publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2009-02-10 | Spontaneous and low-field magnetoimpedance in La0.7Sr0.3CoO3 and La1-xSrxMnO3 (x = 0.18-0.5) | We report ac electrical transport in La0.7Sr0.3CoO3 and La1-xSrxMnO3 (x =
0.18- 0.5) as a function of temperature and frequency in H = 0 and 60 mT. Both
resistive (R) and reactive (X) components of impedance (Z = R+jX) were
measured. It is shown that a smooth decrease of the resistance around the Curie
temperautre in La0.7Sr0.3CoO3 transforms into an abrupt increase followed
closely by a peak in R with increasing frequency. Similar behavior in R was
also found in metallic compositions of the La-Sr-MnO3 series. The observed
anomaly at TC is suppressed by a small dc magnetic field of H = 60 mT which
rrsults in a huge ac magnetoreistance (= 30 % in manganite and =7 % in
cobaltite at f = 2 MHz). The anomaly in R in zero field is also accompanied by
a sudden incrases of X. While the ac magnetoresitance is negative as a function
of field from 100 Hz to 30 MHz, we show that the sign of X changes and a new
double peak structure develops in X for frequencies above 15 MHz. | 0902.1780v1 |
2009-04-24 | Evolution of orbital phases with particle size in nanoscale stoichiometric LaMnO3 | The thermodynamically stable long-range orbital order in bulk LaMnO3 becomes
metastable at nanoscale around a critical particle size d_C~20 nm. The orbital
order-disorder transition switches from reversible to irreversible at d_C while
the resistance in the orbital ordered state decays by 2-4% over a time scale of
~3000s. At well below d_C, of course, a stable orbital disordered phase
emerges. The orthorhombic distortion of the underlying crystallographic
structure (space group Pbnm) decreases systematically with the decrease in
particle size and at far below d_C (e.g., at ~10 nm), the structure becomes
cubic (space group Pm-3m). Using the crystallographic and electrical resistance
data, a phase diagram has been constructed showing the evolution of different
orbital phases as a function of particle size across ~10 nm to bulk for
stoichiometric LaMnO3. | 0904.3878v3 |
2009-06-04 | Sensitivity of Ag/Al Interface Specific Resistances to Interfacial Intermixing | We have measured an Ag/Al interface specific resistance, 2AR(Ag/Al)(111) =
1.4 fOhm-m^2, that is twice that predicted for a perfect interface, 50% larger
than for a 2 ML 50%-50% alloy, and even larger than our newly predicted 1.3
fOhmm^2 for a 4 ML 50%-50% alloy. Such a large value of 2ARAg/Al(111) confirms
a predicted sensitivity to interfacial disorder and suggests an interface
greater than or equal to 4 ML thick. From our calculations, a predicted
anisotropy ratio, 2AR(Ag/Al)(001)/2AR(Ag/Al)(111), of more then 4 for a perfect
interface, should be reduced to less than 2 for a 4 ML interface, making it
harder to detect any such anisotropy. | 0906.0934v1 |
2009-06-04 | Perpendicular-current Studies of Electron Transport Across Metal/Metal Interfaces | We review what we have learned about the scattering of electrons by the
interfaces between two different metals (M1/M2) in the
current-perpendicular-to-plane (CPP) geometry. In this geometry, the intrinsic
quantity is the specific resistance, AR, the product of the area through which
the CPP current flows times the CPP resistance. We describe results for both
non-magnetic/non-magnetic (N1/N2) and ferromagnetic/non-magnetic (F/N) pairs.
We focus especially upon cases where M1/M2 are lattice matched (i.e., have the
same crystal structure and the same lattice parameters to within ~ 1%), because
in these cases no-free-parameter calculations of 2AR agree surprisingly well
with measured values. But we also list and briefly discuss cases where M1/M2
are not lattice matched, either having different crystal structures, or lattice
parameters that differ by several percent. The published calculations of 2AR in
these latter cases do not agree so well with measured values. | 0906.0936v1 |
2009-06-26 | Upper bound for the conductivity of nanotube networks | Films composed of nanotube networks have their conductivities regulated by
the junction resistances formed between tubes. Conductivity values are enhanced
by lower junction resistances but should reach a maximum that is limited by the
network morphology. By considering ideal ballistic-like contacts between
nanotubes we use the Kubo formalism to calculate the upper bound for the
conductivity of such films and show how it depends on the nanotube
concentration as well as on their aspect ratio. Highest measured conductivities
reported so far are approaching this limiting value, suggesting that further
progress lies with nanowires other than nanotubes. | 0906.4906v2 |
2009-06-29 | Upper critical fields of the 11-system iron-chalcogenide superconductor FeSe$_{0.25}$Te$_{0.75}$ | We have performed electrical resistivity measurements of a polycrystalline
sample of FeSe$_{0.25}$Te$_{0.75}$, which exhibits superconductivity at $T_{\rm
c} \sim 14$ K, in magnetic fields up to 55 T to determine the upper critical
field $\mu_{0}H_{\rm c2}$. In this compound, very large slopes of
$\mu_{0}H_{\rm c2}$ at the onset, the mid-point, the zero-resistivity
temperatures on superconductivity are determined to be -13.7, -10.1, and -6.9
T/K, respectively. The observed $\mu_{0}H_{\rm c2}(T)$s of this compound are
considerably smaller than those expected from the Werthamer-Helfand-Hohenberg
model, manifesting the Pauli limiting behavior. These results suggest that this
compound has a large Maki parameter, but it is smaller than that calculated for
a weak-coupling superconductor, indicating a large superconducting gap of this
compound as a strong-coupling superconductor. | 0906.5248v1 |
2009-07-17 | Phase diagram of CeFeAs$_{1-x}$P$_{x}$O obtained from electric resistivity, magnetization, and specific heat measurements | We performed a systematic study on the properties of CeFeAs$_{1-x}$P$_{x}$O
($0\leq x\leq 1$) by electrical resistivity, magnetization and specific heat
measurements. The c-axis lattice constant decreases significantly with
increasing P content, suggesting a remarkable chemical pressure. The Fe-3d
electrons show the enhanced metallic behavior upon P-doping and undergo a
magnetic quantum phase transition around $x \approx 0.4$. Meanwhile, the Ce-4f
electrons develop a ferromagnetic order near the same doping level. The
ferromagnetic order is vanishingly small around $x=0.9$. The data suggest a
heavy-fermion-like behavior as $x\geq 0.95$. No superconductivity is observed
down to 2 K. Our results show the ferromagnetic ordered state as an
intermediate phase intruding between the antiferromagnetic bad metal and the
nonmagnetic heavy fermion metal and support the cerium-containing iron
pnictides as a unique layered Kondo lattice system. | 0907.2961v2 |
2009-07-31 | Top and side gated epitaxial graphene field effect transistors | Three types of first generation epitaxial graphene field effect transistors
(FET) are presented and their relative merits are discussed. Graphene is
epitaxially grown on both the carbon and silicon faces of hexagonal silicon
carbide and patterned with electron beam lithography. The channels have a Hall
bar geometry to facilitate magnetoresistance measurements. FETs patterned on
the Si-face exhibit off-to-on channel resistance ratios that exceed 30. C-face
FETs have lower off-to-on resistance ratios, but their mobilities (up to 5000
cm2/Vs) are much larger than that for Si-face transistors. Initial
investigations into all-graphene side gate FET structures are promising. | 0908.0017v1 |
2009-08-02 | Spin-dependent transport in nanocomposite C:Co films | The magneto-transport properties of nanocomposite C:Co (15 and 40 at.% Co)
thin films are investigated. The films were grown by ion beam co-sputtering on
thermally oxidized silicon substrates in the temperature range from 200 to 500
degC. Two major effects are reported: (i) a large anomalous Hall effect
amounting to 2 \mu ohm cm, and (ii) a negative magnetoresistance. Both the
field-dependent resistivity and Hall resistivity curves coincide with the
rescaled magnetization curves, a finding that is consistent with spin-dependent
transport. These findings suggest that C:Co nanocomposites are promising
candidates for carbon-based Hall sensors and spintronic devices. | 0908.0127v1 |
2009-09-16 | Superconductivity at 39 K in New Iron Pnictide Oxide (Fe2As2)(Sr4(Mg,Ti)2O6) | We have discovered a new iron pnictide oxide superconductor
(Fe2As2)(Sr4(Mg,Ti)2O6). This material is isostructual with (Fe2As2)(Sr4M2O6)
(M = Sc, Cr), which was found in our previous study. The structure of this
compound is tetragonal with a space group of P4/nmm and consists of the
anti-fluorite type FeAs and perovskite-type blocking layers. The lattice
constants are a = 3.935 A and c = 15.952 A for (Fe2As2)(Sr4MgTiO6). In both
magnetization and resistivity measurements, this compound exhibits
superconductivity below 10 K. Moreover, ratio of Mg and Ti in this compound can
be changed toward Ti-rich composition. (Fe2As2)(Sr4Mg1-xTi1+xO6) phase is
obtained at 0 < x as a main phase, and Tc and superconducting volume fraction
increase with increasing x. The highest Tc(onset) was confirmed at 39 K for x =
0.6 in resistivity measurement. | 0909.2945v3 |
2009-09-25 | Electrical, magnetic, magnetodielectric and magnetoabsorption studies in multiferroic GaFeO3 | We report electrical, magnetic, magnetodielectric and magnetoabsorption
properties of a polycrystalline GaFeO3. The resistivity measurement shows that
the sample is highly insulating below 200 K and the resistivity above 200 K
obey the Arrhenius law with an activation energy of Ea = 0.67 eV. An anomaly
occurs in the temperature dependence of permittivity (e) near the ferrimagnetic
transition temperature (TC = 228 K) in a zero magnetic field and it is
suppressed under H = 60 mT which indicates a possible magnetoelectric coupling
in GaFeO3 with a fractional change of de/e = -1.8% at 60 mT around TC. The
coercivity (HC) of the sample increases dramatically with lowering temperature
below 200 K from 0.1 T at 200 K to 0.9 T at 5 K. Magnetoabsorption was studied
with a LC resonance technique and we found a close correlation between the
shift in the resonance frequency due to applied magnetic field and the coercive
field measured using dc magnetization measurements. Our results obtained with
multiple techniques suggest that GaFeO3 is an interesting ferrimagnet with
potential applications in future multiferroic devices. | 0909.4609v1 |
2009-10-11 | Anomalous Hall resistance in Ge:Mn systems with low Mn concentrations | Taking Mn doped Germanium as an example, we evoke the consideration of a
two-band-like conduction in diluted ferromagnetic semiconductor (FMS). The main
argument for claiming Ge:Mn as a FMS is the occurrence of the anomalous Hall
effect (AHE). Usually, the reported AHE (1) is observable at temperatures above
10 K, (2) exhibits no hysteresis, and (3) changes the sign of slope. We
observed a similar Hall resistance in Mn implanted Ge with the Mn concentration
as low as 0.004%. We show that the puzzling AHE features can be explained by
considering a two-band-like conduction in Ge:Mn. | 0910.1981v1 |
2009-10-20 | Sharp fall of electrical resistance for a small application of magnetic field on a metastable form of a compound, Tb5Si3, under pressure | We report an unusual sensitivity of electrical resistivity (rho) to an
application of a small magnetic field in an intermetallic compound, Tb5Si3,
under pressure. In this compound, there is a magnetic field-induced first-order
magnetic transition at 1.8 K. Under pressure, there is a metastable magnetic
phase after reducing the field to zero. This metastable phase is relatively of
higher rho and interestingly a small magnetic field (less than 2 kOe) in the
reverse direction results in a sharp fall of rho to restore virgin state rho.
The present finding could be relevant to spintronic applications. | 0910.3794v1 |
2009-11-11 | Neutron powder diffraction investigation of the structural and magnetic properties of (La1-yYy)FeAsO | The structural, magnetic and resistive properties of (La1-yYy)FeAsO compounds
(y = 0.10, 0.20, 0.30) have been investigated by means of X-ray and neutron
powder diffraction as well as by resistivity measurements. The temperatures at
which the structural transition from tetragonal to orthorhombic and the
magnetic ordering take place progressively reduce by similar amounts with
increasing Y substitution on account of the progressive chemical pressure
increase. We propose that the structural transition could be originated by a
cooperative Jahn-Teller distortion involving the alignment of the fully
occupied Fe 3d(z2) orbitals in the Fe plane along the y axis, leading to the
branching of the cell parameters a and b. The magnetic structure develops after
the occurrence of the structural transition, but before its completion. | 0911.2153v1 |
2009-11-23 | Magnetic field and contact resistance dependence of non-local charge imbalance | Crossed Andreev reflection (CAR) in metallic nanostructures, a possible basis
for solid-state electron entangler devices, is usually investigated by
detecting non-local voltages in multi-terminal superconductor/normal metal
devices. This task is difficult because other subgap processes may mask the
effects of CAR. One of these processes is the generation of charge imbalance
(CI) and the diffusion of non-equilibrium quasi-particles in the
superconductor. Here we demonstrate a characteristic dependence of non-local CI
on a magnetic field applied parallel to the superconducting wire, which can be
understood by a generalization of the standard description of CI to non-local
experiments. These results can be used to distinguish CAR and CI and to extract
CI relaxation times in superconducting nanostructures. In addition, we
investigate the dependence of non-local CI on the resistance of the injector
and detector contacts and demonstrate a quantitative agreement with a recent
theory using only material and junction characteristics extracted from separate
direct measurements. | 0911.4427v1 |
2009-12-16 | Cooling dynamics and thermal interface resistance of glass-embedded metal nanoparticles | The cooling dynamics of glass-embedded noble metal nanoparticles with
diameters ranging from 4 to 26 nm were studied using ultrafast pump-probe
spectroscopy. Measurements were performed probing away from the surface plasmon
resonance of the nanoparticles to avoid spurious effects due to glass heating
around the particle. In these conditions, the time-domain data reflect the
cooling kinetics of the nanoparticle. Cooling dynamics are shown to be
controlled by both thermal resistance at the nanoparticule?glass interface, and
heat diffusion in the glass matrix. Moreover, the interface conductances are
deduced from the experiments and found to be correlated to the acoustic
impedance mismatch at the metal/glass interface. | 0912.3058v1 |
2009-12-29 | Interplay of bulk and interface effects in the electric-field driven transition in magnetite | Contact effects in devices incorporating strongly-correlated electronic
materials are comparatively unexplored. We have investigated the
electrically-driven phase transition in magnetite (100) thin films by
four-terminal methods. In the lateral configuration, the channel length is less
than 2 $\mu$m, and voltage-probe wires $\sim$100 nm in width are directly
patterned within the channel. Multilead measurements quantitatively separate
the contributions of each electrode interface and the magnetite channel. We
demonstrate that on the onset of the transition contact resistances at both
source and drain electrodes and the resistance of magnetite channel decrease
abruptly. Temperature dependent electrical measurements below the Verwey
temperature indicate thermally activated transport over the charge gap. The
behavior of the magnetite system at a transition point is consistent with a
theoretically predicted transition mechanism of charge gap closure by electric
field. | 0912.5374v1 |
2010-01-08 | Low-magnetic-field control of dielectric constant at room temperature realized in Ba0.5Sr1.5Zn2Fe12O22 | We show that room temperature resistivity of Ba0.5Sr1.5Zn2Fe12O22 single
crystals increases by more than three orders of magnitude upon being subjected
to optimized heat treatments. The increase in the resistivity allows the
determination of magnetic field (H)-induced ferroelectric phase boundaries up
to 310 K through the measurements of dielectric constant at a frequency of 10
MHz. Between 280 and 310 K, the dielectric constant curve shows a peak centered
at zero magnetic field and thereafter decreases monotonically up to 0.1 T,
exhibiting a magnetodielectric effect of 1.1%. This effect is ascribed to the
realization of magnetic field-induced ferroelectricity at an H value of less
than 0.1 T near room temperature. Comparison between electric and magnetic
phase diagrams in wide temperature- and field-windows suggests that the
magnetic field for inducing ferroelectricity has decreased near its helical
spin ordering temperature around 315 K due to the reduction of spin anisotropy
in Ba0.5Sr1.5Zn2Fe12O22. | 1001.1319v1 |
2010-03-05 | Weak superconducting fluctuations and small anisotropy of the upper critical fields in an Fe1.05Te0.85Se0.15 single crystal | We have investigated the temperature dependence of the resistive upper
critical fields ($\mu_{0}H_{\rm c2}(T)$) for an
Fe$_{1.05}$Te$_{0.85}$Se$_{0.15}$ single crystal, which exhibit
superconductivity at $T_{\rm c} \sim 14 K, in magnetic fields of up to 55 T.
Two-dimensional feature and superconducting fluctuations of the samples are
found to be weak, because the resistive broadening effect on applied magnetic
fields of up to 14 T is small. The Pauli paramagnetic effect is obviously
evidenced by the strong suppression of the $\mu_{0}H_{\rm c2}^{ab}(T)$ ($H
\parallel ab$) curve and nearly isotropic $\mu_{0}H_{\rm c2}(0) \approx 47 T is
seen for both $H \parallel ab$ and $H \parallel c$. This fact is almost
identical to the results of Fe$_{1+y}$Te$_{0.6}$Se$_{0.4}$ single crystals
reported previously. We have discussed that the small anisotropy of the upper
critical field at low temperatures in Fe$_{1+y}$(Te,Se) systems against the
variation of the Te/Se ratio. | 1003.1171v3 |
2010-03-19 | Lateral Spin Injection in Germanium Nanowires | Electrical injection of spin-polarized electrons into a semiconductor, large
spin diffusion length, and an integration friendly platform are desirable
ingredients for spin-based devices. Here we demonstrate lateral spin injection
and detection in germanium nanowires, by using ferromagnetic metal contacts and
tunnel barriers for contact resistance engineering. Using data measured from
over 80 samples, we map out the contact resistance window for which lateral
spin transport is observed, manifestly showing the conductivity matching
required for spin injection. Our analysis, based on the spin diffusion theory,
indicates that the spin diffusion length is larger than 100 {\mu}m in germanium
nanowires at 4.2 K. | 1003.3787v2 |
2010-03-28 | Scanning Gate Microscopy on Graphene: Charge Inhomogeneity and Extrinsic Doping | We have performed scanning gate microscopy (SGM) on graphene field effect
transistors (GFET), using a biased metallic nanowire coated with a dielectric
layer as a contact mode tip and local top gate. Electrical transport through
graphene at various back gate voltages is monitored as a function of tip
voltage and tip position. Near the Dirac point, the dependence of graphene
resistance on tip voltage shows a significant variation with tip position. SGM
imaging reveals mesoscopic domains of electron-doped and hole-doped regions.
Our measurements indicate a substantial spatial fluctuation (on the order of
10^12/cm^2) in the carrier density in graphene due to extrinsic local doping.
Important sources for such doping found in our samples include metal contacts,
edges of graphene, structural defects, and resist residues. | 1003.5404v1 |
2010-04-07 | Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin injection device | The nonlocal spin resistance is measured as a function of temperature in a
Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin
injection, the spin resistance is observed up to room temperature and decays
exponentially with temperature at a rate of 0.018\,K$^{-1}$. Post-growth
annealing at 440\,K increases the spin signal at low temperatures, but the
decay rate also increases to 0.030\,K$^{-1}$. From measurements of the
diffusion constant and the spin lifetime in the GaAs channel, we conclude that
sample annealing modifies the temperature dependence of the spin transfer
efficiency at injection and detection contacts. Surprisingly, the spin transfer
efficiency increases in samples that exhibit minority-spin injection. | 1004.1034v1 |
2010-05-01 | Reversible Fluorination of Graphene: towards a Two-Dimensional Wide Bandgap Semiconductor | We report the synthesis and evidence of graphene fluoride, a two-dimensional
wide bandgap semiconductor derived from graphene. Graphene fluoride exhibits
hexagonal crystalline order and strongly insulating behavior with resistance
exceeding 10 G$\Omega$ at room temperature. Electron transport in graphene
fluoride is well described by variable-range hopping in two dimensions due to
the presence of localized states in the band gap. Graphene obtained through the
reduction of graphene fluoride is highly conductive, exhibiting a resistivity
of less than 100 k$\Omega$ at room temperature. Our approach provides a new
path to reversibly engineer the band structure and conductivity of graphene for
electronic and optical applications. | 1005.0113v1 |
2010-07-15 | Quantum Hall Resistance Overshoot in 2-Dimensional Electron Gases - Theory and Experiment | We present a systematical experimental investigation of an unusual transport
phenomenon observed in two dimensional electron gases in Si/SiGe
heterostructures under integer quantum Hall effect (IQHE) conditions. This
phenomenon emerges under specific experimental conditions and in different
material systems. It is commonly referred to as Hall resistance overshoot,
however, lacks a consistent explanation so far. Based on our experimental
findings we are able to develop a model that accounts for all of our
observations in the framework of a screening theory for the IQHE. Within this
model the origin of the overshoot is attributed to a transport regime where
current is confined to co-existing evanescent incompressible strips of
different filling factors. | 1007.2586v1 |
2010-08-10 | Transition from a ferromagnetic insulating to a ferromagnetic metallic state in nanoparticles of Nd0.8Sr0.2MnO3 : Study of the electronic - and magneto - transport properties | A detailed investigation of the electronic - and magneto - transport
properties of Nd0.8Sr0.2MnO3 with the variation of grain size (down to 42 nm)
is presented here. Interestingly, we observe that the ferromagnetic insulating
state is suppressed and a metallic state is stabilized as the grain size of the
sample is reduced. As a result, metal insulator transition is observed in this
low doped manganite which is insulating in nature in its bulk form.
Destabilization of polaronic order in the ferromagnetic insulating state due to
enhanced surface disorder on grain size reduction has been attributed to this
effect. A phenomenological model has been proposed to represent the concept of
destabilization of polaron formation in the surface region of the nano grains.
Resistivity and magnetoresistance data have been carefully analyzed employing
different suitable models. Electrical third harmonic resistance has been
measured to directly probe the electrical nonlinearity in the samples. | 1008.1693v1 |
2010-08-18 | A New Strained-Silicon Channel Trench-gate Power MOSFET: Design and Analysis | In this paper, we propose a new trench power MOSFET with strained Si channel
that provides lower on resistance than the conventional trench MOSFET. Using a
20% Ge mole fraction in the Si1-xGex body with a compositionally graded
Si1-xGex buffer in the drift region enables us to create strain in the channel
along with graded strain in the accumulation region. As a result, the proposed
structure exhibits 40% enhancement in current drivability, 28% reduction in the
on-resistance and 72% improvement in peak transconductance at the cost of only
12% reduction in the breakdown voltage when compared to the conventional trench
gate MOSFET. Furthermore, the graded strained accumulation region supports the
confinement of carriers near the trench sidewalls improving the field
distribution in the mesa structure useful for a better damage immunity during
inductive switching. | 1008.3019v1 |
2010-08-24 | Dominant role of impurity scattering over crystalline anisotropy for magnetotransport properties in the quasi-1D Hollandite Ba1.2Rh8O16 | Angular magnetotransport measurements have been performed to tackle the
origin of the magnetoresistance in the quasi-1D Hollandite Ba1.2Rh8O16. Three
samples of different impurities amount were measured. We observe that the low
temperature resistivity upturn is not due to a charge density wave transition,
and a dominant role of impurities scattering for low temperature transport
properties is instead demonstrated. The components of magnetoresistance were
separated by using the Kohler plot and the angular dependency of the resistance
under magnetic field. It shows the major contribution of an isotropic, likely
spin driven, negative magnetoresistance. Galvanomagnetic characteristics are
then consistent with a Kondo effect and appear to be essentially 3D at low
temperature. | 1008.4040v1 |
2010-09-27 | Effect of vertex corrections on the longitudinal transport through multilayered nanostructures: Exact dynamical mean-field theory approach applied to the inhomogeneous Falicov-Kimball model | Inhomogeneous dynamical mean-field theory is employed to calculate the
vertex-corrected electronic charge transport for multilayered devices composed
of semi-infinite metallic lead layers coupled through a strongly correlated
material barrier region. The barrier region can be tuned from a metal to a Mott
insulator through adjusting the interaction strength and the particle filling.
We use the Falicov-Kimball model to describe the barrier region because an
exact expression for the vertex corrections is known, allowing us to determine
their effect on transport. The dc conductivity is calculated and we find the
effects of the vertex corrections are relatively small, manifesting themselves
in a small reduction in the resistance-area product. This reduction saturates
in absolute magnitude as the barrier layer becomes thick, as expected due to
the vanishing nature of the vertex corrections in bulk. The vertex corrections
have a larger relative effect on the resistance-area product for more metallic
and thinner devices. | 1009.5299v1 |
2010-10-08 | A unified first-principles study of Gilbert damping, spin-flip diffusion and resistivity in transition metal alloys | Using a formulation of first-principles scattering theory that includes
disorder and spin-orbit coupling on an equal footing, we calculate the
resistivity $\rho$, spin flip diffusion length $l_{sf}$ and the Gilbert damping
parameter $\alpha$ for Ni$_{1-x}$Fe$_x$ substitutional alloys as a function of
$x$. For the technologically important Ni$_{80}$Fe$_{20}$ alloy, permalloy, we
calculate values of $\rho = 3.5 \pm 0.15$ $\mu$Ohm-cm, $l_{sf}=5.5 \pm 0.3$ nm,
and $\alpha= 0.0046 \pm 0.0001$ compared to experimental low-temperature values
in the range $4.2-4.8$ $\mu$Ohm-cm for $\rho$, $5.0-6.0$ nm for $l_{sf}$, and
$0.004-0.013$ for $\alpha$ indicating that the theoretical formalism captures
the most important contributions to these parameters. | 1010.1626v3 |
2010-10-23 | Silicon Oxide is a Non-Innocent Surface for Molecular Electronics and Nanoelectronics Studies | Silicon oxide (SiOx) has been widely used in many electronic systems as a
supportive and insulating medium. Here we demonstrate various electrical
phenomena such as negative differential resistance, resistive switching and
current hysteresis intrinsic to a thin layer of SiOx. These behaviors can
largely mimic numerous electrical phenomena observed in molecules and other
nanomaterials, suggesting that substantial caution should be paid when studying
conduction in electronic systems with SiOx as a component. The actual switching
can be the result of SiOx and not the presumed molecular or nanomaterial
component. These electrical properties and the underlying mechanisms are
discussed in detail. | 1010.4853v1 |
2010-11-17 | Oxidation resistance of graphene-coated Cu and Cu/Ni alloy | The ability to protect refined metals from reactive environments is vital to
many industrial and academic applications. Current solutions, however,
typically introduce several negative effects, including increased thickness and
changes in the metal physical properties. In this paper, we demonstrate for the
first time the ability of graphene films grown by chemical vapor deposition to
protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy
from air oxidation. SEM, Raman spectroscopy, and XPS studies show that the
metal surface is well protected from oxidation even after heating at 200
\degree C in air for up to 4 hours. Our work further shows that graphene
provides effective resistance against hydrogen peroxide. This protection method
offers significant advantages and can be used on any metal that catalyzes
graphene growth. | 1011.3875v1 |
2010-12-20 | Conduction Electron Scattering and Spin-Flipping at Sputtered Co/Ni Interfaces | Current-perpendicular-to-plane magnetoresistance (CPP-MR) measurements let us
quantify conduction electron scattering and spin-flipping at a sputtered
ferromagnetic/ferromagnetic (F1/F2 = Co/Ni) interface, with important
consequences for CPP-MR and spin-torque experiments with perpendicular
anisotropy. We use ferromagnetically coupled ([Ni/Co]xn)Ni multilayers, and
Py-based, symmetric double exchange-biased spin-valves (DEBSVs) containing
inserts of ferromagnetically coupled ([Co/Ni]xn)Co or ([Ni/Co]xn)Ni
multilayers, to derive Co/Ni interface specific resistances AR(Co/Ni)(Up) =
0.03 (+0.02)(-0.03) f-ohm-m^2 and AR(Co/Ni)(down) = 1.00 +/- 0.07 f-ohm-m^2,
and interface spin-flipping parameter delta(Co/Ni) = 0.35 +/- 0.05. The
specific resistances are consistent with our no-free-parameter calculations for
an interface thickness between 2 and 4 monolayers (ML) that is compatible with
expectations. | 1012.4388v1 |
2011-01-19 | Negative differential resistance in scanning tunneling microscopy: simulations on C$_{60}$-based molecular overlayers | We determine the conditions in which negative differential resistance (NDR)
appears in the C$_{60}$-based molecular device of [Phys. Rev. Lett. {\bf 100},
036807 (2008)] by means of ab-initio electron-transport simulations. Our
calculations grant access to bias-dependent intrinsic properties of the
molecular device, such as electronic levels and their partial widths. We show
that these quantities depend on the molecule-molecule and molecule-electrode
interactions of the device. Hence, NDR can be tuned by modifying the bias
behavior of levels and widths using both types of interactions. | 1101.3714v1 |
2011-01-26 | Metal-insulator transition in ultrathin LaNiO3 films | Transport in ultrathin films of LaNiO3 evolves from a metallic to a strongly
localized character as the film's thickness is reduced and the sheet resistance
reaches a value close to h/e2, the quantum of resistance in two dimensions. In
the intermediate regime, quantum corrections to the Drude low- temperature
conductivity are observed; they are accurately described by weak localization
theory. Remarkably, the negative magnetoresistance in this regime is isotropic,
which points to magnetic scattering associated with the proximity of the system
to either a spin glass state or the charge ordered antiferromagnetic state
observed in other rare earth nickelates. | 1101.5111v2 |
2011-03-31 | Aharonov-Casher effect in Bi$_{\rm 2}$Se$_{\rm 3}$ square-ring interferometers | Electrical control of spin dynamics in Bi$_{\rm 2}$Se$_{\rm 3}$ was
investigated in ring-type interferometers. Aharonov-Bohm and
Altshuler-Aronov-Spivak resistance oscillations against magnetic field, and
Aharorov-Casher resistance oscillations against gate voltage were observed in
the presence of a Berry phase of $\pi$. A very large tunability of spin
precession angle by gate voltage has been obtained, indicating that Bi$_{\rm
2}$Se$_{\rm 3}$-related materials with strong spin-orbit coupling are promising
candidates for constructing novel spintronic devices. | 1103.6115v1 |
2011-06-02 | Evidence for semiconducting behavior with a narrow band gap of Bernal graphite | We have studied the resistivity of a large number of highly oriented graphite
samples with areas ranging from several mm$^2$ to a few $\mu$m$^2$ and
thickness from $\sim 10 $nm to several tens of micrometers. The measured
resistance can be explained by the parallel contribution of semiconducting
graphene layers with low carrier density $< 10^9$ cm$^{-2}$ and the one from
metallic-like internal interfaces. The results indicate that ideal graphite
with Bernal stacking structure is a narrow-gap semiconductor with an energy gap
$E_g \sim 40 $meV. | 1106.0437v3 |
2011-07-25 | Unveiling a nematic quantum critical point in multi-orbital systems | Electronic nematicity, proposed to exist in a number of transition metal
materials, can have different microscopic origins. In particular, the
anisotropic resistivity and meta-magnetic jumps observed in Sr3Ru2O7 are
consistent with an earlier proposal that the isotropic-nematic transition is
generically first order and accompanied by meta-magnetism when tuned by a
magnetic field. However, additional striking experimental features such as a
non-Fermi liquid resistivity and critical thermodynamic behavior imply the
presence of an unidentified quantum critical point (QCP). Here we show that
orbital degrees of freedom play an essential role in revealing a nematic QCP,
even though it is overshadowed by a nearby meta-nematic transition at low
temperature. We further present a finite temperature phase diagram including
the entropy landscape and discuss our findings in light of the phenomena
observed in Sr3Ru2O7. | 1107.5052v5 |
2011-08-25 | Structural and Electrical Characterization of Bi2Se3 Nanostructures Grown by Metalorganic Chemical Vapor Deposition | We characterize nanostructures of Bi2Se3 that are grown via metalorganic
chemical vapor deposition using the precursors diethyl selenium and trimethyl
bismuth. By adjusting growth parameters, we obtain either single-crystalline
ribbons up to 10 microns long or thin micron-sized platelets. Four-terminal
resistance measurements yield a sample resistivity of 4 mOhm-cm. We observe
weak anti-localization and extract a phase coherence length l_phi = 178 nm and
spin-orbit length l_so = 93 nm at T = 0.29 K. Our results are consistent with
previous measurements on exfoliated samples and samples grown via physical
vapor deposition. | 1108.4978v2 |
2011-09-14 | Growth of atomically smooth thin films of the electronically phase separated manganite (La$_{0.5}$Pr$_{0.5}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ | Atomically flat, epitaxial, and stoichiometric thin films of the
electronically phase separated compound
(La$_{0.5}$Pr$_{0.5}$)$_{0.67}$Ca$_{0.33}$MnO$_{3}$ were grown on as-received
and treated NdGaO$_{3}$ substrates by fine tuning of oxygen pressure during
deposition. Optimal thin films with step flow growth mode show superior
physical properties compared to thin films grown in off-optimal oxygen
pressures, {\em viz.} the highest maximum temperature coefficient of
resistance, the highest peak-resistivity temperature, and reduced coercive
fields. Transport, magnetization, and x-ray diffraction measurements indicate
that the oxygen pressure during growth plays a critical role in the formation
of oxygen vacancies, cation vacancies, and grain boundaries. | 1109.3225v1 |
2011-09-23 | A single layer hydrogen silsesquioxane (HSQ) based lift-off process for germanium and platinum | Primarily used as etch mask, single layer hydrogen silsesquioxane has never
been investigated for lift-off technique. In this article, we propose a new
technique where a single layer of hydrogen silsesquioxane, a negative tone
electron beam resist, is used to make lift-off of germanium and platinum.
Removal of exposed hydrogen silsesquioxane is tested for various concentrations
of hydrofluoric acid. Ultrasonic agitation is also used to reduce the formation
of flakes due to accumulation of matter (evaporated metal in our case) along
the sidewalls of the lift-off narrow slots. Results demonstrate potential in
applying the hydrogen silsesquioxane as a negative tone lift-off resist to
pattern nanometer scale features into germanium and platinum layers. | 1109.5187v1 |
2011-11-03 | Estimation of the spin polarization for Heusler-compound thin films by means of nonlocal spin-valve measurements: Comparison of Co$_{2}$FeSi and Fe$_{3}$Si | We study room-temperature generation and detection of pure spin currents
using lateral spin-valve devices with Heusler-compound electrodes, Co$_{2}$FeSi
(CFS) or Fe$_{3}$Si (FS). The magnitude of the nonlocal spin-valve (NLSV)
signals is seriously affected by the dispersion of the resistivity peculiarly
observed in the low-temperature grown Heusler compounds with ordered
structures. From the analysis based on the one-dimensional spin diffusion
model, we find that the spin polarization monotonically increases with
decreasing the resistivity, which depends on the structural ordering, for both
CFS and FS electrodes, and verify that CFS has relatively large spin
polarization compared with FS. | 1111.0742v2 |
2011-11-27 | A first-order magnetic phase transition near 15 K with novel magnetic-field-induced effects in Er5Si3 | We present magnetic characterization of a binary rare-earth intermetallic
compound Er5Si3, crystallizing in Mn5Si3-type hexagonal structure, through
magnetization, heat-capacity, electrical resistivity, and magnetoresistance
measurements. Our investigations confirm that the compound exhibits two
magnetic transitions with decreasing temperature, first one at 35 K and the
second one at 15 K. The present results reveal that the second magnetic
transition is a disorder-broadened first-order transition, as shown by thermal
hysteresis in the measured data. Another important finding is that, below 15 K,
there is a magnetic-field-induced transition with a hysteretic effect with the
electrical resistance getting unusually enhanced at this transition and the
magnetorsistance (MR) is found to exhibit intriguing magnetic-field dependence
indicating novel magnetic phase-co-existence phenomenon. It thus appears that
this compound is characterized by interesting magnetic anomalies in the
temperature-magnetic-field phase diagram. | 1111.6240v1 |
2011-12-20 | Approximate Theory of Temperature Coefficient of Resistivity of Amorphous Semiconductors | In this paper, we develop an approximate theory of the temperature
coefficient of resistivity (TCR) and conductivity based upon the recently
proposed Microscopic Response Method. By introducing suitable approximations
for the lattice dynamics, localized and extended electronic states, we produce
new explicit forms for the conductivity and TCR, which depend on easily
accessible material parameters. The theory is in reasonable agreement with
experiments on a-Si:H and a-Ge:H. A long-standing puzzle, a \textquotedblleft
kink\textquotedblright\ in the experimental $% \log_{10}\sigma $ vs. 1/T curve,
is predicted by the theory and attributed to localized to extended transitions,
which have not been properly handled in earlier theories. | 1112.4723v2 |
2011-12-23 | Microscopic Details of the Integer Quantum Hall Effect in an Anti-Hall Bar | Due to the lack of simulation tools that take into account the actual
geometry of complicated quantum Hall samples there are lots of experiments that
are not yet fully understood. Already some years ago R. G. Mani recorded a
shift of the Hall resistance transitions to lower magnetic fields in samples of
a Hall bar with embedded anti-Hall bar by using partial gating. We use a
Nonequilibrium Network Model (NNM) to simulate this geometry and find
qualitative agreement. Fitting the simulated resistance curves to the
experimental results we can not only determine the carrier concentration but
also obtain an estimate of the screened gating potential and especially the
amplitude and lengthscale of potential fluctuations from charge inhomogenities
which are not easily accessible by experiment. | 1112.5673v1 |
2012-02-27 | Coaxial Nanowire Resonant Tunneling Diodes from non-polar AlN/GaN on Silicon | Resonant tunneling diodes are formed using AlN/GaN core-shell nanowire
heterostructures grown by plasma assisted molecular beam epitaxy on n-Si(111)
substrates. By using a coaxial geometry these devices take advantage of
non-polar (m-plane) nanowire sidewalls. Device modeling predicts non-polar
orientation should enhance resonant tunneling compared to a polar structure and
that AlN double barriers will lead to higher peak-to-valley current ratios
compared to AlGaN barriers. Electrical measurements of ensembles of nanowires
show negative differential resistance appearing only at cryogenic temperature.
Individual nanowire measurements show negative differential resistance at room
temperature with peak current density of 5*10^5 A/cm^2. | 1202.6052v2 |
2012-04-09 | Magnetic-field induced resistivity minimum with in-plane linear magnetoresistance of the Fermi liquid in SrTiO3-x single crystals | We report novel magnetotransport properties of the low temperature Fermi
liquid in SrTiO3-x single crystals. The classical limit dominates the
magnetotransport properties for a magnetic field perpendicular to the sample
surface and consequently a magnetic-field induced resistivity minimum emerges.
While for the field applied in plane and normal to the current, the linear
magnetoresistance (MR) starting from small fields (< 0.5 T) appears. The large
anisotropy in the transverse MRs reveals the strong surface interlayer
scattering due to the large gradient of oxygen vacancy concentration from the
surface to the interior of SrTiO3-x single crystals. Moreover, the linear MR in
our case was likely due to the inhomogeneity of oxygen vacancies and oxygen
vacancy clusters, which could provide experimental evidences for the unusual
quantum linear MR proposed by Abrikosov [A. A. Abrikosov, Phys. Rev. B 58, 2788
(1998)]. | 1204.1901v1 |
2012-04-20 | Size-dependent electronic-transport mechanism and sign reversal of magnetoresistance in Nd0.5Sr0.5CoO3 | A detailed investigation of electronic-transport properties of Nd0.5Sr0.5CoO3
has been carried out as a function of grain size ranging from micrometer order
down to an average size of 28 nm. Interestingly, we observe a size induced
metal-insulator transition in the lowest grain size sample while the bulk-like
sample is metallic in the whole measured temperature regime. An analysis of the
temperature dependent resistivity in the metallic regime reveals that the
electron-electron interaction is the dominating mechanism while other processes
like electron-magnon and electron-phonon scatterings are also likely to be
present. The fascinating observation of enhanced low temperature upturn and
minimum in resistivity on reduction of grain size is found due to
electron-electron interaction (quantum interference effect). This effect is
attributed to enhanced disorder on reduction of grain size. Interestingly, we
observed a cross over from positive to negative magnetoresistance in the low
temperature regime as the grain size is reduced. This observed sign reversal is
attributed to enhanced phase separation on decreasing the grain size of the
cobaltite. | 1204.4572v1 |
2012-04-22 | Anomalous ferromagnetism and non-Fermi-liquid behavior in the Kondo lattice CeRuSi2 | The structural, electronic and magnetic properties of the Kondo-lattice
system CeRuSi2 are experimentally investigated and analyzed in the series of
other ternary cerium compounds. This system is shown to be an excellent model
system demonstrating coexistence of the Kondo effect and anomalous
ferromagnetism with a small magnetic moment which is confirmed by magnetic and
\mu SR measurements. Data on specific heat, resistivity and Seebeck coefficient
are presented. Being deduced from the resistivity and specific heat data, the
non-Fermi-liquid behavior is observed at low temperatures, which is unusual for
a ferromagnetic Kondo system. A comparison with other magnetic Kondo lattices
is performed. | 1204.4903v3 |
2012-07-02 | Evolution of the magnetism of Tb(Co_{x}Ni_{1-x})_{2}B_{2}C | The magnetic properties of polycrystalline Tb(Co_{x}Ni_{1-x})_{2}B_{2}C
(x=0.2,0.4,0.6,0.8) samples were probed by magnetization, specific heat, ac
susceptibility, and resistivity techniques. For x{\neq}0.4, the obtained curves
are consistent with the features expected for the corresponding magnetic modes,
namely k_{1}=(0.55,0,0) at x=0;
k_{2}=([nicefrac]\nicefrac{1}{2}</LaTeX>,0,[nicefrac]<LaTeX>\nicefrac{1}{2}) at
x= 0.2; k_{3}=(0,0,[nicefrac]\nicefrac{1}{3}) at x= 0.6, and k_{4}=(0,0,0) at
x= 0.8 and 1. For x=0.4, even though the neutron diffraction indicates a k_{2}
mode, but with a reduced magnetic moment, the magnetization, the ac
susceptibility, and resistivity indicate two magnetic events; furthermore,
deviation from Curie-Weiss behavior is observed below 150 K for this sample.
These features, together with the evolution of both magnetic moment and
critical temperature, are attributed to an interplay between competing magnetic
couplings; for the particular x=0.4 case, additional factors such as
crystalline electric field effects may be in operation. | 1207.0519v1 |
2012-07-19 | Mobility enhancement and highly efficient gating of monolayer MoS2 transistors with Polymer Electrolyte | We report electrical characterization of monolayer molybdenum disulfide
(MoS2) devices using a thin layer of polymer electrolyte consisting of
poly(ethylene oxide) (PEO) and lithium perchlorate (LiClO4) as both a
contact-barrier reducer and channel mobility booster. We find that bare MoS2
devices (without polymer electrolyte) fabricated on Si/SiO2 have low channel
mobility and large contact resistance, both of which severely limit the
field-effect mobility of the devices. A thin layer of PEO/ LiClO4 deposited on
top of the devices not only substantially reduces the contact resistance but
also boost the channel mobility, leading up to three-orders-of-magnitude
enhancement of the field-effect mobility of the device. When the polymer
electrolyte is used as a gate medium, the MoS2 field-effect transistors exhibit
excellent device characteristics such as a near ideal subthreshold swing and an
on/off ratio of 106 as a result of the strong gate-channel coupling. | 1207.4824v1 |
2012-07-20 | Magnetic, magnetocaloric and magnetotransport properties of RSn_{1+x}Ge_{1-x} compounds (R=Gd, Tb, Er; x=0.1) | We have studied the magnetic, magnetocaloric and magnetotransport properties
of RSn1+xGe1-x(R=Gd, Tb, Er; x=0.1) series by means of magnetization, heat
capacity and resistivity measurements. It has been found that all the compounds
crystallize in the orthorhombic crystal structure described by the
centrosymmetric space group Cmcm (No. 63). The magnetic susceptibility and heat
capacity data suggest that all the compounds are antiferromagnetic. Large
negative values of {\theta}p in case of GdSn1.1Ge0.9 and TbSn1.1Ge0.9 indicate
that strong antiferromagnetic interactions are involved, which is also
reflected in the magnetization isotherms. On the other hand ErSn1.1Ge0.9 shows
weak antiferromagnetic interaction. The heat capacity data have been analyzed
by fitting the temperature dependence and the values of {\theta}D and {\gamma}
have been estimated. Among these three compounds, ErSn1.1Ge0.9 shows
considerable magnetic entropy change of 9.5 J/kg K and an adiabatic temperature
change of 3.2 K for a field of 50 kOe. The resistivity data in different
temperature regimes have been analyzed and the dominant contributions have been
identified. All the compounds show small but positive magnetoresistance. | 1207.4971v1 |
2012-07-30 | The Effect of Electrode Size on Memristor Properties: An Experimental and Theoretical Study | The width of the electrodes is not included in the current phenomenological
models of memristance, but is included in the memory-conservation (mem-con)
theory of memristance. An experimental study of the effect of changing the top
electrode width was performed on titanium dioxide sol-gel memristors. It was
demonstrated that both the on resistance, Ron, and the off resistance, Roff,
decreased with increasing electrode size. The memory function part of the
mem-con model could fit the relationship between Ron and electrode size.
Similarly, the conservation function fits the change in Roff. The
experimentally measured hysteresis did not fit the phenomenological model's
predictions. Instead the size of the hysteresis increased with increasing
electrode size, and correlated well to decreasing Ron. | 1207.6933v1 |
2012-08-06 | A Variant of the Point Defect Model for Passivity of Metals | A variant of the point defect model originally enunciated by Macdonald and
co-workers is advanced and its theoretical implications for the steady state
current density, barrier layer thickness and the concentration of metal vacancy
at the metal/film interface are deduced. The differences between the original
point defect model and the present variant are also highlighted. The empirical
parameters alpha and beta in the original point defect model are replaced with
two physical parameters Rcont and Rhof which represent respectively the
electronic contact resistance at the metal/film interface and the electronic
resistivity of the oxide film. The present variant correctly describes the
annihilation of the metal vacancies at the metal/film interface and also
enforces the conservation of particle and defect volumes during the solid-state
reactions leading to the natural inclusion of the famous Pilling-Bedsworth
ratio RPB into the model. Diagnostics which help to check the model predictions
with experiments are given. Use of this variant to describe stress-induced
failure of the barrier oxide leading to pitting is also discussed. | 1208.1096v1 |
2012-08-27 | Suppression of superconductivity in layered Bi4O4S3 by Ag doping | We report X-ray diffraction, magnetization and transport measurements for
polycrystalline samples of the new layered superconductor Bi4-xAgxO4S3
(0<x<0.2). The superconducting transition temperature (TC) decreases gradually
and finally suppressed for x>0.10. Accordingly, the resistivity changes from a
metallic behavior for x<0.1 to a semiconductor-like behavior for x>0.1. The
analysis of Seebeck coefficient shows there are two types of electron-like
carriers dominate at different temperature regions, indicative of a multiband
effect responsible for the transport properties. The suppression of
superconductivity and the increased resistivity can be attributed to a shift of
the Fermi level to the lower-energy side upon doping, which reduces the density
of states at EF. Further, our result indicates the superconductivity in the
parent Bi4O4S3 is intrinsic and the dopant Ag prefers to enter the BiS2 layers,
which may essentially modify the electronic structure. | 1208.5307v1 |
2012-09-27 | Theoretical investigation of direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and quantum well interband tunnel junctions for multi-junction solar cells | Direct and phonon-assisted tunneling currents in InAlGaAs-InGaAs bulk and
double quantum well interband tunnel heterojunctions are simulated rigorously
using the non-equilibrium Green's function formalism for coherent and
dissipative quantum transport in combination with a simple two-band
tight-binding model for the electronic structure. A realistic band profile and
associated built-in electrostatic field is obtained via self-consistent
coupling of the transport formalism to Poisson's equation. The model reproduces
experimentally observed features in the current-voltage characteristics of the
device, such as the structure appearing in the negative differential resistance
regime due to quantization of emitter states. Local maps of density of states
and current spectrum reveal the impact of quasi-bound states, electric fields
and electron-phonon scattering on the interband tunneling current. In this way,
resonances appearing in the current through the double quantum well structure
in the negative differential resistance regime can be related to the alignment
of subbands in the coupled quantum wells. | 1209.6314v1 |
2012-10-11 | Prediction of semi-metallic tetragonal Hf2O3 and Zr2O3 from first-principles | A tetragonal phase is predicted for Hf2O3 and Zr2O3 using density functional
theory. Starting from atomic and unit cell relaxations of substoichiometric
monoclinic HfO2 and ZrO2, such tetragonal structures are only reached at zero
temperature by introducing the oxygen vacancy pair with the lowest formation
energy. The tetragonal Hf2O3 and Zr2O3 structures belong to space group P-4m2
and are more stable than their corundum structure counterparts. These phases
are semi-metallic, as confirmed through further G0W0 calculations. The carrier
concentrations are estimated to be 1.77E21 cm^{-3} for both electrons and holes
in tetragonal Hf2O3, and 1.75E21 cm^{-3} for both electrons and holes in
tetragonal Zr2O3. The tetragonal Hf2O3 phase is probably related to the low
resistivity state of hafnia-based resistive random access memory (RRAM). | 1210.3348v1 |
2012-10-12 | Superconducting LaAlO3/SrTiO3 Nanowires | We report superconductivity in quasi-1D nanostructures created at the
LaAlO3/SrTiO3 interface. Nanostructures having line widths w~10 nm are formed
from the parent two-dimensional electron liquid using conductive atomic force
microscope lithography. Nanowire cross-sections are small compared to the
superconducting coherence length in LaAlO3/SrTiO3 (w<<xi~100 nm), placing them
in the quasi-1D regime. Broad superconducting transitions with temperature and
finite resistances in the superconducting state well below Tc~200 mK are
observed. V-I curves show switching between the superconducting and normal
states that are characteristic of superconducting nanowires. The four-terminal
resistance in the superconducting state shows an unusual dependence on the
current path, varying by as much as an order of magnitude. | 1210.3606v1 |
2012-10-26 | Spin injection from a half-metal at finite temperatures | Spin injection from a half-metallic electrode in the presence of thermal spin
disorder is analyzed using a combination of random matrix theory,
spin-diffusion theory, and explicit simulations for the tight-binding s-d
model. It is shown that efficient spin injection from a half-metal is possible
as long as the effective resistance of the normal metal does not exceed a
characteristic value, which does not depend on the resistance of the
half-metallic electrode, but is rather controlled by spin-flip scattering at
the interface. This condition can be formulated as \alpha<(l/L)/T, where \alpha
is the relative deviation of the magnetization from saturation, l and L the
mean-free path and the spin-diffusion length in the non-magnetic channel, and T
the transparency of the tunnel barrier at the interface (if present). The
general conclusions are confirmed by tight-binding s-d model calculations. A
rough estimate suggests that efficient spin injection from true half-metallic
ferromagnets into silicon or copper may be possible at room temperature across
a transparent interface. | 1210.7194v2 |
2012-12-03 | Resistive switching in ferroelectric BiFeO3 by 1.7 eV change of the Schottky barrier height | Using metal-ferroelectric junctions as switchable diodes was proposed several
decades ago. This was shown to actually work in PbZr(1-x)TixO3 (PZT) by Blom et
al. [P.W. M. Blom et al., Phys. Rev. Lett. 73, 2107 (1994)], who reported
switching in the rectification direction and changes of the current of about 2
orders of magnitude upon switching the polarization direction of the
ferroelectric layer. This form of resistive switching enables the read out of a
ferroelectric memory state at higher speed compared to the capacitive design,
without destroying the information in each reading cycle. Recently, Jiang and
coworkers have shown that these Schottky barrier effects are enormous in
BiFeO3, giving thousand times more switched charge than found by in PZT [A.Q.
Jiang. et al., Adv. Mat. 23, 1277 (2011)]. Here, by performing local
conductivity measurements, we attribute this to a large change of the Schottky
barrier height between the as-grown, down-polarized domains and the
up-polarized domains. These measurements allow to estimate the relative effect
of polarization charges and screening charges on the conduction through the
ferroelectric. | 1212.0483v1 |
2012-12-18 | Low temperature transport properties of multigraphene structures on 6H-SiC obtained by thermal graphitization: evidences of a presence of nearly perfect graphene layer | Transport properties of multigraphene layers on 6H-SiC substrates fabricated
by thermal graphitization of SiC were studied. The principal result is that
these structures were shown to contain a nearly perfect graphene layer situated
between the SiC substrate and multgraphene layer. It was found that the curves
of magnetoresistance and Shubnikov- de Haas oscillations shown the features,
typical for single-layered graphene. The low temperature resistance
demonstrated an increase with temperature increase, which also corresponds to a
behavior typical for single-layered graphene (antilocalization). However at
higher temperatures the resistance decreased with an increase of temperature,
which corresponds to a weak localization. We believe that the observed behavior
can be explained by a parallel combination of contributions to the conductivity
of single-layered graphene and of multigraphene, the latter allowing to escape
damages of the graphene by atmosphere effect. | 1212.4272v1 |
2013-01-07 | Quantum Hall Effect in Hydrogenated Graphene | The quantum Hall effect is observed in a two-dimensional electron gas formed
in millimeter-scale hydrogenated graphene, with a mobility less than 10
$\mathrm{cm^{2}/V\cdot s}$ and corresponding Ioffe-Regel disorder parameter
$(k_{F}\lambda)^{-1}\gg1$. In zero magnetic field and low temperatures, the
hydrogenated graphene is insulating with a two-point resistance of order of
$250 h/e^2$. Application of a strong magnetic field generates a negative
colossal magnetoresistance, with the two-point resistance saturating within
0.5% of $h/2e^{2}$ at 45T. Our observations are consistent with the opening of
an impurity-induced gap in the density of states of graphene. The interplay
between electron localization by defect scattering and magnetic confinement in
two-dimensional atomic crystals is discussed. | 1301.1257v1 |
2013-01-12 | Magnetic field-tuned Aharonov-Bohm oscillations and evidence for non-Abelian anyons at v=5/2 | We show that the resistance of the v=5/2 quantum Hall state, confined to an
interferometer, oscillates with magnetic field consistent with an Ising-type
non-Abelian state. In three quantum Hall interferometers of different sizes,
resistance oscillations at v=7/3 and integer filling factors have the magnetic
field period expected if the number of quasiparticles contained within the
interferometer changes so as to keep the area and the total charge within the
interferometer constant. Under these conditions, an Abelian state such as the
(3,3,1) state would show oscillations with the same period as at an integer
quantum Hall state. However, in an Ising-type non-Abelian state there would be
a rapid oscillation associated with the "even-odd effect" and a slower one
associated with the accumulated Abelian phase due to both the Aharonov-Bohm
effect and the Abelian part of the quasiparticle braiding statistics. Our
measurements at v=5/2 are consistent with the latter. | 1301.2639v1 |
2013-02-07 | Thermal Conductivity and Phonon Transport in Suspended Few-Layer Hexagonal Boron Nitride | The thermal conductivity of suspended few-layer hexagonal boron nitride
(h-BN) was measured using a micro-bridge device with built-in resistance
thermometers. Based on the measured thermal resistance values of 11-12 atomic
layer h-BN samples with suspended length ranging between 3 and 7.5 um, the
room-temperature thermal conductivity of a 11-layer sample was found to be
about 360 Wm-1K-1, approaching the basal plane value reported for bulk h-BN.
The presence of a polymer residue layer on the sample surface was found to
decrease the thermal conductivity of a 5-layer h-BN sample to be about 250
Wm-1K-1 at 300 K. Thermal conductivities for both the 5 layer and the 11 layer
samples are suppressed at low temperatures, suggesting increasing scattering of
low frequency phonons in thin h-BN samples by polymer residue. | 1302.1890v1 |
2013-02-08 | Comparative study of the electronic structure, phonon spectra and electron-phonon interaction of ZrB2 and TiB2 | The electronic structure, optical and x-ray absorption spectra, angle
dependence of the cyclotron masses and extremal cross sections of the Fermi
surface, phonon spectra, electron-phonon Eliashberg and transport spectral
functions, temperature dependence of electrical resistivity of the MB2 (M=Ti
and Zr) diborides were investigated from first principles using the full
potential linear muffin-tin orbital method. The calculations of the dynamic
matrix were carried out within the framework of the linear response theory. A
good agreement with experimental data of optical and x-ray absorption spectra,
phonon spectra, electron-phonon spectral functions, electrical resistivity,
cyclotron masses and extremal cross sections of the Fermi surface was achieved. | 1302.2144v1 |
2013-02-15 | Storing magnetic information in IrMn/MgO/Ta tunnel junctions via field-cooling | Tunneling junctions containing no ferromagnetic elements have been fabricated
and we show that distinct resistance states can be set by field cooling the
devices from above the N\'eel along different orientations. Variations of the
resistance up to 10% are found upon field cooling in applied fields of 2T,
in-plane or out of plane. Below TN, we found that the metastable states are
insensitive to magnetic fields thus constituting a memory element robust
against external magnetic fields. Our work provides the demonstration of an
electrically readable magnetic memory device, which contains no ferromagnetic
elements and stores the information in an antiferromagnetic active layer. | 1302.3837v1 |
2013-03-06 | Highly reproducible metal/graphene contacts and stable electrical performance by UV-Ozone treatment | Resist residue from the device fabrication process is a general and
significant source of the metal/graphene contact interface contamination. In
this paper, Ultraviolet-Ozone (UVO) treatment is proven to be an effective way
of cleaning the metal/graphene interface. Electrical measurements of devices,
which were fabricated by using UVO treatment of the metal/graphene contact
region, show that stable and highly reproducible low contact resistance between
metal and graphene is obtained without affecting the electrical properties of
the graphene channel itself. | 1303.1353v2 |
2013-03-15 | Thermoelectric Properties of Polycrystalline NiSi3P4 | The Hall and Seebeck coefficients, electrical resistivity and thermal
conductivity of polycrystalline NiSi3P4 were characterized from 2 to 775K.
Undoped NiSi3P4 behaves like a narrow gap semiconductor, with activated
electrical resistivity \rho below room temperature and a large Seebeck
coefficient of ~400uV/K at 300K. Attempts to substitute boron for silicon
resulted in the production of extrinsic holes, yielding moderately-doped
semiconductor behavior with \rho increasing with increasing temperature above
~150\,K. Hall carrier densities are limited to approximately 5x10^{19}/cm^3 at
200K, which would suggest the solubility limit of boron is reached if boron is
indeed incorporated into the lattice. These extrinsic samples have a Hall
mobility of ~12cm^2/V/s at 300K, and a parabolic band equivalent effective mass
of ~3.5 times the free electron mass. At 700,K, the thermoelectric figure of
merit zT reaches ~0.1. Further improvements in thermoelectric performance would
require reaching higher carrier densities, as well as a mechanism to further
reduce the lattice thermal conductivity, which is ~5W/m/K at 700K. Alloying in
Ge results in a slight reduction of the thermal conductivity at low
temperatures, with little influence observed at higher temperatures. | 1303.3772v1 |
2013-03-29 | Hysteretic superconducting resistive transition in Ba0.07K0.93Fe2As2 | We have observed hysteresis in superconducting resistive transition curves of
Ba$_{0.07}$K$_{0.93}$Fe$_2$As$_2$ ($T_c\sim$8 K) below about 1 K for in-plane
fields. The hysteresis is not observed as the field is tilted away from the
$ab$ plane by 20$^{\circ}$ or more. The temperature and angle dependences of
the upper critical field indicate a strong paramagnetic effect for in-plane
fields. We suggest that the hysteresis can be attributed to a first-order
superconducting transition due to the paramagnetic effect. Magnetic torque data
are also shown. | 1303.7281v4 |
2013-04-04 | Benchtop Fabrication of Memristive Atomic Switch Networks | Recent advances in nanoscale science and technology provide possibilities to
directly self-assemble and integrate functional circuit elements within the
wiring scheme of devices with potentially unique architectures. Electroionic
resistive switching circuits comprising highly interconnected fractal
electrodes and metal-insulator-metal interfaces, known as atomic switch
networks, have been fabricated using simple benchtop techniques including
solution-phase electroless deposition. These devices are shown to activate
through a bias-induced forming step that produces the frequency dependent,
nonlinear hysteretic switching expected for gapless-type atomic switches and
memristors. By eliminating the need for complex lithographic methods, such an
approach toward device fabrication provides a more accessible platform for the
study of ionic resistive switches and memristive systems. | 1304.1243v2 |
2013-04-08 | Ultra Low Power Associative Computing with Spin Neurons and Resistive Crossbar Memory | Emerging resistive-crossbar memory (RCM) technology can be promising for
computationally-expensive analog pattern-matching tasks. However, the use of
CMOS analog-circuits with RCM would result in large power-consumption and poor
scalability, thereby eschewing the benefits of RCM-based computation. We
propose the use of low-voltage, fast-switching, magneto-metallic spin-neurons
for ultra low-power non-Boolean computing with RCM. We present the design of
analog associative memory for face recognition using RCM, where, substituting
conventional analog circuits with spin-neurons can achieve ~100x lower power.
This makes the proposed design ~1000x more energy-efficient than a 45nm-CMOS
digital ASIC, thereby significantly enhancing the prospects of RCM based
computational hardware. | 1304.2281v1 |
2013-04-28 | Hidden Fermi Liquid, Scattering Rate Saturation and Nernst Effect: a DMFT Perspective | We investigate the transport properties of a correlated metal within
dynamical mean field theory. Canonical Fermi liquid behavior emerges only below
a very low temperature scale $T_{FL}$. Surprisingly the quasiparticle
scattering rate follows a quadratic temperature dependence up to much higher
temperatures and crosses over to saturated behavior around a temperature scale
$T_{sat}$. We identify these quasiparticles as constituents of the hidden Fermi
liquid. The non-Fermi liquid transport above $T_{FL}$, in particular the
linear-in-$T$ resistivity, is shown to be a result of a strongly temperature
dependent band dispersion. We derive simple expressions for resistivity, Hall
angle, thermoelectric power and Nernst coefficient in terms of a temperature
dependent renormalized band structure and the quasiparticle scattering rate. We
discuss possible tests of the DMFT picture of transport using ac measurements. | 1304.7486v1 |
2013-05-10 | Geometric treatment of conduction electron scattering by crystal lattice strains and dislocations | A theory for conduction electron scattering by inhomogeneous crystal lattice
strains is developed, based on the differential geometric treatment of
deformations in solids. The resulting fully covariant Schr\"odinger equation
shows that the electrons can be described as moving in a non-Euclidean
background space in the continuum limit of the deformed lattice. Unlike
previous work, the formalism is applicable to cases involving purely elastic
strains as well as discrete and continuous distributions of dislocations --- in
the latter two cases it clearly demarcates the effects of the dislocation
strain field and core and differentiates between elastic and plastic strain
contributions respectively. The electrical resistivity due to the strain field
of edge dislocations is then evaluated using perturbation theory and the
Boltzmann transport equation. The resulting numerical estimate for Cu shows
good agreement with experimental values, indicating that the electrical
resistivity of edge dislocations is not entirely due to the core, contrary to
current models. Possible application to the study of strain effects in
constrained quantum systems is also discussed. | 1305.2455v3 |
2013-05-15 | Origin of Rigidity in Dry Granular Solids | Solids are distinguished from fluids by their ability to resist shear. In
traditional solids, the resistance to shear is associated with the emergence of
broken translational symmetry as exhibited by a non-uniform density pattern. In
this work, we focus on the emergence of shear-rigidity in a class of solids
where this paradigm is challenged. Dry granular materials have no energetically
or entropically preferred density modulations. We show that, in contrast to
traditional solids, the emergence of shear rigidity in these granular solids is
a collective process, which is controlled solely by boundary forces, the
constraints of force and torque balance, and the positivity of the contact
forces. We develop a theoretical framework based on these constraints, which
connects rigidity to broken translational symmetry in the space of forces, not
positions of grains. We apply our theory to experimentally generated
shear-jammed (SJ) states and show that these states are indeed characterized by
a persistent, non-uniform density modulation in force space, which emerges at
the shear-jamming transition. | 1305.3484v2 |
2013-06-24 | Polarization Controlled Ohmic to Schottky Transition at a Metal/Doped Ferroelectric Interface | Ferroelectric polar displacements have recently been observed in conducting
electron-doped BaTiO3. The co-existence of a ferroelectric phase and
conductivity opens the door to new functionalities which may provide a unique
route for novel device applications. Using first-principles methods and
electrostatic modeling we explore the effect that the switchable polarization
of electron-doped BaTiO3 (n-BaTiO3) has on the electronic properties of the
SrRuO3/n-BaTiO3 (001) interface. Ferroelectric polarization controls the
accumulation or depletion of electron charge at the interface, and the
associated bending of the n-BTO conduction band determines the transport regime
across the interface. The interface exhibits a Schottky tunnel barrier for one
polarization orientation, whereas an Ohmic contact is present for the opposite
polarization orientation, leading to a large change in interface resistance
associated with polarization reversal. Calculations reveal a large (five orders
of magnitude) change in the interface resistance as a result of polarization
switching. | 1306.5763v2 |
2013-07-04 | Impact of intrinsic deformations on the negative differential resistance of monolayer MoS$_2$ ultra-short channel MOSFET | In this work we present a study on the impact of various intrinsic
deformations like ripples, twist, wrap on the electronic properties of
ultra-short monolayer MoS2 channels. The effect of deformation (3-7o twist or
wrap and 0.3-0.7 buckling amplitude) on a 3.5 nm planar monolayer MoS2 MOSFET
is evaluated by the density functional theory and the non-equilibrium Green`s
function (DFT-NEGF) approach. We study the channel density of states,
transmission spectra and the ID-VD characteristics under the varying
conditions, with focus on the negative differential resistance (NDR) behavior.
Our results show significant change in the NDR peak to valley ratio (PVR) and
the NDR window with such minor intrinsic deformations, especially with the
rippling. | 1307.1306v2 |
2013-07-24 | Extremely Large Magnetoresistance in the Nonmagnetic Metal PdCoO2 | Extremely large magnetoresistance is realized in the nonmagnetic layered
metal PdCoO2. In spite of a highly conducting metallic behavior with a simple
quasi-two-dimensional hexagonal Fermi surface, the interlayer resistance
reaches up to 35000% for the field along the [1-10] direction. Furthermore, the
temperature dependence of the resistance becomes nonmetallic for this field
direction, while it remains metallic for fields along the [110] direction. Such
severe and anisotropic destruction of the interlayer coherence by a magnetic
field on a simple Fermi surface is ascribable to orbital motion of carriers on
the Fermi surface driven by the Lorentz force, but seems to have been largely
overlooked until now. | 1307.6503v2 |
2013-08-08 | Magneto-Transport Properties of Single Crystalline LaFeAsO | Measurements of magnetization, specific heat, electrical resistivity, Hall
effect, and magnetoresistance on single crystalline samples of LaFeAsO grown in
a NaAs flux are reported. While this material is known to be a semimetal, the
temperature dependence of the electrical resistivity data presented herein is
reminiscent of semiconducting behavior and exhibits distinct features
associated with a structural transition and spin density wave (SDW) order.
Magnetoresistance and Hall coefficient measurements were performed in magnetic
fields up to 9 T applied perpendicular to the basal plane using a van der Pauw
configuration. The charge carrier density and mobility indicate that electrons
are the majority charge carriers and exhibit features indicative of the
structural transition and SDW formation. Low temperature X-ray diffraction
measurements have confirmed that the structural transition in these samples
occurs near 140 K, compared to a transition temperature of 156 K observed in
polycrystalline samples. Isotherms of magnetoresistivity measured as a function
of magnetic field can be scaled onto a single curve in which the scaling field
is a linear function of temperature between 2.2 K and 180 K. | 1308.1885v1 |
2013-08-20 | Probing long-range correlations in the Berezinskii-Kosterlitz-Thouless fluctuation regime of ultra-thin NbN superconducting films using transport noise measurements | We probe the presence of long-range correlations in phase fluctuations by
analyzing the higher-order spectrum of resistance fluctuations in ultra-thin
NbN superconducting films. The non-Gaussian component of resistance
fluctuations is found to be sensitive to film thickness close to the
transition, which allows us to distinguish between mean field and
Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transitions. The
extent of non-Gaussianity was found to be bounded by the BKT and mean field
transition temperatures and depend strongly on the roughness and structural
inhomogeneity of the superconducting films. Our experiment outlines a novel
fluctuation-based kinetic probe in detecting the nature of superconductivity in
disordered low-dimensional materials. | 1308.4234v2 |
2013-09-04 | Current-Induced Gap Suppression in the Mott Insulator Ca$_2$RuO$_4$ | We present nonlinear conduction phenomena in the Mott insulator Ca2RuO4
investigated with a proper evaluation of self-heating effects. By utilizing a
non-contact infrared thermometer, the sample temperature was accurately
determined even in the presence of large Joule heating. We find that the
resistivity continuously decreases with currents under an isothermal
environment. The nonlinearity and the resulting negative differential
resistance occurs at relatively low current range, incompatible with
conventional mechanisms such as hot electron or impact ionization. We propose a
possible current-induced gap suppression scenario, which is also discussed in
non-equilibrium superconducting state or charge-ordered insulator. | 1309.0909v1 |
2013-09-06 | Spin density wave order and fluctuations in Mn3Si: a transport study | We present a comprehensive transport investigation of the itinerant
antiferromagnet Mn3Si which undergoes a spin density wave (SDW) order below
T_N~21.3K. The electrical resistivity, the Hall-, Seebeck and Nernst effects
exhibit pronounced anomalies at the SDW transition, while the heat conductivity
is phonon dominated and therefore is insensitive to the intrinsic electronic
ordering in this compound. At temperatures higher than T_N our data provide
strong evidence for a large fluctuation regime which extends up to ~200K in the
resistivity, the Seebeck effect and the Nernst effect. From the comparison of
our results with other prototype SDW materials, viz. LaFeAsO and Chromium, we
conclude that many of the observed features are of generic character. | 1309.1636v1 |
2013-09-06 | Metal-insulator transition induced in SrTi_{1-x}V_xO_3 thin films | Epitaxial SrTi1-xVxO3 thin films with thicknesses of ~16 nm were grown on
(001)-oriented LSAT substrates using the pulsed electron-beam deposition
technique. The transport study revealed a temperature driven metal-insulator
transition (MIT) at 95 K for the film with x = 0.67. The films with higher
vanadium concentration (x > 0.67) were metallic, and the electrical resistivity
followed the T^2 law corresponding to a Fermi liquid system. In the insulating
region of x < 0.67, the temperature dependence of electrical resistivity for
the x = 0.5 and 0.33 films can be scaled with the variable range hopping model.
The possible mechanisms behind the observed MIT were discussed, including the
effects of electron correlation, lattice distortion and Anderson localization. | 1309.1745v1 |
2013-09-10 | Magnetoresistance evidence on surface state and field-dependent bulk gap in Kondo insulator SmB6 | Recently, the resistance saturation at low temperature in Kondo insulator
SmB6, a long-standing puzzle in condensed matter physics, was proposed to
originate from topological surface state. Here,we systematically studied the
magnetoresistance of SmB6 at low temperature up to 55 Tesla. Both temperature-
and angular-dependent magnetoresistances show a similar crossover behavior
below 5 K. Furthermore, the angular-dependent magnetoresistance on different
crystal face confirms a two-dimensional surface state as the origin of
magnetoresistances crossover below 5K. Based on two-channels model consisting
of both surface and bulk states, the field-dependence of bulk gap with critical
magnetic field (Hc) of 196 T is extracted from our temperature-dependent
resistance under different magnetic fields. Our results give a consistent
picture to understand the low-temperature transport behavior in SmB6,
consistent with topological Kondo insulator scenario. | 1309.2378v3 |
2013-09-27 | Evidence for a Kondo destroying quantum critical point in YbRh2Si2 | The heavy-fermion metal YbRh$_{2}$Si$_{2}$ is a weak antiferromagnet below
$T_{N} = 0.07$ K. Application of a low magnetic field $B_{c} = 0.06$ T ($\perp
c$) is sufficient to continuously suppress the antiferromagnetic (AF) order.
Below $T \approx 10$ K, the Sommerfeld coefficient of the electronic specific
heat $\gamma(T)$ exhibits a logarithmic divergence. At $T < 0.3$ K, $\gamma(T)
\sim T^{-\epsilon}$ ($\epsilon: 0.3 - 0.4$), while the electrical resistivity
$\rho(T) = \rho_{0} + aT$ ($\rho_{0}$: residual resistivity). Upon
extrapolating finite-$T$ data of transport and thermodynamic quantities to $T =
0$, one observes (i) a vanishing of the "Fermi surface crossover" scale
$T^{*}(B)$, (ii) an abrupt jump of the initial Hall coefficient $R_{H}(B)$ and
(iii) a violation of the Wiedemann Franz law at $B = B_{c}$, the field-induced
quantum critical point (QCP). These observations are interpreted as evidence of
a critical destruction of the heavy quasiparticles, i.e., propagating Kondo
singlets, at the QCP of this material. | 1309.7260v1 |
2013-09-29 | An Efficient Authorship Protection Scheme for Shared Multimedia Content | Many electronic content providers today like Flickr and Google, offer space
to users to publish their electronic media (e.g. photos and videos) in their
cloud infrastructures, so that they can be publicly accessed. Features like
including other information, such as keywords or owner information into the
digital material is already offered by existing providers. Despite the useful
features made available to users by such infrastructures, the authorship of the
published content is not protected against various attacks such as compression.
In this paper we propose a robust scheme that uses digital invisible
watermarking and hashing to protect the authorship of the digital content and
provide resistance against malicious manipulation of multimedia content. The
scheme is enhanced by an algorithm called MMBEC, that is an extension of an
established scheme MBEC, towards higher resistance. | 1309.7640v1 |
2013-10-11 | Enhanced low-energy magnetic excitations via suppression of the itinerancy in Fe0.98-zCuzTe0.5Se0.5 | We have performed resistivity and inelastic neutron scattering measurements
on three samples of Fe0.98-zCuzTe0.5Se0.5 with z = 0, 0.02, and 0.1. It is
found that with increasing Cu doping the sample's resistivity deviates
progressively from that of a metal. However, in contrast to expectations that
replacing Fe with Cu would suppress the magnetic correlations, the low-energy
(no larger than 12 meV) magnetic scattering is enhanced in strength, with
greater spectral weight and longer dynamical spin-spin correlation lengths.
Such enhancements can be a consequence of either enlarged local moments or a
slowing down of the spin fluctuations. In either case, the localization of the
conduction states induced by the Cu doping should play a critical role. Our
results are not applicable to models that treat 3d transition metal dopants
simply as effective electron donors. | 1310.3064v1 |
2013-10-28 | Emergence of pressure-induced metamagnetic-like state in Mn-doped CdGeAs2 chalcopyrite | The effect of hydrostatic pressure on resistivity and magnetic ac
susceptibility has been studied in Mn-doped CdGeAs2 room-temperature (RT)
ferromagnetic chalcopyrite with two types of MnAs micro-clusters. The slight
increase of temperature by about 30 K in the region between RT and Curie
temperature TC causes a significant change in the positions of pressure-induced
semiconductor-metal transition and magnetic phase transitions in low pressure
area. By conducting measurements of the anomalous Hall resistance in the field
H \leq 5 kOe, we present experimental evidence for pressure-induced
metamagnetic-like state during the paramagnetic phase at pressure P = 5 GPa. | 1310.7451v1 |
2013-12-13 | Temperature-dependent structural property and power factor of n type thermoelectric Bi0.90Sb0.10 and Bi0.86Sb0.14 alloys | Thermal variation of structural property, linear thermal expansion
coefficient, resistivity, thermopower and power factor of polycrystalline
Bi1-xSbx (x=0.10, 0.14) samples are reported. Temperature-dependent powder
diffraction experiments indicate that samples do not undergo any structural
phase transition. Rietveld refinement technique has been used to perform
detailed structural analysis. Temperature dependence of thermal expansion
coefficient is found to be stronger for Bi0.90Sb0.10. Also, power factor for
direct band gap Bi0.90Sb0.10 is higher as compared to that for indirect band
gap Bi0.86Sb0.14. Role of electron-electron and electron-phonon scattering on
resistivity, thermopower and power factor have been discussed. | 1312.3898v1 |
2014-02-11 | Taming the resistive switching in Fe/MgO/V/Fe magnetic tunnel junctions: An ab initio study | A possible mechanism for the resistive switching observed experimentally in
Fe/MgO/V/Fe junctions is presented. Ab initio total energy calculations within
the local density approximation and pseudopotential theory shows that by moving
the oxygen ions across the MgO/V interface one obtains a metastable state. It
is argued that this state can be reached by applying an electric field across
the interface. In addition, the ground state and the metastable state show
different electric conductances. The latter results are discussed in terms of
the changes of the density of states at the Fermi level and the charge transfer
at the interface due to the oxygen ion motion. | 1402.2517v2 |
2014-02-24 | Coplanar waveguide based ferromagnetic resonance in ultrathin film magnetic nanostructures: impact of conducting layers | We report broadband ferromagnetic resonance (FMR) measurements based on a
coplanar waveguide (CPW) of ultrathin magnetic film structures that comprise
in-plane/out-of-plane decoupled layers deposited on nonmagnetic buffer layers
of various thickness or other buffer structures with a diverse sheet
resistance. We show that the excitation of the fundamental mode can be
substantially (up to 10 times) enhanced in the structures deposited on buffer
layers with a low sheet resistance in comparison to the structures deposited on
thin or weakly conducting buffer layers. The results are analyzed in terms of
shielding of the electromagnetic field of CPW by the conducting buffer layers.
The effect of enhancement of FMR absorption can be attractive for applications
in spintronic devices that utilize magnetization dynamics of ultrathin
ferromagnetic layers. | 1402.5844v2 |
2014-03-05 | Electrical and optical properties of fluid iron from compressed to expanded regime | Using quantum molecular dynamics simulations, we show that the electrical and
optical properties of fluid iron change drastically from compressed to expanded
regime. The simulation results reproduce the main trends of the electrical
resistivity along isochores and are found to be in good agreement with
experimental data. The transition of expanded fluid iron into a nonmetallic
state takes place close to the density at which the constant volume derivative
of the electrical resistivity on internal energy becomes negative. The study of
the optical conductivity, absorption coefficient, and Rosseland mean opacity
shows that, quantum molecular dynamics combined with the Kubo-Greenwood
formulation provides a powerful tool to calculate and benchmark the electrical
and optical properties of iron from expanded fluid to warm dense region. | 1403.1030v1 |
2014-03-06 | Correlation between bulk thermodynamic measurements and the low temperature resistance plateau in SmB6 | Topological insulators are materials characterized by dissipationless,
spin-polarized surface states resulting from non-trivial band topologies.
Recent theoretical models and experiments suggest that SmB6 is the first
topological Kondo insulator, in which the topologically non-trivial band
structure results from electron-electron interactions via Kondo hybridization.
Here, we report that the surface conductivity of SmB6 increases systematically
with bulk carbon content. Further, addition of carbon is linked to an increase
in n-type carriers, larger low temperature electronic contributions to the
specific heat with a characteristic temperature scale of T* = 17 K, and a
broadening of the crossover to the insulating state. Additionally, X-ray
absorption spectroscopy shows a change in Sm valence at the surface. Our
results highlight the importance of phonon dynamics in producing a Kondo
insulating state and demonstrate a correlation between the bulk thermodynamic
state and low temperature resistance of SmB6. | 1403.1462v2 |
2014-03-25 | Quantum Resistor-Capacitor Circuit with Majorana Fermion Modes in Chiral Topological Superconductor | We investigate the mesoscopic resistor-capacitor circuit consisting of a
quantum dot coupled to spatially separated Majorana fermion modes in a chiral
topological superconductor. We find substantially enhanced relaxation
resistance due to the nature of Majorana fermions, which are their own
anti-particles and composed of particle and hole excitations in the same
abundance. Further, if only a single Majorana mode is involved, the
zero-frequency relaxation resistance is completely suppressed due to a
destructive interference. As a result, the Majorana mode opens an exotic
dissipative channel on a superconductor which is typically regarded as
dissipationless due to its finite superconducting gap. | 1403.6239v2 |
2014-04-26 | Electric field control of magnetic properties and magneto-transport in composite multiferroics | We study magnetic state and electron transport properties of composite
multiferroic system consisting of a granular ferromagnetic thin film placed
above the ferroelectric substrate. Ferroelectricity and magnetism in this case
are coupled by the long-range Coulomb interaction. We show that magnetic state
and magneto-transport strongly depend on temperature, external electric field,
and electric polarization of the substrate. Ferromagnetic order exists at
finite temperature range around ferroelectric Curie point. Outside the region
the film is in the superparamagnetic state. We demonstrate that magnetic phase
transition can be driven by an electric field and magneto-resistance effect has
two maxima associated with two magnetic phase transitions appearing in the
vicinity of the ferroelectric phase transition. We show that positions of these
maxima can be shifted by the external electric field and that the magnitude of
the magneto-resistance effect depends on the mutual orientation of external
electric field and polarization of the substrate. | 1404.6671v2 |
2014-05-24 | Visible light enhanced field effect at LaAlO3/SrTiO3 interface | Electrical field and light-illumination have been two most widely used
stimuli in tuning the conductivity of semiconductor devices. Via capacitive
effect electrical field modifies the carrier density of the devices, while
light-illumination generates extra carriers by exciting trapped electrons into
conduction band1. Here, we report on an unexpected light illumination enhanced
field effect in a quasi-two-dimensional electron gas (q2DEG) confined at the
LaAlO3/SrTiO3 (LAO/STO) interface which has been the focus of emergent
phenomenon exploration2-14. We found that light illumination greatly
accelerates and amplifies the field effect, driving the field-induced
resistance growth which originally lasts for thousands of seconds into an
abrupt resistance jump more than two orders of magnitude. Also, the
field-induced change in carrier density is much larger than that expected from
the capacitive effect, and can even be opposite to the conventional
photoelectric effect. This work expands the space for novel effect exploration
and multifunctional device design at complex oxide interfaces. | 1405.6250v1 |
2014-06-25 | Compressive strain-induced metal-insulator transition in orthorhombic SrIrO3 thin films | We have investigated the electronic properties of epitaxial orthorhombic
SrIrO3 thin-films under compressive strain. The metastable, orthorhombic SrIrO3
thin-films are synthesized on various substrates using an epi-stabilization
technique. We have observed that as in-plane lattice compression is increased,
the dc-resistivity (\r{ho}) of the thin films increases by a few orders of
magnitude, and the d\r{ho}/dT changes from positive to negative values.
However, optical absorption spectra show Drude-like, metallic responses without
an optical gap opening for all compressively-strained thin films. Transport
measurements under magnetic fields show negative magneto-resistance at low
temperature for compressively-strained thin-films. Our results suggest that
weak localization is responsible for the strain-induced metal-insulator
transition for the orthorhombic SrIrO3 thin-films. | 1406.6640v1 |
2014-06-28 | Exceptional Suppression of Flux-Flow Resistivity in FeSe$_{0.4}$Te$_{0.6}$ by Back-Flow from Excess Fe Atoms and Se/Te Substitutions | We measured the microwave surface impedance of FeSe$_{0.4}$Te$_{0.6}$ single
crystals with- and without external magnetic fields. The superfluid density
exhibited a quadratic temperature dependence, indicating a strong pair-breaking
effect. The flux-flow resistivity behaved as $\rho_f(B\ll B_{\rm
c2})/\rho_n=\alpha B/B_{\rm c2}$. The observed $\alpha$ value of $\approx0.66$
was considerably smaller than that of other Fe-based materials ($\alpha\geq1$)
and was attributed to a back-flow of superfluids remarkable in disordered
superconductors. This is the first-time observation of the back-flow phenomenon
caused by an origin other than the vortex pinning in multiple-band systems. | 1406.7383v2 |
2014-07-08 | Non thermal and purely electronic resistive transition in narrow gap Mott insulators | Mott insulator to metal transitions under electric field are currently the
subject of numerous fundamental and applied studies. This puzzling effect,
which involves non-trivial out-of-equilibrium effects in correlated systems, is
indeed at play in the operation of a new class of electronic memories, the Mott
memories. However the combined electronic and thermal effects are difficult to
disentangle in Mott insulators undergoing such transitions. We report here a
comparison between the properties under electric field of a canonical Mott
insulator and a model built on a realistic 2D resistor network able to capture
both thermal effects and electronic transitions. This comparison made
specifically on the family of narrow gap Mott insulators AM4Q8, (A = Ga or Ge;
M=V, Nb or Ta, and Q = S or Se) unambiguously establishes that the resistive
transition experimentally observed under electric field arises from a purely
electronic mechanism. | 1407.2038v1 |
2014-12-08 | Role of Se vacancies on Shubnikov de Haas oscillations in Bi2Se3: a combined magneto-resistance and positron annihilation study | Magneto resistance measurements coupled with positron lifetime measurements,
to characterize the vacancy type defects, have been carried out on the
topological insulator (TI) system Bi2Se3, of varying Se/Bi ratio. Pronounced
Shubnikov de Haas (SdH) oscillations are seen in nominal Bi2Se3.1 crystals for
measurements performed in magnetic fields up to 15 T in the 4 K to 10 K
temperature range, with field applied perpendicular to the (001) plane of the
crystal. The quantum oscillations, characteristic of 2D electronic structure,
are seen only in the crystals that have a lower concentration of Se vacancies,
as inferred from positron annihilation spectroscopy. | 1412.2466v1 |
2014-12-08 | Effect of Electron-Phonon Coupling on Thermal Transport across Metal-Nonmetal Interface - A Second Look | The effect of electron-phonon (e-ph) coupling on thermal transport across
metal-nonmetal interfaces is yet to be completely understood. In this paper, we
use a series of molecular dynamics (MD) simulations with e-ph coupling effect
included by Langevin dynamics to calculate the thermal conductance at a model
metal-nonmetal interface. It is found that while e-ph coupling can present
additional thermal resistance on top of the phonon-phonon thermal resistance,
it can also make the phonon-phonon thermal conductance larger than the pure
phonon transport case. This is because the e-ph interaction can disturb the
phonon subsystem and enhance the energy communication between different phonon
modes inside the metal. This facilitates redistributing phonon energy into
modes that can more easily transfer energy across the interfaces. Compared to
the pure phonon thermal conduction, the total thermal conductance with e-ph
coupling effect can become either smaller or larger depending on the coupling
factor. This result helps clarify the role of e-ph coupling in thermal
transport across metal-nonmetal interface. | 1412.2791v3 |
2014-12-15 | Percolation conductivity in hafnium sub-oxides | In this study, we demonstrated experimentally that formation of chains and
islands of oxygen vacancies in hafnium sub-oxides (HfO$_x$, $x<2$) leads to
percolation charge transport in such dielectrics. Basing on the model of
\'{E}fros-Shklovskii percolation theory good quantitative agreement between the
experimental and theoretical data of current-voltage characteristics were
achieved. Based on the percolation theory suggested model shows that hafnium
sub-oxides consist of mixtures of metallic Hf nanoscale clusters of 1-2 nm
distributed onto non-stoichiometric HfO$_x$. It was shown that reported
approach might describe low resistance state current-voltage characteristics of
resistive memory elements based on HfO$_x$. | 1412.4478v1 |
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