publicationDate
stringlengths 10
10
| title
stringlengths 17
233
| abstract
stringlengths 20
3.22k
| id
stringlengths 9
12
|
|---|---|---|---|
2022-04-02 | Traction of Interlocking Spikes on a Granular Material | The interlock drive system generates traction by inserting narrow articulated
spikes into the ground and by leveraging the soil's strength to resist
horizontal draft forces. The system promises high tractive performance in low
gravity environments where tires have little traction for lack of weight. At
Earth and Space 2021 we reported the performance of such spikes on a silty clay
loam, a cohesive soil. We found that in such soil, traction below a critical
depth is provided by a zone of lateral soil failure. We also found that the
articulation translates a horizontal draft force into a vertical penetration
force strong enough to penetrate a narrow spike to a depth where the soil can
sustain the draft force, in a self-regulating way. It is conceivable that a
granular material like regolith or sand with little to no cohesive strength
provides less vertical penetration resistance and less resistance to a
horizontal draft force than a cohesive soil, which leads to the question of
whether and how much tractive force an interlocking spike can generate on a
granular material. Here we report on field trials that study different spike
designs in dry and unsaturated moist sand. The results demonstrate that a loose
granular material requires larger spikes than a cohesive soil, that these
larger spikes penetrate dry and moist sand reliably, and that they promise good
tractive efficiency. The trials indicate that on sand, a larger spike diameter
can improve the pull/weight ratio without a loss of tractive performance. | 2205.00840v2 |
2015-02-12 | RF Transport Electromagnetic Properties of CVD Graphene from DC to 110 MHz | We report measurement of the radio-frequency (RF) transport electromagnetic
properties of chemical vapour deposition (CVD) graphene over the DC to 110 MHz
frequency range at room temperature. Graphene on Si/SiO2 substrate was mounted
in a shielded four terminal-pair (4TP) adaptor which enabled direct connection
to a calibrated precision impedance analyser for measurements. Good agreement
is observed for the DC four-probe resistance and the 4TP resistance at 40 Hz,
both yielding R ~ 104 {\Omega}. In general the apparent graphene channel
electromagnetic properties are found to be strongly influenced by the substrate
parasitic capacitance and resistance, particularly for high-frequencies f > 1
MHz. A phenomenological lumped-parameter equivalent circuit model is presented
which matches the frequency response of the graphene 4TP impedance device over
approximately seven decades of the frequency range of the applied transport
alternating current. Based on this model, it is shown for the first time, that
the intrinsic graphene channel resistance of the 4TP device is
frequency-independent (i.e. dissipationless) with RG ~ 105 {\Omega} or sheet
resistance of approximately 182 {\Omega} / sq. The parasitic substrate
impedance of the device is found shunt RG with RP ~ 2.2 {\Omega} in series with
CP ~ 600 pF. These results suggest that our new RF 4TP method is in good
agreement with the conventional DC four-probe method for measuring the
intrinsic sheet resistance of single-atom thick materials and could potentially
open up new applications in RF electronics, AC quantum Hall effect metrology
and sensors based on graphene 4TP devices operating over broad range of
frequencies. | 1502.03835v1 |
2015-12-11 | Intrinsic high electrical conductivity of stoichiometric SrNbO3 epitaxial thin films | SrVO3 and SrNbO3 are perovskite-type transition-metal oxides with the same d1
electronic configuration. Although SrNbO3 (4d1) has a larger d orbital than
SrVO3 (3d1), the reported electrical resistivity of SrNbO3 is much higher than
that of SrVO3, probably owing to nonstoichiometry. In this paper, we grew
epitaxial, high-conductivity stoichiometric SrNbO3 using pulsed laser
deposition. The growth temperature strongly affected the Sr/Nb ratio and the
oxygen content of the films, and we obtained stoichiometric SrNbO3 at a very
narrow temperature window around 630 ${\deg}$C. The stoichiometric SrNbO3
epitaxial thin films grew coherently on KTaO3 (001) substrates with high
crystallinity. The room-temperature resistivity of the stoichiometric film was
$2.82 {\times} 10^{-5} {\Omega}$cm, one order of magnitude lower than the
lowest reported value of SrNbO3 and comparable with that of SrVO3. We observed
a T-square dependence of resistivity below $T^{\ast}$ = 180 K and non-Drude
behavior in near-infrared absorption spectroscopy, attributable to the
Fermi-liquid nature caused by electron correlation. Analysis of the T-square
coefficient A of resistivity experimentally revealed that the 4d orbital of Nb
that is larger than the 3d ones certainly contributes to the high electrical
conduction of SrNbO3. | 1512.03588v1 |
2020-08-22 | Indium-Tin-Oxide Transistors with One Nanometer Thick Channel and Ferroelectric Gating | In this work, we demonstrate high performance indium-tin-oxide (ITO)
transistors with the channel thickness down to 1 nm and ferroelectric
Hf0.5Zr0.5O2 as gate dielectric. On-current of 0.243 A/mm is achieved on
sub-micron gate-length ITO transistors with a channel thickness of 1 nm, while
it increases to as high as 1.06 A/mm when the channel thickness increases to 2
nm. A raised source/drain structure with a thickness of 10 nm is employed,
contributing to a low contact resistance of 0.15 {\Omega}mm and a low contact
resistivity of 1.1{\times}10-7 {\Omega}cm2. The ITO transistor with a recessed
channel and ferroelectric gating demonstrates several advantages over 2D
semiconductor transistors and other thin film transistors, including large-area
wafer-size nanometer thin film formation, low contact resistance and contact
resistivity, atomic thin channel being immunity to short channel effects, large
gate modulation of high carrier density by ferroelectric gating, high-quality
gate dielectric and passivation formation, and a large bandgap for the
low-power back-end-of-line (BEOL) CMOS application. | 2008.09881v1 |
2022-12-13 | Collapse of Metallicity and High-$T_c$ Superconductivity in the High-Pressure phase of FeSe$_{0.89}$S$_{0.11}$ | We investigate the high-pressure phase of the iron-based superconductor
FeSe$_{0.89}$S$_{0.11}$ using transport and tunnel diode oscillator studies. We
construct detailed pressure-temperature phase diagrams that indicate that
outside of the nematic phase, the superconducting critical temperature reaches
a minimum before it is quickly enhanced towards 40 K above 4 GPa. The
resistivity data reveal signatures of a fan-like structure of non-Fermi liquid
behaviour which could indicate the existence of a putative quantum critical
point buried underneath the superconducting dome around 4.3 GPa. Further
increasing the pressure, the zero-field electrical resistivity develops a
non-metallic temperature dependence and the superconducting transition broadens
significantly. Eventually, the system fails to reach a fully zero-resistance
state despite a continuous finite superconducting transition temperature, and
any remaining resistance at low temperatures becomes strongly
current-dependent. Our results suggest that the high-pressure, high-$T_c$ phase
of iron chalcogenides is very fragile and sensitive to uniaxial effects of the
pressure medium, cell design and sample thickness which can trigger a
first-order transition. These high-pressure regions could be understood
assuming a real-space phase separation caused by concomitant electronic and
structural instabilities. | 2212.06824v1 |
2023-03-30 | Highly tunable NbTiN Josephson junctions fabricated with focused helium ion beam | We demonstrate a "direct writing" method for the fabrication of planar
Josephson junctions from high quality superconducting niobium titanium nitride
(NbTiN) thin films using focused He-ion beam irradiation. Compared to the
materials previously used in such processing, YBCO and MgB$_2$, NbTiN has much
better mechanical and electrical properties, as well as good corrosion
resistance. We show that we can control the suppression of superconductivity in
NbTiN as a function of the helium ion beam fluence, and that this controllable
critical temperature suppression combined with the high spatial resolution and
position control of the He-ion beam in a helium ion microscope enables us to
successfully fabricate Josephson junctions with highly tunable weak links.
Because of the continuous nature of the disorder-induced metal-insulator
transition, this method allows the creation of barriers with wide range of
resistivities ranging from the metallic to the insulating state, with the
critical current and the junction resistance varying over two orders of
magnitude. Electrical transport measurements show that junctions follow closely
the ideal resistively and capacitively shunted junction behavior, have high
characteristic voltages ($0.2-1.4$ mV) and show Shapiro steps up to very high
orders. This suggests that these type of junctions are suitable for a wide
range of applications in superconducting electronics and quantum information
technology, with the bonus that a whole device can be fabricated from just a
single thin film, with the excellent electrical and microwave characteristics
offered by NbTiN. | 2303.17348v1 |
2020-09-05 | Corrosion Resistance of Sulfur-Selenium Alloy Coatings | Despite decades of research, metallic corrosion remains a long-standing
challenge in many engineering applications. Specifically, designing a material
that can resist corrosion both in abiotic as well as biotic environments
remains elusive. Here we design a lightweight sulfur-selenium (S-Se) alloy with
high stiffness and ductility that can serve as a universal corrosion-resistant
coating with protection efficiency of ~99.9% for steel in a wide range of
diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7
orders of magnitude lower than bare metal in abiotic (simulated seawater and
sodium sulfate solution) and biotic (sulfate-reducing bacterial medium)
environments. The coating is strongly adhesive and mechanically robust. We
attribute the high corrosion resistance of the alloy in diverse environments to
its semi-crystalline, non-porous, anti-microbial, and viscoelastic nature with
superior mechanical performance, enabling it to successfully block a variety of
diffusing species. | 2009.02451v1 |
2006-09-08 | Peak resistance temperature and low temperature resistivity in thin film $La_{1-x} Ca_x Mn O_3$ mixtures for x <= 1/3 | The electrical resistivity of La$_{1-x}$Ca$_{x}$MnO$_{3}$ thin films grown on
(001) NdGaO$_{3}$ and (100) SrTiO$_{3}$ substrates by off-axis sputtering has
been studied as a function of the Calcium doping level. The samples have very
narrow rocking curves and excellent in plane registry with the substrate. A
strong correlation between the peak resistance temperature and the polaronic
hopping energy is seen which is not simply linear. The low temperature
resistivity is seen to be fit better by a model of single magnon scattering,
and a near linear correlation between the resistivity due to magnon scattering
and static impurities is observed. | 0609206v1 |
2011-10-18 | Superior performance of multilayered fluoropolymer films in low voltage electrowetting | The requirement for low operational voltage in electrowetting devices, met
using thin dielectrics, is usually connected with serious material failure
issues. Dielectric breakdown (visible as electrolysis) is frequently evident
slightly beyond the onset of the contact angle saturation. Here, plasma
enhanced chemical vapor deposition (PECVD) is used to deposit thin fluorocarbon
films prior to the spin-coating of Teflon\textregistered amorphous
fluoropolymer on tetraethoxysilane (TEOS) substrates. The resulting
multilayered hydrophobic top coating improves the electrowetting performance of
the stack, by showing high resistance to dielectric breakdown at high applied
voltages and for continuous long term application of DC and AC voltage. Leakage
current measurements during electrowetting experiments with the proposed
composite coating showed that current remains fairly constant at consecutive
electrowetting tests in contrast to plain Teflon\textregistered coating in
which material degradation is evident by a progressive increase of the leakage
current after multiple electrowetting tests. Since the proposed composite
coating demonstrates increased resistance to material failure and to dielectric
breakdown even at thin configurations, its integration in electrowetting
devices may impact their reliability, robustness and lifetime. | 1110.4075v1 |
2023-12-11 | High-speed sensing of RF signals with phase change materials | RF radiation spectrum is central to wireless and radar systems among numerous
high-frequency device technologies. Here, we demonstrate sensing of RF signals
in the technologically relevant 2.4 GHz range utilizing vanadium dioxide (VO2),
a quantum material that has garnered significant interest for its
insulator-to-metal transition. We find the electrical resistance of both
stoichiometric as well as off-stoichiometric vanadium oxide films can be
modulated with RF wave exposures from a distance. The response of the materials
to the RF waves can be enhanced by either increasing the power received by the
sample or reducing channel separation. We report a significant ~73% drop in
resistance with a 5 {\mu}m channel gap of the VO2 film at a characteristic
response time of 16 microseconds. The peak sensitivity is proximal to the phase
transition temperature boundary that can be engineered via doping and crystal
chemistry. Dynamic sensing measurements highlight the films' rapid response and
broad-spectrum sensitivity. Engineering electronic phase boundaries in
correlated electron systems could offer new capabilities in emerging
communication technologies. | 2312.06459v1 |
2015-09-14 | Torsional chiral magnetic effect in Weyl semimetal with topological defect | We propose a torsional response raised by lattice dislocation in Weyl
semimetals akin to chiral magnetic effect; i.e. a fictitious magnetic field
arising from screw or edge dislocation induces charge current. We demonstrate
that, in sharp contrast to the usual chiral magnetic effect which vanishes in
real solid state materials, the torsional chiral magnetic effect exists even
for realistic lattice models, which implies the experimental detection of the
effect via SQUID or nonlocal resistivity measurements in Weyl semimetal
materials. | 1509.03981v3 |
2016-05-02 | Study of glass properties as electrode for RPC | Operation and performance of the Resistive Plate Chambers (RPCs) mostly
depend on the quality and characteristics of the electrode materials. The
India-based Neutrino Observatory collaboration has chosen glass RPCs as the
active detector elements for its Iron Calorimeter detector and is going to
deploy RPCs in an unprecedented scale. Therefore, it is imperative that we
study the electrode material aspects in detail. We report here, systematic
characterization studies on the glasses from two manufacturers. RPC detectors
were built using these glasses and performances of the same were compared with
their material properties. | 1605.01044v1 |
2010-07-06 | Effects of chemical substitution on transport properties of Bi-based high temperature superconductors | This report describes some transport and magnetic properties of doped Bi2212
and Bi2223 superconducting whiskers. These materials have advantages over
polycrystalline sample as well as large bulk crystals in that they provide
narrow transitions in resistance versus temperature as well as in magnetization
versus temperature curves. In addition they are easy to grow and and have short
oxygen annealing times. Here Data on transport and magnetic properties of these
superconducting whiskers are presented. | 1007.0971v1 |
2021-07-03 | Thin film of Al-Ga-Pd-Mn quasicrystalline alloy | Thin film quasicrystal coatings have unique properties such as very high
electrical and thermal resistivity and very low surface energy. A nano
quasicrystalline thin film of icosahedral Al-Ga-Pd-Mn alloy, has produced by
flash evaporation followed by annealing. Attempts will be made to discuss the
micromechanisms for the formation of quasicrystalline thin film in Al-Ga-Pd-Mn
alloys | 2107.01478v1 |
2014-03-06 | Normalized Contact Force to Minimize "Electrode-Lead" Resistance in a Nanodevice | In this report, the contact resistance between "electrode" and "lead" is
investigated for reasonable measurements of samples' resistance in a
polypyrrole (PPy) nanowire device. The sample's resistance, including
"electrode-lead" contact resistance, shows a decrease as force applied to the
interface increases. Moreover, the sample's resistance becomes reasonably
similar to, or lower than, values calculated by resistivity of PPy reported in
previous studies. The decrease of electrode-lead contact resistance by
increasing the applying force was analyzed by using Holm theory: the general
equation of relation between contact resistance ($R_H$) of two-metal thin films
and contact force ($R_H$ $\propto$ $1/\sqrt{F}$). The present investigation can
guide a reliable way to minimize electrode-lead contact resistance for
reasonable characterization of nanomaterials in a microelectrode device. | 1403.1357v1 |
2004-11-12 | Microwave induced resistance oscillations on a high-mobility 2DEG: absorption/reflection and temperature damping experiments | In this work we address experimentally a number of unresolved issues related
to microwave induced resistance oscillations (MIRO) and the zero-resistance
states observed recently on very high-mobility 2D electron gases in GaAs/AlGaAs
heterostructures. In particular, we examine electrodynamic effects via
reflection/absorption experiments and study the exact waveform of MIRO and
their damping due to temperature. It is shown that electrodynamic effects due
to metallic-like reflection and plasmons are important producing a wide
cyclotron resonance line and a number of oscillations which do not coincide
with the MIRO. To describe the MIRO waveform a simple model was employed
involving radiation-induced scattering with displacement. A very good
correlation was found between the temperature dependencies of the quantum
lifetime from MIRO and the transport scattering time from the electron
mobility. The results are compared with measurements of Shubnikov-de Haas
oscillations down to 30 mK on the same sample. | 0411338v1 |
2007-04-20 | Photoelectric phenomena in structures based on high-resistivity semiconductor crystals with a thin insulator layer at the semiconductor-metal boundary | A previously unknown effect-giant spatial redistribution of the electric
field strength in a crystal under illumination of the structure - was
discovered and investigated in real photoresistors on high-resistivity
(semi-insulating) semiconductor CdTe crystals (in metal-thin insulator-
semiconductor-thin insulator -metal structures).
A new concept is proposed for photoelectric phenomena in high- resistivity
semiconductor crystals. The concept is based on the idea that the
redistribution of the field under such conditions that the carrier lifetime
remains unchanged under illumination plays a determining role in these
phenomena. The nature of the effect is described, the dependence of the
characteristics of the structures on the parameters of the crystal and the
insulator layers is explained by the manifestation of this effect, and ways to
produce structures with prescribed photoelectric characteristics for new
devices and scientific methods are examined. | 0704.2703v1 |
2009-03-15 | Current-induced electroresistance in Nd0.5Ca0.5Mn0.95Ni0.05O3 | We have investigated the dc and pulsed current-induced electroresistance in
phase separated manganite Nd0.5Ca0.5Mn0.95Ni0.05O3 (NCMONi05) as a function of
temperature and magnetic field. It is shown that the negative differential
resistance which appears above a threshold current (Ic) and hysteresis in the
V-I progressively vanish with increasing period of the current pulses. However
a strong non-linearity in V-I exists even for a pulse period of 6s. The peak
voltage at Ic decreases in magnitude and shifts towards higher current values
with increasing strength of the magnetic field. The strong nonlinear behavior
and the negative differential resistance in the dc current sweep are
accompanied by a rapid increase of the sample surface temperature and therefore
primarily arise from the Joule heating in the sample. While the Joule heating
assists electroresistance in the high dc current regime, the nonlinearity in
the pulsed current sweep and the resistivity switching between a high and low
value induced by controlling the width and period of pulses can not be
explained solely on the basis of Joule heating. | 0903.2616v2 |
2009-09-15 | Broken symmetry states and divergent resistance in suspended bilayer graphene | Graphene [1] and its bilayer have generated tremendous excitement in the
physics community due to their unique electronic properties [2]. The intrinsic
physics of these materials, however, is partially masked by disorder, which can
arise from various sources such as ripples [3] or charged impurities [4].
Recent improvements in quality have been achieved by suspending graphene flakes
[5,6], yielding samples with very high mobilities and little charge
inhomogeneity. Here we report the fabrication of suspended bilayer graphene
devices with very little disorder. We observe fully developed quantized Hall
states at magnetic fields of 0.2 T, as well as broken symmetry states at
intermediate filling factors $\nu = 0$, $\pm 1$, $\pm 2$ and $\pm 3$. The
devices exhibit extremely high resistance in the $\nu = 0$ state that grows
with magnetic field and scales as magnetic field divided by temperature. This
resistance is predominantly affected by the perpendicular component of the
applied field, indicating that the broken symmetry states arise from many-body
interactions. | 0909.2883v1 |
2010-03-06 | Reduction of high reset currents in unipolar resistance switching Pt/SrTiOx/Pt capacitors using acceptor doping | The high reset current, IR, in unipolar resistance switching is an important
issue which should be resolved for practical applications in nonvolatile
memories. We showed that,during the forming and set processes, the compliance
current, Icomp, can work as a crucial parameter to reduce IR. Doping with Co or
Mn can significantly reduce the leakage current in capacitors made using SrTiOx
film, opening a larger operation window for Icomp. By decreasing Icomp with
acceptor doping, we could reduce IR in SrTiOx films by a factor of
approximately 20. Our work suggests that the decrease of Icomp by carrier
doping could be a viable alternative for reducing IR in unipolar resistance
switching. | 1003.1390v1 |
2011-11-01 | High pressure transport properties of the topological insulator Bi2Se3 | We report x-ray diffraction, electrical resistivity, and magnetoresistance
measurements on Bi2Se3 under high pressure and low temperature conditions.
Pressure induces profound changes in both the room temperature value of the
electrical resistivity as well as the temperature dependence of the
resistivity. Initially, pressure drives Bi2Se3 towards increasingly insulating
behavior and then, at higher pressures, the sample appears to enter a fully
metallic state coincident with a change in the crystal structure. Within the
low pressure phase, Bi2Se3 exhibits an unusual field dependence of the
transverse magnetoresistance that is positive at low fields and becomes
negative at higher fields. Our results demonstrate that pressures below 8 GPa
provide a non-chemical means to controllably reduce the bulk conductivity of
Bi2Se3. | 1111.0098v1 |
2011-11-14 | Study of Resistive Micromegas in a Mixed Neutron and Photon Radiation Field | The Muon ATLAS Micromegas Activity (MAMMA) focuses on the development and
testing of large-area muon detectors based on the bulk-Micromegas technology.
These detectors are candidates for the upgrade of the ATLAS Muon System in view
of the luminosity upgrade of Large Hadron Collider at CERN (sLHC). They will
combine trigger and precision measurement capability in a single device. A
novel protection scheme using resistive strips above the readout electrode has
been developed. The response and sparking properties of resistive Micromegas
detectors were successfully tested in a mixed (neutron and gamma) high
radiation field supplied by the Tandem accelerator, at the N.C.S.R. Demokritos
in Athens. Monte-Carlo studies have been employed to study the effect of 5.5
MeV neutrons impinging on Micromegas detectors. The response of the Micromegas
detectors on the photons originating from the inevitable neutron inelastic
scattering on the surrounding materials of the experimental facility was also
studied. | 1111.3185v1 |
2015-01-26 | Linear magneto-resistance versus weak antilocalization effects in Bi$_2$Te$_3$ films | In chalcogenide topological insulator materials, two types of
magneto-resistance (MR) effects are widely discussed: a positive MR dip around
zero magnetic field associated with the weak antilocalization (WAL) effect and
a linear MR effect which generally persists to high fields and high
temperatures. We have studied the MR of topological insulator Bi2Te3 films from
the metallic to semiconducting transport regime. While in metallic samples, the
WAL is difficult to identify due to the smallness of the WAL compared to the
samples' conductivity, the sharp WAL dip in the MR is clearly present in the
samples with higher resistivity. To correctly account for the low field MR by
the quantitative theory of WAL according to the Hikami-Larkin-Nagaoka (HLN)
model, we find that the classical (linear) MR effect should be separated from
the WAL quantum correction. Otherwise the WAL fitting alone yields an
unrealistically large coefficient $\alpha$ in the HLN analysis. | 1501.06500v2 |
2018-04-05 | Observation of transition from semiconducting to metallic ground state in high-quality single crystalline FeSi | We report anomalous physical properties of single-crystalline FeSi over a
wide temperature range 1.8-400 K. X-ray diffraction, specific heat, and
magnetization measurements indicate that the FeSi crystals synthesized in this
study are of high quality with a very low concentration of magnetic impurities
($\sim$0.01$\%$). The electrical resistivity $\rho$($T$) can be described by
activated behavior with an energy gap $\Delta$ = 57 meV between 67 K and 150 K.
At temperatures below 67 K, $\rho$($T$) is significantly lower than an
extrapolation of the activated behavior, and the Hall coefficient and
magneto-resistivity undergo a sign change in this region. At $\sim$19 K, a
transition from semiconducting to metallic-like behavior is observed with
deceasing temperature. Whereas the transition temperature is very robust in a
magnetic field, the magnitude of the resistivity below $\sim$30 K is very
sensitive to magnetic field. There is no indication of a bulk phase transition
or onset of magnetic order in the vicinity of either 67 K or 19 K from specific
heat and magnetic susceptibility measurements. These measurements provide
evidence for a conducting surface state in FeSi at low temperatures. | 1804.02036v1 |
2014-08-12 | Nematic spin correlations in the tetragonal state of uniaxial strained BaFe2-xNixAs2 | Understanding the microscopic origins of electronic phases in high-transition
temperature (high-Tc) superconductors is important for elucidating the
mechanism of superconductivity. In the paramagnetic tetragonal phase of
BaFe2-xTxAs2 (where T is Co or Ni) iron pnictides, an in-plane resistivity
anisotropy has been observed. Here we use inelastic neutron scattering to show
that low-energy spin excitations in these materials change from four-fold
symmetric to two-fold symmetric at temperatures corresponding to the onset of
the in-plane resistivity anisotropy. Because resistivity and spin excitation
anisotropies both vanish near optimal superconductivity, we conclude that they
are likely intimately connected. | 1408.2756v1 |
2017-07-01 | Memory vs. irreversibility in thermal densification of amorphous glasses | We report on dynamic effects associated with thermally-annealing amorphous
indium-oxide films. In this process the resistance of a given sample may
decrease by several orders of magnitude at room-temperatures, while its
amorphous structure is preserved. The main effect of the process is
densification - increased system density. The study includes the evolution of
the system resistivity during and after the thermal-treatment, the changes in
the conductance-noise, and accompanying changes in the optical properties. The
sample resistance is used to monitor the system dynamics during the annealing
period as well as the relaxation that ensues after its termination. These
reveal slow processes that fit well a stretched-exponential law, a behavior
that is commonly observed in structural glasses. There is an intriguing
similarity between these effects and those obtained in high-pressure
densification experiments. Both protocols exhibit the "slow spring-back"
effect, a familiar response of memory-foams. A heuristic picture based on a
modified Lennard-Jones potential for the effective interparticle interaction is
argued to qualitatively account for these densification-rarefaction phenomena
in amorphous materials whether affected by thermal-treatment or by application
of high-pressure. | 1707.00173v1 |
2021-05-24 | Characterization of self-heating in cryogenic high electron mobility transistors using Schottky thermometry | Cryogenic low noise amplifiers based on high electron mobility transistors
(HEMTs) are widely used in applications such as radio astronomy, deep space
communications, and quantum computing, and the physical mechanisms governing
the microwave noise figure are therefore of practical interest. In particular,
the contribution of thermal noise from the gate at cryogenic temperatures
remains unclear owing to a lack of experimental measurements of thermal
resistance under these conditions. Here, we report measurements of gate
junction temperature and thermal resistance in a HEMT at cryogenic and room
temperatures using a Schottky thermometry method. At temperatures $\sim 20$ K,
we observe a nonlinear trend of thermal resistance versus power that is
consistent with heat dissipation by phonon radiation. Based on this finding, we
consider heat transport by phonon radiation at the low-noise bias and liquid
helium temperatures and estimate that the thermal noise from the gate is
several times larger than previously assumed owing to self-heating. We conclude
that without improvements in thermal management, self-heating results in a
practical lower limit for microwave noise figure of HEMTs at cryogenic
temperatures. | 2105.11571v1 |
2021-10-06 | Temperature dependent striction effect in a single crystalline Nd2Fe14B revealed using a novel high temperature resistivity measurement technique | We studied the temperature dependence of resistivity in a single crystalline
Nd2Fe14B using a newly developed high temperature probe. This novel probe uses
mechanical pin connectors instead of conducting glue/paste. From warming and
cooling curves, the Curie temperature was consistently measured around Tc = 580
K. In addition, anomalous discrete jumps were found only in cooling curves
between 400 and 500 K, but not shown in warming curves. More interestingly,
when the jumps occurred during cooling, the resistivity was increased. This
phenomenon can be understood in terms of temperature dependent striction effect
induced by the re-orientation of magnetic domains well below the Curie
temperature. | 2110.02909v1 |
2022-11-15 | Pressure-Induced Insulator-to-Metal Transition in van der Waals compound CoPS$_3$ | We have studied the insulator-to-metal transition and crystal structure
evolution under high pressure in the van der Waals compound CoPS$_3$ through
$\textit{in-situ}$ electrical resistance, Hall resistance, magnetoresistance,
X-ray diffraction, and Raman scattering measurements. CoPS$_3$ exhibits a
$C2/m$ $\rightarrow$ $P\overline{3}$ structural transformation at 7 GPa
accompanied by a 2.9$\%$ reduction in the volume per formula unit.
Concomitantly, the electrical resistance decreases significantly, and CoPS$_3$
becomes metallic. This metallic CoPS$_3$ is a hole-dominant conductor with
multiple conduction bands. The linear magnetoresistance and the small volume
collapse at the metallization suggest the incomplete high-spin $\rightarrow$
low-spin transition in the metallic phase. Thus, the metallic CoPS$_3$ possibly
possesses an inhomogeneous magnetic moment distribution and short-range
magnetic ordering. This report summarizes the comprehensive phase diagram of
$M$PS$_3$ ($M$ = V, Mn, Fe, Co, Ni, and Cd) that metalize under pressures. | 2211.07925v4 |
2020-05-03 | Resistive Switching Behaviour of Organic Molecules | Organic electronics is very promising due to the flexibility, modifiability
as well as variety of the available organic molecules. Efforts are going on to
use organic materials for the realization of memory devices. In this regard
resistive switching devices surely will play a key role. In this paper an
effort has been made to illustrate the general information about resistive
switching devices as well as switching mechanisms involving organic materials.
As a whole a general overview of the emerging topic resistive switching has
been given. | 2005.01033v1 |
2023-06-17 | An account of Natural material based Non Volatile Memory Device | The development in electronic sector has brought a remarkable change in the
life style of mankind. At the same time this technological advancement results
adverse effect on environment due to the use of toxic and non degradable
materials in various electronic devices. With the emergence of environmental
problems, the green, reprogrammable, biodegradable, sustainable and
environmental-friendly electronic devices have become one of the best solutions
for protecting our environment from hazardous materials without compromising
the growth of the electronic industry. Natural material has emerged as the
promising candidate for the next generation electronic devices due to its easy
processing, transparency, flexibility, abundant resources, sustainability,
recyclability, and simple extraction. This review targets the characteristics,
advancements, role, limitations, and prospects of using natural materials as
the functional layer of a resistive switching memory device with a primary
focus on the switching/memory properties. Among the available memory devices,
resistive random access memory (RRAM), write once read many (WORM) unipolar
memory etc. devices have a huge potential to become the non-volatile memory of
the next generation owing to their simple structure, high scalability, and low
power consumption. The motivation behind this work is to promote the use of
natural materials in electronic devices and attract researchers towards a green
solution of hazardous problems associated with the electronic devices. | 2306.10382v1 |
2016-10-10 | Determination of the resistivity anisotropy of orthorhombic materials via transverse resistivity measurements | Measurements of the resistivity anisotropy can provide crucial information
about the electronic structure and scattering processes in anisotropic and
low-dimensional materials, but quantitative measurements by conventional means
often suffer very significant systematic errors. Here we describe a novel
approach to measuring the resistivity anisotropy of orthorhombic materials,
using a single crystal and a single measurement, that is derived from a
$\frac{\pi}{4}$ rotation of the measurement frame relative to the
crystallographic axes. In this new basis the transverse resistivity gives a
direct measurement of the resistivity anisotropy, which combined with the
longitudinal resistivity also gives the in-plane elements of the conventional
resistivity tensor via a 5-point contact geometry. This is demonstrated through
application to the charge-density wave compound ErTe$_3$, and it is concluded
that this method presents a significant improvement on existing techniques in
many scenarios. | 1610.03122v1 |
2019-08-28 | Temperature-dependent hardness of diamond-structured covalent materials | Understanding temperature-dependent hardness of covalent materials is not
only of fundamental scientific interest, but also of crucial importance for
technical applications. In this work, a temperature-dependent hardness formula
for diamond-structured covalent materials is constructed on the basis of the
dislocation theory. Our results show that, at low temperature, the Vickers
hardness is mainly controlled by Poisson's ratio and shear modulus with the
latter playing a dominant role. With increasing temperature, the plastic
deformation mechanism undergoes a transition from shuffle-set dislocation
control to glide-set dislocation control, leading to a steeper drop of hardness
at high temperature. In addition, an intrinsic parameter, a3G, is revealed for
diamond-structured covalent materials, which measures the resistance to soften
at high temperature. Our hardness model shows remarkable agreement with
experimental data. Current work not only sheds lights on the physical origin of
hardness, but also provides a direct principle for superhard materials design. | 1909.11032v2 |
2014-06-11 | Evidence of surface transport and weak anti-localization in single crystal of Bi2Te2Se topological insulator | Topological insulators are known to their metallic surface states, a result
of strong-spin-orbital coupling, that show unique surface transport phenomenon.
But these surface transports are buried in presence of metallic bulk
conduction. We synthesized very high quality Bi$_2$Te$_2$Se single crystals by
modified Bridgman method, that possess high bulk resistivity of
$>$20~$\Omega$cm below 20~K, whereas the bulk is mostly inactive and surface
transport dominates. Temperature dependence resistivity follows the activation
law like a gap semiconductor in temperature range 20-300~K. We designed a
special measurement geometry, which aims to extract the surface transport from
the bulk. This special geometry is applied to measure the resistance and found
that Bi$_2$Te$_2$Se single crystal exhibits a cross over from bulk to surface
conduction at 20~K. Simultaneously, the material also shows strong evidence of
weak anti-localization in magneto-transport due to the protection against
scattering by conducting surface states. This novel simple geometry is an easy
route to find the evidence of surface transport in topological insulators,
which are the promising materials for future spintronic applications. | 1406.2879v1 |
2019-05-29 | Growth of metallic delafossite PdCoO2 by molecular beam epitaxy | The Pd, and Pt based ABO2 delafossites are a unique class of layered,
triangular oxides with 2D electronic structure and a large conductivity that
rivals the noble metals. Here, we report successful growth of the metallic
delafossite PdCoO2 by molecular beam epitaxy (MBE). The key challenge is
controlling the oxidation of Pd in the MBE environment where phase-segregation
is driven by the reduction of PdCoO2 to cobalt oxide and metallic palladium.
This is overcome by combining low temperature (300 {\deg}C) atomic
layer-by-layer MBE growth in the presence of reactive atomic oxygen with a
post-growth high-temperature anneal. Thickness dependence (5-265 nm) reveals
that in the thin regime (<75 nm), the resistivity scales inversely with
thickness, likely dominated by surface scattering; for thicker films the
resistivity approaches the values reported for the best bulk-crystals at room
temperature, but the low temperature resistivity is limited by structural
twins. This work shows that the combination of MBE growth and a post-growth
anneal provides a route to creating high quality films in this interesting
family of layered, triangular oxides. | 1905.12549v2 |
2019-06-21 | Current localisation and redistribution as the basis of discontinuous current controlled negative differential resistance in NbOx | In-situ thermo-reflectance imaging is used to show that the discontinuous,
snap-back mode of current-controlled negative differential resistance (CC-NDR)
in NbOx-based devices is a direct consequence of current localization and
redistribution. Current localisation is shown to result from the creation of a
conductive filament either during electroforming or from current bifurcation
due to the super-linear temperature dependence of the film conductivity. The
snap-back response then arises from current redistribution between regions of
low and high current-density due to the rapid increase in conductivity created
within the high current density region. This redistribution is further shown to
depend on the relative resistance of the low current-density region with the
characteristics of NbOx cross-point devices transitioning between continuous
and discontinuous snap-back modes at critical values of film conductivity,
area, thickness and temperature, as predicted. These results clearly
demonstrate that snap-back is a generic response that arises from current
localization and redistribution within the oxide film rather than a
material-specific phase transition, thus resolving a long-standing controversy. | 1906.08980v2 |
2017-12-03 | Spin transport in two-layer-CVD-hBN/graphene/hBN heterostructures | We study room temperature spin transport in graphene devices encapsulated
between a layer-by-layer-stacked two-layer-thick chemical vapour deposition
(CVD) grown hexagonal boron nitride (hBN) tunnel barrier, and a few-layer-thick
exfoliated-hBN substrate. We find mobilities and spin-relaxation times
comparable to that of SiO$_2$ substrate based graphene devices, and obtain a
similar order of magnitude of spin relaxation rates for both the Elliott-Yafet
and D'Yakonov-Perel' mechanisms. The behaviour of
ferromagnet/two-layer-CVD-hBN/graphene/hBN contacts ranges from transparent to
tunneling due to inhomogeneities in the CVD-hBN barriers. Surprisingly, we find
both positive and negative spin polarizations for high-resistance
two-layer-CVD-hBN barrier contacts with respect to the low-resistance contacts.
Furthermore, we find that the differential spin injection polarization of the
high-resistance contacts can be modulated by DC bias from -0.3 V to +0.3 V with
no change in its sign, while its magnitude increases at higher negative bias.
These features mark a distinctive spin injection nature of the
two-layer-CVD-hBN compared to the bilayer-exfoliated-hBN tunnel barriers. | 1712.00815v1 |
2004-09-06 | Calculation of resistance for weak scattering, strong scattering and insulating quasi-one dimensional systems | A parameter free calculation of the resistivity is applied to liquid metals
near the melting point ranging from weak to strong scattering limit. The method
is based on length dependent resistance calculations for quasi-one dimensional
systems and was applied on structures with up to 10000 atoms. The calculated
value for conductance fluctuations is in good agreement with theoretical
predictions. The resistivities are compared with the Kubo-Greenwood and the
extended Ziman formula with the same scattering potential and similar
structure. The resistance calculation is applicable for insulating materials as
well, which is demonstrated for crystalline and amorphous silicon. | 0409131v2 |
2012-07-02 | Magneto-resistance in three-dimensional composites | In this paper we study the magneto-resistance, i.e. the second-order term of
the resistivity perturbed by a low magnetic field, of a three-dimensional
composite material. Extending the two-dimensional periodic framework of [4], it
is proved through a H-convergence approach that the dissipation energy induced
by the effective magneto-resistance is greater or equal to the average of the
dissipation energy induced by the magneto-resistance in each phase of the
composite. This inequality validates for a composite material the Kohler law
which is known for a homogeneous conductor. The case of equality is shown to be
very sensitive to the magnetic fi eld orientation. We illustrate the result
with layered and columnar periodic structures. | 1207.0468v1 |
2020-06-30 | Roadmap for Gain-Bandwidth-Product Enhanced Photodetectors | Photodetectors are key optoelectronic building blocks performing the
essential optical-to-electrical signal conversion, and unlike solar cells,
operate at a specific wavelength and at high signal or sensory speeds. Towards
achieving high detector performance, device physics, however, places a
fundamental limit of the achievable detector sensitivity, such as responsivity
and gain, when simultaneously aimed to increasing the detectors temporal
response, speed, known as the gain-bandwidth product (GBP). While detectors GBP
has been increasing in recent years, the average GBP is still relatively modest
(~10^6-10^7 Hz-A/W). Here we discuss photodetector performance limits and
opportunities based on arguments from scaling length theory relating
photocarrier channel length, mobility, electrical resistance with optical
waveguide mode constrains. We show that short-channel detectors are synergistic
with slot-waveguide approaches, and when combined, offer a high-degree of
detector design synergy especially for the class of nanometer-thin materials.
Indeed, we find that two dimensional material-based detectors are not limited
by their low mobility and can, in principle, allow for 100 GHz fast response
rates. However, contact resistance is still a challenge for such thin
materials, a research topic that is still not addressed yet. An interim
solution is to utilize heterojunction approaches for functionality separation.
Nonetheless, atomistically- and nanometer-thin materials used in such
next-generation scaling length theory based detectors also demand high material
quality and monolithic integration strategies into photonic circuits including
foundry-near processes. As it stands, this letter aims to guide the community
if achieving the next generation photodetectors aiming for a performance target
of GBP = 10^12 Hz-A/W. | 2006.16937v1 |
2005-06-01 | Insulator-metal transition in a conservative system: An evidence for mobility coalescence in island silver films | Aging, which manifests itself as an irreversible increase in electrical
resistance in island metal films is of considerable interest from both academic
as well as applications point of view. Aging is attributed to various causes,
oxidation of islands and mobility of islands followed by coalescence (mobility
coalescence) being the main contenders. The effect of parameters like substrate
temperature, substrate cleaning, residual gases in the vacuum chamber,
ultrasonic vibration of the substrate, suggest that the mobility coalescence is
responsible for the aging in island metal films. Electron microscopy studies
show evidence for mobility of islands at high substrate temperatures. The
comparison of aging data of island silver films deposited on glass substrates
in ultra high vacuum and high vacuum suggests that the oxidation of islands, as
being responsible for aging in these films, can be ruled out. Further, under
certain conditions of deposition, island silver films exhibit a dramatic and
drastic fall in electrical resistance, marking the insulator-metal transition.
This interesting transition observed in a conservative system - after the
stoppage of deposition of the film- is a clear evidence for mobility
coalescence of islands even at room temperature. The sudden fall in resistance
is preceded by fluctuations in resistance with time and fluctuations are
attributed to the making and breaking of the percolation path in the film. | 0506022v2 |
2010-09-22 | Hall-effect and resistivity measurements in CdTe and ZnTe at high pressure: Electronic structure of impurities in the zincblende phase and the semi-metallic or metallic character of the high-pressure phases | We carried out high-pressure resistivity and Hall-effect measurements in
single crystals of CdTe and ZnTe up to 12 GPa. Slight changes of transport
parameters in the zincblende phase of CdTe are consitent with the shallow
character of donor impurities. Drastic changes in all the transport parameters
of CdTe were found around 4 GPa, i.e. close to the onset of the cinnabar to
rock-salt transition. In particular, the carrier concentration increases by
more than five orders of magnitude. Additionally, an abrupt decrease of the
resistivity was detected around 10 GPa. These results are discussed in
comparison with optical, thermoelectric, and x-ray diffraction experiments. The
metallic character of the Cmcm phase of CdTe is confirmed and a semi-metallic
character is determined for the rock-salt phase. In zincblende ZnTe, the
increase of the hole concentration by more than two orders of magnitude is
proposed to be due to a deep-to-shallow transformation of the acceptor levels.
Between 9 and 11 GPa, transport parameters are consistent with the
semiconducting character of cinnabar ZnTe. A two orders of magnitude decrease
of the resistivity and a carrier-type inversion occurs at 11 GPa, in agreement
with the onset of the transition to the Cmcm phase of ZnTe. A metallic
character for this phase is deduced. | 1009.4304v1 |
2019-10-18 | Atomically Controlled Tunable Doping in High Performance WSe2 Devices | Two-dimensional transitional metal dichalcogenide (TMD) field-effect
transistors (FETs) are promising candidates for future electronic applications,
owing to their excellent transport properties and potential for ultimate device
scaling. However, it is widely acknowledged that substantial contact resistance
associated with the contact-TMD interface has impeded device performance to a
large extent. It has been discovered that O2 plasma treatment can convert WSe2
into WO3-x and substantially improve contact resistances of p-type WSe2 devices
by strong doping induced thinner depletion width. In this paper, we carefully
study the temperature dependence of this conversion, demonstrating an oxidation
process with a precise monolayer control at room temperature and multilayer
conversion at elevated temperatures. Furthermore, the lateral oxidation of WSe2
under the contact revealed by HR-STEM leads to potential unpinning of the metal
Fermi level and Schottky barrier lowering, resulting in lower contact
resistances. The p-doping effect is attributed to the high electron affinity of
the formed WO3-x layer on top of the remaining WSe2 channel, and the doping
level is found to be dependent on the WO3-x thickness that is controlled by the
temperature. Comprehensive materials and electrical characterizations are
presented, with a low contact resistance of ~528 ohm-um and record high
on-state current of 320 uA/um at -1V bias being reported. | 1910.08619v1 |
2004-03-23 | Systematic approach to the growth of high-quality single-crystals of Sr3Ru2O7 | We describe a simple procedure for optimising the growth condition for high
quality single crystals of the strontium ruthenate perovskites using an image
furnace. The procedure involves carefully measuring the mass lost during
crystal growth in order to predict the optimal initial atomic ratio. Using this
approach we have succeeded in growing crystals of Sr3Ru2O7 with a residual
resistivity as low as 0.25 ??cm. The procedure we describe here is expected to
be useful for other systems when a standard travelling-solvent floating-zone
(TSFZ) method cannot be used because of high volatility of a constituent
material. | 0403572v1 |
2022-03-22 | High-field magnetoresistance of microcrystalline and nanocrystalline Ni metal at 3 K and 300 K | The magnetoresistance (MR) and the magnetization isotherms were studied up to
high magnetic fields at T = 3 K and 300 K for a microcrystalline ($\mu$c) Ni
foil corresponding to bulk Ni and for a nanocrystalline (nc) Ni foil. At T = 3
K, for the $\mu$c-Ni sample with a residual resistivity ratio (RRR) of 331, the
field dependence of the resistivity was similar to what was reported previously
for high-purity ferromagnets whereas the MR(H) behavior for the nc-Ni sample
with RRR = 9 resembled that what was observed at low temperatures for Ni-based
alloys with low impurity concentration. In the magnetically saturated state,
the resistivity increased with magnetic field for both samples at T = 3 K and
the field dependence was dominated by the ordinary MR due to the Lorentz force
acting on the electron trajectories. However, the MR(H) curves were found to be
saturating for $\mu$c-Ni and non-saturating for nc-Ni, the difference arising
from their very different electron mean free paths. At T = 300 K, the MR(H)
curves of both Ni samples were very similar to those known for bulk Ni. After
magnetic saturation, the resistivity decreased nearly linearly with magnetic
field which behavior is due to the suppression of thermally-induced magnetic
disorder with increasing magnetic field. The MR(H) data were analyzed at both
temperatures with the help of Kohler plots from which the resistivity
anisotropy splitting ($\Delta\rho_{AMR}$) and the anisotropic magnetoresistance
(AMR) ratio were derived. It was demonstrated that at T = 300 K,
$\rho(H\rightarrow 0)=\rho(B\rightarrow 0)$ due to the negligible contribution
of the ordinary MR. The data for the two Ni samples at 3 K and 300 K were found
to indicate an approximately linear scaling of $\Delta\rho_{AMR}$ with the
zero-field resistivity. This implies that the AMR ratio does not vary
significantly with temperature in either microstructural state of Ni. | 2203.11568v1 |
2023-09-18 | Theoretical analysis on the possibility of superconductivity in a trilayer Ruddlesden-Popper nickelate La$_4$Ni$_3$O$_{10}$ under pressure and its experimental examination: comparison with La$_3$Ni$_2$O$_7$ | We study the possibility of superconductivity in a trilayer Ruddlesden-Popper
nickelate La$_4$Ni$_3$O$_{10}$ under pressure both theoretically and
experimentally, making comparison with the recently discovered high $T_c$
superconductor La$_3$Ni$_2$O$_7$, a bilayer nickelate. Through DFT
calculations, we find that a structural phase transition from monoclinic to
tetragonal takes place around 10 - 15 GPa. Using the tetragonal crystal
structure, we theoretically investigate the possibility of superconductivity,
where a combination of fluctuation exchange approximation and linearized
Eliashberg equation is applied to a six-orbital model constructed from first
principles band calculation. The obtained results suggests that
La$_4$Ni$_3$O$_{10}$ may also become superconducting under high pressure with
$T_c$ comparable to some cuprates, although it is not as high as
La$_3$Ni$_2$O$_7$. We also perform experimental studies using our
polycrystalline samples of La$_3$Ni$_2$O$_{7.01}$ and La$_4$Ni$_3$O$_{9.99}$.
The superconducting transition of La$_3$Ni$_2$O$_{7.01}$, with a maximum onset
$T_c$ of 67.0 K at a pressure of 26.5 GPa, is confirmed by a drop in the
electrical resistance, as well as the magnetic field dependence of the
resistance. Quite interestingly, similar temperature and magnetic field
dependencies of the resistance are observed also for La$_4$Ni$_3$O$_{9.99}$,
where a drop in the resistance is observed at lower temperatures compared to
La$_3$Ni$_2$O$_{7.01}$, under pressures of 32.8 GPa and above. Given the
theoretical expectation, the reduction in the resistance can most likely be
attributed to the occurrence of superconductivity in La$_4$Ni$_3$O$_{9.99}$.
The temperature at which the resistance deviates from a linear behavior,
considered as the onset $T_c$, monotonically increases up to 23 K at 79.2 GPa,
which is opposite to the pressure dependence of $T_c$ in La3Ni2O7.01. | 2309.09462v4 |
2019-07-16 | Pressure-Induced Large Volume Collapse, Plane-to-Chain, Insulator to Metal Transition in CaMn$_2$Bi$_2$ | In-situ high pressure single crystal X-ray diffraction study reveals that the
quantum material CaMn$_2$Bi$_2$ undergoes a unique plane to chain structural
transition between 2 and 3 GPa, accompanied by a large volume collapse.
CaMn2Bi2 displays a new structure type above 2.3 GPa, with the puckered Mn
honeycomb lattice of the trigonal ambient-pressure structure converting to
one-dimensional (1D) zigzag chains in the high-pressure monoclinic structure.
Single crystal measurements reveal that the pressure-induced structural
transformation is accompanied by a dramatic two order of magnitude drop of
resistivity; although the ambient pressure phase displays semiconducting
behavior at low temperatures, metallic temperature dependent resistivity is
observed for the high pressure phase, as, surprisingly, are two resistivity
anomalies with opposite pressure dependences. Based on the electronic structure
calculations, we hypothesized that the newly emerged electronic state under
high pressure is associated with a Fermi surface instability of the quasi-1D Mn
chains, while we infer that the other is a magnetic transition. Assessment of
the total energies for hypothetical magnetic structures for high pressure
CaMn$_2$Bi$_2$ indicates that ferrimagnetism is thermodynamically favored. | 1907.07203v1 |
2014-10-09 | Chloride Molecular Doping Technique on 2D Materials: WS2 and MoS2 | Low-resistivity metal-semiconductor (M-S) contact is one of the urgent
challenges in the research of 2D transition metal dichalcogenides (TMDs). Here,
we report a chloride molecular doping technique which greatly reduces the
contact resistance (Rc) in the few-layer WS2 and MoS2. After doping, the Rc of
WS2 and MoS2 have been decreased to 0.7 kohm*um and 0.5 kohm*um, respectively.
The significant reduction of the Rc is attributed to the achieved high electron
doping density thus significant reduction of Schottky barrier width. As a
proof-ofconcept, high-performance few-layer WS2 field-effect transistors (FETs)
are demonstrated, exhibiting a high drain current of 380 uA/um, an on/off ratio
of 4*106, and a peak field-effect mobility of 60 cm2/V*s. This doping technique
provides a highly viable route to diminish the Rc in TMDs, paving the way for
high-performance 2D nano-electronic devices. | 1410.2563v1 |
2021-04-08 | Electrical Properties of Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon | We present a superconductor-semiconductor material system that is both
scalable and monolithically integrated on a silicon substrate. It uses
selective area growth of Al-InAs hybrid structures on a planar III-V buffer
layer, grown directly on a high resistivity silicon substrate. We characterized
the electrical properties of this material system at millikelvin temperatures
and observed a high average field-effect mobility of $\mu \approx
3200\,\mathrm{cm^2/Vs}$ for the InAs channel, and a hard induced
superconducting gap. Josephson junctions exhibited a high interface
transmission, $\mathcal{T} \approx 0.75 $, gate voltage tunable switching
current with a product of critical current and normal state resistance,
$I_{\mathrm{C}}R_{\mathrm{N}} \approx 83\,\mathrm{\mu V}$, and signatures of
multiple Andreev reflections. These results pave the way for scalable and high
coherent gate voltage tunable transmon devices and other
superconductor-semiconductor hybrids fabricated directly on silicon. | 2104.03621v1 |
2021-09-21 | Strain effects on the wear rate of severely deformed copper | A variety of severe plastic deformation (SPD) techniques have been developed
to process materials to high strains and impart microstructural refinement.
High pressure torsion (HPT) is one technique that imparts inhomogeneous strain
to process discs with low strain in the center and high strain at the outer
edge. In the literature, this inhomogeneity is typically ignored when
characterizing wear properties after HPT. In this work, the wear rate of pure
copper discs processed by HPT was characterized by conducting dry sliding
reciprocating wear tests at a few judicious locations on the discs. From only
two discs, the wear resistance across many ranges of strains was captured.
These measurements agreed with the literature for other SPD processes at
varying strains. Wear rates dropped and plateaued at about 25% that of the
unprocessed state when processing past equivalent strains of around 15, after
which microstructural and microhardness saturation has also been observed. Some
indication of a relationship between the direction of the imposed SPD shearing
and the sliding wear direction was also observed. The incremental
microstructure, microhardness, and wear resistance evolution past equivalent
strains of ~15 indicate that for high purity copper these properties receive no
clear benefit from higher SPD strains. | 2109.09907v1 |
2016-07-07 | Lithium transport through Lithium-ion battery cathode coatings | The surface coating of cathodes using insulator films has proven to be a
promising method for high-voltage cathode stabilization in Li-ion batteries.
However, there is still substantial uncertainty about how these films function,
specifically with regard to important coating design principles such as lithium
solubility and transport through the films. This study uses Density Functional
Theory to examine the diffusivity of interstitial lithium in crystalline
{\alpha}-$AlF_3$, {\alpha}-$Al_2O_3$, m-$ZrO_2$, c-MgO, and {\alpha}-quartz
$SiO_2$, which provide benchmark cases for further understanding of insulator
coatings in general. In addition, we propose an Ohmic electrolyte model to
predict resistivities and overpotential contributions under battery operating
conditions. For the crystalline materials considered we predict that Li+
diffuses quite slowly, with a migration barrier larger than 0.9 eV in all
crystalline materials except {\alpha}-quartz $SiO_2$, which is predicted to
have a migration barrier of 0.276 eV along <001>. These results suggest that
the stable crystalline forms of these insulator materials, except for oriented
{\alpha}-quartz $SiO_2$, are not practical for conformal cathode coatings.
Amorphous $Al_2O_3$ and $AlF_3$ have higher Li+ diffusivities than their
crystalline counterparts. Our predicted amorphous $Al_2O_3$ resistivity (1789
M{\Omega}m) is near the top of the range of fitted resistivities extracted from
previous experiments on nominal $Al_2O_3$ coatings (7.8 to 913 M{\Omega}m)
while our predicted amorphous $AlF_3$ resistivity (114 M{\Omega}m) is close to
the middle of the range. These comparisons support our framework for modeling
and understanding the impact on overpotential of conformal coatings in terms of
their fundamental thermodynamic and kinetic properties, and support that these
materials can provide practical conformal coatings in their amorphous form. | 1607.02125v1 |
2023-04-20 | An Origami-Inspired Design of Highly Efficient Cellular Cushion Materials | Current architectured cellular cushion materials rely mainly on damage and/or
unpredictable collapse of their unit cells to absorb and dissipate energy under
impact. This prevents shape recovery and produces undesirable force
fluctuations that limit reusability and reduce energy absorption efficiency.
Here, we propose to combine advanced manufacturing technologies with Origami
principles to create a new class of architectured cellular viscoelastic cushion
material which combines low weight and high energy absorption efficiency with
damage resistance and full behavior customization. Each unit cell in the
proposed material is inspired by the Kresling Origami topology, which absorbs
impact energy by gracefully folding the different interfaces forming the cell
to create axial and rotational motions. A large part of the absorbed energy is
then dissipated through viscoelasticity and friction between the interfaces.
The result is a nearly ideal cushion material exhibiting high energy absorbing
efficiency (around 70%) combined with high energy dissipation (94% of the
absorbed energy). The material is also tunable for optimal performance,
reliable despite successive impact events, and achieves full shape recovery. | 2304.10238v1 |
2024-01-28 | Discharge quenching mechanism and performance of RPWELL with tunable 3D printed resistive plates, charge evacuation in semiconductive glass RPWELL and discharge quenching for Cryogenic-RWELL over a wide range of resistivity | Resistive electrodes are used in gaseous detectors to quench electrical
discharges. This helps to protect delicate electrodes and readout electronics
and to improve the stability of the detector operation. An RPWELL is a
THGEM-based WELL detector with a resistive plate coupled to a conductive anode.
Till now, the choice of the resistive plate was limited to a few materials,
like LRS Glass and Semitron. These materials have fixed resistivities and,
sometimes, thickness and area limitations. This restricts the potential usage
of the detector to a rather small range of applications, as well as the
possibility of studying in depth the physics processes governing the discharge
quenching mechanism. In our present study, we used a new plastic material doped
with carbon nanotubes to produce resistive plates with a commercial 3D printer.
This method has the flexibility to produce samples of different thicknesses and
different resistivity values. We describe here the sample production and
characterize the RPWELL performance with different resistive plates. In
particular we show the dependence of discharge quenching on the thickness and
resistivity of the plate. The dynamics of the charge carriers in the material
is proposed as an explanation for the long gain recovery time after a
discharge. | 2401.15611v2 |
2009-09-25 | Electric field-induced colossal electroresistance and its relaxation in multiferroic La2NiMnO6 | In this work, we report direct as well as pulsed electric field-induced
resistivity switching and its relaxation in a multiferroic insulator La2NiMnO6.
At a fixed base temperature (Tb), the dc resistivity switches abruptly from a
high to a low value, which is manifested as an upward jump in the dc current
density (J) when the electric field (E) exceeds a threshold value Eth. The
fractional change in the resistance is as much as 70 % at room temperature for
Eth = 95 V/cm. The Eth increases with lowering Tb and follows the relation
Eth(Tb) = Eth(0)exp[-Tb/T0], as similar to the behavior found in charge density
wave systems. It is shown that the abrupt jump in J vanishes under pulsed
electric fields if the period between pulses is long enough. Surprisingly, a
step-like increase in J also occurs at a fixed dc electric field (Ec) and T =
Tb, above a threshold waiting time (tth). The tth decreases with increasing Ec
and Tb. Simultaneous measurement of surface temperature during the J-E sweep
and temporal studies suggest that conductive channels are created in an
insulating matrix due to the local self heating, and the coalescence of these
channels above a threshold E- field or time causes the observed anomalies in J.
However, the dissipated Joule power (P = Ith2R) at the transition from high to
low resistive state in the sample decreases with lowering temperature, which
suggests that the Joule heating is the consequence of transition from the high
to low resistance state rather than itself a driving force of the non linear
electrical transport. In addition, non linear J-E characteristics is also found
even with a pulsed voltage sweep, which suggests that intrinsic mechanisms
other than self heating is still active in this material. | 0909.4612v1 |
2022-07-10 | Diffusion theory of electrical contact resistance of "thermoelectric superlattice metal" couple | The paper proposes a strict diffusion theory of the electrical contact
resistance of a thermoelectric superlattice (TES) - metal couple.The limits of
the contact resistance for traditional thermoeletric materials with parabolic
band spectrum and for superlattices described by Fivaz model are estimated. | 2207.05065v1 |
2018-01-30 | Open Material Property Library With Native Simulation Tool Integrations -- MASTO | Reliable material property data is crucial for trustworthy simulations
throughout different areas of engineering. Special care must be taken when
materials at extreme conditions are under study. Superconductors and devices
assembled from superconductors and other materials, like superconducting
magnets, are often operated at such extreme conditions: at low temperatures
under high magnetic fields and stresses. Typically, some library or database is
used for getting the data. We have started to develop a database for storing
all kind of material property data online called Open Material Property Library
With Native Simulation Tool Integrations -- MASTO. The data that can be
imported includes, but is not limited to, anisotropic critical current surfaces
for high temperature superconducting materials, electrical resistivities as a
function of temperature, RRR and magnetic field, general fits for describing
material behaviour etc. Data can also depend on other data and it can be
versioned to guarantee permanent access. The guiding idea in MASTO is to build
easy-to-use integration for various programming languages, modelling frameworks
and simulation software. Currently, a full-fledged integration is built for
MATLAB to allow users to fetch and use data with one-liners. In this paper we
briefly review some of the material property databases commonly used in
superconductor modelling, present a case study showing how selection of the
material property data can influence the simulation results, and introduce the
principal ideas behind MASTO. This work serves as the reference document for
citing MASTO when it is used in simulations. | 1801.09897v1 |
2018-11-22 | Chemical vapor deposition of hexagonal boron nitride and its use in electronic devices | Dielectrics are insulating materials used in many different electronic
devices and play an important role in all of them. Current advanced electronic
devices use dielectric materials with a high dielectric constant and avoid high
leakage currents. However, these materials show several intrinsic problems, and
also a bad interaction with adjacent materials. Therefore, the race for finding
a suitable dielectric material for current and future electronic devices is
still open. In this context two dimensional [2D] materials have become a
serious option, not only thanks to their advanced properties, but also to the
development of scalable synthesis methods. Graphene has been the most explored
2D material for electronic devices. However, graphene has no band gap, and
therefore it cannot be used as dielectric. MoS2 and other 2D transition metal
dichalcogenides (TMDs) are semiconducting 2D materials that can provide more
versatility in electronic devices. In this PhD thesis I have investigated the
use of monolayer and multilayer hexagonal boron nitride (h-BN) as dielectric
for electronic devices, as it is a 2D material with a band gap of ~5.9 eV. My
work has mainly focused on the synthesis of the h-BN using chemical vapor
deposition, the study of its intrinsic morphological and electrical properties
at the nanoscale, and its performance as dielectric in different electronic
devices, such as capacitors and memristors. Overall, our experiments indicate
that h-BN is a very reliable dielectric material, and that it can be
successfully used in capacitors and memristors. Moreover, h-BN shows additional
performances never observed in traditional dielectrics, such as volatile
resistive switching, which may also open the door for new applications. | 1905.06938v1 |
2020-04-14 | Materials Requirements of High-Speed and Low-Power Spin-Orbit-Torque Magnetic Random-Access Memory | As spin-orbit-torque magnetic random-access memory (SOT-MRAM) is gathering
great interest as the next-generation low-power and high-speed on-chip cache
memory applications, it is critical to analyze the magnetic tunnel junction
(MTJ) properties needed to achieve sub-ns, and ~fJ write operation when
integrated with CMOS access transistors. In this paper, a 2T-1MTJ cell-level
modeling framework for in-plane type Y SOT-MRAM suggests that high spin Hall
conductivity and moderate SOT material sheet resistance are preferred. We
benchmark write energy and speed performances of type Y SOT cells based on
various SOT materials experimentally reported in the literature, including
heavy metals, topological insulators and semimetals. We then carry out detailed
benchmarking of SOT material Pt, beta-W, and BixSe(1-x) with different
thickness and resistivity. We further discuss how our 2T-1MTJ model can be
expanded to analyze other variations of SOT-MRAM, including perpendicular (type
Z) and type X SOT-MRAM, two-terminal SOT-MRAM, as well as spin-transfer-torque
(STT) and voltage-controlled magnetic anisotropy (VCMA)-assisted SOT-MRAM. This
work will provide essential guidelines for SOT-MRAM materials, devices, and
circuits research in the future. | 2004.06268v2 |
2022-04-28 | Degradation model of high-nickel positive electrodes: Effects of loss of active material and cyclable lithium on capacity fade | Nickel-rich layered oxides have been widely used as positive electrode
materials for high-energy-density lithium-ion batteries, but their degradation
has severely affected cell performance, in particular at a high voltage and
temperature. However, the underlying degradation mechanisms have not been well
understood due to the complexity and lack of predictive models.Here we present
a model at the particle level to describe the structural degradation caused by
phase transition in terms of loss of active material (LAM), loss of lithium
inventory (LLI), and resistance increase. The particle degradation model is
then incorporated into a cell-level P2D model to explore the effects of LAM and
LLI on capacity fade in cyclic ageing tests. It is predicted that the loss of
cyclable lithium (trapped in the degraded shell) leads to a shift in the
stoichiometry range of the negative electrode but does not directly contribute
to the capacity loss, and that the loss of positive electrode active materials
dominates the fade of usable cell capacity in discharge. The available capacity
at a given current rate is further decreased by the additional resistance of
the degraded shell layer. The change pattern of the state-of-charge curve
provides information of more dimensions than the conventional capacity-fade
curve, beneficial to the diagnosis of degradation modes. The model has been
implemented into PyBaMM and made available as open source codes. | 2204.13364v2 |
2019-02-26 | Data-driven Exploration of Pressure-Induced Superconductivity in AgIn$_{5}$Se$_{8}$ | Candidates compounds for new thermoelectric and superconducting materials,
which have narrow band gap and flat bands near band edges, were exhaustively
searched by a high-throughput first-principles calculation from an inorganic
materials database named AtomWork. We focused on AgIn$_{5}$Se$_{8}$ which has
high density of state near the Fermi level. AgIn$_{5}$Se$_{8}$ was successfully
synthesized as single crystals using a melt and slow cooling method. The
single-crystal X-ray diffraction analysis revealed the obtained crystal is high
quality without deficiencies. The valence states in AgIn$_{5}$Se$_{8}$ were
determined to be Ag1+, In3+ and Se2- in accordance with a formal charge by the
core level X-ray photoelectron spectroscopy analysis. The electrical resistance
was evaluated under high pressure using a diamond anvil cell with boron-doped
diamond electrodes. Although the sample was insulator with a resistance of
above 40 M{\Omega} at ambient pressure, the resistance markedly decreased with
increase of the pressure, and a pressure-induced superconducting transition was
discovered at 3.4 K under 52.5 GPa. The transition temperature increased up to
3.7 K under further pressure of 74.0 GPa. | 1902.09770v1 |
2020-06-25 | Influence of Yb3+on the structural, electrical and optical properties of sol-gel synthesized Ni-Zn nanoferrites | Polycrystalline Yb substituted NiZn nanoferrites with the compositions of
Ni0.5Zn0.5YbxFe2-xO4 (x= 0.00, 0.04, 0.08, 0.12, 0.16 and 0.20) have been
synthesized using sol gel auto combustion technique. Single phase cubic spinel
structure has been confirmed by the X ray diffraction (XRD) patterns. Larger
lattice constants of the compositions are found with increasing Yb3+
concentration while the average grain size (52 to 18 nm) has noticeable
decrease as Yb3+ content is increased. The presence of all existing elements as
well as the purity of the samples has also been confirmed from energy
dispersive X ray spectroscopic (EDS) analysis. Frequency dependent dielectric
constant, dielectric loss, dielectric relaxation time, AC and DC resistivity of
the compositions have also been examined at room temperature. The DC
resistivity value is found in the order of 10 to power 10 (omega-cm) which is
at least four orders greater than the ferrites prepared by conventional method.
This larger value of resistivity attributes due to very small grain size and
successfully explained using the Verwey and deBoer hopping conduction model.
The contribution of grain and grain boundary resistance has been elucidated
using Cole Cole plot. The study of temperature dependent DC resistivity
confirms the semiconducting nature of all titled compositions wherein bandgap
(optical) increases from 2.73 eV to 3.25 eV with the increase of Yb content.
The high value of resistivity is of notable achievement for the compositions
that make them a potential candidate for implication in the high frequency
applications where reduction of eddy current loss is highly required. | 2006.14180v1 |
2024-04-12 | Electron-phonon interaction, magnetic phase transition, charge density waves and resistive switching in VS2 and VSe2 revealed by Yanson point contact spectroscopy | VS2 and VSe2 have attracted particular attention among the transition metals
dichalcogenides because of their promising physical properties concerning
magnetic ordering, charge density wave (CDW), emergent superconductivity, etc.,
which are very sensitive to stoichiometry and dimensionality reduction. Yanson
point contact (PC) spectroscopic study reveals metallic and nonmetallic states
in VS2 PCs, as well as a magnetic phase transition was detected below 25 K.
Analysis of PC spectra of VS2 testifies the realization of the thermal regime
in PCs. At the same time, rare PC spectra, where the magnetic phase transition
was not visible, shows a broad maximum of around 20 mV, likely connected with
electron-phonon interaction (EPI). On the other hand, PC spectra of VSe2
demonstrate metallic behavior, which allowed us to detect features associated
with EPI and CDW transition. The Kondo effect appeared for both compounds,
apparently due to interlayer vanadium ions. Besides, the resistive switching
was observed in PCs on VSe2 between a low resistive, mainly metallic-type
state, and a high resistive nonmetallic-type state by applying bias voltage
(about 0.4V). In contrast, reverse switching occurs by applying a voltage of
opposite polarity (about 0.4V). The reason may be the alteration of
stoichiometry in the PC core due to the displacement of V ions to interlayer
under a high electric field. The observed resistive switching characterize VSe2
as a potential material, e.g., for non-volatile resistive RAM, neuromorphic
engineering, and for other nanoelectronic applications. At the same time, VSe2
attracts attention as a rare layered van der Waals compound with magnetic
transition. | 2404.08269v1 |
2010-11-12 | Large bulk resistivity and surface quantum oscillations in the topological insulator Bi2Te2Se | Topological insulators are predicted to present novel surface transport
phenomena, but their experimental studies have been hindered by a metallic bulk
conduction that overwhelms the surface transport. We show that a new
topological insulator, Bi2Te2Se, presents a high resistivity exceeding 1 Ohm-cm
and a variable-range hopping behavior, and yet presents Shubnikov-de Haas
oscillations coming from the surface Dirac fermions. Furthermore, we have been
able to clarify both the bulk and surface transport channels, establishing a
comprehensive understanding of the transport in this material. Our results
demonstrate that Bi2Te2Se is the best material to date for studying the surface
quantum transport in a topological insulator. | 1011.2846v1 |
2017-02-14 | Modelling electron-phonon interactions in graphene with curved space hydrodynamics | We introduce a different perspective describing electron-phonon interactions
in graphene based on curved space hydrodynamics. Interactions of phonons with
charge carriers increase the electrical resistivity of the material. Our
approach captures the lattice vibrations as curvature changes in the space
through which electrons move following hydrodynamic equations. In this picture,
inertial corrections to the electronic flow arise naturally effectively
producing electron-phonon interactions. The strength of the interaction is
controlled by a coupling constant, which is temperature independent. We apply
this model to graphene and recover satisfactorily the linear scaling law for
the resistivity that is expected at high temperatures. Our findings open up a
new perspective of treating electron-phonon interactions in graphene, and also
in other materials where electrons can be described by the Fermi liquid theory. | 1702.04156v1 |
2019-10-31 | Vorticity of viscous electronic flow in graphene | In ultra-pure materials electrons may exhibit a collective motion similar to
the hydrodynamic flow of a viscous fluid, the phenomenon with far reaching
consequences in a wide range of many body systems from black holes to
high-temperature superconductivity. Yet the definitive detection of this
intriguing behavior remains elusive. Until recently, experimental techniques
for observing hydrodynamic behavior in solids were based on measuring
macroscopic transport properties, such as the "nonlocal" (or "vicinity")
resistance, which may allow alternative interpretation. Earlier this year two
breakthrough experiments demonstrated two distinct imaging techniques making it
possible to "observe" the electronic flow directly. We demonstrate that a
hydrodynamic flow in a long Hall bar (in the absence of magnetic field)
exhibits a nontrivial vortex structure accompanied by a sign-alternating
nonlocal resistance. An experimental observation of such unique flow pattern
could serve a definitive proof of electronic hydrodynamics. | 1910.14473v2 |
2021-11-09 | Magnetotransport in ferromagnetic Fe$_2$Ge semimetallic thin films | Thin films of the ferromagnet Fe$_2$Ge were grown via molecular beam epitaxy,
and their electrical and magneto-transport properties measured for the first
time. X-ray diffraction and vibrating sample magnetometry measurements
confirmed the crystalline ferromagnetic Fe$_2$Ge phase. The observed high
temperature maximum in the longitudinal resistivity, as well as the observed
suppression of electron-magnon scattering at low temperatures, point to the
presence of strong spin polarization in this material. Measurements of the Hall
resistivity, $\rho_{xy}$, show contributions from both the ordinary Hall effect
and anomalous Hall effect, $\rho_{xy}^{AH}$, from which we determined the
charge carrier concentration and mobility. Measurements also show a small
negative magnetoresistance in both the longitudinal and transverse geometries.
Fe$_2$Ge holds promise as a useful spintronic material, especially for its
semiconductor compatibility. | 2111.05417v1 |
2022-01-18 | In-plane magnetic structure and exchange interactions in the high-temperature antiferromagnet Cr2Al | The ordered tetragonal intermetallic Cr$_2$Al forms the same structure type
as Mn$_2$Au, and the latter has been heavily investigated for its potential in
antiferromagnetic spintronics due to its degenerate in-plane N\'{e}el vector.
We present the single crystal flux growth of Cr$_2$Al and orientation-dependent
magnetic properties. Powder neutron diffraction of Cr$_2$Al and
first-principles simulations reveal that the magnetic ordering is likely
in-plane and therefore identical to Mn$_2$Au, providing a second material
candidate in the MoSi$_2$ structure type to evaluate the fundamental
interactions that govern spintronic effects. The single ordering transition
seen in thermal analysis and resistivity indicates that no canting of the
moments along the $c$ axis is likely. Magnetometry, resistivity, and
differential scanning calorimetry measurements confirm the N\'{e}el temperature
to be $634 \pm 2$ K. First-principles simulations indicate that the system has
a small density of states at the Fermi energy and confirm the lowest-energy
magnetic ground state ordering, while Monte Carlo simulations match the
experimental N\'{e}el temperature. | 2201.07356v1 |
2024-03-26 | Large topological Hall effect arising from spin reorientation in kagome magnet Fe3Ge | Materials systems with spin chirality can provide ultra-high-density,
ultra-fast, and ultralow-power information carriers for digital transformation.
These material systems include magnetic skyrmions, chiral domain walls, spin
reorientation,and so on. The topological Hall effect (THE) has been identified
as the most convenient and effective tool for detecting the presence of spin
chirality in these systems. The research on the THE that may arise from spin
reorientation and specifically in Fe3Ge with spin reorientation remains an
unexplored area, so we study the THE in Fe3Ge Conduct systematic research.
X-Ray Diffraction (XRD) results indicate that our Fe3Ge ribbon sample has a
D019 structure. First-principles calculations and magnetic and electrical
testing confirm spin reorientation in the Fe3Ge ribbon sample at 350 K.The Hall
resistivity test results are consistent with our expectations, indicating the
presence of the THE in the Fe3Ge ribbon sample. The topological Hall
resistivity reaches a maximum value of 0.69 m{\Omega} cm at 400 K. For the
first time, a detailed experimental study of the THE in Fe3Ge with spin
reorientation has been conducted, introducing a new member to the family of
THE. | 2403.17354v1 |
2022-08-23 | Anomalous electrical transport and magnetic skyrmions in Mn-tuned Co9Zn9Mn2 single crystals | \b{eta}-Mn-type CoxZnyMnz (x + y + z = 20) alloys have recently attracted
increasing attention as a new class of chiral magnets with skyrmions at and
above room temperature. However, experimental studies on the transport
properties of this material are scarce. In this work, we report the successful
growth of the \b{eta}-Mn-type Co9.24Zn9.25Mn1.51 and Co9.02Zn9.18Mn1.80 single
crystals and a systematic study on their magnetic and transport properties. The
skyrmion phase was found in a small temperature range just below the Curie
temperature. The isothermal ac susceptibility and dc magnetization as a
function of magnetic field confirm the existence of the skyrmion phase. A
negative linear magnetoresistance over a wide temperature range from 2 K to 380
K is observed and attributed to the suppression of the magnetic ordering
fluctuation under high fields. Both the magnetization and electrical
resistivity are almost isotropic. The quantitative analysis of the Hall
resistance suggests that the anomalous Hall effect of Co9.24Zn9.25Mn1.51 and
Co9.02Zn9.18Mn1.80 single crystals is dominated by the intrinsic mechanism. Our
findings contribute to a deeper understanding of the properties of CoxZnyMnz (x
+ y + z = 20) alloys material and advance their application in spintronic
devices. | 2208.10955v1 |
2007-08-31 | Fundamental Constants | The notion of ``fundamental constant'' is heavily theory-laden. A natural,
fairly precise formulation is possible in the context of the standard model
(here defined to include gravity). Some fundamental constants have profound
geometric meaning. The ordinary gravitational constant parameterizes the
stiffness, or resistance to curvature, of space-time. The cosmological term
parameterizes space-time's resistance to expansion -- which may be, and
apparently is at present, a {\it negative} resistance, i.e. a tendency toward
expansion. The three gauge couplings of the strong, electromagnetic, and weak
interactions parameterize resistance to curvature in internal spaces. The
remaining fundamental couplings, of which there are a few dozen, supply an
ungainly accommodation of inertia. The multiplicity and variety of fundamental
constants are esthetic and conceptual shortcomings in our present understanding
of foundational physics. I discuss some ideas for improving the situation. I
then briefly discuss additional constants, primarily cosmological, that enter
into our best established present-day world model. Those constants presently
appear as macroscopic state parameters, i.e. as empirical ``material
constants'' of the Universe. I mention a few ideas for how they might become
fundamental constants in a future theory. In the course of this essay I've
advertised several of my favorite speculations, including a few that might be
tested soon. | 0708.4361v1 |
2014-02-10 | Tuning the band gap of PbCrO4 through high-pressure: Evidence of wide-to-narrow semiconductor transitions | The electronic transport properties and optical properties of lead(II)
chromate (PbCrO4) have been studied at high pressure by means of resistivity,
Hall-effect, and optical-absorption measurements. Band-structure
first-principle calculations have been also performed. We found that the
low-pressure phase is a direct band-gap semiconductor (Eg = 2.3 eV) that shows
a high resistivity. At 3.5 GPa, associated to a structural phase transition, a
band-gap collapse takes place, becoming Eg = 1.8 eV. At the same pressure the
resistivity suddenly decreases due to an increase of the carrier concentration.
In the HP phase, PbCrO4 behaves as an n-type semiconductor, with a donor level
probably associated to the formation of oxygen vacancies. At 15 GPa a second
phase transition occurs to a phase with Eg = 1.2 eV. In this phase, the
resistivity increases as pressure does probably due to the self-compensation of
donor levels and the augmentation of the scattering of electrons with ionized
impurities. In the three phases the band gap red shifts under compression. At
20 GPa, Eg reaches a value of 0.8 eV, behaving PbCrO4 as a narrow-gap
semiconductor. | 1402.2139v1 |
2015-08-11 | Pressure induced electronic topological transition in Sb2S3 | Pressure induced electronic topological transitions in the wide band gap
semiconductor Sb2S3 (Eg = 1.7-1.8 eV) with similar crystal symmetry (SG: Pnma)
to its illustrious analog, Sb2Se3, has been studied using Raman spectroscopy,
resistivity and the available literature on the x-ray diffraction studies. In
this report, the vibrational and the transport properties of Sb2S3 have been
studied up to 22 GPa and 11 GPa, respectively. We observed the softening of
phonon modes Ag(2), Ag(3) and B2g and a sharp anomaly in their line widths at 4
GPa. The resistivity studies also shows an anomaly around this pressure. The
changes in resistivity as well as Raman line widths can be ascribed to the
changes in the topology of the Fermi surface which induces the electron-phonon
and the strong phonon-phonon coupling, indicating a clear evidence of the
electronic topological transition (ETT) in Sb2S3. The pressure dependence of
a/c ratio plot obtained from the literature showed a minimum at ~ 5 GPa, which
is consistent with our high pressure Raman and resistivity results. Finally, we
give the plausible reasons for the non-existence of a non-trivial topological
state in Sb2S3 at high pressures. | 1508.02516v1 |
2018-11-19 | Room-temperature Low-field Colossal Magneto-resistance in Double-perovskite Manganite | The gigantic decrease of resistance by an applied magnetic field, which is
often referred to as colossal magnetoresistance (CMR), has been an attracting
phenomenon in strongly correlated electron systems. The discovery of CMR in
manganese oxide compounds has developed the science of strong coupling among
charge, orbital, and spin degrees of freedom. CMR is also attracting scientists
from the viewpoint of possible applications to sensors, memories, and so on.
However, no application using CMR effect has been achieved so far, partly
because the CMR materials which satisfy all of the required conditions for the
application, namely, high operating temperature, low operating magnetic field,
and sharp resistive change, have not been discovered. Here we report a
resistance change of more than two-orders of magnitude at a magnetic field
lower than 2 T near 300 K in an A-site ordered NdBaMn_2_O_6_ crystal. When
temperature and a magnetic field sweep from insulating (metallic) phase to
metallic (insulating) phase, the insulating (metallic) conduction changes to
the metallic (insulating) conduction within 1 K and 0.5 T, respectively. The
CMR is ascribed to the melting of the charge ordering. The entropy change which
is estimated from the B-T phase diagram is smaller than what is expected for
the charge and orbital ordering. The suppression of the entropy change is
attributable to the loss of the short range ferromagnetic fluctuation of Mn
spin moments, which an important key of the high temperature and low magnetic
field CMR effect. | 1811.07596v1 |
2018-10-17 | Perspectives of HgTe Topological Insulators for Quantum Hall Metrology | We report the studies of high-quality HgTe/(Cd,Hg)Te quantum wells (QWs) with
a width close to the critical one $d_c$, corresponding to the topological phase
transition and graphene like band structure in view of their applications for
Quantum Hall Effect (QHE) resistance standards. We show that in the case of
inverted band ordering, the coexistence of conducting topological helical edge
states together with QHE chiral states degrades the precision of the resistance
quantization. By experimental and theoretical studies we demonstrate how one
may reach very favorable conditions for the QHE resistance standards: low
magnetic fields allowing to use permanent magnets ( B $\leq$ 1.4T) and
simultaneously realtively high teperatures (liquid helium, T $\geq$ 1.3K). This
way we show that HgTe QW based QHE resistance standards may replace their
graphene and GaAs counterparts and pave the way towards large scale fabrication
and applications of QHE metrology devices. | 1810.07449v1 |
2019-07-25 | Reducing sheet resistance of self-assembled transparent graphene films by defect patching and doping with UV/ozone treatment | Liquid phase exfoliation followed by Langmuir-Blodgett self-assembly (LBSA)
is a promising method for scalable production of thin graphene films for
transparent conductor applications. However, monolayer assembly into thin films
often induces a high density of defects, resulting in a large sheet resistance
that hinders practical use. We introduce UV/ozone as a novel photochemical
treatment that reduces sheet resistance of LBSA graphene threefold, while
preserving the high optical transparency. The effect of such treatment on our
films is opposite to the effect it has on mechanically exfoliated or CVD films,
where UV/ozone creates additional defects in the graphene plane, increasing
sheet resistance. Raman scattering shows that exposure to UV/ozone reduces the
defect density in LBSA graphene, where edges are the dominant defect type. FTIR
spectroscopy indicates binding of oxygen to the graphene lattice during
exposure to ozone. In addition, work function measurements reveal that the
treatment dopes the LBSA film, making it more conductive. Such defect patching
paired with doping leads to an accessible way of improving the transparent
conductor performance of LBSA graphene, making solution-processed thin films a
candidate for industrial use. | 1907.10916v2 |
2019-10-17 | Link between magnetism and resistivity upturn in cuprates: a thermal conductivity study of La$_{2-x}$Sr$_x$CuO$_4$ | A key unexplained feature of cuprate superconductors is the upturn in their
normal state electrical resistivity $\rho(T)$ seen at low temperature inside
the pseudogap phase. We examined this issue via measurements of the thermal
conductivity $\kappa(T)$ down to 50 mK and in fields up to 17 T on the cuprate
La$_{2-x}$Sr$_x$CuO$_4$ at dopings $p = 0.13$, 0.136, 0.143 and 0.18. At $p$ =
0.136, 0.143, and 0.18, we observe an initial increase of the electronic
thermal conductivity $\kappa_0/T$ as a function of field, as expected in a
$d$-wave superconductor. For $p$ = 0.136 and 0.143, further increasing the
field then leads to a decrease of $\kappa_0/T$, which correlates with the onset
of spin density-wave order as observed in neutron scattering experiments on the
same samples. This decrease of $\kappa_0/T$ with field is imposed by the
Wiedemann-Franz law and the high value of the resistivity in the high-field
normal state of these samples. Our study therefore provides a direct link
between magnetism and the resistivity upturn in the pseudogap phase of
cuprates. We discuss this scenario in the broader context of other cuprates. | 1910.08126v1 |
2021-08-18 | High Entropy Alloy CrFeNiCoCu sputtered films | High entropy alloy(HEA) films of CrFeCoNiCu were prepared by sputtering,
their structure was characterized, and their electric properties measured by
temperature dependent Hall and Seebeck measurement. The HEA films show a solid
solution with fcc structure, and a 111 texture with columnar grains of widths
15-30 nm extending through film thickness with very many twins. The residual
electrical resistivity of the films is around 140 {\mu}{\Omega}cm and the
temperature dependence of the resistivity is metal-like. The temperature
coefficient of resistivity (TCR) is small (2 ppm/K). The Hall coefficient is
positive while the Seebeck coefficients is negative. This is interpreted as
arising from an electronic structure where the Fermi level passes through band
states having both holes and electrons as indicated by band structure
calculations. The HEA structure appears stable for annealing in vacuum, while
annealing in an oxygen containing atmosphere causes the surface to oxidize and
grow a Cr-rich oxide on the surface. This is then accompanied by demixing of
the HEA solid solution and a decrease in residual resistance of the film. | 2108.08373v2 |
2022-05-03 | Structural and electronic phase transitions in Zr$_{1.03}$Se$_{2}$ at high pressure | A detailed high pressure investigation is carried out using x-ray
diffraction, Raman spectroscopy and low temperature resistivity measurements on
hexagonal ZrSe$_{2}$ having an excess of 3 at.\% Zr. Structural studies show
that the sample goes through a gradual structural transition from hexagonal to
monoclinic phase, with a mixed phase in the pressure range 5.9 GPa to 14.8 GPa.
Presence of a minimum in the $c/a$ ratio in the hexagonal phase and a minimum
in the full width half maximum of the $A_{1g}$ mode at about the same pressure
indicates an electronic phase transition. The sample shows a metallic
characteristic in its low temperature resistivity data at ambient pressure,
which persist till about 5.1 GPa and can be related the presence of slight
excess Zr. At and above 7.3 GPa, the sample shows a metal to semiconductor
transition with the opening of a very small band gap, which increases with
pressure. The low temperature resistivity data show an upturn, which flattens
with an increase in pressure. The phenomenological analysis of the low
temperature resistivity data indicates the presence of Kondo effect in the
sample, which may be due to the excess Zr. | 2205.01322v1 |
2022-06-08 | Quantized anomalous Hall resistivity achieved in molecular beam epitaxy-grown MnBi2Te4 thin films | The intrinsic magnetic topological insulator MnBi2Te4 provides a feasible
pathway to high temperature quantum anomalous Hall (QAH) effect as well as
various novel topological quantum phases. Although quantized transport
properties have been observed in exfoliated MnBi2Te4 thin flakes, it remains a
big challenge to achieve molecular beam epitaxy (MBE)-grown MnBi2Te4 thin films
even close to the quantized regime. In this work, we report the realization of
quantized anomalous Hall resistivity in MBE-grown MnBi2Te4 thin films with the
chemical potential tuned by both controlled in-situ oxygen exposure and top
gating. We find that elongated post-annealing obviously elevates the
temperature to achieve quantization of the Hall resistivity, but also increases
the residual longitudinal resistivity, indicating a picture of high-quality QAH
puddles weakly coupled by tunnel barriers. These results help to clarify the
puzzles in previous experimental studies on MnBi2Te4 and to find a way out of
the big difficulty in obtaining MnBi2Te4 samples showing quantized transport
properties. | 2206.03773v2 |
2022-07-23 | Anomalous resistivity upturn in the van der Waals ferromagnet Fe$_5$GeTe$_2$ | Fe$_5$GeTe$_2$ (n = 3, 4, 5) have recently attracted increasing attention due
to their two-dimensional van der Waals characteristic and high temperature
ferromagnetism, which make promises for spintronic devices. The Fe(1) split
site is one important structural characteristic of Fe$_5$GeTe$_2$ which makes
it very different from other Fe$_5$GeTe$_2$ (n = 3, 4) systems. The local
atomic disorder and short-range order can be induced by the split site. In this
work, the high-quality van der Waals ferromagnet Fe$_5$GeTe$_2$ were grown to
study the low-temperature transport properties. We found a resistivity upturn
below 10 K. The temperature and magnetic field dependence of the resistivity
are in good agreement with a combination of the theory of disorder-enhanced
three-dimensional electron-electron and single-channel Kondo effect. The Kondo
effect exists only at low magnetic field B < 3 T, while electron-electron
dominates the appearance for the low-temperature resistivity upturn. We believe
that the enhanced three-dimensional electron-electron interaction in this
system is induced by the local atomic structural disorder due to the split site
of Fe(1). Our results indicate that the split site of Fe plays an important
role for the exceptional transport properties. | 2207.11383v1 |
2000-09-21 | High-pressure study of the non-Fermi liquid material U_2Pt_2In | The effect of hydrostatic pressure (p<= 1.8 GPa) on the non-Fermi liquid
state of U_2Pt_2In is investigated by electrical resistivity measurements in
the temperature interval 0.3-300 K. The experiments were carried out on
single-crystals with the current along (I||c) and perpendicular (I||a) to the
tetragonal axis. The pressure effect is strongly current-direction dependent.
For I||a we observe a rapid recovery of the Fermi-liquid T^2-term with
pressure. The low-temperature resistivity can be analysed satisfactorily within
the magnetotransport theory of Rosch, which provides strong evidence for the
location of U_2Pt_2In at an antiferromagnetic quantum critical point. For I||c
the resistivity increases under pressure, indicating the enhancement of an
additional scattering mechanism. In addition, we have measured the pressure
dependence of the antiferromagnetic ordering temperature (T_N= 37.6 K) of the
related compound U_2Pd_2In. A simple Doniach-type diagram for U_2Pt_2In and
U_2Pd_2In under pressure is presented. | 0009324v1 |
2002-04-19 | Spin-injection through an Fe/InAs Interface | The spin-dependence of the interface resistance between ferromagnetic Fe and
InAs is calculated from first-principles for specular and disordered (001)
interfaces. Because of the symmetry mismatch in the minority-spin channel, the
specular interface acts as an efficient spin filter with a transmitted current
polarisation between 98 an 89%.
The resistance of a specular interface in the diffusive regime is comparable
to the resistance of a few microns of bulk InAs.
Symmetry-breaking arising from interface disorder reduces the spin asymmetry
substantially and we conclude that efficient spin injection from Fe into InAs
can only be realized using high quality epitaxial interfaces. | 0204422v1 |
2002-10-01 | Free and Trapped Injected Carriers in C60 Crystals | We report on the conductance from two-contact carrier injection in C60 single
crystals. In the nonlinear regime, the current and voltage obey a power law, I
\~ V^m, where m can be as high as 10 at room temperature. This nonlinear
behavior - the resistance decreases by 6 orders of magnitude without saturation
- is among the highest reported for organic systems, and can be explained by
injection of free carriers into the trap-filling region. We find that H2
annealing suppresses shallow traps and enhances nonlinearity. Two limiting
types of temperature dependence of the nonlinear resistance are observed -
decreasing and increasing resistance at the orientational ordering temperature.
A simple model incorporating deep traps is presented to understand this
behavior and the impact of this model on possible field-effect transistor
action is discussed. | 0210029v1 |
2003-02-03 | Critical Current Density and Resistivity of MgB2 Films | The high resistivity of many bulk and film samples of MgB2 is most readily
explained by the suggestion that only a fraction of the cross-sectional area of
the samples is effectively carrying current. Hence the supercurrent (Jc) in
such samples will be limited by the same area factor, arising for example from
porosity or from insulating oxides present at the grain boundaries. We suggest
that a correlation should exist, Jc ~ 1/{Rho(300K) - Rho(50K)}, where Rho(300K)
- Rho(50K) is the change in the apparent resistivity from 300 K to 50 K. We
report measurements of Rho(T) and Jc for a number of films made by hybrid
physical-chemical vapor deposition which demonstrate this correlation, although
the "reduced effective area" argument alone is not sufficient. We suggest that
this argument can also apply to many polycrystalline bulk and wire samples of
MgB2. | 0302017v1 |
2003-03-19 | Structural and Electronic Properties of Amorphous and Polycrystalline In2Se3 Films | Structural and electronic properties of amorphous and single-phase
polycrystalline films of gamma- and kappa-In2Se3 have been measured. The stable
gamma phase nucleates homogeneously in the film bulk and has a high
resistivity, while the metastable kappa phase nucleates at the film surface and
has a moderate resistivity. The microstructures of hot-deposited and
post-annealed cold-deposited gamma films are quite different but the electronic
properties are similar. The increase in the resistivity of amorphous In2Se3
films upon annealing is interpreted in terms of the replacement of In-In bonds
with In-Se bonds during crystallization. Great care must be taken in the
preparation of In2Se3 films for electrical measurements as the presence of
excess chalcogen or surface oxidation may greatly affect the film properties. | 0303369v1 |
2003-04-16 | Initial dissipation and current-voltage characteristics of superconductors containing fractal clusters of a normal phase | The influence of fractal clusters of a normal phase on distinctive features
of current-voltage characteristic of percolative type-II superconductors is
considered. The results of high-resolution measurements of the differential
resistance of BPSCCO/Ag composites are discussed in the context of magnetic
flux dynamics. The region of initial dissipation is observed on current-voltage
characteristics in the neighborhood of the transition into a resistive state.
In the course of this stage of resistive transition the vortices start to break
away from the normal-phase clusters, which act as pinning centers. The effect
of transport current on vortex depinning is investigated. A broad current range
of initial dissipation is considered as an evidence of fractal nature of the
normal-phase clusters. | 0304354v2 |
2003-12-12 | Electronic behavior in mats of single-walled carbon nanotubes under pressure | Single-walled carbon nanotubes (SWNTs) have many interesting properties; they
may be metallic or semiconducting depending on their diameter and helicity of
the graphene sheet. Hydrostatic or quasi-hydrostatic high pressures can probe
many electronic features. Resistance - temperature measurements in SWNTs from
normal condition and under 0.4 GPa of quasi-hydrostatic pressures reveal a
semiconducting-like behavior. From 0.5 to about 2.0 GPa the resistance changes
to a Kondo-like feature due to magnetic impurities used to catalyse the
nanotube formation. Above 2.0 GPa, they become metallic and at about 2.4 GPa
the resistance decreases dramatically around 3 K suggesting a superconducting
transition. | 0312307v1 |
2004-08-12 | Impedance spectroscopy study on post-annealing-tuned polycrystalline CaCu3Ti4O12 films: Evidence of Barrier Layer Capacitor Effects | In this paper, impedance spectroscopy study was performed to establish the
electrical property and microstructure relations of the as-deposited and
post-annealed polycrystalline CCTO films prepared on Pt/Ti/SiO2/Si (100)
substrates by pulsed-laser deposition (PLD). Our results demonstrated that the
as-deposited polycrystalline CCTO film was made of insulating grain boundaries
with semiconducting grains, indicating that the high-dielectric-constant is
attributed to the barrier layer capacitor (BLC) effects. The simple
resistor-capacitor (RC) equivalent circuit and the modified constant phase
element (CPE) circuit were used to describe the impedance spectroscopy, and
excellent agreement between the calculated and measured curves was obtained in
the CPE circuit. The resistance and capacitance of the grains and grain
boundaries can be tuned by changing the annealing atmosphere and temperature.
Under oxygen-absent annealing atmosphere, the electric resistances of the grain
boundaries changed greatly but the resistance of the grains has almost no
change. While under oxygen annealing atmosphere, the reverse happened. On the
basis of this result, it is demonstrated that the origin of the
semiconductivity of the grains in CCTO polycrystalline films arises from their
oxygen-loss, while the grain boundaries are close to oxygen- stoicheometry. | 0408275v2 |
2004-12-03 | Resistance noise scaling in a 2D system in GaAs | The 1/f resistance noise of a two-dimensional (2D) hole system in a high
mobility GaAs quantum well has been measured on both sides of the 2D
metal-insulator transition (MIT) at zero magnetic field (B=0), and deep in the
insulating regime. The two measurement methods used are described: I or V
fixed, and measurement of resp. V or I fluctuations. The normalized noise
magnitude SR/R^2 increases strongly when the hole density is decreased, and its
temperature (T) dependence goes from a slight increase with T at the largest
densities, to a strong decrease at low density. We find that the noise
magnitude scales with the resistance, SR /R^2 ~ R^2.4. Such a scaling is
expected for a second order phase transition or a percolation transition. The
possible presence of such a transition is investigated by studying the
dependence of the conductivity as a function of the density. This dependence is
consistent with a critical behavior close to a critical density p* lower than
the usual MIT critical density pc. | 0412084v1 |
2005-10-21 | Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6 | The superconductor YB6 has the second highest critical temperature Tc among
the boride family MBn. We report measurements of the specific heat,
resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K,
using a single crystal with Tc = 7.2 K. The superconducting gap is
characteristic of medium-strong coupling. The specific heat, resistivity and
expansivity curves are deconvolved to yield approximations of the phonon
density of states, the spectral electron-phonon scattering function and the
phonon density of states weighted by the frequency-dependent Grueneisen
parameter respectively. Lattice vibrations extend to high frequencies >100 meV,
but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of
yttrium ions in oversized boron cages, appears to provide most of the
superconducting coupling and gives rise to an unusual temperature behavior of
several observable quantities. A surface critical field Hc3 is also observed. | 0510572v3 |
2006-03-31 | Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals | We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation. | 0603850v1 |
2007-06-29 | NMR relaxation and resistivity from rattling phonons in pyrochlore superconductors | We calculate the temperature dependence of NMR relaxation rate and electrical
resistivity for coupling to a local, strongly anharmonic phonon mode. We argue
that the two-phonon Raman process is dominating NMR relaxation. Due to the
strong anharmonicity of the phonon an unusual temperature dependence is found
having a low temperature peak and becoming constant towards higher
temperatures. The electrical resistivity is found to vary like T^2 at low
temperatures and following a sqrt{T} behavior at high temperatures. Both
results are in qualitative agreement with recent observations on
beta-pyrochlore oxide superconductors. | 0706.4345v2 |
2007-07-04 | NaV2O4: a Quasi-1D Metallic Antiferromagnet with Half-Metallic Chains | NaV2O4 crystals were grown under high pressure using a NaCl flux, and the
crystals were characterized with X-ray diffraction, electrical resistivity,
heat capacity, and magnetization. The structure of NaV2O4 consists of double
chains of edge-sharing VO6 octahedra. The resistivity is highly anisotropic,
with the resistivity perpendicular to the chains more than 20 times greater
than that parallel to the chains. Magnetically, the intrachain interactions are
ferromagnetic and the interchain interactions are antiferromagnetic; 3D
antiferromagnetic order is established at 140 K. First principles electronic
structure calculations indicate that the chains are half metallic.
Interestingly, the case of NaV2O4 seems to be a quasi-1D analogue of what was
found for half-metallic materials. | 0707.0519v3 |
2007-09-11 | Transport properties and magnetic field induced localization in the misfit cobaltite [Bi$_2$Ba$_{1.3}$K$_{0.6}$Co$_{0.1}$]$^{RS}$[CoO$_2$]$_{1.97}$ single crystal | Resistivity under magnetic field, thermopower and Hall coefficient are
systematically studied for
[Bi$_2$Ba$_{1.3}$K$_{0.6}$Co$_{0.1}$]$^{RS}$[CoO$_2$]$_{1.97}$ single crystal.
In-plane resistivity ($\rho_{ab}$(T)) shows metallic behavior down to 2 K with
a $T^2$ dependence below 30 K; while out-of-plane resistivity ($\rho_{c}(T)$)
shows metallic behavior at high temperature and a thermal activation
semiconducting behavior below about 12 K. Striking feature is that magnetic
field induces a ln(1/$T$) diverging behavior in both $\rho_{ab}$ and
$\rho_{c}(T)$ at low temperature. The positive magnetoresistance (MR) could be
well fitted by the formula based on multi-band electronic structure. The
ln(1/$T$) diverging behavior in $\rho_{ab}$ and $\rho_{c}(T)$ could arise from
the magnetic-field-induced 2D weak localization or spin density wave. | 0709.1519v1 |
2007-11-29 | Magnetoelectric Effects on Composite Nano Granular $Fe/TiO_{2-δ}$ Films | Employing a new experimental technique to measure magnetoelectric response
functions, we have measured the magnetoelectric effect in composite films of
nano granular metallic iron in anatase titanium dioxide at temperatures below
50 K. A magnetoelectric resistance is defined as the ratio of a transverse
voltage to bias current as a function of the magnetic field. In contrast to the
anomalous Hall resistance measured above 50 K, the magnetoelectic resistance
below 50 K is significantly larger and exhibits an even symmetry with respect
to magnetic field reversal $H\to -H$. The measurement technique required
attached electrodes in the plane of the film composite in order to measure
voltage as a function of bias current and external magnetic field. To our
knowledge, the composite films are unique in terms of showing magnetoelectric
effects at low temperatures, $<$ 50 K, and anomalous Hall effects at high
temperatures, $>$ 50 K. | 0711.4776v1 |
2009-04-23 | Microscopic origin of bipolar resistive switching of nanoscale titanium oxide thin films | We report a direct observation of the microscopic origin of the bipolar
resistive switching behavior in nanoscale titanium oxide films. Through a
high-resolution transmission electron microscopy, an analytical TEM technique
using energy-filtering transmission electron microscopy and an in situ x-ray
photoelectron spectroscopy, we demonstrated that the oxygen ions piled up at
top interface by an oxidation-reduction reaction between the titanium oxide
layer and the top Al metal electrode. We also found that the drift of oxygen
ions during the on/off switching induced the bipolar resistive switching in the
titanium oxide thin films. | 0904.3628v2 |
2009-08-25 | Bipolar resistive switching characteristics of poly(3,4-ethylene-dioxythiophene): poly(styrenesulfonate) thin film | We investigated the reversible resistive switching of
poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) thin films
sandwiched between Al electrodes. The J-V sweep curve showed a hysteretic
behavior which depends on the polarity of the applied voltage bias. From the
analysis of I-V curves, it was revealed that the charge transport through the
junction was governed by the bulk space-charge-limited conduction (SCLC) model.
Using transmission electron microscopy (TEM) analysis, it was confirmed that
the initial high resistance state of PEDOT:PSS films is related with the
segregation of PSS- chains induced by redox reaction between a Al metal
electrode and PEDOT:PSS film. Positive space charges present on the top region
of PEDOT:PSS films can be proposed as a possible trap centers of electron
trapping and detrapping process. | 0908.3527v1 |
2010-02-02 | Memristor Behaviour in Nano-Sized Vertical Lsmo/Lsmo Tunnel Junctions | We report a memory resistance (memristor) behavior with nonlinear
current-voltage characteristics and bipolar hysteretic resistance switching in
the nanocolumnar manganite (LSMO) films. The switching from a high (HRS) to a
low (LRS) resistance occurs at a bias field ~1 MV/cm. Applied electric field
drops mostly at the insulating interfacial LSMO layer and couples to correlated
polarons at the LSMO(111)/LSMO(111) vertical interfaces. The observed
memristance behaviour has an electronic (polaronic) origin and is caused by an
electric-field-controlled Jahn-Teller (JT) effect, followed by the orbital
reconstruction and formation of a metastable orbitally disordered interfacial
phase (LRS). Compared to the earlier reported ionic memristor in Ti-O films, an
electronic (polaronic) nano-sized LSMO memristor shows an additional
(re-entrant) LRS-HRS switching at higher fields because of the second minimum
in the elastic energy of a JT system. | 1002.0495v1 |
2010-02-11 | Synthesis, anisotropy, and superconducting properties of LiFeAs single crystal | A LiFeAs single crystal with $T_c^{onset}$$\sim$19.7 K was grown successfully
in a sealed tungsten crucible using the Bridgeman method. The electrical
resistivity experiments revealed a ratio of room temperature to residual
resistivity (RRR) of approximately 46 and 18 for the in-plane and out-of plane
directions. The estimated anisotropic resistivity, $\gamma_\rho$=$\rho_c$ /
$\rho_{ab}$, was approximately 3.3 at $T_c^{onset}$. The upper critical fields
had large $H_{c2} ^{\shortparallel ab}$ and $H_{c2}^{\shortparallel c}$ values
of 83.4 T and 72.5 T, respectively, and an anisotropy ratio is
$\gamma_H$=$H_{c2}^{\shortparallel ab}$ / $H_{c2} ^{\shortparallel
c}$$\sim$1.15. The high upper critical field value and small anisotropy
highlight the potential use of LiFeAs in a variety of applications. The
calculated critical current density $(J_c)$ from the $M$-$H$ loop is
approximately 10$^3$ A/cm$^2$ | 1002.2249v1 |
2010-07-15 | Role of interface reaction on resistive switching of Metal/a-TiO2/Al RRAM devices | For the clear understanding of the role of interface reaction between top
metal electrode and titanium oxide layer, we investigated the effects of
various top metals on the resistive switching in Metal/a-TiO2/Al devices. The
top Al device with the highest oxygen affinity showed the best memory
performance, which is attributed to the fast formation of interfacial layer
(Al-Ti-O), as confirmed by high resolution transmission electron microscopy and
electron dispersive spectroscopy. Hence, we concluded that the interface layer,
created by the redox reaction between top metal electrode and TiO2 layer, plays
a crucial role in bipolar resistive switching behaviors of metal/TiO2/Al
systems. | 1007.2463v1 |