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2023-11-14 | Observation of high-temperature superconductivity in the high-pressure tetragonal phase of La2PrNi2O7-δ | The recent discovery of high-temperature superconductivity in the
Ruddlesden-Popper phase La3Ni2O7 under high pressure marks a significant
breakthrough in the field of 3d transition-metal oxide superconductors. For an
emerging novel class of high-Tc superconductors, it is crucial to find more
analogous superconducting materials with a dedicated effort toward broadening
the scope of nickelate superconductors. Here, we report on the observation of
high-Tc superconductivity in the high-pressure tetragonal I4/mmm phase of
La2PrNi2O7 above ~10 GPa, which is distinct from the reported orthorhombic Fmmm
phase of La3Ni2O7 above 14 GPa. For La2PrNi2O7, the onset and the
zero-resistance temperatures of superconductivity reach Tconset = 78.2 K and
Tczero = 40 K at 15 GPa. This superconducting phase shares the samilar
structural symmetry as many cuprate superconductors, providing a fresh platform
to investigate underlying mechanisms of nickelate superconductors. | 2311.08212v2 |
1999-01-11 | SQUID based resistance bridge for shot noise measurement on low impedance samples | We present a resistance bridge which uses a SQUID to measure the shot noise
in low impedance samples. The experimental requirements are high DC bias
currents (typically 10mA) together with high AC sensitivity (pA/VHz). This
system is used to investigate the shot noise in
Superconductor/Normal/Superconductor junctions where Andreev reflection
enhanced shot noise is expected. Because our setup has an intrinsic noise much
smaller than the thermal noise of the resistance bridge at 4.2K, reliable
results can be obtained on impedances out of the range of classical measurement
schemes. | 9901090v2 |
1999-05-12 | Nonmonotonic Temperature-dependent Resistance in Low Density 2D Hole Gases | The low temperature longitudinal resistance-per-square Rxx(T) in ungated
GaAs/AlGaAs quantum wells of high peak hole mobility 1.7x10^6 cm^2/Vs is
metallic for 2D hole density p as low as 3.8x10^9 cm-2. The electronic
contribution to the resistance, R_{el}(T), is a nonmonotonic function of T,
exhibiting thermal activation, R_{el}(T) ~ exp{-E_a/kT}, for kT<<E_F and a
heretofore unnoted decay R_{el}(T) ~ 1/T for k_T>EF. The form of R_{el}(T) is
independent of density, indicating a fundamental relationship between the low
and high T scattering mechanisms in the metallic state. | 9905176v1 |
2005-07-28 | Phononless thermally activated transport through a disordered array of quantum wires | Phononless plasmon assisted transport through a long disordered array of
finite length quantum wires is investigated analytically. Two temperature
regimes, the low- and the high-temperature ones, with qualitatively different
temperature dependencies of thermally activated resistance are identified. The
characteristics of plasmon assisted and phonon assisted transport mechanisms
are compared. Generically strong electron-electron interaction in quantum wires
results in a qualitative change of the temperature dependence of thermally
activated resistance in comparison to phonon assisted transport. At high
temperatures, the thermally activated resistance is determined by the Luttinger
liquid interaction parameter of the wires. | 0507687v1 |
2007-02-22 | High-field Hall resistivity and magnetoresistance in electron-doped Pr_2-xCe_xCuO_{4-δ} | We report resistivity and Hall effect measurements in electron-doped
Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ films in magnetic field up to 58 T. In
contrast to hole-doped cuprates, we find a surprising non-linear magnetic field
dependence of Hall resistivity at high field in the optimally doped and
overdoped films. We also observe a crossover from quadratic to linear field
dependence of the positive magnetoresistance in the overdoped films. A spin
density wave induced Fermi surface reconstruction model can be used to
qualitatively explain both the Hall effect and magnetoresistance. | 0702534v2 |
2007-01-13 | First Tests of Thick GEMs with Electrodes Made of a Resistive Kapton | We have developed a new design of a GEM-like detector with single-layer
electrodes made of a resistive kapton. This detector can operate at gains close
to 10E5 even in pure Ar and Ne and if transited to discharges at higher gains
they, due to the high resistivity of electrodes, do not damage either the
detector or the front-end electronics. Gains ~ 106 can be achieved in a
cascaded mode of the operation. The detector can operate without gain
degradation at counting rates up to 10E4Hz/cm2 and thus it could be very useful
in many applications which require safe high gain operation, for example in
RICH, TPCs, calorimetric. | 0701154v1 |
1995-07-03 | Percolation transition of the vortex lattice and c-axis resistivity in high-temperature superconductors | We use the three-dimensional Josephson junction array system as a model for
studying the temperature dependence of the c-axis resistivity of high
temperature superconductors, in the presence of an external magnetic field H
applied in the c-direction. We show that the temperature at which the
dissipation becomes different from zero corresponds to a percolation transition
of the vortex lattice. In addition, the qualitative features of the resistivity
vs. temperature curves close to the transition are obtained starting from the
geometrical configurations of the vortices. The results apply to the cases H
greater than 0 and H=0. | 9507001v1 |
2007-06-21 | Addendum: "On the nature of the phase transition in the itinerant helimagnet MnSi", arXiv:cond-mat/0702460v1 [cond-mat.str-el] | New high resolution data for heat capacity, heat capacity under applied
magnetic fields and resistivity of high quality single crystal of MnSi are
reported. Striking mirror symmetry between temperature derivative of
resistivity and thermal expansion coefficient of MnSi is displayed. Close
similarity between variation of the heat capacity and the temperature
derivative of resistivity through the phase transition is observed. It is shown
that the heat capacity and thermal expansion coefficient of the helical phase
are not influenced by moderate magnetic field. | 0706.3093v1 |
2009-02-24 | Phonon-induced Resistance Oscillations in Very-high Mobility 2D Electron Systems | We report on temperature dependence of acoustic phonon-induced resistance
oscillations in very high mobility two-dimensional electron systems. We observe
that the temperature dependence is non-monotonic and that higher order
oscillations are best developed at progressively lower temperatures. Our
analysis shows that, in contrast to Shubnikov-de Haas effect, phonon-induced
resistance oscillations are sensitive to electron-electron interactions
modifying the single particle lifetime. | 0902.4208v1 |
2009-09-11 | Resistive g-modes in a reversed field pinch plasma | First direct experimental evidence of high frequency, high toroidal mode
number (n>20), magnetic fluctuations due to unstable resistive interchange
modes (g-modes) resonant in the edge region of a reversed field pinch (RFP)
plasma is presented. Experimental characterization of time and space
periodicities of the modes is provided by means of highly resolved in-vessel
edge and insertable magnetic diagnostics. It is found that the spectral mode
properties are in good agreement with the predictions of the theoretical linear
resistive magnetohydrodynamic stability analysis. A simple model is proposed
for the observed saturation levels of the modes. | 0909.2153v1 |
2010-07-16 | Zero differential resistance in two-dimensional electron systems at large filling factors | We report on a state characterized by a zero differential resistance observed
in very high Landau levels of a high-mobility two-dimensional electron system.
Emerging from a minimum of Hall field-induced resistance oscillations at low
temperatures, this state exists over a continuous range of magnetic fields
extending well below the onset of the Shubnikov-de Haas effect. The minimum
current required to support this state is largely independent on the magnetic
field, while the maximum current increases with the magnetic field tracing the
onset of inter-Landau level scattering. | 1007.2832v1 |
2013-10-09 | Effect of Temperature and Charged Particle Fluence on the Resistivity of Polycrystalline CVD Diamond Sensors | The resistivity of polycrystalline chemical vapor deposition diamond sensors
is studied in samples exposed to fluences relevant to the environment of the
High Luminosity Large Hadron Collider. We measure the leakage current for a
range of bias voltages on samples irradiated with 800 MeV protons up to
1.6\times 10^{16} p/cm^2. The proton beam at LANSCE, Los Alamos National
Laboratory, was applied to irradiate the samples. The devices' resistivity is
extracted for temperatures in the -10^\circC to +20^\circC range. | 1310.2620v1 |
2016-07-04 | Vortex motion and flux-flow resistivity in dirty multiband superconductors | The conductivity of vortex lattices in multiband superconductors with high
concentration of impurities is calculated based on microscopic kinetic theory.
Both the limits of high and low fields are considered, when the magnetic
induction is close to or much smaller than the critical field strength
$H_{c2}$, respectively. It is shown that in contrast to single-band
superconductors the resistive properties are not universal but depend on the
pairing constants and ratios of diffusivities in different bands. The low-field
magneto-resistance can strongly exceed Bardeen-Stephen estimation in a
quantitative agreement with experimental data for two-band superconductor
MgB$_2$. | 1607.00708v2 |
2023-02-27 | Ferromagnetism and Metal-Insulator transition in F-doped LaMnO3 | We present our studies on polycrystalline samples of fluorine doped LaMnO3
(LaMnO3-yFy). LaMnO2.5F0.5 exhibits remarkable magnetic and electrical
properties. It shows ferromagnetic and metallic behavior with a high Curie
temperature of ~ 239 K and a high magnetoresistance of -64. This drastic change
in magnetic properties in comparison to pure LaMnO3 is ascribed to the presence
of mixed-valence Mn ions driven by the F-doping at the O-sites, which enables
double exchange (DE) in LMOF. Furthermore, the resistivity data exhibits two
resistivity peaks at 239 K and 213 K, respectively. Our results point towards
the possibility of multiple double exchange hopping paths of two distinct
resistances existing simultaneously in the sample below 213 K. | 2302.13845v1 |
2009-07-25 | Superconductivity in Undoped Single Crystals of BaFe2As2: Field and Current Dependence | In previous work in undoped MFe2As2, partial drops in the resistivity
indicative of traces of superconductivity have been observed in some samples of
M=Ba (Tc ~ 20 K, up to 25% drop in resistivity) and M=Ca (Tc ~ 10 K, up to 45 %
drop in resistivity.) A complete drop in the resistivity to 0, along with a
finite fraction of Meissner flux expulsion, has been observed in M=Sr, Tc = 22
K. Using In-flux grown single crystal samples of undoped BaFe2As2, we find a
complete drop in the resistivity to 0 in most samples beginning at Tc(onset) =
22.5 K. However, in contrast to the SrFe2As2 results, there is no measurable
Meissner effect and no suppression of the resistive superconducting transition
with annealing. The current sensitivity of the superconducting resistive
transition in our samples of BaFe2As2 is quite strong, with an increase in the
current density of a factor of 15 to ~ 1.5 A/cm2 not changing Tc(onset) but
broadening the transition significantly and causing the resistivity to remain
finite as T approaches 0. To investigate if this unusually low critical current
is indicative of filamentary conduction lacking the apparent anisotropy seen in
the critical magnetic field, Hc2, measurements of, e. g., the bulk
superconductor Co-doped BaFe2As2, Hc2 was measured in both crystalline
directions. These BaFe2As2 samples show Hc2(T) values in the ab-plane and along
the c-axis comparable to those seen in BaFe2-xCoxAs2, which has a similar Tc.
Since the lack of Tc suppression after annealing argues against strain-induced
superconductivity as proposed for the other undoped MFe2As2 materials, another
possible cause for the superconductivity in BaFe2As2 is discussed. | 0907.4429v1 |
2019-03-12 | Signatures of Anelastic Domain Relaxation in Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ Investigated by Mechanical Modulation of Resistivity | The resistive response of Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ to AC
mechanical deformation is considered in the multi-domain state. This resistance
change depends both upon the anelastic relaxation of domain walls and upon the
relation between resistance and the domain wall configuration. Samples are
adhered to the surface of a piezoelectric stack, which is driven by an AC
voltage while the AC modulation of the sample resistance is measured. As the
response time of electrons is faster than that of the lattice, the phase
difference $\phi$ between the AC resistance modulation and the AC deformation
of the piezoelectric is entirely due to anelastic relaxation effects in the
sample. An expression is derived for relating $\phi$ to a sample's complex
compliance, $J(\omega)$, in this experimental configuration. Measurements of
Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ for x= (0.025, 0.052) reveal a peak in the
out-of-phase resistivity modulation in the orthorhombic antiferromagnetic state
well below the Ne\'el temperature $T_N$ and structural transition $T_S$.
Meanwhile, for a composition that is tetragonal at all temperatures, x=0.07,
the resistance modulation remains entirely in phase over the same temperatures,
establishing domain motion as a probable cause of the observed effects in the
samples that do undergo the tetragonal-to-orthorhombic transition. Fits are
provided of $\tan\phi$ for a sample with x=0.025 for various amplitude
excitations on the piezoelectric stack, from which the apparent activation
energy $E_a$ for domain wall motion is found to decreases with increasing
amplitude of the deformation along the $[110]_T$ axis. We find
$\frac{dE_a}{d\varepsilon^0_{[110,110]_T}} = -1115\pm 196$ eV with $E_a = 9.09
\pm 0.74 \times 10^{-3}$ eV in the zero strain limit if we assume linearity
over the entire range of strain amplitudes. | 1903.04732v1 |
2005-02-09 | Structure, magnetic and transport properties of Ti-substituted La0.7Sr0.3MnO3 | Ti-substituted perovskites, La0.7Sr0.3Mn1-xTixO3, with x between 0 to 0.20,
were investigated by neutron diffraction, magnetization, electric resistivity,
and magnetoresistance (MR) measurements. All samples show a rhombohedral
structure (space group R3c) from 10 K to room temperature. At room temperature,
the cell parameters a, c and the unit cell volume increase with increasing Ti
content. However, at 10 K, the cell parameter a has a maximum value for x =
0.10, and decreases for x greater than 0.10, while the unit cell volume remains
nearly constant for x greater than 0.10. The average (Mn,Ti)-O bond length
increases up to x=0.15, and the (Mn,Ti)-O-(Mn,Ti) bond angle decreases with
increasing Ti content to its minimum value at x=0.15 at room temperature. Below
the Curie temperature T_C, the resistance exhibits metallic behavior for the x
_ 0.05 samples. A metal (semiconductor) to insulator transition is observed for
the x_ 0.10 samples. A peak in resistivity appears below T_C for all samples,
and shifts to a lower temperature as x increases. The substitution of Mn by Ti
decreases the 2p-3d hybridization between O and Mn ions, reduces the bandwidth
W, and increases the electron-phonon coupling. Therefore, the TC shifts to a
lower temperature and the resistivity increases with increasing Ti content. A
field-induced shift of the resistivity maximum occurs at x less than or equal
to 0.10. The maximum MR effect is about 70% for La0.7Sr0.3Mn0.8Ti0.2O3. The
separation of TC and the resistivity maximum temperature Tmax enhances the MR
effect in these compounds due to the weak coupling between the magnetic
ordering and the resistivity as compared with La0.7Sr0.3MnO3. | 0502235v1 |
2020-12-08 | Quantitative measurement of the thermal contact resistance between a glass microsphere and a plate | Accurate measurements of the thermal resistance between micro-objects made of
insulating materials are complex because of their small size, low conductivity,
and the presence of various ill-defined gaps. We address this issue using a
modified scanning thermal microscope operating in vacuum and in air. The
sphere-plate geometry is considered. Under controlled heating power, we measure
the temperature on top of a glass microsphere glued to the probe as it
approaches a glass plate at room temperature with nanometer accuracy. In
vacuum, a jump is observed at contact. From this jump in temperature and the
modeling of the thermal resistance of a sphere, the sphere-plate contact
resistance $ R_K=(1.4 \pm 0.18)\times10^7 \ \mathrm{K.W^{-1}}$ and effective
radius $r=(36 \pm 4)$ nm are obtained. In air, the temperature on top of the
sphere shows a decrease starting from a sphere-plate distance of 200
$\mathrm{\mu m}$. A jump is also observed at contact, with a reduced amplitude.
The sphere-plate coupling out of contact can be described by the resistance
shape factor of a sphere in front of a plate in air, placed in a circuit
involving a series and a parallel resistance that are determined by fitting the
approach curve. The contact resistance in air $R^*_K=(1.2 \pm 0.46)\times 10^7
\ \mathrm{K.W^{-1}}$ is then estimated from the temperature jump. The method is
quantitative without requiring any tedious multiple-scale numerical simulation,
and is versatile to describe the coupling between micro-objects from large
distances to contact in various environments. | 2012.04291v1 |
2002-01-19 | Antiferromagnetic Order Induced by an Applied Magnetic Field in a High-Temperature Superconductor | One view of the cuprate high-transition temperature (high-Tc) superconductors
is that they are conventional superconductors where the pairing occurs between
weakly interacting quasiparticles, which stand in one-to-one correspondence
with the electrons in ordinary metals - although the theory has to be pushed to
its limit. An alternative view is that the electrons organize into collective
textures (e.g. charge and spin stripes) which cannot be mapped onto the
electrons in ordinary metals. The phase diagram, a complex function of various
parameters (temperature, doping and magnetic field), should then be approached
using quantum field theories of objects such as textures and strings, rather
than point-like electrons. In an external magnetic field, magnetic flux
penetrates type-II superconductors via vortices, each carrying one flux
quantum. The vortices form lattices of resistive material embedded in the
non-resistive superconductor and can reveal the nature of the ground state -
e.g. a conventional metal or an ordered, striped phase - which would have
appeared had superconductivity not intervened. Knowledge of this ground state
clearly provides the most appropriate starting point for a pairing theory. Here
we report that for one high-Tc superconductor, the applied field which imposes
the vortex lattice, also induces antiferromagnetic order. Ordinary
quasiparticle pictures cannot account for the nearly field-independent
antiferromagnetic transition temperature revealed by our measurements. | 0201349v1 |
2013-01-22 | Exceptional ballistic transport in epitaxial graphene nanoribbons | Graphene electronics has motivated much of graphene science for the past
decade. A primary goal was to develop high mobility semiconducting graphene
with a band gap that is large enough for high performance applications.
Graphene ribbons were thought to be semiconductors with these properties,
however efforts to produce ribbons with useful bandgaps and high mobility has
had limited success. We show here that high quality epitaxial graphene
nanoribbons 40 nm in width, with annealed edges, grown on sidewall SiC are not
semiconductors, but single channel room temperature ballistic conductors for
lengths up to at least 16 micrometers. Mobilities exceeding one million
corresponding to a sheet resistance below 1 Ohm have been observed, thereby
surpassing two dimensional graphene by 3 orders of magnitude and theoretical
predictions for perfect graphene by more than a factor of 10. The graphene
ribbons behave as electronic waveguides or quantum dots. We show that transport
in these ribbons is dominated by two components of the ground state transverse
waveguide mode, one that is ballistic and temperature independent, and a second
thermally activated component that appears to be ballistic at room temperature
and insulating at cryogenic temperatures. At room temperature the resistance of
both components abruptly increases with increasing length, one at a length of
160 nm and the other at 16 micrometers. These properties appear to be related
to the lowest energy quantum states in the charge neutral ribbons. Since
epitaxial graphene nanoribbons are readily produced by the thousands, their
room temperature ballistic transport properties can be used in advanced
nanoelectronics as well. | 1301.5354v2 |
2022-01-25 | KCo$_2$As$_2$: A New Portal for the Physics of High-Purity Metals | High-quality single crystals of KCo$_2$As$_2$ with the body-centered
tetragonal ThCr$_2$Si$_2$ structure were grown using KAs self flux. Structural,
magnetic, thermal, and electrical transport were investigated. No clear
evidence for any phase transitions was found in the temperature range 2 to 300
K. The in-plane electrical resistivity $\rho$ versus temperature $T$ is highly
unusual, showing a $T^4$ behavior below 30 K and an anomalous positive
curvature up to 300 K which is different from the linear behavior expected from
the Bloch-Gr\"uneisen theory for electron scattering by acoustic phonons. This
positive curvature has been previously observed in the in-plane resistivity of
high-conductivity layered delafossites such as PdCoO$_2$ and PtCoO$_2$. The
in-plane $\rho(T\to0) = 0.36~\mu\Omega$ cm of KCo$_2$As$_2$ is exceptionally
small for this class of compounds. The material also exhibits a nearly linear
magnetoresistance at low $T$ which attains a value of about 40% at $T=2$K and
magnetic field $H= 80$ kOe. The magnetic susceptibility $\chi$ of KCo$_2$As$_2$
is isotropic and about an order of magnitude smaller than the values for the
related compounds SrCo$_2$As$_2$ and BaCo$_2$As$_2$. The $\chi$ increases above
100 K which is found from our first-principles calculations to arise from a
sharp peak in the electronic density of states just above the Fermi energy
$E_{\rm F}$. Heat capacity $C_{\rm p}(T)$ data at low $T$ yield an electronic
density of states $N(E_{\rm F})$ that is about 36% larger than predicted by the
first-principles theory. The $C_{\rm p}(T)$ data near room temperature suggest
the presence of excited optic vibration modes which may also be the source of
the positive curvature in $\rho(T)$. Our results show that KCo$_2$As$_2$
provides a new avenue for investigating the physics of high-purity metals. | 2201.10325v1 |
2023-01-25 | Investigation of Planckian behavior in a high-conductivity oxide: PdCrO$_2$ | The layered delafossite metal PdCrO$_2$ is a natural heterostructure of
highly conductive Pd layers Kondo coupled to localized spins in the adjacent
Mott insulating CrO$_2$ layers. At high temperatures $T$ it has a $T$-linear
resistivity which is not seen in the isostructural but non-magnetic PdCoO$_2$.
The strength of the Kondo coupling is known, as-grown crystals are extremely
high purity and the Fermi surface is both very simple and experimentally known.
It is therefore an ideal material platform in which to investigate 'Planckian
metal' physics. We do this by means of controlled introduction of point
disorder, measurement of the thermal conductivity and Lorenz ratio and studying
the sources of its high temperature entropy. The $T$-linear resistivity is seen
to be due mainly to elastic scattering and to arise from a sum of several
scattering mechanisms. Remarkably, this sum leads to a scattering rate within
10$\%$ of the Planckian value of $k_BT/$$\hbar$. | 2301.10631v1 |
1995-06-01 | Role of phason-defects on the conductance of a 1-d quasicrystal | We have studied the influence of a particular kind of phason-defect on the
Landauer resistance of a Fibonacci chain. Depending on parameters, we sometimes
find the resistance to decrease upon introduction of defect or temperature, a
behavior that also appears in real quasicrystalline materials. We demonstrate
essential differences between a standard tight-binding model and a full
continuous model. In the continuous case, we study the conductance in relation
to the underlying chaotic map and its invariant. Close to conducting points,
where the invariant vanishes, and in the majority of cases studied, the
resistance is found to decrease upon introduction of a defect. Subtle
interference effects between a sudden phason-change in the structure and the
phase of the wavefunction are also found, and these give rise to resistive
behaviors that produce exceedingly simple and regular patterns. | 9506004v2 |
1997-12-12 | Surface Resistance Imaging with a Scanning Near-Field Microwave Microscope | We describe near-field imaging of sample sheet resistance via frequency
shifts in a resonant coaxial scanning microwave microscope. The frequency
shifts are related to local sample properties, such as surface resistance and
dielectric constant. We use a feedback circuit to track a given resonant
frequency, allowing measurements with a sensitivity to frequency shifts as
small as one parts in 50000 for a 30 ms sampling time. The frequency shifts can
be converted to sheet resistance based on a simple model of the system. | 9712142v1 |
1997-12-15 | Quantitative Imaging of Sheet Resistance with a Scanning Near-Field Microwave Microscope | We describe quantitative imaging of the sheet resistance of metallic thin
films by monitoring frequency shift and quality factor in a resonant scanning
near-field microwave microscope. This technique allows fast acquisition of
images at approximately 10 ms per pixel over a frequency range from 0.1 to 50
GHz. In its current configuration, the system can resolve changes in sheet
resistance as small as 0.6 Ohms/sq for 100 Ohms/sq films. We demonstrate its
use at 7.5 GHz by generating a quantitative sheet resistance image of a
YBa2Cu3O7 (YBCO) thin film on a 5 cm-diameter sapphire wafer. | 9712171v1 |
1999-07-13 | Na-site substitution effects of the thermoelectric properties of NaCo_2O_4 | The resistivity and thermopower of Na$_{1+x}$Co$_2$O$_4$ and
Na$_{1.1-x}$Ca$_x$Co$_2$O$_4$ are measured and analyzed. In
Na$_{1+x}$Co$_2$O$_4$, whereas the resistivity increases with $x$, the
thermopower is nearly independent of $x$. This suggests that the excess Na is
unlikely to supply carriers, and decreases effective conduction paths in the
sample. In Na$_{1.1-x}$Ca$_x$Co$_2$O$_4$, the resistivity and the thermopower
increase with $x$, and the Ca$^{2+}$ substitution for Na$^+$ reduces the
majority carriers in NaCo$_2$O$_4$. This means that they are holes, which is
consistent with the positive sign of the thermopower. Strong correlation in
this compound is evidenced by the peculiar temperature dependence of the
resistivity. | 9907179v1 |
1999-11-06 | Electrical Resistivity of a Thin Metallic Film | The electrical resistivity of a pure sample of a thin metallic film is found
to depend on the boundary conditions. This conclusion is supported by a
free-electron model calculation and confirmed by an ab initio relativistic
Korringa-Kohn-Rostoker computation. The low-temperature resistivity is found to
be zero for a free-standing film (reflecting boundary conditions) but nonzero
when the film is sandwiched between two semi-infinite samples of the same
material (outgoing boundary conditions). In the latter case, this resistivity
scales inversely with the number of monolayers and is due to the background
diffusive scattering by a finite lattice. | 9911093v1 |
2000-03-09 | On the Mooij Rule | Weak localization leads to the same correction to both the conductivity and
the electron-phonon coupling constant $\lambda$ (and $\lambda_{tr}$).
Consequently the temperature dependence of the (thermal) electrical resistivity
is decreasing as the conductivity is decreasing due to weak localization, which
results in the decrease of the temperature coefficient of resistivity (TCR)
with increasing the residual resistivity. When $\lambda$ is approaching zero,
only residual resistivity part remains and gives rise to the negative TCR.
Accordingly, the Mooij rule is a manifestation of weak localization correction
to the conductivity and the electron-phonon interaction. This study may provide
a new means of probing the phonon-mechanism in exotic superconductors. | 0003144v1 |
2001-05-04 | Weak localization and the Mooij rule in disordered metals | Weak localization leads to the same correction to both the conductivity and
the McMillan's electron-phonon coupling constant $\lambda$ (and
$\lambda_{tr}$). Consequently the temperature dependence of the thermal
electrical resistivity is decreasing as the conductivity is decreasing due to
weak localization, which results in the decrease of the temperature coefficient
of resistivity (TCR) with increasing the residual resistivity. When $\lambda$
and $\lambda_{tr}$ are approaching zero, only residual resistivity part remains
and gives rise to the negative TCR. Accordingly, the Mooij rule is a
manifestation of weak localization correction to the conductivity and the
electron-phonon interaction. This study may provide a new means of probing the
phonon-mechanism in exotic superconductors. | 0105090v1 |
2001-10-31 | Stationary Regime of Random Resistor Networks Under Biased Percolation | The state of a 2-D random resistor network, resulting from the simultaneous
evolutions of two competing biased percolations, is studied in a wide range of
bias values. Monte Carlo simulations show that when the external current $I$ is
below the threshold value for electrical breakdown, the network reaches a
steady state with a nonlinear current-voltage characteristic. The properties of
this nonlinear regime are investigated as a function of different model
parameters. A scaling relation is found between $<R>/<R>_0$ and $I/I_0$, where
$<R>$ is the average resistance, $<R>_0$ the linear regime resistance and $I_0$
the threshold value for the onset of nonlinearity. The scaling exponent is
found to be independent of the model parameters. A similar scaling behavior is
also found for the relative variance of resistance fluctuations. These results
compare well with resistance measurements in composite materials performed in
the Joule regime up to breakdown. | 0110646v1 |
2002-05-27 | Resistivity and thermoelectric power measurements on CeFe$_2$ and its pseudobinaries | Resistivity and thermoelectric power (TEP) measurements on CeFe$_2$ and two
of its pseudo-binaries Ce(Fe, 5% Ir)$_2$ and Ce(Fe, 7% Ru)$_2$ between 78K and
275K are reported. The resistivity data are analysed in terms of contributions
from scattering due to phonon, magnon, spin fluctuation and lattice defects,
and also from interband scattering. Attempts are made to analyze the TEP data
in terms of these resistivity components. Thermal hysteresis is observed in the
temperature dependence of TEP in the Ir and Ru doped CeFe$_2$ samples around
the ferromagnetic to antiferromagnetic transition, indicating the first order
nature of this transition. | 0205539v1 |
2003-02-12 | Temperature Dependence of the Dielectric Constant and Resistivity of Diluted Magnetic Semiconductors | We study the effect that the ferromagnetic order has on the electrical
properties of Diluted Magnetic Semiconductors. We analyze the temperature
dependence of the dielectric constant and of the resistivity of
Ga$_{1-x}$Mn$_x$As. In our treatment the electronic structure of the
semiconductor is described by a six band Kohn-Luttinger Hamiltonian, the
thermal fluctuations of the Mn magnetic moments are treated in the mean field
approximation, the carrier-carrier interaction within the random phase
approximation, and the transport properties using the relaxation time
approximation. We find that the Thomas-Fermi length changes near 8% when going
from the ferromagnetic to the paramagnetic phase. We also find, in good
agreement with the experiments, that the resistivity changes near 20% when
going from zero to the Curie temperature. We explain this change in the
resistivity in terms of the variation of the Fermi surface and the transport
scattering time when going from the ferromagnetic phase to the paramagnetic
phase. | 0302237v1 |
2003-02-19 | Small-polaron hopping conductivity in bilayer manganite La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ | We report anisotropic resistivity measurements on a
La$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ single crystal over a temperature $T$ range
from 2 to 400 K and in magnetic fields $H$ up to 14 T. For $T\geq 218$ K, the
temperature dependence of the zero-field in-plane $\rho_{ab}(T)$ resistivity
obeys the adiabatic small polaron hopping mechanism, while the out-of-plane
$\rho_{c}(T)$ resistivity can be ascribed by an Arrhenius law with the same
activation energy. Considering the magnetic character of the polarons and the
close correlation between the resistivity and magnetization, we developed a
model which allows the determination of $\rho_{ab,c}(H,T)$. The excellent
agreement of the calculations with the measurements indicates that small
polarons play an essential role in the electrical transport properties in the
paramagnetic phase of bilayer manganites. | 0302392v1 |
2003-07-21 | Detecting percolative metal-insulator transition in manganites by resistive relaxation | We report an experimental study of the time dependence of resistivity of a
La$_{0.9}$Sr$_{0.1}$MnO$_{3}$ ultrathin film in order to elucidate the
underlying mechanism for metal-insulator transition and colossal
magnetoresistance CMR effect. There is a clear change of sign in the resistive
relaxation rate across the metal-insulator transition driven by temperature or
magnetic field. When measuring in increasing temperature or decreasing magnetic
field, the resistivity increases with time in the metallic state but decreases
with time in the insulating state. These relaxation processes indicate that the
metal-insulator transition and the associated CMR are a direct result of phase
separation and of percolation of the metallic phase. | 0307501v1 |
2004-11-24 | Electrical Spin Injection in Multi-Wall carbon NanoTubes with transparent ferromagnetic contacts | We report on electrical spin injection measurements on MWNTs . We use a
ferromagnetic alloy Pd$_{1-x}$Ni$_{x}$ with x $\approx$ 0.7 which allows to
obtain devices with resistances as low as 5.6 $k\Omega$ at 300 $K$. The yield
of device resistances below 100 $k\Omega$, at 300 $K$, is around 50%. We
measure at 2 $K$ a hysteretic magneto-resistance due to the magnetization
reversal of the ferromagnetic leads. The relative difference between the
resistance in the antiparallel (AP) orientation and the parallel (P)
orientation is about 2%. | 0411623v2 |
2005-04-22 | Possible Localization Behavior of the Inherent Conducting Polymer (CH$_3$)$_{0.9}$ReO$_3$ | Polymeric methyltrioxorhenium (poly-MTO) represents the first example of an
inherent conducting organometallic oxide. It adopts the structural motives and
transport properties of some classical perovskites in two dimensions. In this
study we present resistivity data down to 30 mK which exhibit a crossover from
a metallic (d$\rho$/d$T >$ 0) to an insulating (d$\rho$/d$T <$ 0) behavior at
about 30 K. Below 30 K an unusual resistivity behavior, similar to that of some
doped cuprate systems, is observed: initially the resistivity increases
approximately as $\rho \sim$ log$(1/T$) before it starts to saturate below 2 K.
Furthermore, a linear positive magnetoresistance is found (up to 7 T).
Temperature dependent magnetization and specific heat measurements in various
magnetic fields indicate that the unusual resistivity behavior may be driven by
spatial localization of the d$^1$ moments at the Re atoms. | 0504585v1 |
2005-04-27 | Colossal resistivity change besides magnetoresistance: an extended theoretical framework for electronic transport of manganites | Current theoretical approaches to manganites mainly stem from magnetic
framework, in which the electronic transport is thought to be spin-dependent
and the double exchange mechanism plays a core role. However, quite a number of
experimental observations can yet not be reasonably explained. For example,
multiplicate insulator-metal transitions and resistivity reduction induced by
perturbations other than magnetic field, such as electric current, are not well
understood. A comprehensive analysis on earlier extensive studies is performed
and two types of origins for resistivity change are highlighted. Besides the
insulated-to-metallic transition induced by external field such as magnetic
field, the insulated-to-insulated transition induced extrinsically is even a
more important source for the colossal resistivity change. We propose an
extended framework for the electronic transport of manganites, in which the
contribution of charge degree of freedom is given a special priority. | 0504706v2 |
2006-01-31 | Phase coexistence and resistivity near the ferromagnetic transition of manganites | Pairing of oxygen holes into heavy bipolarons in the paramagnetic phase and
their magnetic pair-breaking in the ferromagnetic phase [the so-called
current-carrier density collapse (CCDC)] has accounted for the first-order
ferromagnetic phase transition, colossal magnetoresistance (CMR), isotope
effect, and pseudogap in doped manganites. Here we propose an explanation of
the phase coexistence and describe the magnetization and resistivity of
manganites near the ferromagnetic transition in the framework of CCDC. The
present quantitative description of resistivity is obtained without any fitting
parameters by using the experimental resistivities far away from the transition
and the experimental magnetization, and essentially model independent. | 0601712v2 |
2006-02-03 | Boundary resistance in magnetic multilayers | Quasiclassical boundary conditions for electrochemical potentials at the
interface between diffusive ferromagnetic and non-magnetic metals are derived
for the first time. An expression for the boundary resistance accurately
accounts for the momentum conservation law as well as essential gradients of
the chemical potentials. Conditions are established at which spin-asymmetry of
the boundary resistance has positive or negative sign. Dependence of the spin
asymmetry and the absolute value of the boundary resistance on the exchange
splitting of the conduction band opens up new possibility to estimate spin
polarization of the conduction band of ferromagnetic metals. Consistency of the
theory is checked on existing experimental data. | 0602070v1 |
2006-06-23 | Angular dependence of domain wall resistivity in artificial magnetic domain structures | We exploit the ability to precisely control the magnetic domain structure of
perpendicularly magnetized Pt/Co/Pt trilayers to fabricate artificial domain
wall arrays and study their transport properties. The scaling behaviour of this
model system confirms the intrinsic domain wall origin of the
magnetoresistance, and systematic studies using domains patterned at various
angles to the current flow are excellently described by an angular-dependent
resistivity tensor containing perpendicular and parallel domain wall
resistivities. We find that the latter are fully consistent with Levy-Zhang
theory, which allows us to estimate the ratio of minority to majority spin
carrier resistivities, rho-down/rho-up~5.5, in good agreement with thin film
band structure calculations. | 0606614v1 |
2006-07-26 | Angle-dependent magnetotransport in cubic and tetragonal ferromagnets: Application to (001)- and (113)A-oriented (Ga,Mn)As | General expressions for the longitudinal and transverse resistivities of
single-crystalline cubic and tetragonal ferromagnets are derived from a series
expansion of the resistivity tensor with respect to the magnetization
orientation. They are applied to strained (Ga,Mn)As films, grown on (001)- and
(113)A-oriented GaAs substrates, where the resistivities are theoretically and
experimentally studied for magnetic fields rotated within various planes
parallel and perpendicular to the sample surface. We are able to model the
measured angular dependences of the resistivities within the framework of a
single ferromagnetic domain, calculating the field-dependent orientation of the
magnetization by numerically minimizing the free-enthalpy density.
Angle-dependent magnetotransport measurements are shown to be a powerful tool
for probing both anisotropic magnetoresistance and magnetic anisotropy. The
anisotropy parameters of the (Ga,Mn)As films inferred from the magnetotransport
measurements agree with those obtained by ferromagnetic resonance measurements
within a factor of two. | 0607679v1 |
2006-11-14 | Calculations of spin-disorder resistivity from first principles | Spin-disorder resistivity of Fe and Ni is studied using the noncollinear
density functional theory. The Landauer conductance is averaged over random
disorder configurations and fitted to Ohm's law. The distribution function is
approximated by the mean-field theory. The dependence of spin-disorder
resistivity on magnetization in Fe is found to be in excellent agreement with
the results for the isotropic s-d model. In the fully disordered state,
spin-disorder resistivity for Fe is close to experiment, while for fcc Ni it
exceeds the experimental value by a factor of 2.3. This result indicates strong
magnetic short-range order in Ni at the Curie temperature. | 0611377v2 |
2007-04-04 | Vortex Dynamics at the Initial Stage of Resistive Transition in Superconductors with Fractal Cluster Structure | The effect of fractal normal-phase clusters on vortex dynamics in a
percolative superconductor is considered. The superconductor contains
percolative superconducting cluster carrying a transport current and clusters
of a normal phase, acting as pinning centers. A prototype of such a structure
is YBCO film, containing clusters of columnar defects, as well as the BSCCO/Ag
sheathed tape, which is of practical interest for wire fabrication. Transition
of the superconductor into a resistive state corresponds to the percolation
transition from a pinned vortex state to a resistive state when the vortices
are free to move. The dependencies of the free vortex density on the fractal
dimension of the cluster boundary as well as the resistance on the transport
current are obtained. It is revealed that a mixed state of the vortex glass
type is realized in the superconducting system involved. The current-voltage
characteristics of superconductors containing fractal clusters are obtained and
their features are studied. | 0704.0494v1 |
2008-02-19 | Temperature memory and resistive glassy behaviors of a perovskite manganite | This paper reports the observations of long-time relaxation, aging, and
temperature memory behaviors of resistance and magnetization in the
ferromagnetic state of a polycrystalline La0.7Ca0.3Mn0.925Ti0.075O3 compound.
The observed glassy dynamics of the electrical transport appears to be
magnetically originated and has a very close association with the magnetic
glassiness of the sample. Phase separation and strong correlation between
magnetic interactions and electronic conduction play the essential roles in
producing such a resistive glassiness. We explain the observed effects in terms
of a coexistence of two competing thermomagnetic processes, domain growth and
magnetic freezing, and propose that hole-doped perovskite manganites can be
considered as "resistive glasses". | 0802.2729v1 |
2008-02-26 | Effects of heat dissipation on unipolar resistance switching in Pt/NiO/Pt capacitors | We fabricated Pt/NiO/Pt capacitor structures with various bottom electrode
thicknesses, $t_{BE}$, and investigated their resistance switching behaviors.
The capacitors with $t_{BE} \geq 50$ nm exhibited typical unipolar resistance
memory switching, while those with $t_{BE} \leq 30$ nm showed threshold
switching. This interesting phenomenon can be explained in terms of the
temperature-dependent stability of conducting filaments. In particular, the
thinner $t_{BE}$ makes dissipation of Joule heat less efficient, so the
filaments will be at a higher temperature and become less stable. This study
demonstrates the importance of heat dissipation in resistance random access
memory. | 0802.3739v1 |
2008-08-25 | Stability and normal zone propagation speed in YBCO coated conductors with increased interfacial resistance | We will discuss how stability and speed of normal zone propagation in
YBCO-coated conductors is affected by interfacial resistance between the
superconducting film and the stabilizer. Our numerical simulation has shown
that the increased interfacial resistance substantially increases speed of
normal zone propagation and decreases the stability margins. Optimization of
the value of the resistance may lead to a better compromise between stability
and quench protection requirements than what is found in currently manufactured
coated conductors. | 0808.3409v3 |
2008-12-12 | Magnetic tunnel junctions with ferroelectric barriers: Prediction of four resistance states from first-principles | Magnetic tunnel junctions (MTJs), composed of two ferromagnetic electrodes
separated by a thin insulating barrier layer, are currently used in spintronic
devices, such as magnetic sensors and magnetic random access memories.
Recently, driven by demonstrations of ferroelectricity at the nanoscale,
thin-film ferroelectric barriers were proposed to extend the functionality of
MTJs. Due to the sensitivity of conductance to the magnetization alignment of
the electrodes (tunnelling magnetoresistance) and the polarization orientation
in the ferroelectric barrier (tunnelling electroresistance), these multiferroic
tunnel junctions (MFTJs) may serve as four-state resistance devices. Based on
first-principles calculations we demonstrate four resistance states in
SrRuO3/BaTiO3/SrRuO3 MFTJs with asymmetric interfaces. We find that the
resistance of such a MFTJ is significantly changed when the electric
polarization of the barrier is reversed and/or when the magnetizations of the
electrodes are switched from parallel to antiparallel. These results reveal the
exciting prospects of MFTJs for application as multifunctional spintronic
devices. | 0812.2393v1 |
2008-12-23 | Specific Resistance of Pd/Ir Interfaces | From measurements of the current-perpendicular-to-plane (CPP) total specific
resistance (AR = area times resistance) of sputtered Pd/Ir multilayers, we
derive the interface specific resistance, 2AR(Pd/Ir) = 1.02 +/- 0.06 fOhmm^2,
for this metal pair with closely similar lattice parameters. Assuming a single
fcc crystal structure with the average lattice parameter, no-free-parameter
calculations, including only spd orbitals, give for perfect interfaces,
2AR(Pd/Ir)(Perf) = 1.21 +/-0.1 fOhmm^2, and for interfaces composed of two
monolayers of a random 50%-50% alloy, 2AR(Pd/Ir)(50/50) = 1.22 +/- 0.1 fOhmm^2.
Within mutual uncertainties, these values fall just outside the range of the
experimental value. Updating to add f-orbitals gives 2AR(Pd/Ir)(Perf) = 1.10
+/- 0.1 fOhmm^2 and 2AR(Pd/Ir)(50-50) = 1.13 +/- 0.1 fOhmm^2, values now
compatible with the experimental one. We also update, with f-orbitals,
calculations for other pairs | 0812.4421v1 |
2010-01-11 | Anomalous Hall Effect in Fe/Gd Bilayers | Non-monotonic dependence of anomalous Hall resistivity on temperature and
magnetization, including a sign change, was observed in Fe/Gd bilayers. To
understand the intriguing observations, we fabricated the Fe/Gd bilayers and
single layers of Fe and Gd simultaneously. The temperature and field
dependences of longitudinal resistivity, Hall resistivity and magnetization in
these films have also been carefully measured. The analysis of these data
reveals that these intriguing features are due to the opposite signs of Hall
resistivity/or spin polarization and different Curie temperatures of Fe and Gd
single-layer films. | 1001.1586v2 |
2010-10-26 | Evanescent incompressible strips as origin of the observed Hall resistance overshoot | In this work we provide a systematic explanation to the unusual non-monotonic
behavior of the Hall resistance observed at two-dimensional electron systems.
We use a semi-analytical model based on the interaction theory of the integer
quantized Hall effect to investigate the existence of the anomalous, \emph{i.e}
overshoot, Hall resistance $R_{H}$. The observation of the overshoot resistance
at low magnetic field edge of the plateaus is elucidated by means of
overlapping evanescent incompressible strips, formed due to strong magnetic
fields and interactions. Utilizing a self-consistent numerical scheme we also
show that, if the magnetic field is decreased the $R_{H}$ decreases to its
expected value. The effects of the sample width, temperature, disorder strength
and magnetic field on the overshoot peaks are investigated in detail. Based on
our findings, we predict a controllable procedure to manipulate the maxima of
the peaks, which can be tested experimentally. Our model does not depend on
specific and intrinsic properties of the material, provided that a single
particle gap exists. | 1010.5432v1 |
2010-12-13 | Distinct electronic nematicities between electron and hole underdoped iron pnictides | We systematically investigated the in-plane resistivity anisotropy of
electron-underdoped $EuFe_{2-x}Co_xAs_2$ and $BaFe_{2-x}Co_xAs_2$, and
hole-underdoped $Ba_{1-x}K_xFe_2As_2$. Large in-plane resistivity anisotropy
was found in the former samples, while {\it tiny} in-plane resistivity
anisotropy was detected in the latter ones. When it is detected, the anisotropy
starts above the structural transition temperature and increases smoothly
through it. As the temperature is lowered further, the anisotropy takes a
dramatic enhancement through the magnetic transition temperature. We found that
the anisotropy is universally tied to the presence of non-Fermi liquid T-linear
behavior of resistivity. Our results demonstrate that the nematic state is
caused by electronic degrees of freedom, and the microscopic orbital
involvement in magnetically ordered state must be fundamentally different
between the hole and electron doped materials. | 1012.2731v1 |
2011-01-31 | Phase Mixing of Nonlinear Visco-resistive Alfvén Waves | We investigate the behaviour of nonlinear, nonideal Alfv\'en wave propagation
within an inhomogeneous magnetic environment. The governing MHD equations are
solved in 1D and 2D using both analytical techniques and numerical simulations.
We find clear evidence for the ponderomotive effect and visco-resistive
heating. The ponderomotive effect generates a longitudinal component to the
transverse Alfv\'en wave, with a frequency twice that of the driving frequency.
Analytical work shows the addition of resistive heating. This leads to a
substantial increase in the local temperature and thus gas pressure of the
plasma, resulting in material being pushed along the magnetic field. In 2D, our
system exhibits phase mixing and we observe an evolution in the location of the
maximum heating, i.e. we find a drifting of the heating layer. Considering
Alfv\'en wave propagation in 2D with an inhomogeneous density gradient, we find
that the equilibrium density profile is significantly modified by both the flow
of density due to visco-resistive heating and the nonlinear response to the
localised heating through phase mixing. | 1101.5945v1 |
2011-03-04 | Voltage bias induced modification of all oxide Pr0.5Ca0.5MnO3/SrTi0.95Nb.05O3 junctions | In this paper we report what happens to a pristine oxide junction
Pr0.5Ca0.5MnO3/SrTi0.95Nb.05O3 (PCMO/Nb:STO), when it is subjected to cycling
of voltage bias of moderate value ({\pm}4V). It is found that the initial
cycling leads to formation of a permanent state of lower resistance where the
lower resistance arises predominantly due to development of a shunt across the
device film (PCMO). On successive voltage cycling with increasing magnitude,
this state transforms into states of successive lower resistance that can be
transformed back to the initial stable state on cycling to below a certain
bias. A simple model based on p-n junction with shunt has been used to obtain
information on the change of the junction on voltage cycling. It has been shown
that the observation can be explained if the voltage cycling leads to lowering
of barrier at the interface and also reduction in series resistance. It is
suggested that this lowering can be related to the migration of oxygen ions and
vacancies at the junction region. Cross-sectional imaging of the junction shows
formation of permanent filamentary bridges across the thickness of the PCMO
after the pristine p-n junction is first taken through a voltage cycle, which
would explain appearance of a finite shunt across the p-n junction. | 1103.0884v1 |
2011-07-11 | Magnetotransport properties of iron microwires fabricated by focused electron beam induced autocatalytic growth | We have prepared iron microwires in a combination of focused electron beam
induced deposition (FEBID) and autocatalytic growth from the iron
pentacarbonyl, Fe(CO)5, precursor gas under UHV conditions. The electrical
transport properties of the microwires were investigated and it was found that
the temperature dependence of the longitudinal resistivity (rhoxx) shows a
typical metallic behaviour with a room temperature value of about 88
micro{\Omega} cm. In order to investigate the magnetotransport properties we
have measured the isothermal Hall-resistivities in the range between 4.2 K and
260 K. From these measurements positive values for the ordinary and the
anomalous Hall coefficients were derived. The relation between anomalous Hall
resistivity (rhoAN) and longitudinal resistivity is quadratic, rhoAN rho^2 xx,
revealing an intrinsic origin of the anomalous Hall effect. Finally, at low
temperature in the transversal geometry a negative magnetoresistance of about
0.2 % was measured. | 1107.2014v1 |
2011-08-11 | Effect of Electron-electron Interaction on Surface Transport in Three-Dimensional Topological Insulators | We study the effect of electron-electron interaction on the surface
resistivity of three-dimensional (3D) topological insulators. In the absence of
umklapp scattering, the existence of the Fermi-liquid ($T^2$) term in
resistivity of a two-dimensional (2D) metal depends on the Fermi surface
geometry, in particular, on whether it is convex or concave. On doping, the
Fermi surface of 2D metallic surface states in 3D topological insulators of the
Bi$_2$Te$_3$ family changes its shape from convex to concave due to hexagonal
warping, while still being too small to allow for umklapp scattering. We show
that the $T^2$ term in the resistivity is present only in the concave regime
and demonstrate that the resistivity obeys a universal scaling form valid for
an arbitrary 2D Fermi surface near a convex/concave transition. | 1108.2435v1 |
2011-10-31 | Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier | We present results on the magnetoresistance of the system Ni/Al203/n-doped
Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K
reveal a 75% magnetoresistance that decreases in value up to approximately 30K
where the effect disappears. We observe minimum resistance in the antiparallel
configurations of the source and drain of Ni. As a possibility, it seems to
indicate the existence of a magnetic state at the Si/oxide interface. The
average spin diffusion length obtained is of 650 nm approximately. Results are
compared to the window of resistances that seems to exist between the tunnel
barrier resistance and two threshold resistances but the spin transfer seems to
work in the range and outside the two thresholds. | 1110.6810v1 |
2012-08-22 | Why is the bulk resistivity of topological insulators so small? | As-grown topological insulators (TIs) are typically heavily-doped $n$-type
crystals. Compensation by acceptors is used to move the Fermi level to the
middle of the band gap, but even then TIs have a frustratingly small bulk
resistivity. We show that this small resistivity is the result of band bending
by poorly screened fluctuations in the random Coulomb potential. Using
numerical simulations of a completely compensated TI, we find that the bulk
resistivity has an activation energy of just 0.15 times the band gap, in good
agreement with experimental data. At lower temperatures activated transport
crosses over to variable range hopping with a relatively large localization
length. | 1208.4601v2 |
2012-09-26 | Substrate effect on the resistive switching in BiFeO3 thin films | BiFeO3 thin films have been deposited on Pt/sapphire and Pt/Ti/SiO2/Si
substrates with pulsed laser deposition using the same growth conditions,
respectively. Au was sputtered as the top electrode. The microscopic structure
of the thin film varies by changing the underlying substrate. Thin films on
Pt/sapphire are not resistively switchable due to the formation of Schottky
contacts at both the top and the bottom interface. However, thin films on
Pt/Ti/SiO2/Si exhibit an obvious resistive switching behavior under forward
bias. The conduction mechanisms in BiFeO3 thin films on Pt/sapphire and
Pt/Ti/SiO2/Si substrates are discussed to understand the different resistive
switching behaviors. | 1209.5868v1 |
2012-10-22 | Thickness-dependent structural, magnetic and transport properties of epitaxial Co2FeAl Heusler alloy thin films | We report on a systematic study of the structural, magnetic properties and
the anomalous Hall effect, in the Heusler alloy Co2FeAl (CFA) epitaxial films
on MgO(001), as a function of film thickness. It was found that the epitaxial
CFA films show a highly ordered B2 structure with an in-plane uniaxial magnetic
anisotropy. An analysis of the electrical transport properties reveals that the
lattice and magnon scattering contributions to the longitudinal resistivity.
Independent on the thickness of films, the anomalous Hall resistivity of CFA
films is found to be dominated by skew scattering only. Moreover, the anomalous
Hall resistivity shows weakly temperature dependent behavior, and its absolute
value increases as the thickness decreases. We attribute this temperature
insensitivity in the anomalous Hall resistivity to the weak temperature
dependent of tunneling spin-polarization in the CFA films, while the thickness
dependence behavior is likely due to the increasing significance of interface
or free surface electronic states. | 1210.5807v1 |
2012-12-06 | Barkhausen-type noise in the resistance of antiferromagnetic Cr thin films | We present an experimental study of the changes generated on the electrical
resistance $R(T)$ of epitaxial Cr thin films by the transformation of quantized
spin density wave domains as the temperature is changed. A characteristic
resistance noise appears only within the same temperature region where a
cooling-warming cycle in $R(T)$ displays hysteretic behavior. We propose an
analysis based on an analogy with the Barkhausen noise seen in ferromagnets.
There fluctuations in the magnetization $M(H)$ occur when the magnetic field
$H$ is swept. By mapping $M \rightarrow \Psi_0$ and $H \rightarrow T$, where
$\Psi_0$ corresponds to the order parameter of the spin density wave, we
generalize the Preisach model in terms of a random distribution of {\it
resistive hysterons} to explain our results. These hysterons are related to
distributions of quantized spin density wave domains with different sizes,
local energies and number of nodes. | 1212.1411v1 |
2012-12-10 | YCr6Ge6 as a Candidate Compound for a Kagome Metal | We show that YCr6Ge6, comprising a kagome lattice made up of Cr atoms, is a
plausible candidate compound for a kagome metal that is expected to exhibit
anomalous phenomena such as flat-band ferromagnetism. Resistivity,
magnetization, and heat capacity are measured on single crystals of YCr6Ge6,
and band structure calculations are performed to investigate the electronic
structure. Curie-Weiss-like behavior in magnetic susceptibility, T2 dependence
in resistivity, and a Sommerfeld coefficient doubly enhanced from a calculated
value indicate a moderately strong electron correlation. Interestingly, the
in-plane resistivity is twice as large as the interplane resistivity, which is
contrary to the simple expectation from the layered structure. Band structure
calculations demonstrate that there are partially flat bands slightly below the
Fermi level near the {\Gamma} point, which is ascribed to Cr 3d3z2-r2 bands and
may govern the properties of this compound. | 1212.1976v1 |
2013-03-26 | Quantum corrections to conductivity in Si doped ZnO thin films | Si doped ZnO thin films with Si concentrations ranging from 0.4 to 10 % have
been grown by sequential pulsed laser deposition on sapphire substrates. The
resistivity of the films first decreased from ~ 6.6x10-3 to 4.7x10-4 ohm-cm as
the Si concentration was increased from ~ 0.4 to 2% and then it increased with
further increase in Si concentration. The electron concentrations in the films
were in the range from 3x1019 to 4x1020 cm-3 showing their degenerate nature.
However, temperature dependent resistivity measurements in the range from 300
to 4.2 K revealed negative temperature coefficient of resistivity (TCR) for the
0.4, 6 and 10% Si doped ZnO films in the entire measurement temperature range.
The 0.6, 0.9 and 2% Si doped films showed a transition from negative to
positive TCR with increasing temperature. The negative magnetoresistance found
in the films at low temperatures and 0.5 T magnetic field pointed to weak
localization as the dominant contributor towards negative TCR. A quantitative
fit of the temperature dependent resistivity data for all the films could be
obtained by considering the quantum correction to conductivity arising due to
disorder induced weak localization effect. | 1303.6443v2 |
2013-08-29 | Percolation model for a selective response of the resistance of composite semiconducting np-systems towards reducing gases | It is shown that a two-component percolation model can explain an
experimentally observed behavior, namely that a network built up by a mixture
of sintered nanocrystalline semiconducting n- and p-grains can exhibit
selective behavior, i.e. respond with a resistance increase when exposed to a
reducing gas A and with a resistance decrease in response to another reducing
gas B. To this end, a simple model is developed based on realistic assumptions
about the reactions on the grain surfaces. The resistance is calculated by
random walk simulations with nn-, pp- and np-bonds between the grains and the
results are found in very good agreement with the experiments. Contrary to
former assumptions, the np-bonds are crucial to obtain this accordance. | 1308.6442v2 |
2013-11-08 | Low-Contact-Resistance Graphene Devices with Nickel-Etched-Graphene Contacts | The performance of graphene-based transistors is often limited by the large
electrical resistance across the metal-graphene contact. We report an approach
to achieve ultra-low resistance metal contacts to graphene transistors. Through
a process of metal-catalyzed etching in hydrogen, multiple nano-sized pits with
zigzag edges are created in the graphene that form strong chemical bonds with
deposited nickel metallization for source-drain contacts without the need for
further annealing. This facile contact treatment prior to electrode
metallization results in contact resistance as low as 100 ohm-um in
single-layer graphene field-effect transistors, and 11 ohm-um in bilayer
graphene transistors. The treatment is compatible with complementary
metal-oxide-semiconductor fabrication processes, and holds great promise to
meet the contact performance required for the integration of graphene in future
integrated circuits. | 1311.1944v2 |
2014-06-14 | Negative magnetoresistance dynamics in expanded graphite under hydrostatic pressure up to 1.8 GPa | Basal plane resistivity of expanded graphite was studied under simultaneous
influence of hydrostatic pressure up to 1.8 GPa and magnetic field 0.8 T in the
77-300 K temperature region. Magnetic field induces negative magnetoresistance
in the sample within all temperature and pressure range studied. A change in
resistivity of the sample under maximum pressure reaches 80%. Significant
change in resistivity dependence on temperature under the pressure of 0.6 GPa
suggests for ordering transition in the sample studied. Negative
magnetoresistance in the graphite reaches about 15% at 0.6 GPa. Magnetic field
acts in the same way as pressure and potentiates the transition formation and
further magnetoresistance dynamics. The effects observed are mostly of elastic
character according to resistivity of the unloaded sample. | 1406.3770v1 |
2014-06-23 | Control of Thermoelectric Properties of ZnO using Electric Double Layer | We have successfully controlled thermoelectric properties of ZnO by changing
carrier concentration using an electric double layer transistor (EDLT) which is
a feld effect transistor gated by electrolyte solution. The resistivity and the
thermopower decreased abruptly by applying gate voltage larger than a threshold
voltage ( 2V), indicating the increase of carrier concentration on the ZnO
surface. The temperature dependence of resistivity became metallic, which is
characterized by weak temperature dependence of the resistivity, when gate
voltage exceeded 2V. Corresponding to the resistivity, the temperature
dependence of thermopower changed remarkably. The thickness of the induced
metallic layer was estimated to be about 10nm from the critical carrier
concentration of metal-insulator transition, and the power factor was
calculated to ~8*10-5Wm-1K2. Although the power factor is not as large as bulk
ZnO ceramics of optimum doping condition, EDLT is considered to be a useful way
to optimize thermoelectric properties by tuning carrier concentration. | 1406.5850v1 |
2014-09-28 | Universal Ratio of Intrinsic Resistivities of Spin Helix in B20 (Fe-Co)Si Magnets | The B20 magnets with the Dzyaloshinskii-Moriya (D-M) interaction exhibit spin
helix and Skyrmion spin textures unattainable in traditional Heisenberg
ferromagnets. We have determined the intrinsic resistivity of the spin helix,
which is a macroscopic Bloch domain wall, in B20 (Fe-Co)Si magnets. We found a
universal resistance ratio of gamma = 1.35 with current parallel and
perpendicular to the helix, independent of composition and temperature. This
gamma value is much smaller than 3, the well-known minimum value for domain
wall resistivity in traditional ferromagnets, due to the significant spin-orbit
coupling in the B20 magnets. | 1409.7869v1 |
2014-11-13 | Graphene-Passivated Nickel as an Oxidation-Resistant Electrode for Spintronics | We report on graphene-passivated ferromagnetic electrodes (GPFE) for spin
devices. GPFE are shown to act as spin-polarized oxidation-resistant
electrodes. The direct coating of nickel with few layer graphene through a
readily scalable chemical vapour deposition (CVD) process allows the
preservation of an unoxidized nickel surface upon air exposure. Fabrication and
measurement of complete reference tunneling spin valve structures demonstrates
that the GPFE is maintained as a spin polarizer and also that the presence of
the graphene coating leads to a specific sign reversal of the
magneto-resistance. Hence, this work highlights a novel oxidation-resistant
spin source which further unlocks low cost wet chemistry processes for
spintronics devices. | 1411.3476v1 |
2014-11-22 | Crystal growth, resistivity and Hall effect of the delafossite metal PtCoO$_2$ | We report single crystal growth of the delafossite oxide PtCoO$_2$, and basic
transport measurements on single crystals etched to well-defined geometries
using focused ion beam techniques. The room temperature resistivity is 2.1
$\mu\Omega$ cm, and the Hall coefficient is consistent with the existence of
one free electron per Pt. Although the residual resistivity ratio is greater
than fifty, a slight upturn of resistivity is seen below 15 K. The angle
dependence of the in-plane magnetoresistance is also reported. | 1411.6162v2 |
2015-03-02 | High-Q operation of SRF cavities: The potential impact of thermocurrents on the RF surface resistance | For many new accelerator applications, superconducting radio frequency (SRF)
systems are the enabling technology. In particular for CW applications, much
effort is being expended to minimize the power dissipation (surface resistance)
of niobium cavities. Starting in 2009, we suggested a means of reducing the
residual resistance by performing a thermal cycle [1], a procedure of warming
up a cavity after initial cooldown to about 20K and cooling it down again. In
subsequent studies [2], this technique was used to manipulate the residual
resistance by more than a factor of 2. It was postulated that thermocurrents
during cooldown generate additional trapped magnetic flux that impacts the
cavity quality factor. Here, we present a more extensive study that includes
measurements of two additional passband modes and that confirms the effect. In
this paper, we also discuss simulations that support the claim. While the
layout of the cavity LHe tank system is cylindrically symmetric, we show that
the temperature dependence of the material parameters results in a
non-symmetric current distribution. Hence a significant amount of magnetic flux
can be generated at the RF surface. | 1503.00601v2 |
2015-05-28 | Effect of the interface resistance in non-local Hanle measurements | We use lateral spin valves with varying interface resistance to measure
non-local Hanle effect in order to extract the spin-diffusion length of the
non-magnetic channel. A general expression that describes spin injection and
transport, taking into account the influence of the interface resistance, is
used to fit our results. Whereas the fitted spin-diffusion length value is in
agreement with the one obtained from standard non-local measurements in the
case of a finite interface resistance, in the case of transparent contacts a
clear disagreement is observed. The use of a corrected expression, recently
proposed to account for the anisotropy of the spin absorption at the
ferromagnetic electrodes, still yields a deviation of the fitted spin-diffusion
length which increases for shorter channel distances. This deviation shows how
sensitive the non-local Hanle fittings are, evidencing the complexity of
obtaining spin transport information from such type of measurements. | 1505.07592v1 |
2016-01-25 | Lower limits of line resistance in nanocrystalline Back End of Line Cu interconnects | The strong non-linear increase in Cu interconnect line resistance with a
decrease in linewidth presents a significant obstacle to their continued
downscaling. In this letter we use first principles density functional theory
based electronic structure of Cu interconnects to find the lower limits of
their line resistance for metal linewidths corresponding to future technology
nodes. We find that even in the absence of scattering due to grain boundaries,
edge roughness or interfaces, quantum confinement causes a severe reduction in
current carrying capacity of Cu. We discuss the causes of transport orientation
dependent anisotropy of quantum confinement in Cu. We also find that when the
simplest scattering mechanism in the grain boundary scattering dominated limit
is added to otherwise coherent electronic transmission in monocrystalline
nanowires, the lower limits of line resistance are significantly higher than
projected roadmap requirements in the International Technology Roadmap for
Semiconductors. | 1601.06675v2 |
2016-05-12 | NdCeCuO - NdCeO boundary and resistive switchings in mesoscopic structures on base of epitaxial NdCeCuO films | Reverse and stable bipolar resistive switching effect was observed in planar
NdCeCuO - NdCeO - Ag heterostructures. It was shown that the current voltage
charactereriscs of the BRSE observed has a diode character. Simulations were
used to consider the influence of the nonuniform distribution of an electric
field at the interface of a heterojunction on the effect of bipolar resistive
switching in investigated structures. The inhomogeneous distribution of the
electric field near the contact edge creates regions of higher electric field
strength which, in turn, stimulates motion and redistribution of defects,
changes of the resistive properties of the whole structure and formation of a
percolation channel. | 1605.03913v1 |
2016-08-25 | Resistive Switching in Aqueous Nanopores by Shock Electrodeposition | Solid-state programmable metallization cells have attracted considerable
attention as memristive elements for Redox-based Resistive Random Access Memory
(ReRAM) for low-power and low-voltage applications. In principle, liquid-state
metallization cells could offer the same advantages for aqueous systems, such
as biomedical lab-on-a-chip devices, but robust resistive switching has not yet
been achieved in liquid electrolytes, where electrodeposition is notoriously
unstable to the formation of fractal dendrites. Here, the recently discovered
physics of shock electrodeposition are harnessed to stabilize aqueous copper
growth in polycarbonate nanopores, whose surfaces are modified with charged
polymers. Stable bipolar resistive switching is demonstrated for 500 cycles
with <10s retention times, prior to any optimization of the geometry or
materials. | 1608.07007v1 |
2017-02-17 | An alternative to the spin-coupled interface resistance for describing heat generation | Using a macroscopic approach, we studied theoretically the heat generation in
a typical spin valve with nonmagnetic spacer layer of finite thickness. Our
analysis shows that the spin-dependent heat generation cannot be interpreted as
the Joule heating of the spin-coupled interface resistance except for some
special segments. Moreover, the spin-coupled interface resistance can be
negative in certain situation, and thus its "Joule heating" should be
understood instead as the work done by the extra field in the ferromagnetic
layers and at the spin-selective interfaces. Effective resistances are proposed
as alternatives so that the spin-dependent heat generation can still be
expressed in a form resembling Joule's law. | 1702.05283v1 |
2017-09-27 | Kapitza thermal resistance across individual grain boundaries in graphene | We study heat transport across individual grain boundaries in suspended
monolayer graphene using extensive classical molecular dynamics (MD)
simulations. We construct bicrystalline graphene samples containing grain
boundaries with symmetric tilt angles using the two-dimensional phase field
crystal method and then relax the samples with MD. The corresponding Kapitza
resistances are then computed using nonequilibrium MD simulations. We find that
the Kapitza resistance depends strongly on the tilt angle and shows a clear
correlation with the average density of defects in a given grain boundary, but
is not strongly correlated with the grain boundary line tension. We also show
that quantum effects are significant in quantitative determination of the
Kapitza resistance by applying the mode-by-mode quantum correction to the
classical MD data. The corrected data are in good agreement with quantum
mechanical Landauer-B\"utticker calculations. | 1709.09529v1 |
2017-12-08 | A Novel Effect of Electron Spin Resonance on Electrical Resistivity | We extend the well known phenomenon of magnetoresistance (extra resistivity
of materials in transverse magnetic field) to a new and unexplored regime where
in addition to a transverse magnetic field, a transverse AC field of resonant
frequency is also applied. In a magnetic field, electron spin levels are Zeeman
split. In a resonant AC field, we uncover a new channel of momentum relaxation
in which electrons in upper Zeeman level can deexcite to lower Zeeman level by
generating spin fluctuation excitation in the lattice (similar to what happens
in Electron Spin Resonance (ESR) spectroscopy). An additional resistivity due
to this novel mechanism is predicted in which momentum randomization of Zeeman
split electrons happen via bosonic excitations (spin fluctuations). An order of
magnitude of this additional resistivity is calculated. The whole work is based
upon an extension of Einstein's derivation of equilibrium Planckian formula to
near equilibrium systems. | 1712.03062v1 |
2017-12-11 | Finite Size Effects in Highly Scaled Ruthenium Interconnects | Ru has been considered a candidate to replace Cu-based interconnects in VLSI
circuits. Here, a methodology is proposed to predict the resistivity of (Ru)
interconnects. First, the dependence of the Ru thin film resistivity on the
film thickness is modeled by the semiclassical Mayadas-Shatzkes (MS) approach.
The fitting parameters thus obtained are then used as input in a modified MS
model for nanowires to calculate wire resistivities. Predicted experimental
resistivities agreed within about 10%. The results further indicate that grain
boundary scattering was the dominant scattering mechanism in scaled Ru
interconnects. | 1712.03859v2 |
2017-12-23 | A micromechanics-based analytical solution for the effective thermal conductivity of composites with orthotropic matrices and interfacial thermal resistance | We obtained an analytical solution for the effective thermal conductivity of
composites composed of orthotropic matrices and spherical inhomogeneities with
interfacial thermal resistance using a micromechanics-based homogenization. We
derived the closed form of a modified Eshelby tensor as a function of the
interfacial thermal resistance. We then predicted the heat flux of a single
inhomogeneity in the infinite media based on the modified Eshelby tensor, which
was validated against the numerical results obtained from the finite element
analysis. Based on the modified Eshelby tensor and the localization tensor
accounting for the interfacial resistance, we derived an analytical expression
for the effective thermal conductivity tensor for the composites by a
mean-field approach called the Mori-Tanaka method. Our analytical prediction
matched very well with the effective thermal conductivity obtained from finite
element analysis with up to 10% inhomogeneity volume fraction. | 1712.08715v2 |
2019-09-06 | Strong suppression of the resistivity near the transition to superconductivity in narrow micro-bridges in external magnetic fields | We have investigated a series of superconducting bridges based on homogeneous
amorphous WSi and MoSi films, with bridge widths w ranging from 2 um to 1000 um
and film thicknesses d ~ 4-6 nm and 100 nm. Upon decreasing the bridge widths
below the respective Pearl lengths, we observe in all cases distinct changes in
the characteristics of the resistive transitions to superconductivity. For each
of the films, the resistivity curves R(B,T) separate at a well-defined and
field-dependent temperature T*(B) with decreasing the temperature, resulting in
a dramatic suppression of the resistivity and a sharpening of the transitions
with decreasing bridge width w. The associated excess conductivity in all the
bridges scales as 1/w, which may suggest the presence of a highly conducting
region that is dominating the electric transport in narrow bridges. We argue
that this effect can only be observed in materials with sufficiently weak
vortex pinning. | 1909.02915v2 |
2019-09-13 | Tunable resistivity exponents in the metallic phase of epitaxial nickelates | We report a detailed analysis of the electrical resistivity exponent of thin
films of NdNiO3 as a function of epitaxial strain. Strain-free thin-films show
a linear dependence of the resistivity vs temperature, consistent with a
classical Fermi gas ruled by electron-phonon interactions. In addition, the
apparent temperature exponent, n, can be tuned with the epitaxial strain
between n= 1 and n= 3. We discuss the critical role played by quenched random
disorder in the value of n. Our work shows that the assignment of
Fermi/Non-Fermi liquid behaviour based on experimentally obtained resistivity
exponents requires an in-depth analysis of the degree of disorder in the
material. | 1909.06256v1 |
2014-08-08 | Effects of Lifshitz Transition on Charge Transport in Magnetic Phases of Fe-Based Superconductors | The unusual temperature dependence of the resistivity and its in-plane
anisotropy observed in the Fe-based superconducting materials, particularly
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, has been a longstanding puzzle. Here we
consider the effect of impurity scattering on the temperature dependence of the
average resistivity within a simple two-band model of a dirty spin density wave
metal. The sharp drop in resistivity below the N\'eel temperature $T_N$ in the
parent compound can only be understood in terms of a Lifshitz transition
following Fermi surface reconstruction upon magnetic ordering. We show that the
observed resistivity anisotropy in this phase, arising from nematic defect
structures, is affected by the Lifshitz transition as well. | 1408.1933v3 |
2019-07-01 | A perspective on effective medium models of thermal conductivity in (ultra)nanocrystalline diamond films | Thermal conductivity of nanocrystalline and ultra-nanocrystalline films is
analyzed with effective medium theory (EMT) models. The existing EMT models use
the spherical inclusion approximation. Although this approximation works quite
well it is inconsistent, mostly with respect to the maximal packing of 74{\%},
which may be unrealistic for polycrystalline films. To check the consistency of
these models we devise an EMT model with arbitrarily shaped inclusions. We pick
the EMT model with cubic inclusions and we compare its results with the results
of the EMT model with spherical inclusions. It is found a very good agreement
between both calculations. This agreement is explained by general geometrical
arguments. We further employ these models to analyze thermal conductivity of
nanocrystalline and ultra-nanocrystalline diamond films. It is noticed that the
effective conductivity is strongly affected not only by the boundary Kapitza
resistance but also by intra-grain scattering for grain sizes below 100 nm.
Generally, both intra-grain conductivity and Kapitza resistance increase with
grain size. However, the effect of Kapitza resistance increase is negligible
due to the geometrical factor accompanying Kapitza resistance contribution to
the effective conductivity. | 1907.00753v1 |
2016-03-02 | Giant Frictional Drag in Double Bilayer Graphene Heterostructures | We study the frictional drag between carriers in two bilayer graphene flakes
separated by a 2 $-$ 5 nm thick hexagonal boron nitride dielectric. At
temperatures ($T$) lower than $\sim$ 10 K, we observe a large anomalous
negative drag emerging predominantly near the drag layer charge neutrality. The
anomalous drag resistivity increases dramatically with reducing {\it T}, and
becomes comparable to the layer resistivity at the lowest {\it T} = 1.5 K. At
low $T$ the drag resistivity exhibits a breakdown of layer reciprocity. A
comparison of the drag resistivity and the drag layer Peltier coefficient
suggests a thermoelectric origin of this anomalous drag. | 1603.00757v1 |
2017-04-05 | Stateful characterization of resistive switching TiO2 with electron beam induced currents | Metal oxide resistive switches are increasingly important as possible
artificial synapses in next generation neuromorphic networks. Nevertheless,
there is still no codified set of tools for studying properties of the devices.
To this end, we demonstrate electron beam induced current measurements as a
powerful method to monitor the development of local resistive switching in TiO2
based devices. By comparing beam-energy dependent electron beam induced
currents with Monte Carlo simulations of the energy absorption in different
device layers, it is possible to deconstruct the origins of filament image
formation and relate this to both morphological changes and the state of the
switch. By clarifying the contrast mechanisms in electron beam induced current
microscopy it is possible to gain new insights into the scaling of the
resistive switching phenomenon and observe the formation of a current leakage
region around the switching filament. Additionally, analysis of symmetric
device structures reveals propagating polarization domains. | 1704.01475v2 |
2017-08-31 | Antiferromagnetic anisotropy determination by spin Hall magnetoresistance | An electric method for measuring magnetic anisotropy in antiferromagnetic
insulators (AFIs) is proposed. When a metallic film with strong spin-orbit
interactions, e.g., platinum (Pt), is deposited on an AFI, its resistance
should be affected by the direction of the AFI N eel vector due to the spin
Hall magnetoresistance (SMR). Accordingly, the direction of the AFI N eel
vector, which is affected by both the external magnetic field and the magnetic
anisotropy, is reflected in resistance of Pt. The magnetic field angle
dependence of the resistance of Pt on AFI is calculated by consider- ing the
SMR, which indicates that the antiferromagnetic anisotropy can be obtained
experimentally by monitoring the Pt resistance in strong magnetic fields.
Calculations are performed for realistic systems such as Pt/Cr2O3, Pt/NiO, and
Pt/CoO. | 1708.09564v1 |
2019-08-12 | Graphene-based spinmechatronic valve | Interlayer twist between van der Waals graphene crystals led to the discovery
of superconducting and insulating states near the magic angle. In this work, we
exploit this mechanical degree of freedom by twisting the graphene middle layer
in a trilayer graphene spacer between two metallic lead (Magnetic and
nonmagnetic). A large difference in conductance is found depending on the angle
of twist between the middle layer graphene and the ones at the interface this
difference, called twisting resistance, reach more than 1000% in the
non-magnetic Cu case. For the magnetic Ni case, the magneto-resistance
decreases and the difference in conductance between twisted and not twisted
depends strongly on the relative magnetization configuration. For the parallel
configuration, the twisting resistance is about -40%, while for the
anti-parallel configuration it can reach up to 130%. Furthermore, we show that
the twisting resistance can be enhanced by inserting a thin Cu layer at the
interface of Ni/graphene where it reaches a value of 200% and 1600% for
parallel and antiparallel configurations, respectively. These finding could
pave the way toward the integration of 2D materials on novel spinmechatronics
based devices. | 1908.04076v1 |
2019-08-15 | Observation of Highly Nonlinear Resistive Switching of Al2O3/TiO2-x Memristors at Cryogenic Temperature (1.5 K) | In this work, we investigate the behavior of Al2O3/TiO2-x cross-point
memristors in cryogenic environment. We report successful resistive switching
of memristor devices from 300 K down to 1.5 K. The I-V curves exhibit negative
differential resistance effects between 130 and 1.5 K, attributed to a
metal-insulator transition (MIT) of the Ti4O7 conductive filament. The
resulting highly nonlinear behavior is associated to a maximum ION/IOFF ratio
of 84 at 1.5 K, paving the way to selector-free cryogenic passive crossbars.
Finally, temperature-dependant thermal activation energies related to the
conductance at low bias (20 mV) are extracted for memristors in low resistance
state, suggesting hopping-type conduction mechanisms. | 1908.05545v4 |
2018-07-28 | Anomalous Hall Effect and Spin Fluctuations in Ionic Liquid Gated SrCoO$_3$ Thin Films | The recent realization of epitaxial SrCoO$_3$ thin films has triggered a
renewed interest in their electronic, magnetic, and ionic properties. Here we
uncover several unusual magneto-transport properties of this compound,
suggesting that it hosts persistent spin fluctuation down to low temperatures.
We achieve the metallic SrCoO$_3$ with record-low resistivity from insulating
SrCoO$_{2.5}$ by the ionic liquid gating. We find a linear relationship between
the anomalous Hall resistivity and the longitudinal resistivity, which cannot
be accounted for by the conventional mechanisms. We theoretically propose that
the impurity induced chiral spin fluctuation gives rise to such a dependence.
The existence of spin fluctuation manifests itself as negatively enhanced
magneto-resistance of SrCoO$_3$ when the temperature approaches zero. Our study
brings further insight into the unique spin state of SrCoO$_3$ and unveils a
novel skew scattering mechanism for the anomalous Hall effect. | 1807.10877v1 |
2019-01-14 | Phonon and electronic structures and resistance of layered electride Ca2N: DFT calculations | The phonon and electronic properties, the Eliashberg function and the
temperature dependence of resistance of electride Ca2N are investigated by the
DFT-LDA plane-wave method. The phonon dispersion, the partial phonon density of
states and the atomic eigenvectors of zero-center phonons are studied. The
electronic band dispersion and partial density of states conclude that Ca2N is
a metal and the Ca 3p, 4s and N 2p orbitals are hybridized. For the analysis of
an electron - phonon interaction (EPI) and its contribution to resistance the
Eliashberg function was calculated and a temperature dependence of resistance
caused EPI was found. The present results are in good agreement with experiment
data. | 1901.04594v1 |
2020-05-22 | VoteAgain: A scalable coercion-resistant voting system | The strongest threat model for voting systems considers coercion resistance:
protection against coercers that force voters to modify their votes, or to
abstain. Existing remote voting systems either do not provide this property;
require an expensive tallying phase; or burden users with the need to store
cryptographic key material and with the responsibility to deceive their
coercers. We propose VoteAgain, a scalable voting scheme that relies on the
revoting paradigm to provide coercion resistance. VoteAgain uses a novel
deterministic ballot padding mechanism to ensure that coercers cannot see
whether a vote has been replaced. This mechanism ensures tallies take
quasilinear time, making VoteAgain the first revoting scheme that can handle
elections with millions of voters. We prove that VoteAgain provides ballot
privacy, coercion resistance, and verifiability; and we demonstrate its
scalability using a prototype implementation of all cryptographic primitives. | 2005.11189v3 |
2020-06-06 | Radiative Resistance at The Nano-scale: Thermal Barrier | In present article the radiative thermal current and radiative resistance are
introduced and investigated in a system of parallel slabs. The system is placed
in an environment with a constant temperature and subjected to a constant
temperature gradient, which causes a radiative energy flux through the system.
We have calculated the steady-state temperatures profile of the system,
assuming that the material and thickness of the middle slab could be different
from the other slabs. We propose the exact formulation for calculating the
thermal current and thermal resistances in both linear and nonlinear regimes.
According to our results, the middle slab acts as a thermal barrier and
depending on the width of this barrier, an extreme thermal isolation is
achievable. Simulation results indicate that the thermal resistance of the
barrier is an increasing function of the thickness for near-field separation
distances but it is virtually insensitive to the barrier width in far field
regime. The long range character of the radiative heat transfer, which occurs
in system with identical slabs is also discussed. | 2006.03842v4 |
2020-08-16 | Strange metal behavior of the Hall angle in twisted bilayer graphene | Twisted bilayer graphene (TBG) with interlayer twist angles near the magic
angle $\approx 1.08^{\circ}$ hosts flat bands and exhibits correlated states
including Mott-like insulators, superconductivity and magnetism. Here we report
combined temperature-dependent transport measurements of the longitudinal and
Hall resistivities in close to magic-angle TBG. While the observed longitudinal
resistivity follows linear temperature $T$ dependence consistent with previous
reports, the Hall resistance shows an anomalous $T$ dependence with the
cotangent of the Hall angle cot $\Theta{_H} \propto T^2$. Boltzmann theory for
quasiparticle transport predicts that both the resistivity and cot $\Theta{_H}$
should have the same $T$ dependence, contradicting the observed behavior. This
failure of quasiparticle-based theories is reminiscent of other correlated
strange metals such as cuprates. | 2008.06907v1 |
2020-08-23 | Negative resistance state in superconducting NbSe$_2$ induced by surface acoustic waves | We report a negative resistance, namely, a voltage drop along the opposite
direction of a current flow, in the superconducting gap of NbSe$_2$ thin films
under the irradiation of surface acoustic waves (SAWs). The amplitude of the
negative resistance becomes larger by increasing the SAW power and decreasing
temperature. As one possible scenario, we propose that soliton-antisoliton
pairs in the charge density wave of NbSe$_2$ modulated by the SAW serve as a
time-dependent capacitance in the superconducting state, leading to the dc
negative resistance. The present experimental result would provide a previously
unexplored way to examine nonequilibrium manipulation of the superconductivity. | 2008.09948v1 |
2020-11-17 | Effect of Substrate Roughness on Oxidation Resistance of an Aluminized Ni-Base Superalloy | In the present work, it is shown that the surface preparation method used on
two Ni-based superalloys prior to aluminizing chemical vapor deposition (CVD)
is one of the most important factors determining the oxidation resistance of
aluminized Ni-based superalloys. It was found that grit blasting the substrate
surface negatively affects the oxidation resistance of the aluminized coatings.
For grit blasted and aluminized IN 625, a thicker outer NiAl coating was formed
compared to that of IN 738. In contrast, no effect on NiAl coating thickness
was found for grit blasted and aluminized IN 738. However, a thicker
interdiffusion zone (IDZ) was observed. It was shown that the systems with
grit-blasted surfaces reveal worse oxidation resistance during thermal shock
tests, namely, a higher mass loss was observed for both grit blasted and
aluminized alloys, as compared to ground and aluminized alloys. A possible
reason for this effect of remaining alumina particles originating from surface
grit blasting on the diffusion processes and stress distribution at the
coating/substrate is proposed. | 2011.08921v1 |
2021-04-23 | Microstructure and wear resistance of Fe-Cr-C-Mo-V-Ti-N hardfacing layers | In this paper, to improve wear resistance of components such as screws under
severe friction-wear, Fe-Cr-C-Mo-V-Ti-N hardfacing coatings were further
developed. The hardfacing coatings were acquired by shielded manual arc welding
(SMAW) method. The ferroalloys added into the coating flux of the hardfaced
electrode were jointly nitrided. The microstructure of the coatings was carried
out using X-ray diffraction(XRD), optical microscope(OM), field emission
scanning electron microscope (FESEM) and energy dispersive Xray spectrometry
(EDS). In addition, FactSage 7.0 software was employed to calculate the
equilibrium phase diagram of the hardfacings. The wear resistance was performed
on a pin-on-disc machine. The Fe-Cr-C- Mo-V-Ti-N hardfacings exhibited higher
wear resistance than cladding layer without nitrides. | 2104.11402v1 |
2021-05-27 | Systematic manipulation of the surface conductivity of SmB$_6$ | We show that the resistivity plateau of SmB$_6$ at low temperature, typically
taken as a hallmark of its conducting surface state, can systematically be
influenced by different surface treatments. We investigate the effect of
inflicting an increasing number of hand-made scratches and microscopically
defined focused ion beam-cut trenches on the surfaces of flux-grown
Sm$_{1-x}$Gd$_x$B$_6$ with $x =$ 0, 0.0002. Both treatments increase the
resistance of the low-temperature plateau, whereas the bulk resistance at
higher temperature largely remains unaffected. Notably, the temperature at
which the resistance deviates from the thermally activated behavior decreases
with cumulative surface damage. These features are more pronounced for the
focused ion beam treated samples, with the difference likely being related to
the absence of microscopic defects like subsurface cracks. Therefore, our
method presents a systematic way of controlling the surface conductance. | 2105.13057v1 |
2021-06-23 | A new symmetry-based extraction method of Schottky diode parameters from resistance-compensated I-V characteristics | We present a novel resistance-compensated I-V method to extract the series
resistance, ideality factor, barrier height and built-in potential of a
metal-semiconductor diode. We show that a reduced equation arises from a unique
but hitherto unreported symmetry in the Schottky equation when it is written as
an ordinary differential equation. In spite of the intense mathematical
justification, we show how this new equation is directly applicable to an
empirical data set through a simple algorithm. We test the method on a new
Al/p-Si/Bi$_2$Se$_3$/Al Schottky diode and compare it with the Cheung-Cheung
method on the same data. The series resistance was found to change
exponentially with applied bias with a rate constant that depends on the
incident illumination. The barrier height decreased with bias but was
independent of the incident illumination. The trends in the results of the
method agree strongly with the literature and may yield more accurate diode
parameters compared to other electrical methods. | 2106.12324v1 |
2021-08-19 | Influence of charged walls and defects on DC resistivity and dielectric relaxation in Cu-Cl boracite | Charged domain walls form spontaneously in Cu-Cl boracite on cooling through
the phase transition. These walls exhibit changed conductivity compared to the
bulk and motion consistent with the existence of negative capacitance. Here, we
present the dielectric permittivity and DC resistivity of bulk Cu-Cl boracite
as a function of temperature (-140 {\deg}C to 150 {\deg}C) and frequency (1 mHz
to 10 MHz). The thermal behaviour of the two observed dielectric relaxations
and the DC resistivity is discussed. We propose that the relaxations can be
explained by the existence of point defects, most likely local complexes
created by a change of valence of Cu and accompanying oxygen vacancies. In
addition, the sudden change in resistivity seen at the phase transition
suggests that conductive domain walls contribute significantly to the
conductivity in the ferroelectric phase. | 2108.08582v2 |
2022-01-10 | Designs for programmable quantum resistance standards based on epitaxial graphene p-n junctions | We report the fabrication and measurement of top gated epitaxial graphene p-n
junctions where exfoliated hexagonal boron nitride (h-BN) is used as the gate
dielectric. The four-terminal longitudinal resistance across a single junction
is well quantized at the von Klitzing constant R_K with a relative uncertainty
of 10-7. After the exploration of numerous parameter spaces, we summarize the
conditions upon which these devices could function as potential resistance
standards. Furthermore, we offer designs of programmable electrical resistance
standards over six orders of magnitude by using external gating. | 2201.03621v1 |
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