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2024-02-11 | Reducing the metal-graphene contact resistance through laser-induced defects | Graphene has been extensively studied for a variety of electronic and
optoelectronic applications. The reported contact resistance between metal and
graphene, or rather its specific contact resistance (R{_C}), ranges from a few
tens of {\Omega} {\mu}m up to a few k{\Omega} {\mu}m. Manufacturable solutions
for defining ohmic contacts to graphene remain a subject of research. Here, we
report a scalable method based on laser irradiation of graphene to reduce the
R{_C} in nickel-contacted devices. A laser with a wavelength of {\lambda} = 532
nm is used to induce defects at the contact regions, which are monitored
\textit{in-situ} using micro-Raman spectroscopy. Physical damage is observed
using \textit{ex-situ} atomic force and scanning electron microscopy. The
transfer line method (TLM) is used to extract R{_C} from back-gated graphene
devices with and without laser treatment under ambient and vacuum conditions. A
significant reduction in R{_C} is observed in devices where the contacts are
laser irradiated, which scales with the laser power. The lowest R{_C} of about
250 {\Omega} {\mu}m is obtained for the devices irradiated with a laser power
of 20 mW, compared to 900 {\Omega} {\mu}m for the untreated devices. The
reduction is attributed to an increase in defect density, which leads to the
formation of crystallite edges and in-plane dangling bonds that enhance the
injection of charge carriers from the metal into the graphene. Our work
suggests laser irradiation as a scalable technology for R{_C} reduction in
graphene and potentially other two-dimensional materials. | 2402.07151v1 |
2024-04-19 | A Soft e-Textile Sensor for Enhanced Deep Learning-based Shape Sensing of Soft Continuum Robots | The safety and accuracy of robotic navigation hold paramount importance,
especially in the realm of soft continuum robotics, where the limitations of
traditional rigid sensors become evident. Encoders, piezoresistive, and
potentiometer sensors often fail to integrate well with the flexible nature of
these robots, adding unwanted bulk and rigidity. To overcome these hurdles, our
study presents a new approach to shape sensing in soft continuum robots through
the use of soft e-textile resistive sensors. This sensor, designed to
flawlessly integrate with the robot's structure, utilizes a resistive material
that adjusts its resistance in response to the robot's movements and
deformations. This adjustment facilitates the capture of multidimensional force
measurements across the soft sensor layers. A deep Convolutional Neural Network
(CNN) is employed to decode the sensor signals, enabling precise estimation of
the robot's shape configuration based on the detailed data from the e-textile
sensor. Our research investigates the efficacy of this e-textile sensor in
determining the curvature parameters of soft continuum robots. The findings are
encouraging, showing that the soft e-textile sensor not only matches but
potentially exceeds the capabilities of traditional rigid sensors in terms of
shape sensing and estimation. This advancement significantly boosts the safety
and efficiency of robotic navigation systems. | 2404.12627v1 |
1996-01-23 | Transport Properties, Thermodynamic Properties, and Electronic Structure of SrRuO3 | SrRuO$_3$ is a metallic ferromagnet. Its electrical resistivity is reported
for temperatures up to 1000K; its Hall coefficient for temperatures up to 300K;
its specific heat for temperatures up to 230K. The energy bands have been
calculated by self-consistent spin-density functional theory, which finds a
ferromagnetic ordered moment of 1.45$\mu_{{\rm B}}$ per Ru atom. The measured
linear specific heat coefficient $\gamma$ is 30mJ/mole, which exceeds the
theoretical value by a factor of 3.7. A transport mean free path at room
temperature of $\approx 10 \AA$ is found. The resistivity increases nearly
linearly with temperature to 1000K in spite of such a short mean free path that
resistivity saturation would be expected. The Hall coefficient is small and
positive above the Curie temperature, and exhibits both a low-field and a
high-field anomalous behavior below the Curie temperature. | 9601106v1 |
1997-08-26 | Scaling and the Metal-Insulator Transition in Si/SiGe Quantum Wells | The existence of a metal-insulator transition at zero magnetic field in two-
dimensional electron systems has recently been confirmed in high mobility
Si-MOSFETs. In this work, the temperature dependence of the resistivity of
gated Si/SiGe/Si quantum well structures has revealed a similar metal-
insulator transition as a function of carrier density at zero magnetic field.
We also report evidence for a Coulomb gap in the temperature dependence of
the resistivity of the dilute 2D hole gas confined in a SiGe quantum well.
In addition, the resistivity in the insulating phase scales with a single
parameter, and is sample independent. These results are consistent with the
occurrence of a metal-insulator transition at zero magnetic field in SiGe
square quantum wells driven by strong hole-hole interactions. | 9708201v1 |
1999-10-29 | Neighbor-junction state effect on the fluxon motion in a Josephson stack | We study experimentally and theoretically the influence of phase-whirling
(resistive) state in one junction of a two-fold Josephson stack on the fluxon
motion in the other junction. In experiment, we measure the fluxon velocity
versus current in one junction as a function of the state (Meissner or
resistive) of the neighboring junction. The analysis, made for the limit of
high fluxon density, shows that the interaction with the resistive state
results in an increase of the effective damping for the moving fluxon and,
therefore, in reduction of its velocity. Numerical simulations confirm this
result for various fluxon densities. The experimental data are in good
agreement with the theoretical predictions. In addition, the fluxon step
measured experimentally has a rather peculiar structure with back and forth
bending regions which is understood as a manifestation of the photon absorption
in the neighboring junction. | 9910489v1 |
2000-03-02 | Probing spin-charge separation using spin transport | Pedagogical discussions are given on what constitutes a signature of
spin-charge separation. A proposal is outlined to probe spin-charge separation
in the normal state of the high $T_c$ cuprates using spin transport.
Specifically, the proposal is to compare the temperature dependences of the
spin resistivity and electrical resistivity: Spin-charge separation will be
manifested in the different temperature dependences of these two resistivities.
We also estimate the spin diffusion length and spin relaxation time scales, and
we argue that it should be experimentally feasible to measure the spin
transport properties in the cuprates using the spin-injection technique. The
on-going spin-injection experiments in the cuprates and related theoretical
issues are also discussed. | 0003033v2 |
2000-06-01 | Superconducting properties of [BaCuO_x]_2/[CaCuO_2]_n artificial structures with ultrathick CaCuO_2 blocks | The electrical transport properties of [BaCuO_x]_2/[CaCuO_2]_n
(CBCCO-2xn)underdoped high temperature superconducting superlattices grown by
Pulsed Laser Deposition have been investigated. Starting from the optimally
doped CBCCO-2x2 superlattice, having three CuO_2 planes and T_c around 80 K, we
have systematically increased the number n up to 15 moving toward the
underdoped region and hence decreasing T_c. For n>11 the artificial structures
are no longer superconducting, as expected, for a uniformly distributed charge
carriers density inside the conducting block layer. The sheet resistance of
such artificial structures (n nearly equal to 11) turns out to be quite
temperature independent and close to the 2D quantum resistance 26 kOhm. A
further increase of the number of CuO_2 planes results in an insulator-type
dependence of R(T) in the wide range of temperatures from room temperature to 1
K. The value of the sheet resistance separating the Superconducting and the
Insulating regimes supports the fermionic scenario of the
Superconductor-Insulator transition in these systems. | 0006023v2 |
2000-08-02 | Evidence for small or intermediate-size polarons in the ferromagnetic state of manganites | Oxygen-isotope effects on the intrinsic resistivity have been studied in
high-quality epitaxial thin films of La_{0.75}Ca_{0.25}MnO_{3} and
Nd_{0.7}Sr_{0.3}MnO_{3}. We found that the residual resistivity \rho_{o}
increases by about 15(3)% upon replacing ^{16}O by ^{18}O. This provides strong
evidence for the presence of small or intermediate-size polarons in the
metallic ferromagnetic state. Furthermore, the temperature dependent part of
the resistivity at low temperatures consists of an AT^{4.5} term contributed
from 2-magnon scattering, and a B\omega_{s}/\sinh^{2}(\hbar\omega_{s}/2k_{B}T)
term which arises from scattering by a soft optical phonon mode. The absolute
magnitudes of the coefficient A and the phonon frequency \hbar\omega_{s} for
both isotope samples are in quantitative agreement with theoretical
predictions. | 0008029v1 |
2000-10-06 | Fluctuation Effects in High Sheet Resistance Superconducting Films | As the normal state sheet resistance, $R_n$, of a thin film superconductor
increases, its superconducting properties degrade. For $R_n\simeq h/4e^2$
superconductivity disappears and a transition to a nonsuperconducting state
occurs. We present electron tunneling and transport measurements on ultrathin,
homogeneously disordered superconducting films in the vicinity of this
transition. The data provide strong evidence that fluctuations in the amplitude
of the superconducting order parameter dominate the tunneling density of states
and the resistive transitions in this regime. We briefly discuss possible
sources of these amplitude fluctuation effects. We also describe how the data
suggest a novel picture of the superconductor to nonsuperconductor transition
in homogeneous 2D systems. | 0010114v1 |
2001-07-29 | Pressure-induced Superconductivity in a Ferromagnet UGe$_2$ -- Resistivity Measurements in Magnetic Field -- | The electrical resistivity measurements in the magnetic field are carried out
on the pressure-induced superconductor UGe$_2$. The superconductivity is
observed from 1.06 to 1.44 GPa. The upper critical field of $H_{C2}$ is
anisotropic where $H_{C2}(T)$ exhibits positive curvature for $H//b$ and
$c$-axis. The characteristic enhancement of $H_{C2}$ is reconfirmed for
$H//a$-axis. In the temperature and field dependence of resistivity at $P >
P_{C}$ where the ferromagnetic ordering disappears, it is observed that the
application of the external field along the {\it a}-axis increases the
coefficient of Fermi liquid behavior $AT^{2}$ correspondingly to the
metamagnetic transition. | 0107584v1 |
2001-10-26 | Two-dimensional metal in a parallel magnetic field | We have investigated the effect of an in plane parallel magnetic field (B_||)
on two high mobility metallic-like dilute two-dimensional hole gas (2DHG)
systems in GaAs quantum wells. The experiments reveal that, while suppressing
the magnitude of the low temperature resistance drop, B_|| does not affect E_a,
the characteristic energy scale of the metallic resistance drop. The field B_c
at which the metallic-like resistance drop vanishes is dependent on both the
width of quantum well and the orientation of B_||. It is unexpected that E_a is
unaffected by B_|| up to Bc depite that the Zeeman energy at B_c is roughly
equal to E_a. | 0110571v1 |
2002-05-07 | Doping Dependence of Anisotropic Resistivities in Trilayered Superconductor Bi2Sr2Ca2Cu3O10+delta (Bi-2223) | The doping dependence of the themopower, in-plane resistivity rho_ab(T),
out-of-plane resistivity rho_c(T), and susceptibility has been systematically
measured for high-quality single crystal Bi2Sr2Ca2Cu3O10+delta. We found that
the transition temperature Tc and pseudogap formation temperature T_rho_c*,
below which rho_c shows a typical upturn, do not change from their optimum
values in the "overdoped" region, even though doping actually proceeds. This
suggests that, in overdoped region, the bulk $T_c$ is determined by the always
underdoped inner plane, which have a large superconducting gap, while the
carriers are mostly doped in the outer planes, which have a large phase
stiffness. | 0205121v1 |
2002-09-19 | Temperature dependence of electrical resistivity of high-Tc cuprates - from pseudogap to overdoped regions | The effects of planar hole concentration, p, and in-plane disorder, Zn (y),
on the DC resistivity, r(T), of sintered samples of
Y_{1-x}Ca_xBa_2(Cu_{1-y}Zn_y)_3O_{7-d} were investigated over a wide doping
range by changing both the oxygen deficiency (d) and Ca content (x). From the
r(T,p) data we extracted characteristic crossover temperatures on the
underdoped and overdoped sides, T* and T_m respectively, above which r(T) is
linear. We compare our results with a number of other polycrystalline, thin
film and single crystal cuprate superconductors and find similar behavior in
the p-dependence of T*(p), T_m(p), and the resistivity exponent, m(p), in fits
to r(T) = r_0 + aT^m on the overdoped side. Our findings point towards the
possible existence of a quantum critical point (QCP) at the doping p=0.19 +/-
0.01. | 0209457v1 |
2002-10-23 | Crossover from coherent to incoherent electronic excitations in the normal state of Bi2Sr2CaCu2O8 | Angle resolved photoemission spectroscopy (ARPES) and resistivity
measurements are used to explore the overdoped region of the high temperature
superconductor Bi2Sr2CaCu2O8+delta. We find evidence for a new crossover line
in the phase diagram between a coherent metal phase for lower temperatures and
higher doping, and an incoherent metal phase for higher temperatures and lower
doping. The former is characterized by two well-defined spectral peaks in ARPES
due to coherent bilayer splitting and superlinear behavior in the resistivity,
whereas the latter is characterized by a single broad spectral feature in ARPES
and a linear temperature dependence of the resistivity. | 0210531v1 |
2003-01-14 | Resistance Noise Scaling in a Dilute Two-Dimensional Hole System in GaAs | We have measured the resistance noise of a two-dimensional (2D)hole system in
a high mobility GaAs quantum well, around the 2D metal-insulator transition
(MIT) at zero magnetic field. The normalized noise power $S_R/R^2$ increases
strongly when the hole density p_s is decreased, increases slightly with
temperature (T) at the largest densities, and decreases strongly with T at low
p_s. The noise scales with the resistance, $S_R/R^2 \sim R^{2.4}$, as for a
second order phase transition such as a percolation transition. The p_s
dependence of the conductivity is consistent with a critical behavior for such
a transition, near a density p* which is lower than the observed MIT critical
density p_c. | 0301222v2 |
2003-01-29 | Radiation-Induced Magnetoresistance Oscillations in a 2D Electron Gas | Recent measurements of a 2D electron gas subjected to microwave radiation
reveal a magnetoresistance with an oscillatory dependence on the ratio of
radiation frequency to cyclotron frequency. We perform a diagrammatic
calculation and find radiation-induced resistivity oscillations with the
correct period and phase. Results are explained via a simple picture of current
induced by photo-excited disorder-scattered electrons. The oscillations
increase with radiation intensity, easily exceeding the dark resistivity and
resulting in negative-resistivity minima. At high intensity, we identify
additional features, likely due to multi-photon processes, which have yet to be
observed experimentally. | 0301569v3 |
2003-02-05 | A low density finite temperature apparent "insulating" phase in 2D systems | We propose that the observed low density ``insulating'' phase of a 2D
semiconductor system, with the carrier density being just below ($n < n_c$) the
so-called critical density where the derivative of resistivity changes sign at
low temperatures (i.e. resistivity $\rho(T)$ increases with increasing $T$ for
$n > n_c$ whereas it decreases with increasing $T$ for $n < n_c$), is in fact a
``high-temperature'' crossover version of the same effective metallic phase
seen at higher densities ($n>n_c$). This low density ($n<n_c$) finite
temperature crossover 2D effective insulating phase is characterized by
$\rho(T)$ with power law temperature dependence in contrast to the truly
insulating state (occurring at still lower densities) whose resistivity
increases exponentially with decreasing temperature. | 0302112v1 |
2003-05-02 | Quantum Gunn effect: Zero-resistance state in 2D electron gas | Usually the conductivity is quantized as the inverse of the resistivity,
\rho=hc/ie^2, \sigma=ie^2/hc and the velocity versus the electric field is
linear, v=\mu E where \mu is the mobility of the electrons.However,when the
applied electric field exceeds a certain value, microwaves are emitted and the
relation v=\mu E breaks down so that the velocity actually reduces as E
increases. In this region, when magnetic field is applied, the conductivity
quantizes like the magnetic field, i.e., in units of hc/e which is different
from the usual quantization. Because of the flux quantization, the resistivity
will touch zero in the region of high electric field. Factors like 4/5 arise
due to new spin dependence of the effective charge. | 0305032v1 |
2004-02-06 | Counterflow measurements in strongly correlated GaAs hole bilayers: evidence for electron-hole pairing | We study interacting GaAs bilayer hole systems, with very small interlayer
tunneling, in a counterflow geometry where equal currents are passed in
opposite directions in the two, independently contacted layers. At low
temperatures, both the longitudinal and Hall counterflow resistances tend to
vanish in the quantum Hall state at total bilayer filling $\nu=1$,
demonstrating the pairing of oppositely charged carriers in opposite layers.
The temperature dependence of the counterflow Hall resistance is anomalous
compared to the other transport coefficients: even at relatively high
temperatures ($\sim$600mK), it develops a very deep minimum, with a value that
is about an order of magnitude smaller than the longitudinal counterflow
resistivity. | 0402186v2 |
2004-02-20 | Chemical Control of Spin Chirality in $(Nd_{1-x} Dy_x)_2 Mo_2 O_7$ | Magnetization and Hall resistivity have been investigated for single crystals
of Dy-doped Nd$_{2}$Mo$_{2}$O$_{7}$. A sharp decrease of the Hall resistivity
upon a metamagnetic transition, perhaps associated with magnetic-field ($H$)
induced flop of Dy$^{3+}$ moments, has been observed in the Dy-doped crystals
only for $H \parallel [111]$ direction. In addition, the sign of the Hall
resistivity at a high field, both for $H \parallel [100]$ and for $H \parallel
[111]$, changes with the Dy-doping. These results are explained in terms of the
sign change of Mo spin chirality that is controlled by the Dy$^{3+}$ moments
with a different sign of $f$-$d$ interaction from the Nd$^{3+}$ moments. | 0402510v1 |
2004-05-11 | Probing Spin-Polarized Currents in the Quantum Hall Regime | An experiment to probe spin-polarized currents in the quantum Hall regime is
suggested that takes advantage of the large Zeeman-splitting in the
paramagnetic diluted magnetic semiconductor zinc manganese selenide
(Zn$_{1-x}$Mn$_x$Se). In the proposed experiment spin-polarized electrons are
injected by ZnMnSe-contacts into a gallium arsenide (GaAs) two-dimensional
electron gas (2DEG) arranged in a Hall bar geometry. We calculated the
resulting Hall resistance for this experimental setup within the framework of
the Landauer-B\"uttiker formalism. These calculations predict for 100%
spininjection through the ZnMnSe-contacts a Hall resistance twice as high as in
the case of no spin-polarized injection of charge carriers into a 2DEG for
filling factor $\nu=2$. We also investigated the influence of the equilibration
of the spin-polarized electrons within the 2DEG on the Hall resistance. In
addition, in our model we expect no coupling between the contact and the 2DEG
for odd filling factors of the 2DEG for 100% spininjection, because of the
opposite sign of the g-factors of ZnMnSe and GaAs. | 0405231v1 |
2004-08-27 | Hall resistance and Lorenz ratio models in YBa2Cu3O7 | The 2D models of heat capacity, its conductivity ($\kappa$), Hall resistance
($R_H$) and the Lorenz ratio ($\mathcal{L}$) have been derived using the
ionization energy ($E_I$) based Fermi-Dirac statistics (iFDS). These models
reproduce the experimentally measured $\rho(T)$ and $R_H(T)$. The variation of
$\mathcal{L}$ is proportional to 1/T due to electron-phonon ($e$-$ph$)
scattering in $\kappa$. However, the $e$-$ph$ coupling in the electrical
resistivity has the polaronic effect that complies with iFDS, rather than the
$e$-$ph$ scattering that satisfies the Bloch-Gr\"{u}neisen formula. These
models are purely Fermi liquid and are not associated with any microscopic
theories of high-Tc superconductors. | 0408613v6 |
2004-09-08 | Non-linear Temperature Dependence of Resistivity in Single Crystalline Ag$_5$Pb$_2$O$_6$ | We measured electrical resistivity, specific heat and magnetic susceptibility
of single crystals of highly conductive oxide Ag_5Pb_2O_6, which has a layered
structure containing a Kagome lattice. Both the out-of-plane and in-plane
resistivity show T^2 dependence in an unusually wide range of temperatures up
to room temperature. This behavior cannot be accounted for either by electron
correlation or by electron-phonon scattering with high frequency optic phonons.
In addition, a phase transition with a large diamagnetic signal was found in
the ac susceptibility, which strongly suggests the existence of a
superconducting phase below 48 mK. | 0409184v2 |
2004-09-08 | High pressure investigation of the heavy-fermion antiferromagnet U_3Ni_5Al_19 | Measurements of magnetic susceptibility, specific heat, and electrical
resistivity at applied pressures up to 55 kbar have been carried out on single
crystals of the heavy-fermion antiferromagnet U_3Ni_5Al_19, which crystallizes
in the Gd_3Ni_5Al_19 orthorhombic structure with two inequivalent U sites. At
ambient pressure, a logarithmic T-dependence of the specific heat and T-linear
electrical resistivity below 5 K indicates non-Fermi liquid (NFL) behavior in
the presence of bulk antiferromagnetic order at T_N=23 K. Electrical
resistivity measurements reveal a crossover from non-Fermi liquid to Fermi
liquid behavior at intermediate pressures between 46 kbar and 51 kbar, followed
by a return to NFL T^{3/2} behavior at higher pressures. These results provide
evidence for an ambient pressure quantum critical point and an additional
antiferromagnetic instability at P_c=60 kbar. | 0409202v1 |
2005-04-19 | Nonmonotonic Temperature Dependence of the Hall Resistance for 2D Electron System in Si | Weak field Hall resistance Rxy(T) of the 2D electron system in Si was
measured over the range of temperatures 1-35 K and densities, where the
diagonal resistivity exhibits a ``metallic'' behavior. The Rxy(T) dependence
was found to be non-monotonic with a maximum at temperatures Tm~0.16Tf. The
Rxy(T) variations in the low-temperature domain (T<Tm) agree qualitatively with
the semiclassical model, that takes into account a broadening of the
Fermi-distribution solely. The semiclassical result considerably exceeds an
interaction-induced quantum correction. In the ``high-temperature'' domain
(T>Tm), the Rxy(T) dependence can be qualitatively explained in terms of either
a semiclassical T-dependence of a transport time, or a thermal activation of
carries from a localized band. | 0504475v1 |
2005-06-12 | Classical Hall transition and magnetoresistance in strongly inhomogeneous planar systems | The magneto-transport properties of planar and layered strongly inhomogeneous
two-phase systems are investigated, using the explicit expressions for the
effective conductivities and resistivities obtained by the exact dual
transformation, connecting effective conductivities of in-plane isotropic
two-phase systems with and without magnetic field. These expressions allow to
describe the effective resistivity of various inhomogeneous media at arbitrary
concentrations $x$ and magnetic fields $H$. The corresponding plots of the
$x$-dependence of the Hall constant $R_H(x,H)$ and the magnetoresistance
$R(x,H)$ are constructed for various values of magnetic field at some values of
inhomogeneity parameters. These plots for strongly inhomogeneous systems at
high magnetic fields show a sharp transition between partial Hall resistivities
(or Hall conductivities) with different dependencies of $R_H$ on the phase
concentrations. It is shown that there is a strong correlation between large
linear magnetoresistance effect and this sharp Hall transition. Both these
effects are a consequence of the exact duality symmetry. A possible physical
explanation of these effects and their correlation is proposed. | 0506267v1 |
2005-07-08 | Field-induced non-Fermi-liquid resistivity of stoichiometric YbAgGe single crystals | We have investigated hexagonal YbAgGe down to 70 mK by measuring the
magnetic-field and temperature dependence of the resistivity rho of single
crystals in fields up to 14 T. Our results extend the H-T phase diagram to the
lowest temperatures for H applied in the basal plane and along the c-axis. In
particular, critical fields for the suppression of several magnetic phases are
determined. The temperature dependence of rho(T) is unusual: whereas at low H,
rho(T) reveals a temperature exponent n>=2, we find 1<=n<1.5 and strong
enhancement of the temperature dependence of rho(T) close to and beyond the
highest critical field for each field direction. For H applied in the basal
plane, at high fields a conventional T^2 dependence of rho(T) is reached above
10 T accompanied by an approach to saturation of a strong drop in the residual
resistivity. YbAgGe appears to be one of few Yb-based stoichiometric systems,
where quantum-critical behaviour may be induced by a magnetic field. | 0507211v2 |
2005-08-12 | The microwave induced resistance response of a high mobility 2DEG from the quasi-classical limit to the quantum Hall regime | Microwave induced resistance oscillations (MIROs) were studied experimentally
over a very wide range of frequencies ranging from ~20 GHz up to ~4 THz, and
from the quasi-classical regime to the quantum Hall effect regime. At low
frequencies regular MIROs were observed, with a periodicity determined by the
ratio of the microwave to cyclotron frequencies. For frequencies below 150 GHz
the magnetic field dependence of MIROs waveform is well described by a
simplified version of an existing theoretical model, where the damping is
controlled by the width of the Landau levels. In the THz frequency range MIROs
vanish and only pronounced resistance changes are observed at the cyclotron
resonance. The evolution of MIROs with frequency are presented and discussed. | 0508327v1 |
2005-11-15 | 1/f noise in a dilute GaAs two-dimensional hole system in the insulating phase | We have measured the resistance and the 1/f resistance noise of a
two-dimensional low density hole system in a high mobility GaAs quantum well at
low temperature. At densities lower than the metal-insulator transition one,
the temperature dependence of the resistance is either power-like or simply
activated. The noise decreases when the temperature or the density increase.
These results contradict the standard description of independent particles in
the strong localization regime. On the contrary, they agree with the
percolation picture suggested by higher density results. The physical nature of
the system could be a mixture of a conducting and an insulating phase. We
compare our results with those of composite thin films. | 0511375v1 |
2006-02-03 | Observation of the quantized Hall insulator in the quantum critical regime of the two-dimensional electron gas | We have investigated the Hall resistance $R_H$ near the plateau-insulator
transition of a two-dimensional electron gas in the quantum critical regime.
High-field magnetotransport data taken on a low-mobility InGaAs/InP
heterostructure with the plateau-insulator transition at a critical field $B_c$
of 17.2 T show that the Hall resistance $R_H$ is quantized at $h/e^2$ near the
critical filling fraction ($\nu_c$ = 0.55) when $T \to 0$. By making use of
universal scaling functions extracted from the magnetotransport data we show
that $R_H$ in the insulating phase in the limit $T \to 0$ is quantized at
$h/e^2$ for all values of the scaling parameter $\Delta\nu /(T/T_0)^\kappa$
with $\Delta\nu = \nu - \nu_c$. However, as a function of $\Delta\nu $ (or
magnetic field) the Hall resistance diverges in the limit $T \to 0$ for all
values $\nu < \nu_c$. | 0602093v2 |
2006-12-18 | Nonlinear Current of Strongly Irradiated Quantum Hall Gas | Two dimensional electrons in weakly disordered high Landau levels are
considered. The current-field response in the presence of a strong microwave
field, is computed. The disordered Floquet evolution operator allows us to
treat the short range disorder perturbatively, at any strength of electric
fields. A simplifying Random Matrix Approximation reproduces the broadened
Landau levels density of states and structure factor. We derive the magnitude
of the Microwave Induced Resistivity Oscillations. The disorder short
wavelength cut-off determines the non-linear electric fields of the Zero
Resistance State and the Hall Induced Resistivity Oscillations. We discuss
wider implications of our results on experiments and other theories. | 0612469v2 |
2007-12-13 | Study of GEM-like detectors with resistive electrodes for RICH applications | We have developed prototypes of GEM-like detectors with resistive electrodes
to be used as RICH photodetectors equipped with CsI photocathodes. The main
advantages of these detectors are their intrinsic spark protection and
possibility to operate at high gain (~10E5) in many gases including poorly
quenched ones, allowing for the adoption of windowless configurations in which
the radiator gas is also used in the chamber. Results of systematic studies of
the resistive GEMs combined with CsI photocathodes are presented: its quantum
efficiency, rate characteristics, long-term stability, etc. On the basis of the
obtained results, we believe that the new detector will be a promising
candidate for upgrading the ALICE RICH detector | 0712.2179v1 |
2008-01-06 | Scaling of Hall Resistivity in the Mixed State of MgB2 Films | The longitudinal resistivity (rho_{xx}) and transverse resistivity (rho_{xy})
of MgB2 thin films in the mixed state were studied in detail. We found that the
temperature dependencies of rho_{xx} and \rho_{xy} at a fixed magnetic field
(H) satisfy the scaling law of $\rho_{xy}=A\rho_{xx}^\beta$, where the exponent
beta varies around 2.0 for different fields. In the low field region (below
1T), beta maintains a constant value of 2.0 due to the weak pinning strength of
the vortices, mainly from the superfluid of the pi band. When H>1T, beta drops
abruptly to its lowest value at about 2T because of the proliferation of
quasiparticles from the pi-band and, hence, the motion of the vortices from the
superfluid of the sigma-band dominates the dissipation. As the field is
increased further, the vortex pinning strength is weakened and beta increases
monotonically towards 2.0 at a high field. All the results presented here are
in good agreement with the expectation of the vortex physics of a multi-band
superconductor. | 0801.0838v1 |
2008-02-05 | Effect of small particles on the near-wall dynamics of a large particle in a highly bidisperse colloidal solution | We consider the hydrodynamic effect of small particles on the dynamics of a
much larger particle moving normal to a planar wall in a highly bidisperse
dilute colloidal suspension of spheres. The gap $h_0$ between the large
particle and the wall is assumed to be comparable to the diameter $2a$ of the
smaller particles so there is a length-scale separation between the gap width
$h_0$ and the radius of the large particle $b<<h_0$. We use this length-scale
separation to develop a new lubrication theory which takes into account the
presence of the smaller particles in the space between the larger particle and
the wall. The hydrodynamic effect of the small particles on the motion of the
large particle is characterized by the short time (or high frequency)
resistance coefficient. We find that for small particle-wall separations $h_0$,
the resistance coefficient tends to the asymptotic value corresponding to the
large particle moving in a clear suspending fluid. For $h_0<<a$, the resistance
coefficient approaches the lubrication value corresponding to a particle moving
in a fluid with the effective viscosity given by the Einstein formula. | 0802.0608v1 |
2008-07-16 | Influence of doping on the Hall coefficient in Sr_{14-x}Ca_xCu_24O_41 | We present Hall-effect measurements of two-leg ladder compounds
Sr_{14-x}Ca_xCu_24O_41 (0 <= x <= 11.5) with the aim to determine the number of
carriers participating in dc transport. Distribution of holes between the
ladder and chain subsystems is one of the crucial questions important for
understanding the physics of these compounds. Our Hall effect and resistivity
measurements show typical semiconducting behavior for x < 11.5. However, for
x=11.5, the results are completely different, and the Hall coefficient and
resistivity behavior is qualitatively similar to that of high temperature
copper-oxide superconductors. We have determined the effective number of
carriers at room temperature and compared it to the number of holes in the
ladders obtained by other experimental techniques. We propose that going from
x=0 to x=11.5 less than 1 hole per formula unit is added to the ladders and is
responsible for a pronounced change in resistivity with Ca doping. | 0807.2561v2 |
2008-08-04 | Evidence for the Sr2RuO4 intercalations in the Sr3Ru2O7 region of the Sr3Ru2O7-Sr2RuO4 eutectic system | Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far,
ac susceptibility measurements revealed multiple superconducting transitions
occurring in the Sr3Ru2O7 region cut from Sr3Ru2O7-Sr2RuO4 eutectic crystals.
Based on various experimental results, some of us proposed the scenario in
which Sr2RuO4 thin slabs with a few layers of the RuO2 plane are embedded in
the Sr3Ru2O7 region as stacking faults and multiple superconducting transitions
arise from the distribution of the slab thickness. To examine this scenario, we
measured the resistivity along the ab plane (rho_ab) using a Sr3Ru2O7-region
sample cut from the eutectic crystal, as well as along the c axis (rho_c) using
the same crystal. As a result, we detected resistance drops associated with
superconductivity only in rho_ab, but not in rho_c. These results support the
Sr2RuO4 thin-slab scenario. In addition, we measured the resistivity of a
single crystal of pure Sr3Ru2O7 with very high quality and found that pure
Sr3Ru2O7 does not exhibit superconductivity down to 15 mK. | 0808.0434v1 |
2008-08-18 | Field Re-entrant Superconductivity Induced by the Enhancement of Effective Mass in URhGe | High quality single crystals of a ferromagnetic superconductor URhGe were
successfully grown. The electrical resistivity was measured for the field along
b-axis in the orthorhombic crystal structure in order to study precisely its
field re-entrant superconductivity which occurs in the vicinity of the field
$H_{\rm R}$, where the easy magnetization switches from $c$ to b-axis. The
field re-entrant superconductivity of URhGe is analyzed with special focus on
its dependence with the value of residual resistivity $\rho_0$ and the
coefficient $A$ of $T^2$ term of the resistivity. The experimental results are
well explained by a crude model related with the field dependence of the
effective mass $m^\ast$, where the corresponding critical temperature
$T_{\mathrm{sc}}(m^\ast)$ and the upper critical field $H_{\rm c2}$ are
strongly enhanced. Discussion is made on the interplay between magnetic and
superconducting phase diagram as well as the link between $T_{\mathrm{sc}}$ and
$A$ in other heavy fermion superconductors. | 0808.2500v1 |
2008-10-13 | Observation of a Fractional Quantum Hall State at $ν=1/4$ in a Wide GaAs Quantum Well | We report the observation of an even-denominator fractional quantum Hall
(FQH) state at $\nu=1/4$ in a high quality, wide GaAs quantum well. The sample
has a quantum well width of 50 nm and an electron density of
$n_e=2.55\times10^{11}$ cm$^{-2}$. We have performed transport measurements at
$T\sim35$ mK in magnetic fields up to 45 T. When the sample is perpendicular to
the applied magnetic field, the diagonal resistance displays a kink at
$\nu=1/4$. Upon tilting the sample to an angle of $\theta=20.3^o$ a clear FQH
state at emerges at $\nu=1/4$ with a plateau in the Hall resistance and a
strong minimum in the diagonal resistance. | 0810.2274v1 |
2008-10-23 | Jumps in current-voltage characteristics in disordered films | We argue that giant jumps of current at finite voltages observed in
disordered samples of InO, TiN and YSi manifest a bistability caused by the
overheating of electrons. One of the stable states is overheated and thus
low-resistive, while the other, high-resistive state is heated much less by the
same voltage. The bistability occurs provided that cooling of electrons is
inefficient and the temperature dependence of the equilibrium resistance, R(T),
is steep enough. We use experimental R(T) and assume phonon mechanism of the
cooling taking into account its strong suppression by disorder. Our description
of details of the I-V characteristics does not involve adjustable parameters
and turns out to be in a quantitative agreement with the experiments. We
propose experiments for more direct checks of this physical picture. | 0810.4312v2 |
2008-11-20 | A novel non-Fermi-liquid state in the iron-pnictide FeCrAs | We report transport and thermodynamic properties of stoichiometric single
crystals of the hexagonal iron-pnictide FeCrAs. The in-plane resistivity shows
an unusual "non-metallic" dependence on temperature T, rising continuously with
decreasing T from ~ 800 K to below 100 mK. The c-axis resistivity is similar,
except for a sharp drop upon entry into an antiferromagnetic state at T_N 125
K. Below 10 K the resistivity follows a non-Fermi-liquid power law, rho(T) =
rho_0 - AT^x with x<1, while the specific heat shows Fermi liquid behaviour
with a large Sommerfeld coefficient, gamma ~ 30 mJ/mol K^2. The high
temperature properties are reminiscent of those of the parent compounds of the
new layered iron-pnictide superconductors, however the T -> 0 properties
suggest a new class of non-Fermi liquid. | 0811.3439v1 |
2009-02-25 | Resistive relaxation of a magnetically confined mountain on an accreting neutron star | Three-dimensional numerical magnetohydrodynamic (MHD) simulations are
performed to investigate how a magnetically confined mountain on an accreting
neutron star relaxes resistively. No evidence is found for non-ideal MHD
instabilities on a short time-scale, such as the resistive ballooning mode or
the tearing mode. Instead, the mountain relaxes gradually as matter is
transported across magnetic surfaces on the diffusion time-scale, which
evaluates to $\tau_\mathrm{I} \sim 10^5 - 10^8$ yr (depending on the
conductivity of the neutron star crust) for an accreted mass of $M_a = 1.2
\times 10^{-4} M_\odot$. The magnetic dipole moment simultaneously reemerges as
the screening currents dissipate over $\tau_\mathrm{I}$. For nonaxisymmetric
mountains, ohmic dissipation tends to restore axisymmetry by magnetic
reconnection at a filamentary neutral sheet in the equatorial plane. Ideal-MHD
oscillations on the Alfv\'{e}n time-scale, which can be excited by external
influences, such as variations in the accretion torque, compress the magnetic
field and hence decrease $\tau_\mathrm{I}$ by \change{one order of magnitude}
relative to its standard value (as computed for the static configuration). The
implications of long-lived mountains for gravitational wave emission from
low-mass X-ray binaries are briefly explored. | 0902.4484v1 |
2009-12-09 | Coulomb zero bias anomaly for fractal geometry and conductivity of granular systems near the percolation threshold | A granular system slightly below the percolation threshold is a collection of
finite metallic clusters, characterized by wide spectrum of sizes, resistances,
and charging energies. Electrons hop from cluster to clusters via short
insulating "links" of high resistance. At low temperatures all clusters are
Coulomb blockaded and the dc-conductivity is exponentially suppressed. At
lowest T the leading transport mechanism is variable range cotunneling via
largest (critical) clusters, leading to the modified Efros-Shklovsky law. At
intermediate temperatures the principal suppression of the conductivity
originates from the Coulomb zero bias anomaly occurring, when electron tunnels
between adjacent large clusters with large resistances. Such clusters are
essentially extended objects and their internal dynamics should be taken into
account. In this regime the T-dependence of conductivity is stretched
exponential with a nontrivial index, expressed through the indices of
percolation theory. Due to the fractal structure of large clusters the anomaly
is strongly enhanced: it arises not only in low dimensions, but also in d=3
case. | 0912.1701v1 |
2010-02-16 | Pseudogap Phase Boundary in Overdoped Bi_2Sr_2CaCu_2O_8 Studied by Measuring Out-of-plane Resistivity under the Magnetic Fields | The characteristic pseudogap temperature T* in Bi2Sr2CaCu2O8 system has been
systematically evaluated as a function of doping, especially focusing on its
overdoped region, by measuring the out-of-plane resistivity under the magnetic
fields. Overdoped samples have been prepared by annealing TSFZ-grown
Bi2Sr2CaCu2O8 single crystals under the high oxygen pressures (990 kgf/cm2). At
a zero field, the out-of-plane resistivity showed a metallic behavior down to
Tc (= 62 K), while under the magnetic fields of over 3 T,it showed typical
upturn behavior from around 65 K upon decreasing temperature. This result
suggests that the pseudogap and superconductivity are different phenomena. | 1002.3014v1 |
2010-05-13 | Probing top-gated field effect transistor of reduced graphene oxide monolayer made by dielectrophoresis | We demonstrate top-gated field effect transistor made of reduced graphene
oxide (RGO) monolayer (graphene) by dielectrophoresis. Raman spectrum of RGO
flakes of typical size of 5{\mu}m x 5{\mu}m show a single 2D band at 2687 cm-1,
characteristic of a single layer graphene. The two probe current - voltage
measurements of RGO flakes, deposited in between the patterned electrodes with
a gap of 2.5 {\mu}m using a.c. dielectrophoresis show ohmic behavior with a
resistance of ~ 37k{\Omega}. The temperature dependence of the resistance (R)
of RGO measured between temperatures 305 K to 393 K yields temperature
coefficient of resistance [dR/dT]/R ~ -9.5x10-4 K-1, same as mechanically
exfoliated single layer graphene. The field effect transistor action was
obtained by electrochemical top-gating using solid polymer electrolyte (PEO +
LiClO4) and Pt wire. Ambipolar nature of graphene flakes is observed upto a
doping level of ~ 6x1012/cm2 and carrier mobility of ~ 50 cm2V-1sec-1. The
source - drain current characteristics shows a tendency of current saturation
at high source - drain voltage which is analyzed quantitatively by a diffusive
transport model. | 1005.2258v1 |
2010-08-10 | Temperature-dependent resistivity of suspended graphene | In this paper we investigate the electron-phonon contribution to the
resistivity of suspended single layer graphene. In-plane as well as flexural
phonons are addressed in different temperature regimes. We focus on the
intrinsic electron-phonon coupling due to the interaction of electrons with
elastic deformations in the graphene membrane. The competition between screened
deformation potential vs fictitious gauge field coupling is discussed, together
with the role of tension in the suspended flake. In the absence of tension,
flexural phonons dominate the phonon contribution to the resistivity at any
temperature $T$ with a $T^{5/2}_{}$ and $T^{2}_{}$ dependence at low and high
temperatures, respectively. Sample-specific tension suppresses the contribution
due to flexural phonons, yielding a linear temperature dependence due to
in-plane modes. We compare our results with recent experiments. | 1008.1631v1 |
2010-08-17 | Heat capacity study of BaFe$_{2}$As$_{2}$: effects of annealing | Heat-capacity, X-ray diffraction, and resistivity measurements on a
high-quality BaFe$_{2}$As$_{2}$ sample show an evolution of the
magneto-structural transition with successive annealing periods. After a 30-day
anneal the resistivity in the (ab) plane decreases by more than an order of
magnitude, to 12 $\mu\Omega$cm, with a residual resistance ratio $\sim$36; the
heat-capacity anomaly at the transition sharpens, to an overall width of less
than K, and shifts from 135.4 to 140.2 K. The heat-capacity anomaly in both the
as-grown sample and after the 30-day anneal shows a hysteresis of $\sim$0.15 K,
and is unchanged in a magnetic field $\mu_{0}$H = 14 T. The X-ray and
heat-capacity data combined suggest that there is a first order jump in the
structural order parameter. The entropy of the transition is reported. | 1008.2967v2 |
2010-09-17 | Anomalously strong pinning of the filling factor nu=2 in epitaxial graphene | We explore the robust quantization of the Hall resistance in epitaxial
graphene grown on Si-terminated SiC. Uniquely to this system, the dominance of
quantum over classical capacitance in the charge transfer between the substrate
and graphene is such that Landau levels (in particular, the one at exactly zero
energy) remain completely filled over an extraordinarily broad range of
magnetic fields. One important implication of this pinning of the filling
factor is that the system can sustain a very high nondissipative current. This
makes epitaxial graphene ideally suited for quantum resistance metrology, and
we have achieved a precision of 3 parts in 10^10 in the Hall resistance
quantization measurements. | 1009.3450v3 |
2010-10-14 | Resistivity and Hall effect of LiFeAs: Evidence for electron-electron scattering | LiFeAs is unique among the broad family of FeAs-based superconductors,
because it is superconducting with a rather large $T_c\simeq 18$ K under
ambient conditions although it is a stoichiometric compound. We studied the
electrical transport on a high-quality single crystal. The resistivity shows
quadratic temperature dependence at low temperature giving evidence for strong
electron-electron scattering and a tendency towards saturation around room
temperature. The Hall constant is negative and changes with temperature, what
most probably arises from a van Hove singularity close to the Fermi energy in
one of the hole-like bands. Using band structure calculations based on angular
resolved photoemission spectra we are able to reproduce all the basic features
of both the resistivity as well as the Hall effect data. | 1010.2876v2 |
2010-10-20 | Raychaudhuri's equation and aspects of relativistic charged collapse | We use the Raychaudhuri equation to probe certain aspects related to the
gravitational collapse of a charged medium. The aim is to identify the stresses
the Maxwell field exerts on the fluid and discuss their potential implications.
Particular attention is given to those stresses that resist contraction. After
looking at the general case, we consider the two opposite limits of poor and
high electrical conductivity. In the former there are electric fields but no
currents, while in the latter the situation is reversed. When the conductivity
is low, we find that the main agents acting against the collapse are the
Coulomb forces triggered by the presence of an excess charge. At the ideal
Magnetohydrodynamic (MHD) limit, on the other hand, the strongest resistance
seems to come from the tension of the magnetic forcelines. In either case, we
discuss whether and how the aforementioned resisting stresses may halt the
contraction and provide a set of conditions making this likely to happen. | 1010.4211v2 |
2010-12-30 | Pressure-Driven Quantum Criticality in An Iron-Selenide Superconductor | The discovery of superconductivity of about 30 K in iron selenides with very
large magnetic moments simulates the examination of completing orders. Here we
report a finding of pressure- induced suppression of the superconducting
transition temperature Tc and enhancement of the temperature of the resistance
hump TH through charge transfer between two iron sites with different
occupancies. The activation energy for the electric transport of the
high-temperature resistance is observed to go to zero at a critical pressure of
8.7 GPa, at which superconductivity tends to disappear and the
semiconductor-to-metal transition takes place. Beyond the critical point, the
resistance exhibits a metallic behavior over the whole temperature range
studied. All these features indicate the existence of quantum criticality in
iron-selenide superconductors. | 1101.0092v3 |
2011-02-22 | Charged Dilatonic Black Holes and their Transport Properties | We briefly explain the consistency conditions imposed on the effective
holographic theories, which are parameterized by two real exponents
$(\gamma,\delta)$ that control the IR dynamics. The general scaling of DC
resistivity with temperature at low temperature and AC conductivity at low
frequency across the whole $(\gamma,\delta)$ plane are explained. There is a
codimension-one region where the DC resistivity is linear in the temperature.
For massive carriers, it is shown that when the scalar operator is not the
dilaton, the DC resistivity scales as the heat capacity (and entropy) for
$(2+1)$-dimensional systems. Regions are identified where the theory at finite
density is a Mott-like insulator. This contribution is based on arXiv:1005.4690
with emphasis on the transport properties of charged dilatonic black holes with
potential. | 1102.4440v1 |
2011-03-24 | Collective excitations and low temperature transport properties of bismuth | We examine the influence of collective excitations on the transport
properties (resistivity, magneto- optical conductivity) for semimetals,
focusing on the case of bismuth. We show, using an RPA approximation, that the
properties of the system are drastically affected by the presence of an
acoustic plasmon mode, consequence of the presence of two types of carriers
(electrons and holes) in this system. We found a crossover temperature T*
separating two different regimes of transport. At high temperatures T > T* we
show that Baber scattering explains quantitatively the DC resistivity
experiments, while at low temperatures T < T* interactions of the carriers with
this collective mode lead to a T^5 behavior of the resistivity. We examine
other consequences of the presence of this mode, and in particular predict a
two plasmon edge feature in the magneto-optical conductivity. We compare our
results with the experimental findings on bismuth. We discuss the limitations
and extensions of our results beyond the RPA approximation, and examine the
case of other semimetals such as graphite or 1T-TiSe_2. | 1103.4850v1 |
2011-03-29 | Substrate Gating of Contact Resistance in Graphene Transistors | Metal contacts have been identified to be a key technological bottleneck for
the realization of viable graphene electronics. Recently, it was observed that
for structures that possess both a top and a bottom gate, the electron-hole
conductance asymmetry can be modulated by the bottom gate. In this letter, we
explain this observation by postulating the presence of an effective thin
interfacial dielectric layer between the metal contact and the underlying
graphene. Electrical results from quantum transport calculations accounting for
this modified electrostatics corroborate well with the experimentally measured
contact resistances. Our study indicates that the engineering of metal-
graphene interface is a crucial step towards reducing the contact resistance
for high performance graphene transistors. | 1103.5773v2 |
2011-05-28 | A New numerical scheme for resistive relativistic MHD using method of characteristics | We present a new numerical method of special relativistic resistive
magnetohydrodynamics with scalar resistivity that can treat a range of
phenomena, from nonrelativistic to relativistic (shock, contact discontinuity,
and Alfv\'en wave). The present scheme calculates the numerical flux of fluid
by using an approximate Riemann solver, and electromagnetic field by using the
method of characteristics. Since this scheme uses appropriate characteristic
velocities, it is capable of accurately solving problems that cannot be
approximated as ideal magnetohydrodynamics and whose characteristic velocity is
much lower than light velocity. The numerical results show that our scheme can
solve the above problems as well as nearly ideal MHD problems. Our new scheme
is particularly well suited to systems with initially weak magnetic field, and
mixed phenomena of relativistic and non-relativistic velocity; for example, MRI
in accretion disk, and super Alfv\'enic turbulence. | 1105.5683v1 |
2011-06-02 | High Lundquist Number Resistive MHD Simulations of Magnetic Reconnection: Searching for Secondary Island Formation | Recently, secondary island formation due to the tearing instability of the
Sweet-Parker current sheet was identified as a possible mechanism that can lead
to fast reconnection (less sensitive dependence on Lundquist number $S$) both
in numerical simulations using Particle-in-Cell (PIC) method [Daughton et al.
2009], as well as using resistive magnetohydrodynamics (MHD) [Lapenta 2008;
Bhattacharjee et al. 2009]. This instability is thought to appear when $S$ is
greater than a certain threshold. These recent results prompt us to perform
more resistive MHD simulations of a basic reconnection configuration based on
the island coalescence instability, using much higher resolutions and larger
$S$. Our simulations are based on a fairly standard pseudo spectral code, which
has been tested for accuracy, convergence, and compared well with codes using
other methods [Ng et al. 2008]. In our simulations, formation of plasmoids were
not found, except when insufficient resolution was used, or when a small amount
of noise was added externally. The reconnection rate is found to follow the
Sweet-Parker scaling when no noise is added, but increases to a level
independent of $S$ with noise, when plasmoids form. Latest results with $S$ up
to $2 \times 10^5$ will be presented. | 1106.0521v1 |
2011-08-03 | Unusual Field-Insensitive Phase Transition and Kondo Behavior in SmTi$_2$Al$_{20}$ | Magnetization, electrical resistivity and specific heat measurements were
performed on high-quality single crystalline SmTi$_2$Al$_{20}$ (residual
resistivity ratio $\sim$ 40) grown by Al self-flux method. A Kondo-like $\log
T$ dependence in the resistivity is observed below 50 K. We discovered a
field-insensitive phase transition at $T_{x}$ = 6.5 K and a field-insensitive
heavy fermion behavior with the electronic specific heat coefficient $\gamma$ =
150 mJ/(K$^{2}$ mol). Specific heat analysis reveals that the ground state is a
$\Gamma_{8}$ quartet state and the Sm magnetic dipole moment $m_{{\rm Sm}}$
($\sim 0.5 \mu_{{\rm B}}$ at $T \simeq$ 0) orders below $T_{x}$ in spite of the
field-insensitive behavior. Possible reasons for the field insensitiveness will
be discussed. | 1108.0751v1 |
2011-08-15 | Current-Controlled Negative Differential Resistance due to Joule Heating in TiO2 | We show that Joule heating causes current-controlled negative differential
resistance (CC-NDR) in TiO2 by constructing an analytical model of the
voltage-current V(I) characteristic based on polaronic transport for Ohm's Law
and Newton's Law of Cooling, and fitting this model to experimental data. This
threshold switching is the 'soft breakdown' observed during electroforming of
TiO2 and other transition-metal-oxide based memristors, as well as a precursor
to 'ON' or 'SET' switching of unipolar memristors from their high to their low
resistance states. The shape of the V(I) curve is a sensitive indicator of the
nature of the polaronic conduction. | 1108.3120v1 |
2011-08-25 | Generalized four-point characterization method for resistive and capacitive contacts | In this paper, a four-point characterization method is developed for
resistive samples connected to either resistive or capacitive contacts.
Provided the circuit equivalent of the complete measurement system is known
including coaxial cable and connector capacitances as well as source output and
amplifier input impedances, a frequency range and capacitive scaling factor can
be determined, whereby four-point characterization can be performed. The
technique is demonstrated with a discrete element test sample over a wide
frequency range using lock-in measurement techniques from 1 Hz - 100 kHz. The
data fit well with a circuit simulation of the entire measurement system. A
high impedance preamplifier input stage gives best results, since lock-in input
impedances may differ from manufacturer specifications. The analysis presented
here establishes the utility of capacitive contacts for four-point
characterizations at low frequency. | 1108.5006v1 |
2011-09-09 | Details of Sample Dependence and Transport Properties of URu2Si2 | Resistivity and specific heat measurements were performed in the low carrier
unconventional superconductor URu2Si2 on various samples with very different
qualities. The superconducting transition temperature (TSC) and the hidden
order transition temperature (THO) of these crystals were evaluated as a
function of the residual resistivity ratio (RRR). In high quality single
crystals the resistivity does not seem to follow a T2 dependence above TSC,
indicating that the Fermi liquid regime is restricted to low temperatures.
However, an analysis of the isothermal longitudinal magnetoresistivity points
out that the T2 dependence may be "spoiled" by residual inhomogeneous
superconducting contribution. We discuss a possible scenario concerning the
distribution of TSC related with the fact that the hidden order phase is very
sensitive to the pressure inhomogeneity. | 1109.1953v1 |
2011-11-15 | Phenomenology of retained refractoriness: On semi-memristive discrete media | We study two-dimensional cellular automata, each cell takes three states:
resting, excited and refractory. A resting cell excites if number of excited
neighbours lies in a certain interval (excitation interval). An excited cell
become refractory independently on states of its neighbours. A refractory cell
returns to a resting state only if the number of excited neighbours belong to
recovery interval. The model is an excitable cellular automaton abstraction of
a spatially extended semi-memristive medium where a cell's resting state
symbolises low-resistance and refractory state high-resistance. The medium is
semi-memristive because only transition from high- to low-resistance is
controlled by density of local excitation. We present phenomenological
classification of the automata behaviour for all possible excitation intervals
and recovery intervals. We describe eleven classes of cellular automata with
retained refractoriness based on criteria of space-filling ratio, morphological
and generative diversity, and types of travelling localisations. | 1111.3525v1 |
2011-12-06 | Homogeneous bilayer graphene film based flexible transparent conductor | Graphene is considered a promising candidate to replace conventional
transparent conductors due to its low opacity, high carrier mobility and
flexible structure. Multi-layer graphene or stacked single layer graphenes have
been investigated in the past but both have their drawbacks. The uniformity of
multi-layer graphene is still questionable, and single layer graphene stacks
require many transfer processes to achieve sufficiently low sheet resistance.
In this work, bilayer graphene film grown with low pressure chemical vapor
deposition was used as a transparent conductor for the first time. The
technique was demonstrated to be highly efficient in fabricating a conductive
and uniform transparent conductor compared to multi-layer or single layer
graphene. Four transfers of bilayer graphene yielded a transparent conducting
film with a sheet resistance of 180 {\Omega}_{\square} at a transmittance of
83%. In addition, bilayer graphene films transferred onto plastic substrate
showed remarkable robustness against bending, with sheet resistance change less
than 15% at 2.14% strain, a 20-fold improvement over commercial indium oxide
films. | 1112.1378v1 |
2012-04-12 | Nonequilibrium quasiparticles and electron cooling by normal metal - superconductor tunnel junctions | We consider a model NISIN system with two junctions in series, where N is a
normal metal, S is a superconductor and I is an insulator. We assume that the
resistance of the first junction is high, while the resistance of the second
one is low. In this case the first junction cools the left normal electrode,
while the second junction partially removes excited quasiparticles from the
superconductor. We consider cooling properties of this double junction
structure. It is shown that the cooling power depends strongly on the ratio of
the resistances of the two junctions. In conclusion, we derive a generalized
expression for the cooling power of a NIS tunnel junction taking into account
charge imbalance effects. | 1204.2719v1 |
2012-05-31 | High-pressure study of non-Fermi liquid and spin-glass-like behavior in CeRhSn | We present measurements of the temperature dependence of electrical
resistivity of CeRhSn up to ~ 27 kbar. At low temperatures, the electrical
resistivity varies linearly with temperature for all pressures, indicating
non-Fermi liquid behavior. Below a temperature Tf ~ 6 K, the electrical
resistivity deviates from a linear dependence. We found that the
low-temperature feature centered at T = Tf shows a pressure dependence dTf/dP ~
30 mK/kbar which is typical of canonical spin glasses. This interplay between
spin-glass-like and non-Fermi liquid behavior was observed in both CeRhSn and a
Ce0.9La0.1RhSn alloy. | 1205.6997v1 |
2012-07-13 | Effect of boron doping in the microwave surface resistance of neutron irradiated melt-textured Y_1.6Ba_2.3Cu_3.3O_7-x samples | We report on the microwave surface resistance of melt-textured
Y_1.6Ba_2.3Cu_3.3O_7-x samples, doped with different amount of B_2O_3 and,
subsequently, irradiated by thermal neutrons at the fluence of 1.476 \times
10^17 cm^-2. The microwave surface resistance has been measured as a function
of temperature and DC magnetic field. The experimental results are
quantitatively discussed in the framework of the Coffey and Clem theory,
properly adapted to take into account the d-wave nature of cuprate
superconductors. By fitting the experimental data at zero DC field, we have
highlighted the effects of the induced defects in the general properties of the
samples, including the intergranular region. The analysis of the results
obtained at high DC fields allowed us to investigate the fluxon dynamics and
deduce the depinning frequency; in particular, we have shown that the addition
of B_2O_3 up to 0.1 wt% increases the effectiveness of the defects to hinder
the fluxon motion induced by the microwave current. | 1207.3306v1 |
2012-08-31 | A Piggyback resistive Micromegas | A novel read-out architecture has been developed for the Micromegas detector.
The anode element is made of a resistive layer on a ceramic substrate. The
detector part is entirely separated from the read-out element. Without
significant loss, signals are transmitted by capacitive coupling to the
read-out pads. The detector provides high gas gain, good energy resolution and
the resistive layer assures spark protection to the electronics. This assembly
could be combined with modern pixel array electronic ASICs. This readout
organization is free on how the pixels are designed, arranged and connected. We
present first results taken with a MediPix read-out chip. | 1208.6525v2 |
2012-10-18 | Design and Simulation of Molecular Nonvolatile Single-Electron Resistive Switches | We have carried out a preliminary design and simulation of a single-electron
resistive switch based on a system of two linear, parallel,
electrostatically-coupled molecules: one implementing a single-electron
transistor and another serving as a single-electron trap. To verify our design,
we have performed a theoretical analysis of this "memristive" device, based on
a combination of ab-initio calculations of the electronic structures of the
molecules and the general theory of single-electron tunneling in systems with
discrete energy spectra. Our results show that such molecular assemblies, with
a length below 10 nm and a footprint area of about 5 nm$^2$, may combine
sub-second switching times with multi-year retention times and high ($> 10^3$)
ON/OFF current ratios, at room temperature. Moreover, Monte Carlo simulations
of self-assembled monolayers (SAM) based on such molecular assemblies have
shown that such monolayers may also be used as resistive switches, with
comparable characteristics and, in addition, be highly tolerant to defects and
stray offset charges. | 1210.5253v1 |
2012-12-11 | Anisotropic magnetization, resistivity and heat capacity of single crystalline R3Ni2-xSn7 (R = La, Ce, Pr and Nd) | We present a detailed study of R3Ni2-xSn7 (R = La, Ce, Pr and Nd) single
crystals by measurements of crystal structure, stoichiometry, temperature
dependent magnetic susceptibility, magnetization, electrical resistivity,
magnetoresistance, and specific heat. This series forms with partial Ni
occupancy with x varying from ~ 0.1 for R = La to ~0.7 for R = Nd. The
electrical resistivity of this series follows metallic behavior at high
temperatures. Determination of clear anisotropies as well as antiferromagnetic
ordering temperatures for R3Ni2-xSn7 (R = Ce, Pr and Nd) have been made. For
Pr3Ni1.56Sn7 and Nd3Ni1.34Sn7, multiple magnetic transitions take place upon
cooling. Metamagnetic transitions in this family (R = Ce, Pr and Nd) were
detected for applied magnetic fields below 70 kOe. An H-T phase diagram of
Ce3Ni1.69Sn7 was assembled to shed light on its low field properties and to
rule out possible quantum critical effects. | 1212.2542v1 |
2013-01-21 | Transparent conducting silver nanowire networks | We present a transparent conducting electrode composed of a periodic
two-dimensional network of silver nanowires. Networks of Ag nanowires are made
with wire diameters of 45-110 nm and pitch of 500, 700 and 1000 nm. Anomalous
optical transmission is observed, with an averaged transmission up to 91% for
the best transmitting network and sheet resistances as low as 6.5 {\Omega}/sq
for the best conducting network. Our most dilute networks show lower sheet
resistance and higher optical transmittance than an 80 nm thick layer of ITO
sputtered on glass. By comparing measurements and simulations we identify four
distinct physical phenomena that govern the transmission of light through the
networks: all related to the excitation of localized surface plasmons and
surface plasmon polaritons on the wires. The insights given in this paper
provide the key guidelines for designing high-transmittance and low-resistance
nanowire electrodes for optoelectronic devices, including thin-film solar
cells. For these latter, we discuss the general design principles to use the
nanowire electrodes also as a light trapping scheme. | 1301.4834v1 |
2013-01-25 | The Role of the Equation of State in Resistive Relativistic Magnetohydrodynamics | We have investigated the role of the equation of state in resistive
relativistic magnetohydrodynamics using a newly developed resistive
relativistic magnetohydrodynamic code. A number of numerical tests in
one-dimension and multi-dimensions are carried out in order to check the
robustness and accuracy of the new code. The code passes all the tests in
situations involving both small and large uniform conductivities. Equations of
state which closely approximate the single-component perfect relativistic gas
are introduced. Results from selected numerical tests using different equations
of state are compared. The main conclusion is that the choice of the equation
of state as well as the value of the electric conductivity can result in
considerable dynamical differences in simulations involving shocks,
instabilities, and magnetic reconnection. | 1301.6052v1 |
2013-01-28 | On conditions of negativity of friction resistance for non-stationary modes of blood flow and possible mechanism of affecting of environmental factors on energy effectiveness of cardio-vascular system functioning | It is shown that initiated by action of molecular viscosity impulse flow,
directed usually from the moving fluid to limiting it solid surface, can, under
certain conditions, turn to zero and get negative values in the case of
non-stationary flow caused by alternating in time longitudinal (along the pipe
axis) pressure gradient. It is noted that this non-equilibrium mechanism of
negative friction resistance in the similar case of pulsating blood flow in the
blood vessels, in addition to the stable to turbulent disturbances swirled
blood flow structure providing, can also constitute hydro-mechanical basis of
the observed but not explained yet paradoxically high energy effectiveness of
the normal functioning of the cardio-vascular system (CVS). We consider
respective mechanism of affecting on the stability of the normal work of CVS by
environmental variable factors using shifting of hydro-dynamic mode with
negative resistance realization range boundaries and variation of linear
hydro-dynamic instability leading to the structurally stable swirled blood flow
organization. | 1301.6603v1 |
2013-02-18 | Resistive wall mode and neoclassical tearing mode coupling in rotating tokamak plasmas | A model system of equations has been derived to describe a toroidally
rotating tokamak plasma, unstable to Resistive Wall Modes (RWMs) and metastable
to Neoclassical Tearing Modes (NTMs), using a linear RWM model and a nonlinear
NTM model. If no wall is present, the NTM growth shows the typical
threshold/saturation island widths, whereas a linearly unstable kink mode grows
exponentially in this model plasma system. When a resistive wall is present,
the growth of the linearly unstable RWM is accelerated by an unstable island: a
form of coupled RWM-NTM mode. Crucially, this coupled system has no threshold
island width, giving the impression of a triggerless NTM, observed in high beta
tokamak discharges. Increasing plasma rotation at the island location can
mitigate its growth, decoupling the modes to yield a conventional RWM with no
threshold width. | 1302.4250v2 |
2013-03-21 | On-sample water content measurement for a complete local monitoring in triaxial testing of unsaturated soils | To provide a complete local monitoring of the state of an unsaturated soil
sample during triaxial testing, a local water content measurement device was
adapted to a triaxial device comprising the measurement of local displacements
(Hall effect transducers) and suction (High capacity transducer). Water content
was locally monitored by means of a resistivity probe. The water
content/resistivity calibration curves of an intact natural unsaturated loess
from Northern France extracted by block sampling at two depths (1 and 3.3 m)
were carefully determined, showing good accuracy and repeatability. The
validity of two models giving the resistivity of unsaturated soils with respect
to their water content was examined. | 1303.5348v1 |
2013-07-02 | Structure of Intratumor Heterogeneity: Is Cancer Hedging Its Bets? | Development of resistance limits transferability of most anticancer therapies
into curative treatment and understanding mechanisms beyond it remains a big
challenge. Many high resolution experimental observations show enormous
intratumor heterogeneity at molecular, genetic and cellular levels which is
made responsible for emerging resistance to therapy. Therefore, researchers
search techniques to influence development of intratumor heterogeneity, which
requires understanding its role within the context of integrative, logically
consistent, framework, such as evolutionary theory. Although it is agreed that
intratumor heterogeneity increases probability of the emergence of therapy
resistant clones, more instructive role of its structure in the process of
cancer dynamics and metastasis is needed. In the paper, intratumor
heterogeneity is viewed as a product of two, in general stochastic, processes,
evolutionary optimization and changing environment, respectively. In
evolutionary theory, common risk-diversifying strategy displayed by isogenic
populations in unpredictably changing environments is bet-hedging. We suggest,
that the structure of intratumor heterogeneity is evolutionary trait evolving
to maximize the clonal fitness in changing (or uncertain) environment and that
its structure corresponds to bet-hedging strategy. We advocate our view by
reviewing and combining important cancer relevant concepts. | 1307.0607v1 |
2013-07-25 | Memory Effect and Triplet Pairing Generation in the Superconducting Exchange Biased Co/CoOx/Cu41Ni59/Nb/Cu41Ni59 Layered Heterostructure | We fabricated a nanolayered hybrid superconductor-ferromagnet spin-valve
structure, the resistive state of which depends on the preceding magnetic field
polarity. The effect is based on a strong exchange bias (about -2 kOe) on a
diluted ferromagnetic copper-nickel alloy and generation of a long range odd in
frequency triplet pairing component. The difference of high and low resistance
states at zero magnetic field is 90% of the normal state resistance for a
transport current of 250 {\mu}A and still around 42% for 10 {\mu}A. Both logic
states of the structure do not require biasing fields or currents in the idle
mode. | 1307.6742v1 |
2013-08-28 | Tunneling at $ν_T=1$ in Quantum Hall Bilayers | Interlayer tunneling measurements in the strongly correlated bilayer
quantized Hall phase at $\nu_T=1$ are reported. The maximum, or critical
current for tunneling at $\nu_T=1$, is shown to be a well-defined global
property of the coherent phase, insensitive to extrinsic circuit effects and
the precise configuration used to measure it, but also exhibiting a surprising
scaling behavior with temperature. Comparisons between the experimentally
observed tunneling characteristics and a recent theory are favorable at high
temperatures, but not at low temperatures where the tunneling closely resembles
the dc Josephson effect. The zero-bias tunneling resistance becomes extremely
small at low temperatures, vastly less than that observed at zero magnetic
field, but nonetheless remains finite. The temperature dependence of this
tunneling resistance is similar to that of the ordinary in-plane resistivity of
the quantum Hall phase. | 1308.6269v2 |
2013-10-22 | The Effect of Toroidal Magnetic Field on Thickness of a Viscose-Resistive Hot Accreting Flow | By taking into account the effect of toroidal magnetic field and its
correspond heating, we determine the thickness of advection-dominated accretion
flows. We consider an axisymetric, rotating, steady viscous-resistive,
magnetized accretion flow under an advection dominated stage. The dominant
mechanism of energy dissipation is assumed to be turbulence viscosity and
magnetic diffusivity. We adopt a self-similar assumption in the radial
direction to obtain the dynamical quantities, that is, radial, azimuthal, sound
and Alfv\' en velocities. Our results show the vertical component of magnetic
force acts in the opposite direction of gravity and compresses the disc, thus
compared with the non-magnetic case, in general the disc half-thikness,
$\Delta\theta$, significantly is reduced. On the other hand, two parameters,
appearing due to action of magnetic field and reaction of the flow, affect the
disc thickness. The first one, $\beta_0$, showing the magnetic field strength
at the equatorial plane, decreases $\Delta\theta$. The other one, $\eta_0$ is
the magnetic resistivity parameter and when it increases, $\Delta\theta$
increases, too. | 1310.6317v1 |
2014-02-13 | Theory of measurements of d.c. and a.c. resistivity in anisotropic superconductors in tilted magnetic fields | The vortex dynamics of uniaxial anisotropic superconductors with arbitrary
angles between the magnetic field, the applied current and the anisotropy axis
is theoretically studied, by focusing on the models for electrical transport
experiments in the linear regime. The vortex parameters, such as the viscous
drag, the vortex mobility and the pinning constant (in the weak point pinning
regime), together with the vortex motion resistivity, are derived in tensor
form by considering the very different free flux flow and pinned Campbell
regimes. The results are extended to high frequency regimes where additional
effects like thermal depinning/creep take place. The applicability to the
various tensor quantities of the well-known scaling laws for the angular
dependence on the field orientation is commented, illustrating when and with
which cautions the scaling approach can be used to discriminate between
intrinsic and extrinsic effects. It is shown that the experiments do not
generally yield the intrinsic values of the vortex parameters and vortex
resistivities. Explicit expressions relating measured and intrinsic quantities
are given and their use exemplified in data analyses of angular measurements. | 1402.3164v1 |
2014-05-05 | Colossal negative magnetoresistance in a 2D electron gas | We report on a colossal negative magnetoresistance (MR) in GaAs/AlGaAs
quantum well which, at low temperatures, is manifested by a drop of the
resistivity by more than an order of magnitude at a magnetic field $B \approx
1$ kG. In contrast to MR effects discussed earlier, the MR reported here is not
parabolic, even at small $B$, and persists to much higher in-plane magnetic
fields and temperatures. Remarkably, the temperature dependence of the
resistivity at $B \approx 1$ kG is linear over the entire temperature range
studied (from 1 to 30 K) and appears to coincide with the high-temperature
limit of the zero-field resistivity, hinting on the important role of acoustic
phonons. | 1405.1090v1 |
2014-09-30 | Formation of magnetic moments and resistance upturn at grain boundaries of two-dimensional electron systems | Electronic correlations control the normal state of bulk high-Tc cuprates.
Strong correlations also suppress the charge transport through cuprate grain
boundaries (GBs). The question then arises if these correlations can produce
magnetic states at cuprate GBs. We analyze the formation of local magnetic
moments at the GB of a correlated two-dimensional electron systems which is
represented by an inhomogeneous Hubbard model. The model Hamiltonian is
diagonalized after the implementation of a mean-field decoupling. The formation
of local magnetic moments is supported by a sufficiently strong variance in the
bond kinetic energies at the GB. Local scattering potentials can assist or
suppress the formation of a magnetic GB state, depending on the details of
their spacial distribution. Grain boundary induced stripes are formed in the
vicinity the GB and decay into the bulk. Moreover, we observe the build-up of
conducting channels which are confined by magnetic clusters. The grain boundary
resistance increases at decreasing temperatures. This low-temperature behavior
is caused by the suppression of current correlations in the state with local
magnetic GB moments. The resistance upturn at low temperatures is in
qualitative agreement with experiments. | 1409.8559v1 |
2014-10-30 | Magnetoresistance of layered conductors under conditions of topological phase transition | The resistance of layered conductors with a multisheet Fermi surface (FS), in
a high magnetic field, in the immediate vicinity of Lifshic's topological
transition when the separate FS sheets are drown together by an external
action, pressure in part (and eventual change of the FS connectivity) is
studied theoretically. Analysis of magnetoresistance near topological
transition is illustrated for the case of FS in the shape of lightly corrugated
cylinder and two corrugated planes distributed with a repeated period in the
pulse space. It yields, that as the FS plane sheets approach sufficiently the
cylinder, the charge carriers produce a magnetic breakdown of one FS sheet to
another, decreasing a sharp anisotropy of magnetoresistance to the in-plane
current. Instead of square increase with a magnetic field, the slower
resistance growth remains linear in the field within a broad magnetic-field
range. In the intimate vicinity of topological transition, when the energy gap
between FS layers is negligibly small, the resistance is saturated. | 1410.8330v1 |
2014-11-10 | The Resistive-WELL detector: a compact spark-protected single amplification-stage MPGD | In this work we present a novel idea for a compact spark-protected single
amplification stage Micro-Pattern Gas Detector (MPGD). The detector
amplification stage, realized with a structure very similar to a GEM foil, is
embedded through a resistive layer in the readout board. A cathode electrode,
defining the gas conversion/drift gap, completes the detector mechanics. The
new structure, that we call Resistive-WELL (R-WELL), has some characteristics
in common with previous MPGDs, such as C.A.T. and WELL, developed more than ten
years ago. The prototype object of the present study has been realized in the
2009 by TE-MPE-EM Workshop at CERN. The new architecture is a very compact
MPGD, robust against discharges and exhibiting a large gain
($\sim$6$\times$10$^3$), simple to construct and easy for engineering and then
suitable for large area tracking devices as well as huge calorimetric apparata. | 1411.2466v1 |
2015-01-01 | Fast Generation of Random Spanning Trees and the Effective Resistance Metric | We present a new algorithm for generating a uniformly random spanning tree in
an undirected graph. Our algorithm samples such a tree in expected
$\tilde{O}(m^{4/3})$ time. This improves over the best previously known bound
of $\min(\tilde{O}(m\sqrt{n}),O(n^{\omega}))$ -- that follows from the work of
Kelner and M\k{a}dry [FOCS'09] and of Colbourn et al. [J. Algorithms'96] --
whenever the input graph is sufficiently sparse.
At a high level, our result stems from carefully exploiting the interplay of
random spanning trees, random walks, and the notion of effective resistance, as
well as from devising a way to algorithmically relate these concepts to the
combinatorial structure of the graph. This involves, in particular,
establishing a new connection between the effective resistance metric and the
cut structure of the underlying graph. | 1501.00267v1 |
2015-03-16 | On Resistive Networks of Constant Power Devices | This brief examines the behavior of DC circuits comprised of resistively
interconnected constant power devices, as may arise in DC microgrids containing
micro-sources and constant power loads. We derive a sufficient condition for
all operating points of the circuit to lie in a desirable set, where the
average nodal voltage level is high and nodal voltages are tightly clustered
near one another. Our condition has the elegant physical interpretation that
the ratio of resistive losses to total injected power should be small compared
to a measure of network heterogeneity, as quantified by a ratio of conductance
matrix eigenvalues. Perhaps surprisingly, the interplay between the circuit
topology, branch conductances and the constant power devices implicitly defines
a nominal voltage level for the circuit, despite the explicit absence of
voltage-regulated nodes. | 1503.04769v1 |
2015-08-04 | Electron Viscosity, Current Vortices and Negative Nonlocal Resistance in Graphene | Quantum-critical states of diverse strongly correlated systems are predicted
to feature universal collision-dominated transport resembling that of viscous
fluids. However, investigation of these phenomena has been hampered by the lack
of known macroscopic signatures of the hydrodynamic regime at criticality. Here
we identify vorticity as such a signature and link it with an easily verifiable
striking macroscopic transport behavior. Produced by the viscous flow,
vorticity can drive electric current against an applied field, resulting in a
negative nonlocal voltage. We argue that the latter may play the same role for
the viscous regime as zero electrical resistance does for superconductivity.
Besides offering a diagnostic of viscous transport which distinguishes it from
ohmic currents, the sign-changing electrical response affords a robust tool for
directly measuring the viscosity-to-resistivity ratio. The strongly interacting
electron-hole plasma in high-mobility graphene provides a bridge between
quantum-criticality and the wealth of fluid mechanics phenomena. | 1508.00836v2 |
2015-10-13 | Charge order and suppression of superconductivity in HgBa2CuO4 at high pressures | New insight into the superconducting properties of HgBa2CuO4 (Hg-1201)
cuprates is provided by combined measurements of the electrical resistivity and
single crystal X-ray diffraction under pressure. The changes induced by
increasing pressure up to 20GPa in optimally doped single crystals were
investigated. The resistivity measurements as a function of temperature show a
metallic behavior up to ~10GPa that gradually passes to an insulating state,
typical of charge ordering, that totally suppresses superconductivity above
13GPa. The changes in resistivity are accompanied by the apparition of sharp
Bragg peaks in the X-ray diffraction patterns indicating that the charge
ordering is accompanied by a 3D oxygen ordering appearing at 10GPa of
wavevector [0.25, 0, L]. As pressure induces a charge transfer of about 0.02 at
10GPa, our results are the first observation of charge order competing with
superconductivity that develops in the over-doped region of the phase diagram
of a cuprate. | 1510.03750v1 |
2015-11-15 | Synchronization of two memristive coupled van der Pol oscillators | The objective of this paper is to explore the possibility to couple two van
der Pol (vdP) oscillators via a resistance-capacitance (RC) network comprising
a Ag-TiOx-Al memristive device. The coupling was mediated by connecting the
gate terminals of two programmable unijunction transistors (PUTs) through the
network. In the high resistance state (HRS) the memresistance was in the order
of MOhm leading to two independent selfsustained oscillators characterized by
the different frequencies f1 and f2 and no phase relation between the
oscillations. After a few cycles and in dependency of the mediated pulse
amplitude the memristive device switched to the low resistance state (LRS) and
a frequency adaptation and phase locking was observed. The experimental results
are underlined by theoretically considering a system of two coupled vdP
equations. The presented neuromorphic circuitry conveys two essentials
principle of interacting neuronal ensembles: synchronization and memory. The
experiment may path the way to larger neuromorphic networks in which the
coupling parameters can vary in time and strength and are realized by
memristive devices. | 1511.06363v1 |
2015-12-07 | Universality of DC Electrical Conductivity from Holography | We propose a universal formula of dc electrical conductivity in rotational-
and translational- symmetries breaking systems via the holographic duality.
This formula states that the ratio of the determinant of the dc electrical
conductivities along any spatial directions to the black hole area density in
zero-charge limit has a universal value. As explicit illustrations, we give
several examples elucidating the validation of this formula: We construct an
anisotropic black brane solution, which yields linear in temperature for the
in-plane resistivity and insulating behavior for the out-of-plane resistivity;
We also construct a spatially isotropic black brane solution that both the
linear-T and quadratic-T contributions to the resistivity can be realized. | 1512.01917v3 |
2016-01-26 | Observation of An Anisotropic Wigner Crystal | We report a new correlated phase of two-dimensional charged carriers in high
magnetic fields, manifested by an anisotropic insulating behavior at low
temperatures. It appears near Landau level filling factor $\nu=1/2$ in hole
systems confined to wide GaAs quantum wells when the sample is tilted in
magnetic field to an intermediate angle. The parallel field component
($B_{||}$) leads to a crossing of the lowest two Landau levels, and an
elongated hole wavefunction in the direction of $B_{||}$. Under these
conditions, the in-plane resistance exhibits an insulating behavior, with the
resistance along $B_{||}$ more than 10 times smaller than the resistance
perpendicular to $B_{||}$. We interpret this anisotropic insulating phase as a
two-component, striped Wigner crystal. | 1601.07135v1 |
2016-02-05 | Investigating Reliability Aspects of Memristor based RRAM with Reference to Write Voltage and Frequency | In this paper, we report the effect of write voltage and frequency on
memristor based Resistive Random Access Memory (RRAM). The above said
parameters have been investigated on the linear drift model of memristor. With
a variation of write voltage from 0.2V to 1.2V and a subsequent frequency
modulation from 1, 2, 4, 10, 100 and 200 Hz the corresponding effects on memory
window, Low Resistance State (LRS) and High Resistance State (HRS) have been
reported. Thus the lifetime ({\tau}) reliability analysis of memristor based
RRAM is carried out using above results. It is found that, the HRS is
independent of write voltage, whereas LRS shows dependency on write voltage and
frequency. The simulation results showcase that the memristor possess higher
memory window and lifetime ({\tau}) in the higher voltage with lower frequency
region, which has been attributed to the fewer data losses in the memory
architecture. | 1602.01947v1 |
2016-06-23 | Device and Circuit Interaction Analysis of Stochastic Behaviors in Cross-Point RRAM Arrays | Stochastic behaviors of resistive random access memory (RRAM) play an
important role in the design of cross-point memory arrays. A Monte Carlo
compact model of oxide RRAM is developed and calibrated with experiments on
various device stack configurations. With Monte Carlo SPICE simulations, we
show that an increase in array size and interconnect wire resistance will
statistically deteriorate write functionality. Write failure probability (WFP)
has an exponential dependency on device uniformity and supply voltage (VDD),
and the array bias scheme is a key knob. Lowering array VDD leads to higher
effective energy consumption (EEC) due to the increase in WFP when the
variation statistics are included in the analysis. Random-access simulations
indicate that data sparsity statistically benefits write functionality and
energy consumption. Finally, we show that a pseudo-sub-array topology with
uniformly distributed pre-forming cells in the pristine high resistance state
is able to reduce both WFP and EEC, enabling higher net capacity for memory
circuits due to improved variation tolerance. | 1606.07457v3 |
2016-07-05 | The Importance of the Electron Mean Free Path for Superconducting RF Cavities | Impurity-doping is an exciting new technology in the field of SRF, producing
cavities with record-high quality factor $Q_0$ and BCS surface resistance that
decreases with increasing RF field. Recent theoretical work has offered a
promising explanation for this anti-Q-slope, but the link between the
decreasing surface resistance and the short mean free path of doped cavities
has remained elusive. In this work we investigate this link, finding that the
magnitude of this decrease varies directly with the mean free path: shorter
mean free paths correspond with stronger anti-Q-slopes. We draw a theoretical
connection between the mean free path and the overheating of the
quasiparticles, which leads to the reduction of the anti-Q-slope towards the
normal Q-slope of long-mean-free-path cavities. We also investigate the
sensitivity of the residual resistance to trapped magnetic flux, a property
which is greatly enhanced for doped cavities, and calculate an optimal doping
regime for a given amount of trapped flux. | 1607.01411v2 |
2016-08-01 | Graphene-based, mid-infrared, room-temperature pyroelectric bolometers with ultrahigh temperature coefficient of resistance | Graphene is ideally suited for photonic and optoelectronic applications, with
a variety of photodetectors (PDs) in the visible, near-infrared (NIR), and THz
reported to date, as well as thermal detectors in the mid-infrared (MIR). Here,
we present a room temperature-MIR-PD where the pyroelectric response of a
LiNbO3 crystal is transduced with high gain (up to 200) into resistivity
modulation for graphene, leading to a temperature coefficient of resistance up
to 900%/K, two orders of magnitude higher than the state of the art, for a
device area of 300x300um2. This is achieved by fabricating a floating metallic
structure that concentrates the charge generated by the pyroelectric substrate
on the top-gate capacitor of the graphene channel. This allows us to resolve
temperature variations down to 15umK at 1 Hz, paving the way for a new
generation of detectors for MIR imaging and spectroscopy | 1608.00569v1 |
2016-08-07 | Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe$_4$ | Systematic measurements of temperature dependent magnetization, resistivity
and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as
well as resistivity under pressures up to 5.25 GPa were conducted on single
crystals of CrAuTe$_4$. Magnetization data suggest that magnetic moments are
aligned antiferromagnetically along the crystallographic $c$-axis below
$T_\textrm{N}$ = 255 K. ARPES measurements show band reconstruction due to the
magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high
fields, quantum oscillations. The Neel temperature decreases monotonically
under pressure, decreasing to $T_\textrm{N}$ = 236 K at 5.22 GPa. The pressure
dependencies of (i) $T_\textrm{N}$, (ii) the residual resistivity ratio, and
(iii) the size and power-law behavior of the low temperature magnetoresistance
all show anomalies near 2 GPa suggesting that there may be a phase transition
(structural, magnetic, and/or electronic) induced by pressure. For pressures
higher than 2 GPa a significantly different quantum oscillation frequency
emerges, consistent with a pressure induced change in the electronic states. | 1608.02213v2 |
2016-08-11 | Anisotropic and strong negative magneto-resistance in the three-dimensional topological insulator Bi2Se3 | We report on high-field angle-dependent magneto-transport measurements on
epitaxial thin films of Bi2Se3, a three-dimensional topological insulator. At
low temperature, we observe quantum oscillations that demonstrate the
simultaneous presence of bulk and surface carriers. The magneto- resistance of
Bi2Se3 is found to be highly anisotropic. In the presence of a parallel
electric and magnetic field, we observe a strong negative longitudinal
magneto-resistance that has been consid- ered as a smoking-gun for the presence
of chiral fermions in a certain class of semi-metals due to the so-called axial
anomaly. Its observation in a three-dimensional topological insulator implies
that the axial anomaly may be in fact a far more generic phenomenon than
originally thought. | 1608.03615v1 |
2016-08-15 | Effect of electrical properties of glass electrodes on the performance of RPC detectors for the INO-ICAL experiment | The India-based Neutrino Observatory (INO) collaboration has chosen glass
Resistive Plate Chambers (RPCs) as the active detector elements for the Iron
Calorimeter (ICAL) experiment. In the present work, we study the electrical
properties such as bulk resistivity and relative permittivity of the glasses
from two different manufacturers and compared the performances of RPCs built
using these glasses. We conclude that the glass electrodes with larger bulk
resistivy and permittivity are better suited for manufacturing RPCs for the
ICAL experiment, as these detectors could be operated at lower bias currents
and voltages, and produce better time resolutions compared to those built with
glass electrodes of smaller bulk resistivity and permittivity. | 1608.04230v1 |
2016-12-02 | Random walk hitting times and effective resistance in sparsely connected Erdős-Rényi random graphs | We prove expectation and concentration results for the following random
variables on an Erd\H{o}s-R\'enyi random graph $\mathcal{G}\left(n,p\right)$ in
the sparsely connected regime $\log n + \log\log \log n \leq np < n^{1/10}$:
effective resistances, random walk hitting and commute times, the Kirchoff
index, cover cost, random target times, the mean hitting time and Kemeny's
constant. For the effective resistance between two vertices our concentration
result extends further to $np\geq c\log n, \; c>0$. To achieve these results,
we show that a strong connectedness property holds with high probability for
$\mathcal{G}(n,p)$ in this regime. | 1612.00731v2 |
2016-12-26 | Analysis of claims that the brain extracellular impedance is high and non-resistive | Numerous measurements in the brain of the impedance between two extracellular
electrodes have shown that it is approximately resistive in the range of
biological interest, $<10\,$kHz, and has a value close to that expected from
the conductivity of physiological saline and the extracellular volume fraction
in brain tissue. Recent work from the group of Claude B\'edard and Alain
Destexhe has claimed that the impedance of the extracellular space is some
three orders of magnitude greater than these values and also displays a
$1/\sqrt{f}$ frequency dependence (above a low-frequency corner frequency).
Their measurements were performed between an intracellular electrode and an
extracellular electrode. It is argued that they incorrectly extracted the
extracellular impedance because of an inaccurate representation of the large,
confounding impedance of the neuronal membrane. In conclusion, no compelling
evidence has been provided to undermine the well established and physically
plausible consensus that the brain extracellular impedance is low and
approximately resistive | 1612.08457v5 |
2017-02-02 | Influence of thermal boundary conditions on the current-driven resistive transition in $\mathbf{VO_2}$ microbridges | We investigate the resistive switching behaviour of $\mathrm{VO_2}$
microbridges under current bias as a function of temperature and thermal
coupling with the heat bath. Upon increasing the electrical current bias, the
formation of the metallic phase can progress smoothly or through sharp jumps.
The magnitude and threshold current values of these sharp resistance drops show
random behaviour and are dramatically influenced by thermal dissipation
conditions. Our results also evidence how the propagation of the metallic phase
induced by electrical current in $\mathrm{VO_2}$, and thus the shape of the
resulting high-conductivity path, are not predictable. We discuss the origin of
the switching events through a simple electro-thermal model based on the domain
structure of $\mathrm{VO_2}$ films that can be useful to improve the stability
and controllability of future $\mathrm{VO_2}$-based devices. | 1702.00805v1 |
2017-06-05 | Enhancement of superconductivity in NbN nanowires by negative electron-beam lithography with positive resist | We performed comparative experimental investigation of superconducting NbN
nanowires which were prepared by means of positive-and negative electron-beam
lithography with the same positive tone Poly-methyl-methacrylate (PMMA) resist.
We show that nanowires with a thickness 4.9 nm and widths less than 100 nm
demonstrate at 4.2 K higher critical temperature and higher density of critical
and retrapping currents when they are prepared by negative lithography. Also
the ratio of the experimental critical-current to the depairing critical
current is larger for nanowires prepared by negative lithography. We associate
the observed enhancement of superconducting properties with the difference in
the degree of damage that nanowire edges sustain in the lithographic process. A
whole range of advantages which is offered by the negative lithography with
positive PMMA resist ensures high potential of this technology for improving
performance metrics of superconducting nanowire singe-photon detectors. | 1706.01289v2 |
2017-09-26 | Timing and Charge measurement of single gap Resistive Plate Chamber Detectors for INO-ICAL Experiment | The recently approved India-based Neutrino Observatory will use the world's
largest magnet to study atmospheric muon neutrinos. The 50 kiloton Iron
Calorimeter consists of iron alternating with single-gap resistive plate
chambers. A uniform magnetic field of $\sim$1.5 T is produced in the iron using
toroidal-shaped copper coils. Muon neutrinos interact with the iron target to
produce charged muons, which are detected by the resistive plate chambers, and
tracked using orthogonal pick up strips. Timing information for each layer is
used to discriminate between upward and downward traveling muons. The design of
the readout electronics for the detector depends critically on an accurate
model of the charge induced by the muons, and the dependence on bias voltages.
In this paper, we present timing and charge response measurements using
prototype detectors under different operating conditions. We also report the
effect of varying gas mixture, particularly $SF_6$, on the timing response. | 1709.08946v1 |
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