publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2009-12-08 | Anisotropy of upper critical field in one-dimensional organic system, (TMTTF)$_2$PF$_6$ under extremely high pressure | We have measured the temperature dependent resistivity of (TMTTF)$_2$PF$_6$
to 7 GPa using a turnbuckle DAC (diamond anvil cell) and in magnetic field up
to 5 T. Unlike many other organic conductors, a zero resistance was observed in
the superconducting state even under high pressures. Superconductivity was
observed over a range of $P$ = 4.18 GPa to 6.03 GPa and showed a peak $T_c$ of
2.25 K at 4.58 GPa. The temperature dependence of the upper critical magnetic
field $H_{c2}(T)$ was determined via resistivity at $P$ = 4.58 GPa, for the
intrachain ($a$), interchain ($b'$), and interlayer ($c^*$) configurations and
the $H_{c2}(T)$ displays positive curvature without saturation, which may be
originated by a FFLO state, for magnetic field along a-axis and $b'$-axis in T
$\ge$ 0.5 K for $P$ = 4.48 GPa. This feature is suppressed with increasing
pressure and the orbital pair breaking mechanism becomes dominant. The values
of the Ginzberg-Landau coherence length for three different axes obtained from
this work shows that (TMTTF)$_2$PF$_6$ is an anisotropic three - dimensional
superconductor. | 0912.1391v1 |
2011-01-06 | Pressure effect on superconductivity of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs) | We performed the high hydrostatic pressure resistivity measurements (up to
1.7 GPa) on the newly discovered superconductors $A_{x}$Fe$_2$Se$_2$ ($A$ = K
and Cs) single crystals. Two batches of single crystals $K_xFe_2Se_2$ with
different transition temperatures ($T_c$) were used to study the effect of
pressure. The $T_c$ of the first one gradually decreases with increasing
pressure from 32.6 K at ambient pressure. While a dome-like behavior was
observed for the crystal with $T_c=31.1$ K, and $T_c$ reaches its maximum value
of 32.7 K at the pressure of 0.48 GPa. It indicates that there exists a optimal
doping with maximum $T_c$ of 32.7K in $K_xFe_2Se_2$ system. The behavior of
$T_c$ vs. pressure for $Cs_xFe_2Se_2$ also shows a dome-like behavior, and
$T_c$ reaches its maximum value of 31.1 K at the pressure of 0.82 GPa. The hump
observed in temperature dependence of resistivity for all the samples tends to
shift to high temperature with increasing pressure. The resistivity hump could
arise from the vacancy of Fe or Se. | 1101.1234v1 |
2011-08-08 | Sub-micrometer epitaxial Josephson junctions for quantum circuits | We present a fabrication scheme and testing results for epitaxial
sub-micrometer Josephson junctions. The junctions are made using a
high-temperature (1170 K) "via process" yielding junctions as small as 0.8 mu m
in diameter by use of optical lithography. Sapphire (Al2O3) tunnel-barriers are
grown on an epitaxial Re/Ti multilayer base-electrode. We have fabricated
devices with both Re and Al top electrodes. While room-temperature (295 K)
resistance versus area data are favorable for both types of top electrodes, the
low-temperature (50 mK) data show that junctions with the Al top electrode have
a much higher subgap resistance. The microwave loss properties of the junctions
have been measured by use of superconducting Josephson junction qubits. The
results show that high subgap resistance correlates to improved qubit
performance. | 1108.1830v2 |
2011-09-29 | Comparative Survival Analysis of Deinococcus Radiodurans and the Haloarchaea Natrialba Magadii and Haloferax Volcanii, Exposed to Vacuum Ultraviolet Irradiation | The haloarchaea Natrialba magadii and Haloferax volcanii, as well as the
radiation-resistant bacterium Deinococcus radiodurans, were exposed to
vacuum-UV (V-UV) radiation at the Brazilian Synchrotron Light Laboratory
(LNLS). Cell monolayers (containing 105 - 106 cells per sample) were prepared
over polycarbonate filters and irradiated under high vacuum (10-5 Pa) with
polychromatic synchrotron radiation. N. magadii was remarkably resistant to
high vacuum with a survival fraction of ((3.77 \pm 0.76) x 10-2), larger than
the one of D. radiodurans ((1.13 \pm 0.23) x 10-2). The survival fraction of
the haloarchaea H. volcanii, of ((3.60 \pm 1.80) x 10-4), was much smaller.
Radiation resistance profiles were similar between the haloarchaea and D.
radiodurans for fluencies up to 150 J m-2. For fluencies larger than 150 J m-2
there was a significant decrease in the survival of haloarchaea, and in
particular H. volcanii did not survive. Survival for D. radiodurans was 1%
after exposure to the higher V-UV fluency (1350 J m-2) while N. magadii had a
survival lower than 0.1%. Such survival fractions are discussed regarding the
possibility of interplanetary transfer of viable micro-organisms and the
possible existence of microbial life in extraterrestrial salty environments
such as the planet Mars and the Jupiter's moon Europa. This is the first work
reporting survival of haloarchaea under simulated interplanetary conditions. | 1109.6590v1 |
2013-08-06 | Impurity effect and suppression to superconductivity in Na(Fe$_{0.97-x}$Co$_{0.03}$T$_x$)As (T=Cu, Mn) | We report the successful growth and the impurity scattering effect of single
crystals of Na(Fe$_{0.97-x}$Co$_{0.03}$T$_x$)As (T=Cu, Mn). The temperature
dependence of DC magnetization at high magnetic fields is measured for
different concentrations of Cu and Mn. Detailed analysis based on the
Curie-Weiss law indicates that the Cu doping weakens the average magnetic
moments, while doping Mn enhances the local magnetic moments greatly,
suggesting that the former may be non- or very weak magnetic impurities, and
the latter give rise to magnetic impurities. However, it is found that both
doping Cu and Mn will enhance the residual resistivity and suppress the
superconductivity at the same rate in the low doping region, being consistent
with the prediction of the S$^{\pm}$ model. For the Cu-doped system, the
superconductivity is suppressed completely at a residual resistivity $\rho_0$ =
0.87 m$\Omega$ cm at which a strong localization effect is observed. However,
in the case of Mn doping, the behavior of suppression to \emph{T}$_{c}$ changes
from a fast speed to a slow one and keeps superconductive even up to a residual
resistivity of 2.86 m$\Omega$ cm. Clearly the magnetic Mn impurities are even
not as detrimental as the non- or very weak magnetic Cu impurities to
superconductivity in the high doping regime. | 1308.1356v1 |
2013-10-31 | A Technique for Write-endurance aware Management of Resistive RAM Last Level Caches | Due to increasing cache sizes and large leakage consumption of SRAM device,
conventional SRAM caches contribute significantly to the processor power
consumption. Recently researchers have used non-volatile memory devices to
design caches, since they provide high density, comparable read latency and low
leakage power dissipation. However, their high write latency may increase the
execution time and hence, leakage energy consumption. Also, since their write
endurance is small, a conventional energy saving technique may further
aggravate the problem of write-variations, thus reducing their lifetime. In
this paper, we present a cache energy saving technique for non-volatile caches,
which also attempts to improve their lifetime by making writes equally
distributed to the cache. Our technique uses dynamic cache reconfiguration to
adjust the cache size to meet program requirement and turns off the remaining
cache to save energy. Microarchitectural simulations performed using an x86-64
simulator, SPEC2006 benchmarks and a resistive-RAM LLC (last level cache) show
that over an 8MB baseline cache, our technique saves 17.55% memory subsystem
(last level cache + main memory) energy and improves the lifetime by 1.33X.
Over the same resistive-RAM baseline, an SRAM of similar area with no cache
reconfiguration leads to an energy loss of 186.13%. | 1311.0041v2 |
2014-06-11 | Signatures of localization in the effective metallic regime of high mobility Si MOSFETs | Combining experimental data, numerical transport calculations, and
theoretical analysis, we study the temperature-dependent resistivity of
high-mobility 2D Si MOSFETs to search for signatures of weak localization
induced quantum corrections in the effective metallic regime above the critical
density of the so-called two-dimensional metal-insulator transition (2D MIT).
The goal is to look for the effect of logarithmic insulating localization
correction to the metallic temperature dependence in the 2D conductivity so as
to distinguish between the 2D MIT being a true quantum phase transition versus
being a finite-temperature crossover. We use the Boltzmann theory of
resistivity including the temperature dependent screening effect on charged
impurities in the system to fit the data. We analyze weak perpendicluar field
magnetoresistance data taken in the vicinity of the transition and show that
they are consistent with weak localization behavior in the strongly disordered
regime $k_F\ell\gtrsim1$. Therefore we supplement the Botzmann transport theory
with a logarithmic in temperature quantum weak localization correction and
analyze the competition of the insulating temperature dependence of this
correction with the metallic temperature dependence of the Boltzmann
conductivity. Using this minimal theoretical model we find that the logarithmic
insulating correction is masked by the metallic temperature dependence of the
Botzmann resistivity and therefore the insulating $\log T$ behavior may be
apparent only at very low temperatures which are often beyond the range of
temperatures accessible experimentally. Analyzing the low-$T$ experimental Si
MOSFET transport data we identify signatures of the putative insulating
behavior at low temperature and density in the effective metallic phase. | 1406.3024v2 |
2016-04-13 | Remarkable magnetostructural coupling around the magnetic transition in CeCo$_{0.85}$Fe$_{0.15}$Si | We report a detailed study of the magnetic properties of
CeCo$_{0.85}$Fe$_{0.15}$Si under high magnetic fields (up to 16 Tesla)
measuring different physical properties such as specific heat, magnetization,
electrical resistivity, thermal expansion and magnetostriction.
CeCo$_{0.85}$Fe$_{0.15}$Si becomes antiferromagnetic at $T_N \approx$ 6.7 K.
However, a broad tail (onset at $T_X \approx$ 13 K) in the specific heat
precedes that second order transition. This tail is also observed in the
temperature derivative of the resistivity. However, it is particularly
noticeable in the thermal expansion coefficient where it takes the form of a
large bump centered at $T_X$. A high magnetic field practically washes out that
tail in the resistivity. But surprisingly, the bump in the thermal expansion
becomes a well pronounced peak fully split from the magnetic transition at
$T_N$. Concurrently, the magnetoresistance also switches from negative to
positive just below $T_X$. The magnetostriction is considerable and
irreversible at low temperature ($\frac {\Delta L}{L} \left(16 T\right) \sim$
4$\times$10$^{-4}$ at 2 K) when the magnetic interactions dominate. A broad
jump in the field dependence of the magnetostriction observed at low $T$ may be
the signature of a weak ongoing metamagnetic transition. Taking altogether, the
results indicate the importance of the lattice effects in the development of
the magnetic order in these alloys. | 1604.03985v1 |
2018-01-19 | High pressure effects on non-fluorinated BiS2-based superconductors La$_{1-x}$M$_x$OBiS$_2$ (M = Ti and Th) | Layered \textit{Ln}OBiS$_2$ compounds with \textit{Ln} = La, Ce, Pr, Nd, and
Yb can be rendered conducting and superconducting via two routes, substitution
of F for O or the tetravalent ions Ti, Zr, Hf, and Th for trivalent \textit{Ln}
ions. Electrical resistivity measurements on non-fluorinated
La$_{0.80}$Ti$_{0.20}$OBiS$_2$ and La$_{0.85}$Th$_{0.15}$OBiS$_2$
superconductors were performed between $\sim$1.5 K and 300 K and under pressure
up to 2.4 GPa. For both compounds, the superconducting transition temperature
$T_c$, which is $\sim$2.9 K at ambient pressure, gradually increases with
pressure to 3.2-3.7 K at $\sim$1 GPa, above which it is suppressed and the
superconducting transitions become very broad. Measurements of the normal state
electrical resistivity of the two compounds reveal discontinuous changes of the
resistivity as a function of pressure at $\sim$0.6 GPa. Surprisingly, above 1.3
GPa, semiconducting-like behavior reappears in La$_{0.80}$Ti$_{0.20}$OBiS$_2$.
This study reveals a new high-pressure phase of La$_{1-x}$$M$$_x$OBiS$_2$
containing the tetravalent ions $M$ = Ti, Th which does not favor
superconductivity. In contrast, application of pressure to fluorinated
LaO$_0.5$F$_0.5$BiS$_2$ produces an abrupt tetragonal-monoclinic transition to
a metallic phase with an enhanced $T_c$. These results demonstrate that the
response of the normal and superconducting properties of LaOBiS$_2$-based
compounds depends strongly on the atomic site where the electron donor ions are
substituted. | 1801.06568v1 |
2018-05-23 | Discovery of a new nontoxic cuprate superconducting system Ga-Ba-Ca-Cu-O | Superconductivity is observed in a new nontoxic cuprate system Ga-Ba-Ca-Cu-O,
with Tc = 82K for GaBa2Ca5Cu6O14+{\delta} (Ga-1256) and Tc = 116K probably for
GaBa2Ca3Cu4O10+{\delta} (Ga-1234) or GaBa2Ca2Cu3O8+{\delta} (Ga-1223),
respectively. All compounds are fabricated by solid state reaction method under
high pressure and high temperature. Samples are characterized by resistivity,
magnetization and X-ray diffraction (XRD) measurements. The temperature
dependence of magnetization measured in both zero-field-cooled and field-cooled
processes on one sample (S1) shows two superconducting transitions at about 82K
and 113K. The estimated shielding fraction for the phase with Tc of 82K is
about 67%, while the fraction for another phase with Tc of 113K is quite small.
The XRD Rietveld refinement for S1 indicates two main phases existing in the
sample, Ga-1256 with fraction of about 58% and non-superconducting Ca0.85CuO2
with fraction of about 42%, respectively. Thus, we can conclude the
superconducting phase with transition temperature of 82K is due to Ga-1256. The
resistivity measurement also confirms the superconductivity for S1, and the
resistivity reaches zero at about 82K. The temperature dependence of
magnetization for another sample (S2) shows much higher superconducting
shielding fraction for the phase with Tc of 116K, which may be a promising
prospective for the synthesis of Ga-1234 or Ga-1223 phase. | 1805.09268v1 |
2018-06-11 | Development of a new Front End electronics in Silicon and Silicon-Germanium technology for the Resistive Plate Chamber detector for high rate experiments | The upgrade of the Resistive Plate Chamber (RPC) detector, in order to
increase the detector rate capability and to be able to work efficiently in
high rate environment, consists in the reduction of the operating voltage along
with the detection of signals which are few hundred {\mu}V small. The approach
chosen by this project to achieve this objective is to develop a new kind of
Front End electronics which, thanks to a mixed technology in Silicon and
Silicon-Germanium, enhance the detector performances increasing its rate
capability. The Front End developed is composed by a preamplifier in Silicon
BJT technology with a very low inner noise (1000 $e^{-}$ rms) and an
amplification factor of 0.3-0.4 mV/fC and a new kind of discriminator in SiGe
HJT technology which allows a minimum threshold of the order of 0.5 mV. The
performances of this kind of Front End will be shown. The results are obtained
by using the CERN H8 beamline with a full-size RPC chamber of 1 mm gas gap and
1.2 mm thickness of electrodes equipped with this kind of Front End
electronics. | 1806.04113v1 |
2019-09-16 | High-Throughput In-Memory Computing for Binary Deep Neural Networks with Monolithically Integrated RRAM and 90nm CMOS | Deep learning hardware designs have been bottlenecked by conventional
memories such as SRAM due to density, leakage and parallel computing
challenges. Resistive devices can address the density and volatility issues,
but have been limited by peripheral circuit integration. In this work, we
demonstrate a scalable RRAM based in-memory computing design, termed XNOR-RRAM,
which is fabricated in a 90nm CMOS technology with monolithic integration of
RRAM devices between metal 1 and 2. We integrated a 128x64 RRAM array with CMOS
peripheral circuits including row/column decoders and flash analog-to-digital
converters (ADCs), which collectively become a core component for scalable
RRAM-based in-memory computing towards large deep neural networks (DNNs). To
maximize the parallelism of in-memory computing, we assert all 128 wordlines of
the RRAM array simultaneously, perform analog computing along the bitlines, and
digitize the bitline voltages using ADCs. The resistance distribution of low
resistance states is tightened by write-verify scheme, and the ADC offset is
calibrated. Prototype chip measurements show that the proposed design achieves
high binary DNN accuracy of 98.5% for MNIST and 83.5% for CIFAR-10 datasets,
respectively, with energy efficiency of 24 TOPS/W and 158 GOPS throughput. This
represents 5.6X, 3.2X, 14.1X improvements in throughput, energy-delay product
(EDP), and energy-delay-squared product (ED2P), respectively, compared to the
state-of-the-art literature. The proposed XNOR-RRAM can enable intelligent
functionalities for area-/energy-constrained edge computing devices. | 1909.07514v1 |
2019-05-01 | Measurement of azimuthal dependent muon flux by 2\,m\,$\times$\,2\,m RPC stack at IICHEP-Madurai | The proposed 50 \,kton\, INO-ICAL experiment is an upcoming underground high
energy physics experiment planned to be commissioned at Bodi hills near Theni,
India ($9^{\circ}57'N$, $77^{\circ}16'E$) to study various properties of
neutrino oscillations using atmospheric neutrinos produced by extensive air
shower phenomenon. The resistive plate chamber has been chosen as the active
detector element for the proposed INO-ICAL. An experimental setup consisting a
stack of 12 layers of glass resistive plate chambers each with a size of
$\sim$2\,m$\times$2\,m has been built at IICHEP, Madurai to study the
performance and long-term stability of the resistive plate chambers(RPCs)
commercially produced in large quantities by the Indian industries as well as
its electronics for the front-end and subsequent signal processing. In this
study, the azimuthal dependence of muon flux at various zenith angles at
Madurai (9$^{\circ}$56'N, 78$^{\circ}$00'E and at an altitude of 160\,m above
mean sea level) has been presented along with the comparison of Monte Carlo
from CORSIKA and HONDA predictions. | 1905.00739v2 |
2019-05-20 | Imaging and monitoring the Reykjanes supercritical geothermal reservoir in Iceland with time-lapse CSEM and MT measurements | We have investigated the benefits and drawbacks of active EM surveying
(Controlled-Source EM or CSEM) for monitoring geothermal reservoirs in the
presence of strong industrial noise with an actual time-lapse survey over the
Reykjanes geothermal field in Iceland before and after the thermal stimulation
of the supercritical RN-15/IDDP-2 geothermal well. It showed that a high CSEM
survey repeatability can be achieved with electric field measurements (within a
few percent) but that time-lapse MT survey is a challenging task because of the
high level of cultural noise in this industrialized environment. To assess the
quality of our CSEM dataset, we inverted the data and confronted the resulting
resistivity model with the resistivity logged in the RN-15/IDDP-2 well. We
obtained a good match up to 2-3km depth, i.e. enough to image the caprock and
the liquid-dominated reservoir but not deep enough to image the reservoir in
supercritical conditions. To obtain such an image, we had to jointly invert
legacy MT data with our CSEM data. On the monitoring aspects, the analysis of
changes in electric fields did not allow to identify any CSEM signal related to
the thermal stimulation of the RN-15/IDDP-2 well. One possible explanation is
the weakness of the time-lapse CSEM signal compared the achieved CSEM survey
repeatability as a result of a limited resistivity change over a limited volume
within the reservoir. | 1905.07899v1 |
2020-03-10 | High performance picosecond- and micron-level 4D particle tracking with 100% fill-factor Resistive AC-Coupled Silicon Detectors (RSD) | In this paper we present a complete characterization of the first batch of
Resistive AC-Coupled Silicon Detectors, called RSD1, designed at INFN Torino
and manufactured by Fondazione Bruno Kessler (FBK) in Trento. With their 100%
fill-factor, RSD represent the new enabling technology for high-precision
4D-tracking. Indeed, being based on the well-known charge multiplication
mechanism of Low-Gain Avalanche Detectors (LGAD), they benefit from the very
good timing performances of such technology together with an unprecedented
resolution of the spatial tracking, which allows to reach the micron-level
scale in the track reconstruction. This is essentially due to the absence of
any segmentation structure between pads (100% fill-factor) and to other two
innovative key-features: the first one is a properly doped n+ resistive layer,
slowing down the charges just after being multiplied, and the second one is a
dielectric layer grown on Silicon, inducing a capacitive coupling on the metal
pads deposited on top of the detector. The very good spatial resolution
(micron-level) we measured experimentally - higher than the nominal pad pitch -
comes from the analogical nature of the readout of signals, whose amplitude
attenuates from the pad center to its periphery, while the outstanding results
in terms of timing (less than 14 ps, even better than standard LGAD) are due to
a combination of very-fine pitch, analogical response and charge
multiplication. | 2003.04838v2 |
2023-02-14 | Resistive Heating Induced by Streaming Cosmic Rays Around a Galaxy in the Early Universe | It is expected that cosmic rays (CRs) escape from high-redshift galaxies at
redshift $z\sim 10 \, - \, 20$ because CRs are accelerated by supernova
remnants of the first stars. Although ultraviolet and X-ray photons are widely
considered the main source of heating of the intergalactic medium, CRs can also
contribute to it. When the CRs propagate in the intergalactic medium, in
addition to the heating process due to CR ionization, resistive heating occurs
due to the electron return current induced by the streaming CRs. We evaluate
the heating rate around a galaxy as a function of the distance from the galaxy.
We find that the resistive heating induced by CRs dominates over the other
heating processes in the vicinity of the galaxy $r \lesssim 10^2 \,
\mathrm{kpc}$ until the temperature reaches $T\sim 10^4 \, \mathrm{K}$. We also
recalculate the strength of the magnetic field generated by streaming CRs under
the presence of X-ray heating and show that achieved strength can be about $1$
order of magnitude smaller when the X-ray heating is included. The presence of
the "first" CRs could be confirmed from the characteristic signature of CR
heating imprinted on the $21$-$\mathrm{cm}$ line map in future radio
observations. | 2302.07028v1 |
2023-04-21 | Bragg's law for X-ray scattering by quantum thermodynamic time crystals, Q-balls, as manifestation of the mechanism of High-T$_c$ superconductivity | Proposed by the author Q-ball mechanism of the pseudogap state and high-Tc
superconductivity in cuprates was recently supported by micro X-ray diffraction
data in HgBa$_2$CuO$_{4+y}$. This provides a remarkable opportunity to
investigate X-ray diffraction produced by the quantum thermodynamic time
crystals, a direct embodiment of those are just the Euclidean Q-balls
considered in the aforementioned theory. Simultaneously, it is also
demonstrated that T-linear temperature dependence of electrical resistivity in
the Q-ball phase arises due to scattering of electrons on the condensed
charge/spin fluctuations inside the Q-balls. This gives a clue concerning
possible mechanism of T-linear behaviour of electrical resistivity in the
strange metal phase of high-T$_c$ cuprates. For this purpose the Green's
functions of X-ray photons and fermions scattered by the Q-balls in the
pseudogap phase of high-Tc superconductors are calculated using the Feynman
diagrammatic technique. The Bragg's peaks intensity, provided by the imaginary
part of the retarded photon Green's function, is calculated. In total, obtained
results describe X-ray and electron scattering on the finite size Q-ball of
CDW/SDW density, that oscillates with bosonic frequency $\Omega=2\pi nT$ in
Matsubara time, i.e. the quantum thermodynamic time crystal. It is found, that
theoretical results are in good correspondence with X-ray diffraction data in
HgBa$_2$CuO$_{4+y}$ reported recently. The T-linear dependence of electrical
resistivity arises due to inverse temperature dependence of the Q-ball radius
as function of temperature. | 2304.10874v2 |
2023-07-09 | Design Space Exploration and Comparative Evaluation of Memory Technologies for Synaptic Crossbar Arrays: Device-Circuit Non-Idealities and System Accuracy | In-memory computing (IMC) utilizing synaptic crossbar arrays is promising for
deep neural networks to attain high energy efficiency and integration density.
Towards that end, various CMOS and post-CMOS technologies have been explored as
promising synaptic device candidates which include SRAM, ReRAM, FeFET,
SOT-MRAM, etc. However, each of these technologies has its own pros and cons,
which need to be comparatively evaluated in the context of synaptic array
designs. For a fair comparison, such an analysis must carefully optimize each
technology, specifically for synaptic crossbar design accounting for device and
circuit non-idealities in crossbar arrays such as variations, wire resistance,
driver/sink resistance, etc. In this work, we perform a comprehensive design
space exploration and comparative evaluation of different technologies at 7nm
technology node for synaptic crossbar arrays, in the context of IMC robustness
and system accuracy. Firstly, we integrate different technologies into a
cross-layer simulation flow based on physics-based models of synaptic devices
and interconnects. Secondly, we optimize both technology-agnostic design knobs
such as input encoding and ON-resistance as well as technology-specific design
parameters including ferroelectric thickness in FeFET and MgO thickness in
SOT-MRAM. Our optimization methodology accounts for the implications of device-
and circuit-level non-idealities on the system-level accuracy for each
technology. Finally, based on the optimized designs, we obtain inference
results for ResNet-20 on CIFAR-10 dataset and show that FeFET-based crossbar
arrays achieve the highest accuracy due to their compactness, low leakage and
high ON/OFF current ratio. | 2307.04261v1 |
2023-09-28 | Study of Bulk Damage of High Dose Gamma Irradiated p-type Silicon Diodes with Various Resistivities | The bulk damage of p-type silicon detectors caused by high doses of gamma
irradiation has been studied. The study was carried out on three types of
n$^{+}$-in-p silicon diodes with comparable geometries but different initial
resistivities. This allowed to determine how different initial parameters of
studied samples influence radiation-induced changes in the measured
characteristics. The diodes were irradiated by a Cobalt-60 gamma source to
total ionizing doses ranging from 0.50 up to 8.28 MGy, and annealed for 80
minutes at 60 {\deg}C. The Geant4 toolkit for simulation of the passage of
particles through matter was used to simulate the deposited energy homogeneity,
to verify the equal distribution of total deposited energies through all the
layers of irradiated samples, and to calculate the secondary electron spectra
in the irradiation box. The main goal of the study was to characterize the
gamma-radiation induced displacement damage by measuring current-voltage
characteristics (IV), and the evolution of the full depletion voltage with the
total ionizing dose, by measuring capacitance-voltage characteristics (CV). It
has been observed that the bulk leakage current increases linearly with total
ionizing dose, and the damage coefficient depends on the initial resistivity of
the silicon diode. The effective doping concentration and therefore full
depletion voltage significantly decreases with increasing total ionizing dose,
before starting to increase again at a specific dose. We assume that this
decrease is caused by the effect of acceptor removal. Another noteworthy
observation of this study is that the IV and CV measurements of the gamma
irradiated diodes do not reveal any annealing effect. | 2309.16293v1 |
2023-10-17 | Improving Interface Physics Understanding in High-Frequency Cryogenic Normal Conducting Cavities | As progress towards real implementations of cryogenic high gradient normal
conducting accelerating cavities continues, a more mature understanding of the
surface physics in this novel environment becomes increasingly necessary. To
this end, we here focus on developing a deeper understanding of one cavity
figure of merit, the radiofrequency (RF) surface resistivity, $R_s$. A
combination of experimental measurements and theory development form the basis
of this work. For many cases, existing theory is sufficient but there are
nuances leading to systemic errors in prediction which we address here. In
addition, for certain cases there exist unexpected local minimum in $R_s$ found
at temperatures above 0K. We compare here several alternative models for RF
surface resistivity those which incorporate thin film like behavior which we
use to predict the location of the local minimum in surface resistivity. Our
experimental results focus on C-band frequencies for the benefit of several
future cryogenic linear accelerator concepts intended to operate in this
regime. To this end we have measured factor of $2.89\pm 0.05$ improvements in
quality factor at $77$K and $4.61\pm 0.05$ at 45K. We further describe the test
setup and cooling capabilities to address systematic issues associated with the
measurements as well as a comparison of RF cavity preparation and the
significant effect on $R_s$. Some implications of our measurements to linear
accelerators combined with the theoretical considerations are extended to a
wider range of frequencies especially the two additional aforementioned bands.
Additional possible implications for condensed matter physics studies are
mentioned. | 2310.11578v1 |
2024-01-18 | Hazard resistance-based spatiotemporal risk analysis for distribution network outages during hurricanes | Blackouts in recent decades show an increasing prevalence of power outages
due to extreme weather events such as hurricanes. Precisely assessing the
spatiotemporal outages in distribution networks, the most vulnerable part of
power systems, is critical to enhance power system resilience. The Sequential
Monte Carlo (SMC) simulation method is widely used for spatiotemporal risk
analysis of power systems during extreme weather hazards. However, it is found
here that the SMC method can lead to large errors by directly applying the
fragility function or failure probability of system components in
time-sequential analysis, particularly overestimating damages under evolving
hazards with high-frequency sampling. To address this issue, a novel hazard
resistance-based spatiotemporal risk analysis (HRSRA) method is proposed. This
method converts the time-varying failure probability of a component into a
hazard resistance as a time-invariant value during the simulation of evolving
hazards. The proposed HRSRA provides an adaptive framework for incorporating
high-spatiotemporal-resolution meteorology models into power outage
simulations. By leveraging the geographic information system data of the power
system and a physics-based hurricane wind field model, the superiority of the
proposed method is validated using real-world time-series power outage data
from Puerto Rico during Hurricane Fiona 2022. | 2401.10418v1 |
2024-02-06 | Characterisation of resistive MPGDs with 2D readout | Micro-Pattern Gaseous Detectors (MPGDs) with resistive anode planes provide
intrinsic discharge robustness while maintaining good spatial and time
resolutions. Typically read out with 1D strips or pad structures, here the
characterisation results of resistive anode plane MPGDs with 2D strip readout
are presented. A uRWELL prototype is investigated in view of its use as a
reference tracking detector in a future gaseous beam telescope. A MicroMegas
prototype with a fine-pitch mesh (730 line-pairs-per-inch) is investigated,
both for comparison and to profit from the better field uniformity and thus the
ability to operate the detector more stable at high gains. Furthermore, the
measurements are another application of the RD51 VMM3a/SRS electronics. | 2402.03899v1 |
2019-01-24 | Materials Informatics for Heat Transfer: Recent Progresses and Perspectives | With the advances in materials and integration of electronics and
thermoelectrics, the demand for novel crystalline materials with ultimate
high/low thermal conductivity is increasing. However, search for optimal
thermal materials is challenge due to the tremendous degrees of freedom in the
composition and structure of crystal compounds and nanostructures, and thus
empirical search would be exhausting. Materials informatics, which combines the
simulation/experiment with machine learning, is now gaining great attention as
a tool to accelerate the search of novel thermal materials. In this review, we
discuss recent progress in developing materials informatics for heat transport:
the exploration of crystals with high/low thermal conductivity via
high-throughput screening, and nanostructure design for high/low thermal
conductance using the Bayesian optimization and Monte Carlo tree search. The
progresses show that the materials informatics method are useful for designing
thermal functional materials. We end by addressing the remaining issues and
challenges for further development. | 1901.08504v1 |
2011-01-20 | Optical and DC conductivity of the two-dimensional Hubbard model in the pseudogap regime and across the antiferromagnetic quantum critical point, including vertex corrections | The conductivity of the two-dimensional Hubbard model is particularly
relevant for high-temperature superconductors. Vertex corrections are expected
to be important because of strongly momentum dependent self-energies. We use
the Two-Particle Self-Consistent approach that satisfies crucial constraints
such as the Mermin-Wagner theorem, the Pauli principle and sum rules in order
to reach non-perturbative regimes. This approach is reliable from weak to
intermediate coupling. A functional derivative approach ensures that vertex
corrections are included in a way that satisfies the f sum-rule. The two types
of vertex corrections that we find are the antiferromagnetic analogs of the
Maki-Thompson and Aslamasov-Larkin contributions of superconducting
fluctuations to the conductivity but, contrary to the latter, they include
non-perturbative effects. The resulting analytical expressions must be
evaluated numerically. The calculations are impossible unless a number of
advanced numerical algorithms are used. A maximum entropy approach is specially
developed for analytical continuation of our results. The numerical results are
for nearest neighbor hoppings. In the pseudogap regime induced by
two-dimensional antiferromagnetic fluctuations, the effect of vertex
corrections is dramatic. Without vertex corrections the resistivity increases
as we enter the pseudogap regime. Adding vertex corrections leads to a drop in
resistivity, as observed in some high temperature superconductors. At high
temperature, the resistivity saturates at the Ioffe-Regel limit. At the quantum
critical point and beyond, the resistivity displays both linear and quadratic
temperature dependence and there is a correlation between the linear term and
the superconducting transition temperature. A hump is observed in the
mid-infrared range of the optical conductivity in the presence of
antiferromagnetic fluctuations. | 1101.4037v2 |
2022-10-26 | Bolometric detection of Josephson inductance in a highly resistive environment | The Josephson junction is a building block of quantum circuits. Its behavior,
well understood when treated as an isolated entity, is strongly affected by
coupling to an electromagnetic environment. In 1983, Schmid predicted that a
Josephson junction shunted by a resistance exceeding the resistance quantum
$\mathbf{\textit{R}}_\mathrm{Q} = h/4e^2 \approx 6.45$ k$\mathbf{\Omega}$ for
Cooper pairs would become insulating since the phase fluctuations would destroy
the coherent Josephson coupling. However, recent microwave measurements have
questioned this interpretation. Here, we insert a small Josephson junction in a
Johnson-Nyquist-type setup where it is driven by weak current noise arising
from thermal fluctuations. Our heat probe minimally perturbs the junction's
equilibrium, shedding light on features not visible in charge transport. We
find that the Josephson critical current completely vanishes in DC charge
transport measurement, and the junction demonstrates Coulomb blockade in
agreement with the theory. Surprisingly, thermal transport measurements show
that the Josephson junction acts as an inductor at high frequencies,
unambiguously demonstrating that a supercurrent survives despite the Coulomb
blockade observed in DC measurements. The discrepancy between these two
measurements highlights the difference between the low and the high frequency
response of a junction and calls for further theoretical and experimental
inputs on the dynamics of Josephson junctions \textcolor{black}{operating at
high frequencies in highly resistive environments. | 2210.14953v4 |
2019-09-09 | High Dielectric Ternary Oxides from Crystal Structure Prediction and High-throughput Screening | The development of new high dielectric materials is essential for advancement
in modern electronics. Oxides are generally regarded as the most promising
class of high dielectric materials for industrial applications as they possess
both high dielectric constants and large band gaps. Most previous researches on
high dielectrics were limited to already known materials. In this study, we
conducted an extensive search for high dielectrics over a set of ternary oxides
by combining crystal structure prediction and density functional perturbation
theory calculations. From this search, we adopted multiple stage screening to
identify 440 new low-energy high dielectric materials. Among these materials,
33 were identified as potential high dielectrics favorable for modern device
applications. Our research has opened an avenue to explore novel high
dielectric materials by combining crystal structure prediction and high
throughput screening. | 1909.04195v1 |
2003-06-17 | Materials Aspects of High-Temperature Superconductors for Applications | Materials aspects of cuprate high-temperature superconductors (HTS) are
reviewed with respect to technical applications. The structural chemistry
common to all HTS and their critical temperatures for the onset of
superconductivity are presented. Intrinsic problems for the production of
technically applicable HTS materials are discussed and how these problems have
been overcome for a number of technically applicable HTS materials. | 0306442v1 |
2010-05-20 | Non Super-Cell SuperConductivity Of High Tc Materials | Recently we have described materials interface transport coupling rigorously
utilizing NEGF nonequilibrium Green's functions, and have discussed the
Hamiltonian terms that from Green's theorem and boundary conditions can be
rewritten as Self Energy. We derive the application of our theory to the high
$Tc$ Superconducting materials interfaces that are the composition of the high
temperature superconducting materials. The derivation models a non super-cell
geometry of plaquettes that will describe the superconducting 2D material in
abrupt coupling with the material of insulating or normal conducting
composition. | 1005.3618v1 |
2012-05-24 | CuBr2-A New Multiferroic Material with High Critical Temperature | A new multiferroic material, CuBr2, is reported for the first time. CuBr2 has
not only a high transition temperature (close to liquid nitrogen temperature)
but also low dielectric loss and strong magnetoelectric coupling. These
findings reveal the importance of anion effects in the search for the high
temperature multiferroics materials among these low-dimensional spin systems. | 1205.5318v1 |
1998-07-24 | Destruction of localized electron pairs above the magnetic-field-driven superconductor-insulator transition in amorphous InO films | We have investigated the field-induced superconductivity-destroying quantum
transition in amorphous indium oxide films at low temperatures down to 30 mK.
It has been found that, on the high-field side of the transition, the
magnetoresistance reaches a maximum and the phase can be insulating as well as
metallic. With further increasing magnetic field the film resistance drops and
approaches in the high-field limit the resistance value at transition point so
that at high fields the metallic phase occurs for both cases. We give a
qualitative account of this behavior in terms of field-induced destruction of
localized electron pairs. | 9807332v2 |
1999-10-22 | Weak localisation, hole-hole interactions and the "metal"-insulator transition in two dimensions | A detailed investigation of the metallic behaviour in high quality
GaAs-AlGaAs two dimensional hole systems reveals the presence of quantum
corrections to the resistivity at low temperatures. Despite the low density
($r_{s}>10$) and high quality of these systems, both weak localisation
(observed via negative magnetoresistance) and weak hole-hole interactions
(giving a correction to the Hall constant) are present in the so-called
metallic phase where the resistivity decreases with decreasing temperature. The
results suggest that even at high $r_{s}$ there is no metallic phase at T=0 in
two dimensions. | 9910368v2 |
2000-08-28 | Josephson-Vortex-Glass Transition in Strong Fields | A vortex-glass transition due to point disorder in layered superconductors is
studied for the case with an applied field {\it parallel} to the layers. Our
calculation of tilt responses indicates that, irrespective of the magnitude of
the field, the resulting glass phase, Josephson-vortex-glass (JG), should have
a transverse Meissner effect, as in a planar splayed glass phase, only for a
tilt perpendicular to the layers. Further, focusing on the high field (and/or
high anisotropy) region $B \sqrt{\Gamma} > \phi_0/d^2$, where $\Gamma$ is the
mass anisotropy in the Lawrence-Doniach model, the JG transition line
$T_{JG}(B)$ is shown to have a similar form to a $B$-$T$ line following from
the {\it disorder-free} Lindemann criterion and to decrease with increasing $B
\sqrt{\Gamma}$, in marked contrast to the disorder-free melting line {\it
insensitive to} $B \sqrt{\Gamma}$ in such the high field region. This
$T_{JG}(B)$ line seems to have been recently observed in a.c. susceptibility
and in-plane resistivity measurements in BSCCO and qualitatively explains a
field dependence at lower temperatures of previous BSCCO resistivity data
showing the so-called in-plane Lorentz force-free behavior. | 0008397v1 |
2005-06-01 | Spin polarization induced tenfold magneto-resistivity of highly metallic 2D holes in a narrow GaAs quantum well | We observe that an in-plane magnetic field ($B_{||}$) can induce an order of
magnitude enhancement in the low temperature ($T$) resistivity ($\rho$) of
metallic 2D holes in a narrow (10nm) GaAs quantum well. Moreover, we show the
first observation of saturating behavior of $\rho(B_{||})$ at high $B_{||}$ in
GaAs system, which suggests our large positive $\rho(B_{||})$ is due to the
spin polarization effect alone. We find that this tenfold increase in
$\rho(B_{||})$ even persists deeply into the 2D metallic state with the high
$B_{||}$ saturating values of $\rho$ lower than 0.1$\times$h/e$^2$. The
dramatic effect of $B_{||}$ we observe on the highly conductive 2D holes (with
$B$=0 conductivity as high as 75e$^2$/h) sets strong constraint on models for
the spin dependent transport in dilute metallic 2D systems. | 0506031v3 |
2005-09-06 | Conduction anisotropy and Hall effect in the organic conductor (TMTTF)2AsF6: evidence for Luttinger liquid and charge ordering | We present the high-temperature (70 K < T < 300 K) resistivity anisotropy and
Hall effect measurements of the quasi-one-dimensional (1D) organic conductor
(TMTTF)2AsF6. The temperature variations of the resistivity are pronouncedly
different for the three different directions, with metallic-like at high
temperatures for the a-axis only. Above 220 K the Hall coefficient R_H is
constant, positive and strongly enhanced over the expected value; and the
corresponding carrier concentration is almost 100 times lower than calculated
for one hole/unit cell. Our results give evidence for the existence of a
high-temperature regime above 200 K where the 1D Luttinger liquid features
appear in the transport properties. Our measurements also give strong evidence
of charge ordering in (TMTTF)2AsF6. At the charge-ordering transition T_{CO}
\approx 100 K, R_H(T) abruptly changes its behavior, switches sign and rapidly
increases with further temperature decrease. | 0509147v1 |
2003-08-19 | Nanolithography with metastable helium atoms in a high-power standing-wave light field | We have created periodic nanoscale structures in a gold substrate with a
lithography process using metastable triplet helium atoms that damage a
hydrofobic resist layer on top of the substrate. A beam of metastable helium
atoms is transversely cooled and guided through an intense standing-wave light
field. Compared to commonly used low-power optical masks, a high-power light
field (saturation parameter of 10E7) increases the confinement of the atoms in
the standing-wave considerably, and makes the alignment of the experimental
setup less critical. Due to the high internal energy of the metastable helium
atoms (20 eV), a dose of only one atom per resist molecule is required. With an
exposure time of only eight minutes, parallel lines with a separation of 542 nm
and a width of 100 nm (1/11th of the wavelength used for the optical mask) are
created. | 0308076v1 |
2007-05-10 | Manifestations of fine features of the density of states in the transport properties of KOs2O6 | We performed high-pressure transport measurements on high-quality single
crystals of KOs2O6, a beta-pyrochlore superconductor. While the resistivity at
high temperatures might approach saturation, there is no sign of saturation at
low temperatures, down to the superconducting phase. The anomalous resistivity
is accompanied by a nonmetallic behavior in the thermoelectric power (TEP) up
to temperatures of at least 700 K, which also exhibits a broad hump with a
maximum at 60 K. The pressure influences mostly the low-energy electronic
excitations. A simple band model based on enhanced density of states in a
narrow window around the Fermi energy (EF) explains the main features of this
unconventional behavior in the transport coefficients and its evolution under
pressure. | 0705.1401v1 |
2008-05-06 | Coherence-incoherence crossover in the normal state of iron-oxypnictides and importance of the Hund's rule coupling | A new class of high temperature superconductors based on iron and arsenic was
recently discovered, with superconducting transition temperature as high as 55
K. Here we show, using microscopic theory, that the normal state of the iron
pnictides at high temperatures is highly anomalous, displaying a Curie Weiss
susceptibility and a linear temperature dependence of the resistivity. Below a
coherence scale T*, the resistivity sharply drops and susceptibility crosses
over to Pauli-like temperature dependence. Remarkably, the
coherence-incoherence crossover temperature is a very strong function of the
strength of the Hund's rule coupling J_Hund. On the basis of the normal state
properties, we estimate J_Hund to be 0.35-0.4 eV. In the atomic limit, this
value of J_Hund leads to the critical ratio of the exchange constants
J_1/J_2~2. While normal state incoherence is in common to all strongly
correlated superconductors, the mechanism for emergence of the incoherent state
in iron-oxypnictides, is unique due to its multiorbital electronic structure. | 0805.0722v2 |
2009-06-11 | The enigma of the nu=0 quantum Hall effect in graphene | We apply Laughlin's gauge argument to analyze the $\nu=0$ quantum Hall effect
observed in graphene when the Fermi energy lies near the Dirac point, and
conclude that this necessarily leads to divergent bulk longitudinal resistivity
in the zero temperature thermodynamic limit. We further predict that in a
Corbino geometry measurement, where edge transport and other mesoscopic effects
are unimportant, one should find the longitudinal conductivity vanishing in all
graphene samples which have an underlying $\nu=0$ quantized Hall effect. We
argue that this $\nu=0$ graphene quantum Hall state is qualitatively similar to
the high field insulating phase (also known as the Hall insulator) in the
lowest Landau level of ordinary semiconductor two-dimensional electron systems.
We establish the necessity of having a high magnetic field and high mobility
samples for the observation of the divergent resistivity as arising from the
existence of disorder-induced density inhomogeneity at the graphene Dirac
point. | 0906.2209v2 |
2009-09-21 | Epitaxial LaFeAsOF thin films grown by pulsed laser deposition | Superconducting and epitaxially grown LaFeAsOF thin films were successfully
prepared on (001)-oriented LaAlO3 substrates using pulsed laser deposition. The
prepared thin films show exclusively a single in-plane orientation with
epitaxial relation (001)[100] parallel to (001)[100] and a FWHM value of 1deg.
Furthermore, resistive measurement of the superconducting transition
temperature revealed a Tc90 of 25K with a high residual resistive ratio of 6.8.
The applied preparation technique, standard thin film pulsed laser deposition
at room temperature in combination with a subsequent post annealing process, is
suitable for fabrication of high quality LaFeAsO1-xFx thin films. A high upper
critical field of 76.2 T was evaluated for magnetic fields applied
perpendicular to the c-axis and the anisotropy was calculated to be 3.3
assuming single band superconductivity. | 0909.3788v1 |
2010-01-31 | Saturation of the Anomalous Hall Effect in Critically Disordered Ultra-thin CNi3 Films | We demonstrate that a distinct high-disorder anomalous Hall effect phase
emerges at the correlated insulator threshold of ultra-thin, amorphous,
ferromagnetic CNi3 films. In the weak localization regime, where the sheet
conductance G >> e^2/h, the anomalous Hall resistance of the films increases
with increasing disorder and the Hall conductance scales as Gxy ~ G^1.6.
However, at sufficiently high disorder the system begins to enter the 2D
correlated insulator regime, at which point the Hall resistance Rxy abruptly
saturates and the scaling exponent becomes 2. Tunneling measurements show that
the saturation behavior is commensurate with the emergence of the 2D Coulomb
gap, suggesting that e-e interactions mediate the high-disorder phase. | 1002.0099v1 |
2012-07-16 | Pressure effects on the superconducting thin film Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ | We report electrical resistivity measurements on a high-quality
Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ thin film ($x=0.4$) under pressure. The
superconducting transition temperature (=39.95 K) of the optimally-doped thin
film shows a dome shape with pressure, reaching a maximal value 40.8 K at 11.8
kbar. The unusually high superconducting transition temperature and its
anomalous pressure dependence are ascribed to a lattice mismatch between the
LaAlO$_3$ substrate and the thin film. The local temperature exponent of the
resistivity ($n=d\text{ln}\Delta\rho/d\text{ln}T$) shows a funnel shape around
the optimal pressure, suggesting that fluctuations associated with the
anomalous normal state are responsible for high-temperature superconductivity. | 1207.3826v1 |
2012-10-09 | Quantum oscillations in a d-wave vortex liquid | The observation of quantum oscillations in underdoped cuprates has generated
intense debate about the nature of the field-induced resistive state and its
implications for the `normal state' of high T_c superconductors. Quantum
oscillations suggest an underlying Fermi liquid state at high magnetic fields H
and low temperatures, in contrast with the high-temperature, zero-field
pseudogap state seen in spectroscopy. Recent heat capacity measurements show
quantum oscillations together with a large and singular field-dependent
suppression of the electronic density of states (DOS), which suggests a
resistive state that is affected by the d-wave superconducting gap. We present
a theoretical analysis of the electronic excitations in a vortex-liquid state,
with short range pairing correlations in space and time, that is able to
reconcile these seemingly contradictory observations. We show that phase
fluctuations lead to large suppression of the DOS that goes like $\sqrt{H}$ at
low fields, in addition to quantum oscillations with a period determined by a
Fermi surface reconstructed by a competing order parameter. | 1210.2466v1 |
2013-04-07 | Ageing studies of resistive Micromegas detectors for the HL-LHC | Resistive-anode Micromegas detectors are in development since several years,
in an effort to solve the problem of sparks when working in high flux and high
radiations environment like in the HL-LHC (ten times the luminosity of the
LHC). They have been chosen as one of the technologies that will be part of the
ATLAS New Small Wheel project (forward muon system). An ageing study is
mandatory to assess their capabilities to handle the HL-LHC environment on a
long-term period. A prototype has been exposed to several types of irradiations
(X-rays, cold neutrons, 60 Co gammas) up to an equivalent HL-LHC time of more
than five years without showing any degradation of the performances in terms of
gain and energy resolution. Beam test studies took place in October 2012 to
assess the tracking performances (efficiency, spatial resolution,...). Results
of ageing studies and beam test performances are reported in this paper. | 1304.2053v1 |
2013-07-31 | Quartz Capillary Cladding Anthracene and Polycyclic Aromatic Hydrocarbon(PAH)-Core Scintillating/WLS Fibers for High Rates and Radiation Damage Resistance | Quartz capillary tube/fibers have been filled with anthracene by a melt and
vacuum inbibition process to fabricate a scintillating core fiber. Other
polcyclic aromatic hydrocarbons(PAH), such as p-Terphenyl (pTP), stilbene or
naphthalene are also well-suited to scintillating/shifting fiber cores. The
resulting scintillating core with quartz cladding capillary fibers (250-750
micron cores) had a high specific light output when tested with muons (8 p.e.
per MIP). These PAH core quartz capillary cladding scintillating/shifting
optical fibers have the potential of high radiation resistance, fast response,
and are applicable to many energy and intensity frontier experiments. | 1307.8376v1 |
2013-08-08 | Ultra-low Energy, High Performance and Programmable Magnetic Threshold Logic | We propose magnetic threshold-logic (MTL) design based on non-volatile
spin-torque switches. A threshold logic gate (TLG) performs summation of
multiple inputs multiplied by a fixed set of weights and compares the sum with
a threshold. MTL employs resistive states of magnetic tunnel junctions as
programmable input weights, while, a low-voltage domain-wall shift based
spin-torque switch is used for thresholding operation. The resulting MTL gate
acts as a low-power, configurable logic unit and can be used to build fully
pipelined, high-performance programmable computing blocks. Multiple stages in
such a MTL design can be connected using energy-efficient ultralow swing
programmable interconnect networks based on resistive switches. Owing to
memory-based compact logic and interconnect design and low-voltage, high-speed
spintorque based threshold operation, MTL can achieve more than two orders of
magnitude improvement in energy-delay product as compared to look-up table
based CMOS FPGA. | 1308.4169v1 |
2015-09-28 | High resolution experimental parameter space of a chaotic circuit | We have obtained a high resolution parameter space of an experimental Chua's
circuit and shown that the topology of the chaotic and periodic regions present
not only expected features previously observed from high resolution numerical
simulations of idealised Chua's circuit, but also novel unexpected features.
Unmatched feedback resistances cause the formation of at least two competing
spirals with consequent disrupted or malformed shrimps. We have also confirmed
experimentally that the period-adding bifurcation route is formed by periodic
regions whose size decrease exponentially with their period, and consequently,
periodic behaviour with higher period is unlikely to be observed. The
higher-resolution span of parameters was possible by the use of a newly
designed potentiometer that could be potentially used in other electronic
equipments to reveal hidden behaviours. To have such resistances we developed
in series arrays of resistors short-circuited by relays as discrete
potentiometers with 1024 steps, and resolutions of 0.100 $\Omega$ for $r_L$ in
series with the inductor, and 0.200 $\Omega$ for R connecting the two
capacitors. | 1509.08425v2 |
2015-10-01 | Comment on "Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system" (A. P. Drozdov et al., Nature 525, 73 (2015)) | It is demonstrated that resistive transition at 203 K observed in metallic
sulfur hydride system at high pressure can be magnetic (rather than
superconducting (SC)) in nature. The onset temperature of genuine
superconducting transition in these compounds appears to be essentially lower
on temperature. The normal-state magnetic (AF SDW) phase transition preceding a
superconducting one (Tc < Tm) is characteristic for HTSC cuprates, pnictides
(selenides) and organic superconductors. The resistive drop is provided by
disappearing of magnetic (AF spin fluctuation) scattering of conduction
electrons and hence formation of AF SDW order in the normal state. The
formation of such modulated magnetic structure in sulfur hydride seems to be
possible because of magnetic properties of metallic hydrogen at high densities
(in analogy with iron). Such unconventional picture with two successive phase
transitions: magnetic (AF SDW) and only then superconducting one is naturally
described by Keldysh-Kopaev theory of dielectric (metal-insulator) phase
transition in systems with coexistence of superconducting (e-e) and dielectric
(e-h)pairings. | 1510.00123v1 |
2016-11-24 | Puddle-induced resistance oscillations in the breakdown of the graphene quantum Hall effect | We report on the stability of the quantum Hall plateau in wide Hall bars made
from a chemically gated graphene film grown on SiC. The $\nu=2$ quantized
plateau appears from fields $B \simeq 5$ T and persists up to $B \simeq 80$ T.
At high current density, in the breakdown regime, the longitudinal resistance
oscillates with a $1/B$ periodicity and an anomalous phase, which we relate to
the presence of additional electron reservoirs. The high field experimental
data suggest that these reservoirs induce a continuous increase of the carrier
density up to the highest available magnetic field, thus enlarging the quantum
plateaus. These in-plane inhomogeneities, in the form of high carrier density
graphene pockets, modulate the quantum Hall effect breakdown and decrease the
breakdown current. | 1611.08179v1 |
2017-02-08 | Fine structure of high-power microwave-induced resistance oscillations | We report on observation of a fine structure of microwave-induced resistance
oscillations in an ultraclean two-dimensional electron gas. This fine structure
is manifested by multiple secondary sharp extrema, residing beside the primary
ones, which emerge at high radiation power. Theoretical considerations reveal
that this fine structure originates from multiphoton-assisted scattering off
short-range impurities. Unique properties of the fine structure allow us to
access all experimental parameters, including microwave power, and to separate
different contributions to photoresistance. Furthermore, we show that the fine
structure offers a convenient means to quantitatively assess the correlation
properties of the disorder potential in high-quality systems, allowing
separation of short- and long-range disorder contributions to the electron
mobility. | 1702.02556v1 |
2018-04-20 | Sensitivity optimization of micro-machined thermo-resistive flow-rate sensors on silicon substrates | We report on an optimized micro-machined thermal flow-rate sensor as part of
an autonomous multi-parameter sensing device for water network monitoring. The
sensor has been optimized under the following constraints: low power
consumption and high sensitivity, while employing a large thermal conductivity
substrate, namely silicon. The resulting device consists of a platinum
resistive heater deposited on a thin silicon pillar ~ 100 $\mu$m high and 5
$\mu$m wide in the middle of a nearly 100 $\mu$m wide cavity. Operated under
the anemometric scheme, the reported sensor shows a larger sensitivity in the
velocity range up to 1 m/s compared to different sensors based on similar high
conductivity substrates such as bulk silicon or silicon membrane with a power
consumption of 44 mW. Obtained performances are assessed with both CFD
simulation and experimental characterization. | 1804.07524v1 |
2014-10-24 | Doping dependence of the upper critical field, superconducting current density and thermally activated flux flow activation energy in polycrystalline CeFeAsO1-xFx superconductors | We report the results from resistivity and magnetic measurements on
polycrystalline Ce oxypnictide (CeFeAsO1-xFx) samples where x spans from 0.13
to 0.25. We find that the orbital limiting field is as high as 150 T and it
systematically decreases with increasing doping. The Maki parameter is greater
than one across the phase diagram and the large Maki parameter suggests that
orbital and Pauli limiting effects contribute to the upper critical field. The
broadening of the superconducting transition in the resistivity data was
interpreted using the thermally activated flux flow (TAFF) model where we find
that the TAFF activation energy, U0(B), is proportional to B^{-(gamma)} from 1
T to high fields, and (gamma) does not significantly change with doping.
However, U0 and the superconducting critical current, Jc, are peaked in the
mid-doping region (x = 0.15 to x = 0.20), and not in the low (x < 0.15) or high
doping (x > 0.20) regions. Furthermore, U0 is correlated with Jc and follows
the two fluid model for granular samples. | 1410.6546v1 |
2015-05-22 | Growth and Characterization of Millimeter-sized Single Crystals of CaFeAsF | High-quality and sizable single crystals are crucial for studying the
intrinsic properties of unconventional superconductors, which are lacking in
the 1111 phase of the Fe-based superconductors. Here we report the successful
growth of CaFeAsF single crystals with the sizes of 1-2 mm using the self-flux
method. Owning to the availability of the high-quality single crystals, the
structure and transport properties were investigated with a high reliability.
The structure was refined by using the single-crystal x-ray diffraction data,
which confirms the reports earlier on the basis of powder data. A clear anomaly
associated with the structural transition was observed at 121 K from the
resistivity, magnetoresistance, and magnetic susceptibility measurements.
Another kink-feature at 110 K, most likely an indication of the
antiferromagnetic transition, was also detected in the resistivity data. Our
results supply a basis to propel the physical investigations on the 1111 phase
of the Fe-based superconductors. | 1505.06014v1 |
2020-04-01 | Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors | Hafnium is an elemental superconductor which crystallizes in a hexagonal
close packed structure, has a transition temperature $T_{C} \simeq 400 mK$, and
has a high normal state resistivity around $90 \mu \Omega. cm$. In Microwave
Kinetic Inductance Detectors (MKIDs), these properties are advantageous since
they allow for creating detectors sensitive to optical and near infra-red
radiation. In this work, we study how sputter conditions and especially the
power applied to the target during the deposition, affect the hafnium $T_{C}$,
resistivity, stress, texture and preferred crystal orientation. We find that
the position of the target with respect to the substrate strongly affects the
orientation of the crystallites in the films and the internal quality factor,
$Q_{i}$, of MKIDs fabricated from the films. In particular, we demonstrate that
a DC magnetron sputter deposition at a normal angle of incidence, low pressure,
and low plasma power promotes the growth of compressive (002)-oriented films
and that such films can be used to make high quality factor MKIDs with $Q_{i}$
up to 600,000. | 2004.00736v1 |
2007-10-03 | Scaling analysis of normal state properties of high-temperature superconductors | We propose a model-independent scaling method to study the physical
properties of high-temperature superconductors in the normal state. We have
analyze the experimental data of the c-axis resistivity, the in-plane
resistivity, the Hall coefficient, the magnetic susceptibility, the
spin-lattice relaxation rate, and the thermoelectric power using this method.
It is shown that all these physical quantities exhibit good scaling behaviors,
controlled purely by the pseudogap energy scale in the normal state. The doping
dependence of the pseudogap obtained from this scaling analysis agrees with the
experimental results of angle-resolved photoemission and other measurements. It
sheds light on the understanding of the basic electronic structure of high-Tc
oxides. | 0710.0693v3 |
2007-10-18 | Transport and percolation in a low-density high-mobility two-dimensional hole system | We present a study of the temperature and density dependence of the
resistivity of an extremely high quality two-dimensional hole system grown on
the (100) surface of GaAs. For high densities in the metallic regime ($p\agt 4
\times 10^{9}$ cm$^{-2}$), the nonmonotonic temperature dependence ($\sim
50-300$ mK) of the resistivity is consistent with temperature dependent
screening of residual impurities. At a fixed temperature of $T$= 50 mK, the
conductivity vs. density data indicates an inhomogeneity driven
percolation-type transition to an insulating state at a critical density of
$3.8\times 10^9$ cm$^{-2}$. | 0710.3542v1 |
2014-01-16 | High-quality multi-terminal suspended graphene devices | We introduce a new scheme to realize suspended, multi-terminal graphene
structures that can be current annealed successfully to obtain uniform, very
high quality devices. A key aspect is that the bulky metallic contacts are not
connected directly to the part of graphene probed by transport measurements,
but only through etched constriction, which prevents the contacts from acting
invasively. The device high quality and uniformity is demonstrated by a
reproducibly narrow (delta_n ~ 10^9 cm^-2) resistance peak around charge
neutrality, by carrier mobility values exceeding 10^6 cm^2/V/s, by the
observation of integer quantum Hall plateaus starting at 30 mT and of symmetry
broken states at about 200 mT, and by the occurrence of a negative
multi-terminal resistance directly proving the occurrence of ballistic
transport. As these multi-terminal devices enable measurements that cannot be
done in a simpler two-terminal configuration, we anticipate that their use in
future studies of graphene-based systems will be particularly relevant. | 1401.4033v1 |
2019-08-30 | Pressure-induced suppression of charge density wave and emergence of Superconductivity in 1T-VSe2 | We report pressure evolution of charge density wave (CDW) order and emergence
of superconductivity (SC) in 1T-VSe2 single crystal by studying resistance and
magnetoresistance behavior under high pressure. With increasing
quasi-hydrostatic pressure the CDW order enhances with increase ofthe ordering
temperature up to 240K at 12 GPa. Upon further increase of pressure, the
resistance anomaly due to CDW order gets suppressed drastically and
superconductivity emerges at ~15 GPa, with the onset critical temperature (Tc)
~ 4K. The pressure dependence of Tc is found negligible, different from the
significant increase or a dome-shape seen in iso-structural layered diselenide
superconductors. The high pressure magnetoresistance and Hall measurements
suggest successive electronic structural changes with Fermi surface
modifications at 6 GPa and 12GPa. From the observed negative magnetoresistance
in this pressure range and absence of coexisting CDW and SC phases, we propose
that intra-layer spin-fluctuation can play a role in the emergence of
superconductivity in the high pressure phase. | 1908.11678v1 |
2015-04-16 | Phonon-limited carrier mobility and resistivity from carbon nanotubes to graphene | Under which conditions do the electrical transport properties of
one-dimensional (1D) carbon nanotubes (CNTs) and 2D graphene become equivalent?
We have performed atomistic calculations of the phonon-limited electrical
mobility in graphene and in a wide range of CNTs of different types to address
this issue. The theoretical study is based on a tight-binding method and a
force-constant model from which all possible electron-phonon couplings are
computed. The electrical resistivity of graphene is found in very good
agreement with experiments performed at high carrier density. A common
methodology is applied to study the transition from 1D to 2D by considering
CNTs with diameter up to 16 nm. It is found that the mobility in CNTs of
increasing diameter converges to the same value, the mobility in graphene. This
convergence is much faster at high temperature and high carrier density. For
small-diameter CNTs, the mobility strongly depends on chirality, diameter, and
existence of a bandgap. | 1504.04206v2 |
2019-08-15 | Analysis of Skin Effect in High Frequency Isolation Transformers | In this paper, a high frequency transformer with different conductors and
winding arrangements, at presence of eddy currents and skin effect, is studied.
By using different winding structures, and conductor types, such as circular,
square shaped, and foil wires, the skin effect in the windings is studied and
current density within the conductors at a high frequency of 20 MHz and a lower
frequency of 20 kHz are investigated using finite element method (FEM)
simulation. Moreover, magnetic field distribution in the transformers at 20 MHz
is obtained and displayed. Also, magnetizing inductance, leakage inductance and
AC winding resistance for all of the transformer types are found and compared,
and frequency response for the transformers are obtained and shown. Lastly,
based on the results, the skin effect increases the AC winding resistance and
decreases the leakage inductance as the frequency increases. Furthermore,
different winding arrangements, conductors, and transformer types show a wide
range of parasitic and loss behavior, which enable the designers to compromise
between various parameters in different applications, especially new fast
switches such as SiC and GaN. | 1910.01983v1 |
2020-08-31 | An Integrated Approach to Produce Robust Models with High Efficiency | Deep Neural Networks (DNNs) needs to be both efficient and robust for
practical uses. Quantization and structure simplification are promising ways to
adapt DNNs to mobile devices, and adversarial training is the most popular
method to make DNNs robust. In this work, we try to obtain both features by
applying a convergent relaxation quantization algorithm, Binary-Relax (BR), to
a robust adversarial-trained model, ResNets Ensemble via Feynman-Kac Formalism
(EnResNet). We also discover that high precision, such as ternary (tnn) and
4-bit, quantization will produce sparse DNNs. However, this sparsity is
unstructured under advarsarial training. To solve the problems that adversarial
training jeopardizes DNNs' accuracy on clean images and the struture of
sparsity, we design a trade-off loss function that helps DNNs preserve their
natural accuracy and improve the channel sparsity. With our trade-off loss
function, we achieve both goals with no reduction of resistance under weak
attacks and very minor reduction of resistance under strong attcks. Together
with quantized EnResNet with trade-off loss function, we provide robust models
that have high efficiency. | 2008.13305v4 |
2021-11-19 | Resistance-Time Co-Modulated PointNet for Temporal Super-Resolution Simulation of Blood Vessel Flows | In this paper, a novel deep learning framework is proposed for temporal
super-resolution simulation of blood vessel flows, in which a
high-temporal-resolution time-varying blood vessel flow simulation is generated
from a low-temporal-resolution flow simulation result. In our framework,
point-cloud is used to represent the complex blood vessel model,
resistance-time aided PointNet model is proposed for extracting the time-space
features of the time-varying flow field, and finally we can reconstruct the
high-accuracy and high-resolution flow field through the Decoder module. In
particular, the amplitude loss and the orientation loss of the velocity are
proposed from the vector characteristics of the velocity. And the combination
of these two metrics constitutes the final loss function for network training.
Several examples are given to illustrate the effective and efficiency of the
proposed framework for temporal super-resolution simulation of blood vessel
flows. | 2111.10372v1 |
2021-11-27 | Longevity Study on the CMS Resistive Plate Chambers for HL-LHC | The CMS Resistive Plate Chamber (RPC) system has been certified for 10 years
of LHC operation. In the next years, during the High luminosity LHC (HL-LHC)
phase, the LHC instantaneous luminosity will increase to a factor five more
than the existing LHC luminosity. This will subject the present CMS RPC system
to background rates and operating conditions much higher with respect to those
for which the detectors have been designed. Those conditions could affect the
detector properties and introduce nonrecoverable aging effects. A dedicated
longevity test is set up in the CERN Gamma Irradiation Facility (GIF++) to
determine if the present RPC detectors can survive the hard background
conditions during the HL-LHC running period. During the irradiation test, the
RPC detectors are exposed to a high gamma radiation for a long period and the
detector main parameters are monitored as a function of the integrated charge.
Based on collecting a large fraction of the expected integrated charge at the
LH-LHC, The results of the irradiation test will be presented. | 2111.13995v1 |
2022-08-24 | Multi-mode Analysis of Surface Losses in a Superconducting Microwave Resonator in High Magnetic Fields | This paper reports on a surface impedance measurement of a niobium titanium
superconducting radio frequency (SRF) cavity in a magnetic field (up to
$10\,{\rm T}$). A novel method is employed to decompose the surface resistance
contributions of the cylindrical cavity end caps and walls using measurements
from multiple $TM$ cavity modes. The results confirm that quality factor
degradation of a NbTi SRF cavity in a high magnetic field is primarily from
surfaces perpendicular to the field (the cavity end caps), while parallel
surface resistances (the walls) remain relatively constant. This result is
encouraging for applications needing high Q cavities in strong magnetic fields,
such as the Axion Dark Matter eXperiment (ADMX), because it opens the
possibility of hybrid SRF cavity construction to replace conventional copper
cavities. | 2208.11799v1 |
2022-12-19 | Eco-friendly Resistive Plate Chambers for detectors in future HEP applications | Resistive Plate Chamber detectors are largely used in current High Energy
Physics experiments, typically operated in avalanche mode with large fractions
of Tetrafluoroethane (C2H2F4), a gas recently banned by the European Union due
to its high Global Warming Potential (GWP). An intense R&D activity is ongoing
to improve RPC technology in view of future HEP applications. In the last few
years the RPC EcoGas@GIF++ Collaboration has been putting in place a joint
effort between the ALICE, ATLAS, CMS, LHCb/SHiP and EP-DT Communities to
investigate the performance of present and future RPC generations with
eco-friendly gas mixtures. Detectors with different layout and electronics have
been operated with ecological gas mixtures, with and without irradiation at the
CERN Gamma Irradiation Facility (GIF++). Results of these performance studies
together with plans for an aging test campaign are discussed in this article. | 2212.09572v1 |
2023-01-02 | Noise-resistant quantum memory enabled by Hamiltonian engineering | Nuclear spins in quantum dots are promising candidates for fast and scalable
quantum memory. By utilizing the hyperfine interaction between the central
electron and its surrounding nuclei, quantum information can be transferred to
the collective state of the nuclei and be stored for a long time. However,
nuclear spin fluctuations in a partially polarized nuclear bath deteriorate the
quantum memory fidelity. Here we introduce a noise-resistant protocol to
realize fast and high-fidelity quantum memory through Hamiltonian engineering.
With analytics and numerics, we show that high-fidelity quantum state transfer
between the electron and the nuclear spins is achievable at relatively low
nuclear polarizations, due to the strong suppression of nuclear spin noises.
For a realistic quantum dot with $10^4$ nuclear spins, a fidelity surpassing
80% is possible at a polarization as low as 30%. Our approach reduces the
demand for high nuclear polarization, making experimentally realizing quantum
memory in quantum dots more feasible. | 2301.00575v1 |
2023-11-06 | Persistent Homology for High-dimensional Data Based on Spectral Methods | Persistent homology is a popular computational tool for analyzing the
topology of point clouds, such as the presence of loops or voids. However, many
real-world datasets with low intrinsic dimensionality reside in an ambient
space of much higher dimensionality. We show that in this case traditional
persistent homology becomes very sensitive to noise and fails to detect the
correct topology. The same holds true for existing refinements of persistent
homology. As a remedy, we find that spectral distances on the
$k$-nearest-neighbor graph of the data, such as diffusion distance and
effective resistance, allow to detect the correct topology even in the presence
of high-dimensional noise. Moreover, we derive a novel closed-form formula for
effective resistance, and describe its relation to diffusion distances.
Finally, we apply these methods to high-dimensional single-cell RNA-sequencing
data and show that spectral distances allow robust detection of cell cycle
loops. | 2311.03087v2 |
2023-05-01 | Leveraging Language Representation for Material Recommendation, Ranking, and Exploration | Data-driven approaches for material discovery and design have been
accelerated by emerging efforts in machine learning. However, general
representations of crystals to explore the vast material search space remain
limited. We introduce a material discovery framework that uses natural language
embeddings derived from language models as representations of compositional and
structural features. The discovery framework consists of a joint scheme that
first recalls relevant candidates, and next ranks the candidates based on
multiple target properties. The contextual knowledge encoded in language
representations conveys information about material properties and structures,
enabling both representational similarity analysis for recall, and multi-task
learning to share information across related properties. By applying the
framework to thermoelectrics, we demonstrate diversified recommendations of
prototype structures and identify under-studied high-performance material
spaces. The recommended materials are corroborated by first-principles
calculations and experiments, revealing novel materials with potential high
performance. Our framework provides a task-agnostic means for effective
material recommendation and can be applied to various material systems. | 2305.01101v2 |
2019-07-12 | Data-driven materials science: status, challenges and perspectives | Data-driven science is heralded as a new paradigm in materials science. In
this field, data is the new resource, and knowledge is extracted from materials
data sets that are too big or complex for traditional human reasoning -
typically with the intent to discover new or improved materials or materials
phenomena. Multiple factors, including the open science movement, national
funding, and progress in information technology, have fueled its development.
Such related tools as materials databases, machine learning, and
high-throughput methods are now established as parts of the materials research
toolset. However, there are a variety of challenges that impede progress in
data-driven materials science: data veracity, integration of experimental and
computational data, data longevity, standardization, and the gap between
industrial interests and academic efforts. In this perspective article, we
discuss the historical development and current state of data-driven materials
science, building from the early evolution of open science to the rapid
expansion of materials data infrastructures. We also review key successes and
challenges so far, providing a perspective on the future development of the
field. | 1907.05644v2 |
2024-04-09 | Predicting the future applications of any stoichiometric inorganic material through learning from past literature | Through learning from past literature, artificial intelligence models have
been able to predict the future applications of various stoichiometric
inorganic materials in a variety of subfields of materials science. This
capacity offers exciting opportunities for boosting the research and
development (R&D) of new functional materials. Unfortunately, the previous
models can only provide the prediction for existing materials in past
literature, but cannot predict the applications of new materials. Here, we
construct a model that can predict the applications of any stoichiometric
inorganic material (regardless of whether it is a new material). Historical
validation confirms the high reliability of our model. Key to our model is that
it allows the generation of the word embedding of any stoichiometric inorganic
material, which cannot be achieved by the previous models. This work constructs
a powerful model, which can predict the future applications of any
stoichiometric inorganic material using only a laptop, potentially
revolutionizing the R&D paradigm for new functional materials | 2404.06120v1 |
2019-10-29 | Observation of spin-momentum locked surface states in amorphous Bi$_{2}$Se$_{3}$ | Crystalline symmetries have played a central role in the identification of
topological materials. The use of symmetry indicators and band representations
have enabled a classification scheme for crystalline topological materials,
leading to large scale topological materials discovery. In this work we address
whether amorphous topological materials, which lie beyond this classification
due to the lack of long-range structural order, exist in the solid state. We
study amorphous Bi$_2$Se$_3$ thin films, which show a metallic behavior and an
increased bulk resistance. The observed low field magnetoresistance due to weak
antilocalization demonstrates a significant number of two dimensional surface
conduction channels. Our angle-resolved photoemission spectroscopy data is
consistent with a dispersive two-dimensional surface state that crosses the
bulk gap. Spin resolved photoemission spectroscopy shows this state has an
anti-symmetric spin texture resembling that of the surface state of crystalline
Bi$_2$Se$_3$. These experimental results are consistent with theoretical
photoemission spectra obtained with an amorphous tight-binding model that
utilizes a realistic amorphous structure. This discovery of amorphous materials
with topological properties uncovers an overlooked subset of topological matter
outside the current classification scheme, enabling a new route to discover
materials that can enhance the development of scalable topological devices. | 1910.13412v4 |
2022-04-26 | Unusually strong electronic correlation and field-induced ordered phase in YbCo$_2$ | We report the first study of electrical resistivity, magnetization, and
specific heat on YbCo$_2$. The measurements on a single-phased sample of
YbCo$_2$ bring no evidence of magnetic ordering down to 0.3 K in a zero
magnetic field. The manifestations of low Kondo temperature are observed. The
specific heat value divided by temperature, C/T, keeps increasing
logarithmically beyond 7 J/mol.K2 with decreasing temperature down to 0.3 K
without no sign of magnetic ordering, suggesting a very large electronic
specific heat. Analysis of the magnetic specific heat indicates that the large
portion of the low-temperature specific heat is not explained simply by the low
Kondo temperature but is due to the strong intersite magnetic correlation in
both the 3d and 4f electrons. Temperature-dependent measurements under static
magnetic fields up to 7 T are carried out, which show the evolution of
field-induced transition above 2 T. The transition temperature increases with
increasing field, pointing to a ferromagnetic character. The extrapolation of
the transition temperature to zero field suggests that YbCo$_2$ is in the very
proximity of the quantum critical point. These results indicate that in the
unique case of YbCo$_2$, the itinerant electron magnetism of Co 3d-electrons
and the Kondo effect within the vicinity of quantum criticality of Yb 4f-local
moments can both play a role. | 2204.12025v2 |
2019-10-02 | High-throughput Density Functional Perturbation Theory and Machine Learning Predictions of Infrared, Piezoelectric and Dielectric Responses | Many technological applications depend on the response of materials to
electric fields, but available databases of such responses are limited. Here,
we explore the infrared, piezoelectric and dielectric properties of inorganic
materials by combining high-throughput density functional perturbation theory
and machine learning approaches. We compute {\Gamma}-point phonons, infrared
intensities, Born-effective charges, piezoelectric, and dielectric tensors for
5015 non-metallic materials in the JARVIS-DFT database. We find 3230 and 1943
materials with at least one far and mid-infrared mode, respectively. We
identify 577 high-piezoelectric materials, using a threshold of 0.5 C/m2. Using
a threshold of 20, we find 593 potential high-dielectric materials.
Importantly, we analyze the chemistry, symmetry, dimensionality, and geometry
of the materials to find features that help explain variations in our datasets.
Finally, we develop high-accuracy regression models for the highest infrared
frequency and maximum Born-effective charges, and classification models for
maximum piezoelectric and average dielectric tensors to accelerate discovery. | 1910.01183v2 |
2022-06-21 | A method to computationally screen for tunable properties of crystalline alloys | Conventionally, high-throughput computational materials searches start from
an input set of bulk compounds extracted from material databases, and this set
is screened for candidate materials for specific applications. In contrast,
many functional materials, and especially semiconductors, are heavily
engineered alloys or solid solutions of multiple compounds rather than a single
bulk compound. To improve our ability to design functional materials, in this
work we propose a framework and open-source code to automatically construct
possible "alloy pairs" and "alloy systems" and detect "alloy members" from a
set of existing, experimental or calculated ordered compounds, without
requiring any additional metadata beyond their crystal structure. We provide
analysis tools to estimate stability across each alloy. As a demonstration, we
apply this framework to all inorganic materials in the Materials Project
database to create a new database of over 600,000 unique alloy pair entries
that can then be used in materials discovery studies to search for materials
with tunable properties. This new database has been incorporated into the
Materials Project website and linked with corresponding material identifiers
for any user to query and explore. Using an example of screening for p-type
transparent conducting materials, we demonstrate how using this methodology
reveals candidate material systems that might otherwise have been excluded by a
traditional screening. This work lays a foundation from which materials
databases can go beyond stoichiometric compounds, and approach a more realistic
description of compositionally tunable materials. | 2206.10715v3 |
2023-05-20 | PhotoMat: A Material Generator Learned from Single Flash Photos | Authoring high-quality digital materials is key to realism in 3D rendering.
Previous generative models for materials have been trained exclusively on
synthetic data; such data is limited in availability and has a visual gap to
real materials. We circumvent this limitation by proposing PhotoMat: the first
material generator trained exclusively on real photos of material samples
captured using a cell phone camera with flash. Supervision on individual
material maps is not available in this setting. Instead, we train a generator
for a neural material representation that is rendered with a learned relighting
module to create arbitrarily lit RGB images; these are compared against real
photos using a discriminator. We then train a material maps estimator to decode
material reflectance properties from the neural material representation. We
train PhotoMat with a new dataset of 12,000 material photos captured with
handheld phone cameras under flash lighting. We demonstrate that our generated
materials have better visual quality than previous material generators trained
on synthetic data. Moreover, we can fit analytical material models to closely
match these generated neural materials, thus allowing for further editing and
use in 3D rendering. | 2305.12296v2 |
2015-06-30 | Strong, Tough and Stiff Bioinspired Ceramics from Brittle Constituents | High strength and high toughness are usually mutually exclusive in
engineering materials. Improving the toughness of strong but brittle materials
like ceramics thus relies on the introduction of a metallic or polymeric
ductile phase to dissipate energy, which conversely decreases the strength,
stiffness, and the ability to operate at high temperature. In many natural
materials, toughness is achieved through a combination of multiple mechanisms
operating at different length scales but such structures have been extremely
difficult to replicate. Building upon such biological structures, we
demonstrate a simple approach that yields bulk ceramics characterized by a
unique combination of high strength (470 MPa), high toughness (22 MPa.m1/2),
and high stiffness (290 GPa) without the assistance of a ductile phase. Because
only mineral constituents were used, this material retains its mechanical
properties at high temperature (600{\deg}C). The bioinspired,
material-independent design presented here is a specific but relevant example
of a strong, tough, and stiff material, in great need for structural,
transportations, and energy-related applications. | 1506.08979v1 |
2014-03-02 | A comprehensive scenario of the single crystal growth and doping dependence of resistivity and anisotropic upper critical fields in (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ ($0.22 \leq x \leq 1$) | Large high-quality single crystals of hole-doped iron-based superconductor
(Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ were grown over a broad composition range $0.22
\leq x \leq 1$ by inverted temperature gradient method. We found that high
soaking temperature, fast cooling rate, and adjusted temperature window of the
growth are necessary to obtain single crystals of heavily K doped crystals
(0.65$\leq x \leq$ 0.92) with narrow compositional distributions as revealed by
sharp superconducting transitions in magnetization measurements and close to
100% superconducting volume fraction. The crystals were extensively
characterized by x-ray and compositional analysis, revealing monotonic
evolution of the $c$-axis crystal lattice parameter with K substitution.
Quantitative measurements of the temperature-dependent in-plane resistivity,
$\rho(T)$ found doping-independent, constant within error bars, resistivity at
room temperature, $\rho(300K)$, in sharp contrast with significant doping
dependence in electron and isovalent substituted BaFe$_2$As$_2$ based
compositions. The shape of the temperature dependent resistivity, $\rho(T)$,
shows systematic doping-evolution, being close to $T^2$ in overdoped and
revealing significant contribution of the $T$-linear component at optimum
doping. The slope of the upper critical field, $d H_{c2}/dT$, scales linearly
with $T_c$ for both $H\parallel c$, $ H_{c2,c}$, and $H \parallel ab$,
$H_{c2,ab}$. The anisotropy of the upper critical field, $\gamma \equiv
H_{c2,ab} / H_{c2,c}$ determined near zero-field $T_c$ increases from $\sim$2
to 4-5 with increasing K doping level from optimal $x \sim$0.4 to strongly
overdoped $x$=1. | 1403.0227v1 |
2017-12-07 | Effects of high energy proton irradiation on the superconducting properties of Fe(Se,Te) thin films | In this paper we explore the effects of 3.5 MeV proton irradiation on
Fe(Se,Te) thin films grown on CaF2. In particular, we carry out a systematic
experimental investigation with different irradiation fluences up to 7.30x10^16
cm^-2 and different proton implantation depths, in order to clarify whether and
to what extent the critical current is enhanced or suppressed, what are the
effects of irradiation on the critical temperature, the resistivity and the
critical magnetic fields, and finally what is the role played by the substrate
in this context. We find that the effect of irradiation on superconducting
properties is generally small as compared to the case of other iron-based
superconductors. Such effect is more evident on the critical current density
Jc, while it is minor on the transition temperature Tc, on the normal state
resistivity and on the upper critical field Hc2 up to the highest fluences
explored in this work. In addition, our analysis shows that when protons
implant in the substrate far from the superconducting film, the critical
current can be enhanced up to 50% of the pristine value at 7 T and 12 K, while
there is no appreciable effect on critical temperature and critical fields
together with a slight decrease in resistivity. On the contrary, when the
implantation layer is closer to the film-substrate interface, both critical
current and temperature show a decrease accompanied by an enhancement of the
resistivity and the lattice strain. This result evidences that possible
modifications induced by irradiation in the substrate may affect the
superconducting properties of the film via lattice strain. The robustness of
the Fe(Se,Te) system to irradiation induced damage makes it a promising
compound for the fabrication of magnets in high-energy accelerators. | 1712.02558v1 |
2020-04-29 | Self-similar structure of resistive ADAFs with outflow and large-scale magnetic field | The observations and simulations have revealed that large-scale magnetic
field and outflows can exist in the inner regions of an advection-dominated
accretion disc where the resistive diffusion may also be important. In the
present paper, the roles of large-scale magnetic field and outflows in the
structure of resistive advection-dominated accretion discs are explored by
assuming that the accretion flow is radially self-similar. In the non-ideal
magnetohydrodynamic (MHD) approximation, the results show that the angular
velocity is always sub-Keplerian when both the outflow and the large-scale
magnetic field are taken into account. A stronger toroidal field component
leads to faster rotation, while the disc rotates with faster rate if the
vertical field component is weaker. The increase of magnetic diffusivity causes
the infall velocity to be close to Keplerian velocity. Although the previous
studies in the ideal MHD approximation have shown that the disc temperature
decreases due to the vertical field component, we find that the effect of
vertical field component on the temperature of a resistive disc depends on the
magnetic diffusivity. When the magnetic diffusivity is high, the more efficient
mechanism for decreasing the disc temperature can be the outflows, and not the
large-scale magnetic field. In such a limit of the magnetic diffusivity, the
components of the large-scale magnetic field enhance the gas temperature. The
increase of temperature can lead to heating and acceleration of the electrons
and help us to explain the origin of phenomena such as the flares in Sgr A*. On
the other hand, the infall velocity in such a limit rises as the temperature
increases, and therefore the surface density falls to too low values. Any
change in the density profile can alter the structure and the emitted spectrum
of disc. | 2004.14757v1 |
2022-02-28 | Ultra-Efficient Resistance Switching between Charge Ordered Phases in 1T-TaS$_2$ with a Single Picosecond Electrical Pulse | Progress in high-performance computing demands significant advances in memory
technology. Among novel memory technologies that promise efficient device
operation on a sub-ns timescale, resistance switching between charge ordered
phases of the 1T-TaS$_2$ has shown to be potentially useful for the development
of high-speed, energy efficient non-volatile memory device. While ultrafast
switching was previously reported with optical pulses, determination of the
intrinsic speed limits of actual devices that are triggered by electrical
pulses is technically challenging and hitherto still largely unexplored. A new
optoelectronic laboratory-on-a-chip, designed for measurements of ultrafast
memory switching, enables an accurate measurement of the electrical switching
parameters with 100 fs temporal resolution. A photoconductive response is used
for ultrashort electrical pulse generation, while its propagation along a
coplanar transmission line is detected using electro-optical sampling using a
purpose-grown highly-resistive electro-optic (Cd,Mn)Te crystal substrate. By
combining the transmission line and the 1T-TaS$_2$ device in a single
optoelectronic circuit a non-volatile resistance switching with a single 1.9 ps
electrical pulse is demonstrated, with an extremely small switching energy
density per unit area E$_A$ = 9.4 fJ/$\mu$m$^2$. The experiments demonstrate
ultrafast, energy-efficient circuits utilizing switching between non-volatile
charge-ordered states offers a new technological platform for cryogenic memory
devices. | 2202.13831v3 |
2021-10-15 | MHD simulations of small ELMs at low triangularity in ASDEX Upgrade | The development of small- and no-ELM regimes for ITER is a high priority
topic due to the risks associated to type-I ELMs. By considering non-linear
extended MHD simulations of the ASDEX Upgrade tokamak with the JOREK code, we
probe a regime that avoids type-I ELMs completely provided that the separatrix
density is high enough. The dynamics of the pedestal in this regime are
observed to be qualitatively similar to the so-called quasi-continuous exhaust
(QCE) regime in several ways. Repetitive type-I ELMs are substituted by roughly
constant levels of outwards transport caused by peeling-ballooning modes (with
dominant ballooning characteristics) which are localised in the last 5\% of the
confined region (in normalised poloidal flux). The simulated low triangularity
plasma transitions to a type-I ELMy H-mode if the separatrix density is
sufficiently reduced or if the input heating power is sufficiently increased.
The stabilising factors that play a role in the suppression of the small ELMs
are also investigated by analysing the simulations, and the importance of
including diamagnetic effects in the simulations is highlighted. By considering
a scan in the pedestal resistivity and by measuring the poloidal velocity of
the modes (and comparing to theoretical estimates for ideal and resistive
modes), we identify the underlying instabilities as resistive
peeling-ballooning modes. Decreasing the resistivity below
experimentally-relevant conditions (i.e., going towards ideal MHD), the
peeling-ballooning modes that constrain the pedestal below the type-I ELM
stability boundary display sharply decreasing growth rates. | 2110.07908v1 |
2022-01-05 | Superconducting $I$$\overline{4}$3$m$ CSH$_7$ model applied to resistive transition temperature data for compressed C-S-H at high pressure | This article updates version 1 by restricting consideration to only the
resistive data and excluding the questioned 287.7-K datum reported for
carbonaceous sulfur hydride in Snider et al., Nature $\textbf{585}$, 373
(2020). The superconducting transitions are considered in terms of the
theoretically-discovered compressed $I$$\overline{\textrm{4}}$3$m$ CSH$_7$
structure of Sun et al., Phys. Rev. B $\textbf{101}$, 174102 (2020), which
comprises a sublattice similar to $Im$$\overline{\textrm{3}}$$m$ H$_3$S with
CH$_4$ intercalates. Positing an electronic genesis of the superconductivity, a
model is presented in analogy with earlier work on superconductivity in
$Im$$\overline{\textrm{3}}$$m$ H$_3$S, in which pairing is induced via purely
electronic Coulomb interactions across the mean distance $\zeta$ between the S
and H$_4$ tetrahedra enclosing C. Theoretical superconducting transition
temperatures for $I$$\overline{\textrm{4}}$3$m$ CSH$_7$ are derived as
$T$$_{\textrm{C0}}$ = (2/3)$^{1/2}$ $\sigma^{1/2}$ $\beta$/$a$$\zeta$, where
$\beta$ = 1247.4 $\mathring{\mathrm{A}}$$^2$K is a universal constant, $\sigma$
is the participating charge fraction, and $a$ is the lattice parameter.
Analysis suggests persistent bulk superconductivity with a pressure-dependent
$\sigma$, increasing from $\sigma$ = 3.5, determined previously for
$Im$$\overline{3}$$m$ H$_3$S, to $\sigma$ = 7.5 at high pressure owing to
additionally participating C-H bond electrons. With $a$ and $\zeta$ determined
by theoretical structure, calculations of $T$$_{\textrm{C0}}$ at the highest
pressures, 258 and 271 GPa, are in agreement with resistive transitions to
within an overall uncertainty of $\pm$ 3.5 K. | 2201.01860v3 |
2021-12-02 | Mechanistic Data Science for Modeling and Design of Aerospace Composite Materials | Polymer matrix composites exhibit remarkable lightweight and high strength
properties that make them attractive for aerospace applications. Constituents'
materials such as advanced polymers and fibers or fillers with their
hierarchical structure embed these exceptional properties to the composite
materials. This hierarchical structure in multiple length scales provides an
opportunity for designing the composite materials for optimized properties.
However, the high dimensional design space for the constituents' materials and
architectures choice of the composites makes it a challenging design problem.
To tackle this high dimensional design space, a systematic, efficient approach
named mechanistic data science framework is proposed in this work to identify
the governing mechanisms of materials systems from the limited available data
and create a composite knowledge database. Our composite knowledge database
comprises the knowledge of polymers at the nanoscale with nano reinforcement,
the unidirectional structure at the microscale, and woven structure at
mesoscale mechanisms that can be further used for the part scale composite
design and analysis. The mechanistic data science framework presented in this
work can be further extended to other materials systems that will provide the
materials designer with the necessary tools to evaluate a new materials system
design rapidly. | 2112.00968v1 |
2024-01-31 | Incorporating quasiparticle and excitonic properties into material discovery | In recent years, GW-BSE has been proven to be extremely successful in
studying the quasiparticle (QP) bandstructures and excitonic effects in the
optical properties of materials. However, the massive computational cost
associated with such calculations restricts their applicability in
high-throughput material discovery studies. Recently, we developed a Python
workflow package, $py$GWBSE, to perform high-throughput GW-BSE simulations. In
this work, using $py$GWBSE we create a database of various QP properties and
excitonic properties of over 350 chemically and structurally diverse materials.
Despite the relatively small size of the dataset, we obtain highly accurate
supervised machine learning (ML) models via the dataset. The models predict the
quasiparticle gap with an RMSE of 0.36 eV, exciton binding energies of
materials with an RMSE of 0.29 eV, and classify materials as high or low
excitonic binding energy materials with classification accuracy of 90%. We
exemplify the application of these ML models in the discovery of 159
visible-light and 203 ultraviolet-light photoabsorber materials utilizing the
Materials Project database. | 2401.17831v1 |
2020-12-10 | Growth of Two-dimensional Compound Materials: Controllability, Material Quality, and Growth Mechanism | CONSPECTUS: Two-dimensional (2D) compound materials are promising materials
for use in electronics, optoelectronics, flexible devices, etc. because they
are ultrathin and cover a wide range of properties. Among all methods to
prepare 2D materials, chemical vapor deposition (CVD) is promising because it
produces materials with a high quality and reasonable cost. So far, much
efforts have been made to produce 2D compound materials with large domain size,
controllable number of layers, fast-growth rate, and high quality features,
etc. However, due to the complicated growth mechanism like sublimation and
diffusion processes of multiple precursors, maintaining the controllability,
repeatability, and high quality of CVD grown 2D binary and ternary materials is
still a big challenge, which prevents their widespread use. Here, taking 2D
transition metal dichalcogenides (TMDCs) as examples, we review current
progress and highlight some promising growth strategies for the growth of 2D
compound materials. The key technology issues which affect the CVD process,
including non-metal precursor, metal precursor, substrate engineering,
temperature, and gas flow, are discussed. Also, methods in improving the
quality of CVD-grown 2D materials and current understanding on their growth
mechanism are highlighted. Finally, challenges and opportunities in this field
are proposed. We believe this review will guide the future design of
controllable CVD systems for the growth of 2D compound materials with good
controllability and high quality, laying the foundations for their potential
applications. | 2012.05486v1 |
2022-03-17 | Quasi-solid-state electrolyte for ultra-high safety and cycle stability battery | All-solid-state lithium batteries (ASSLB) have been regarded as the most
promising candidate to achieve the next generation energy storage with high
energy and high safety. However, some bottlenecks, including high interfacial
resistance, bad electrochemical stability, and low conductivity, have hindered
its further development. Here, we developed a Pyr13FSI/LiFSI-based gel
electrolyte and used it in the LFP/LTO full battery system to achieve a
lithium-ion battery with high safety and cycle stability. The presence of ionic
liquid in the electrolyte reduces the crystallinity of PVDF-HFP polymer matrix,
increases the ion conductivity of the electrolyte, and greatly improves the
electrode-electrolyte interface contact. These advantages enable the battery to
work at room temperature and reach a specific capacity of 123mAh/g at the
current of 1C. The slightly change in interfacial resistances between the gel
electrolyte and electrodes with the increase of the cycle numbers is confirmed
through electrochemical impedance spectroscopy. The high electrochemical
stability of the electrolyte in the LFP/LTO system makes the battery exhibit
good cycle stability, and the battery maintains 80% of its initial capacity
after 2000 cycles at the current of 1C. In addition, benefitting from the
excellent properties of ionic liquids, such as non-flammability, negligible
vapour pressure, and high conductivity, the obtained gel electrolyte based
LFP/LTO pouch battery exhibits high safety and cycle stability. | 2203.09269v1 |
2012-11-25 | HIV drug resistance: problems and perspectives | Access to combination antiretroviral treatment (ART) has improved greatly
over recent years. At the end of 2011, more than eight million HIV infected
people were receiving antiretroviral therapy in low-income and middle-income
countries. ART generally works well in keeping the virus suppressed and the
patient healthy. However, treatment only works as long as the virus is not
resistant against the drugs used. In the last decades, HIV treatments have
become better and better at slowing down the evolution of drug resistance, so
that some patients are treated for many years without having any resistance
problems. However, for some patients, especially in low-income countries, drug
resistance is still a serious threat to their health. This essay will review
what is known about transmitted and acquired drug resistance, multi-class drug
resistance, resistance to newer drugs, resistance due to treatment for the
prevention of mother-to-child transmission, the role of minority variants
(low-frequency drug-resistance mutations), and resistance due to pre-exposure
prophylaxis. | 1211.5807v2 |
2022-07-16 | Random 2D nanowire networks: Finite-size effect and the effect of busbar/nanowire contact resistance on their electrical conductivity | We have studied the resistance of two-dimensional random percolating networks
of zero-width metallic nanowires (rings or sticks). We toke into account the
nanowire resistance per unit length, the junction (nanowire/nanowire contact)
resistance, and the busbar/nanowire contact resistance. Using a mean-field
approximation (MFA), we derived the total resistance of the nanoring-based
networks as a function of their geometrical and physical parameters. We have
proposed a way of accounting for the contribution of the busbar/nanowire
contact resistance toward the network resistance. The MFA predictions have been
confirmed by our Monte Carlo (MC) numerical simulations. Our study evidenced
that the busbar/nanowire contact resistance has a significant effect on the
electrical conductivity when the junction resistance dominates over wire
resistance. | 2207.07841v2 |
1995-01-09 | Resonant Tunneling and Charging Effects, a Path Integral Approach | Electron tunneling through small metallic islands with low capacitance is
studied. The large charging energy in these systems is responsible for
nonperturbative Coulomb blockade effects. We further consider the effect of
electron interactions in the electrodes. In junctions with high resistance
compared to the quantum resistance transport can be described by sequential
tunneling. If the resistance is lower, quantum fluctuations, higher order
coherent processes, and eventually resonant tunneling become important. We
present a path integral real-time approach, which allows a systematic
diagrammatic classification of these processes. An important process is
``inelastic resonant tunneling'', where different electrons tunnel coherently
between the electrodes and the island. Physical quantities like the current and
the average charge on the island can be deduced. We find a strong
renormalization of the system parameters and, in addition, a finite lifetime
broadening. It results in a pronounced broadening and smearing of the Coulomb
oscillations of the conductance. These effects are important in an
experimentally accessible range of temperatures. The electron interaction in
the electrodes is modeled by a Luttinger liquid. It leads to non-analytic
kernels in the effective action. The diagrammatic expansions can be performed
also in this case, resulting in power-law current-voltage characteristics. | 9501028v1 |
1997-11-11 | Transport Properties of Heavy Fermion Compounds | A technique for measuring the electrical resistivity and absolute thermopower
is presented for pressures up to 30 GPa, temperatures down to 25 mK and
magnetic fields up to 10 T. With the examples of CeCu2Ge2 and CeCu2Si2 we focus
on the interplay of normal phase and superconducting properties. With
increasing pres- sure, the behaviour of CeCu2Ge2 evolves from that of an
antiferromagnetically ordered Kondo system to that characteristic of an
intermediate valence compound as the Kondo temperature increases by about two
orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a
superconducting phase occurs which com- petes at low pressure with magnetic
ordering. For CeCu2Si2 the effective mass of carriers is probed by both the
coefficient of the Fermi liquid law and the ini- tial slope of the upper
critical field. The magnetic instability is studied no- tably for CeRu2Ge2 and
Yb-based compounds for which pressure-induced magnetic ordering tends to
develop. Finally, contrary to conventional wisdom, we argue that in heavy
fermions a large part of the residual resistivity is most likely not
independent of temperature; tentatively ascribed to Kondo hole, it can be very
pressure as well as sample dependent. [electrical resistivity, thermoelectric
power, heavy fermion, magnetic order, superconductivity] | 9711089v1 |
1999-01-14 | Multiple Andreev reflections in diffusive SNS structures | We report new measurements on sup-gap energy structure originating from
multiple Andreev reflections in mesoscopic SNS junctions. The junctions were
fabricated in a planar geometry with high transparency superconducting contacts
of Al deposited on highly diffusive and surface d-doped n++-GaAs. For samples
with a normal GaAs region of active length 0.3um the Josephson effect with a
maximal supercurrent Ic=3mA at T=237mK was observed. The sub-gap structure was
observed as a series of local minima in the differential resistance at dc bias
voltages V=2D/ne with n=1,2,4 i.e. only the even sub-gap positions. While at
V=2D/e (n=1) only one dip is observed, the n=2, and the n=4 sub-gap structures
each consists of two separate dips in the differential resistance. The mutual
spacing of these two dips is independent of temperature, and the mutual spacing
of the n=4 dips is half of the spacing of the n=2 dips. The voltage bias
positions of the sub-gap differential resistance minima coincide with the
maxima in the oscillation amplitude when a magnetic field is applied in an
interferometer configuration, where one of the superconducting electrodes has
been replaced by a flux sensitive open loop. | 9901140v2 |
2000-07-13 | Josephson junction array type I-V characteristics of quench-condensed ultra thin films of Bi | In this communication we report studies of d.c current-voltage (I-V)
characteristics of ultra thin films of Bi, quench condensed on single crystal
sapphire substrates at T = 15K. The hysteretic I-V characteristics are
explained using a resistively and capacitively shunted junction (RCSJ) model of
Josephson junction arrays. The Josephson coupling energy($E_J$) and the
charging energy($E_c$) are calculated for different thickness($d$) values. A
low resistance state is found in the low current regime below the critical
current, $I_c$. This resistance $R_0$ is found to have a minimum at a
particular thickness ($d_c$) value. Reflection High Energy Electron Diffraction
(RHEED) studies are done on these films. A distinct appearance of a diffuse
ring near $d_c$ is observed in the diffraction images, consistent with the
recent STM studies(Ekinci and Valles, PRL {\bf 82}(1999) 1518). These films
show an irreversible annealing when temperature is increased. The annealing
temperature ($T_a$) also has a maximum at the same thickness. Althoguh the
R$_s$ vs T of quench condensed Bi films suggest that the films are uniform, our
results indicate that even in thick films, the order parameter is not fully
developed over the complete area of the film. These results are discussed
qualitatively. | 0007222v1 |
2001-04-26 | Electron Quasiparticles Drive the Superconductor-to-Insulator Transition in Homogeneously Disordered Thin Films | Transport data on Bi, MoGe, and PbBi/Ge homogeneously-disordered thin films
demonstrate that the critical resistivity, $R_c$, at the nominal
insulator-superconductor transition is linearly proportional to the normal
sheet resistance, $R_N$. In addition, the critical magnetic field scales
linearly with the superconducting energy gap and is well-approximated by
$H_{c2}$. Because $R_N$ is determined at high temperatures and $H_{c2}$ is the
pair-breaking field, the two immediate consequences are: 1)
electron-quasiparticles populate the insulating side of the transition and 2)
standard phase-only models are incapable of describing the destruction of the
superconducting state. As gapless electronic excitations populate the
insulating state, the universality class is no longer the 3D XY model. The lack
of a unique critical resistance in homogeneously disordered films can be
understood in this context. In light of the recent experiments which observe an
intervening metallic state separating the insulator from the superconductor in
homogeneously disordered MoGe thin films, we argue that the two transitions
that accompany the destruction of superconductivity are 1) superconductor to
Bose metal in which phase coherence is lost and 2) Bose metal to localized
electron insulator via pair-breaking. | 0104504v2 |
2001-05-24 | Dilute electron gas near the metal-insulator transition in two dimensions | In recent years systematic experimental studies of the temperature dependence
of the resistivity in a variety of dilute, ultra clean two dimensional
electron/hole systems have revived the fundamental question of localization or,
alternatively, the existence of a metal-insulator transition in the presence of
strong electron-electron interactions in two dimensions. We argue that under
the extreme conditions of ultra clean systems not only is the electron-electron
interaction very strong but the role of other system specific properties are
also enhanced. In particular, we emphasize the role of valleys in determining
the transport properties of the dilute electron gas in silicon inversion layers
(Si-MOSFETs). It is shown that for a high quality sample the temperature
behavior of the resistivity in the region close to the critical region of the
metal-insulator transition is well described by a renormalization group
analysis of the interplay of interaction and disorder if the electron band is
assumed to have two distinct valleys. The decrease in the resistivity up to
five times has been captured in the correct temperature interval by this
analysis, without involving any adjustable parameters. The considerable
variance in the data obtained from different Si-MOSFET samples is attributed to
the sample dependent scattering rate across the two valleys, presenting thereby
with a possible explanation for the absence of universal behavior in Si-MOSFET
samples of different quality. | 0105471v1 |
2002-03-06 | c-Axis Transport and Resistivity Anisotropy of Lightly- to Moderately-Doped La_{2-x}Sr_{x}CuO_{4} Single Crystals: Implications on the Charge Transport Mechanism | Both the in-plane and the out-of-plane resistivities (\rho_{ab} and \rho_{c})
are measured in high-quality La_{2-x}Sr_{x}CuO_{4} (LSCO) single crystals in
the lightly- to moderately-doped region, x = 0.01 to 0.10, and the resistivity
anisotropy is determined. In all the samples studied, the anisotropy ratio \rho
_{c}/\rho_{ab} quickly increases with decreasing temperature, although in
non-superconducting samples the strong localization effect causes \rho
_{c}/\rho_{ab} to decrease at low temperatures. Most notably, it is found that
\rho_{c}/\rho_{ab} at moderate temperatures (100 - 300 K) is almost completely
independent of doping in the non-superconducting regime (x = 0.01 to 0.05);
this indicates that the same charge confinement mechanism that renormalizes the
c-axis hopping rate is at work down to x = 0.01. It is discussed that this
striking x-independence of \rho_{c}/\rho_{ab} is consistent with the idea that
holes form a self-organized network of hole-rich regions, which also explains
the unusually metallic in-plane transport of the holes in the lightly-doped
region. Furthermore, the data for x > 0.05 suggest that the emergence of the
superconductivity is related to an increase in the c-axis coupling. | 0203107v1 |
2002-05-15 | Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ} single crystals for a wide range of hole doping | To elucidate how the temperature dependence of the resistivity anisotropy of
the cuprate superconductors changes with hole doping, both the in-plane and the
out-of-plane resistivities (\rho_{ab} and \rho_{c}) are measured in a series of
high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6+\delta} (BSLCO) single crystals for a
wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu,
p, of 0.03 - 0.18. The anisotropy ratio, \rho_{c}/\rho_{ab}, shows a systematic
increase with decreasing p at moderate temperatures, except for the most
underdoped composition where the localization effect enhances \rho_{ab} and
thus lowers \rho_{c}/\rho_{ab}. The exact p dependence of \rho_{c}/\rho_{ab} at
a fixed temperature is found to be quite peculiar, which is discussed to be due
to the effect of the pseudogap that causes \rho_{c}/\rho_{ab} to be
increasingly more enhanced as p is reduced. The pseudogap also causes a rapid
growth of \rho_{c}/\rho_{ab} with decreasing temperature, and, as a result, the
\rho_{c}/\rho_{ab} value almost reaches 10^6 in underdoped samples just above
T_c. Furthermore, it is found that the temperature dependence of \rho_{c} of
underdoped samples show two distinct temperature regions in the pseudogap
phase, which suggests that the divergence of \rho_{c} below the pseudogap
temperature is governed by two different mechanisms. | 0205305v2 |
2003-05-08 | Anisotropic magnetization, specific heat and resistivity of RFe2Ge2 single crystals | We have grown RFe2Ge2 single crystals for R = Y and ten members of the
lanthanide series (Pr, Nd, Sm, Gd-Tm, Lu) using Sn flux as the solvent. The
method yields clean, high quality crystal plates as evidenced by residual
resistivities and RRR values in the range of 3-12 uOhm cm and 20-90
respectively. The crystals are also virtually free of magnetic impurities or
secondary phases, allowing the study of the intrinsic anisotropic magnetic
behavior of each compound. Characterization was made with X-Ray diffraction,
and temperature and field dependent magnetization, specific heat and
resistivity. Very strong anisotropies arising mostly from CEF effects were
observed for all magnetic rare earths except Gd. Antiferromagnetic ordering
occurred at temperatures between 16.5 K (Nd) and 1.1 K (Ho) that roughly scale
with the de Gennes factor for the heavy rare earths. For some members there is
also a lower temperature transition associated with changes in the magnetic
structure. Tm did not order down to 0.4 K, and appears to be a van Vleck
paramagnet. All members which ordered above 2 K showed a metamagnetic
transition at 2 K for fields below 70 kOe. The calculated effective moments per
rare earth atom are close to the expected free ion values of R^3+ except for Sm
which displays anomalous behavior in the paramagnetic state. The non-magnetic
members of this series (Y, Lu) are characterized by an unusually large
electronic specific heat coefficient (gamma ~ 60 mJ/mol K^2) and
temperature-independent susceptibility term (chi_0 ~ 0.003 emu/mol), indicative
of a relatively large density of states at the Fermi surface. | 0305173v1 |
2004-09-15 | Current-Induced Pair Breaking in Magnesium Diboride | The transport of electrical current through a superconductor falls into three
broad regimes: non-dissipative, dissipative but superconducting, and normal or
non-superconducting. These regimes are demarkated by two definitions of
critical current: one is the threshold current above which the superconductor
enters a dissipative (resistive) state; the other is the thermodynamic
threshold above which the superconductivity itself is destroyed and the
superconducting order parameter vanishes. The first threshold defines the
conventional critical current density Jc and the second defines the depairing
(or pair-breaking) current Jd. Type II superconductors in the mixed state have
quantized flux vortices, which tend to move when acted upon by the Lorentz
driving force of an applied transport current. In such a mixed state the
resistance vanishes only when vortices are pinned in place by defects and the
applied current is below the threshold Jc required to overcome pinning and
mobilize the vortices. Typically Jd >> Jc and a direct experimental measurement
of Jd over the entire temperature range (0 < T < Tc) is prohibited by the
enormous power dissipation densities (p ~ 10^10 -- 10^12 W/cm^3) needed to
reach the normal state. In this work, intense pulsed signals were used to
extend transport measurements to unprecedented power densities (p ~ 10^9 --
10^10 W/cm^3). This together with MgB2's combination of low normal-state
resistivity and high transition temperature have permitted a direct estimation
of \jd over the entire temperature range. This review describes our
experimental investigation of current-induced depairing in MgB2, and provides
an introduction to the phenomenological theories of superconductivity and how
the observations fit in their context. | 0409402v1 |
2005-06-09 | Pressure-induced valence change in the rare earth metals:The case of Praseodymium | The rare earth metal praseodymium (Pr) transforms from the d-fcc crystal
structure (Pr-III) to {$\alpha$}-U one (Pr-IV) at 20 GPa with a large volume
collapse (${\rm\Delta} V/V$ = 0.16), which is associated with the valence
change of the Pr ion. The two 4{\it f} electrons in the Pr ion is supposed to
be itinerant in the Pr-IV phase. In order to investigate the electronic state
of the phase IV, we performed the high pressure electrical resistance
measurement using the diamond anvil cell up to 32 GPa. In the Pr-IV phase, the
temperature dependence of the resistance shows an upward negative curvature,
which is similar to the itinerant 5{\it f} electron system in actinide metals
and compounds. This suggests the narrow quasiparticle band of the 4{\it f}
electrons near the Fermi energy. A new phase boundary is found at $T_{0}$ in
the Pr-IV phase. From the temperature and magnetic field dependences of the
resistance at 26 GPa, the ground state of the Pr-IV phase is suggested to be
magnetic. Several possibilities for the origin of $T_{0}$ are discussed. | 0506222v1 |
2004-10-20 | The penetration of plasma clouds across magnetic boundaries : the role of high frequency oscillations | Experiments are reported where a collisionfree plasma cloud penetrates a
magnetic barrier by self-polarization. We here focus on the resulting anomalous
magnetic field diffusion into the plasma cloud, two orders of magnitude faster
than classical, which is one important aspect of the plasma cloud penetration
mechanism. Without such fast magnetic diffusion, clouds with kinetic beta below
unity would not be able to penetrate magnetic barriers at all. Tailor-made
diagnostics has been used for measurements in the parameter range with the
kinetic beta ? 0.5 to 10, and with normalized width w/r(gi) of the order of
unity. Experimental data on hf fluctuations in density and in electric field
has been combined to yield the effective anomalous transverse resistivity
eta(EFF). It is concluded that they are both dominated by highly nonlinear
oscillations in the lower hybrid range, driven by a strong diamagnetic current
loop that is set up in the plasma in the penetration process. The anomalous
magnetic diffusion rate, calculated from the resistivity eta(EFF), is
consistent with single-shot multi-probe array measurements of the diamagnetic
cavity and the associated quasi-dc electric structure. An interpretation of the
instability measurements in terms of the resistive term in the generalized (low
frequency) Ohm's law is given. | 0410168v1 |
2007-12-13 | Andreev reflections at large ferromagnet/high-T_C superconductor area junctions with rough interface | Sub-gap conductance at a large area junction with a rough interface of a
ferromagnet and a high-T$_{C}$ superconductor is superimposed by multiple peaks
which is not expected from an ideal point contact Andreev reflection process.
We demonstrate this phenomenon by measuring resistance as a function of bias
voltage of a Co/Y$_{1}$Ba$_{2}$Cu$_{3}$O$_{7-\delta}$ junction with contact
area 50 x 70 $\mu$ $m^{2}$ at various temperatures. In order to analyze such
Andreev reflection data, the interface is assumed to have random potentials
which can create local electric fields. The Blonder-Tinkham-Klapwijk theory is
modified with the inclusion of a broadening parameter due to finite life time
effects of quasi particles. An additional voltage drop due to local electric
fields at the rough interface has been included in terms of an extra energy
shift which may be related to the asymmetry of normalized resistance data. Spin
polarization has been introduced for the ferromagnet. The presented model
explains the multi-peak nature and asymmetry of Andreev reflection data
experimentally observed at large area junctions. Extension of the model also
interprets the experimentally observed anomalous enhancement of resistance
peaks in the sub-gap region which may result from crossing the critical current
limit across the junction. | 0712.2131v2 |
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