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2020-08-11 | Anomalous Hall effect in half-metallic Heusler compound Co$_{2}$Ti$X$ ($X$=Si, Ge) | Though Weyl fermions have recently been observed in several materials with
broken inversion symmetry, there are very few examples of such systems with
broken time reversal symmetry. Various Co$_{2}$-based half-metallic
ferromagnetic Heusler compounds are lately predicted to host Weyl type
excitations in their band structure. These magnetic Heusler compounds with
broken time reversal symmetry are expected to show a large momentum space Berry
curvature, which introduces several exotic magneto-transport properties. In
this report, we present systematic analysis of experimental results on
anomalous Hall effect (AHE) in Co$_2$Ti$X$ ($X$=Si and Ge). This study is an
attempt to understand the role of Berry curvature on AHE in Co$_2$Ti$X$ family
of materials. The anomalous Hall resistivity is observed to scale quadratically
with the longitudinal resistivity for both the compounds. The detailed analysis
indicates that in anomalous Hall conductivity, the intrinsic Karplus-Luttinger
Berry phase mechanism dominates over the extrinsic skew scattering and
side-jump mechanism. | 2008.04837v1 |
2021-03-24 | Manipulating Berry curvature of SrRuO3 thin films via epitaxial strain | Berry curvature plays a crucial role in exotic electronic states of quantum
materials, such as intrinsic anomalous Hall effect. As Berry curvature is
highly sensitive to subtle changes of electronic band structures, it can be
finely tuned via external stimulus. Here, we demonstrate in SrRuO3 thin films
that both the magnitude and sign of anomalous Hall resistivity can be
effectively controlled with epitaxial strain. Our first-principles calculations
reveal that epitaxial strain induces an additional crystal field splitting and
changes the order of Ru d orbital energies, which alters the Berry curvature
and leads to the sign and magnitude change of anomalous Hall conductivity.
Furthermore, we show that the rotation of Ru magnetic moment in real space of
tensile strained sample can result in an exotic nonmonotonic change of
anomalous Hall resistivity with the sweeping of magnetic field, resembling the
topological Hall effect observed in non-coplanar spin systems. These findings
not only deepen our understanding of anomalous Hall effect in SrRuO3 systems,
but also provide an effective tuning knob to manipulate Berry curvature and
related physical properties in a wide range of quantum materials. | 2103.12973v1 |
2022-06-06 | Anomalous Transport Properties of Re$_3$Ge$_7$ | Single crystals of intermetallic Re$_3$Ge$_7$ were grown and characterized by
measuring magnetization, electrical resistivity, Hall coefficient, and specific
heat. Magnetization measurements show the material is weakly diamagnetic. A
phase transition is indicated by a kink in magnetic susceptibility at $T_{c} =
58.5$K and is confirmed by a $\lambda$-like anomaly in specific heat. In
zero-field, the temperature dependence of electrical resistivity $\rho(T)$
follows a typical metallic behavior above $T_c$ and sharply increases below
$T_c$, showing a metal-to-insulator-like transition. When a magnetic field is
applied, strong effects on the transport properties are observed. The
temperature dependence of magnetoresistivity $\Delta\rho$ = $\rho (T, H)$ -
$\rho (T, H=0)$ develops a maximum around 30 K, deviating from ordinary
metallic behavior. Analysis of the Hall coefficient measurements indicates that
the carrier density is 0.04 per formula unit at 300 K and drops by two orders
of magnitude below $T_c$. The effective mass of charge carriers is inferred
from the analysis of the Shubnikov-de Haas quantum oscillations to be close to
the bare electron mass. | 2206.02943v1 |
2022-06-28 | Colossal piezoresistance in narrow-gap Eu5In2Sb6 | Piezoresistance, the change of a material's electrical resistance ($R$) in
response to an applied mechanical stress ($\sigma$), is the driving principle
of electromechanical devices such as strain gauges, accelerometers, and
cantilever force sensors. Enhanced piezoresistance has been traditionally
observed in two classes of uncorrelated materials: nonmagnetic semiconductors
and composite structures. We report the discovery of a remarkably large
piezoresistance in Eu$_5$In$_2$Sb$_6$ single crystals, wherein anisotropic
metallic clusters naturally form within a semiconducting matrix due to
electronic interactions. Eu$_5$In$_2$Sb$_6$ shows a highly anisotropic
piezoresistance, and uniaxial pressure along [001] of only 0.4~GPa leads to a
resistivity drop of more than 99.95\% that results in a colossal
piezoresistance factor of $5000\times10^{-11}$Pa$^{-1}$. Our result not only
reveals the role of interactions and phase separation in the realization of
colossal piezoresistance, but it also highlights a novel route to
multi-functional devices with large responses to both pressure and magnetic
field. | 2206.14073v1 |
2022-07-06 | Sn2Pd: a possible superconducting material with topological surface states | In this article, we report the detailed magneto transport measurements of the
topological semimetal (TSM) candidate, Sn2Pd. Single crystal of Sn2Pd is
synthesized through the self-flux method. Phase purity and crystalline
morphology are confirmed through powder X ray diffraction (PXRD) pattern and
field emission scanning electron microscopy (FESEM) image. Signatures of
superconducting transition are seen in both transport and magneto transport
measurements, which are further supported by the AC magnetization studies.
Sn2Pd is found to show superconductivity onset at below 2.8K, but not the zero
resistivity down to 2K. Although, isothermal magneto resistivity measurements
below superconducting onset (2.8K) clearly exhibited superconductor-like
behavior, but is not observed in heat capacity measurements, indicating the
same to be of weak nature. Magnetotransport measurements performed in a normal
state of Sn2Pd show the presence of a weak antilocalization (WAL) effect, which
is confirmed by modeling of low field magneto-conductivity (MC) through Hikami
Larkin Nagaoka (HLN) formalism. Here, it is worth mentioning that the present
article is the first report on magneto transport measurements of Sn2Pd, which
show the same to be a topological material with a weak superconducting phase
below around 2.8K. | 2207.02579v1 |
2023-03-17 | On the determination of the thermal shock parameter of MAX phases: A combined experimental-computational study | Thermal shock resistance is one of the performance-defining properties for
applications where extreme temperature gradients are required. The thermal
shock resistance of a material can be described by means of the thermal shock
parameter RT. Here, the thermo-mechanical properties required for the
calculation of RT are quantum-mechanically predicted, experimentally
determined, and compared for Ti3AlC2 and Cr2AlC MAX phases. The coatings are
synthesized utilizing direct current magnetron sputtering without additional
heating, followed by vacuum annealing. It is shown that the RT of both Ti3AlC2
and Cr2AlC obtained via simulations are in good agreement with the
experimentally obtained ones. Comparing the MAX phase coatings, both
experiments and simulations indicate superior thermal shock behavior of Ti3AlC2
compared to Cr2AlC, attributed primarily to the larger linear coefficient of
thermal expansion of Cr2AlC. The results presented herein underline the
potential of ab initio calculations for predicting the thermal shock behavior
of ionically-covalently bonded materials. | 2303.10266v2 |
2023-05-18 | Observation and enhancement of room temperature bilinear magnetoelectric resistance in sputtered topological semimetal Pt3Sn | Topological semimetal materials have become a research hotspot due to their
intrinsic strong spin-orbit coupling which leads to large charge-to-spin
conversion efficiency and novel transport behaviors. In this work, we have
observed a bilinear magnetoelectric resistance (BMER) of up to 0.1 nm2A-1Oe-1
in a singlelayer of sputtered semimetal Pt3Sn at room temperature. Different
from previous observations, the value of BMER in sputtered Pt3Sn does not
change out-of-plane due to the polycrystalline nature of Pt3Sn. The observation
of BMER provides strong evidence of the existence of spin-momentum locking in
the sputtered polycrystalline Pt3Sn. By adding an adjacent CoFeB magnetic
layer, the BMER value of this bilayer system is doubled compared to the single
Pt3Sn layer. This work broadens the material system in BMER study, which paves
the way for the characterization of topological states and applications for
spin memory and logic devices. | 2305.10720v2 |
2023-09-12 | In operando cryo-STEM of pulse-induced charge density wave switching in TaS$_2$ | The charge density wave (CDW) material 1T-TaS$_2$ exhibits a pulse-induced
insulator-to-metal transition, which shows promise for next-generation
electronics such as memristive memory and neuromorphic hardware. However, the
rational design of TaS$_2$ devices is hindered by a poor understanding of the
switching mechanism, the pulse-induced phase, and the influence of material
defects. Here, we operate a 2-terminal TaS$_2$ device within a scanning
transmission electron microscope (STEM) at cryogenic temperature, and directly
visualize the changing CDW structure with nanoscale spatial resolution and down
to 300 {\mu}s temporal resolution. We show that the pulse-induced transition is
driven by Joule heating, and that the pulse-induced state corresponds to nearly
commensurate and incommensurate CDW phases, depending on the applied voltage
amplitude. With our in operando cryo-STEM experiments, we directly correlate
the CDW structure with the device resistance, and show that dislocations
significantly impact device performance. This work resolves fundamental
questions of resistive switching in TaS$_2$ devices critical for engineering
reliable and scalable TaS$_2$ electronics. | 2309.06406v1 |
2024-05-15 | Laser Printing of Silver and Silver Oxide | We show that direct laser writing (DLW) in aqueous silver nitrate with a 1030
nm femtosecond (fs) laser results in deposition of a mixture of silver oxide
and silver, in contrast to the pure silver deposition previously reported with
780 nm fs DLW. However, adding photoinitiator prevents silver oxide formation
in a concentration-dependent manner. As a result, the resistivity of the
material can also be controlled by photoinitiator concentration with
resistivity being reduced from approximately 9e-3 $\Omega m$ to 3e-7 $\Omega
m$. Silver oxide peaks dominate the X-ray diffraction spectra when no
photoinitiator is present, while the peaks disappear with photoinitiator
concentrations above 0.05wt%. While femtosecond pulses are needed to initiate
deposition, a continues-wave laser when well overlapped with the previously
written material and supplying enough average power can lead to further
printing, suggesting thermal deposition can also occur where the photoinitiator
molecule also acts as a general reducing agent that prevents oxide formation.
We also compare the surface quality of printed lines for different
photoinitiator concentrations and laser printing conditions. A THz polarizer
and metamaterial are printed as a demonstration of silver oxide printing. | 2405.09340v1 |
2022-03-15 | High Rate and High Precision Timing and Calorimeter Detectors | High precision timing, high rate calorimeters, and radiation resistance are
becoming an important issue in particle physics especially in Energy and
Intensity Frontiers. We discuss doped Zinc Oxide (ZnO:Ga or GZO; ZnO:X where X
is Al, Cu or others) as a very fast scintillator and wavelength shifter (WLS),
Total internal reflection films, and PMT capable of counting at 300 MHz with 10
ps timing precision, with superior radiation resistance. | 2203.09942v1 |
1998-01-20 | QHE, magnetoresistance and disordered transport on 2D mesoscopic plaquettes | The transport properties of a rectangular mesoscopic plaquette in the
presence of a perpendicular magnetic field are studied in a tight-binding model
with randomly distributed traps. The longitudinal and Hall resistances are
calculted in the four-probe Landauer-B\"{u}ttiker formalism which accounts
automatically both for the quantum coherence and the trapping-induced
localization. The localized character of eigenvectors and the specific aspect
of the density of states at a given magnetic flux are correlated with the
behaviour of the mentioned resistances as function of the Fermi energy. The
Hall insulator and quantum Hall regimes are evidentiated. The dependence on
magnetic field of the configurational averages of the longitudinal and Halll
resistance is studied in a purely quantum-mechanical approach. Both negative
and positive magnetoresistances are found. | 9801192v1 |
1998-07-16 | Low temperature resistivity in a nearly half-metallic ferromagnet | We consider electron transport in a nearly half-metallic ferromagnet, in
which the minority spin electrons close to the band edge at the Fermi energy
are Anderson-localized due to disorder. For the case of spin-flip scattering of
the conduction electrons due to the absorption and emission of magnons, the
Boltzmann equation is exactly soluble to the linear order. From this solution
we calculate the temperature dependence of the resistivity due to single magnon
processes at sufficiently low temperature, namely $k_BT\ll D/L^2$, where $L$ is
the Anderson localization length and $D$ is the magnon stiffness. And depending
on the details of the minority spin density of states at the Fermi level, we
find a $T^{1.5}$ or $T^{2}$ scaling behavior for resistivity. Relevance to the
doped perovskite manganite systems is discussed. | 9807244v1 |
1998-11-26 | Kinetics of electric field induced oxygen ion migration in epitaxial metallic oxide films | In this paper we report the observation of curent induced change of
resistance of thin metallic oxide films. The resistance changes at a very low
current (current density $J \geq 10^{3}$ A/cm$^{2}$). We find that the time
dependence associated with the processes (increase of resistance) show a
streched exponential type dependence at lower temperature, which crosses over
to a creep type behavior at $T \geq$ 350 K. The time scale associated shows a
drastic drop in the magnitude at $T \approx$ 350 K, where a long range
diffusion sets in increasing the conductivity noise. The phenomena is like a
"glass-transition" in the random lattice of oxygen ions. | 9811377v1 |
1999-09-14 | Anomalous temperature behavior of resistivity in lightly doped manganites around a metal-insulator phase transition | An unusual temperature and concentration behavior of resistivity in
$La_{0.7}Ca_{0.3}Mn_{1-x}Cu_xO_3$ has been observed at slight $Cu$ doping
($0\leq x \leq 0.05$). Namely, introduction of copper results in a splitting of
the resistivity maximum around a metal-insulator transition temperature
$T_0(x)$ into two differently evolving peaks. Unlike the original $Cu$-free
maximum which steadily increases with doping, the second (satellite) peak
remains virtually unchanged for $x<x_c$, increases for $x\ge x_c$ and finally
disappears at $x_m\simeq 2x_c$ with $x_c\simeq 0.03$. The observed phenomenon
is thought to arise from competition between substitution induced strengthening
of potential barriers (which hamper the charge hopping between neighboring $Mn$
sites) and weakening of carrier's kinetic energy. The data are well fitted
assuming a nonthermal tunneling conductivity theory with randomly distributed
hopping sites. | 9909196v1 |
1999-11-25 | Anomaly of AC resistance in magnetic nanoparticle alloys at spin-glass-like transition | (withdrawn) A combined study of magnetic susceptibility and AC resistance was
performed on melt-spun Cu-Co granular magnetic ribbons. The AC resistance as a
function of temperature has a sharp maximum. We associate it with a diverging
correlation length at the temperature of collective freezing of magnetic
moments via increasing magnetic losses in the induced non-uniform field.
Application of this model to the experimental data allows a direct
determination of the critical exponent of correlation length on both sides of
the transition. Giant AC magnetoresistance is observed at the freezing
temperature. | 9911414v2 |
1999-12-14 | Giant AC magnetoresistance and anisotropic AC magnetoresistance in granular magnetic alloys | (withdrawn)AC resistance of melt-spun granular magnetic Cu85Co15 ribbons was
measured as a function of temperature in the range 5-300 K, magnetic field Hdc
in the range -60 kOe to 60 kOe, and frequency in the range 1-1000 Hz. A sharp
peak of zero-field resistance, which scales with frequency, and an associated
isotropic giant AC magnetoresistance in small fields are observed around the
temperature of collective freezing of interacting magnetic moments. Anomalous
behavior of AC resistance in large fields (Hdc > 20 kOe) is observed in a much
broader temperature range. This effect is not only frequency- dependent, but
also highly sensitive to anisotropy. We call it anisotropic AC
magnetoresistance. | 9912259v2 |
2000-07-31 | Electrical transport properties of bulk Ni$_{c}$Fe$_{1-c}$ alloys and related spin-valve systems | Within the Kubo-Greenwood formalism we use the fully relativistic,
spin-polarized, screened Korringa-Kohn-Rostoker method together with the
coherent-potential approximation for layered systems to calculate the
resistivity for the permalloy series Ni$_{c}$Fe$_{1-c}$. We are able to
reproduce the variation of the resistivity across the entire series; notably
the discontinuous behavior in the vicinity of the structural phase transition
from bcc to fcc. The absolute values for the resistivity are within a factor of
two of the experimental data. Also the giant magnetoresistance of a series of
permalloy-based spin-valve structures is estimated; we are able to reproduce
the trends and values observed on prototypical spin-valve structures. | 0007507v1 |
2001-10-19 | Transport, magnetic, thermodynamic and optical properties in Ti-doped Sr_2RuO_4 | We report on electrical resistivity, magnetic susceptibility and
magnetization, on heat capacity and optical experiments in single crystals of
Sr_2Ru_(1-x)Ti_xO_4. Samples with x=0.1 and 0.2 reveal purely semiconducting
resistivity behavior along c and the charge transport is close to localization
within the ab-plane. A strong anisotropy in the magnetic susceptibility appears
at temperatures below 100 K. Moreover magnetic ordering in c-direction with a
moment of order 0.01 mu_B/f.u. occurs at low temperatures. On doping the
low-temperature linear term of the heat capacity becomes reduced significantly
and probably is dominated by spin fluctuations. Finally, the optical
conductivity reveals the anisotropic character of the dc resistance, with the
in-plane conductance roughly following a Drude-type behavior and an insulating
response along c. | 0110412v1 |
2002-01-10 | Linear and nonlinear regime of a Random Resistor Network under biased percolation | We investigate the steady state of a two-dimensional random resistor network
subjected to two competing biased percolations as a function of the bias
strength. The properties of the linear and nonlinear regimes are studied by
means of Monte Carlo simulations. In constant current conditions, a scaling
relation is found between $<R>/<R>_0$ and $I/I_0$, where $<R>$ is the average
network resistance, $<R>_0$ the Ohmic resistance and $I_0$ an appropriate
threshold value for the onset of nonlinearity. A similar scaling relation is
found also for the relative variance of resistance fluctuations. These results
are in good agreement with electrical breakdown measurements performed in
composite materials. | 0201152v1 |
2002-04-11 | In-plane Anisotropy on Resistivity and Thermopower in The Misfit Layered Oxide Bi2-xPbxSr2Co2Oy | We investigated the in-plane anisotropy on the resistivity and thermopower of
Bi2-xPbxSr2Co2Oy single crystals, which have a misfit structure between the
hexagonal CoO2 layer and the rock salt Bi2Sr2O4 layer. The resistivity and
thermopower show significantly large anisotropy, which exceeds two at maximum.
This anisotropy would come from the anisotropic pseudogap formation enhanced by
the misfit structure. The thermopower changes with Pb doping to take a maximum
at x=0.4. The misfit structure improves the thermoelectric properties through
chemical pressure. The power factor is as large as 9 muW/cmK2 at 100 K for
x=0.6, which is the highest value for thermoelectric oxides at 100 K. | 0204245v1 |
2002-05-23 | Nonlinear AC resistivity in s-wave and d-wave disordered granular superconductors | We model s-wave and d-wave disordered granular superconductors with a
three-dimensional lattice of randomly distributed Josephson junctions with
finite self-inductance. The nonlinear ac resistivity of these systems was
calculated using Langevin dynamical equations. The current amplitude dependence
of the nonlinear resistivity at the peak position is found to be a power law
characterized by exponent $\alpha$. The later is not universal but depends on
the self-inductance and current regimes. In the weak current regime $\alpha$ is
independent of the self-inductance and equal to 0.5 or both of s- and d-wave
materials. In the strong current regime this exponent depends on the screening.
We find $\alpha \approx 1$ for some interval of inductance which agrees with
the experimental finding for d-wave ceramic superconductors. | 0205475v1 |
2002-12-06 | Ab initio and finite-temperature molecular dynamics studies of lattice resistance in tantalum | This manuscript explores the apparent discrepancy between experimental data
and theoretical calculations of the lattice resistance of bcc tantalum. We
present the first results for the temperature dependence of the Peierls stress
in this system and the first ab initio calculation of the zero-temperature
Peierls stress to employ periodic boundary conditions, which are those best
suited to the study of metallic systems at the electron-structure level. Our ab
initio value for the Peierls stress is over five times larger than current
extrapolations of experimental lattice resistance to zero-temperature. Although
we do find that the common techniques for such extrapolation indeed tend to
underestimate the zero-temperature limit, the amount of the underestimation
which we observe is only 10-20%, leaving open the possibility that mechanisms
other than the simple Peierls stress are important in controlling the process
of low temperature slip. | 0212156v2 |
2003-02-21 | Spin-Glass-like Transition and Hall Resistivity of Y2-xBixIr2O7 | Various physical properties of the pyrochlore oxide Y2-xBixIr2O7 have been
studied. The magnetizations M measured under the conditions of the
zero-field-cooling(ZFC) and the field-cooling(FC) have different values below
the temperature T=TG. The anomalous T-dependence of the electrical
resistivities r and the thermoelectric powers S observed at around TG indicates
that the behavior of the magnetization is due to the transition to the state
with the spin freezing. In this spin-frozen state, the Hall resistivities rH
measured with the ZFC and FC conditions are found to have different values,
too, in the low temperature phase (T<TG). Possible mechanisms which induce such
the hysteretic behavior are discussed. | 0302437v1 |
2003-04-11 | X-ray-induced electrical conduction in the insulating phase of thiospinel CuIr2S4 | Effects of x-ray irradiation on the crystal structure and the electrical
resistance were examined at low temperatures for the insulating phase of spinel
compound CuIr2S4. We found that the resistance decreases by more than five
decades by irradiation at 8.5 K. The structural change from triclinic to
tetragonal was observed at the same time. The x-ray-induced conductance is
deduced to result from the destruction of Ir4+ dimers formed in the insulating
phase. Slow relaxation of the resistance in the x-ray-induced state is also
reported. | 0304256v1 |
2003-04-18 | Magnetoresistance and percolation in the LaNi(1-x)Co(x)O3 solid solution | A detailed study of the zero-field electrical resistivity and
magnetoresistance for the metallic members of the LaNi_{1-x}Co{x}O3 solid
solution with 0.3<=x<=0.6 is reported. The low temperature resistivity of the
compounds with 0.3<=x<=0.5 exhibits a logarithmic dependence that is
characteristic of systems with spin fluctuations. It is suggested that the
effect of the magnetic field dependence on the spin fluctuations plays a vital
role in determining the magnetoresistive behavior of these compounds. Concrete
experimental evidence that classify the chemically induced metal-to-insulator
transition (x_{c}=0.65) as a percolative phenomenon is provided. The
resistivity data for the x=0.6 metallic compound are analyzed in the framework
of cluster percolation threshold theory. The results of this analysis are
consistent with the suggestion that the growth of magnetic metallic clusters in
the presence of a magnetic field is mainly responsible for the observed giant
magnetoresistance effect at low temperatures for the compounds with x>=0.6. | 0304423v2 |
2003-08-27 | Room temperature domain wall pinning in bent ferromagnetic nanowires | Mechanically bent nickel nanowires show clear features in their room
temperature magnetoresistance when a domain wall is pinned at the location of
the bend. By varying the direction of an applied magnetic field, the wire can
be prepared either in a single-domain state or a two-domain state. The presence
or absence of the domain wall acts to shift the switching fields of the
nanowire. In addition, a comparison of the magnetoresistance of the nanowire
with and without a domain wall shows a shift in the resistance correlated with
the presence of a wall. The resistance is decreased by 20-30 milli-Ohms when a
wall is present, compared to an overall resistance of 40-60 Ohms. A model of
the magnetization was developed that allowed calculation of the magnetostatic
energy of the nanowires, giving an estimate for the nucleation energy of a
domain wall. | 0308579v1 |
2003-11-27 | Fabrication and Electrical Properties of Pure VO2 Phase Films | We have grown VO2 thin films by laser ablation for electronic device
applications. In obtaining the thin films of the pure VO2 phase, oxygen partial
pressure is a critical parameter because vanadium oxides have several phases
with the oxygen concentration. It is found that the pure VO2 films are
epitaxially grown on Al2O3 substrate in the narrow ranges of 55-60 mTorr in an
Ar+10% O2 ambient, and that the mixed phase films are synthesized when the
deposition pressure slightly deviates from the optimum pressure. The (100)
oriented VO2 films undergo an abrupt metal-insulator transition (MIT) with
resistance change of an order of 104 at 338K. In the films of mixed phases, the
small change of the resistance is observed at the same temperature. The
polycrystalline films grown on SiO2/Si substrate undergo a broaden MIT of the
resistance. Furthermore, the abrupt MIT and collective current motion appearing
in metal are observed when the electric field is applied to the film. | 0311616v2 |
2004-01-20 | Non-Gaussian Resistance Noise near Electrical Breakdown in Granular Materials | The distribution of resistance fluctuations of conducting thin films with
granular structure near electrical breakdown is studied by numerical
simulations. The film is modeled as a resistor network in a steady state
determined by the competition between two biased processes, breaking and
recovery. Systems of different sizes and with different levels of internal
disorder are considered. Sharp deviations from a Gaussian distribution are
found near breakdown and the effect increases with the degree of internal
disorder. However, we show that in general this non-Gaussianity is related to
the finite size of the system and vanishes in the large size limit.
Nevertheless, near the critical point of the conductor-insulator transition,
deviations from Gaussianity persist when the size is increased and the
distribution of resistance fluctuations is well fitted by the universal
Bramwell-Holdsworth-Pinton distribution. | 0401352v1 |
2004-07-23 | Thermal and Electrical Properties of gamma-NaxCoO2 (0.70 < x < 0.78) | We have performed specific heat and electric resistivity measurements of
Na$_{x}$CoO$_{2}$ ($x=0.70$-0.78). Two anomalies have been observed in the
specific heat data for $x=0.78$, corresponding to magnetic transitions at
$T_{c}=22$ K and $T_{k}\simeq 9$ K reported previously. In the electrical
resistivity, a steep decrease at $T_{c}$ and a bending-like variation at
$T_{b}$(=120K for $x=0.78$) have been observed. Moreover, we have investigated
the $x$-dependence of these parameters in detail. The physical properties of
this system are very sensitive to $x$, and the inconsistent results of previous
reports can be explained by a small difference in $x$. Furthermore, for a
higher $x$ value, a phase separation into Na-rich and Na-poor domains occurs as
we previously proposed, while for a lower $x$ value, from characteristic
behaviors of the specific heat and the electrical resistivity at the
low-temperature region, the system is expected to be in the vicinity of the
magnetic instability which virtually exists below $x=0.70$. | 0407614v1 |
2004-09-24 | Hysteretic current-voltage characteristics and resistance switching at a rectifying Ti/Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$ interface | We have characterized the vertical transport properties of epitaxial layered
structures composed of Pr$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (PCMO) sandwiched between
SrRuO$_{3}$ (SRO) bottom electrode and several kinds of top electrodes such as
SRO, Pt, Au, Ag, and Ti. Among the layered structures, Ti/PCMO/SRO is distinct
due to a rectifying current-voltage ($I$--$V$) characteristic with a large
hysteresis. Corresponding to the hysteresis of the $I$--$V$ characteristics,
the contact resistance of the Ti/PCMO interface reversibly switches between two
stable states by applying pulsed voltage stress. We propose a model for the
resistance switching at the Ti/PCMO interface, in which the width and/or height
of a Schottky-like barrier are altered by trapped charge carriers in the
interface states. | 0409657v1 |
2004-12-27 | Depinning at the initial stage of the resistive transition in superconductors with a fractal cluster structure | Depinning of vortices in percolative superconductor containing fractal
clusters of a normal phase is considered. Transition of the superconductor into
a resistive state corresponds to the percolation transition from a pinned
vortex state to a resistive state when the vortices are free to move. The
motion of the magnetic flux transferred by these vortices gives rise to the
region of initial dissipation on current-voltage characteristic. The influence
of normal phase clusters on distinctive features of current-voltage
characteristics of percolative type-II superconductors is considered. It is
found that an increase in the fractal dimension of the normal phase clusters
causes the initial dissipation region to broaden out. The reason of this effect
is an increase in the density of free vortices broken away from the pinning
centers by the Lorentz force. Dependencies of the free vortex density on the
fractal dimension of the normal phase cluster boundaries are obtained. | 0412702v1 |
2005-04-20 | Resistive relaxation in field-induced insulator-metal transition of a (La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ bilayer manganite single crystal | We have investigated the resistive relaxation of a
(La$_{0.4}$Pr$_{0.6}$)$_{1.2}$Sr$_{1.8}$Mn$_{2}$O$_{7}$ single crystal, in
order to examine the slow dynamics of the field-induced insulator to metal
transition of bilayered manganites. The temporal profiles observed in remanent
resistance follow a stretched exponential function accompanied by a slow
relaxation similar to that obtained in magnetization and magnetostriction data.
We demonstrate that the remanent relaxation in magnetotransport has a close
relationship with magnetic relaxation that can be understood in the framework
of an effective medium approximation by assuming that the first order parameter
is proportional to the second order one. | 0504500v1 |
2005-05-19 | Comparison of Measured and Calculated Specific Resistances of Pd/Pt Interfaces | We compare specific resistances (AR equals area A times resistance R) of
sputtered Pd/Pt interfaces measured in two different ways with
no-free-parameter calculations. One way gives 2AR(Pd/Pt) of 0.29 (0.03)
fohm-m(2) and the other 0.17 (0.13) fohm-m(2). From these we derive a best
estimate of 2AR(Pd/Pt) of 0.28 (0.06) fohm-m(2), which overlaps with
no-free-parameter calculations: 2AR(predicted) of 0.30 (0.04) fohm-m(2) for
flat, perfect interfaces, or 0.33 (0.04) fohm-m(2) for interfaces composed of 2
monolayers of a 50percent-50percent PdPt alloy. These results support three
prior examples of agreement between calculations and measurements for pairs of
metals having the same crystal structure and the same lattice parameter to
within 1 percent. We also estimate the spin-flipping probability at Pd/Pt
interfaces as 0.13 (0.08). | 0505488v2 |
2006-01-19 | Spatially extended nature of resistive switching in perovskite oxide thin films | We report the direct observation of the electric pulse induced
resistance-change (EPIR) effect at the nano scale on La1-xSrxMnO3 (LSMO) thin
films by the current measurement AFM technique. After a switching voltage of
one polarity is applied across the sample by the AFM tip, the conductivity in a
local nanometer region around the AFM tip is increased, and after a switching
voltage of the opposite polarity is applied, the local conductivity is reduced.
This reversible resistance switching effect is observed under both continuous
and short pulse voltage switching conditions. It is important for future
nanoscale non-volatile memory device applications. | 0601451v1 |
2006-09-11 | Imaging of Microscopic Sources of Resistive and Reactive Nonlinearities in Superconducting Microwave Devices | The technique of low-temperature Laser Scanning Microscopy (LSM) has been
applied to the investigation of local microwave properties in operating
YBa2Cu3O7/LaAlO3 thin-film resonators patterned into a meandering strip
transmission line. By using a modified newly developed procedure of
spatially-resolved complex impedance partition, the influence of inhomogeneous
current flow on the formation of nonlinear (NL) microwave response in such
planar devices is analyzed in terms of the independent impact from resistive
and inductive components. The modified procedure developed here is dramatically
faster than our previous method. The LSM capability to probe the spatial
variations of two-tone, third-order intermodulation currents on micron length
scales is used to find the 2D distribution of the local sources of microwave
NL. The results show that the dominant sources of microwave NL are strongly
localized in the resistive domains. | 0609244v1 |
2006-09-24 | Swift-heavy-ion-irradiation-induced enhancement in electrical conductivity of chemical solution deposited La0.7Ba0.3MnO3 thin films | Epitaxial thin films of La0.7Ba0.3MnO3 manganite, deposited using Chemical
Solution Deposition technique, were irradiated by 200 MeV Ag+15 ions with a
maximum ion dose up to 1x10^12 ions/cm2. Temperature- and magnetic
field-dependent resistivity measurements on all the films (before and after
irradiation) reveal a sustained decrease in resistivity with increasing ion
dose. A maximum dose of 1x10^12 ions/cm2 suppresses resistivity by factors of 3
and 10, at 330 K [insulator-metal (I-M) transition] and at 10 K, respectively.
On the other hand, with increasing ion dose, the magnetoresistance (MR)
enhances in the vicinity of I-M transition but decreases at low temperatures.
These results, corroborated by surface morphology of films, suggest that the
origin of such properties lies in the irradiation induced improved
crystallinity and epitaxial orientation, enhanced connectivity between grains,
and conglomeration of grains which result in better conductivity at grain
boundaries. | 0609613v1 |
2006-10-06 | Resistive hystersis effects in perovskite oxide-based heterostructure junctions | In this paper, we report the electrical and structural properties of the
oxide-based metal/ferroelectric/metal (MFM) junctions. The heterostructures are
composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and,
BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the
dimensions of 400 x 200 micom2, have been fabricated upon LCMO/BTO/LCMO
heterostructures by photolithography and Ar-ion milling technique. The DC
current-voltage (I-V) characteristics of the MFM junctions were carried out. At
300 K, the devices showed the linear (I-V) characteristics, whereas at 77 K,
(I-V) curves exhibited some reproducible switching behaviours with well-defined
remnant currents. The resulting resistance modulation is very different from
what was already reported in ultrathin ferroelectric layers displaying
resistive switching. A model is presented to explain the datas | 0610172v1 |
2007-02-26 | Dielectrophoretically Assembled Polymer Nanowires for Gas Sensing | We measured the electronic properties and gas sensing response of nanowires
containing segments of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)
(PEDOT/PSS) that were synthesized using anodic aluminum oxide (AAO) membranes.
The nanowires have a "striped" structure of gold-PEDOT/PSS-gold and are
typically 8 um long (1 um-6 um-1 um for each section, respectively) and 220 nm
in diameter. Dielectrophoretic assembly was used to position single nanowires
on pre-fabricated gold electrodes. A polymer conductivity of 11.5 +/- 0.7 S/cm
and a contact resistance of 27.6 +/- 4 kOhm were inferred from resistance
measurements of nanowires of varying length and diameter. When used as gas
sensors, the wires showed a resistance change of 10.5%, 9%, and 4% at the
saturation vapor pressure of acetone, methanol and ethanol, respectively.
Sensor response and recovery were rapid (seconds) with excellent
reproducibility in time and across devices. "Striped" template-grown nanowires
are thus intriguing candidates for use in electronic nose vapor sensing
systems. | 0702619v1 |
2007-03-23 | On the Kondo problem and thermodynamics of dilute magnetic alloys | An argument is given showing that Coulomb attraction between conduction
electrons and impurity ions in a dilute magnetic alloy (DMA) can be
disregarded, provided the system's inverse temperature beta is replaced by an
effective inverse temperature t < beta. This replacement allows to remove the
singularity in Kondo's expression for DMA impurity resistivity and extend his
theory to 0 K. The extended Kondo formula agrees with experimental data on
resistivity of CuFe in the range of low temperatures and in the neighbourhood
of the resistivity minimum.
Using an asymptotic solution of the thermodynamics of a dilute s-d system at
inverse temperature t, the impurity thermodynamic functions are derived and
shown to provide good agreement with experimental data on CuFe, CuCr and
(LaCe)Al_2 alloys in the low-temperature range. The magnitude of these
functions agrees with experiment and does not require rescaling as in previous
s-d theories. Nonlinear dependence of CuFe heat capacity on impurity
concentration has been accounted for the first time. | 0703617v1 |
2007-05-14 | Scaling analysis of the magnetoresistance in Ga_{1-x}Mn_xAs | We compare experimental resistivity data on Ga_{1-x}Mn_xAs films with
theoretical calculations using a scaling theory for strongly disordered
ferromagnets. All characteristic features of the temperature dependence of the
resistivity can be quantitatively understood through this approach as
originating from the close vicinity of the metal-insulator transition. In
particular, we find that the magnetic field induced changes in resistance
cannot be explained within a mean-field treatment of the magnetic state, and
that accounting for thermal fluctuations is crucial for a quantitative
analysis. Similarly, while the non-interacting scaling theory is in reasonable
agreement with the data, we find clear evidence in favor of interaction effects
at low temperatures. | 0705.2016v2 |
2007-06-07 | Meta-nematic transitions in a bilayer system: Application to the bilayer ruthenate | It was suggested that the two consecutive metamagnetic transitions and the
large residual resistivity discovered in Sr$_3$Ru$_2$O$_7$ can be understood
via the nematic order and its domains in a single layer system. However, a
recently reported anisotropy between two longitudinal resistivities induced by
tilting the magnetic field away from the c-axis cannot be explained within the
single layer nematic picture. To fill the gap in our understanding within the
nematic order scenario, we investigate the effects of bilayer coupling and
in-plane magnetic field on the electronic nematic phases in a bilayer system.
We propose that the in-plane magnetic field in the bilayer system modifies the
energetics of the domain formation, since it breaks the degeneracy of two
different nematic orientations. Thus the system reveals a pure nematic phase
with a resistivity anisotropy in the presence of an in-plane magnetic field. In
addition to the nematic phase, the bilayer coupling opens a novel route to a
hidden nematic phase that preserves the x-y symmetry of the Fermi surfaces. | 0706.1069v3 |
2007-06-12 | Graphene Spin Transistor | Graphitic nanostructures, e.g. carbon nanotubes (CNT) and graphene, have been
proposed as ideal materials for spin conduction[1-7]; they have long electronic
mean free paths[8] and small spin-orbit coupling[9], hence are expected to have
very long spin-scattering times. In addition, spin injection and detection in
graphene opens new opportunities to study exotic electronic states such as the
quantum Hall[10,11] and quantum spin Hall[9] states, and spin-polarized edge
states[12] in graphene ribbons. Here we perform the first non-local four-probe
experiments[13] on graphene contacted by ferromagnetic Permalloy electrodes. We
observe sharp switching and often sign-reversal of the non-local resistance at
the coercive field of the electrodes, indicating definitively the presence of a
spin current between injector and detector. The non-local resistance changes
magnitude and sign quasi-periodically with back-gate voltage, and
Fabry-Perot-like oscillations[6,14,15] are observed, consistent with
quantum-coherent transport. The non-local resistance signal can be observed up
to at least T = 300 K. | 0706.1597v1 |
2007-08-20 | Negative magnetoresistance of ultra-narrow superconducting nanowires in the resistive state | We present a phenomenological model qualitatively explaining negative
magnetoresistance in quasi-one-dimensional superconducting channels in the
resistive state. The model is based on the assumption that fluctuations of the
order parameter (phase slips) are responsible for the finite effective
resistance of a narrow superconducting wire sufficiently close to the critical
temperature. Each fluctuation is accompanied by an instant formation of a
quasi-normal region of the order of the non-equilibrium quasiparticle
relaxation length 'pinned' to the core of the phase slip. The effective
time-averaged voltage measured in experiment is a sum of two terms. First one
is the conventional contribution linked to the rate of the fluctuations via the
Josephson relation. Second term is the Ohmic contribution of this quasi-normal
region. Depending on material properties of the wire, there might be a range of
magnetic fields where the first term is not much affected, while the second
term is effectively suppressed contributing to the experimentally observed
negative magnetoresistance. | 0708.2602v2 |
2007-11-23 | Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2 | The linear dispersion relation in graphene[1,2] gives rise to a surprising
prediction: the resistivity due to isotropic scatterers (e.g. white-noise
disorder[3] or phonons[4-8]) is independent of carrier density n. Here we show
that acoustic phonon scattering[4-6] is indeed independent of n, and places an
intrinsic limit on the resistivity in graphene of only 30 Ohm at room
temperature (RT). At a technologically-relevant carrier density of 10^12 cm^-2,
the mean free path for electron-acoustic phonon scattering is >2 microns, and
the intrinsic mobility limit is 2x10^5 cm^2/Vs, exceeding the highest known
inorganic semiconductor (InSb, ~7.7x10^4 cm^2/Vs[9]) and semiconducting carbon
nanotubes (~1x10^5 cm^2/Vs[10]). We also show that extrinsic scattering by
surface phonons of the SiO2 substrate[11,12] adds a strong temperature
dependent resistivity above ~200 K[8], limiting the RT mobility to ~4x10^4
cm^2/Vs, pointing out the importance of substrate choice for graphene
devices[13]. | 0711.3646v2 |
2008-02-11 | Anomalous Hall effect in Fe/Cu bilayers | The scaling of anomalous Hall resistivity on the longitudinal resistivity has
been intensively studied in the different magnetic systems, including
multilayers and granular films, to examine which mechanism, skew scattering or
side-jump, dominates. The basis of the scaling law is that both the
resistivities are due to the electron scattering at the imperfections in the
materials. By studying of anomalous Hall effect (AHE) in the simple Fe/Cu
bilayers, we demonstrate that the measured anomalous Hall effect should not
follow the scaling laws derived from skew scattering or side-jump mechanism due
to the short-circuit and shunting effects of the non-magnetic layers. | 0802.1462v1 |
2008-04-09 | Theory of a continuous Mott transition in two dimensions | We study theoretically the zero temperature phase transition in two
dimensions from a Fermi liquid to a paramagnetic Mott insulator with a spinon
Fermi surface. We show that the approach to the bandwidth controlled Mott
transition from the metallic side is accompanied by a vanishing quasiparticle
residue and a diverging effective mass. The Landau parameters $F^0_s, F^0_a$
also diverge. Right at the quantum critical point there is a sharply defined
`critical Fermi surface' but no Landau quasiparticle. The critical point has a
$Tln\frac{1}{T}$ specific heat and a non-zero $T = 0$ resistivity. We predict
an interesting {\em universal resistivity jump} in the residual resistivity at
the critical point as the transition is approached from the metallic side. The
crossovers out of the critical region are also studied. Remarkably the initial
crossover out of criticality on the metallic side is to a Marginal Fermi Liquid
metal. At much lower temperatures there is a further crossover into the Landau
Fermi liquid. The ratio of the two crossover scales vanishes on approaching the
critical point. Similar phenomena are found in the insulating side. The filling
controlled Mott transition is also studied. Implications for experiments on the
layered triangular lattice organic material $\kappa-(ET)_2Cu_2(CN)_3$ are
discussed. | 0804.1555v1 |
2008-04-28 | Lattice Resistance to Dislocation Motion at the Nanoscale | In this letter we propose a model that demonstrates the effect of free
surface on the lattice resistance experienced by a moving dislocation in
nanodimensional systems. This effect manifests in an enhanced velocity of
dislocation due to the proximity of the dislocation line to the surface. To
verify this finding, molecular dynamics simulations for an edge dislocation in
bcc molybdenum are performed and the results are found to be in agreement with
the numerical implementations of this model. The reduction in this effect at
higher stresses and temperatures, as revealed by the simulations, confirms the
role of lattice resistance behind the observed change in the dislocation
velocity. | 0804.4360v2 |
2008-05-13 | The Role of Electrical and Thermal Contact Resistance for Joule Breakdown of Single-Wall Carbon Nanotubes | Several data sets of electrical breakdown in air of single-wall carbon
nanotubes (SWNTs) on insulating substrates are collected and analyzed. A
universal scaling of the Joule breakdown power with nanotube length is found,
which appears independent of the insulating substrates used or their thickness.
This suggests the thermal resistances at the interface between SWNT and
insulator, and between SWNT and electrodes, govern heat sinking from the
nanotube. Analytical models for the breakdown power scaling are presented,
providing an intuitive, physical understanding of the breakdown process. The
electrical and thermal resistance at the electrode contacts limit the breakdown
behavior for sub-micron SWNTs, the breakdown power scales linearly with length
for microns-long tubes, and a minimum breakdown power (~ 0.05 uW) is observed
for the intermediate (~ 0.5 um) length range. | 0805.1937v1 |
2008-06-09 | Transport properties and superconductivity in $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with double FeAs layers | We synthesized the samples $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with
$ThCr_2Si_2$-type structure. These samples were systematically characterized by
resistivity, thermoelectic power (TEP) and Hall coefficient ($R_H$).
$BaFe_2As_2$ shows an anomaly in resistivity at about 140 K. Substitution of La
for Ba leads to a shift of the anomaly to low temperature, but no
superconducting transition is observed. Potassium doping leads to suppression
of the anomaly in resistivity and induces superconductivity at 38 K as reported
by Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurements
indicate that the TEP is negative for $BaFe_2As_2$ and La-doped $BaFe_2As_2$,
indicating n-type carrier; while potassium doping leads to change of the sign
in $R_H$ and TEP. It definitely indicates p-type carrier in superconducting
$Ba_{1-x}K_xFe_2As_2$ with double FeAs layers, being in contrast to the case of
$LnO_{1-x}F_xFeAs$ with single FeAs layer. A similar superconductivity is also
observed in the sample with nominal composition $Ba_{1-x}K_xOFe_2As_2$. | 0806.1459v1 |
2009-02-21 | Negative nonlocal resistance in mesoscopic gold Hall bars: Absence of giant spin Hall effect | We report the observation of negative nonlocal resistances in multiterminal
mesoscopic gold Hall bar structures whose characteristic dimensions are larger
than the electron mean-free path. Our results can only be partially explained
by a classical diffusive model of the nonlocal transport, and are not
consistent with a recently proposed model based on spin Hall effects. Instead,
our analysis suggests that a quasiballistic transport mechanism is responsible
for the observed negative nonlocal resistance. Based on the sensitivity of our
measurements and the spin Hall effect model, we find an upper limit for the
spin Hall angle in gold of 0.022 at 4.5 K. | 0902.3686v1 |
2009-08-26 | Piezoresistance in chemically synthesized polypyrrole thin films | The resistance of chemically synthesized polypyrrole (PPy) thin films is
investigated as a function of the pressure of various gases as well as of the
film thickness. A physical, piezoresistive response is found to coexist with a
chemical response if the gas is chemically active, like, e.g., oxygen. The
piezoresistance is studied separately by exposing the films to the chemically
inert gases such as nitrogen and argon. We observe that the character of the
piezoresistive response is a function not only of the film thickness, but also
of the pressure. Films of a thickness below 70 nm show a decreasing resistance
as pressure is applied, while for thicker films, the piezoresistance is
positive. Moreover, in some films of thickness of about 70 nm, the
piezoresistive response changes from negative to positive as the gas pressure
is increased above 500 mbars. This behavior is interpreted in terms of a total
piezoresistance which is composed of a surface and a bulk component, each of
which contributes in a characteristic way. These results suggest that in
polypyrrole, chemical sensing and piezoresistivity can coexist, which needs to
be kept in mind when interpreting resistive responses of such sensors. | 0908.3840v1 |
2009-09-28 | The effects of superconductor-stabilizer interfacial resistance on quench of current-carrying coated conductor | We present the results of numerical analysis of a model of normal zone
propagation in coated conductors. The main emphasis is on the effects of
increased contact resistance between the superconducting film and the
stabilizer on the speed of normal zone propagation, the maximum temperature
rise inside the normal zone, and the stability margins. We show that with
increasing contact resistance the speed of normal zone propagation increases,
the maximum temperature inside the normal zone decreases, and stability margins
shrink. This may have an overall beneficial effect on quench protection quality
of coated conductors. We also briefly discuss the propagation of solitons and
development of the temperature modulation along the wire. | 0909.5209v1 |
2009-11-02 | Giant anomalous Hall resistivity of the room temperature ferromagnet Fe3Sn2 - a frustrated metal with the kagome-bilayer structure | We have investigated magnetic and transport properties of the {\it
kagom\'{e}-bilayer} ferromagnet Fe$_{3}$Sn$_{2}$. A soft ferromagnetism and a
large anomalous Hall effect are observed. The saturated Hall resistivity of
Fe$_{3}$Sn$_{2}$ is 3.2 $\mu\Omega$cm at 300 K, which is almost 20 times higher
than that of typical itinerant-ferromagnets such as Fe and Ni. The anomalous
Hall coefficient $R_{{\rm s}}$ is 6.7$\times10^{-9}$ $\Omega$cm/G at 300 K,
which is three orders of magnitude larger than that of pure Fe. $R_{{\rm s}}$
obeys an unconventional scaling to the longitudinal resistivity, $\rho_{xx}$,
of $R_{{\rm s}} \propto \rho_{xx}^{3.3}$. Such a relationship cannot be
explained by the skew and/or side-jump mechanisms and indicates that the origin
of the anomalous Hall effect in the frustrated magnet Fe$_{3}$Sn$_{2}$ is
indeed extraordinary. | 0911.0289v1 |
2010-04-19 | Towards a Quantitative Description of Solid Electrolyte Conductance Switches | We present a quantitative analysis of the steady state electronic transport
in a resistive switching device. The device is composed of a thin film of
Ag$_{2}$S (solid electrolyte) contacted by a Pt nano-contact acting as
ion-blocking electrode, and a large area Ag reference electrode. When applying
a bias voltage both ionic and electronic transport occurs, and depending on the
polarity it causes an accumulation of ions around the nano-contact. At small
applied voltages (pre-switching) we observed this as a strongly nonlinear
current-voltage curve, which have been modeled using the Hebb-Wagner treatment
for polarization of a mixed conductor. This model correctly describes the
transport of the electrons within the polarized solid electrolyte in the steady
state up until the resistance switching, covering the entire range of
non-stoichiometries, and including the supersaturation range just before the
deposition of elemental silver. In this way, it is a step towards a
quantitative understanding of the processes that lead to resistance switching. | 1004.3079v1 |
2010-05-18 | A general figure of merit for thick and thin transparent conductive carbon nanotube coatings | We suggest a wavelength-dependent figure of merit for transparent conducting
nanotube networks, composed of the sheet resistance and the optical density. We
argue that this would be more useful than other suggestions prevailing in the
literature, because it relies on more realistic assumptions regarding the
optical parameters of real nanotubes: it takes into account the fact that the
dc resistivity depends on the concentration of free carriers, while the visible
absorption is caused by bound carriers. Based on sheet resistance measurements
and wide-range transmission spectra, we compare several commercial nanotube
types and find correlation between metal enrichment and figure of merit. A
simple graphical approach is suggested to determine if the required optical and
transport properties can be achieved by varying the thickness of the nanotube
layer or a more aggressive treatment is needed. The procedure can be extended
to oxide coatings as well. | 1005.3125v1 |
2010-05-30 | On the Corrosion Resistance of Porous Electroplated Zinc Coatings in Different Corrosive Media | The corrosion resistance of an electroplated (EP) Zn coating whose surface
was chemically etched to produce surface defects (pores) is investigated in
this work. Impedance and DC polarisation measururements were employed to study
the behaviour of such coating in various corrosive media (NaCl, NaOH and rain
water). Four different faradaic relaxation processes were clearly revealed in
different NaCl concentrations (from 0.1M to 1M). In the most concentrated
solutions at least three relaxation processes at low frequencies (LF) appeared
and were related to zinc deposition and dissolution. At lower concentrations
and depending on the pH, only one process was observed. The charge transfer
resistance (Rct) and the corrosion current (Icorr) were practically stable in
the pH range 5 to 10. In deaerated NaCl 0.1M, the EIS diagrams showed two
time-constants at very close frequencies. From the EIS diagrams the porous
nature of the coating was highlighted and showed that the dissolution
mechanisms occurred at the base of the pores. | 1005.5554v1 |
2010-06-12 | Ex-situ Tunnel Junction Process Technique Characterized by Coulomb Blockade Thermometry | We investigate a wafer scale tunnel junction fabrication method, where a
plasma etched via through a dielectric layer covering bottom Al electrode
defines the tunnel junction area. The ex-situ tunnel barrier is formed by
oxidation of the bottom electrode in the junction area. Room temperature
resistance mapping over a 150 mm wafer give local deviation values of the
tunnel junction resistance that fall below 7.5 % with an average of 1.3 %. The
deviation is further investigated by sub-1 K measurements of a device, which
has one tunnel junction connected to four arrays consisting of N junctions (N =
41, junction diameter 700 nm). The differential conductance is measured in
single-junction and array Coulomb blockade thermometer operation modes. By
fitting the experimental data to the theoretical models we found an upper limit
for the local tunnel junction resistance deviation of ~5 % for the array of
2N+1 junctions. This value is of the same order as the minimum detectable
deviation defined by the accuracy of our experimental setup. | 1006.2436v1 |
2010-08-24 | Magnetism of mixed quaternary Heusler alloys: (Ni,T)$_{2}$MnSn (T=Cu,Pd) as a case study | The electronic properties, exchange interactions, finite-temperature
magnetism, and transport properties of random quaternary Heusler Ni$_{2}$MnSn
alloys doped with Cu- and Pd-atoms are studied theoretically by means of {\it
ab initio} calculations over the entire range of dopant concentrations. While
the magnetic moments are only weakly dependent on the alloy composition, the
Curie temperatures exhibit strongly non-linear behavior with respect to
Cu-doping in contrast with an almost linear concentration dependence in the
case of Pd-doping. The present parameter-free theory agrees qualitatively and
also reasonably well quantitatively with the available experimental results. An
analysis of exchange interactions is provided for a deeper understanding of the
problem. The dopant atoms perturb electronic structure close to the Fermi
energy only weakly and the residual resistivity thus obeys a simple Nordheim
rule. The dominating contribution to the temperature-dependent resistivity is
due to thermodynamical fluctuations originating from the spin-disorder, which,
according to our calculations, can be described successfully via the disordered
local moments model. Results based on this model agree fairly well with the
measured values of spin-disorder induced resistivity. | 1008.4060v1 |
2010-10-29 | Nd induced Mn spin-reorientation transition in NdMnAsO | A combination of synchrotron X-ray, neutron powder diffraction,
magnetization, heat capacity and electrical resistivity measurements reveals
that NdMnAsO is an antiferromagnetic semiconductor with large Neel temperature
(TN = 359(2) K). At room temperature the magnetic propagation vector k = 0 and
the Mn moments are directed along the crystallographic c-axis (mMn = 2.41(6)
BM). Upon cooling a spin reorientation (SR) transition of the Mn moments into
the ab-plane occurs (TSR = 23 K). This coincides with the long range ordering
of the Nd moments, which are restricted to the basal plane. The magnetic
propagation vector remains k = 0. At base temperature (1.6 K) the fitted
moments are mab,Mn = 3.72(1) BM and mab,Nd = 1.94(1) BM. The electrical
resistivity is characterized by a broad maximum at 250 K, below which it has a
metallic temperature dependence but semiconducting magnitude (rho250K = 50 Ohm
cm, residual resistivity ratio = 2), and a slight upturn at the SR transition. | 1010.6145v1 |
2010-11-04 | Electron interaction-driven insulating ground state in Bi2Se3 topological insulators in the two dimensional limit | We report a transport study of ultrathin Bi2Se3 topological insulators with
thickness from one quintuple layer to six quintuple layers grown by molecular
beam epitaxy. At low temperatures, the film resistance increases
logarithmically with decreasing temperature, revealing an insulating ground
state. The sharp increase of resistance with magnetic field, however, indicates
the existence of weak antilocalization, which should reduce the resistance as
temperature decreases. We show that these apparently contradictory behaviors
can be understood by considering the electron interaction effect, which plays a
crucial role in determining the electronic ground state of topological
insulators in the two dimensional limit. | 1011.1055v1 |
2011-02-03 | Temperature dependent resistivity in bilayer graphene due to flexural phonons | We have studied electron scattering by out-of-plane (flexural) phonons in
doped suspended bilayer graphene. We have found the bilayer membrane to follow
the qualitative behavior of the monolayer cousin. In the bilayer, different
electronic structure combine with different electron-phonon coupling to give
the same parametric dependence in resistivity, and in particular the same
temperature $T$ behavior. In parallel with the single layer, flexural phonons
dominate the phonon contribution to resistivity in the absence of strain, where
a density independent mobility is obtained. This contribution is strongly
suppressed by tension, and in-plane phonons become the dominant contribution in
strained samples. Among the quantitative differences an important one has been
identified: room $T$ mobility in bilayer graphene is substantially higher than
in monolayer. The origin of quantitative differences has been unveiled. | 1102.0807v1 |
2011-05-19 | Anisotropic in-plane resistivity in the nematic phase of the iron pnictides | We show that the interference between scattering by impurities and by
critical spin fluctuations gives rise to anisotropic transport in the
Ising-nematic state of the iron pnictides. The effect is closely related to the
non-Fermi liquid behavior of the resistivity near an antiferromagnetic quantum
critical point. Our theory not only explains the observed sign of the
resistivity anisotropy $\Delta\rho$ in electron doped systems, but also
predicts a sign change of $\Delta\rho$ upon sufficient hole doping.
Furthermore, our model naturally addresses the changes in $\Delta\rho$ upon
sample annealing and alkaline-earth substitution. | 1105.3906v2 |
2011-08-17 | Control of rectifying and resistive switching behavior in BiFeO3 thin films | BiFeO3 thin films have been grown on Pt/Ti/SiO2/Si substrates with pulsed
laser deposition using Au as the top electrode. The resistive switching
property of the Au/BiFeO3/Pt stack has been significantly improved by carefully
tuning the oxygen pressure during the growth, and a large switching ratio of
~4500 has been achieved. The deposition pressure modifies the concentration of
oxygen vacancies and the rectifying behavior of the Au/BiFeO3 junction, and
consequently influences the resistive switching behavior of the whole stack.
The switching takes place homogeneously over the entire electrode, and shows a
long-term retention. | 1108.3454v1 |
2011-09-05 | The direct relation between the coefficient of the low temperature resistivity T^2 term and the superconducting transition temperature Tc | In several superconductors above the superconducting transition temperature
Tc, the electrical resistivity is of the form {\rho} =AT^2. We show that there
exists an empirical relation between Tc and A when both vary with an external
parameter, e.g. pressure. The more resistive the sample the higher the Tc.
Landau theory shows that it is a general feature of Fermi Liquids, as {\rho} is
governed by the scattering that bounds the pairs condensing at Tc. We develop a
method that allows the determination of the coupling constant {\lambda} that is
validated when used to the transport properties of superfluid 3He. | 1109.0853v1 |
2011-10-17 | In Situ Imaging of the Conducting Filament in a Silicon Oxide Resistive Switch | The nature of the conducting filaments in many resistive switching systems
has been elusive. Through in situ transmission electron microscopy, we image
the real-time formation and evolution of the filament in a silicon oxide
resistive switch. The electroforming process is revealed to involve the local
enrichment of silicon from the silicon oxide matrix. Semi-metallic silicon
nanocrystals with structural variations from the conventional diamond cubic
form of silicon are observed, which likely accounts for the conduction in the
filament. The growth and shrinkage of the silicon nanocrystals in response to
different electrical stimuli show energetically viable transition processes in
the silicon forms, offering evidence to the switching mechanism. The study here
also provides insights into the electrical breakdown process in silicon oxide
layers, which are ubiquitous in a host of electronic devices. | 1110.3755v1 |
2011-12-02 | Wigner-Mott scaling of transport near the two-dimensional metal-insulator transition | Electron-electron scattering usually dominates the transport in strongly
correlated materials. It typically leads to pronounced resistivity maxima in
the incoherent regime around the coherence temperature $T^{*}$, reflecting the
tendency of carriers to undergo Mott localization following the demise of the
Fermi liquid. This behavior is best pronounced in the vicinity of
interaction-driven (Mott-like) metal-insulator transitions, where the $T^{*}$
decreases, while the resistivity maximum $\rho_{max}$ increases. Here we show
that, in this regime, the entire family of resistivity curves displays a
characteristic scaling behavior $\rho(T)/\rho_{max}\approx F(T/T_{max}),$ while
the $\rho_{max}$ and $T_{max}\sim T^{*}$ assume a powerlaw dependence on the
quasi-particle effective mass $m^{*}$. Remarkably, precisely such trends are
found from an appropriate scaling analysis of experimental data obtained from
diluted two-dimensional electron gases in zero magnetic fields. Our analysis
provides strong evidence that inelastic electron-electron scattering -- and not
disorder effects -- dominates finite temperature transport in these systems,
validating the Wigner-Mott picture of the two-dimensional metal-insulator
transition. | 1112.0440v2 |
2012-02-15 | Non-linear resistivity and heat dissipation in monolayer graphene | We have experimentally studied the nonlinear nature of electrical conduction
in monolayer graphene devices on silica substrates. This nonlinearity manifests
itself as a nonmonotonic dependence of the differential resistance on applied
DC voltage bias across the sample. At temperatures below ~70K, the differential
resistance exhibits a peak near zero bias that can be attributed to
self-heating of the charge carriers. We show that the shape of this peak arises
from a combination of different energy dissipation mechanisms of the carriers.
The energy dissipation at higher carrier temperatures depends critically on the
length of the sample. For samples longer than 10um the heat loss is shown to be
determined by optical phonons at the silica-graphene interface. | 1202.3394v1 |
2012-04-19 | Observation of Negative Contact Resistances in Graphene Field-Effect Transistors | The gate-voltage (VG) dependence of the contact resistance (RC) in graphene
field-effect transistors is characterized by the transmission line model. The
RC-VG characteristics of Ag, Cu, and Au contacts display a dip around the
charge neutrality point, and become even negative with Ag contacts. The dip
structure is well reproduced by a model calculation that considers a
metal-contact-induced potential variation near the metal contact edges. The
apparently negative RC originates with the carrier doping from the metal
contacts to the graphene channel and appears when the doping effect is more
substantial than the actual contact resistance precisely at the contacts. The
negative RC can appear at the metal contacts to Dirac-cone systems such as
graphene. | 1204.4315v2 |
2012-05-24 | Intrinsic Electron-Phonon Resistivity in Bi2Se3 in the Topological Regime | We measure the temperature-dependent carrier density and resistivity of the
topological surface state of thin exfoliated Bi2Se3 in the absence of bulk
conduction. When the gate-tuned chemical potential is near or below the Dirac
point the carrier density is strongly temperature dependent reflecting thermal
activation from the nearby bulk valence band, while above the Dirac point,
unipolar n-type surface conduction is observed with negligible thermal
activation of bulk carriers. In this regime linear resistivity vs. temperature
reflects intrinsic electron-acoustic phonon scattering. Quantitative comparison
with a theoretical transport calculation including both phonon and disorder
effects gives the ratio of deformation potential to Fermi velocity D/\hbarvF =
4.7 {\AA}-1. This strong phonon scattering in the Bi2Se3 surface state gives
intrinsic limits for the conductivity and charge carrier mobility at room
temperature of ~550 {\mu}S per surface and ~10,000 cm2/Vs. | 1205.5554v2 |
2012-07-21 | Simulation of magnetoresistance in disordered ultracold atomic Bose gases | Anderson localization was first investigated in the context of electrons in
solids. One of the successes was in explaining the puzzle of negative
magneto-resistance - as early as the 1940s it had been observed that electron
diffusion rates in some materials can increase with the application of a
magnetic field. Anderson localization has now been demonstrated in ultra-cold
atomic gases. We present a theoretical study of the two-dimensional ultra-cold
Bose gas in the presence of disorder, to which we apply a synthetic magnetic
field. We demonstrate that, in the ballistic transport regime this leads to
positive magneto-resistance and that, in the diffusive and strong localization
regimes, can also lead to negative magneto-resistance. We propose experimental
scenarios to observe these effects. | 1207.5095v1 |
2012-07-26 | Spin-orbit-coupling induced domain-wall resistance in diffusive ferromagnets | We investigate diffusive transport through a number of domain wall (DW)
profiles of the important magnetic alloy Permalloy taking into account
simultaneously noncollinearity, alloy disorder, and spin-orbit coupling fully
quantum mechanically, from first principles. In addition to observing the known
effects of magnetization mistracking and anisotropic magnetoresistance, we
discover a not-previously identified contribution to the resistance of a DW
that comes from spin-orbit-coupling-mediated spin-flip scattering in a textured
diffusive ferromagnet. This adiabatic DW resistance, which should exist in all
diffusive DWs, can be observed by varying the DW width in a systematic fashion
in suitably designed nanowires. | 1207.6277v2 |
2012-08-01 | Textured Superconductivity in the Presence of a Coexisting Order: Ce115s and Other Heavy-Fermion Compounds | Superconductivity in strongly correlated electron systems frequently emerges
in proximity to another broken symmetry. In heavy-electron superconductors, the
nearby ordered state most commonly is magnetism, and the so-called Ce115
heavy-electron compounds have been particularly instructive for revealing new
relationships between magnetism and superconductivity. From measurements of the
resistive and bulk transitions to superconductivity in these materials, we find
that the resistive transition appears at a temperature considerably higher than
the bulk transition when superconductivity and magnetic order coexist, but this
temperature difference disappears in the absence of long-range magnetic order.
Further, in the pressure-temperature region of coexistence in CeRhIn5, a new
anisotropy in the resistive transition develops even though the tetragonal
crystal structure apparently remains unchanged, implying a form of textured
superconductivity. We suggest that this texture may be a generic response to
coexisting order in these and other heavy-fermion superconductors. | 1208.0253v1 |
2012-09-20 | Surface resistance measurements of HTS thin films using SLAO dielectric resonator | Surface resistance of HTS films is typically measured using Sapphire
dielectric rod resonators enclosed in a copper cavity. In this paper we present
surface resistance measurements of YBa2Cu3O7-{\delta} films using Strontium
Lanthanum Aluminate (SLAO) at a resonant frequency of 18.2 GHz. We have
performed the error analysis of the cavity loaded with SLAO dielectric rod and
also verification measurements using two Sapphire (Al2O3) rod resonators
operating at resonant frequencies of 24.6 GHz and 10 GHz respectively. Good
agreement between the values of Rs of two sets of YBa2Cu3O7-{\delta} films
measured using the SLAO and the Sapphire dielectrics has been obtained after a
frequency scaling of Rs was applied. Using different dielectric rods of the
same size in the same cavity for measurements of Rs of HTS films, it is
feasible to do microwave characterization of the same films at differing
frequencies. | 1209.4519v1 |
2012-12-04 | UV/Ozone treatment to reduce metal-graphene contact resistance | We report reduced contact resistance of single-layer graphene devices by
using ultraviolet ozone (UVO) treatment to modify the metal/graphene contact
interface. The devices were fabricated from mechanically transferred, chemical
vapor deposition (CVD) grown, single layer graphene. UVO treatment of graphene
in the contact regions as defined by photolithography and prior to metal
deposition was found to reduce interface contamination originating from
incomplete removal of poly(methyl methacrylate) (PMMA) and photoresist. Our
control experiment shows that exposure times up to 10 minutes did not introduce
significant disorder in the graphene as characterized by Raman spectroscopy. By
using the described approach, contact resistance of less than 200 {\Omega}
{\mu}m was achieved, while not significantly altering the electrical properties
of the graphene channel region of devices. | 1212.0838v1 |
2013-03-25 | Kinetics of excitations on the Fermi arcs in underdoped cuprates at low temperature | The Fermi-liquid-like (FL) resistivity recently observed in clean HgBa2CuO4
below the pseudogap temperature was related to carriers at the nodal points on
the Fermi surface [4]. We show that this necessitates important implications
for the electronic spectrum of underdoped (UD) cuprates in whole. Photoemission
experiments picture the spectrum as of metallic arcs separated from each other
by regions with large energy gaps. We solved the kinetic equation in such model
rigorously. The Fermi arcs carriers contribute to FL resistivity, if scattering
between the opposite nodal points admits the Umklapp processes. The Hall
coefficient defines the effective number of carriers on arcs and has the
positive sign. For clean materials the expression is applicable only at weak
magnetic fields. We discuss the Fermi arcs concept further in light of recent
experimental findings and argue that the idea of reconstructed FS in UD
cuprates is not consistent with the FL-like resistivity. | 1303.6252v2 |
2013-03-27 | First-Principles Calculation of Thermal Transport in the Metal/Graphene System | Thermal properties in the metal/graphene (Gr) systems are analyzed by using
an atomistic phonon transport model based on Landauer formalism and
first-principles calculations. The specific structures under investigation
include chemisorbed Ni(111)/Gr, physisorbed Cu(111)/Gr and Au(111)/Gr, as well
as Pd(111)/Gr with intermediate characteristics. Calculated results illustrate
a strong dependence of thermal transfer on the details of interfacial
microstructures. In particular, it is shown that the chemisorbed case provides
a generally smaller interfacial thermal resistance than the physisorbed due to
the stronger bonding. However, our calculation also indicates that the weakly
chemisorbed interface of Pd/Gr may be an exception, with the largest thermal
resistance among the considered. Further examination of the electrostatic
potential and interatomic force constants reveal that the mixed bonding force
between the Pd and C atoms results in incomplete hybridization of Pd and
graphene orbital states at the junction, leading effectively to two phonon
interfaces and a larger than expected thermal resistance. Comparison with
available experimental data shows good agreement. The result clearly suggests
the feasibility of phonon engineering for thermal property optimization at the
interface. | 1303.6936v1 |
2013-05-22 | Electron Transport Through Ag-Silicene-Ag Junctions | For several years the electronic structure properties of the novel
two-dimensional system silicene have been studied extensively. Electron
transport across metal-silicence junctions, however, remains relatively
unexplored. To address this issue, we developed and implemented a theoretical
framework that utilizes the tight-binding Fisher-Lee relation to span
non-equilibrium Green's function (NEGF) techniques, the scattering method, and
semiclassical Boltzmann transport theory. Within this hybrid quantum-classical,
two-scale framework, we calculated transmission and reflection coefficients of
monolayer and bilayer Ag-silicene-Ag junctions using the NEGF method in
conjunction with density functional theory; derived and calculated the group
velocities; and computed resistance using the semi-classical Boltzmann
equation. We found that resistances of these junctions are $\sim${}$ 0.08 \fom$
for monolayer silicene junctions and $\sim${}$ 0.3 \fom$ for bilayer ones,
factors of $\sim$8 and $\sim$2, respectively, smaller than Sharvin resistances
estimated via the Landauer formalism. | 1305.5285v1 |
2013-06-13 | Investigation of the quaternary Fe2-xCoxMnSi alloys by structural, magnetic, resistivity and spin polarization measurements | Effects of the Co substitution have been observed on the structural, magnetic
and magneto-transport properties of Fe2-xCoxMnSi alloy. Curie temperature (TC)
and saturation magnetization (MS) of these alloys increased linearly with the
Co substitution. Competitive magnetic interaction between ferromagnetic (FM)
and anti-ferromagnetic (AFM) phases exists in Fe2-xCoxMnSi for x less than 0.2,
AFM phase is completely disappears for x greater than or equal to 0.2. The
value of Rhodes-Wohlfarth ratio pc/ps is greater than one for these alloys
which is the characteristics of iterant magnetism present in the system.
M\"ossbauer spectroscopic measurements have been done to investigate the atomic
disorder and local magnetic moment for some x values. Resistivity measurements
also confirm the stability of ferromagnetism with the concentration of Co and
also show a sign of half metallicity. Resistivity shows semiconducting
behaviour for x = 0.4 which is interesting in view of spin gapless
semiconductors. | 1306.3086v3 |
2013-06-21 | Carrier density modulation in graphene underneath Ni electrode | We investigate the transport properties of graphene underneath metal to
reveal whether the carrier density in graphene underneath source/drain
electrodes in graphene field-effect transistors is fixed. The resistance of the
graphene/Ni double-layered structure has shown a graphene-like back-gate bias
dependence. In other words, the electrical properties of graphene are not
significantly affected by its contact with Ni. This unexpected result may be
ascribed to resist residuals at the metal/graphene interface, which may reduce
the interaction between graphene and metals. In a back-gate device fabricated
using the conventional lithography technique with an organic resist, the
carrier density modulation in the graphene underneath the metal electrodes
should be considered when discussing the metal/graphene contact. | 1306.5086v1 |
2013-07-29 | Molecular Doping of Multilayer MoS2 Field-effect Transistors: Reduction in Sheet and Contact Resistances | For the first time, polyethyleneimine (PEI) doping on multilayer MoS2
field-effect transistors are investigated. A 2.6 times reduction in sheet
resistance, and 1.2 times reduction in contact resistance have been achieved.
The enhanced electrical characteristics are also reflected in a 70% improvement
in ON current, and 50% improvement in extrinsic field-effect mobility. The
threshold voltage also confirms a negative shift upon the molecular doping. All
studies demonstrate the feasibility of PEI molecular doping in MoS2
transistors, and its potential applications in layer-structured semiconducting
2D crystals. | 1307.7643v2 |
2013-09-15 | Large lattice distortions associated with the magnetic transition in La0.7Sr0.3MnO3 | Colossal magnetoresistance (CMR) is associated with the phase transition from
a metallic ferromagnetic to insulating paramagnetic phase, which can be
controlled by an applied magnetic field. The insulating phase occurs due to
trapping of the charge carriers by polaronic lattice distortions, which raise
the resistivity. Theories based on local physics predict that the magnitude of
the resistivity jump at Tc is determined by how much, on average, the amplitude
of these distortions increases at the phase transition. Using neutron
scattering, we measured the average distortion amplitude in La0.7Sr0.3MnO3.
Surprisingly, its increase from below to above Tc is just as large as in other
manganites, which have a much larger resistivity jump. This result suggests
that the strength of CMR is determined not by the size of distortions, but by
their cooperative nature specific to each compound. Existing theories need to
be extended to include correlations between different unit cells to explain and
predict the strength of CMR. | 1309.3747v1 |
2013-09-20 | Surface-resistance measurements using superconducting stripline resonators | We present a method to measure the absolute surface resistance of conductive
samples at a set of GHz frequencies with superconducting lead stripline
resonators at temperatures 1- 6K. The stripline structure can easily be applied
for bulk samples and allows direct calculation of the surface resistance
without the requirement of additional calibration measurements or sample
reference points. We further describe a correction method to reduce
experimental background on high-Q resonance modes by exploiting TEM-properties
of the external cabling. We then show applications of this method to the
reference materials gold, tantalum, and tin, which include the anomalous skin
effect and conventional superconductivity. Furthermore, we extract the complex
optical conductivity for an all-lead stripline resonator to find a coherence
peak and the superconducting gap of lead. | 1309.5331v2 |
2013-10-17 | The Influence of Ca and Y on the Microstructure and Corrosion Resistance of Vacuum Die Casting AZ91 Alloy | The influence of Ca and Y on the microstructure and corrosion resistance of
vacuum die casting AZ91 alloy is investigated using optical microscope,
electron scanning microscope, weight-loss test and electrochemical corrosion
test. The results indicate that the microstructure of AZ91 alloy can be
refined, amount of Mg17Al12 phases is reduced, making Mg17Al12 phases transform
from banding to reticular, and stringer Al2Ca phases and block Al2Y phases are
formed through adding both Ca and Y. The corrosion resistance of AZ91 magnesium
alloy can be increased greatly by adding both Ca and Y. The corrosion rate of
AZ91-1.5Ca-1.0Y alloy is dropped to 16.2% of that of AZ91 alloy immersed in
3.5% NaCl aqueous solution for 24 hours. The corrosion current density of
AZ91-1.5Ca-1.0Y alloy is dropped by one order of magnitude. | 1310.4671v1 |
2013-11-05 | Effect of disorder on the resistivity anisotropy near the electronic nematic phase transition in pure and electron-doped BaFe$_2$As$_2$ | We show that the strain-induced resistivity anisotropy in the tetragonal
state of the representative underdoped Fe-arsenides BaFe$_2$As$_2$,
Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ and Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ is
independent of disorder over a wide range of defect and impurity
concentrations. This result demonstrates that the anisotropy in the in-plane
resistivity in the paramagnetic orthorhombic state of this material is not due
to elastic scattering from anisotropic defects, and is most easily understood
in terms of an intrinsic anisotropy in the electronic structure. | 1311.0933v2 |
2013-11-14 | Mechanically Modulated Tunneling Resistance in Monolayer MoS2 | We report on the modulation of tunneling resistance in MoS2 monolayers by
nano-indentation using an atomic force microscope (AFM). The resistance between
the conductive AFM tip and the bottom electrode separated by a monolayer MoS2
is reversibly reduced by up to 4 orders of magnitude, which is attributed to
enhanced quantum tunneling when the monolayer is compressed by the tip force.
Under the WKB approximation, the experimental data is quantitatively explained
by using the metal-insulator-metal tunneling diode model. As an ideal tunneling
medium, the defect-free, nanometer-thick MoS2 monolayer can serve as the active
layer for non-impacting nano-electro-mechanical switches. | 1311.3608v1 |
2014-03-21 | MoS2 Field-effect Transistors with Graphene/Metal Heterocontacts | For the first time, n-type few-layer MoS2 field-effect transistors with
graphene/Ti as the hetero-contacts have been fabricated, showing more than 160
mA/mm drain current at 1 {\mu}m gate length with an on-off current ratio of
107. The enhanced electrical characteristic is confirmed in a nearly 2.1 times
improvement in on-resistance and a 3.3 times improvement in contact resistance
with hetero-contacts compared to the MoS2 FETs without graphene contact layer.
Temperature dependent study on MoS2/graphene hetero-contacts has been also
performed, still unveiling its Schottky contact nature. Transfer length method
and a devised I-V method have been introduced to study the contact resistance
and Schottky barrier height in MoS2/graphene /metal hetero-contacts structure. | 1403.5485v2 |
2014-07-09 | Thermal transport properties of metal/MoS2 interfaces from first principles | Thermal transport properties at the metal/MoS2 interfaces are analyzed by
using an atomistic phonon transport model based on the Landauer formalism and
first-principles calculations. The considered structures include chemisorbed
Sc(0001)/MoS2 and Ru(0001)/MoS2, physisorbed Au(111)/MoS2, as well as
Pd(111)/MoS2 with intermediate characteristics. Calculated results illustrate a
distinctive dependence of thermal transfer on the details of interfacial
microstructures. More specifically, the chemisorbed case with a stronger
bonding exhibits a generally smaller interfacial thermal resistance than the
physisorbed. Comparison between metal/MoS2 and metal/graphene systems suggests
that metal/MoS2 is significantly more resistive. Further examination of lattice
dynamics identifies the presence of multiple distinct atomic planes and bonding
patterns at the interface as the key origin of the observed large thermal
resistance. | 1407.2335v1 |
2014-10-30 | Highly resistive epitaxial Mg-doped GdN thin films | We report the growth by molecular beam epitaxy of highly resistive GdN, using
intentional doping with magnesium. Mg-doped GdN layers with resistivities of
1000 {\Omega}.cm and carrier concentrations of 10E16 cm-3 are obtained for
films with Mg concentrations up to 5 x 10E19 atoms/cm3. X-ray diffraction
rocking curves indicate that Mg-doped GdN films have crystalline quality very
similar to undoped GdN films, showing that the Mg doping did not affect the
structural properties of the films. A decrease of the Curie temperature with
decreasing the electron density is observed, supporting a recently suggested
magnetic polaron scenario [F. Natali et al., Phys. Rev. B 87, 035202 (2013)]. | 1410.8228v1 |
2014-11-12 | Probing a spin-glass state in SrRuO3 thin films through higher-order statistics of resistance fluctuations | The complex perovskite oxide SrRuO3 shows intriguing transport properties at
low temperatures due to the interplay of spin, charge, and orbital degrees of
freedom. One of the open questions in this system is regarding the origin and
nature of the low-temperature glassy state. In this paper we report on
measurements of higher-order statistics of resistance fluctuations performed in
epitaxial thin films of SrRuO3 to probe this issue. We observe large
low-frequency non-Gaussian resistance fluctuations over a certain temperature
range. Our observations are compatible with that of a spin-glass system with
properties described by hierarchical dynamics rather than with that of a simple
ferromagnet with a large coercivity. | 1411.3101v1 |
2014-12-02 | On the field dependent surface resistance of niobium on copper cavities | The surface resistance Rs of superconducting cavities prepared by sputter
coating a thin niobium film on a copper substrate increases significantly
stronger with the applied RF field compared to cavities of bulk material. A
possible cause is that due to the thermal boundary resistance between the
copper substrate and the niobium film Rs is enhanced due to global heating of
the inner cavity wall. Introducing helium gas in the cavity and measuring its
pressure as a function of applied field allowed to conclude that the inner
surface of the cavity is heated up by only 60+/-60 mK when Rs increases with
Eacc by 100 nOhm. This is more than one order of magnitude less than what one
would expect from global heating. Additionally the effect of cooldown speed and
low temperature baking have been investigated in the framework of these
experiments. It is shown that for current state of the art niobium on copper
cavities there is only a detrimental effect of low temperature baking. A fast
cooldown results in a lowered Rs. | 1412.0892v1 |
2015-01-20 | Generation and detection of pure valley current by electrically induced Berry curvature in bilayer graphene | Valley is a useful degree of freedom for non-dissipative electronics since
valley current that can flow even in an insulating material does not accompany
electronic current. We use dual-gated bilayer graphene in the Hall bar geometry
to electrically control broken inversion symmetry or Berry curvature as well as
the carrier density to generate and detect the pure valley current. We find a
large nonlocal resistance and a cubic scaling between the nonlocal resistance
and the local resistivity in the insulating regime at zero-magnetic field and
70 K as evidence of the pure valley current. The electrical control of the
valley current in the limit of zero conductivity allows non-dissipative
induction of valley current from electric field and thus provides a significant
contribution to the advancement of non-dissipative electronics. | 1501.04776v1 |
2015-02-24 | Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers | Magnetoresistive effects are usually invariant upon inversion of the
magnetization direction. In noncentrosymmetric conductors, however, nonlinear
resistive terms can give rise to a current dependence that is quadratic in the
applied voltage and linear in the magnetization. Here we demonstrate that such
conditions are realized in simple bilayer metal films where the spin-orbit
interaction and spin-dependent scattering couple the current-induced spin
accumulation to the electrical conductivity. We show that the longitudinal
resistance of Ta|Co and Pt|Co bilayers changes when reversing the polarity of
the current or the sign of the magnetization. This unidirectional
magnetoresistance scales linearly with current density and has opposite sign in
Ta and Pt, which we associate with the modification of the interface scattering
potential induced by the spin Hall effect in these materials. Our results
suggest a route to control the resistance and detect magnetization switching in
spintronic devices using a two-terminal geometry, which applies also to
heterostructures including topological insulators. | 1502.06898v2 |
2015-08-17 | Emergence of non-Fermi liquid behaviors in 5d perovskite SrIrO3 thin films: interplay between correlation, disorder, and spin-orbit coupling | We investigate the effects of compressive strain on the electrical
resistivity of 5d iridium based perovskite SrIrO3 by depositing epitaxial films
of thickness 35 nm on various substrates such as GdScO3 (110), DyScO3 (110),
and SrTiO3 (001). Surprisingly, we find anomalous transport behaviors in the
tempeature dependent resistivity, where the temperature exponent evolves
continuously from 4/5 to 1 and to 3/2 with an increase of compressive strain.
Furthermore, magnetoresistance always remains positive irrespective of
resistivity upturns at low temperatures. These observations imply that the
delicate interplay between correlation and disorder in the presence of strong
spin-orbit coupling is responsible for the emergence of the non-Fermi liquid
behaviors in 5d perovskite SrIrO3 thin films. We offer a theoretical framework
for the interpretation of the experimental results. | 1508.03944v1 |
2015-08-31 | Scalable T^2 resistivity in a small single-component Fermi surface | Scattering among electrons generates a distinct contribution to electrical
resistivity that follows a quadratic temperature dependence. In
strongly-correlated electron systems, the prefactor A of this T$^2$ resistivity
scales with the magnitude of the electronic specific heat. Here, we show that
one can change the magnitude of A by four orders of magnitude in metallic
SrTiO3 by tuning the concentration of the carriers and consequently, the Fermi
energy. The T$^2$ behavior persists in the single-band dilute limit despite the
absence of two known mechanisms for T$^2$ behavior, distinct electron
reservoirs and Umklapp processes. The results highlight the absence of a
microscopic theory for momentum decay through electron-electron scattering in
different Fermi liquids. | 1508.07812v1 |
2015-08-31 | In-Line-Test of Variability and Bit-Error-Rate of HfOx-Based Resistive Memory | Spatial and temporal variability of HfOx-based resistive random access memory
(RRAM) are investigated for manufacturing and product designs. Manufacturing
variability is characterized at different levels including lots, wafers, and
chips. Bit-error-rate (BER) is proposed as a holistic parameter for the write
cycle resistance statistics. Using the electrical in-line-test cycle data, a
method is developed to derive BERs as functions of the design margin, to
provide guidance for technology evaluation and product design. The proposed BER
calculation can also be used in the off-line bench test and build-in-self-test
(BIST) for adaptive error correction and for the other types of random access
memories. | 1509.00070v1 |
2015-11-30 | Solidification and loss of hydrostaticity in liquid media used for pressure measurements | We carried out a study of the pressure dependence of the solidification
temperature in nine pressure transmitting media that are liquid at ambient
temperature, under pressures up to 2.3 GPa. These fluids are: 1:1
isopentane/n-pentane, 4:6 light mineral oil/n-pentane, 1:1 isoamyl
alcohol/n-pentane, 4:1 methanol/ethanol, 1:1 FC72/FC84 (Fluorinert), Daphne
7373, isopentane, and Dow Corning PMX silicone oils 200 and 60,000 cst. We
relied on the sensitivity of the electrical resistivity of Ba(Fe1-xRux)2As2
single crystals to the freezing of the pressure media, and cross-checked with
corresponding anomalies observed in the resistance of the manganin coil that
served as the ambient temperature resistive manometer. In addition to
establishing the Temperature-Pressure line separating the liquid (hydrostatic)
and frozen (non-hydrostatic) phases, these data permit rough estimates of the
freezing pressure of these media at ambient temperature. This pressure
establishes the extreme limit for the medium to be considered hydrostatic. For
higher applied pressures the medium has to be treated as non-hydrostatic. | 1512.00087v1 |
2015-12-18 | The effect of quenching from different temperatures on Bi 0.88 Sb 0.12 alloy | Structural, thermal, resistive and magnetic properties of melt quenched Bi
0.88 Sb 0.12 alloys are reported. The samples are heated at three different
temperatures, followed by rapid quenching in liquid nitrogen. Large temperature
difference between liquidus and solidus lines, led to microscopic
in-homogeneity in the alloy. The effect of quenching from different
temperatures in polycrystalline Bi 0.88 Sb 0.12 alloy has been studied. The
parameters such as strain, unit cell volume, and resistivity are found to
increase with temperature. Thermal variation of resistivity depicts non
monotonic temperature dependence. The total negative susceptibility increases
and band gap of semiconducting Bi 0.88 Sb 0.12 samples decreases with
increasing temperature. | 1512.05883v1 |
2015-12-18 | Exchange Bias and Bistable Magneto-Resistance States in Amorphous TbFeCo thin Films | Amorphous TbFeCo thin films sputter deposited at room temperature on
thermally oxidized Si substrate are found to exhibit strong perpendicular
magnetic anisotropy (PMA). Atom probe tomography (APT), scanning transmission
electron microscopy (STEM), and energy dispersive spectroscopy (EDS) mapping
have revealed two nanoscale amorphous phases with different Tb atomic
percentages distributed within the amorphous film. Exchange bias accompanied by
bistable magneto-resistance states has been uncovered near room temperature by
magnetization and magneto-transport measurements. The exchange anisotropy
originates from the exchange interaction between the ferrimagnetic and
ferromagnetic components corresponding to the two amorphous phases. This study
provides a platform for exchange bias and magneto-resistance switching using
single-layer amorphous ferrimagnetic thin films that require no epitaxial
growth. | 1512.06103v1 |
2015-12-23 | Topological Critical Point and Resistivity Anomaly in HfTe5 | There is a long-standing confusion concerning the physical origin of the
anomalous resistivity peak in transition metal pentatelluride HfTe5. Several
mechanisms, like the formation of charge density wave or polaron, have been
proposed, but so far no conclusive evidence has been presented. In this work,
we investigate the unusual temperature dependence of magneto-transport
properties in HfTe5. We find that a three dimensional topological Dirac
semimetal state emerges only at around Tp (at which the resistivity shows a
pronounced peak), as manifested by a large negative magnetoresistance. This
accidental Dirac semimetal state mediates the topological quantum phase
transition between the two distinct weak and strong topological insulator
phases in HfTe5. Our work not only provides the first evidence of a
temperature-induced critical topological phase transition in HfTe5, but also
gives a reasonable explanation on the long-lasting question. | 1512.07360v1 |
2016-01-03 | Detection of DC currents and resistance measurements in longitudinal spin Seebeck effect experiments on Pt/YIG and Pt/NFO | In this work we investigated thin films of the ferrimagnetic insulators YIG
and NFO capped with thin Pt layers in terms of the longitudinal spin Seebeck
effect (LSSE). The electric response detected in the Pt layer under an
out-of-plane temperature gradient can be interpreted as a pure spin current
converted into a charge current via the inverse spin Hall effect. Typically,
the transverse voltage is the quantity investigated in LSSE measurements (in
the range of \mu V). Here, we present the directly detected DC current (in the
range of nA) as an alternative quantity. Furthermore, we investigate the
resistance of the Pt layer in the LSSE configuration. We found an influence of
the test current on the resistance. The typical shape of the LSSE curve varies
for increasing test currents. | 1601.00304v1 |
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