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2015-01-13 | Phase-change memory function of correlated electrons in organic conductors | Phase-change memory (PCM), a promising candidate for next-generation
non-volatile memories, exploits quenched glassy and thermodynamically stable
crystalline states as reversibly switchable state variables. We demonstrate PCM
functions emerging from a charge-configuration degree of freedom in strongly
correlated electron systems. Non-volatile reversible switching between a
high-resistivity charge-crystalline (or charge-ordered) state and a
low-resistivity quenched state, charge glass, is achieved experimentally via
heat pulses supplied by optical or electrical means in organic conductors
$\theta$-(BEDT-TTF)$_2$$X$. Switching that is one order of magnitude faster is
observed in another isostructural material that requires faster cooling to
kinetically avoid charge crystallization, indicating that the material's
critical cooling rate can be useful guidelines for pursuing a faster
correlated-electron PCM function. | 1501.02873v2 |
2015-01-15 | Optimizing the Optical and Electrical Properties of Graphene Ink Thin Films by Laser-annealing | We demonstrate a facile fabrication technique for graphene-based transparent
conductive films. Highly flat and uniform graphene films are obtained through
the incorporation of an efficient laser annealing technique with one-time drop
casting of high-concentration graphene ink. The resulting thin films are
uniform and exhibit a transparency of more than 85% at 550 nm and a sheet
resistance of about 30 k{\Omega}/sq. These values constitute an increase of 45%
in transparency, a reduction of surface roughness by a factor of four and a
decrease of 70% in sheet resistance compared to unannealed films. | 1501.03843v1 |
2015-02-18 | The Role of Transport Agents in MoS2 Single Crystals | We report resistivity, thermoelectric power and thermal conductivity of MoS2
single crystals prepared by chemical vapour transport (CVT) method using I2,
Br2 and TeCl4 as transport agents. The material presents low-lying donor and
acceptor levels, which dominate the in-plane charge transport. Intercalates
into the Van der Waals gap strongly influence the inter-plane resistivity.
Thermoelectric power displays the characteristics of strong electron-phonon
interaction. Detailed theoretical model of thermal conductivity reveals the
presence of high number of defects in the MoS2 structure. We show that these
defects are inherent to CVT growth method, coming mostly from the transport
agent molecules inclusion as identified by Total Reflection X-ray Fluorescence
analysis (TXRF) and in-beam activation analysis (IBAA). | 1502.05161v1 |
2015-08-20 | Transport Conductivity of Graphene at RF and Microwave Frequencies | We measure graphene coplanar waveguides from direct current (DC) to 13.5GHz
and show that the apparent resistance (in the presence of parasitic impedances)
has an quadratic frequency dependence, but the intrinsic conductivity (without
the influence of parasitic impedances) is frequency-independent. Consequently,
in our devices the real part of the complex alternating current conductivity is
the same as the DC value and the imaginary part~0. The graphene channel is
modelled as a parallel resistive-capacitive network with a frequency dependence
identical to that of the Drude conductivity with momentum relaxation
time~2.1ps, highlighting the influence of alternating current (AC) electron
transport on the electromagnetic properties of graphene. This can lead to
optimized design of high-speed analogue field-effect transistors, mixers,
frequency doublers, low-noise amplifiers and radiation detectors. | 1508.04984v1 |
2016-08-17 | Nanocomposite si-c-n coatings | Coatings of ternary nanocomposite Si-C-N ceramic coatings have shown newer
and improved mechanical and functional properties over the coarser and
monolithic coatings. Properties like high hardness, wear resistance, oxidation
resistance, tunable band gap and chemical inertness have been observed for
Si-C-N which makes its potential for numerous applications. Although lot of
research has taken place in Si-C-N coatings, proper understanding of the effect
of different parameters on the coating properties are still not resolved. The
changes occurring in fraction of Si, C and N and the phases forming in the
coatings with variation in deposition conditions require investigations. This
research paper gives a systematic study of the role of different deposition
parameters like substrate temperature, pressure, power on the nucleation and
growth, structure, microstructural bonding and mechanical properties of the
film deposited by magnetron sputtering which adds significantly to the
fundamental knowledge of nanocomposite Si-C-N coatings as well as its
applications. | 1608.05667v1 |
2016-12-21 | Correlation between battery material performance and cooperative electron-phonon interaction in LiCo$_y$Mn$_{2-y}$O$_{4}$ | Understanding the basic physics related to archetypal lithium battery
material (such as LiCo$_y$Mn$_{2-y}$O$_{4}$) is of considerable interest and is
expected to aid designing of cathodes of high capacity. The relation between
electrochemical performance, activated-transport parameters, thermal expansion,
and cooperativity of electron-phonon-interaction distortions in
LiCo$_y$Mn$_{2-y}$O$_{4}$ is investigated. The first order
cooperative-normal-mode transition, detected through coefficient of thermal
expansion, is found to disappear at a critical doping ($y \sim 0.16$);
interestingly, for $y \gtrsim 0.16$ the resistivity does not change much with
doping and the electrochemical capacity becomes constant over repeated cycling.
The critical doping $y \sim 0.16$ results in breakdown of the network of
cooperative/coherent normal-mode distortions; this leads to vanishing of the
first-order transition, establishment of hopping channels with lower
resistance, and enhancing lithiation and delithiation of the battery, thereby
minimizing electrochemical capacity fading. | 1612.07092v1 |
2018-05-07 | High-temperature thermoelectric properties of half-Heusler phases Er$_{1-x}$Ho$_x$NiSb | Polycrystalline samples of Er$_{1-x}$Ho$_x$NiSb ($x$ = 0, 0.2, 0.3, 0.5, 0.7,
0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning
electron microscopy (SEM), and optical metallography. The results proved the
formation of half-Heusler alloys in the entire composition range. Their
electrical transport properties (resistivity, thermoelectric power) were
studied in the temperature interval 350-1000 K. The measured electrical
resistivity spanned between 5 and 25 $\mu \Omega$m. The maximum thermopower of
50-65 $\mu$V/K was observed at temperatures 500-650 K. Replacing Ho for Er
resulted in a non-monotonous variation of the thermoelectric power factor ($PF
= S^2/\rho$). The largest $PF$ of 4.6 $\mu$WcmK$^{-2}$ was found at 660 K for
Er$_{0.5}$Ho$_{0.5}$NiSb. This value is distinctly larger than PF determined
for the terminal phases ErNiSb and HoNiSb. | 1805.02435v1 |
2018-05-16 | Magnetic properties of single crystalline itinerant ferromagnet AlFe2B2 | Single crystals of AlFe$_{2}$B$_{2}$ have been grown using the self flux
growth method and then measured the structural properties, temperature and
field dependent magnetization, and temperature dependent electrical resistivity
at ambient as well as high pressure. The Curie temperature of AlFe$_{2}$B$_{2}$
is determined to be $274$~K. The measured saturation magnetization and the
effective moment for paramagnetic Fe-ion indicate the itinerant nature of the
magnetism with a Rhode-Wohlfarth ratio $ \frac{M_{C}}{M_{sat}}\approx 1.14$.
Temperature dependent resistivity measurements under hydrostatic pressure shows
that transition temperature \textit{T$_C$} is suppressed down to 255 K for $p =
2.24$~GPa pressure with a suppression rate of $\sim -8.9$~K/GPa. The anisotropy
fields and magnetocrystalline anisotropy constants are in reasonable agreement
with density functional theory calculations. | 1805.06373v1 |
2019-09-29 | Structural and electrical properties of ceramic Li-ion conductors based on Li$_{1.3}$Al$_{0.3}$Ti$_{1.7}$(PO$_4$)$_3$-LiF | The work presents the investigations of Li1.3Al0.3Ti1.7(PO4)3-xLiF Li-ion
conducting ceramics with 0 < x < 0.3 by means of X-ray diffractometry (XRD),
7Li, 19F, 27Al and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS
NMR) spectroscopy, thermogravimetry (TG), scanning electron microscopy (SEM),
impedance spectroscopy (IS) and density method. It has been shown that the
total ionic conductivity of both as-prepared and ceramic Li1.3Al0.3Ti1.7(PO4)3
is low due to a grain boundary phase exhibiting high electrical resistance.
This phase consists mainly of berlinite crystalline phase as well as some
amorphous phase containing Al3+ ions. The electrically resistant phases of the
grain boundary decompose during sintering with LiF additive. The processes
leading to microstructure changes and their effect on the ionic properties of
the materials are discussed in the frame of the brick layer model (BLM). The
highest total ionic conductivity at room temperature was measured for
LATP-0.1LiF ceramic sintered at 800{\deg}C and was equal to {\sigma}tot = 1.1 x
10-4 Scm-1. | 1909.13291v2 |
2017-03-19 | A thermodynamic analysis of the spider silk and the importance of complexity | The spider silk is one of the most interesting bio-materials investigated in
the last years. One of the main reasons that brought scientists to study this
organized system is its high level of resistance if compared to other
artificial materials characterized by higher density. Subsequently, researchers
discovered that the spider silk is a complex system formed by different kinds
of proteins, organized (or disorganized) to guarantee the required resistance,
which is function of the final application and of the environmental conditions.
Some spider species are able to make different silks, up to twelve, having a
composition that seems to be function of the final use (i.e. dragline web,
capture web, etc). The aim of this paper is to analyze the properties of the
spider silk by means of a thermodynamic approach, taking advantage of the
well-known theories applied to polymers, and to try to underline and develop
some intriguing considerations. Moreover, this study can be taken as an example
to introduce and discuss the importance of the concept of optionality and of
the anti-fragile systems proposed by N. N. Thaleb in his book "Antifragile:
Things that gain from disorder". | 1703.06497v1 |
2019-07-31 | Large spin Hall magnetoresistance in antiferromagnetic α-Fe2O3/Pt heterostructures | We investigate the spin Hall magnetoresistance (SMR) at room temperature in
thin film heterostructures of antiferromagnetic, insulating, (0001)-oriented
alpha-Fe2O3 (hematite) and Pt. We measure their longitudinal and transverse
resistivities while rotating an applied magnetic field of up to 17T in three
orthogonal planes. For out-of-plane magnetotransport measurements, we find
indications for a multidomain antiferromagnetic configuration whenever the
field is aligned along the film normal. For in-plane field rotations, we
clearly observe a sinusoidal resistivity oscillation characteristic for the SMR
due to a coherent rotation of the Neel vector. The maximum SMR amplitude of
0.25% is, surprisingly, twice as high as for prototypical ferrimagnetic
Y3Fe5O12/Pt heterostructures. The SMR effect saturates at much smaller magnetic
fields than in comparable antiferromagnets, making the alpha-Fe2O3/Pt system
particularly interesting for room-temperature antiferromagnetic spintronic
applications. | 1907.13393v4 |
2020-09-16 | Properties and influence of microstructure and crystal defects in Fe$_2$VAl modified by laser surface remelting | Laser surface remelting can be used to manipulate the microstructure of cast
material. Here, we present a detailed analysis of the microstructure of
Fe$_2$VAl following laser surface remelting. Within the melt pool, elongated
grains grow nearly epitaxially from the heat-affected zone. These grains are
separated by low-angle grain boundaries with 1{\deg}-5{\deg} misorientations.
Segregation of vanadium, carbon, and nitrogen at grain boundaries and
dislocations is observed using atom probe tomography. The local electrical
resistivity was measured by an in-situ four-point-probe technique. A smaller
increase in electrical resistivity is observed at these low-angle grain
boundaries compared to high-angle grain boundaries in a cast sample. This
indicates that grain boundary engineering could potentially be used to
manipulate thermoelectric properties. | 2009.07685v2 |
2016-03-18 | Electronic Structure, Phase Stability and Resistivity of Hybrid Hexagonal C$_x$(BN)$_{1-x}$ Two-dimensional Nanomaterial: A First-principles Study | We use density functional theory based first-principles method to investigate
the bandstructure and phase stability in the laterally grown hexagonal
C$_x$(BN)$_{1-x}$, two-dimensional Graphene and $h$-BN hybrid nanomaterials,
which were synthesized by experimental groups recently (Liu $et al$, Nature
Nanotech, 8, 119 (2013)). Our detail electronic structure calculations on such
materials, with both armchair and zigzag interfaces between the Graphene and $
h$-BN domains, indicate that the band-gap decreases non-monotonically with the
concentration of Carbon. The calculated bandstructure shows the onset of Dirac
cone like features near the band-gap at high Carbon concentration ($x \sim
0.8$). From the calculated energy of formation, the phase stability of
C$_x$(BN)$_{1-x}$ was studied using a regular solution model and the system was
found to be in the ordered phase below a few thousand Kelvin. Furthermore,
using the Boltzmann transport theory we calculate the electrical resistivity
from the bandstrcture of C$_x$(BN)$_{1-x}$ at different temperature ($T$),
which shows a linear behaviour when plotted in the logarithmic scale against
$T^{-1}$, as observed experimentally | 1603.05780v1 |
2017-08-25 | Ballistic geometric resistance resonances in a single surface of a topological insulator | Transport in topological matter has shown a variety of novel phenomena over
the last decade. Although numerous transport studies have been conducted on
three-dimensional topological insulators (3D-TIs), study of ballistic motion
and thus exploration of potential landscapes on a hundred nanometer scale is
for the prevalent TI materials almost impossible due to their low carrier
mobility. Therefore it is unknown whether helical Dirac electrons in TIs, bound
to interfaces between topologically distinct materials, can be manipulated on
the nanometer scale by local gates or locally etched regions. Here we impose a
submicron periodic potential onto a single surface of Dirac electrons in high
mobility strained mercury telluride (HgTe), which is a strong TI. Pronounced
geometric resistance resonances constitute the first observation of a ballistic
effect in 3D-TIs. | 1708.07766v1 |
2018-08-22 | Evidence for Undoped Weyl Semimetal Charge Transport in $Y_{2}Ir_{2}O_{7}$ | Weyl fermions scattering from a random Coulomb potential are predicted to
exhibit resistivity versus temperature $\rho \space \alpha \space T^{-4}$ in a
single particle model. Here we show that, in closed environment-grown
polycrystalline samples of $Y_{2}Ir_{2}O_{7}$, $\rho = \rho_{0} T^{-4}$ over
four orders of magnitude in $\rho$. While the measured prefactor, $\rho_{0}$,
is obtained from the model using reasonable materials parameters, the $T^{-4}$
behavior extends far beyond the model's range of applicability. In particular,
the behavior extends into the low-temperature, high-resistivity region where
the Ioffe-Regel parameter, $k_{T} \ell \ll 2\pi$. Strong on-site Coulomb
correlations, instrumental for predicting a Weyl semimetal state in
$Y_{2}Ir_{2}O_{7}$, are the possible origin of such "bad" Weyl semimetal
behavior. | 1808.07583v4 |
2019-04-07 | Restoration of long range order of Na ions in $Na_xCoO_2$ at high temperatures by sodium site doping | We have systematically investigated the $Na_xCoO_2$ system doped with Cu, Y,
Sn, W, Au and Bi for $x$ = 0:5; 0:75 and 1.00 using density functional theory.
Sn, W, and Bi always substitute a Co while Au always substitutes a Na
regardless of Na concentration. However, for Cu and Y, the substitution site
depends on Na concentration. When compared to the available experimental data,
we find that thermoelectric performance is enhanced when the dopants substitute
a Na site. In this case, surprisingly, resistivity decreases despite the
reduced hole concentration caused by carrier recombination. We propose improved
carrier mobility to be the cause of observed reduced resistivity. | 1904.03644v1 |
2019-08-07 | Fast response of pulsed laser deposited Zinc ferrite thin film as a chemo-resistive gas sensor | Thin films of ZnFe2O4 deposited by pulsed laser technique are here
demonstrated as one of the interesting materials for sensing of ethanol. The
response transients were fitted well to one-site Langmuir adsorption model.
Activation energies for (I) adsorption and reaction of ethanol and (II)
desorption (i.e. recovery process) of ethanol from zinc ferrite thin film
surface were obtained on the basis of this model. In this paper, we showed the
effect of operating temperature and gas-concentration on the response time of
thin film sensor materials. At the operating temperature 340oC, the ZnFe2O4
thin film showed high (84%) as well as immediate response to 500 ppm of
ethanol, with its resistance being saturated within ~12 seconds, which stands
far superior to the response time of nano crystalline powders. Those films were
also observed to have a good repeatability of their sensor response, thus
representing a major step towards low-cost large-scale production of this class
of devices. | 1908.02780v1 |
2012-06-18 | GdN Nanoisland-Based GaN Tunnel Junctions | We show that GdN nanoislands can enhance inter-band tunneling in GaN PN
junctions by several orders of magnitude, enabling low optical absorption
low-resistance tunnel junctions (specific resistivity 1.3 X 10-3 {\Omega}-cm2)
for various optoelectronic applications. We exploit the ability to overgrow
high quality GaN over GdN nanoislands to create new nanoscale heterostructure
designs that are not feasible in planar epitaxy. GdN nanoisland assisted
inter-band tunneling was found to enhance tunneling in both of the polar
orientations of GaN. Tunnel injection of holes was confirmed by low temperature
operation of GaN p-n junction with a tunneling contact layer, showing strong
electroluminescence down to 20K. The availability of tunnel junctions with
negligible absorption could not only improve the efficiency of existing
optoelectronic devices significantly, but also enable new electronic and
optical devices based on wide band gap materials. | 1206.3810v3 |
2015-07-01 | Itinerant Antiferromagnetism in FeMnP0.8Si0.2 Single Crystals | Compounds based on the Fe2P structure have continued to attract interest
because of the interplay between itinerant and localized magnetism in a
non-centrosymmetric crystal structure, and because of the recent developments
of these materials for magnetocaloric applications. Here we report the growth
and characterization of mm size single crystals of FeMnP0.8Si0.2. Single
crystal x-ray diffraction, magnetization, resistivity, Hall and heat capacity
data are reported. Surprisingly, the crystals exhibit itinerant
antiferromagnetic order below 158 K with no hint of ferromagnetic behavior in
the magnetization curves and with the spins ordered primarily in the ab plane.
The room temperature resistivity is close to the Ioffe-Regel limit for a metal.
Single crystal x-ray diffraction indicates a strong preference for Mn to occupy
the larger pyramidal 3g site. The cation site preference in the as-grown
crystals and the antiferromagnetism are not changed after high temperature
anneals and a rapid quench to room temperature. | 1507.00275v1 |
2019-01-22 | S-type Negative Differential Resistance in Semiconducting Transition-Metal Dichalcogenides | Current-controlled (also known as "S-type") negative differential resistance
(NDR) is of crucial importance to many emerging applications including
neuromorphic computing and high-density memristors integration. However, the
experimental realization of S-type NDR based on conventional mechanisms poses
demanding requirements on materials, which greatly limits their potential
applications. Here, we experimentally identify that semiconducting transition
metal dichalcogenides (TMDs) can host a bipolar S-type NDR devices. Theoretical
simulations indicate that the origin of the NDR in these devices arises from a
thermal feedback mechanism. Furthermore, we demonstrate the potential
applications of TMDs based S-type NDR device in signal processing and
neuromorphic electronics. | 1901.07161v1 |
2020-12-30 | High Current Density in Monolayer MoS$_2$ Doped by AlO$_x$ | Semiconductors require stable doping for applications in transistors,
optoelectronics, and thermoelectrics. However, this has been challenging for
two-dimensional (2D) materials, where existing approaches are either
incompatible with conventional semiconductor processing or introduce
time-dependent, hysteretic behavior. Here we show that low temperature (<
200$^\circ$ C) sub-stoichiometric AlO$_x$ provides a stable n-doping layer for
monolayer MoS$_2$, compatible with circuit integration. This approach achieves
carrier densities > 2x10$^{13}$ 1/cm$^2$, sheet resistance as low as ~7
kOhm/sq, and good contact resistance ~480 Ohm.um in transistors from monolayer
MoS$_2$ grown by chemical vapor deposition. We also reach record current
density of nearly 700 uA/um (>110 MA/cm$^2$) in this three-atom-thick
semiconductor while preserving transistor on/off current ratio > $10^6$. The
maximum current is ultimately limited by self-heating and could exceed 1 mA/um
with better device heat sinking. With their 0.1 nA/um off-current, such doped
MoS$_2$ devices approach several low-power transistor metrics required by the
international technology roadmap | 2012.15350v1 |
2021-06-09 | Maximizing Spin-Orbit Torque Generated by the Spin Hall Effect of Pt | Efficient generation of spin-orbit torques (SOTs) is central for the exciting
field of spin-orbitronics. Platinum, the archetypal spin Hall material, has the
potential to be an outstanding provider for spin-orbit torques due to its giant
spin Hall conductivity, low resistivity, high stabilities, and the ability to
be compatible with CMOS circuits. However, pure clean-limit Pt with low
resistivity still provides a low damping-like spin-orbit torque efficiency,
which limits its practical applications. The efficiency of spin-orbit torque in
Pt-based magnetic heterostructures can be improved considerably by increasing
the spin Hall ratio of Pt and spin transmissivity of the interfaces. Here we
reviews recent advances in understanding the physics of spin current
generation, interfacial spin transport, and the metrology of spin-orbit
torques, and summarize progress towards the goal of Pt-based spin-orbit torque
memories and logic that are fast, efficient, reliable, scalable, and
non-volatile. | 2106.04992v2 |
2021-08-12 | Revisiting the Reduction of Thermal Conductivity in Nano- to Micro-Grained Bismuth Telluride: The Importance of Grain-Boundary Thermal Resistance | Nanograined bulk alloys based on bismuth telluride (Bi2Te3) are the dominant
materials for room-temperature thermoelectric applications. In numerous
studies, existing bulk phonon mean free path (MFP) spectra predicted by
atomistic simulations suggest sub-100 nm grain sizes are necessary to reduce
the lattice thermal conductivity by decreasing phonon MFPs. This is in contrast
with available experimental data, where a remarkable thermal conductivity
reduction is observed even for micro-grained Bi2Te3 samples. In this work,
first-principles phonon MFPs along both the in-plane and cross-plane directions
are re-computed for bulk Bi2Te3. These phonon MFPs can explain new and existing
experimental data on flake-like Bi2Te3 nanostructures with various thicknesses.
For polycrystalline Bi2Te3-based materials, a better explanation of the
experimental data requires further consideration of the grain-boundary thermal
resistance that can largely suppress the transport of high-frequency optical
phonons. | 2108.05972v1 |
2022-12-02 | Electric modulation of the Fermi arc spin transport via three-terminal configuration in the topological semimetal nanowires | Spin momentum locking is a key feature of the topological surface state,
which plays an important role in spintronics. The electrical detection of
current-induced spin polarization protected by the spin momentum locking in
non-magnetic systems provides a new platform for developing spintronics while
previous studies were mostly based on magnetic materials. In this study, the
spin transport measurement of Dirac semimetal Cd3As2 was studied by the
three-terminal geometry, and a hysteresis loop signal with high resistance and
low resistance state was observed. The hysteresis was reversed by reversing the
current direction, which illustrates the spin-momentum locking feature of
Cd3As2. Furthermore, we realized the on-off states of the spin signals through
electric modulation of the Fermi arc via the three-terminal configuration,
which enables the great potential of Cd3As2 in spin field-effect transistors. | 2212.01072v1 |
2023-08-02 | Observation of zero resistance above 100$^\circ$ K in Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O | Room-temperature superconductivity has always been regarded as the ultimate
goal in the fields of solid-state physics and materials science, with its
realization holding revolutionary significance, capable of triggering
significant changes in energy transmission and storage. However, achieving it
poses various challenges. Recent research revealed that material
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O displays room-temperature superconductivity
under atmospheric pressure, sparking global interest in further exploration.
Here, we utilized solid-phase synthesis to obtain a polycrystalline sample of
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O. X-ray diffraction confirmed its structural
consistency with referenced literature. Zero resistance, which is important
evidence for superconductivity, was observed above 100$^\circ$ K under ambient
pressure in our experiment. Our finding indicates that
Pb$_{10-x}$Cu$_x$(PO$_4$)$_6$O is a possible candidate for searching
high-temperature superconductors. | 2308.01192v1 |
2024-04-13 | Solution-Processed Inks with Fillers of NbS$_3$ Quasi-One-Dimensional Charge-Density-Wave Material | We report on the solution processing and testing of electronic ink comprised
of quasi-one-dimensional NbS$_3$ charge-density-wave fillers. The ink was
prepared by liquid-phase exfoliation of NbS$_3$ crystals into high-aspect ratio
quasi-1D fillers dispersed in a mixture of isopropyl alcohol and ethylene
glycol solution. The results of the electrical measurements of two-terminal
electronic test structures printed on silicon substrates reveal resistance
anomalies in the temperature range of ~330 K to 370 K. It was found that the
changes in the temperature-dependent resistive characteristics of the test
structures originate from the charge-density-wave phase transition of
individual NbS$_3$ fillers. The latter confirms that the exfoliated NbS$_3$
fillers preserve their intrinsic charge-density-wave quantum condensate states
and can undergo phase transitions above room temperature even after chemical
exfoliation processes and printing. These results are important for developing
"quantum inks" with charge-density-wave fillers for the increased functionality
of future solution-processed electronics. | 2404.09038v1 |
2024-02-16 | Cycling on rough roads: A model for resistance and vibration | Minimising opposing forces is a matter of interest to most cyclists. These
forces arise from passage through air ("drag") and interaction with the road
surface ("resistance"). Recent work recognises that resistance forces arise not
only from the deformation of the tyre ("rolling resistance") but also from
irregularities in the road surface ("roughness resistance"), which lead to
power dissipation in the body of the rider through vibration. The latter effect
may also have an adverse impact on human health. In this work we offer a
quantitative theory of roughness resistance and vibration that links these
effects to a surface characterisation in terms of the International Roughness
Index (IRI). We show that the roughness resistance and the Vibration Dose Value
(or VDV, the usual vibration dosage metric) can be expressed in terms of
elementary formulae. The roughness resistance depends only on the vertical
stiffness of the bicycle and the roughness index. Surprisingly, other
apparently relevant parameters, such as physiological characteristics of the
bicycle rider and other features of the bicycle, do not enter. For roads of
moderate roughness, roughness resistance is larger than rolling resistance. For
very rough roads, roughness resistance is larger than aerodynamic drag. So only
on roads of high quality (in most jurisdictions, accounting for less than 10~\%
of the total) can roughness resistance be ignored. Roughness resistance can be
mitigated by reducing the vertical stiffness of the bicycle. In common with
other recent reports, we find that almost any cycling activity will breach
public health guidelines relating to Vibration Dose Value. | 2405.00019v1 |
2015-05-11 | Pressure-induced semimetal to superconductor transition in a three-dimensional topological material ZrTe5 | As a new type of topological materials, ZrTe5 shows many exotic properties
under extreme conditions. Utilizing resistance and ac magnetic susceptibility
measurements under high pressure, while the resistance anomaly near 128 K is
completely suppressed at 6.2 GPa, a fully superconducting transition emerges
surprisingly. The superconducting transition temperature Tc increases with
applied pressure, and reaches a maximum of 4.0 K at 14.6 GPa, followed by a
slight drop but remaining almost constant value up to 68.5 GPa. At pressures
above 21.2 GPa, a second superconducting phase with the maximum Tc of about 6.0
K appears and coexists with the original one to the maximum pressure studied in
this work. In situ high-pressure synchrotron X-ray diffraction and Raman
spectroscopy combined with theoretical calculations indicate the observed
two-stage superconducting behavior is correlated to the structural phase
transition from ambient Cmcm phase to high-pressure C2/m phase around 6 GPa,
and to a mixture of two high-pressure phases of C2/m and P-1 above 20 GPa. The
combination of structure, transport measurement and theoretical calculations
enable a complete understanding of the emerging exotic properties in
three-dimensional topological materials happened under extreme environments. | 1505.02658v2 |
2015-08-05 | Screening and transport in 2D semiconductor systems at low temperatures | Low temperature carrier transport properties in two-dimensional (2D)
semiconductor systems can be theoretically well-understood within a mean-field
type RPA-Boltzmann theory as being limited by scattering from screened Coulomb
disorder arising from random quenched charged impurities in the environment. In
the current work, we derive a number of simple analytical formula, supported by
realistic numerical calculations, for the relevant density, mobility, and
temperature range where 2D transport should manifest strong intrinsic (i.e.,
arising purely from electronic effects and not from phonon scattering) metallic
temperature dependence in different semiconductor materials arising entirely
from the 2D screening properties, thus providing an explanation for why the
strong temperature dependence of the 2D resistivity can only be observed in
high-quality and low-disorder (i.e., high-mobility) 2D samples and also why
some high-quality 2D materials (i.e., n-GaAs) manifest much weaker metallicity
than other materials. We also discuss effects of interaction and disorder on
the 2D screening properties in this context as well as compare 2D and 3D
screening functions to comment why such a strong intrinsic temperature
dependence arising from screening cannot occur in 3D metallic carrier
transport. Experimentally verifiable predictions are made about the
quantitative magnitude of the maximum possible low-temperature metallicity in
2D systems and the scaling behavior of the temperature scale controlling the
quantum to classical crossover where the system reverses the sign of the
temperature derivative of the 2D resistivity at high temperatures. | 1508.01195v1 |
2007-07-04 | Role of oxygen vacancies in Cr-doped SrTiO3 for resistance-change memory | Transition-metal oxides exhibiting a bistable resistance state are attractive
for non-volatile memory applications. The relevance of oxygen vacancies (VO)
for the resistance-change memory was investigated with x-ray fluorescence,
infrared microscopy, and x-ray absorption spectroscopy using Cr-doped SrTiO3 as
example. We propose that the microscopic origin of resistance switching in this
class of materials is due to an oxygen-vacancy drift occurring in close
proximity to one of the electrodes. | 0707.0563v1 |
2012-12-17 | Measurement of specific contact resistivity using scanning voltage probes | Specific contact resistivity measurements have conventionally been heavy in
both fabrication and simulation/calculation in order to account for complicated
geometries and other effects such as parasitic resistance. We propose a simpler
geometry to deliver current, and the use of a scanning voltage probe to sense
the potential variation along the sample surface, from which the specific
contact resistivity can be straightforwardly deduced. We demonstrate an
analytical example in the case where both materials are thin films.
Experimental data with a scanning Kelvin probe measurement on graphene from the
literature corroborates our model calculation. | 1212.4182v2 |
2013-11-04 | Surface resistivity of hydrogenated amorphous carbon films: Existence of intrinsic graphene on its surface | Surface resistivity of hydrogenated amorphous carbon films was measured as a
function of the applied electrical field. The measured dependence shows a sharp
ambipolar peak near zero gate voltage. Furthermore, we found that in some
samples sheet resistance at the peak is as low as 7.5 k{\Omega}/sq. This value
is the same order of magnitude as the sheet resistance of a defect free
graphene monolayer. Therefore a conclusion is made that an intrinsic graphene
with dimensions of at least millimeters exist on the surface of amorphous
carbon films. These results can open new perspectives not only for graphene
applications, but also for better understanding of this unique material. | 1311.0605v2 |
2014-06-17 | High-Performance MoS2 Field-Effect Transistors Enabled by Chloride Doping: Record Low Contact Resistance (0.5 kohm*um) and Record High Drain Current (460 uA/um) | In this paper, we report a novel chemical doping technique to reduce the
contact resistance (Rc) of transition metal dichalcogenides (TMDs) -
eliminating two major roadblocks (namely, doping and high Rc) towards
demonstration of high-performance TMDs field-effect transistors (FETs). By
using 1,2 dichloroethane (DCE) as the doping reagent, we demonstrate an active
n-type doping density > 2*1019 cm-3 in a few-layer MoS2 film. This enabled us
to reduce the Rc value to a record low number of 0.5 kohm*um, which is ~10x
lower than the control sample without doping. The corresponding specific
contact resistivity (pc) is found to decrease by two orders of magnitude. With
such low Rc, we demonstrate 100 nm channel length (Lch) MoS2 FET with a drain
current (Ids) of 460 uA/um at Vds = 1.6 V, which is twice the best value
reported so far on MoS2 FETs. | 1406.4492v1 |
2015-04-14 | Thermal boundary resistance at Si/Ge interfaces determined by approach-to-equilibrium molecular dynamics simulations | The thermal boundary resistance of Si/Ge interfaces as been determined using
approach-to-equilibrium molecular dynamics simulations. Assuming a reciprocal
linear dependence of the thermal boundary resistance, a length-independent bulk
thermal boundary resistance could be extracted from the calculation resulting
in a value of 3.76x10$^{-9}$ m$^2$ K/W for a sharp Si/Ge interface and thermal
transport from Si to Ge. Introducing an interface with finite thickness of 0.5
nm consisting of a SiGe alloy, the bulk thermal resistance slightly decreases
compared to the sharp Si/Ge interface. Further growth of the boundary leads to
an increase in the bulk thermal boundary resistance. When the heat flow is
inverted (Ge to Si), the thermal boundary resistance is found to be higher.
From the differences in the thermal boundary resistance for different heat flow
direction, the rectification factor of the Si/Ge has been determined and is
found to significantly decrease when the sharp interface is moderated by
introduction of a SiGe alloy in the boundary layer. | 1504.03613v1 |
2019-06-12 | Kapitza resistance in basic chain models with isolated defects | Kapitza thermal resistance is a common feature of material interfaces. It is
defined as the ratio of the thermal drop at the interface to the heat flux
flowing across the interface. One expects that this resistance will depend on
the structure of the interface and on the temperature. We address the heat
conduction in one-dimensional chain models with isotopic and/or coupling
defects and explore the relationship between the interaction potentials and
simulated properties of the Kapitza resistance. It is revealed that in linear
models the Kapitza resistance is well-defined and size-independent (contrary to
the bulk heat conduction coefficient), but depends on the parameters of
thermostats used in the simulation. For $\beta$-FPU model one also encounters
the dependence on the thermostats; in addition, the simulated boundary
resistance strongly depends on the total system size. Finally, in the models
characterized by convergent bulk heat conductivity (chain of rotators,
Frenkel-Kontorova model) the boundary resistance is thermostat- and
size-independent, as one expects. In linear chains, the Kapitza resistance is
temperature-independent; thus, its temperature dependence allows one to judge
on significance of the nonlinear interactions in the phonon scattering
processes at the interface. | 1906.05152v1 |
2022-09-22 | Computational Design of Corrosion-resistant and Wear-resistant Titanium Alloys for Orthopedic Implants | Titanium alloys are promising candidates for orthopedic implants due to their
mechanical resilience and biocompatibility. Current titanium alloys in
orthopedic implants still suffer from low wear and corrosion resistance. Here,
we present a computational method for optimizing the composition of titanium
alloys for enhanced corrosion and wear resistance without compromising on other
aspects such as phase stability, biocompatibility, and strength. We use the
cohesive energy, oxide formation energy, surface work function, and the elastic
shear modulus of pure elements as proxy descriptors to guide us towards alloys
with enhanced wear and corrosion resistance. For the best-selected candidates,
we then use the CALPHAD approach, as implemented in the Thermo-Calc software,
to calculate the phase diagram, yield strength, hardness, Pourbaix diagram, and
the Pilling-Bedworth (PB) ratio. These calculations are used to assess the
thermodynamic stability, biocompatibility, corrosion resistance, and wear
resistance of the selected alloys. Additionally, we provide insights about the
role of silicon on improving the corrosion and wear resistance of alloys. | 2210.00845v1 |
2021-08-17 | Superconducting-like and magnetic transitions in oxygen-implanted diamond-like and amorphous carbon films, and in highly oriented pyrolytic graphite | In our previously published work, we have reported colossal
magnetoresistance, Andreev oscillations, ferromagnetism, and granular
superconductivity in oxygen-implanted carbon fibers, graphite foils, and highly
oriented pyrolytic graphite. In this follow-up research, more results on these
oxygen-implanted graphite samples are presented. We show results from transport
measurements on oxygen-implanted diamond-like carbon thin coatings, amorphous
carbon films, and highly oriented pyrolytic graphite. Significantly, a
three-order magnitude drop in the electrical resistance of the oxygen-implanted
diamond-like carbon films is observed at the 50 K temperature that we have
previously reported for the transition to the superconducting state. Below 50
K, the films resistance oscillates between the high and low resistance states,
less when the sample is under a transverse magnetic field. This metastability
between the insulating and superconducting-like states possibly reflects the
evolution of the amplitude for the superconducting order parameter also known
as the longitudinal Higgs mode. Transitions to low resistance state and
metastability are also observed for amorphous carbon films. Finally, the highly
oriented pyrolytic graphite samples resistance have a thermally activated term
that can be understood on the basis of the LAMH model applied to narrow SC
channels in which thermal fluctuations can cause phase slips. We also find that
in oxygen-implanted carbon materials, the electron charge and spin correlations
do not compete and their interplay rather facilitates the emergence of
high-temperature superconductivity, and thus, additional unexpected effects
like Heisenberg spin waves and magneto-structural transitions are observed. | 2108.07417v1 |
2019-11-20 | Aspects of the Normal State Resistivity of Cuprate Superconductors | Planar normal state resistivity data taken from three families of cuprate
superconductors are compared with theoretical calculations from the recent
extremely correlated Fermi liquid theory (ECFL). The two hole doped cuprate
materials $LSCO$ and $BSLCO$ and the electron doped material $LCCO$ have
yielded rich data sets at several densities $\delta$ and temperatures T,
thereby enabling a systematic comparison with theory. The recent ECFL
resistivity calculations for the highly correlated $t$-$t'$-$J$ model by us
give the resistivity for a wide set of model parameters. After using X-ray
diffraction and angle resolved photoemission data to fix parameters appearing
in the theoretical resistivity, only one parameter, the magnitude of the
hopping $t$, remains undetermined. For each data set, the slope of the
experimental resistivity at a single temperature-density point is sufficient to
determine $t$, and hence the resistivity on absolute scale at all remaining
densities and temperatures. This procedure is shown to give a fair account of
the entire data. | 1911.09119v3 |
2005-10-20 | Dependence of tunnel magnetoresistance in MgO based magnetic tunnel junctions on Ar pressure during MgO sputtering | We investigated dependence of tunnel magnetoresistance effect in
CoFeB/MgO/CoFeB magnetic tunnel junctions on Ar pressure during MgO-barrier
sputtering. Sputter deposition of MgO-barrier at high Ar pressure of 10 mTorr
resulted in smooth surface and highly (001) oriented MgO. Using this MgO as a
tunnel barrier, tunnel magnetoresistance (TMR) ratio as high as 355% at room
temperature (578% at 5K) was realized after annealing at 325 C or higher, which
appears to be related to a highly (001) oriented CoFeB texture promoted by the
smooth and highly oriented MgO. Electron-beam lithography defined
deep-submicron MTJs having a low-resistivity Au underlayer with the
high-pressure deposited MgO showed high TMR ratio at low resistance-area
product (RA) below 10 ohm-um^2 as 27% at RA = 0.8 ohm-um^2, 77% at RA = 1.1
ohm-um^2, 130% at RA = 1.7 ohm-um^2, and 165% at RA = 2.9 ohm-um^2. | 0510531v1 |
2014-09-23 | Fabrication of Flexible Super Capacitor Using Laser Lightscribe Technique | Super capacitors are promising energy storage devices due to their capability
of delivering high peak current and storing high amount of energy in a short
time with very low internal power loss. We fabricated the graphene or graphite
oxide super-capacitor using laser Lightscribe technique. We prepared graphite
oxide by modified hummers method and used PET film as a flexible substrate on
which graphite oxide (GO) was coated. Using Lightscribe drive and software, the
super-capacitor configuration was patterned on the GO coated PET film. During
the writing process, the laser converts GO into graphene. We characterized the
fabricated flexible super-capacitor which exhibits high resistance of 20KOhm
with applied voltage of 10V and further increase of voltage (20V) decreases the
resistance to 8KOhm. We also analyzed the frequency response of the capacitor
using impedance measurement which shows high frequency response and estimated
capacitance is 120nF. We optimized the patterns by running the Lightscribe
repeatedly on the GO coated PET substrate. | 1409.6396v1 |
2019-09-20 | Extraordinary high room-temperature carrier mobility in graphene-WSe$_2$ heterostructures | High carrier mobilities play a fundamental role for high-frequency
electronics, integrated optoelectronics as well as for sensor and spintronic
applications, where device performance is directly linked to the magnitude of
the carrier mobility. Van der Waals heterostructures formed by graphene and
hexagonal boron nitride (hBN) already outperform all known materials in terms
of room temperature mobility. Here, we show that the mobility of today's best
graphene/hBN devices can be surpassed by more than a factor of three by
heterostructures formed by tungsten diselenide (WSe$_2$), graphene and hBN,
which can have mobilities as high as 350,000 cm$^2$/(Vs) at room temperature,
and resistivities as low as 15 Ohm. The resistivity of these devices shows a
much weaker temperature dependence than the one of graphene on any other known
substrate. The origin of this behaviour points to modified acoustic phonon
bands in graphene and questions our understanding of electron-phonon scattering
in van der Waals heterostructures. | 1909.09523v1 |
2015-06-29 | High quality monolayer graphene synthesized by resistive heating cold wall chemical vapour deposition | Emerging flexible and wearable technologies such as healthcare electronics
and energy-harvest devices could be transformed by the unique properties of
graphene. The vision for a graphene-driven industrial revolution is motivating
intensive research on the synthesis of (1) high quality and (2) low cost
graphene. Hot-wall chemical vapour deposition (CVD) is one of the most
competitive growth methods, but its long processing times are incompatible with
production lines. Here we demonstrate the growth of high quality monolayer
graphene using a technique that is 100 times faster than standard hot-wall CVD,
resulting in 99% reduction in production costs. A thorough complementary study
of Raman spectroscopy, atomic force microscopy, scanning electron microscopy
and electrical magneto-transport measurements shows that our cold wall
CVD-grown graphene is of comparable quality to that of natural graphene.
Finally, we demonstrate the first transparent and flexible graphene capacitive
touch-sensor that could enable the development of artificial skin for robots. | 1506.08569v1 |
2015-09-29 | A Nonlinear HP-Type Complementary Resistive Switch | Resistive Switching (RS) is the change in resistance of a dielectric under
the influence of an external current or electric field. This change is
non-volatile, and the basis of both the memristor and resistive random access
memory. In the latter, high integration densities favor the anti-serial
combination of two RS-elements to a single cell, termed the complementary
resistive switch (CRS). Motivated by the irregular shape of the filament
protruding into the device, we suggest a nonlinearity in the
resistance-interpolation function, and thereby expand the original
HP-memristor. We numerically simulate and analytically solve this model.
Further, the nonlinearity allows for its application to the CRS. | 1509.08885v1 |
2003-08-14 | Resistivity Ratio of Niobium Superconducting Cavities | Resistivity measurements have been made on Nb cavities, as well as on Pb and
Cu, at 296, 77, and 4.2 K by means of a contactless induced-current method. For
superconductors, a constant magnetic field drives the material normal below the
transition temperature. These measurements provide a simple means for initial
material evaluation as well as a direct means of monitoring the effects of
material parameters (purity, heat treatment, gas incorporation, etc.) on the
electron mean free path. Approximate determinations of Hc, Hc1, and Hc2 can
also be derived from these measurements. Normal-state thermal conductivity and
the Ginzburg-Landau parameter kappa are calculated from the resistivity
measurements. | 0308266v1 |
2014-01-09 | Rapid Embedded Wire Heating via Resistive Guiding of Laser-Generated Fast Electrons as a Hydrodynamic Driver | Resistively guiding laser-generated fast electron beams in targets consisting
of a resistive wire embedded in lower $Z$ material should allow one to rapidly
heat the wire to over 100eV over a substantial distance without strongly
heating the surrounding material. On the multi-ps timescale this can drive
hydrodynamic motion in the surrounding material. Thus ultra-intense laser solid
interactions have the potential as a controlled driver of radiation
hydrodynamics in solid density material. In this paper we assess the laser and
target parameters needed to achieve such rapid and controlled heating of the
embedded wire. | 1401.1998v1 |
2002-07-19 | Spin Injection: Interface Resistance in Fe/Semiconductor Junctions Calculated from First Principles | We calculate the current spin polarisation and the interface resistance of
Fe/GaAs and Fe/ZnSe (001) spin injection junctions from first principles,
including also the possibility of a Schottky barrier. From our results of
interface resistance we estimate the barrier thickness needed for efficient
spin injection if the process is non-ballistic. | 0207492v1 |
2007-08-01 | Resistance noise in Bi_2Sr_2CaCu_2O$_{8+δ}$ | The resistance noise in a Bi_2Sr_2CaCu_2O$_{8+\delta}$ thin film is found to
increase strongly in the underdoped regime. While the increase of the raw
resistance noise with decreasing temperature appears to roughly track the
previously reported pseudogap temperature for this material, standard noise
analysis rather suggests that the additional noise contribution is driven by
the proximity of the superconductor-insulator transition. | 0708.0117v1 |
2010-06-14 | A conjecture of Biggs concerning the resistance of a distance-regular graph | Previously, Biggs has conjectured that the resistance between any two points
on a distance-regular graph of valency greater than 2 is bounded by twice the
resistance between adjacent points. We prove this conjecture, give the sharp
constant for the inequality, and display the graphs for which the conjecture
most nearly fails. Some necessary background material is included, as well as
some consequences. | 1006.2687v1 |
2019-06-13 | Comment on arXiv:1807.08572, "Coexistence of Diamagnetism and Vanishingly Small Electrical Resistance at Ambient Temperature and Pressure in Nanostructures" | A recent preprint arXiv:1807.08572 reported the observation of a transition
in Ag/Au nanoparticle composites near room temperature and at ambient pressure,
to a vanishingly small four-probe resistance, which was tentatively identified
as a percolating superconducting transition. In this brief comment, I point out
that a vanishing four-probe resistance may also emerge in non-superconducting
systems near conductance percolation threshold. | 1906.05742v1 |
2017-08-18 | A New Method for Characterizing Bulk and Surface Conductivities of Three-Dimensional Topological Insulators: Inverted Resistance Measurements | We introduce a new resistance measurement method that is useful in
characterizing materials with both surface and bulk conduction, such as
three-dimensional topological insulators. The transport geometry for this new
resistance measurement configuration consists of one current lead as a closed
loop that fully encloses the other current lead on the surface, and two voltage
leads that are both placed outside the loop. We show that in the limit where
the transport is dominated by the surface conductivity of the material, the
four-terminal resistance measured from such a transport geometry is
proportional to $\sigma_b/\sigma_s^2$, where $\sigma_b$ and $\sigma_s$ are the
bulk and surface conductivities of the material, respectively. We call this new
type of measurement \textit{inverted resistance measurement}, as the resistance
scales inversely with the bulk resistivity. We discuss possible implementations
of this new method by performing numerical calculations on different geometries
and introduce strategies to extract the bulk and surface conductivities. We
also demonstrate inverted resistance measurements on SmB$_6$, a topological
Kondo insulator, using both single-sided and coaxially-aligned double-sided
Corbino disk transport geometries. Using this new method, we are able to
measure the bulk conductivity, even at low temperatures, where the bulk
conduction is much smaller than the surface conduction in this material. | 1708.05762v2 |
2007-11-02 | Effects of carbon nanotubes on grain boundary sliding in zirconia polycrystals | Mechanical properties of zirconia polycrystals decrease drastically at high
temperature due to thermally activated grain boundary (GB) sliding, leading to
plastic or even super-plastic deformation. As GB sliding is a source of energy
dissipation in the material, mechanical loss measurements are well suited to
study such a mechanism. They reveal, in general, a mechanical loss peak, which
evolves into an exponential increase at higher temperature. When intergranular
glassy films or/and amorphous pockets are presented in polycrystalline
ceramics, the mechanical loss is globally higher and so is the creep rate. Here
we show that introducing carbon nanotubes in zirconia, in particular, reduces
drastically GB sliding and consequently the mechanical loss at high
temperature. The nanotubes were observed at the grain boundaries by
high-resolution transmission electron microscopy and were related to the
reduction of superplasic flow through the boundaries, which should improve the
material creep resistance. | 0711.0381v1 |
2010-01-25 | High-pressure synthesis, crystal and electronic structures of a new scandium tungstate, Sc0.67WO4 | Negative thermal expansion (NTE) materials possess a low-density, open
structure which can respond to high pressure conditions, leading to new
compounds and/or different physical properties. Here we report that one such
NTE material -- white, insulating, orthorhombic Sc2W3O12 -- transforms into a
black compound when treated at 4 GPa and 1400 oC. The high pressure phase,
Sc0.67WO4, crystallizes in a defect-rich wolframite-type structure, a dense,
monoclinic structure (space group P2/c) containing 1-D chains of edge-sharing
WO6 octahedra. The chemical bonding of Sc0.67WO4 vis-a-vis the ambient pressure
Sc2W3O12 phase can be understood on the basis of the Sc defect structure.
Magnetic susceptibility, resistivity, thermoelectric power and IR spectroscopic
measurements reveal that Sc0.67WO4 is a paramagnet whose conductivity is that
of a metal in the presence of weak localization and electron-electron
interactions. Oxygen vacancies are suggested as a potential mechanism for
generating the carriers in this defective wolframite material. | 1001.4561v1 |
2016-10-18 | Low Temperature Thermoelectric Properties of Co- and Cr- doped CuAgSe | High mobility phonon-glass semimetal $CuAgSe$ has shown promise in recent
years as a potential low-temperature thermoelectric material. It exhibits
reasonably strong thermoelectric performance as well as an extremely high
carrier mobility, both of which are enhanced when the material is doped with Ni
at the Cu sites. The exact mechanism by which these enhancements result;
however, is unclear. In order to further investigate the effects of chemical
substitution on the material's thermoelectric properties, we have prepared and
performed various measurements on $CuAgSe$ samples doped with Co and Cr
according to the following compositional formulas: $Cu_{1-x}Co_{x}AgSe$
$(x=0.02, 0.05, 0.10)$ and $Cu_{1-x}Cr_{x}AgSe$ $(x=0.02, 0.05)$. Measurements
of temperature and magnetic field dependent thermal conductivity, electrical
resistivity, and Seebeck coefficient will be discussed. Our results reveal a
remarkable sensitivity of $CuAgSe$'s thermoelectric properties to chemical
doping in general as well as a particular sensitivity to specific dopants. This
demonstrated tunability of $CuAgSe$'s various properties furthers the case that
high mobility phonon glass-semimetals are strong candidates for potential low
temperature thermoelectric applications. | 1610.05634v1 |
2018-03-14 | Ultra High Molecular Weight Polyethylene: optical features at millimeter wavelengths | The next generation of experiments for the measurement of the Cosmic
Microwave Background (CMB) requires more and more the use of advanced
materials, with specific physical and structural properties. An example is the
material used for receiver's cryostat windows and internal lenses. The large
throughput of current CMB experiments requires a large diameter (of the order
of 0.5m) of these parts, resulting in heavy structural and optical requirements
on the material to be used. Ultra High Molecular Weight (UHMW) polyethylene
(PE) features high resistance to traction and good transmissivity in the
frequency range of interest. In this paper, we discuss the possibility of using
UHMW PE for windows and lenses in experiments working at millimeter
wavelengths, by measuring its optical properties: emissivity, transmission and
refraction index. Our measurements show that the material is well suited to
this purpose. | 1803.05228v1 |
2019-08-02 | Machine-learning-assisted thin-film growth: Bayesian optimization in molecular beam epitaxy of SrRuO3 thin films | Materials informatics exploiting machine learning techniques, e.g., Bayesian
optimization (BO), has the potential to offer high-throughput optimization of
thin-film growth conditions through incremental updates of machine learning
models in accordance with newly measured data. Here, we demonstrated BO-based
molecular beam epitaxy (MBE) of SrRuO3, one of the most-intensively studied
materials in the research field of oxide electronics, mainly owing to its
unique nature as a ferromagnetic metal. To simplify the intricate search space
of entangled growth conditions, we ran the BO for a single condition while
keeping the other conditions fixed. As a result, high-crystalline-quality
SrRuO3 film exhibiting a high residual resistivity ratio (RRR) of over 50 as
well as strong perpendicular magnetic anisotropy was developed in only 24 MBE
growth runs in which the Ru flux rate, growth temperature, and
O3-nozzle-to-substrate distance were optimized. Our BO-based search method
provides an efficient experimental design that is not as dependent on the
experience and skills of individual researchers, and it reduces experimental
time and cost, which will accelerate materials research. | 1908.00739v1 |
2002-04-08 | Pressure Effect on the Superconducting and Magnetic Transitions of the Superconducting Ferromagnet RuSr2GdCu2O8 | The superconducting ferromagnet RuSr2GdCu2O8 was investigated at high
pressure. The intra-grain superconducting transition temperature, Tc, is
resolved in ac-susceptibility as well as resistivity measurements. It is shown
that the pressure shift of Tc is much smaller than that of other high-Tc
compounds in a similar doping state. In contrast, the ferromagnetic transition
temperature, Tm, increases with pressure at a relative rate that is about twice
as large as that of Tc. The high-pressure data indicate a possible competition
of the ferromagnetic and superconducting states in RuSr2GdCu2O8. | 0204185v1 |
2004-09-23 | Superconducting and Normal State Properties of Heavily Hole-Doped Diamond | We report measurements of the specific heat, Hall effect, upper critical
field and resistivity on bulk, B-doped diamond prepared by reacting amorphous B
and graphite under high-pressure/high-temperature conditions. These experiments
establish unambiguous evidence for bulk superconductivity and provide a
consistent set of materials parameters that favor a conventional, weak coupling
electron-phonon interpretation of the superconducting mechanism at high hole
doping. | 0409624v1 |
2000-04-10 | Systematic evolution of the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6} in a wide doping range | Recently we have succeeded in growing a series of high-quality
Bi_{2}Sr_{2-x}La_{x}CuO_{6} crystals in a wide range of carrier concentrations.
The data of \rho_{ab}(T) and R_H(T) of those crystals show behaviors that are
considered to be "canonical" to the cuprates. The optimum zero-resistance T_c
has been raised to as high as 38 K, which is almost equal to the optimum T_c of
La_{2-x}Sr_{x}CuO_{4}. | 0004134v1 |
2005-07-20 | Superconductivity in Polycrystalline Diamond Thin Films | Superconductivity was discovered in heavily boron-doped diamond thin films
deposited by the microwave plasma assisted chemical vapor deposition (MPCVD)
method. Advantages of the MPCVD deposited diamond are the controllability of
boron concentration in a wide range, and a high boron concentration, especially
in (111) oriented films, compared to that of the high-pressure high-temperature
method. The superconducting transition temperatures are determined to be 8.7K
for Tc onset and 5.0K for zero resistance by transport measurements. And the
upper critical field is estimated to be around 7T. | 0507476v2 |
2006-11-15 | Silicon detectors: damage, modelling and expected long-time behaviour in physics experiments at ultra high energy | In this contribution, the structural modifications of the material and the
degradation of devices is modelled and compared with experimental data for more
resistivities, temperatures, crystal orientations and oxygen concentrations,
considering the existence of the new primary fourfold coordinated defect,
besides the vacancy and the interstitial. Some estimations of the behaviour of
detectors in concrete environments at the next generations of high energy
physics experiments as LHC, SLHC, VLHC, or ULHC are done. | 0611142v1 |
2008-01-07 | High pressure-high temperature phase diagram of ammonia | The high pressure(P)-high temperature(T) phase diagram of solid ammonia has
been investigated using diamond anvil cell and resistive heating techniques.
The III-IV transition line has been determined up to 20 GPa and 500 K both on
compression and decompression paths. No discontinuity is observed at the
expected location for the III-IV-V triple point. The melting line has been
determined by visual observations of the fluid-solid equilibrium up to 9 GPa
and 900 K. The experimental data is well fitted by a Simon-Glatzel equation in
the covered P-T range. These transition lines and their extrapolations are
compared with reported calculations. | 0801.0913v1 |
2008-07-16 | High-Temperature Superconductivity in Eu0.5K0.5Fe2As2 | Subsequent to our recent report of SDW type transition at 190 K and
antiferromagnetic order below 20 K in EuFe2As2, we have studied the effect of
K-doping on the SDW transition at high temperature and AF order at low
temperature. 50% K doping suppresses the SDW transition and in turn gives rise
to high-temperature superconductivity below T_c = 32 K, as observed in the
electrical resistivity, AC susceptibility as well as magnetization. A well
defined anomaly in the specific heat provides additional evidence for bulk
superconductivity. | 0807.2530v2 |
2017-09-08 | Room temperature ferromagnetism in transparent and conducting Mn-doped $SnO_{2}$ thin films | The magnetization as a function of magnetic field showed hysteretic behavior
at room temperature. According to the temperature dependence of the
magnetization, the Curie temperature $(T_{C})$ is higher than 350 K.
Ferromagnetic Mn-doped tin oxide thin films exhibited low electrical
resistivity and high optical transmittance in the visible region (400-800 nm).
The coexistence of ferromagnetism, high visible transparency and high
electrical conductivity in the Mn-doped $SnO_{2}$ films is expected to be a
desirable trait for spintronics devices. | 1709.05930v1 |
2020-11-18 | The CLICTD Monolithic CMOS Sensor | CLICTD is a monolithic silicon pixel sensor fabricated in a modified 180 nm
CMOS imaging process with a small collection electrode design and a
high-resistivity epitaxial layer. It features an innovative sub-pixel
segmentation scheme and is optimised for fast charge collection and high
spatial resolution. The sensor was developed to target the requirements for the
tracking detector of the proposed future Compact Linear Collider (CLIC). Most
notably, a temporal resolution of a few nanoseconds and a spatial resolution
below 7 microns are demanded. In this contribution, the sensor performance
measured in beam tests is presented with emphasis on recent studies using
assemblies with different thicknesses (down to 50 microns to minimize the
material budget) and inclined particle tracks. | 2011.09389v1 |
2023-11-28 | A Brief Review and Perspective on the Functional Biodegradable Films for Food Packaging | High-performance, environmentally-friendly biodegradable packaging as
substitutes for conventional plastics becomes severe demand to nowadays economy
and society. As an aliphatic aromatic copolyester PBAT is recognized as the
preferred alternative to traditional plastics. However, the relatively high
cost and weak properties obstacles the widespread adoption of PBAT.
Modification pertaining to improve the properties, lower the cost, and include
the functional additives of PBAT is a continuous effort to meet the needs of
food accessibility, antibacterial properties, oxygen resistance, high
mechanical strength, stable size, low moisture absorption, and various gas
permeability for commercial competitiveness. | 2311.16932v1 |
2023-05-18 | Indium-Tin-Oxide for High-performance Electro-optic Modulation | Advances in opto-electronics are often led by discovery and development of
materials featuring unique properties. Recently the material class of
transparent conductive oxides (TCO) has attracted attention for active photonic
devices on-chip. In particular Indium Tin Oxide (ITO) is found to have
refractive index changes on the order of unity. This property makes it possible
to achieve electro-optic modulation of sub-wavelength device scales, when thin
ITO films are interfaced with optical light confinement techniques such as
found in plasmonics; optical modes are compressed to nanometer scale to create
strong light-matter-interactions. Here we review efforts towards utilizing this
novel material for high-performance and ultra-compact modulation. While high
performance metrics are achieved experimentally, there are open questions
pertaining the permittivity modulation mechanism of ITO. Furthermore, we show
that a footprint-saving waveguide inline cavity can enhance obtainable
extinction-ratio to insertion-loss ratios by about one order of magnitude over
non-cavity based version. Moreover, we offer a speed analysis that shows that
the device is resistance limited, but not capacitance or drift-carrier limited.
Interestingly, two bias options exist for ITO and we find that a
side-connection enables devices that should in principle enable several hundred
of GHz fast devices, using our routinely achievable ITO film resistivities.
Finally, we offer a brief discuss about footprint savings of compact ITO
modulators showing a 3-orders of magnitude smaller footprint over Silicon
photonic MZI-based modulators. | 2305.10639v1 |
2024-03-14 | Magnetotransport properties in van-der-Waals \textit{\textbf{R}}Te$_{3}$ (\textit{\textbf{R}} = La, Ce, Tb) | Rare-earth tritellurides are van-der-Waals antiferromagnets which have been
attracting attention as materials not only with high mobility, but also with
various states such as superconductivity under high pressure, incommensurate
charge-density-wave (CDW) phase, and multiple antiferromagnetic phases. In this
work, we performed longitudinal resistivity and Hall resistivity measurements
simultaneously in exfoliated $R$Te$_{3}$ ($R$ =La, Ce, Tb) thin film devices,
in order to investigate the influence of magnetic ordering on transport
properties in van-der-Waals magnetic materials. We have obtained carrier
mobility and concentration using a two-band model, and have observed an
increase in carrier mobility in the antiferromagnets CeTe$_{3}$ and TbTe$_{3}$
due to the magnetic transition. Especially in CeTe$_{3}$, the carrier
concentration has changed drastically below the magnetic transition
temperature, suggesting the interaction between the CDW and antiferromagnetic
phases. In addition, the analysis of the Shubnikov-de Haas oscillations in
CeTe$_{3}$ supports the possibility of Fermi surface modulation by magnetic
ordering. This research will pave the way not only for spintronic devices that
take advantage of high mobility, but also for the study of the correlation
between CDW and magnetism states in low-dimensional materials. | 2403.09250v2 |
2016-02-19 | Magnetic effects in sulfur-decorated graphene | The interaction between two different materials can present novel phenomena
that are quite different from the physical properties observed when each
material stands alone. Strong electronic correlations, such as magnetism and
superconductivity, can be produced as the result of enhanced Coulomb
interactions between electrons. Two-dimensional materials are powerful
candidates to search for the novel phenomena because of the easiness of
arranging them and modifying their properties accordingly. In this work, we
report magnetic effects of graphene, a prototypical non-magnetic
two-dimensional semi-metal, in the proximity with sulfur, a diamagnetic
insulator. In contrast to the well-defined metallic behaviour of clean
graphene, an energy gap develops at the Fermi energy for the graphene/sulfur
compound with decreasing temperature. This is accompanied by a steep increase
of the resistance, a sign change of the slope in the magneto-resistance between
high and low fields, and magnetic hysteresis. A possible origin of the observed
electronic and magnetic responses is discussed in terms of the onset of
low-temperature magnetic ordering. These results provide intriguing insights on
the search for novel quantum phases in graphene-based compounds. | 1602.06214v2 |
2020-09-27 | Non-equilibrium Effects in Dissipative Strongly Correlated Systems | Novel physics arises when strongly correlated system is driven out of
equilibrium by external fields. Dramatic changes in physical properties, such
as conductivity, are empirically observed in strongly correlated materials
under high electric field. In particular, electric-field driven metal-insulator
transitions are well-known as the resistive switching effect in a variety of
materials, such as VO$_2$, V$_2$O$_3$ and other transition metal oxides. To
satisfactorily explain both the phenomenology and its underlying mechanism, it
is required to model microscopically the out-of-equilibrium dissipative lattice
system of interacting electrons. In this thesis, we developed a systematic
method of modeling non-equilibrium steady states for dissipative lattice
systems by means of Non-equilibrium Green's function and Dynamical Mean Field
Theory. We firstly establish a "minimum model" to formulate the strong-field
transport in non-interacting dissipative electron lattice. This model is
exactly soluble and convenient for discussing energy dissipation and
steady-state properties. The formalism is then combined with Dynamical Mean
Field Theory to provide a systematic framework describing the nonequilibrium
steady-state of correlated materials. We use the formalism to study the
strong-field transport properties of correlated materials, Mott insulators and
Dirac electrons in graphene. We concentrate on the microscopic description of
resistive switching. Of particular interest is the filament formation during
the dynamical phase transition, which has been interpreted as a result of the
delicate interplay between dissipation and Mott physics. We will also examine
$IV$ characteristics and particularly the current saturation of Dirac electrons
in graphene. The arXiv version has been updated with minor modifications and
corrections. | 2009.12865v1 |
2020-09-28 | A hybrid optoelectronic Mott insulator | The coupling of electronic degrees of freedom in materials to create
hybridized functionalities is a holy grail of modern condensed matter physics
that may produce novel mechanisms of control. Correlated electron systems often
exhibit coupled degrees of freedom with a high degree of tunability which
sometimes lead to hybridized functionalities based on external stimuli.
However, the mechanisms of tunability and the sensitivity to external stimuli
are determined by intrinsic material properties which are not always
controllable. A Mott metal-insulator transition, which is technologically
attractive due to the large changes in resistance, can be tuned by doping,
strain, electric fields, and orbital occupancy but cannot be, in and of itself,
controlled externally with light. Here we present a new approach to produce
hybridized functionalities using a properly engineered
photoconductor/strongly-correlated hybrid heterostructure, showing control of
the Metal-to-Insulator transition (MIT) using optical means. This approach
combines a photoconductor, which does not exhibit an MIT, with a strongly
correlated oxide, which is not photoconducting. Due to the close proximity
between the two materials, the heterostructure exhibits large volatile and
nonvolatile, photoinduced resistivity changes and substantial photoinduced
shifts in the MIT transition temperatures. This approach can potentially be
extended to other judiciously chosen combinations of strongly correlated
materials with systems which exhibit optically, electrically or magnetically
controllable behavior. | 2009.13606v1 |
2020-01-02 | Thermal Conductivity Measurements in Nanosheets via Bolometric Effect | Thermal conductivity measurement techniques for materials with nanoscale
dimensions require fabrication of very complicated devices or their
applicability is limited to a class of materials. Discovery of new methods with
high thermal sensitivity are required for the widespread use of thermal
conductivity measurements in characterizing materials properties. We propose
and demonstrate a simple non-destructive method with superior thermal
sensitivity to measure the in-plane thermal conductivity of nanosheets and
nanowires using the bolometric effect. The method utilizes laser beam heating
to create a temperature gradient, as small as a fraction of a Kelvin, over the
suspended section of the nanomaterial with electrical contacts. Local
temperature rise due to the laser irradiation alters the electrical resistance
of the device, which can be measured precisely. This resistance change is then
used to extract the temperature profile along the nanomaterial using thermal
conductivity as a fitting parameter. We measured the thermal conductivity of
V2O3 nanosheets to validate the applicability of the method and found an
excellent agreement with the literature. Further, we measured the thermal
conductivity of metallic 2H-TaS2 for the first time and performed ab initio
calculations to support our measurements. Finally, we discussed the
applicability of the method on semiconducting nanosheets and performed
measurements on WS2 and MoS2 thin flakes. | 2001.00368v1 |
2020-11-01 | Bipolar Magnetic Semiconducting Behavior in VNbRuAl: A New Spintronic Material for Spin Filters | We report the theoretical prediction of a new class of spintronic materials,
namely bipolar magnetic semiconductor (BMS), which is also supported by our
experimental data. BMS acquires a unique band structure with unequal band gaps
for spin up and down channels, and thus are useful for tunable spin transport
based applications such as spin filters. The valence band (VB) and conduction
band (CB) in BMS approach the Fermi level through opposite spin channels, and
hence facilitate to achieve reversible spin polarization which are controllable
via applied gate voltage. We report the quaternary Heusler alloy VNbRuAl to
exactly possess the band structure of BMS. The alloy is found to crystallize in
LiMgPdSn prototype structure (space group $F\bar{4}3m$) with B$2$ disorder and
lattice parameter 6.15 \AA . The resistivity and Hall measurements show a two
channel semiconducting behavior and a quasi linear dependence of negative
magneto resistance (MR) indicating the possible semiconducting nature.
Interestingly, VNbRuAl also shows a fully compensated ferrimagnetic (FCF)
behavior with vanishing net magnetization (m$_s$$\sim$ $10^{-3}$ $\mu_B/f.u.$)
and significantly high ordering temperature ($> 900$ K). Unlike conventional
FCF, vanishing moment in this case appears to be the result of a combination of
long range antiferromagnetic (AFM) ordering and the inherent B2 disorder of the
crystal. This study opens up the possibility of finding a class of materials
for AFM spintronics, with great significance both from fundamental and applied
fronts. | 2011.00533v1 |
2021-10-26 | Wet Scandium Etching for hard mask formation on a silicon substrate | Nowadays, microelectronics and nanoelectronics require the search for new
materials, including masks for creating structures. Today, the intermediate
hard mask strategy is one of the key issues in achieving a good balance between
lithography and etching at the microelectronic fabrication. One of the
interesting challenges in microelectronics and photovoltaics is the creation of
interspacing, vertically oriented silicon arrays on Si substrate for
semiconductor devices with multi-function. The fabrication of such structures
is still a serious technological problem and requires searching for new
approaches and materials. In this work, we propose using scandium as a new hard
mask material over silicon due to its high resistance to plasma chemical
etching and low sputtering coefficient. We have shown that a wet etching of the
scandium layer with a thickness of several nanometers can be used to obtain
pattern structures with a resolution of up to 4 microns, which is a good result
for the wet etching approach. Scandium metal was found to be an excellent
resistant mask over silicon under the selected plasma etching conditions.
Therefore, a scandium hard mask can open up new possibilities for the formation
of different microscale topographical patterns. | 2110.13639v3 |
2007-01-03 | Two-dimensional Vortices in Superconductors | Superconductors have two key characteristics. They expel magnetic field and
they conduct electrical current with zero resistance. However, both properties
are compromised in high magnetic fields which can penetrate the material and
create a mixed state of quantized vortices. The vortices move in response to an
electrical current dissipating energy which destroys the zero resistance
state\cite{And64}. One of the central problems for applications of high
temperature superconductivity is the stabilization of vortices to ensure zero
electrical resistance. We find that vortices in the anisotropic superconductor
Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ (Bi-2212) have a phase transition from
a liquid state, which is inherently unstable, to a two-dimensional vortex
solid. We show that at high field the transition temperature is independent of
magnetic field, as was predicted theoretically for the melting of an ideal
two-dimensional vortex lattice\cite{Fis80,Gla91}. Our results indicate that the
stable solid phase can be reached at any field as may be necessary for
applications involving superconducting magnets\cite{Has04,Sca04,COHMAG}. The
vortex solid is disordered, as suggested by previous studies at lower
fields\cite{Lee93,Cub93}. But its evolution with increasing magnetic field
displays unexpected threshold behavior that needs further investigation. | 0701059v1 |
2007-11-01 | Point-contact search for antiferromagnetic giant magnetoresistance | We report the first measurements of effects of large current densities on
current-perpendicular-to-plane magnetoresistance (MR) of magnetic multilayers
containing two antiferromagnetic layers separated by a non-magnetic layer.
These measurements were intended to search for a recently predicted
antiferromagnetic giant magnetoresistance (AGMR) similar to GMR seen in
multilayers containing two ferromagnetic layers separated by a non-magnetic
layer. We report on MR measurements for current injected from point contacts
into sandwiches containing different combinations of layers of F = CoFe and AFM
= FeMn. In addition to: AFM/N/AFM, F/AFM/N/AFM, and F/AFM/N/AFM/F structures,
initial results led us to examine also AFM/F/N/AFM, F/AFM, and single F- and
AFM-layer structures. At low currents, no MR was observed in any samples, and
no MR was observed at any current densities in samples containing only AFMs.
Together, these results indicate that no AGMR is present in these samples. In
samples containing F-layers, high current densities sometimes produced a small
positive MR - largest resistance at high fields. For a given contact
resistance, this MR was usually larger for thicker F-layers, and for a given
current, it was usually larger for larger contact resistances (smaller
contacts). We tentatively attribute this positive MR to suppression at high
currents of spin accumulation induced around and within the F-layers. | 0711.0059v3 |
2008-06-18 | Linear-T resistivity and change in Fermi surface at the pseudogap critical point of a high-Tc superconductor | A fundamental question of high-temperature superconductors is the nature of
the pseudogap phase which lies between the Mott insulator at zero doping and
the Fermi liquid at high doping p. Here we report on the behaviour of charge
carriers near the zero-temperature onset of that phase, namely at the critical
doping p* where the pseudogap temperature T* goes to zero, accessed by
investigating a material in which superconductivity can be fully suppressed by
a steady magnetic field. Just below p*, the normal-state resistivity and Hall
coefficient of La1.6-xNd0.4SrxCuO4 are found to rise simultaneously as the
temperature drops below T*, revealing a change in the Fermi surface with a
large associated drop in conductivity. At p*, the resistivity shows a linear
temperature dependence as T goes to zero, a typical signature of a quantum
critical point. These findings impose new constraints on the mechanisms
responsible for inelastic scattering and Fermi surface transformation in
theories of the pseudogap phase. | 0806.2881v2 |
2016-06-07 | Spin-Orbit Interaction and Kondo Scattering at the PrAlO$_3$/SrTiO$_3$ Interface: Effects of Oxygen Content | We report the effect of oxygen pressure during growth ($P_{O_{2}}$) on the
electronic and magnetic properties of PrAlO$_3$ films grown on $\rm
TiO_{2}$-terminated SrTiO$_3$ substrates. Resistivity measurements show an
increase in the sheet resistance as $P_{O_{2}}$ is increased. The temperature
dependence of the sheet resistance at low temperatures is consistent with Kondo
theory for $P_{O_{2}} \ge 10^{-5}$ torr. Hall effect data exhibit a complex
temperature dependence that suggests a compensated carrier density. We observe
behavior consistent with two different types of carriers at interfaces grown at
$P_{O_{2}} \ge 10^{-4}$ torr. For these interfaces, we measured a moderate
positive magnetoresistance (MR) due to a strong spin-orbit (SO) interaction at
low magnetic fields that evolves into a larger negative MR at high fields.
Positive high MR values are associated with samples where a fraction of
carriers are derived from oxygen vacancies. Analysis of the MR data permitted
the extraction of the SO interaction critical field ( e.g. $ H_{SO}=$1.25 T for
$P_{O_{2}}=10^{-5}$ torr). The weak anti-localization effect due to a strong SO
interaction becomes smaller for higher $P_{O_{2}}$ grown samples, where MR
values are dominated by the Kondo effect, particularly at high magnetic fields. | 1606.02308v1 |
2016-07-20 | Magnetotransport properties of the type II Weyl semimetal candidate Ta3S2 | We have investigated the magnetoresistance (MR) and Hall resistivity
properties of the single crystals of tantalum sulfide, Ta3S2, which was
recently predicted to be a new type II Weyl semimetal. Large MR (up to ~8000%
at 2 K and 16 T), field-induced metal-insulator-like transition and nonlinear
Hall resistivity are observed at low temperatures. The large MR shows a strong
dependence on the field orientation, leading to a giant anisotropic
magnetoresistance (AMR) effect. For the field applied along the b-axis (B//b),
MR exhibits quadratic field dependence at low fields and tends towards
saturation at high fields; while for B//a, MR presents quadratic field
dependence at low fields and becomes linear at high fields without any trend
towards saturation. The analysis of the Hall resistivity data indicates the
coexistence of a large number of electrons with low mobility and a small number
of holes with high mobility. Shubnikov-de Haas (SdH) oscillation analysis
reveals three fundamental frequencies originated from the three-dimensional
(3D) Fermi surface (FS) pockets. We find that the semi-classical multiband
model is sufficient to account for the experimentally observed MR in Ta3S2. | 1607.05798v2 |
2017-10-25 | Device model for pixelless infrared image up-converters based on polycrystalline graphene heterostructures | We develop a device model for pixelless converters of far/mid-infrared
radiation (FIR/MIR) images into near-infrared/visible (NIR/VIR) images. These
converters use polycrystalline graphene layers (PGLs) immersed in the van der
Waals (vdW) materials integrated with light emitting diode (LED). The PGL
serves as an element of the PGL infrared photodetector (PGLIP) sensitive to the
incoming FIR/MIR due to the interband absorption. The spatially non-uniform
photocurrent generated in the PGLIP repeats (mimics) the non-uniform
distribution (image) created by the incident FIR/MIR. The injection of the
nonuniform photocurrent into the LED active layer results in the nonuniform
NIR/VIR image reproducing the FIR/MIR image. The PGL and the entire layer
structure are not deliberately partitioned into pixels. We analyze the
characteristics of such pixelless PGLIP-LED up-converters and show that their
image contrast transfer function and the up-conversion efficiency depend on the
PGL lateral resistivity. The up-converter exhibits high photoconductive gain
and conversion efficiency when the lateral resistivity is sufficiently high.
Several teams have successfully demonstrated the large area PGLs with the
resistivities varying in a wide range. Such layers can be used in the pixelless
PGLIP-LED image up-converters. The PGLIP-LED image up-converters can
substantially surpass the image up-converters based on the quantum-well
infrared photodetector (QWIP) integrated with the LED. These advantages are due
to the use of the interband FIR/NIR absorption and a high photoconductive gain
in the GLIPs. | 1710.09060v1 |
2018-06-18 | Electroluminescence on-off ratio control of n-i-n GaAs/AlGaAs-based resonant tunneling structures | We explore the nature of the electroluminescence (EL) emission of purely
n-doped GaAs/AlGaAs resonant tunneling diodes (RTDs) and the EL evolution with
voltage. A singular feature of such a device is unveiled when the electrical
output current changes from high to low and the EL on-off ratio is enhanced by
2 orders of magnitude compared to the current on-off ratio. By combining the EL
and current properties, we are able to identify two independent impact
ionization channels associated with the coherent resonant tunneling current and
the incoherent valley current. We also perform the same investigation with an
associated series resistance, which induces a bistable electrical output in the
system. By simulating a resistance variation for the current-voltage and the
EL, we are able to tune the EL on-off ratio by up to 6 orders of magnitude. We
further observe that the EL on and off states can be either direct or inverted
compared to the tunneling current on and off states. This electroluminescence,
combined with the unique RTD properties such as the negative differential
resistance (NDR) and high frequency operation, enables the development of high
speed functional opto-electronic devices and optical switches. | 1806.06757v1 |
2012-01-19 | Magnetic Field Effects on Transport Properties of PtSn4 | The anisotropic physical properties of single crystals of orthorhombic PtSn4
are reported for magnetic fields up to 140 kOe, applied parallel and
perpendicular to the crystallographic b-axis. The magnetic susceptibility has
an approximately temperature independent behavior and reveals an anisotropy
between ac-plane and b-axis. Clear de Haas-van Alphen oscillations in fields as
low as 5 kOe and at temperatures as high as 30 K were detected in magnetization
isotherms. The thermoelectric power and resistivity of PtSn4 show the strong
temperature and magnetic field dependencies. A change of the thermoelectric
power at H = 140 kOe is observed as high as ~ 50 mu-V/K. Single crystals of
PtSn4 exhibit very large transverse magnetoresistance of ~ 5x10^5% for the
ac-plane and of ~ 1.4x10^5% for the b-axis resistivity at 1.8 K and 140 kOe, as
well as pronounced Shubnikov-de Haas oscillations. The magnetoresistance of
PtSn4 appears to obey Kohler's rule in the temperature and field range
measured. The Hall resistivity shows a linear temperature dependence at high
temperatures followed by a sign reversal around 25 K which is consistent with
thermoelectric power measurements. The observed quantum oscillations and band
structure calculations indicate that PtSn4 has three dimensional Fermi
surfaces. | 1201.4091v1 |
2020-10-23 | Air-stable, earth-abundant molten chlorides and corrosion-resistant containment for chemically-robust, high-temperature thermal energy storage for concentrated solar power | A dramatic reduction in man-made CO2 emissions could be achieved if the cost
of electricity generated from concentrated solar power (CSP) plants could
become competitive with fossil-fuel-derived electricity. The solar
heat-to-electricity conversion efficiency of CSP plants may be significantly
increased (and the associated electricity cost decreased) by operating CSP
turbines with inlet temperatures >750 C instead of <550 C, and by using thermal
energy storage (TES) at >750 C to allow for rapidly dispatchable and/or
continuous electricity production. Unfortunately, earth-abundant
MgCl2-KCl-based liquids currently being considered as low-cost media for
large-scale, high-temperature TES are susceptible to oxidation in air, with
associated undesired changes in liquid composition and enhanced corrosion of
metal alloys in pipes and tanks containing such liquids. In this paper,
alternative high-temperature, earth-abundant molten chlorides that are stable
in air are identified via thermodynamic calculations. The oxidation resistance,
and corrosion-resistant containment, of such molten chlorides at 750 C are then
demonstrated. Such chemically-robust, low-cost TES media and effective
containment provide critical advances towards the higher-temperature operation
of, and lower-cost electricity generation from, CSP plants. | 2010.12476v1 |
2023-03-03 | Anomalous Random Telegraphy Signal in Suspended Graphene with Oxygen Adsorption | Graphene is a promising material for sensing applications because of its
large specific surface area and low noise. In many applications, graphene will
inevitably be in contact with oxygen since it is the second most abundant gas
in the atmosphere. Therefore, it is of interest to understand how this gas
affects the sensor properties. In this work, the effect of oxygen on the
low-frequency noise of suspended graphene is demonstrated. Devices with
suspended graphene nanoribbons with a width (W) and length (L) of 200 nm were
fabricated. The resistance as a function of time was measured in a vacuum and
pure oxygen atmosphere through an ac lock-in method. After signal processing
with wavelet denoising and analysis, it is demonstrated that oxygen causes
random telegraphy signal (RTS) in the millisecond scale, with an average dwell
time of 2.9 milliseconds in the high-resistance state, and 2 milliseconds in
the low-resistance state. It is also shown that this RTS occurs only at some
periods, which indicates that, upon adsorption, the molecules take some time
until they find the most energetically favorable adsorption state. Also, a
slow-down in the RTS time constants is observed, which infers that less active
sites are available as time goes on because of oxygen adsorption. Therefore, it
is very important to consider these effects to guarantee high sensitivity and
high durability for graphene-based sensors that will be exposed to oxygen
during their lifetime. | 2303.01649v2 |
2007-09-12 | Characterization of Thermal Interface Materials to Support Thermal Simulation | In this paper new characterization equipment for thermal interface materials
is presented. Thermal management of electronic products relies on the
effec-tive dissipation of heat. This can be achieved by the optimization of the
system design with the help of simulation methods. The precision of these
models relies also on the used material data. For the determi-nation of this
data an experimental set-up for a static measurement is presented, which
evaluates thermal conductivity and interface resistance of thermal inter-face
materials (e.g. adhesive, solder, pads, or pastes). A qualitative
structure-property correlation is pro-posed taking into account particle size,
filler content and void formation at the interface based on high resolution FIB
imaging. The paper gives an overview over the set-up and the measurement
technique and discusses experimental and simulation results. | 0709.1849v1 |
2016-02-29 | A Solid-State Dielectric Elastomer Switch for Soft Logic | In this paper we describe a stretchable solid-state electronic switching
material that operates at high voltage potentials, as well as a switch material
benchmarking technique that utilizes a modular dielectric elastomer (artificial
muscle) ring oscillator. The solid-state switching material was integrated into
our oscillator, which self-started after 16s and performed 5 oscillations at a
frequency of 1.05Hz with 3.25kV DC input. Our materials-by-design approach for
the nickel filled polydimethysiloxane (Ni-PDMS) based switch has resulted in
significant improvements over previous carbon-grease based switches in four key
areas, namely sharpness of switching behavior upon applied stretch, magnitude
of electrical resistance change, ease of manufacture, and rate of production.
Switch lifetime was demonstrated to be in the range of tens to hundreds of
cycles with the current process. An interesting and potentially useful
strain-based switching hysteresis behavior is also presented. | 1602.08988v1 |
2019-03-15 | An efficient phase-field model for fatigue fracture in ductile materials | Fatigue fracture in ductile materials, e. g. metals, is caused by cyclic
plasticity. Especially regarding the high numbers of load cycles, plastic
material models resolving the full loading path are computationally very
demanding. Herein, a model with particularly small computational effort is
presented. It provides a macroscopic, phenomenological description of fatigue
fracture by combining the phase-field method for brittle fracture with a
classic durability concept. A local lifetime variable is obtained, which
degrades the fracture resistance progressively. By deriving the stress-strain
path from cyclic material characteristics, only one increment per load cycle is
needed at maximum. The model allows to describe fatigue crack initiation,
propagation and residual fracture and can reproduce Paris behaviour. | 1903.06465v3 |
2021-10-21 | Structures and physical properties of V-based kagome metals CsV$_{6}$Sb$_{6}$ and CsV$_{8}$Sb$_{12}$ | We report two new members of V-based kagome metals CsV$_{6}$Sb$_{6}$ and
CsV$_{8}$Sb$_{12}$. The most striking structural feature of CsV$_{6}$Sb$_{6}$
is the V kagome bilayers. For CsV$_{8}$Sb$_{12}$, there is an intergrowth of
two-dimensional V kagome layers and one-dimensional V chains and the latter
lead to the orthorhombic symmetry of this material. Further measurements
indicate that these two materials exhibit metallic and Pauli paramagnetic
behaviors. More importantly, different from CsV$_{3}$Sb$_{5}$, the charge
density wave state and superconductivity do not emerge in CsV$_{6}$Sb$_{6}$ and
CsV$_{8}$Sb$_{12}$ when temperature is above 2 K. Small magnetoresistance with
saturation behavior and linear field dependence of Hall resistivity at high
field and low temperature suggest that the carriers in both materials should be
uncompensated with much different concentrations. The discovery of these two
new V-based kagome metals sheds light on the exploration of correlated
topological materials based on kagome lattice. | 2110.11452v2 |
2022-05-17 | The Highly Disordered Zintl Phase Ca$_{10}$GdCdSb$_9$ -- New Example of a p-type Semiconductor with Remarkable Thermoelectric Properties | Ca$_{10}$GdCdSb$_9$ is a new Zintl phase with a large unit cell volume (~2500
{\AA}3) and a very complex, disordered structure, which can drive the
realization of ultralow thermal conductivity in this material. The measured
Seebeck coefficient, $\alpha$, for single-crystalline Ca$_{10}$GdCdSb$_9$
approaches 350 $\mu$V/K at 600 K. The experimentally determined electrical
resistivity of Ca$_{10}$GdCdSb$_9$ is very low, leading to a remarkably
high-power factor PF of 23.2 $\mu$W/cm.K$^2$ at 460 K. The extraordinary PF
value in this material, higher than those of the currently known
state-of-the-art materials within the same temperature range, suggests that the
Ca$_{10}$RECdSb$_9$ material system (RE = rare earth metal) could serve as a
viable playground to harnessing new efficient thermoelectric generators. | 2205.08559v1 |
2022-10-12 | Experimental data management platform for data-driven investigation of combinatorial alloy thin films | Experimental materials data are heterogeneous and include a variety of
metadata for processing and characterization conditions, making the
implementation of data-driven approaches for developing novel materials
difficult. In this paper, we introduce the Thin-Film Alloy Database (TFADB), a
materials data management platform, designed for combinatorially investigated
thin-film alloys through various experimental tools. Using TFADB, researchers
can readily upload, edit, and retrieve multidimensional experimental alloy
data, such as composition, thickness, X-ray Diffraction, electrical
resistivity, nanoindentation, and image data. Furthermore,
composition-dependent properties from the database can easily be managed in a
format adequate to be preprocessed for machine learning analyses. High
flexibility of the software allows management of new types of materials data
that can be potentially acquired from new combinatorial experiments. | 2210.06027v1 |
2022-10-18 | Reaction-diffusion pathways for a programmable nanoscale texture of diamond-SiC composite | The diamond-SiC composite has a low density and the highest possible speed of
sound among existing materials except for the diamond. The composite is
synthesized by a complex exothermic chemical reaction between diamond powder
and liquid Si. This makes it an ideal material for protection against impact
loading. Experiments show that a system of patterns is formed at the
diamond-SiC interface. Modeling of reaction-diffusion processes of composite
synthesis proves a formation of ceramic materials with a regular (periodic)
interconnected microstructure in a given system. Composite material with
interconnected structures at the interface has very high mechanical properties
and resistance to impact since its fractioning is intercrystallite. | 2210.10021v1 |
2023-11-02 | Machine Learning Design of Perovskite Catalytic Properties | Discovering new materials that efficiently catalyze the oxygen reduction and
evolution reactions is critical for facilitating the widespread adoption of
solid oxide fuel cell and electrolyzer (SOFC/SOEC) technologies. Here, we
develop machine learning (ML) models to predict perovskite catalytic properties
critical for SOFC/SOEC applications, including oxygen surface exchange, oxygen
diffusivity, and area specific resistance (ASR). The models are based on
trivial-to-calculate elemental features and are more accurate and dramatically
faster than the best models based on ab initio-derived features, potentially
eliminating the need for ab initio calculations in descriptor-based screening.
Our model of ASR enables temperature-dependent predictions, has well calibrated
uncertainty estimates and online accessibility. Use of temporal
cross-validation reveals our model to be effective at discovering new promising
materials prior to their initial discovery, demonstrating our model can make
meaningful predictions. Using the SHapley Additive ExPlanations (SHAP)
approach, we provide detailed discussion of different approaches of model
featurization for ML property prediction. Finally, we use our model to screen
more than 19 million perovskites to develop a list of promising cheap,
earth-abundant, stable, and high performing materials, and find some top
materials contain mixtures of less-explored elements (e.g., K, Bi, Y, Ni, Cu)
worth exploring in more detail. | 2311.01401v1 |
2024-01-22 | Order induces toughness in anisotropic colloidal crystal composites | Spatial ordering of matter elicits exotic properties sometimes absent from a
material's constituents. A few highly mineralised natural materials achieve
high toughness through delocalised damage, whereas synthetic particulate
composites must trade toughness for mineral content. We test whether ordering
the mineral phase in particulate composites through the formation of
macroscopic colloidal crystals can trigger the same damage resistance found in
natural materials. Our macroscopic silica rod based anisotropic colloidal
crystal composites are processed fully at room temperature and pressure, reach
volume fraction of mineral higher than 80%, and aided by a ductile interface,
unveil plastic strain reaching 10% through the collective movement of rods and
damage delocalisation over millimetres. These composites demonstrate key design
rules to break free from conventionally accepted structural materials
properties trade-off. | 2401.11727v1 |
2016-10-24 | Probing Intrinsic Material Conductivity in Two-Terminal Devices: A Resistance-Difference Method | It is generally impossible to separately measure the resistance of the
functional component (i.e., the intrinsic device materials) and the parasitic
component (i.e., terminals, interfaces and serial loads) in a two-terminal
device. Yet such knowledge is important for understanding device physics and
designing device systems. Here, we consider a case where an electric current,
temperature, or magnetic field causes a small but identical relative
conductivity change of the device materials. We find an exact solution to this
relative change by a simple resistance-data analysis of similarly configured
two-terminal devices. The solution is obtainable even if the change is quite
small, say, less than 0.1%. In special cases of small relative changes in
parasitic resistance, the absolute parasitic resistance is also obtainable. Our
method is especially useful for studying the switching and transport
characteristics of the emergent non-volatile resistance memory. | 1610.07666v2 |
2018-03-22 | Status and update of the RaDIATE Collaboration R&D Program | The Radiation Damage In Accelerator Target Environments (RaDIATE)
collaboration was founded in 2012 and currently consists of over 50
participants and 11 institutions globally. Due to the increasing power of
future proton accelerator sources in target facilities, there is a critical
need to further understand the physical and thermo-mechanical radiation
response of target facility materials. Thus, the primary objective of the
RaDIATE collaboration is to draw on existing expertise in the nuclear materials
and accelerator targets fields to generate new and useful materials data for
application within the accelerator and fission/fusion communities. Current
research activities of the collaboration include post irradiation examination
(PIE) of decommissioned components from existing beamlines such as the NuMI
beryllium beam window and graphite NT-02 target material. PIE of these
components includes advanced microstructural analyses (SEM/TEM, EBSD, EDS) and
micro-mechanics technique such as nano-indentation, to help characterize any
microstructural radiation damage incurred during operation. New irradiation
campaigns of various candidate materials at both low and high energy beam
facilities are also being pursued. Beryllium helium implantation studies at the
University of Surrey as well as high energy proton irradiation of various
materials at Brookhaven National Laboratory's BLIP facility have been
initiated. The program also extends to beam-induced thermal shock experiments
using high intensity beam pulses at CERN's HiRadMat facility, followed by
advanced PIE activities to evaluate thermal shock resistance of the materials.
Preliminary results from ongoing research activities, as well as the future
plans of the RaDIATE collaboration R&D program will be discussed. | 1803.08563v1 |
2021-12-22 | Self-repairing high entropy oxides | All biological organisms, from plants to living creatures, can heal minor
wounds and damage. The realization of a similar self-healing capacity in
inorganic materials has been a design target for many decades. This would
represent a breakthrough in materials engineering, enabling many novel
technological applications, since such materials would be able to resist damage
caused by electromagnetic irradiation and/or mechanical impact. Here we
demonstrate that a high-entropy oxide is intrinsically capable of undergoing an
autonomous self-repairing process. Transmission electron microscopy revealed
that the spinel structure of (AlCoCrCu0.5FeNi)3O4 can regrow and repair itself
at the atomic level when damaged. Density functional theory calculations reveal
that the extra enthalpy stored in the high entropy material during fabrication
can be released to effectively heal macroscopic defects by regrowing into a
partially ordered state. This extraordinary self-repairing phenomenon makes
this new material highly desirable as a coating, enabling structures used in
harsh environments to better withstand damage, such as cosmic irradiation in
space, nuclear irradiation in nuclear power facilities, or tribological damage.
Most importantly, our results set the general design principles for the
synthesis of self-repairing materials. | 2112.11747v1 |
2004-01-23 | Crystal growth and anisotropic transport properties of high-Tc superconductors Bi2Sr2Can-1CunO2n+4+d (n = 2, 3) | Large high-quality single crystals of Bi2Sr2Can-1CunO2n+4+d (n = 2, 3) were
successfully grown using an improved traveling solvent floating zone (TSFZ)
method, which features a slow growth rate and steep temperature gradient along
the melting zone. By measuring anisotropic resistivities and susceptibilities
of Bi2Sr2CaCu2O8+d, the characteristic pseudogap temperature T* was studied as
a function of doping. The T* suggest that the pseudogap is not simply a
precursor of high-Tc superconductivity, but that the pseudogap and the
superconducting gap compete with each other. The anisotropic resistivities of
Bi2Sr2Ca2Cu3O10+d were also measured, revealing that the Tc remains fixed in
the overdoped region while anisotropy decreases continuously. This anomalous
behavior will be discussed in terms of the inequivalent hole doping, which
occurs between two inequivalent CuO2 planes in the triple-layer system. | 0401448v3 |
2010-04-28 | Conductivity states changes in plasticized PVC films near breakdown threshold voltages values | The near threshold "soft breakdown" measurements of PVC films conductivity
are investigated. In a wide range of external electric field strength for
various rather thick (>20 mkm) PVC films the resistance shows strong
nonlinearity and seems to enter high conductive state close to the breakdown
threshold. For our "thick" films boundary conditions electrode surface
specifics should not be so important as in thin polymer films experiments. Both
fast, instant mechanisms of nonlinearity, and effects of accumulation and delay
responce were observed. The phenomena corresponding to reversible transitions
in a state with rather high conductivity, seems to be similar to ones
registered earlier in thin layers of some broad-bandgap polymers. In a range of
relatively low field intensity, far from a threshold breakdown, as a result of
reversible switches between normal and high resistivity states a polymer film
in a standard measuring cell formed a relaxation generator giving a loud enough
sound signal with frequency increasing with the increase of external field. | 1004.4972v1 |
2010-12-27 | Superconductivity and Magnetic Properties of high-quality single crystals of $A_{x}$Fe$_2$Se$_2$ ($A$ = K and Cs) | We successfully grew the high-quality single crystals of $A_{x}$Fe$_2$Se$_2$
($A$ = K and Cs) by self-flux method. Sharp superconducting transition was
observed for both types of crystals. The crystals show the onset
superconducting transition temperatures ($T_{\rm c}$) of 31 K and 30 K for K-
and Cs-compounds, respectively, with nearly 100% shielding fraction. The
crystals show quite high resistivity in the normal state of more than 160
m$\Omega$ cm and 1300 m$\Omega$ cm maximum resistivity for
$K_{0.86}Fe_2Se_{1.82}$ and $Cs_{0.86}Fe_{1.66}Se_{2}$ single crystals,
respectively. Much larger upper critical field $H_{\rm c2}$ is inferred from
low-temperature iso-magnetic-field magnetoresistance in these crystals than in
FeSe. The anisotropy $H^{ab}_{\rm c2}$(0)/$H^{c}_{\rm c2}$(0) is around 3 for
both of the two materials. Anisotropic peculiar magnetic behavior in normal
state has been found for $Cs_{0.86}Fe_{1.66}Se_{2}$ | 1012.5552v1 |
2015-09-15 | Epitaxial graphene quantum dots for high-performance THz bolometers | Light absorption in graphene causes a large change in electron temperature,
due to low electronic heat capacity and weak electron phonon coupling [1-3],
making it very attractive as a hot-electron bolometer material. Unfortunately,
the weak variation of electrical resistance with temperature has substantially
limited the responsivity of graphene bolometers. Here we show that quantum dots
of epitaxial graphene on SiC exhibit an extraordinarily high variation of
resistance with temperature due to quantum confinement, higher than 430 Mohm/K
at 2.5 K, leading to responsivities for absorbed THz power above 10^10 V/W.
This is five orders of magnitude higher than other types of graphene hot
electron bolometers. The high responsivity combined with an extremely low
noise-equivalent power, about 0.2 fW/Hz^0.5 at 2.5K, place the performance of
graphene quantum dot bolometers well above commercial cooled bolometers.
Additionally, these quantum dot bolometers have the potential for superior
performance for operation above 77K. | 1509.04646v1 |
2016-11-15 | Linear magnetoresistance in a quasi-free two dimensional electron gas in an ultra-high mobility GaAs quantum well | We report a magnetotransport study of an ultra-high mobility
($\bar{\mu}\approx 25\times 10^6$\,cm$^2$\,V$^{-1}$\,s$^{-1}$) $n$-type GaAs
quantum well up to 33 T. A strong linear magnetoresistance (LMR) of the order
of 10$^5$ % is observed in a wide temperature range between 0.3 K and 60 K. The
simplicity of our material system with a single sub-band occupation and free
electron dispersion rules out most complicated mechanisms that could give rise
to the observed LMR. At low temperature, quantum oscillations are superimposed
onto the LMR. Both, the featureless LMR at high $T$ and the quantum
oscillations at low $T$ follow the empirical resistance rule which states that
the longitudinal conductance is directly related to the derivative of the
transversal (Hall) conductance multiplied by the magnetic field and a constant
factor $\alpha$ that remains unchanged over the entire temperature range. Only
at low temperatures, small deviations from this resistance rule are observed
beyond $\nu=1$ that likely originate from a different transport mechanism for
the composite fermions. | 1611.04857v1 |