive to the presence of atoms adsorbed on its surface. An
ensemble of randomly positioned adatoms, each serving as a scattering center,
leads to the Bolzmann-Drude diffusion of charge determining the resistivity of
the material. An important question, however, is whether the distribution of
adatoms is always genuinely random. In this Article we demonstrate that a
dilute adatoms on graphene may have a tendency towards a spatially correlated
state with a hidden Kekule mosaic order. This effect emerges from the
interaction between the adatoms mediated by the Friedel oscillations of the
electron density in graphene. The onset of the ordered state, as the system is
cooled below the critical temperature, is accompanied by the opening of a gap
in the electronic spectrum of the material, dramatically changing its transport
properties. | 0906.5174v1 |
2012-02-13 | Nanostructured antimony tin oxide synthesized via chemical precipitation method: its characterization and application in humidity sensing | In present investigation we report the synthesis of antimony tin oxide
nanoparticles via chemical precipitation method. The synthesized material was
characterized using X-ray diffractometer, Scanning Electron Microscope,
UV-visible absorption spectroscopy. XRD shows the crystalline nature of the
synthesized material and the crystallite size was estimated by using
Debye-Scherer equation and its minimum value was 3 nm. Pelletization of
synthesized material was done using hydraulic press machine under uniform
pressure of 616 MPa. Then the pellets were annealed at 200, 400 and 600{\deg}C.
Further each pellet was put in humidity sensing chamber and corresponding
variations in resistance with relative humidity (%RH) were measured. The
average sensitivity was calculated by taking the average of all sensitivities
ranging from 10 to 90% RH. The average sensitivity of the pellet annealed at
600{\deg}C was best among all the sensing pellets and was 2.18 K{\Omega}/%RH.
Results were reproducible {\pm}84% after 2 months. | 1205.2336v1 |
2012-02-13 | Effect of nanostructured zinc oxide additives on the humidity and temperature sensing properties of cuprous oxide | Present paper reports the effect of ZnO additives on humidity and temperature
sensing properties of cuprous oxide. The cuprous oxide powder was mixed with
10% and 25% ZnO by weight and these samples were pelletized by using hydraulic
pressing machine. The sensing materials were also investigated by Scanning
Electron Microscope (SEM) and X-ray Diffraction (XRD). SEM images show
morphology and porosity of material. The average particles size of cuprous
oxide was found to be 1.2 micron. The sheet like structures of ZnO is evident
in micrographs. From XRD all peaks are well identified and crystallite size for
defferent peaks has also been calculated. The pellets of sensing materials were
subjected to annealing at temperatures 200, 400 and 600 degrees C respectively
and were exposed to humidity and temperature variations. Electrical resistances
of pellets were found to vary with humidity and temperature and were recorded.
The sensitivity of sensors at various temperature and humidity levels was
calculated. | 1205.2707v1 |
2012-05-29 | Transport Properties of Ni, Co, Fe, Mn Doped Cu0.01Bi2Te2.7Se0.3 for Thermoelectric Device Applications | Bi2Te3 based thermoelectric devices typically use a nickel layer as a
diffusion barrier to block the diffusion of solder or copper atoms from the
electrode into the thermoelectric material. Previous studies have shown
degradation in the efficiency of these thermoelectric devices may be due to the
diffusion of the barrier layer into the thermoelectric material. In this work
Ni, Co, Fe, and Mn are intentionally doped into Cu0.01Bi2Te2.7Se0.3 in order to
understand their effects on the thermoelectric material. Thermoelectric
transport properties including the Seebeck coefficient, thermal conductivity,
electrical resistivity, carrier concentration, and carrier mobility of
Cu0.01Bi2Te2.7Se0.3 doped with 2 atomic percent M (M=Ni, Co, Fe, Mn) as
Cu0.01Bi2Te2.7Se0.3M0.02, are studied in a temperature range of 5-525 K. | 1205.6377v1 |
2012-07-04 | Colossal Magnetoresistance in the Mn2+ Oxypnictides NdMnAsO1-xFx | Colossal magnetoresistance (CMR) is a rare phenomenon in which the electronic
resistivity of a material can be decreased by orders of magnitude upon
application of a magnetic field. Such an effect could be the basis of the next
generation of magnetic memory devices. Here we report CMR in the
antiferromagnetic oxypnictide NdMnAsO1-xFx as a result of competition between
an antiferromagnetic insulating phase with strong electron correlations and a
paramagnetic semiconductor upon application of a magnetic field. The discovery
of CMR in antiferromagnetic Mn2+ oxypnictide materials could open up an array
of materials for further investigation and optimisation for technological
applications. | 1207.0958v1 |
2013-10-28 | The d-p band-inversion topological insulator in bismuth-based skutterudites | Skutterudites, a class of materials with cage-like crystal structure which
have received considerable research interest in recent years, are the breeding
ground of several unusual phenomena such as heavy fermion superconductivity,
exciton-mediated superconducting state and Weyl fermions. Here, we predict a
new topological insulator in bismuth-based skutterudites, in which the bands
involved in the topological band-inversion process are d- and p-orbitals, which
is distinctive with usual topological insulators, for instance in Bi2Se3 and
BiTeI the bands involved in the topological band-inversion process are only
p-orbitals. Due to the present of large d-electronic states, the electronic
interaction in this topological insulator is much stronger than that in other
conventional topological insulators. The stability of the new material is
verified by binding energy calculation, phonon modes analysis, and the finite
temperature molecular dynamics simulations. This new material can provide
nearly zero-resistivity signal current for devices and is expected to be
applied in spintronics devices. | 1310.7413v2 |
2015-05-21 | Ferromagnetism in Cr-doped topological insulator TlSbTe2 | We have synthesized a new ferromagnetic topological insulator by doping Cr to
the ternary topological-insulator material TlSbTe2. Single crystals of
Tl_{1-x}Cr_{x}SbTe2 were grown by a melting method and it was found that Cr can
be incorporated into the TlSbTe2 matrix only within the solubility limit of
about 1%. The Curie temperature \theta_c was found to increase with the Cr
content but remained relatively low, with the maximum value of about 4 K. The
easy axis was identified to be the c-axis and the saturation moment was 2.8
\mu_B (Bohr magneton) at 1.8 K. The in-plane resistivity of all the samples
studied showed metallic behavior with p-type carriers. Shubnikov-de Hass (SdH)
oscillations were observed in samples with the Cr-doping level of up to 0.76%.
We also tried to induce ferromagnetism in TlBiTe2 by doping Cr, but no
ferromagnetism was observed in Cr-doped TlBiTe2 crystals within the solubility
limit of Cr which turned out to be also about 1%. | 1505.05631v1 |
2016-11-22 | Statistical Methods for Thermal Index Estimation Based on Accelerated Destructive Degradation Test Data | Accelerated destructive degradation test (ADDT) is a technique that is
commonly used by industries to access material's long-term properties. In many
applications, the accelerating variable is usually the temperature. In such
cases, a thermal index (TI) is used to indicate the strength of the material.
For example, a TI of 200C may be interpreted as the material can be expected to
maintain a specific property at a temperature of 200C for 100,000 hours. A
material with a higher TI possesses a stronger resistance to thermal damage. In
literature, there are three methods available to estimate the TI based on ADDT
data, which are the traditional method based on the least-squares approach, the
parametric method, and the semiparametric method. In this chapter, we provide a
comprehensive review of the three methods and illustrate how the TI can be
estimated based on different models. We also conduct comprehensive simulation
studies to show the properties of different methods. We provide thorough
discussions on the pros and cons of each method. The comparisons and discussion
in this chapter can be useful for practitioners and future industrial
standards. | 1611.07412v1 |
2017-11-07 | Fracture toughness characterization through notched small punch test specimens | In this work a novel methodology for fracture toughness characterization by
means of the small punch test (SPT) is presented. Notched specimens are
employed and fracture resistance is assessed through a critical value of the
notch mouth displacement {\delta^SPT}. Finite element simulations and
interrupted experiments are used to track the evolution of {\delta^SPT} as a
function of the punch displacement. The onset of crack propagation is
identified by means of a ductile damage model and the outcome is compared to
the crack tip opening displacement estimated from conventional tests at crack
initiation. The proposed numerical-experimental scheme is examined with two
different grades of CrMoV steel and the differences in material toughness
captured. Limitations and uncertainties arising from the different damage
phenomena observed in the lowest toughness material examined are thoroughly
discussed. | 1711.02406v1 |
2018-04-03 | Combination of thermal and electric properties measurement techniques in a single setup suitable for radioactive materials in controlled environments and based on the 3-omega approach | We have designed and developed a new experimental setup, based on the 3-omega
method, to measure thermal conductivity, heat capacity and electrical
resistivity of a variety of samples in a broad temperature range (2-550 K) and
under magnetic fields up to 9 T. The validity of this method is tested by
measuring various types of metallic (copper, platinum, and constantan) and
insulating (SiO_2) materials, which have a wide range of thermal conductivity
values (1-400 Wm-1K-1). We have successfully employed this technique for
measuring the thermal conductivity of two actinide single crystals, uranium
dioxide, and uranium nitride. This new experimental approach for studying
nuclear materials will help to advance reactor fuel development and
understanding. We have also shown that this experimental setup can be adapted
to the Physical Property Measurement System (Quantum Design) environment and/or
other cryocooler systems. | 1804.00821v1 |
2018-11-02 | Non-Equilibrium Phonon Transport Across Nanoscale Interfaces | Despite the ubiquity of applications of heat transport across nanoscale
interfaces, including integrated circuits, thermoelectrics, and
nanotheranostics, an accurate description of phonon transport in these systems
remains elusive. Here we present a theoretical and computational framework to
describe phonon transport with position, momentum and scattering event
resolution. We apply this framework to a single material spherical nanoparticle
for which the multidimensional resolution offers insight into the physical
origin of phonon thermalization, and length-scale dependent anisotropy of
steady-state phonon distributions. We extend the formalism to handle interfaces
explicitly and investigate the specific case of semi-coherent materials
interfaces by computing the coupling between phonons and interfacial strain
resulting from aperiodic array of misfit dislocations. Our framework
quantitatively describes the thermal interface resistance within the
technologically relevant Si-Ge heterostructures. In future, this formalism
could provide new insight into coherent and driven phonon effects in nanoscale
materials increasingly accessible via ultrafast, THz and near-field
spectroscopies. | 1811.01059v1 |
2018-11-07 | Spin Hall effect in 2D metallic delafossite PtCoO$_2$ and vicinity topology | The two-dimensional (2D) metal PtCoO$_2$ is renowned for the lowest room
temperature resistivity among all oxides, close to that of the top two
materials Ag and Cu. In addition, we theoretically predict a strong intrinsic
spin Hall effect. This originates from six strongly-tilted Dirac cones that we
find in the electronic structure near the Fermi surface, where a gap is opened
by large spin-orbit coupling (SOC). This is underpinned by rich topological
properties; in particular, the phenomenology of a mirror Chern metal is
realized not exactly, but very accurately, on account of an approximate
crystalline symmetry. We expect that such 'vicinity topology' to be a feature
of relevance well beyond this material. Our Wilson loop analysis indicates
further elaborate features such as fragile topology. These findings highlight
PtCoO$_2$ as a promising material for spintronic applications as well as a
platform to study the interplay of symmetry and topology. | 1811.03105v1 |
2020-03-22 | Thermoelectric probe of defect state induced by ionic liquid gating in vanadium dioxide | Thermoelectric measurements detect the asymmetry between the density of
states above and below the chemical potential in a material. It provides
insights into small variations in the density of states near the chemical
potential, complementing electron transport measurements. Here, combined
resistance and thermoelectric power measurements are performed on vanadium
dioxide (VO2), a prototypical correlated electron material, under ionic-liquid
(IL) gating. With IL gating, charge transport below the
metal-to-insulator-transition (MIT) temperature remains in the thermally
activated regime, while the Seebeck coefficient exhibits an apparent transition
from semiconducting to metallic behavior. The contrasting behavior indicates
changes in electronic structure upon IL gating, due to the formation of oxygen
defect states. The experimental results are corroborated by numerical
simulations based on a model density of states incorporating a gating induced
defect band. This study reveals thermoelectric measurements to be a convenient
and sensitive probe for the role of defect states induced by IL gating in
suppressing the MIT in VO2, which remains benign in charge transport
measurements, and possibly for studying defect sates in other materials. | 2003.09840v1 |
2017-03-10 | Highly crystalline 2D superconductors | Recent technological advances in controlling materials have developed methods
to produce idealized two-dimensional (2D) electron systems such as
heterogeneous interfaces, molecular-beam-epitaxy (MBE) grown atomic layers,
exfoliated thin flakes and field-effect devices. These 2D electron systems are
highly-crystalline with less disorder in common, some of which indeed show
sheet resistance more than one order of magnitude lower even in atomic layers
or single layers than that of conventional amorphous/granular thin films. Here,
we present a review on the recent developments of highly-crystalline 2D
superconductors and a series of unprecedented physical properties discovered in
these systems. In particular, we highlight the quantum metallic state (or
possible metallic ground state), the quantum Griffiths phase in out-of-plane
magnetic fields, and the superconducting state maintained in anomalously large
in-plane magnetic fields, which were observed in exfoliated 2D materials,
MBE-grown atomic-layer thin films and electric-double-layer (ion-gated)
interfaces. These phenomena are discussed on the basis of weakened disorder
and/or broken spatial inversion symmetry. These novel aspects suggest that
highly-crystalline 2D systems are promising platforms for exploring new quantum
physics and superconductors. | 1703.03541v1 |
2018-10-07 | Log-periodic quantum magneto-oscillations and discrete scale invariance in topological material HfTe5 | Discrete scale invariance (DSI) is a phenomenon featuring intriguing
log-periodicity which can be rarely observed in quantum systems. Here we report
the log-periodic quantum oscillations in the magnetoresistance (MR) and the
Hall traces of HfTe5 crystals, which reveals the appearance of DSI. The
oscillations show the same logB-periodicity in the behavior of MR and Hall,
indicating an overall effect of the DSI on the transport properties. Moreover,
the DSI feature in the Hall resistance signals its close relation to the
carriers. Combined with theoretical simulations, we further clarify the origin
of the log-periodic oscillations and the DSI in the topological materials. Our
work evidences the universality of the DSI in the Dirac materials and paves way
for the full understanding of the novel phenomenon. | 1810.03109v1 |
2019-02-20 | Structural origins of electronic conduction in amorphous copper-doped alumina | We perform an {\it ab initio} modeling of amorphous copper-doped alumina
(a-Al$_2$O$_3$:Cu), a prospective memory material based on resistance
switching, and study the structural origin of electronic conduction in this
material. We generate molecular dynamics based models of a-Al$_2$O$_3$:Cu at
various Cu-concentrations and study the structural, electronic and vibrational
properties as a function of Cu-concentration. Cu atoms show a strong tendency
to cluster in the alumina host, and metallize the system by filling the band
gap uniformly for higher Cu-concentrations. We also study thermal fluctuations
of the HOMO-LUMO energy splitting and observe the time evolution of the size of
the band gap, which can be expected to have an important impact on the
conductivity. We perform a numerical computation of conduction pathways, and
show its explicit dependence on Cu connectivity in the host. We present an
analysis of ion dynamics and structural aspects of localization of classical
normal modes in our models. | 1902.07559v1 |
2017-04-03 | Superconducting Two-Dimensional Metal-Organic Framework | Superconductivity is a fascinating quantum phenomenon characterized by zero
electrical resistance and the Meissner effect. To date, several distinct
families of superconductors (SCs) have been discovered. These include
three-dimensional (3D) bulk SCs in both inorganic and organic materials as well
as two-dimensional (2D) thin film SCs but only in $inorganic$ materials. Here
we predict superconductivity in 2D and 3D $organic$ metal-organic frameworks by
using first-principles calculations. We show that the highly conductive and
recently synthesized Cu-benzenehexathial (BHT) is a Bardeen-Cooper-Schrieffer
SC. Remarkably, the monolayer Cu-BHT has a critical temperature ($T_{c}$) of
4.43 K while $T_{c}$ of bulk Cu-BHT is 1.58 K. Different from the enhanced
$T_{c}$ in 2D inorganic SCs which is induced by interfacial effects, the
$T_{c}$ enhancement in this 2D organic SC is revealed to be the out-of-plane
soft-mode vibrations, analogous to surface mode enhancement originally proposed
by $Ginzburg$. Our findings not only shed new light on better understanding 2D
superconductivity, but also open a new direction to search for SCs by interface
engineering with organic materials. | 1704.00490v1 |
2019-08-07 | Transport phenomena in a free-standing two-dimensional sodium sheet | The advances in the growth techniques provide numerous scope to explore the
possibilities of new 2D materials for potential applications. With the aid of
first-principle calculations we show that 2D Na can be a new addition to the
family of thermodynamically stable 2D materials for device applications. Not
surprisingly, due to half-occupied $3s$ orbital 2D Na possesses the features of
the 2D electron gas (2DEG). The transport properties are examined based on the
accurate solution of Boltzmann transport equation. With practically tunable
carrier density in 2D materials, the intrinsic electrical resistivity of
electron doped 2D Na is $\sim$ 1.4 times larger than that of graphene and falls
below the latter 450 K onwards. The Bloch-Gr\"uneisen temperature is almost
constant at 50 K, independent of the type or density of the charge carriers.
The electronic thermal conductivity of pure 2D Na is $\sim$ 1.24 times larger
than that of its bulk counterpart at 300 K. The Wiedemann-Franz law stands tall
in 2D Na with calculated Lorenz number 2.41 $\times 10^{-8} V^2/deg^2$ at room
temperature. The transport mechanism presented here is expected to occur in all
Na like systems with a clean Fermi surface. | 1908.02431v1 |
2019-12-18 | Observation of multiple Dirac states in a magnetic topological material EuMg2Bi2 | Initiated by the discovery of topological insulators, topologically
non-trivial materials, more specifically topological semimetals and metals have
emerged as new frontiers in the field of quantum materials. In this work, we
perform a systematic measurement of EuMg2Bi2, a compound with antiferromagnetic
transition temperature at 6.7 K, observed via electrical resistivity,
magnetization and specific heat capacity measurements. By utilizing
angle-resolved photoemission spectroscopy in concurrence with first-principles
calculations, we observe Dirac cones at the corner and the zone center of the
Brillouin zone. From our experimental data, multiple Dirac states at G and K
points are observed, where the Dirac nodes are located at different energy
positions from the Fermi level. Our experimental investigations of detailed
electronic structure as well as transport measurements of EuMg2Bi2 suggest that
it could potentially provide a platform to study the interplay between topology
and magnetism. | 1912.08645v1 |
2012-03-28 | Finite element modelling of shock-induced damages on ceramic hip prostheses | The aim of this work was to simulate the behaviour of hip prostheses under
mechanical shocks. When hip joint is replaced by prosthesis, during the swing
phase of the leg, a microseparation between the prosthetic head and the cup
could occur. Two different sizes of femoral heads were studied: 28 and 32 mm
diameter, made, respectively, in alumina and zirconia. The shock-induced stress
was determined numerically using finite element analysis (FEA), Abaqus
software. The influence of inclination, force, material, and microseparation
was studied. In addition, an algorithm was developed from a probabilistic
model, Todinov's approach, to predict lifetime of head and cup. Simulations
showed maximum tensile stresses were reached on the cup's surfaces near to rim.
The worst case was the cup-head mounted at 30^{\circ}. All simulations and
tests showed bulk zirconia had a greater resistance to shocks than bulk
alumina. The probability of failure could be bigger than 0.9 when a porosity
greater than 0.7% vol. is present in the material. Simulating results showed
good agreement with experimental results. The tests and simulations are
promising for predicting the lifetime of ceramic prostheses. | 1203.6154v1 |
2015-04-20 | Giant reversible nanoscale piezoresistance at room temperature in Sr2IrO4 thin films | Layered iridates have been the subject of intense scrutiny on account of
their unusually strong spin-orbit coupling, which opens up a narrow gap in a
material that would otherwise be a metal. This insulating state is very
sensitive to external perturbations. Here, we show that vertical compression at
the nanoscale, delivered using the tip of a standard scanning probe microscope,
is capable of inducing a five orders of magnitude change in the room
temperature resistivity of Sr2IrO4. The extreme sensitivity of the electronic
structure to anisotropic deformations opens up a new angle of interest on this
material, and the giant and fully reversible perpendicular piezoresistance
makes iridates a promising material for room temperature piezotronic devices. | 1504.05245v1 |
2018-12-06 | Crack Growth Behavior in NiTi Shape Memory Alloys Under Mode-I Isothermal Loading: Effect of Stress State | Fracture behavior in nickel-titanium (NiTi) shape memory alloys (SMAs)
subjected to mode-I, isothermal loading is studied using finite element
analysis (FEA). Compact tension (CT) SMA specimen is modeled in Abaqus finite
element suite and crack growth under displacement boundary condition is
investigated for plane strain and plane stress conditions. Parameters for the
SMA material constitutive law implemented in the finite element setup are
acquired from characterization tests conducted on near-equiatomic NiTi SMA.
Virtual crack closure technique (VCCT) is implemented where crack is assumed to
extend when the energy release rate at the crack-tip becomes equal to the
experimentally obtained material-specific critical value. Load-displacement
curves and mechanical fields near the crack-tip in plane strain and plane
stress cases are examined. Moreover, a discussion with respect to the crack
resistance R-curves calculated using the load-displacement response for plane
strain and plane stress conditions is presented. | 1812.02362v1 |
2018-12-24 | Control of Spin Diffusion and Suppression of the Hanle Effect by the Coexistence of Spin and Valley Hall Effects | In addition to spin, electrons in many materials possess an additional
pseudo-spin degree of freedom known as 'valley'. In materials where the spin
and valley degrees of freedom are weakly coupled, they can be both excited and
controlled independently. In this work, we study a model describing the
interplay of the spin and valley Hall effects in such two-dimensional
materials. We demonstrate the emergence of an additional longitudinal neutral
current that is both spin and valley polarized. The additional neutral current
allows to control the spin density by tuning the magnitude of the valley Hall
effect. In addition, the interplay of the two effects can suppress the Hanle
effect, that is, the oscillation of the nonlocal resistance of a Hall bar
device with in-plane magnetic field. The latter observation provides a possible
explanation for the absence of the Hanle effect in a number of recent
experiments. Our work opens also the possibility to engineer the conversion
between the valley and spin degrees of freedom in two-dimensional materials. | 1812.09996v2 |
2019-06-24 | Cross interface model for the thermal transport across interface between overlapped boron nitride nanoribbons | The application of low-dimensional materials for heat dissipation requires a
comprehensive understanding of the thermal transport at the cross interface,
which widely exists in various composite materials and electronic devices. In
this work, we proposed an analytical model, named as cross interface model
(CIM), to accurately reveal the essential mechanism of the two-dimensional
thermal transport at the cross interface. The applicability of CIM is validated
through the comparison of the analytical results with molecular dynamics
simulations for a typical cross interface of two overlapped boron nitride
nanoribbons. Besides, it is figured out that the factor ({\eta}) has important
influence on the thermal transport besides the thermal resistance inside and
between the materials, which is found to be determined by two dimensionless
parameters from its expression. Our investigations deepen the understanding of
the thermal transport at the cross interface and also facilitate to guide the
applications of low-dimensional materials in thermal management. | 1906.09751v1 |
2019-11-05 | Molecular beam epitaxy of CuMnAs | We present a detailed study of the growth of the tetragonal polymorph of
antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore
the parameter space of growth conditions and their effect on the
microstructural and transport properties of the material. We identify its
typical structural defects and compare the properties of epitaxial CuMnAs
layers grown on GaP, GaAs and Si substrates. Finally, we investigate the
correlation between the crystalline quality of CuMnAs and its performance in
terms of electrically induced resistance switching. | 1911.01794v1 |
2019-11-15 | Flexoskeleton printing for versatile insect-inspired robots | One of the many secrets to the success and prevalence of insects is their
versatile, robust, and complex exoskeleton morphology. A fundamental challenge
in insect-inspired robotics has been the fabrication of robotic exoskeletons
that can match the complexity of exoskeleton structural mechanics. Hybrid
robots composed of rigid and soft elements have previously required access to
expensive multi-material 3D printers, multi-step casting and machining
processes, or limited material choice when using consumer-grade fabrication
methods. Here we introduce a new design and fabrication process to rapidly
construct flexible exoskeleton-inspired robots called flexoskeleton printing.
We modify a consumer-grade fused deposition material (FDM) 3D printer to
deposit filament directly onto a heated thermoplastic base layer which provides
extremely strong bond strength between the deposited material and the
inextensible, flexible base layer. This process significantly improves the
fatigue resistance of printed components and enables a new class of
insect-inspired robot morphologies. We demonstrate these capabilities through
design and testing of a wide library of canonical flexoskeleton elements;
ultimately leading to the integration of elements into a flexoskeleton walking
legged robot. | 1911.06897v2 |
2020-01-07 | Molecular beam epitaxy of the magnetic kagome metal FeSn on LaAlO3 (111) | Materials with a layered Kagome lattice are expected to give rise to novel
physics arising from band structures with topological properties, spin liquid
behavior and the formation of skyrmions. Until now, most work on Kagome
materials has been performed on bulk samples due to difficulties in thin film
synthesis. Here, by using molecular beam epitaxy, layered Kagome-structured
FeSn films are synthesized on (111) oriented LaAlO3 substrate. Both in-situ and
ex-situ characterizations indicate these films are highly crystalline and
c-axis oriented, with atomically smooth surfaces. However, the films grow as
disconnected islands, with lateral dimensions on the micron scale. By
patterning Pt electrodes using a focused electron beam, longitudinal and
transverse resistance of single islands have been measured in magnetic fields.
Our work opens a pathway for exploring mesoscale transport properties in thin
films of Kagome materials and related devices. | 2001.01820v2 |
2020-05-11 | Highly flexible electromagnetic interference shielding films based on ultrathin Ni/Ag composites on paper substrates | Highly flexible electromagnetic interference (EMI) shielding material with
excellent shielding performance is of great significance to practical
applications in next-generation flexible devices. However, most EMI materials
suffer from insufficient flexibility and complicated preparation methods. In
this study, we propose a new scheme to fabricate a magnetic Ni particle/Ag
matrix composite ultrathin film on a paper surface. For a ~2 micro meter thick
film on paper, the EMI shielding effectiveness (SE) was found to be 46.2 dB at
8.1 GHz after bending 200,000 times over a radius of ~2 mm. The sheet
resistance (Rsq) remained lower than 2.30 Ohm after bending 200,000 times.
Contrary to the change in Rsq, the EMI SE of the film generally increased as
the weight ratio of Ag to Ni increased, in accordance with the principle that
EMI SE is positively related with an increase in electrical conductivity.
Desirable EMI shielding ability, ultrahigh flexibility, and simple processing
provide this material with excellent application prospects. | 2005.04875v1 |
2020-08-19 | Observation of plateau-like magnetoresistance in twisted Fe3GeTe2/Fe3GeTe2 junction | Controlling the stacking of van der Waals (vdW) materials is found to produce
exciting new findings, since hetero- or homo- structures have added the diverse
possibility of assembly and manipulated functionalities. However, so far, the
homostructure with a twisted angle based on the magnetic vdW materials remains
unexplored. Here, we achieved a twisted magnetic vdW Fe3GeTe2/Fe3GeTe2 junction
with broken crystalline symmetry. A clean and metallic vdW junction is
evidenced by the temperature-dependent resistance and the linear I-V curve.
Unlike the pristine FGT, a plateau-like magnetoresistance (PMR) is observed in
the magnetotransport of our homojunction due to the antiparallel magnetic
configurations of the two FGT layers. The PMR ratio is found to be ~0.05% and
gets monotonically enhanced as temperature decreases like a metallic giant
magnetoresistance (GMR). Such a tiny PMR ratio is at least three orders of
magnitude smaller than the tunneling magnetoresistance (TMR) ratio, justifying
our clean metallic junction without a spacer. Our findings demonstrate the
feasibility of the controllable homostructure and shed light on future
spintronics using magnetic vdW materials. | 2008.08313v1 |
2020-10-24 | Drawing WS2 thermal sensors on paper substrates | Paper based thermoresistive sensors are fabricated by rubbing WS2 powder
against a piece of standard copier paper, like the way a pencil is used to
write on paper. The abrasion between the layered material and the rough paper
surface erodes the material, breaking the weak van der Waals interlayer bonds,
yielding a film of interconnected platelets. The resistance of WS2 presents a
strong temperature dependence, as expected for a semiconductor material in
which charge transport is due to thermally activated carriers. This strong
temperature dependence makes the paper supported WS2 devices extremely
sensitive to small changes in temperature. This exquisite thermal sensitivity,
and their fast response times to sudden temperature changes, is exploited
thereby demonstrating the usability of a WS2-on-paper thermal sensor in a
respiration monitoring device. | 2010.12805v1 |
2021-04-08 | Correlating Nanocrystalline Structure with Electronic Properties in 2D Platinum Diselenide | Platinum diselenide (PtSe${_2}$) is a two-dimensional (2D) material with
outstanding electronic and piezoresistive properties. The material can be grown
at low temperatures in a scalable manner which makes it extremely appealing for
many potential electronics, photonics, and sensing applications. Here, we
investigate the nanocrystalline structure of different PtSe${_2}$ thin films
grown by thermally assisted conversion (TAC) and correlate them with their
electronic and piezoresistive properties. We use scanning transmission electron
microscopy for structural analysis, X-ray photoelectron spectroscopy (XPS) for
chemical analysis, and Raman spectroscopy for phase identification. Electronic
devices are fabricated using transferred PtSe${_2}$ films for electrical
characterization and piezoresistive gauge factor measurements. The variations
of crystallite size and their orientations are found to have a strong
correlation with the electronic and piezoresistive properties of the films,
especially the sheet resistivity and the effective charge carrier mobility. Our
findings may pave the way for tuning and optimizing the properties of TAC-grown
PtSe${_2}$ towards numerous applications. | 2104.03636v1 |
2021-09-16 | Analytic solution to pseudo-Landau levels in strongly bent graphene nanoribbons | Nonuniform elastic strain is known to induce pseudo-Landau levels in Dirac
materials. But these pseudo-Landau levels are hardly resolvable in an analytic
fashion when the strain is strong, because of the emerging complicated space
dependence in both the strain-modulated Fermi velocity and the strain-induced
pseudomagnetic field. We analytically characterize the solution to the
pseudo-Landau levels in experimentally accessible strongly bent graphene
nanoribbons, by treating the effects of the nonuniform Fermi velocity and
pseudomagnetic field on equal footing. The analytic solution is detectable
through the angle-resolved photoemission spectroscopy (ARPES) and allows
quantitative comparison between theories and various transport experiments,
such as the Shubnikov-de Haas oscillation in the complete absence of magnetic
fields and the negative strain-resistivity resulting from the valley anomaly.
The analytic solution can be generalized to twisted two-dimensional materials
and topological materials and will shed a new light on the related experimental
explorations and straintronics applications. | 2109.08182v2 |
2021-09-27 | Layered, Tunable Graphene Oxide-Nylon Heterostructures for Wearable Electrocardiogram Sensors | Nanoscale engineered materials combined with wearable wireless technologies
can deliver a new level of health monitoring. A reduced graphene oxide-nylon
composite material is developed and tested, demonstrating its usefulness as a
material for sensors in wearable, long-term electrocardiogram (ECG) monitoring
via a comparison to one of the widely used ECG sensors. The structural analysis
by scanning electron (SEM) and atomic force microscopy (AFM) shows a limited
number of defects on a macroscopic scale. Fourier Transform Infrared (FTIR) and
Raman spectroscopy confirm the presence of rGOx, and the ratio of D- and
G-features as a function of thickness correlates with the resistivity analysis.
The negligible effect of the defects and the tunability of electrical and
optical properties, together with live ECG data, demonstrate its signal
transduction capability. | 2109.12739v2 |
2022-04-30 | Scattering mechanisms in state-of-the-art GaAs/AlGaAs quantum wells | Motivated by recent breakthrough in molecular beam epitaxy of GaAs/AlGaAs
quantum wells [Y. J. Chung \textit{et al.}, Nature Materials \textbf{20}, 632
(2021)], we examine contributions to mobility and quantum mobility from various
scattering mechanisms and their dependencies on the electron density. We find
that at lower electron densities, $n_e \lesssim 1 \times 10^{11}$ cm$^{-2}$,
both transport and quantum mobility are limited by unintentional background
impurities and follow a power law dependence, $\propto n_e^{\alpha}$, with
$\alpha \approx 0.85$. Our predictions for quantum mobility are in reasonable
agreement with an estimate obtained from the resistivity at filling factor
$\nu= 1/2$ in a sample of Y. J. Chung \textit{et al.} with $n_e = 1 \times
10^{11}$ cm$^{-2}$. Consideration of other scattering mechanisms indicates that
interface roughness (remote donors) is a likely limiting factor of transport
(quantum) mobility at higher electron densities. Future measurements of quantum
mobility should yield information on the distribution of background impurities
in GaAs and AlGaAs. | 2205.00365v3 |
2023-07-20 | Superconductivity in a van der Waals layered quasicrystal | van der Waals (vdW) layered transition-metal chalcogenides are attracting
significant attention owing to their fascinating physical properties. This
group of materials consists of abundant members with various elements, having a
variety of different structures. However, all vdW layered materials studied to
date have been limited to crystalline materials, and the physical properties of
vdW layered quasicrystals have not yet been reported. Here, we report on the
discovery of superconductivity in a vdW layered quasicrystal of Ta1.6Te. The
electrical resistivity, magnetic susceptibility, and specific heat of the
Ta1.6Te quasicrystal fabricated by reaction sintering, unambiguously validated
the occurrence of bulk superconductivity at a transition temperature of ~1 K.
This discovery can pioneer new research on assessing the physical properties of
vdW layered quasicrystals as well as two-dimensional quasicrystals; moreover,
it paves the way toward new frontiers of superconductivity in thermodynamically
stable quasicrystals, which has been the predominant challenge facing condensed
matter physics since the discovery of quasicrystals almost four decades ago. | 2307.10679v1 |
2023-08-21 | Coupling Between Magnetic and Transport Properties in Magnetic Layered Material Mn2-xZnxSb | We synthesized single crystals for Mn2-xZnxSb and studied their magnetic and
electronic transport properties. This material system displays rich magnetic
phase tunable with temperature and Zn composition. In addition, two groups of
distinct magnetic and electronic properties, separated by a critical Zn
composition of x = 0.6, are discovered. The Zn-less samples are metallic and
characterized by a resistivity jump at the magnetic ordering temperature, while
the Zn-rich samples lose metallicity and show a metal-to-insulator
transition-like feature tunable by magnetic field. Our findings establish
Mn2-xZnxSb as a promising material platform that offers opportunities to study
how the coupling of spin, charge, and lattice degrees of freedom governs
interesting transport properties in 2D magnets, which is currently a topic of
broad interest. | 2308.10764v1 |
2023-10-08 | An innovative clay metaBrick-based motif to enhance thermal and acoustic insulation | Metamaterials have gained popularity in recent years as a promising avenue
for producing innovative materials with distinctive properties that offer
unprecedented features. In this study, we address the thermal and acoustic
challenges of building materials. We numerically and experimentally investigate
a clay metaBrick, which is an innovative metamaterial design based on the
existing hollow brick that has shown strong sound and thermal performances. We
evaluate the acoustic and thermal characteristics of the clay metaBrick,
including sound transmission and heat resistance, using the finite element
method. Furthermore, we validate the results experimentally by investigating
the behaviors of the wall built on metaBricks in two tests: sound and thermal.
We contrast the findings of the metaBrick based wall with performances of a
standard hollow brick wall. The metaBrick offers enhanced acoustic and thermal
insulation properties compared to the standard brick, with a compressive
strength above standards required in the building materials. | 2310.05148v1 |
2024-03-18 | The Role of Temperature on Irradiation Defect Evolution near Surfaces and Grain Boundaries in Tungsten | This study explores the impact of temperature on defect dynamics in tungsten,
emphasizing its application in nuclear fusion reactors as Plasma Facing
Components (PFCs). Through atomistic simulations, the research elucidates the
intricate interplay of defect production, annihilation, and redistribution
under irradiation at room (300K) and elevated temperatures (1000K). It
demonstrates that higher temperatures significantly increase the number and
mobility of defects, leading to a substantial rise in the total number of
surviving Frenkel Pairs (FPs), with a notable preference for surface
distribution. This redistribution is attributed to energy gradient-driven
relocation processes, enhanced by the defects' increased mobility at elevated
temperatures. Moreover, the study reveals that elevated temperatures promote
biased accumulation of interstitial defects in grain boundaries, especially in
configurations that facilitate efficient interstitial migration, indicating a
strategy for minimizing lattice interstitial accumulation under irradiation.
These findings underscore the critical role of temperature in modulating
irradiation-induced defect dynamics in tungsten, providing valuable insights
for designing and selecting materials with optimized irradiation resistance for
use in extreme conditions of nuclear fusion reactors. The research suggests a
material design approach that accounts for temperature effects to enhance the
durability and performance of nuclear fusion materials. | 2403.12259v1 |
2024-03-19 | Unveiling the Reactivity of Oxygen and Ozone on C2N Monolayer: A First-Principles Study | The process of environmental oxidation is pivotal in determining the physical
and chemical properties of two-dimensional (2D) materials. Its impact holds
great significance for the practical application of these materials in
nanoscale devices functioning under ambient conditions. This study delves into
the influence of O2 and O3 exposure on the structural and electronic
characteristics of the C2N monolayer, focusing on the kinetics of adsorption
and dissociation reactions. Employing first-principles density functional
theory calculations alongside climbing image nudged elastic band calculations,
we observe that the C2N monolayer exhibits resistance to oxidation and
ozonation, evidenced by energy barriers of 0.05 eV and 0.56 eV, respectively.
These processes are accompanied by the formation of epoxide (C-O-C) groups.
Furthermore, the dissociation mechanism involves charge transfers from the
monolayer to the molecules. Notably, the dissociated configurations demonstrate
higher bandgaps compared to the pristine C2N monolayer, attributed to robust
C-O hybridization. These findings suggest the robustness of C2N monolayers
against oxygen/ozone exposures, ensuring stability for devices incorporating
these materials. | 2403.12454v1 |
2024-05-13 | Significant improvement in sensitivity of an anomalous Nernst heat flux sensor by composite structure | Heat flux sensors (HFS) have attracted significant interest for their
potential in managing waste heat efficiently. A recently proposed HFS, that
works on the basis of the anomalous Nernst effect (ANE), offers several
advantages in its simple structure leading to easy fabrication, low cost, and
reduced thermal resistance. However, enhancing sensitivity through traditional
material selection is now challenging due to a small number of materials
satisfying the required coexistence of a large transverse Seebeck coefficient
and low thermal conductivity. In this study, by utilizing composite structures
and optimizing the device geometry, we have achieved a substantial improvement
in the sensitivity of an ANE-based HFS. We developed composite structures
comprised of a plastic substrate with an uneven surface and three-dimensional
(3D) uneven TbCo films, fabricated using nanoimprint techniques and sputtering.
This approach resulted in a sensitivity that is approximately four times
greater than that observed in previous studies. Importantly, this method is
independent of the material properties and can significantly enhance the
sensitivity. Our findings could lead to the development of highly sensitive HFS
devices and open new avenues for the fabrication of 3D devices. | 2405.07758v1 |
2003-08-25 | Formation of Semi-relativisitc Jets from Magnetospheres of Accreting Neutron Stars: Injection of Hot Bubbles into a Magnetic Tower | We present the results of 2.5-dimensional resistive magnetohydrodynamic (MHD)
simulations of the magnetic interaction between a weakly magnetized neutron
star and its accretion disk. General relativistic effects are simulated by
using the pseudo-Newtonian potential. We find that well-collimated jets
traveling along the rotation axis of the disk are formed by the following
mechanism: (1) The magnetic loops connecting the neutron star and the disk are
twisted due to the differential rotation between the neutron star and the disk.
(2) Twist injection from the disk initiates expansion of the loop. (3) The
expanding magnetic loops create a magnetic tower in which accelerated disk
material travel as collimated bipolar jets. The propagation speed of the
working surface of the jet is the order of 10% of the speed of light ($\sim
0.1c$). (4) Magnetic reconnection taking place inside the expanding magnetic
loops injects hot bubbles intermittently into the magnetic tower. The ejection
speed of the bubble is the order of the local Alfv\'{e}n speed of the launching
point and $\sim 0.2c$ in our simulations. (5) The hot bubbles moving inside the
tower catch up with the working surface of the jet. High energy electrons
created by the magnetic reconnection are a plausible source of radio emission.
Our model can explain the formation process of a narrow jet from a weakly
magnetized ($|{\boldmath$B_{*}$}|\le 10^{9}$ gauss) neutron star and the
correlation between radio flares of the core and of the lobe observed in Sco
X-1. | 0308437v2 |
2009-01-28 | Strong enhancement of Jc in binary and alloyed in-situ MgB2 wires by a new approach: Cold high pressure densification | Cold high pressure densification (CHPD) is presented as a new way to
substantially enhance the critical current density of in situ MgB2 wires at 4.2
and 20 K at fields between 5 and 14 T. The results on two binary MgB2 wires and
an alloyed wire with 10 wt.% B4C are presented The strongest enhancement was
measured at 20K, where cold densification at 1.85 GPa on a binary Fe/MgB2 wire
raised both Jcpara and Jcperp by more than 300% at 5T, while Birr was enhanced
by 0.7 T. At 4.2K, the enhancement of Jc was smaller, but still reached 53% at
10 T. After applying pressures up to 6.5 GPa, the mass density dm of the
unreacted (B+Mg) mixture inside the filaments reached 96% of the theoretical
density. After reaction under atmospheric pressure, this corresponds to a
highest mass density df in the MgB2 filaments of 73%. After reaction, the
electrical resistance of wires submitted to cold densification was found to
decrease, reflecting an improved connectivity. A quantitative correlation
between filament mass density and the physical properties was established.
Monofilamentary rectangular wires with aspect ratios a/b < 1.25 based on low
energy ball milled powders exhibited very low anisotropy ratios, Gamma =
Jcpara/Jcperp being < 1.4 at 4.2 K and 10T. The present results can be
generalized to alloyed MgB2 wires, as demonstrated on a wire with B4C
additives. Based on the present data, it follows that cold densification has
the potential of further improving the highest Jcpara and Jcperp values
reported so far for in situ MgB2 tapes and wires with SiC and C additives.
Investigations are under work in our laboratory to determine whether the
densification method CHPD can be applied to longer wire or tape lengths. | 0901.4546v1 |
2011-01-24 | Stabilization of an ambient pressure, collapsed tetragonal phase in CaFe2As2 and tuning of the orthorhombic / antiferromagnetic transition temperature by over 70 K by control of nano-precipitates | We have found a remarkably large response of the transition temperature of
CaFe2As2 single crystals grown out of excess FeAs to annealing / quenching
temperature. Whereas crystals that are annealed at 400 C exhibit a first order
phase transition from a high temperature tetragonal to a low temperature
orthorhombic and antiferromagnetic state near 170 K, crystals that have been
quenched from 960 C exhibit a transition from a high temperature tetragonal
phase to a low temperature, non-magnetic, collapsed tetragonal phase below 100
K. By use of temperature dependent electrical resistivity, magnetic
susceptibility, X-ray diffraction, Mossbauer spectroscopy and nuclear magnetic
resonance measurements we have been able to demonstrate that the transition
temperature can be reduced in a monotonic fashion by varying the annealing /
quenching temperature from 400 to 850 C with the low temperature state
remaining antiferromagnetic for transition temperatures larger than 100 K and
becoming collapsed tetragonal / non-magnetic for transition temperatures below
90 K. This suppression of the orthorhombic / antiferromagnetic phase transition
and its ultimate replacement with the collapsed tetragonal / non-magnetic phase
is similar to what has been observed for CaFe2As2 under hydrostatic pressure.
Transmission electron microscopy studies indicate that there is a temperature
dependent, width of formation of CaFe2As2 with a decreasing amount of excess Fe
and As being soluble in the single crystal at lower annealing temperatures. For
samples quenched from 960 C there is a fine (of order 10 nm), semi-uniform
distribution of precipitate that can be associated with an average strain field
whereas for samples annealed at 400 C the excess Fe and As form mesoscopic
grains that induce little strain throughout the CaFe2As2 lattice. | 1101.4595v1 |
2011-10-14 | Numerical Investigation of Design Strategies to Achieve Long-Life Pavements | Increasing the HMA base thickness and modifying the HMA mixture properties to
improve the resistance to fatigue cracking are among the most popular methods
for achieving long-lasting pavements. Such methods are based on the idea of
reducing the tensile strain at the bottom of the HMA layer below the Fatigue
Endurance Limit (FEL), a level of strain below which no cumulative damage
occurs to the HMA mixture. This study investigates the effectiveness of several
design strategies involved in long-life, perpetual pavement design. A 3D Finite
Element model of the pavement involving a linear viscoelastic constitutive
model for HMA materials and non-uniform tire contact stresses is developed
using ABAQUS 6.11. The effects of asphalt base course thickness and mixture
type, rich binder layer, and aggregate subbase layer are examined. Four asphalt
base course mixture types, namely dense graded, polymer modified, high modulus,
and standard binder, are studied as a function of the asphalt base course
thickness. The results underline a better performance of the high-modulus
asphalt base, as compared to the other base course mixtures. The aggregate
subbase layer on top of subgrade soil showed a relatively minor effect on the
longitudinal and lateral strain response at the bottom of asphalt base course.
The addition of a rich binder layer at the bottom of the asphalt base course
showed a significant reduction in tensile strains. Tables are provided as a
guideline to assess the different alternatives in design of long-life perpetual
pavements. | 1110.3318v7 |
2013-06-21 | Crystallographic, Electronic, Thermal and Magnetic Properties of Single-Crystal SrCo2As2 | In tetragonal SrCo2As2 single crystals, inelastic neutron scattering
measurements demonstrated that strong stripe-type antiferromagnetic (AFM)
correlations occur at a temperature T = 5 K [W. Jayasekara et al.,
arXiv:1306.5174] that are the same as in the isostructural AFe2As2 (A = Ca, Sr,
Ba) parent compounds of high-Tc superconductors. This surprising discovery
suggests that SrCo2As2 may also be a good parent compound for high-Tc
superconductivity. Here, structural and thermal expansion, electrical
resistivity rho, angle-resolved photoemission spectroscopy (ARPES), heat
capacity Cp, magnetic susceptibility chi, 75As NMR and neutron diffraction
measurements of SrCo2As2 crystals are reported together with LDA band structure
calculations that shed further light on this fascinating material. The c-axis
thermal expansion coefficient alpha_c is negative from 7 to 300 K, whereas
alpha_a is positive over this T range. The rho(T) shows metallic character. The
ARPES measurements and band theory confirm the metallic character and in
addition show the presence of a flat band near the Fermi energy E_F. The band
calculations exhibit an extremely sharp peak in the density of states D(E_F)
arising from a flat d_{x^2 - y^2} band. A comparison of the Sommerfeld
coefficient of the electronic specific heat with chi(T = 0) suggests the
presence of strong ferromagnetic itinerant spin correlations which on the basis
of the Stoner criterion predicts that SrCo2As2 should be an itinerant
ferromagnet, in conflict with the magnetization data. The chi(T) does have a
large magnitude, but also exhibits a broad maximum at 115 K suggestive of
dynamic short-range AFM spin correlations, in agreement with the neutron
scattering data. The measurements show no evidence for any type of phase
transition between 1.3 and 300 K and we propose that metallic SrCo2As2 has a
gapless quantum spin-liquid ground state. | 1306.5222v3 |
2014-02-17 | Unravelling the effect of SrTiO3 antiferrodistortive phase transition on the magnetic properties of La0.7Sr0.3MnO3 thin films | Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films, with different thickness ranging
from 20 nm up to 330 nm, were deposited on (100)-oriented strontium titanate
(STO) substrates by pulsed laser deposition, and their structure and morphology
characterized at room temperature. Magnetic and electric transport properties
of the as-processed thin films reveal an abnormal behavior in the temperature
dependent magnetization M(T) below the antiferrodistortive STO phase transition
(TSTO) and also an anomaly in the magnetoresistance and electrical resistivity
close to the same temperature. Up to 100 nm LSMO thin films, an in-excess
magnetization and pronounced changes in the coercivity are evidenced, achieved
through the interface-mediated magnetoelastic coupling with antiferrodistortive
domain wall movement occurring below TSTO. Contrarily, for thicker LSMO thin
films, above 100 nm, an in-defect magnetization is observed. This reversed
behavior can be understood within the emergence in the upper layer of the film,
observed by high resolution transmission electron microscopy, of a branched
structure needed to relax elastic energy stored in the film which leads to
randomly oriented magnetic domain reconstructions. For enough high-applied
magnetic fields, as thermodynamic equilibrium is reached, a fully suppression
of the anomalous magnetization occurs, wherein the temperature dependence of
the magnetization starts to follow the expected Brillouin behavior. | 1402.4040v1 |
2017-12-04 | Effect of crystalline anisotropy on vertical (-201) and (010) beta-Ga2O3 Schottky barrier diodes on EFG single-crystal substrates | Vertical (-201) and (010) beta-Ga2O3 Schottky barrier diodes (SBDs) were
fabricated on single-crystal substrates grown by edge-defined film-fed growth
(EFG) method. High resolution X-ray diffraction (HRXRD) and atomic force
microscopy (AFM) confirmed good crystal quality and surface morphology of the
substrates. The electrical properties of both devices, including
current-voltage (I-V) and capacitance-voltage (C-V) characteristics, were
comprehensively measured and compared. The (-201) and (010) SBDs exhibited
on-resistances (Ron) of 0.56 and 0.77 m{\Omega}cm2, turn-on voltages (Von) of
1.0 and 1.3 V, Schottky barrier heights (SBH) of 1.05 and 1.20 eV, electron
mobilities of 125 and 65 cm2/(Vs), respectively, with a high on-current of ~1.3
kA/cm2 and on/off ratio of ~109. The (010) SBD had a larger Von and SBH than
(-201) SBD due to anisotropic surface properties (i.e., surface Fermi level
pinning and band bending), as supported by X-ray photoelectron spectroscopy
(XPS) measurements. Temperature-dependent I-V also revealed the inhomogeneous
nature of the SBH in both devices, where (-201) SBD showed a more uniform SBH
distribution. The homogeneous SBH was also extracted: 1.33 eV for (-201) SBD
and 1.53 eV for (010) SBD. The reverse leakage current of the devices was well
described by the two-step trap-assisted tunneling model and the one-dimensional
variable range hopping conduction (1D-VRH) model. The (-201) SBD showed larger
leakage current due to its lower SBH and smaller activation energy. These
results indicate the crystalline anisotropy of beta-Ga2O3 can affect the
electrical properties of vertical SBDs and should be taken into consideration
when designing beta-Ga2O3 electronics. | 1712.01318v1 |
2018-04-30 | Detailed study on the Fermi surfaces of the type-II Dirac semimetallic candidates PdTe2 and PtTe2 | We present a detailed quantum oscillatory study on the Dirac type-II
semimetallic candidates PdTe$_{2}$ and PtTe$_{2}$ \emph{via} the temperature
and the angular dependence of the de Haas-van Alphen (dHvA) and Shubnikov-de
Haas (SdH) effects. In high quality single crystals of both compounds, i.e.
displaying carrier mobilities between $10^3$ and $10^4$ cm$^2$/Vs, we observed
a large non-saturating magnetoresistivity (MR) which in PtTe$_2$ at a
temperature $T = 1.3$ K, leads to an increase in the resistivity up to $5
\times 10^{4}$ % under a magnetic field $\mu_0 H = 62$ T. These high mobilities
correlate with their light effective masses in the range of 0.04 to 1 bare
electron mass according to our measurements. For PdTe$_{2}$ the experimentally
determined Fermi surface cross-sectional areas show an excellent agreement with
those resulting from band-structure calculations. Surprisingly, this is not the
case for PtTe$_{2}$ whose agreement between calculations and experiments is
relatively poor even when electronic correlations are included in the
calculations. Therefore, our study provides a strong support for the existence
of a Dirac type-II node in PdTe$_2$ and probably also for PtTe$_2$. Band
structure calculations indicate that the topologically non-trivial bands of
PtTe$_2$ do not cross the Fermi-level ($\varepsilon_F$). In contrast, for
PdTe$_2$ the Dirac type-II cone does intersect $\varepsilon_F$, although our
calculations also indicate that the associated cyclotron orbit on the Fermi
surface is located in a distinct $k_z$ plane with respect to the one of the
Dirac type-II node. Therefore it should yield a trivial Berry-phase. | 1805.00087v1 |
2017-03-20 | Pseudogap temperature $T^\star$ of cuprate superconductors from the Nernst effect | We use the Nernst effect to delineate the boundary of the pseudogap phase in
the temperature-doping phase diagram of cuprate superconductors. New data for
the Nernst coefficient $\nu(T)$ of YBa$_{2}$Cu$_{3}$O$_{y}$ (YBCO),
La$_{1.8-x}$Eu$_{0.2}$Sr$_x$CuO$_4$ (Eu-LSCO) and
La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ (Nd-LSCO) are presented and compared with
previous data including La$_{2-x}$Sr$_x$CuO$_4$ (LSCO). The temperature $T_\nu$
at which $\nu/T$ deviates from its high-temperature behaviour is found to
coincide with the temperature at which the resistivity deviates from its
linear-$T$ dependence, which we take as the definition of the pseudogap
temperature $T^\star$- in agreement with gap opening detected in ARPES data. We
track $T^\star$ as a function of doping and find that it decreases linearly vs
$p$ in all four materials, having the same value in the three LSCO-based
cuprates, irrespective of their different crystal structures. At low $p$,
$T^\star$ is higher than the onset temperature of the various orders observed
in underdoped cuprates, suggesting that these orders are secondary
instabilities of the pseudogap phase. A linear extrapolation of $T^\star(p)$ to
$p=0$ yields $T^\star(p\to 0)\simeq T_N(0)$, the N\'eel temperature for the
onset of antiferromagnetic order at $p=0$, suggesting that there is a link
between pseudogap and antiferromagnetism. With increasing $p$, $T^\star(p)$
extrapolates linearly to zero at $p\simeq p_{\rm c2}$, the critical doping
below which superconductivity emerges at high doping, suggesting that the
conditions which favour pseudogap formation also favour pairing. We also use
the Nernst effect to investigate how far superconducting fluctuations extend
above $T_{\rm c}$, as a function of doping, and find that a narrow fluctuation
regime tracks $T_{\rm c}$, and not $T^\star$. This confirms that the pseudogap
phase is not a form of precursor superconductivity. | 1703.06927v2 |
2022-02-06 | Direct observation of vortices in an electron fluid | Vortices are the hallmarks of hydrodynamic flow. Recent studies indicate that
strongly-interacting electrons in ultrapure conductors can display signatures
of hydrodynamic behavior including negative nonlocal resistance, Poiseuille
flow in narrow channels, and a violation of the Wiedemann-Franz law. Here we
provide the first visualization of whirlpools in an electron fluid. By
utilizing a nanoscale scanning superconducting quantum interference device on a
tip (SQUID-on-tip) we image the current distribution in a circular chamber
connected through a small aperture to an adjacent narrow current carrying strip
in high-purity type-II Weyl semimetal WTe2. In this geometry, the Gurzhi
momentum diffusion length and the size of the aperture determine the vortex
stability phase diagram. We find that the vortices are present only for small
apertures, whereas the flow is laminar (non-vortical) for larger apertures,
consistent with the theoretical analysis of the hydrodynamic regime and in
contrast to the expectations of ballistic transport in WTe2 at low
temperatures. Moreover, near the vortical-to-laminar transition, we observe a
single vortex in the chamber splitting into two vortices, a behavior that can
occur only in the hydrodynamic regime and cannot be sustained by ballistic
transport. These findings suggest a novel mechanism of hydrodynamic flow:
instead of the commonly considered electron-electron scattering at the bulk,
which becomes extremely weak at low temperatures, the spatial diffusion of
charge carriers' momenta is enabled by small-angle scattering at the planar
surfaces of thin pure crystals. This surface-induced para-hydrodynamics opens
new avenues for exploring and utilizing electron fluidics in high-mobility
electron systems. | 2202.02798v1 |
2014-01-21 | Random strain fluctuations as dominant disorder source for high-quality on-substrate graphene devices | We have performed systematic investigations of transport through graphene on
hexagonal boron nitride (hBN) substrates, together with confocal Raman
measurements and a targeted theoretical analysis, to identify the dominant
source of disorder in this system. Low-temperature transport measurements on
many devices reveal a clear correlation between the carrier mobility $\mu$ and
the width $n^*$ of the resistance peak around charge neutrality, demonstrating
that charge scattering and density inhomogeneities originate from the same
microscopic mechanism. The study of weak-localization unambiguously shows that
this mechanism is associated to a long-ranged disorder potential, and provides
clear indications that random pseudo-magnetic fields due to strain are the
dominant scattering source. Spatially resolved Raman spectroscopy measurements
confirm the role of local strain fluctuations, since the line-width of the
Raman 2D-peak --containing information of local strain fluctuations present in
graphene-- correlates with the value of maximum observed mobility. The
importance of strain is corroborated by a theoretical analysis of the relation
between $\mu$ and $n^*$ that shows how local strain fluctuations reproduce the
experimental data at a quantitative level, with $n^*$ being determined by the
scalar deformation potential and $\mu$ by the random pseudo-magnetic field
(consistently with the conclusion drawn from the analysis of
weak-localization). Throughout our study, we compare the behavior of devices on
hBN substrates to that of devices on SiO$_2$ and SrTiO$_3$, and find that all
conclusions drawn for the case of hBN are compatible with the observations made
on these other materials. These observations suggest that random strain
fluctuations are the dominant source of disorder for high-quality graphene on
many different substrates, and not only on hexagonal boron nitride. | 1401.5356v2 |
2018-12-07 | Chemical Aspects of the Antiferromagnetic Topological Insulator MnBi$_{2}$Te$_{4}$ | Crystal growth of MnBi$_{2}$Te$_{4}$ has delivered the first experimental
corroboration of the 3D antiferromagnetic topological insulator state. Our
present results confirm that the synthesis of MnBi$_{2}$Te$_{4}$ can be
scaled-up and strengthen it as a promising experimental platform for studies of
a crossover between magnetic ordering and non-trivial topology. High-quality
single crystals of MnBi$_{2}$Te$_{4}$ are grown by slow cooling within a narrow
range between the melting points of Bi$_{2}$Te$_{3}$ (586 {\deg}C) and
MnBi$_{2}$Te$_{4}$ (600 {\deg}C). Single crystal X-ray diffraction and electron
microscopy reveal ubiquitous antisite defects in both cation sites and,
possibly, Mn vacancies. Powders of MnBi$_{2}$Te$_{4}$ can be obtained at
subsolidus temperatures, and a complementary thermochemical study establishes a
limited high-temperature range of phase stability. Nevertheless, quenched
powders are stable at room temperature and exhibit long-range antiferromagnetic
ordering below 24 K. The expected Mn(II) out-of-plane magnetic state is
confirmed by the magnetization, X-ray photoemission, X-ray absorption and
linear dichroism data. MnBi$_{2}$Te$_{4}$ exhibits a metallic type of
resistivity in the range 4.5-300 K. The compound is an n-type conductor that
reaches a thermoelectric figure of merit up to ZT = 0.17. Angle-resolved
photoemission experiments provide evidence for a surface state forming a gapped
Dirac cone. | 1812.03106v1 |
2018-12-19 | Universal relaxation in a holographic metallic density wave phase | In this work, we uncover a universal relaxation mechanism of pinned density
waves, combining Gauge/Gravity duality and effective field theory techniques.
Upon breaking translations spontaneously, new gapless collective modes emerge,
the Nambu-Goldstone bosons of broken translations. When translations are also
weakly broken (eg by disorder or lattice effects), these phonons are pinned
with a mass $m$ and damped at a rate $\Omega$, which we explicitly compute.
This contribution to $\Omega$ is distinct from that of topological defects. We
show that $\Omega\simeq G m^2\Xi$, where $G$ is the shear modulus and $\Xi$ is
related to a diffusivity of the purely spontaneous state. This result follows
from the smallness of the bulk and shear moduli, as would be the case in a
phase with fluctuating translational order. At low temperatures, the collective
modes relax quickly into the heat current, so that late time transport is
dominated by the thermal diffusivity. In this regime, the resistivity in our
model is linear in temperature and the ac conductivity displays a significant
rearranging of the degrees of freedom, as spectral weight is shifted from an
off-axis, pinning peak to a Drude-like peak. These results could shed light on
transport properties in cuprate high $T_c$ superconductors, where quantum
critical behavior and translational order occur over large parts of the phase
diagram and transport shows qualitatively similar features. | 1812.08118v3 |
2020-06-16 | Topological Dirac states in a layered telluride TaPdTe$_5$ with quasi-one-dimensional PdTe$_2$ chains | We report the synthesis and systematic studies of a new layered ternary
telluride TaPdTe5 with quasi-one-dimensional PdTe2 chains. This compound
crystalizes in a layered orthorhombic structure with space group Cmcm. Analysis
of its curved field-dependent Hall resistivity, using the two-band model,
indicates the hole-dominated transport with a high mobility ${\mu}_h$ = 2.38
$\times$ 10$^3$ cm$^2$ V$^{-1}$ s$^{-1}$ at low temperatures. The in-plane
magnetoresistance (MR) displays significant anisotropy with field applied along
the crystallographic $b$ axis. The MR with the current applied along the
$c$-axis is also measured in high magnetic fields up to 51.7 T. Remarkably, it
follows a power-law dependence and reaches (9.5 $\times$ 10$^3$)% at 2.1 K
without any signature of saturation. The De Haas-van Alphen oscillations show a
small Fermi-surface pocket with a nontrivial Berry phase. The Shubnikov-de Haas
(SdH) oscillations are detected at low temperatures and under magnetic fields
above 28.5 T. Two effective masses $m^*$ (0.26$m_e$ and 0.41$m_e$) are
extracted from the oscillatory SdH data. Our first-principles calculations
unveil a topological Dirac cone in its surface states, and, in particular, the
topological index indicates that TaPdTe$_5$ is a topologically nontrivial
material. | 2006.09070v2 |
2020-11-03 | Pressure induced superconductivity in MnSe | The rich phenomena in the FeSe and related compounds have attracted great
interests as it provides fertile material to gain further insight into the
mechanism of high temperature superconductivity. A natural follow-up work was
to look into the possibility of superconductivity in MnSe. It was shown that
MnP becomes superconducting with Tc ~ 1 K under pressure. We demonstrated in
this work that high pressure can effectively suppress the complex magnetic
characters of MnSe crystal when observed at ambient condition. MnSe under
pressure is found to undergo several structural transformations: the cubic
phase first partially transforms to the hexagonal phase at about 12 GPa, the
crystal exhibits the coexistence of cubic, hexagonal and orthorhombic phases
from 16 GPa to 30 GPa, and above 30 GPa the crystal shows a single orthorhombic
phase. Superconductivity with Tc ~ 5 K was first observed at pressure ~12 GPa
by magnetic measurements (~16 GPa by resistive measurements). The highest Tc is
~ 9 K (magnetic result) at ~35 GPa. Our observations suggest the observed
superconductivity may closely relate to the pressure-induced structural change.
However, the interface between the metallic and insulating boundaries may also
play an important role to the pressure induced superconductivity in MnSe. | 2011.01510v1 |
2020-12-24 | Structure, Electrical and Optical Properties of ITO Thin Films and their Influence on Performance of CdS/CdTe Thin-Film Solar Cells | In terms of mixing graded TiO2 and SnO2 powders by solid-state reaction
method, ITO was prepared. Using electron beam gun technology, ITO films with
different thicknesses were prepared. The influence of film thickness on
structure, electrical and optical properties was studied. The XRD patterns were
utilized to determine the structural parameters (lattice strain and crystallite
size) of ITO with different thicknesses. It is observed that the average
crystallite size increases as the film thickness increases, but the lattice
strain decreases. SEM shows that as the film thickness increases, the grain
size of ITO increases and improves. The electrical properties of ITO films with
different thicknesses were measured by the standard four-point probe method. It
can be seen that as the thickness of the ITO film increases from 75 nm to 325
nm, the resistivity decreases from 29x10^-4 Ohm/cm to 1.65x10^-4 Ohm/cm. This
means that ITO films with lower electrical properties will be more suitable for
high-efficiency CdTe solar cells. Three optical layer models (adhesive layer of
the substrate/B-spline layer of ITO film/surface roughness layer) are used to
calculate the film thickness with high-precision ellipsometry. In the higher
T(lambda) and R(lambda) absorption regions, the absorption coefficient is
determined to calculate the optical energy gap, which increases from 3.56 eV to
3.69 eV. Finally, the effects of ITO layers of various thicknesses on the
performance of CdS/CdTe solar cells are also studied. When the thickness of the
ITO window layer is 325 nm, Voc = 0.82 V, Jsc = 17 mA/cm2, and FF = 57.4%, the
highest power conversion efficiency (PCE) is 8.6%. | 2012.13086v1 |
2021-12-26 | The thickness dependence of quantum oscillations in ferromagnetic Weyl metal SrRuO$_{3}$ | Quantum oscillations in resistivity and magnetization at high magnetic fields
are a macroscopic fingerprint of the energy quantization due to the cyclotron
motion of quasiparticles. In a thin Weyl semimetal, a unique thickness
dependent Weyl-orbit quantum oscillation was proposed to exist, originating
from a nonlocal cyclotron orbit via the electron tunneling between the top and
bottom Fermi-arc surface states. Here, untwinned and high crystalline Weyl
metal SrRuO$_3$ thin films with different thicknesses were grown on miscut
SrTiO$_3$ (001) substrates. Magneto-transport measurements were carried out in
magnetic fields up to 35 T, and quantum oscillations with different frequencies
were observed and compared to the calculated band structure. In particular, we
discovered a frequency $F \approx$ 30 T at low temperatures and above 3 T that
corresponds to a small Fermi pocket with a light effective mass. Its
oscillation amplitude appears to be at maximum for film thicknesses in a range
of 10 to 20 nm, and the phase of the oscillation exhibits a systematic change
with the film thickness. After isolating the well separated frequencies, the
constructed Landau fan diagram shows an unusual concave downward curvature in
the 1/$\mu_0H_n$-$n$ curve, where $n$ is the Landau level index. Based on the
rigorous analysis of the thickness and field-orientation dependence of the
quantum oscillations, the oscillation with $F \approx$ 30 T is attributed to be
of surface origin, which is related to the Fermi-arc surface state originating
from non-overlapping Weyl nodes projected on the film's surface plane. Those
findings can be understood within the framework of the Weyl-orbit quantum
oscillation effect with non-adiabatic corrections. | 2112.13331v2 |
2022-08-04 | Strong-Coupling Superconductivity with $T_c$ $\sim$ 10.8 K Induced by P Doping in the Topological Semimetal Mo$_5$Si$_3$ | By performing P doping on the Si sites in the topological semimetal
Mo$_5$Si$_3$, we discover strong-coupling superconductivity in
Mo$_5$Si$_{3-x}$P$_x$ (0.5 $\le$ $x$ $\le$ 2.0). Mo$_5$Si$_3$ crystallizes in
the W$_5$Si$_3$-type structure with space group of $I4/mcm$ (No. 140), and is
not a superconductor itself. Upon P doping, the lattice parameter $a$ decreases
while $c$ increases monotonously. Bulk superconductivity is revealed in
Mo$_5$Si$_{3-x}$P$_x$ (0.5 $\le$ $x$ $\le$ 2.0) from resistivity,
magnetization, and heat capacity measurements. $T_c$ in
Mo$_5$Si$_{1.5}$P$_{1.5}$ reaches as high as 10.8 K, setting a new record among
the W$_5$Si$_3$-type superconductors. The upper and lower critical fields for
Mo$_5$Si$_{1.5}$P$_{1.5}$ are 14.56 T and 105 mT, respectively. Moreover,
Mo$_5$Si$_{1.5}$P$_{1.5}$ is found to be a fully gapped superconductor with
strong electron-phonon coupling. First-principles calculations suggest that the
enhancement of electron-phonon coupling is possibly due to the shift of the
Fermi level, which is induced by electron doping. The calculations also reveal
the nontrivial band topology in Mo$_5$Si$_3$. The $T_c$ and upper critical
field in Mo$_5$Si$_{3-x}$P$_x$ are fairly high among pseudobinary compounds.
Both of them are higher than those in NbTi, making future applications
promising. Our results suggest that the W$_5$Si$_3$-type compounds are ideal
platforms to search for new superconductors. By examinations of their band
topologies, more candidates for topological superconductors can be expected in
this structural family. | 2208.02392v1 |
2023-05-19 | Machine Learning Moment Tensor Potential for Modelling Dislocation and Fracture in L1$_0$-TiAl and D0$_{19}$-Ti$_3$Al Alloys | Dual-phase $\gamma$-TiAl and $\alpha_2$-Ti$_{3}$Al alloys exhibit high
strength and creep resistance at high temperatures. However, they suffer from
low tensile ductility and fracture toughness at room temperature. Experimental
studies show unusual plastic behaviour associated with ordinary and
superdislocations, making it necessary to gain a detailed understanding on
their core properties in individual phases and at the two-phase interfaces.
Unfortunately, extended superdislocation cores are widely dissociated beyond
the length scales practical for routine first-principles density-functional
theory (DFT) calculations, while extant interatomic potentials are not
quantitatively accurate to reveal mechanistic origins of the unusual
core-related behaviour in either phases. Here, we develop a highly-accurate
moment tensor potential (MTP) for the binary Ti-Al alloy system using a DFT
dataset covering a broad range of intermetallic and solid solution structures.
The optimized MTP is rigorously benchmarked against both previous and new DFT
calculations, and unlike existing potentials, is shown to possess outstanding
accuracy in nearly all tested mechanical properties, including lattice
parameters, elastic constants, surface energies, and generalized stacking fault
energies (GSFE) in both phases. The utility of the MTP is further demonstrated
by producing dislocation core structures largely consistent with expectations
from DFT-GSFE and experimental observations. The new MTP opens the path to
realistic modelling and simulations of bulk lattice and defect properties
relevant to the plastic deformation and fracture processes in $\gamma$-TiAl and
$\alpha_2$-Ti$_{3}$Al dual-phase alloys. | 2305.11825v2 |
2023-06-05 | Imaging the Meissner effect and flux trapping in a hydride superconductor at megabar pressures using a nanoscale quantum sensor | By directly altering microscopic interactions, pressure provides a powerful
tuning knob for the exploration of condensed phases and geophysical phenomena.
The megabar regime represents an exciting frontier, where recent discoveries
include novel high-temperature superconductors, as well as structural and
valence phase transitions. However, at such high pressures, many conventional
measurement techniques fail. Here, we demonstrate the ability to perform local
magnetometry inside of a diamond anvil cell with sub-micron spatial resolution
at megabar pressures. Our approach utilizes a shallow layer of Nitrogen-Vacancy
(NV) color centers implanted directly within the anvil; crucially, we choose a
crystal cut compatible with the intrinsic symmetries of the NV center to enable
functionality at megabar pressures. We apply our technique to characterize a
recently discovered hydride superconductor, CeH$_9$. By performing simultaneous
magnetometry and electrical transport measurements, we observe the dual
signatures of superconductivity: local diamagnetism characteristic of the
Meissner effect and a sharp drop of the resistance to near zero. By locally
mapping the Meissner effect and flux trapping, we directly image the geometry
of superconducting regions, revealing significant inhomogeneities at the micron
scale. Our work brings quantum sensing to the megabar frontier and enables the
closed loop optimization of superhydride materials synthesis. | 2306.03122v1 |
2023-06-24 | Exploration of strongly correlated states in SmB6 through a comparison of its two-coil pick-up response to that of Bi2Se3 | Earlier studies on the Kondo insulator SmB6 reveal the presence of a bulk
Kondo insulating gap between 30 - 50 K, and the emergence of a conducting
surface state only below 4 K. Here, we compare the two-coil mutual inductance
pick-up response of SmB6 single crystal with that of a conventional topological
insulator (TI), Bi2Se3 single crystal. From these studies we identify three
distinct temperature regimes for SmB6, viz., (i) T >= T*(~ 66 K), (ii) (40 K~)
T_g <= T < T*, and (iii) T < T_g. At T* in SmB6, we observe a peak in the
temperature-dependent AC pickup signal which corresponds to the peak in the
broad hump feature in the bulk DC susceptibility measurements and features in
the resistivity measurements. A dip in the pickup signal at T_g in SmB6
correlates with the evidence for the opening of a bulk Kondo gap in transport
measurements. Our study of the pickup signal in SmB6 suggests the presence of a
thin (submicron order thickness) high conducting surface layer from a
temperature just below T_g. In this T regime in SmB6, the pickup signal shows a
distinct square root frequency (f) dependence compared to the linear f
dependence found in Bi2Se3. Across all the different T regimes, distinct AC
frequency dependence and scaling properties are observed. Our results suggest
that above T*, weak exchange interactions cause electrons to scatter from
random ion sites. Electronic correlations gradually strengthen with the onset
of Kondo like hybridization, setting in from below T*, and at T_g, a strongly
correlated Kondo gap opens up in the bulk of the material. The appearance of
the thin high conducting surface layer is nearly coincident with the onset of
bulk Kondo insulating state below T_g in SmB6. | 2306.13901v1 |
2024-01-07 | Tantalum airbridges for scalable superconducting quantum processors | The unique property of tantalum (Ta), particularly its long coherent lifetime
in superconducting qubits and its exceptional resistance to both acid and
alkali, makes it promising for superconducting quantum processors. It is a
notable advantage to achieve high-performance quantum processors with neat and
unified fabrication of all circuit elements, including coplanar waveguides
(CPW), qubits, and airbridges, on the tantalum film-based platform. Here, we
propose a reliable tantalum airbridges with separate or fully-capped structure
fabricated via a novel lift-off method, where a barrier layer with aluminium
(Al) film is first introduced to separate two layers of photoresist and then
etched away before the deposition of tantalum film, followed by cleaning with
piranha solution to remove the residual photoresist on the chip. We
characterize such tantalum airbridges as the control line jumpers, the ground
plane crossovers and even coupling elements. They exhibit excellent
connectivity, minimal capacitive loss, effectively suppress microwave and flux
crosstalk and offer high freedom of coupling. Besides, by presenting a
surface-13 tunable coupling superconducting quantum processor with median $T_1$
reaching above 100 $\mu$s, the overall adaptability of tantalum airbridges is
verified. The median single-qubit gate fidelity shows a tiny decrease from
about 99.95% for the isolated Randomized Benchmarking to 99.94% for the
simultaneous one. This fabrication method, compatible with all known
superconducting materials, requires mild conditions of film deposition compared
with the commonly used etching and grayscale lithography. Meanwhile, the
experimental achievement of non-local coupling with controlled-Z (CZ) gate
fidelity exceeding 99.2% may further facilitate qLDPC codes, laying a
foundation for scalable quantum computation and quantum error correction with
entirely tantalum elements. | 2401.03537v1 |
2024-04-16 | A Young Super Star Cluster Powering a Nebula of Retained Massive Star Ejecta | We suggest that "Godzilla", an intriguing source in the lensed Sunburst
galaxy at $z=2.37$, is a young super star cluster powering a compact nebula
within gravitationally trapped stellar ejecta. Employing HST photometry and
spectroscopy from MUSE and X-Shooter at VLT, we infer physical and chemical
properties of the cluster and nebula, finding Godzilla is young (4-6 Myr),
massive ($\sim 10^{6-7}M_\odot$), a stellar metallicity $Z \simeq 0.25Z_\odot$,
and has the FUV component more compact than a few pc. The nebula gas is
significantly enriched with N and He, indicating stellar wind material, and has
highly elevated O relative to the sub-solar stellar metallicity, which
indicates entrainment of CCSNe ejecta. The high gas density $n_{\rm e} \simeq
10^{7-8}{\rm cm}^{-3}$ implies a highly pressurized intracluster environment.
We propose the high pressure is due to CCSN-driven supersonic turbulence in
warm, self-shielding gas, which has accumulated in the cluster center after
runaway radiative cooling and is dense enough to resist removal by CCSNe. The
nebula gas shows sub-solar C/O, Ne/O and Si/O values, which may reflect the
CCSN element yields for initial stellar masses $>40M_\odot$. A comparison to
element yield synthesis models for young star clusters shows that the gas
abundance pattern is consistent with complete retention and mixture of stellar
winds and CCSNe ejecta until the inferred cluster age. The O and He enhancement
we find may have implications for the formation of multiple stellar populations
in globular clusters, as Godzilla likely has already formed second-generation
stars prior to the onset of CCSNe and evolved star winds, in order not to
contradict the non-observation of O and large He enhancement in
second-generation stars. | 2404.10755v2 |
2023-02-09 | Scattering-dependent transport of SrRuO3 films: From Weyl fermion transport to hump-like Hall effect anomaly | Recent observation of quantum transport phenomena of Weyl fermions has
brought much attention to 4d ferromagnetic perovskite SrRuO3 as a magnetic Weyl
semimetal. Besides, the hump-like Hall effect anomaly, which might have a
topological origin, has also been reported for this material. Here, we show
that the emergence of such phenomena is governed by the degree of scattering
determined by the defect density (Ru-deficiency- and/or interface-driven-defect
scattering) and measurement temperature (phonon scattering), where the former
is controlled by varying the growth conditions of the SrRuO3 films in molecular
beam epitaxy as well as the film thickness. The resulting electronic transport
properties can be classified into three categories: clean, intermediate, and
dirty regimes. The transport of Weyl fermions emerges in the clean regime,
whereas that of topologically trivial conduction electrons in the ferromagnetic
metal state prevail in the intermediate and dirty regimes. In the clean and
intermediate regimes, anomalous Hall resistivity obeys a scaling law
incorporating the intrinsic Karplus-Luttinger (Berry phase) and extrinsic
side-jump mechanisms. The hump-like Hall effect anomaly is observed only in the
dirty regime, which is contrary to the scaling law between anomalous Hall
resistivity and longitudinal resistivity. Hence, we conclude that this anomaly
is not inherent to the material and does not have a topological origin. We also
provide defect- and temperature-dependent transport phase diagrams of
stoichiometric SrRuO3 and Ru-deficient SrRu0.7O3 where the appearance of Weyl
fermions and hump-like Hall effect anomaly are mapped. These diagrams may serve
as a guideline for designing SrRu1-xO3-based spintronic and topological
electronic devices. | 2302.04568v1 |
2024-02-29 | Magnetism, heat capacity and electronic structure of EuCd$_2$P$_2$ in view of its colossal magnetoresistance | The mechanism of the peculiar transport properties around the magnetic
ordering temperature of semiconducting antiferromagnetic EuCd$_2$P$_2$ is not
yet understood. With a huge peak in the resistivity observed above the N\'eel
temperature, $T_{\rm N}=10.6\,\rm K$, it exhibits a colossal magnetoresistance
effect. Recent reports on observations of ferromagnetic contributions above
$T_{\rm N}$ as well as metallic behavior below this temperature have motivated
us to perform a comprehensive characterization of this material, including its
resistivity, heat capacity, magnetic properties and electronic structure. Our
transport measurements revealed quite different temperature dependence of
resistivity with the maximum at $14\,\rm K$ instead of previously reported
$18\,\rm K$. Low-field susceptibility data support the presence of static
ferromagnetism above $T_{\rm N}$ and show a complex behavior of the material at
small applied magnetic fields. Namely, signatures of reorientation of magnetic
domains are observed up to $T=16\,\rm K$. Our magnetization measurements
indicate a magnetocrystalline anisotropy which also leads to a preferred
alignment of the magnetic clusters above $T_{\rm N}$. The momentum-resolved
photoemission experiments at temperatures from $24\,\rm K$ down to $2.5\,\rm K$
indicate the permanent presence of a fundamental band gap without change of the
electronic structure when going through $T_N$ that is in contradiction with
previous results. We performed \textit{ab initio} band structure calculations
which are in good agreement with the measured photoemission data when assuming
an antiferromagnetic ground state. Calculations for the ferromagnetic phase
show a much smaller bandgap, indicating the importance of possible
ferromagnetic contributions for the explanation of the colossal
magnetoresistance effect in the related EuZn$_2$P$_2$. | 2402.18911v1 |
2023-01-14 | Discovery of 2D materials using Transformer Network based Generative Design | Two-dimensional (2D) materials have wide applications in superconductors,
quantum, and topological materials. However, their rational design is not well
established, and currently less than 6,000 experimentally synthesized 2D
materials have been reported. Recently, deep learning, data-mining, and density
functional theory (DFT)-based high-throughput calculations are widely performed
to discover potential new materials for diverse applications. Here we propose a
generative material design pipeline, namely material transformer
generator(MTG), for large-scale discovery of hypothetical 2D materials. We
train two 2D materials composition generators using self-learning neural
language models based on Transformers with and without transfer learning. The
models are then used to generate a large number of candidate 2D compositions,
which are fed to known 2D materials templates for crystal structure prediction.
Next, we performed DFT computations to study their thermodynamic stability
based on energy-above-hull and formation energy. We report four new
DFT-verified stable 2D materials with zero e-above-hull energies, including
NiCl$_4$, IrSBr, CuBr$_3$, and CoBrCl. Our work thus demonstrates the potential
of our MTG generative materials design pipeline in the discovery of novel 2D
materials and other functional materials. | 2301.05824v1 |
2014-05-15 | Effect of high pressure annealing on the normal state transport of LaO0.5F0.5BiS2 | We study normal state electrical, thermoelectrical and thermal transport in
polycrystalline BiS2-based compounds, which become superconducting by F doping
on the O site. In particular we explore undoped LaOBiS2 and doped
LaO0.5F0.5BiS2 samples, prepared either with or without high pressure
annealing, in order to evidence the roles of doping and preparation conditions.
The high pressure annealed sample exhibits room temperature values of
resistivity ro around 5 mohmcm, Seebeck coefficient S around -20 microV/K and
thermal conductivity k around 1.5 W/Km, while the Hall resistance RH is
negative at all temperatures and its value is -10-8 m3/C at low temperature.
The sample prepared at ambient pressure exhibits RH positive in sign and five
times larger in magnitude, and S negative in sign and slightly smaller in
magnitude. These results reveal a complex multiband evolution brought about by
high pressure annealing. In particular, the sign inversion and magnitude
suppression of RH, indicating increased electron-type carrier density in the
high pressure sample, may be closely related to previous findings about change
in lattice parameters and enhancement of superconducting Tc by high pressure
annealing. As for the undoped sample, it exhibits the 10 times larger
resistivity, 10 times larger |S| and 10 times larger |RH| than its doped
counterpart, consistently with its insulating nature. Our results point out the
dramatic effect of preparation conditions in affecting charge carrier density
as well as structural, band and electronic parameters in these systems. | 1405.3832v2 |
2021-09-05 | On the design of particle filters inspired by animal noses | Passive filtering is a common strategy used to reduce airborne disease
transmission and particulate contaminants in buildings and individual covers.
The engineering of high-performance filters with relatively low flow resistance
but high virus- or particle-blocking efficiency is a nontrivial problem of
paramount relevance, as evidenced in the variety of industrial filtration
systems and the worldwide use of face masks. In this case, standard N95-level
covers have high virus-blocking efficiency, but they can cause breathing
discomfort. Next-generation industrial filters and masks should retain
sufficiently small droplets and aerosols while having low resistance. We
introduce a novel 3D printable particle filter inspired by animals' complex
nasal anatomy. Unlike standard random-media-based filters, the proposed concept
relies on equally spaced channels with tortuous airflow paths. These two
strategies induce distinct effects: a reduced resistance and a high likelihood
of particle trapping by altering their trajectories with tortuous paths and
induced local flow instability. The structures are tested for pressure drop and
particle filtering efficiency over a wide range of airflow rates. We have also
cross-validated the observed efficiency through numerical simulations. The
designed filters exhibit a lower pressure drop than the commercial mask and air
filters (N95, surgical, and high-efficiency particulate air (HEPA)). The
concept provides a new approach to developing scalable, flexible,
high-efficiency air filters for various engineering applications. | 2109.08018v1 |
1997-09-27 | Low-temperature electrical transport and double exchange in La(Pb,Ca)MnO | The resistivity in the ferromagnetic state of flux-grown
La_{2/3}(Pb,Ca)_{1/3}MnO_3 single crystals, measured in magnetic fields up to 7
T, reveals a strong quadratic temperature dependence at and above 50 K. At
lower temperatures, this contribution drops precipitously leaving the
resistivity essentially temperature independent below 20 K. The Seebeck
coefficient also reflects a change of regime at the same temperature. We
attribute this behavior to a cut-off of single magnon scattering processes at
long wavelengths due to the polarized bands of a double-exchange ferromagnet. | 9709305v3 |
1998-01-07 | Theory of the Resistive Transition in Overdoped $Tl_2Ba_2CuO_{6+x}$: Implications for the angular dependence of the quasiparticle scattering rate in High-$T_c$ superconductors | We show that recent measurements of the magnetic field dependence of the
magnetization, specific heat and resistivity of overdoped $T_c \sim 17K$
$Tl_{2}Ba_{2}CuO_{6+\delta}$ in the vicinity of the superconducting $H_{c2}$
imply that the vortex viscosity is anomalously small and that the material
studied is inhomogeneous with small, a few hundred $\AA$, regions in which the
local $T_{c}$ is much higher than the bulk $T_{c}$. The anomalously small
vortex viscosity can be derived from a microscopic model in which the
quasiparticle lifetime varies dramatically around the Fermi surface, being
small everywhere except along the zone diagonal (``cold spot''). We propose
experimental tests of our results. | 9801059v1 |
1998-08-25 | P-wave Pairing and Colossal Magnetoresistance in Manganese Oxides | We point out that the existing experimental data of most manganese oxides
show the {\sl frustrated} p-wave superconducting condensation in the
ferromagnetic phase in the sense that the superconducting coherence is not long
enough to cover the whole system. The superconducting state is similar to the
$A_{1}$ state in superfluid He-3. The sharp drop of resistivity, the steep jump
of specific heat, and the gap opening in tunneling are well understood in terms
of the p-wave pairing. In addition, colossal magnetoresistance (CMR) is
naturally explained by the superconducting fluctuations with increasing
magnetic fields. The finite resistivity may be due to some magnetic
inhomogeneities. This study leads to the possibility of room temperature
superconductivity. | 9808275v1 |
1998-10-30 | Hall Effect of La2/3(Ca,Pb)1/3MnO3 Single Crystals near the Critical Temperature | The Hall resistivity rho_{xy} of a La_{2/3}(Ca,Pb)_{1/3}MnO_3 single crystal
has been measured as a function of temperature and field. The overall behavior
is similar to that observed previously in thin-films. At 5 K, rho_{xy} is
positive and linear in field, indicating that the anomalous contribution $R_S$
is negligible. However, the effective carrier density in a free electron model
is n_{eff}=2.4 holes/Mn, even larger than the 0.85-1.9 holes/Mn reported for
thin-films and far larger than the 0.33 holes/Mn expected from the doping
level. As temperature increases, a strong, negative contribution to rho_{xy}
appears, that we ascribe to R_S. Using detailed magnetization data, we separate
the ordinary (\propto B) and anomalous (\propto M) contributions. Below T_C,
R_S \propto rho_{xx}, indicating that magnetic skew scattering is the dominant
mechanism in the metallic ferromagnetic regime. At and above the
resistivity-peak temperature, we find that rho_{xy}/rho_{xx}M is a constant,
independent of temperature and field. This implies that the anomalous Hall
coefficient is proportional to the magnetoresistance. A different explanation
based on two fluid model is also presented. | 9810410v1 |
1998-11-28 | Negative Differential Resistance in the Scanning Tunneling Spectroscopy of Organic molecules | The conductance-voltage spectrum of molecular nanostructures measured by
scanning tunneling spectroscopy (STS) is generally assumed to reflect the local
density of states of the molecule. This excludes the possibility of observing
negative differential resistance (NDR). We report here the observation of NDR
in the scanning tunneling microscope (STM) current-voltage (I-V)
characteristics of self-assembled monolayer (SAM) of 4-p-Terphenylthiol
molecules on gold substrate measured using a platinum probe. We argue that the
NDR arises from narrow structures in the local density of states at the tip
apex atom and show that depending on the electrostatic potential profile across
the system, NDR could be observed in one or both bias directions. | 9811402v1 |
1998-12-27 | Field Induced Transition from Metal to Insulator in the CMR Manganites | The gigantic reduction of the electric resistivity under the applied magnetic
field, CMR effect, is now widely accepted to appear in the vicinity of the
insulator to metal transition of the perovskite manganites. Recently, we have
discovered the first order transition from ferromagnetic metal to insulator in
$\rm La_{0.88}Sr_{0.12}MnO_3$ of the CMR manganite. This phase transition
induces the tremendous increase of the resistivity under the external magnetic
field just near above the phase transition temperature. We report here fairly
detailed results from the systematic experiments including neutron and
synchrotron X-ray scattering studies. | 9812404v1 |
1999-01-25 | Influence of Cu on spin-polaron tunneling in the ferromagnetic state of La(2/3)Ca(1/3)Mn(1-x)Cu(x)O(3) from the resistivity data | Nearly a 50% decrease of resistivity \rho (T,x) due to just 4% Cu doping on
the Mn site of La(2/3)Ca(1/3)Mn(1-x)Cu(x)O(3) is observed. Attributing the
observed phenomenon to the substitution induced decrease of the spin polaron
energy E_s(x) below the Curie point T_C(x)=T_C(0)(1-x), all data are found to
be well fitted by the nonthermal coherent tunneling expression \rho (T,x) =
\rho_0*exp(-\gamma M^2(T,x)) assuming
M(T,x)=M_R(x)+M_0(x)*tanh{\sqrt{[T_C(x)/T]^2-1}} for the magnetization in the
ferromagnetic state. The best fits through all the data points yield M_0(x)=
\sqrt(1-x)M_0(0), M_R(x)=\sqrt(x)M_0(0), and E_s(x)=E_s(0)(1-x)^4 for the Cu
induced modifications of the Mn spins dominated zero-temperature spontaneous
magnetization, the residual paramagnetic contribution, and spin-polaron energy,
respectively, with E_s(0)=0.12 eV. | 9901263v1 |
1999-03-03 | c-axis Tunneling in Nb/Au/YBaCuO Structures | We present the experimental results for Nb/Au/YBaCuO structures, in which the
current flows along (001) direction of YBaCuO film. The theoretical evaluations
show, that at the experimental values of the Au/YBaCuO interface transparency,
determined from the interface resistance D~10^-6, the critical current of the
structure is of the fluctuation order of magnitude due to the sharp decrease of
the amplitude potential of the superconducting carriers on this interface.
Obtained I-V-curves could be interpreted in terms of contact between d-type
pairing superconductor or gapless isotropic superconductor with normal metal.
No critical current was observed for investigated structures with
characteristic interface resistance RnS~10^-6 Ohm cm^2, 2 orders of magnitude
lower, than for known experimental data. PACS: 74.50.+r, 74.72.Bk | 9903065v1 |
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