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2021-06-05 | On the anomalous low-resistance state and exceptional Hall component in hard-magnetic Weyl nanoflakes | Magnetic topological materials, which combine magnetism and topology, are
expected to host emerging topological states and exotic quantum phenomena. In
this study, with the aid of greatly enhanced coercive fields in high-quality
nanoflakes of the magnetic Weyl semimetal Co3Sn2S2, we investigate anomalous
electronic transport properties that are difficult to reveal in bulk Co3Sn2S2
or other magnetic materials. When the magnetization is antiparallel to the
applied magnetic field, the low longitudinal resistance state occurs, which is
in sharp contrast to the high resistance state for the parallel case.
Meanwhile, an exceptional Hall component that can be up to three times larger
than conventional anomalous Hall resistivity is also observed for transverse
transport. These anomalous transport behaviors can be further understood by
considering nonlinear magnetic textures and the chiral magnetic field
associated with Weyl fermions, extending the longitudinal and transverse
transport physics and providing novel degrees of freedom in the spintronic
applications of emerging topological magnets. | 2106.02906v1 |
2023-08-30 | Chemical heterogeneity enhances hydrogen resistance in high-strength steels | When H, the lightest, smallest and most abundant atom in the universe, makes
its way into a high-strength alloy (>650 MPa), the material's load-bearing
capacity is abruptly lost. This phenomenon, known as H embrittlement, was
responsible for the catastrophic and unpredictable failure of large engineering
structures in service. The inherent antagonism between high strength
requirements and H embrittlement susceptibility strongly hinders the design of
lightweight yet reliable structural components needed for carbon-free
hydrogen-propelled industries and reduced-emission transportation solutions.
Inexpensive and scalable alloying and microstructural solutions that enable
both, an intrinsically high resilience to H and high mechanical performance,
must be found. Here we introduce a counterintuitive strategy to exploit
typically undesired chemical heterogeneity within the material's microstructure
that allows the local enhancement of crack resistance and local H trapping,
thereby enhancing the resistance against H embrittlement. We deploy this
approach to a lightweight, high-strength steel and produce a high-number
density Mn-rich zones dispersed within the microstructure. These solute-rich
buffer regions allow for local micro-tuning of the phase stability, arresting
H-induced microcracks thus interrupting the H-assisted damage evolution chain,
regardless of how and when H is introduced and also regardless of the
underlying embrittling mechanisms. A superior H embrittlement resistance,
increased by a factor of two compared to a reference material with a
homogeneous solute distribution within each microstructure constituent, is
achieved at no expense of the material's strength and ductility. | 2308.16048v1 |
2021-01-29 | Novel design strategies for modulating conductive stretchable system response based on periodic assemblies | Soft electronics have recently gathered considerable interest thanks to their
bio-mechanical compatibility. An important feature of such deformable
conductors is their electrical response to strain. While development of
stretchable materials with high gauge factors has attracted considerable
attention, there is a growing need for stretchable conductors whose response to
deformation can be accurately engineered to provide arbitrary resistance-strain
relationships. The rare studies addressing this issue have focused on
deterministic geometries of single rigid materials, limiting the scope of such
strategies. Herein, we introduce the novel concept of periodic stretchable
patterns combining multiple conductive materials to produce tailored responses.
Using shortest-path algorithms, we establish a computationally efficient
selection method to obtain required resistance-strain relationship. Using this
algorithm, we identify and experimentally demonstrate constant
resistance-strain responses up to 50% elongation using a single micro-textured
material. Finally, we demonstrate counter-intuitive sinusoidal responses by
integrating three materials, with interesting applications in sensing and soft
robotics. | 2101.12600v1 |
2009-03-07 | Correlation between resistance fluctuations and temperature dependence of conductivity in graphene | The weak temperature dependence of the resistance R(T) of monolayer
graphene1-3 indicates an extraordinarily high intrinsic mobility of the charge
carriers. Important complications are the presence of mobile scattering centres
that strongly modify charge transport, and the presence of strong mesoscopic
conductance fluctuations that, in graphene, persist to relatively high
temperatures4,5. In this Letter, we investigate the surprisingly varied changes
in resistance that we find in graphene flakes as temperature is lowered below
70 K. We propose that these changes in R(T) arise from the temperature
dependence of the scattered electron wave interference that causes the
resistance fluctuations. Using the field effect transistor configuration, we
verify this explanation in detail from measurements of R(T) by tuning to
different gate voltages corresponding to particular features of the resistance
fluctuations. We propose simple expressions that model R(T) at both low and
high charge carrier densities. | 0903.1334v1 |
2021-04-20 | Accelerated Discovery of Molten Salt Corrosion-resistant Alloy by High-throughput Experimental and Modeling Methods Coupled to Data Analytics | Insufficient availability of molten salt corrosion-resistant alloys severely
limits the fruition of a variety of promising molten salt technologies that
could otherwise have significant societal impacts. To accelerate alloy
development for molten salt applications and develop fundamental understanding
of corrosion in these environments, here we present an integrated approach
using a set of high-throughput alloy synthesis, corrosion testing, and modeling
coupled with automated characterization and machine learning. By using this
approach, a broad range of Cr-Fe-Mn-Ni alloys were evaluated for their
corrosion resistances in molten salt simultaneously demonstrating that
corrosion-resistant alloy development can be accelerated by thousands of times.
Based on the obtained results, we unveiled a sacrificial mechanism in the
corrosion of Cr-Fe-Mn-Ni alloys in molten salts which can be applied to protect
the less unstable elements in the alloy from being depleted, and provided new
insights on the design of high-temperature molten salt corrosion-resistant
alloys. | 2104.10235v1 |
2014-12-05 | Resistance switching devices based on amorphous insulator-metal thin films | Nanometallic devices based on amorphous insulator-metal thin films are
developed to provide a novel non-volatile resistance-switching random-access
memory (RRAM). In these devices, data recording is controlled by a bipolar
voltage, which tunes electron localization length, thus resistivity, through
electron trapping/detrapping. The low-resistance state is a metallic state
while the high-resistance state is an insulating state, as established by
conductivity studies from 2K to 300K. The material is exemplified by a Si3N4
thin film with randomly dispersed Pt or Cr. It has been extended to other
materials, spanning a large library of oxide and nitride insulator films,
dispersed with transition and main-group metal atoms. Nanometallic RRAMs have
superior properties that set them apart from other RRAMs. The critical
switching voltage is independent of the film thickness/device
area/temperature/switching speed. Trapped electrons are relaxed by
electron-phonon interaction, adding stability which enables long-term memory
retention. As electron-phonon interaction is mechanically altered, trapped
electron can be destabilized, and sub-picosecond switching has been
demonstrated using an electromagnetically generated stress pulse. AC impedance
spectroscopy confirms the resistance state is spatially uniform, providing a
capacitance that linearly scales with area and inversely scales with thickness.
The spatial uniformity is also manifested in outstanding uniformity of
switching properties. Device degradation, due to moisture, electrode oxidation
and dielectrophoresis, is minimal when dense thin films are used or when a
hermetic seal is provided. The potential for low power operation, multi-bit
storage and complementary stacking have been demonstrated in various RRAM
configurations. | 1412.2083v1 |
2003-11-05 | Thermoelectric power of Bi and Bi(1-x)Te(x), x=0.0014,in porous Vycor glass | Semiconductor quantum wires constitute a promising thermoelectric material
because of the increase of the electronic density of states in low-dimensional
materials. We studied the magnetic-field-dependent resistance and Seebeck
coefficient of a high-density network of 6-nm-diameter wires of Bi and of
Bi(1-x)Te(x), x=0.0014, in porous Vycor glass. The resistance R increases as
temperature decreases from 300 K down to 0.3 K for both composites. However, in
contrast to recent results that demonstrate the semiconducting behavior of the
resistance and very large enhancements of the thermoelectric power of
composites containing Bi nanowires with diameters of 9 and 15 nm, we find that
the resistance is not thermally activated and that the thermoelectric power of
the composites is of the same order of magnitude as the thermoelectric power of
bulk Bi. Our results are consistent with the nanowires having carrier density
that is enhanced by surface effects. | 0311112v1 |
2009-06-27 | Resistive switching in nanogap systems on SiO2 substrates | Voltage-controlled resistive switching is demonstrated in various gap systems
on SiO2 substrate. The nanosized gaps are made by different means using
different materials including metal, semiconductor, and metallic nonmetal. The
switching site is further reduced by using multi-walled carbon nanotubes and
single-walled carbon nanotubes. The switching in all the gap systems shares the
same characteristics. This independence of switching on the material
compositions of the electrodes, accompanied by observable damage to the SiO2
substrate at the gap region, bespeaks the intrinsic switching from
post-breakdown SiO2. It calls for caution when studying resistive switching in
nanosystems on oxide substrates, since oxide breakdown extrinsic to the
nanosystem can mimic resistive switching. Meanwhile, the high ON/OFF ratio
(10E5), fast switching time (2 us, test limit), durable cycles demonstrated
show promising memory properties. The intermediate states observed reveal the
filamentary conduction nature. | 0906.5100v1 |
2010-02-12 | Experimental Study of Resistive Bistability in Metal Oxide Junctions | We have studied resistive bistability (memory) effects in junctions based on
metal oxides, with a focus on sample-to-sample reproducibility which is
necessary for the use of such junctions as crosspoint devices of hybrid
CMOS/nanoelectronic circuits. Few-nm-thick layers of NbOx, CuOx and TiOx have
been formed by thermal and plasma oxidation, at various deposition and
oxidation conditions, both with or without rapid thermal post-annealing (RTA).
The resistive bistability effect has been observed for all these materials,
with particularly high endurance (over 1000 switching cycles) obtained for
single-layer TiO2 junctions, and the best reproducibility reached for
multi-layer junctions of the same material. Fabrication optimization has
allowed us to improve the OFF/ON resistance ratio to about 1000, but the
sample-to-sample reproducibility is so far lower than that required for large
scale integration. | 1002.2650v1 |
2018-03-30 | Reliability assessment in advanced nanocomposite materials for orthopaedic applications | Alumina-zirconia nano-composites were recently developed as alternative
bearing materials for orthopedics. Previous, preliminary reports show that such
alumina-zirconia nanocomposites exhibit high crack resistance and low wear
rate. In this paper, additional information is given in terms of wear, crack
resistance and ageing behaviour: femoral heads are inspected after 7 million
cycles of wear testing on a hip simulator, crack resistance is measured and
compared to other ceramics used today in orthopedics, slow crack growth is
reported under static and cyclic fatigue, and aging resistance is assessed. We
also report on the load to failure of femoral heads prototypes during
compression tests. This overall reliability assessment ensures a potential
future development for these kinds of new nanocomposites in the orthopedic
field. | 1804.08702v1 |
2018-10-18 | Topological Hall effect in thin films of Mn$_{1.5}$PtSn | Spin chirality in metallic materials with non-coplanar magnetic order can
give rise to a Berry phase induced topological Hall effect. Here, we report the
observation of a large topological Hall effect in high-quality films of
Mn$_{1.5}$PtSn that were grown by means of magnetron sputtering on MgO(001).
The topological Hall resistivity is present up to $\mu_{0}H \approx 4~$T below
the spin reorientation transition temperature, $T_{s}=185$~K. We find, that the
maximum topological Hall resistivity is of comparable magnitude as the
anomalous Hall resistivity. Owing to the size, the topological Hall effect is
directly evident prior to the customarily performed subtraction of magnetometry
data. Further, we underline the robustness of the topological Hall effect in
Mn\textsubscript{2-x}PtSn by extracting the effect for multiple stoichiometries
(x~=~0.5, 0.25, 0.1) and film thicknesses (t = 104, 52, 35~nm) with maximum
topological Hall resistivities between $0.76~\mu\Omega$cm and
$1.55~\mu\Omega$cm at 150~K. | 1810.08232v1 |
2019-06-19 | Origin of current-controlled negative differential resistance modes and the emergence of composite characteristics with high complexity | Current-controlled negative differential resistance has significant potential
as a fundamental building block in brain-inspired neuromorphic computing.
However, achieving desired negative differential resistance characteristics,
which is crucial for practical implementation, remains challenging due to
little consensus on the underlying mechanism and unclear design criteria. Here,
we report a material-independent model of current-controlled negative
differential resistance to explain a broad range of characteristics, including
the origin of the discontinuous snap-back response observed in many transition
metal oxides. This is achieved by explicitly accounting for a non-uniform
current distribution in the oxide film and its impact on the effective circuit
of the device, rather than a material-specific phase transition. The
predictions of the model are then compared with experimental observations to
show that the continuous S-type and discontinuous snap-back characteristics
serve as fundamental building blocks for composite behaviour with higher
complexity. Finally, we demonstrate the potential of our approach for
predicting and engineering unconventional compound behaviour with novel
functionality for emerging electronic and neuromorphic computing applications. | 1907.02651v1 |
2022-05-06 | Interfacial resistive switching by multiphase polarization in ion-intercalation nanofilms | Nonvolatile resistive-switching (RS) memories promise to revolutionize
hardware architectures with in-memory computing. Recently, ion-interclation
materials have attracted increasing attention as potential RS materials for
their ion-modulated electronic conductivity. In this Letter, we propose RS by
multiphase polarization (MP) of ion-intercalated thin films between
ion-blocking electrodes, in which interfacial phase separation triggered by an
applied voltage switches the electron-transfer resistance. We develop an
electrochemical phase-field model for simulations of coupled ion-electron
transport and ion-modulated electron-transfer rates and use it to analyze the
MP switching current and time, resistance ratio, and current-voltage response.
The model is able to reproduce the complex cyclic voltammograms of lithium
titanate (LTO) memristors, which cannot be explained by existing models based
on bulk dielectric breakdown. The theory predicts the achievable switching
speeds for multiphase ion-intercalation materials and could be used to guide
the design of high-performance MP-based RS memories. | 2205.02980v2 |
2023-09-13 | Amorphous VO$_x$ films with high temperature coefficient of the resistivity grown by reactive e-beam evaporation of V metal | Amorphous VO$_x$ films without a hysteretic phase transition are stable with
respect to thermal cycling and highly demanded as sensitive elements of the
resistive thermometers and microbolometers. In this paper we present simple and
low-temperature growth of amorphous vanadium oxide films by reactive electron
beam evaporation of vanadium metal in $\sim 10^{-4}$ mBar oxygen atmosphere.
The temperature coefficient of the resistivity (TCR) of the films is weakly
sensitive to substrate material and temperature and could be tuned by oxygen
pressure in the growth chamber up to -2.2\% /K. The resistivity value is stable
for months. It depends on the substrate material and substrate temperature
during the evaporation. Simplicity and controllability of the method should
lead to various laboratory and industrial applications. | 2309.07036v1 |
2007-01-02 | Negative Differential Resistance of Electrons in Graphene Barrier | The graphene is a native two-dimensional crystal material consisting of a
single sheet of carbon atoms. In this unique one-atom-thick material, the
electron transport is ballistic and is described by a quantum relativistic-like
Dirac equation rather than by the Schrodinger equation. As a result, a graphene
barrier behaves very differently compared to a common semiconductor barrier. We
show that a single graphene barrier acts as a switch with a very high on-off
ratio and displays a significant differential negative resistance, which
promotes graphene as a key material in nanoelectronics. | 0701011v1 |
2019-10-07 | Growth and Characterization of Polycrystalline NbO2 Thin Films on Crystalline and Amorphous Substrates | NbO2 is a potential material for nanometric memristor devices, both in the
amorphous and the crystalline form. We fabricated NbO2 thin films using
RF-magnetron sputtering from a stoichiometric target. The as-deposited films
were amorphous regardless of the sputtering parameters. Post deposition vacuum
annealing of the films was necessary to achieve crystallinity. A high degree of
crystallinity was obtained by optimizing annealing duration and temperature.
The resistivity of the material increases as it undergoes a structural
transition from amorphous to crystalline with the crystalline films being one
order of magnitude more resistive. | 1910.02824v1 |
2004-04-18 | Anisotropy of superconductivity of as-grown MgB$_2$ thin films by molecular beam epitaxy | Superconducting thin films of magnesium diboride (MgB$_2$) were prepared on
MgO (001) substrate by a molecular beam epitaxy (MBE) method with the
co-evaporation conditions of low deposition rate in ultra-high vacuum. The
structural and physical properties of the films were studied by RHEED, XRD,
XPS, resistivity and magnetization measurements.All films demonstrated
superconductivity without use of any post-annealing process.The highest {\it
T}$_{c,onset}$ determined by resistivity measurement was about 33K in the
present samples.Anisotropic superconducting properties were evaluated by the
resistivity and magnetic measurements.We will discuss the anisotropy of
superconductivity for as-grown MgB$_2$ thin films. | 0404415v1 |
2005-08-02 | Epitaxial growth and transport properties of Nb-doped SrTiO$_{3}$ thin films | Nb-doped SrTiO$_{3}$ epitaxial thin films have been prepared on (001)
SrTiO$_{3}$ substrates using pulsed laser deposition. A high substrate
temperature ($>1000^{\circ}{C}$) was found to be necessary to achieve
2-dimensional growth. Atomic force microscopy reveals atomically flat surfaces
with 3.9 \AA $ $ steps. The films show a metallic behavior, residual
resistivity ratios between 10 and 100, and low residual resistivity of the
order of 10$^{-4}$$\Omega$cm. At 0.3 K, a sharp superconducting transition,
reaching zero resistance, is observed. | 0508073v1 |
2011-11-07 | Monte Carlo Study of Magnetic Resistivity in Semiconducting MnTe | We investigate in this paper properties of the spin resistivity in the
magnetic semiconducting MnTe of NiAs structure. MnTe is a crossroad
semiconductor with a large band gap. It is an antiferromagnet with the N\'eel
temperature around 310K. Due to this high N\'eel temperature, there are many
applications using its magnetic properties. The method we use here is the Monte
Carlo simulation in which we take into account the interaction between
itinerant spins and lattice Mn spins. Our results show a very good agreement
with experiments on the shape of the spin resistivity near the N\'eel
temperature. | 1111.1507v1 |
2016-11-21 | Ramsey Interferometry of Particle-Hole Pairs in Tunnel Junctions | We present a method to probe real-time dynamics in quantum mesoscopic systems
using Ramsey interferometry. This allows us to explore the effect of
interactions on quasi-particles in the time domain. We investigate the
dephasing effects of an ohmic environment on an electron-hole pair in a tunnel
junction. We show that dynamical Coulomb blockade phenomena can be observed for
resistances much smaller than the quantum of resistance. Moreover, the
crossover between high and low impedance limits can be probed for a constant
resistance by a proper control of the voltage modulation. | 1611.06738v1 |
2010-11-08 | Normal state resistivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$: evidence for multiband strong-coupling behavior | We present theoretical analysis of the normal state resistivity in multiband
superconductors in the framework of Eliashberg theory. The results are compared
with measurements of the temperature dependence of normal state resistivity of
high-purity Ba$_{0.68}$K$_{0.32}$Fe$_{2}$As$_{2}$ single crystals with the
highest reported transition temperature $T_c$ = 38.5 K. The experimental data
demonstrate strong deviations from the Bloch-Gr\"{u}neisen behavior, namely the
tendency to saturation of the resistivity at high temperatures. The observed
behavior of the resistivity is explained within the two band scenario when the
first band is strongly coupled and relatively clean, while the second band is
weakly coupled and is characterized by much stronger impurity scattering. | 1011.1900v3 |
2014-03-18 | Electron-Phonon Interactions and the Intrinsic Electrical Resistivity of Graphene | We present a first-principles study of the temperature- and density-dependent
intrinsic electrical resistivity of graphene. We use density-functional theory
and density-functional perturbation theory together with very accurate Wannier
interpolations to compute all electronic and vibrational properties and
electron-phonon coupling matrix elements; the phonon-limited resistivity is
then calculated within a Boltzmann-transport approach. An effective
tight-binding model, validated against first-principles results, is also used
to study the role of electron-electron interactions at the level of many-body
perturbation theory. The results found are in excellent agreement with recent
experimental data on graphene samples at high carrier densities and elucidate
the role of the different phonon modes in limiting electron mobility. Moreover,
we find that the resistivity arising from scattering with transverse acoustic
phonons is 2.5 times higher than that from longitudinal acoustic phonons. Last,
high-energy, optical, and zone-boundary phonons contribute as much as acoustic
phonons to the intrinsic electrical resistivity even at room temperature and
become dominant at higher temperatures. | 1403.4603v1 |
2018-06-03 | Influence of hydrogen on electron-phonon coupling and intrinsic electrical resistivity in zirconium: a first-principles study | The paper presents the first-principle calculation of the electron-phonon
coupling and the temperature dependence of the intrinsic electrical resistivity
of the zirconium-hydrogen system with various hydrogen concentrations. The
nature of the anomalous decrease in the electrical resistivity of the Zr-H
system with the increase of hydrogen concentration (at the high concentrations
of H/Zr$>$1.5) was studied. It was found that the hydrogen concentration, where
the resistivity starts to decrease, is very close to the critical concentration
of the $\delta-\varepsilon$ phase transition. It was shown that the tetragonal
lattice distortion due to the $\delta-\varepsilon$ phase transition of the Zr-H
system eliminates imaginary phonon frequencies and the strong electron-phonon
coupling of the $\delta$ phase and, as a result, leads to the reduction of the
electrical resistivity of the Zr-H system at a high hydrogen concentration. | 1806.00847v3 |
2021-12-29 | Significant reduction in semiconductor interface resistance via interfacial atomic mixing | The contact resistance between two dissimilar semiconductors is determined by
the carrier transmission through their interface. Despite the ubiquitous
presence of interfaces, quantitative simulation of charge transport across such
interfaces is difficult, limiting the understanding of interfacial charge
transport. This work employs Green's functions to study the charge transport
across representative Si/Ge interfaces. For perfect interfaces, it is found
that the transmittance is small and the contact resistance is high, not only
because the mismatch of carrier pockets makes it hard to meet the momentum
conservation requirement, but also because of the incompatible symmetries of
the Bloch wave functions of the two sides. In contrast, atomic mixing at the
interface increases the carrier transmittance as the interface roughness opens
many nonspecular transmission channels, which greatly reduces the contact
resistance compared with the perfect interface. Specifically, we show that
disordered interfaces with certain symmetries create more nonspecular
transmission. The insights from our study will benefit the future design of
high-performance heterostructures with low contact resistance. | 2112.14400v2 |
2005-02-26 | Josephson junction decoupling is the main origin of AC resistivity in the superconducting state | The origin of AC resistivity in the high Tc superconductors is not addressed
adequately in literature. We found out, Josephson Junction (JJ) decoupling is
the main origin of the AC resistivity in high Tc superconductors. We have
measured the AC resistivity in the superconductors in the low frequency range
by measuring the complex AC impedance of superconducting YBa2Cu3O7 (YBCO)
polycrystalline samples. Our data shows that under certain conditions when the
number density of Josephson Junctions (JJ) present in the sample and the JJ
critical current crosses a threshold value, AC resistivity in the
superconducting state keeps on increasing with lowering temperature. The
underlying mechanism is an interesting interplay of JJ coupling energy,
amplitude of the supply AC voltage and the current applied to the
superconducting sample. The effect of the applied AC current of different
frequencies and the variation of temperature were studied in detail. To find
out the exact relation between the JJ coupling energy, JJ number density,
applied AC frequency, the amplitude of AC current and the AC resistivity in the
superconductors, we have studied samples of different grain sizes, pressurized
with different pressure and sintered at different physical situations. These
results have important implications for the understanding of the origin of AC
resistivity and characterization of superconducting samples. In this paper we
also extend the capability of the AC impedance studies in superconductors for
the characterization of materials for device applications. | 0502639v1 |
2022-08-03 | Low Resistance Ohmic Contact On Epitaxial MOVPE-grown $β$-Ga$_2$O$_3$ and $β$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ Films | We report on the realization of record low resistance Ohmic contacts to
MOVPE-grown heavily Si-doped $\beta$-Ga$_2$O$_3$ and
$\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ epitaxial films. Transfer length measurement
(TLM) patterns were fabricated on the heavily Si-doped homoepitaxial
$\beta$-Ga$_2$O$_3$ films with electron concentration (n) ranging from 1.77 to
3.23e20 cm^-3. Record low specific contact resistance and total contact
resistance (Rc) of 1.62e-7 Ohm.cm^2 and 0.023 Ohm.mm were realized for
$\beta$-Ga$_2$O$_3$: Si films with n > 3e20 cm^-3. TLM structures were also
fabricated on heavily Si doped coherently strained $\beta$-(Al$_x$Ga$_1-x$)$_2$
O$_3$ (x=12%, 17% and 22%) films. The film with 12% Al composition (n=1.23e20
cm^-3) showed \r{ho}c of 5.85e-6 Ohm.cm^2, but it increased to 2.19e-4 Ohm.cm^2
for a layer with a 22% Al composition. Annealing the samples post metal
deposition has generally led to a decrease in contact resistance, but for high
Al content $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$, the contact resistance did not
change significantly after the annealing process. The low contact resistance
values measured in this work are very promising for the fabrication of high
frequency power devices. | 2208.02322v1 |
2022-11-30 | High-efficiency energy harvesting based on nonlinear Hall rectifier | Noncentrosymmetric quantum materials can convert AC input current into DC
transverse current through the nonlinear Hall effect at zero magnetic field. We
analyze the AC-DC power conversion efficiency of such ``Hall rectifier'' and
suggest its application in wireless charging and energy harvesting. Our key
observation is that the development of Hall voltage results in a change of
longitudinal resistance, resulting in a violation of Ohm's law due to the
nonlinear Hall effect. This feedback mechanism balances the input power and the
output power and hence is crucial to understanding the power transfer from
source to load. We derive a general expression for the power conversion
efficiency in terms of material parameters, external load resistance, and input
power. As the Hall current is perpendicular to the electric field and does not
generate Joule heating by itself, we obtain high power conversion efficiency
when the Hall angle (which increases with the input power) is large and the
load resistance is optimized. Promising materials for high-efficiency Hall
rectifiers are also discussed. | 2211.17219v2 |
2011-02-28 | Introduction to bulk metallic glass composite and its recent applications | Bulk metallic glass (BMG) materials are hot topics in recent years, not to
mention BMG matrix composites, which further improve the magnetic and
mechanical properties of BMG materials. BMG and BMG matrix materials are fast
developing and promising materials in modern industry due to their
extraordinary properties such as high strength, low density, excellent
resistibility to high temperature and corrosion. In this paper, I reviewed
processing and application of several recently developed BMG and BMG matrix
materials. | 1102.5758v1 |
2008-05-04 | Increase of the wear resistance of carbide layers deposited by Pulsed Laser Deposition in addition with an auxiliary laser | Carbides stand out because of their high hardness and wear-resistance. Thus
these materials are often discussed for coatings of machine tools etc. Within
this work Boron Carbide (B4C) and Carbide (C) thin films were deposited on Si
(100) substrates by pulsed-laser deposition technique. In order to improve the
wear-resistance of the deposited films, we introduced a new working technique
including the application of a second excimer laser in a special working mode.
Thereby one laser was used to ablate the carbide material from a target and to
deposit the material on the substrate. The light of the second laser was
directed directly onto the substrate in order to modify the ablated material.
We report on details for film deposition and film properties determined by
Scanning Electron Microscope, Energy Dispersive X-Ray Spectroscopy, X-Ray
Diffraction, Rutherford Backscattering, Raman Spectroscopy and tribological
experiments. | 0805.0430v1 |
2017-10-24 | Lithographic performance of ZEP520A and mr-PosEBR resists exposed by electron beam and extreme ultraviolet lithography | Pattern transfer by deep anisotropic etch is a well-established technique for
fabrication of nanoscale devices and structures. For this technique to be
effective, the resist material plays a key role and must have high resolution,
reasonable sensitivity and high etch selectivity against the conventional
silicon substrate or underlayer film. In this work, the lithographic
performance of two high etch resistance materials was evaluated: ZEP520A
(Nippon Zeon Co.) and mr-PosEBR (micro resist technology GmbH). Both materials
are positive tone, polymer-based and non-chemically amplified resists. Two
exposure techniques were used: electron beam lithography (EBL) and extreme
ultraviolet (EUV) lithography. These resists were originally designed for EBL
patterning, where high quality patterning at sub-100 nm resolution was
previously demonstrated. In the scope of this work, we also aim to validate
their extendibility to EUV for high resolution and large area patterning. To
this purpose, the same EBL process conditions were employed at EUV. The figures
of merit, i.e. dose to clear, dose to size, and resolution, were extracted and
these results are discussed systematically. It was found that both materials
are very fast at EUV (dose to clear lower than 12 mJ/cm2) and are capable of
resolving dense lines/space arrays with a resolution of 25 nm half-pitch. The
quality of patterns was also very good and the sidewall roughness was below 6
nm. Interestingly, the general-purpose process used for EBL can be extended
straightforwardly to EUV lithography with comparable high quality and yield.
Our findings open new possibilities for lithographers who wish to devise novel
fabrication schemes exploiting EUV for fabrication of nanostructures by deep
etch pattern transfer. | 1710.08733v1 |
2016-04-14 | Study of Glass and Bakelite properties as electrodes in RPCs | India-based Neutrino Observatory (INO) collaboration is planning to build a
magnetized Iron-CALorimeter detector (ICAL) for the study of atmospheric
neutrinos. ICAL detector will be a stack of 151 layers of magnetized iron
plates interleaved with Resistive Plate Chambers (RPCs) as active detector
elements with a total mass of 50 kton. Resistive Plate Chambers are gaseous
detectors made up of two parallel electrodes of high bulk resistivity like
float glass and bakelite. These detectors are extensively used in several high
energy physics experiments since 1980s because of high count rate, excellent
time as well as spatial resolutions, simple to fabricate and operate. Due to
detector aging issue, it is necessary to characterize electrode material so as
to select appropriate electrode material before fabricating the detector. In
the present studies, we measured bulk resistivity and surface current of glass
as well as bakelite. Bulk resistivity of bakelite is ~ 100 times less than that
of glass and surface current of bakelite is higher than that of glass. Also
glass does not need any kind of surface treatment to achieve better surface
uniformity. Therefore, glass electrodes are preferred over bakelite electrodes
in most of the cases. Locally manufactured Asahi glass of ~2 mm thickness and
bakelite sheets were tested during the studies as reported in this paper before
the various stages of detector fabrication. | 1604.04130v2 |
2023-01-11 | Resistive Switching and Current Conduction Mechanisms in Hexagonal Boron Nitride Threshold Memristors with Nickel Electrodes | The two-dimensional (2D) insulating material hexagonal boron nitride (h BN)
has attracted much attention as the active medium in memristive devices due to
its favorable physical properties, among others, a wide bandgap that enables a
large switching window. Metal filament formation is frequently suggested for
h-BN devices as the resistive switching (RS) mechanism, usually supported by
highly specialized methods like conductive atomic force microscopy (C-AFM) or
transmission electron microscopy (TEM). Here, we investigate the switching of
multilayer hexagonal boron nitride (h-BN) threshold memristors with two nickel
(Ni) electrodes through their current conduction mechanisms. Both the high and
the low resistance states are analyzed through temperature-dependent
current-voltage measurements. We propose the formation and retraction of nickel
filaments along boron defects in the h-BN film as the resistive switching
mechanism. We corroborate our electrical data with TEM analyses to establish
temperature-dependent current-voltage measurements as a valuable tool for the
analysis of resistive switching phenomena in memristors made of 2D materials.
Our memristors exhibit a wide and tunable current operation range and low
stand-by currents, in line with the state of the art in h-BN-based threshold
switches, a low cycle-to-cycle variability of 5%, and a large On/Off ratio of
10${^7}$. | 2301.10158v2 |
2021-08-21 | Resistivity size effect due to surface steps on ruthenium thin films computed with a realistic tight-binding model | A realistic tight-binding model is developed and employed to elucidate the
resistivity size effect due to steps on Ru thin films. The resistivity of two
different film orientations, $(0001)$ and $(1 \bar{1}00)$, is computed for
transport along a $[1 1 \bar{2} 0]$ direction both for smooth surfaces and for
surfaces with monolayer-high steps. In the case of smooth films, the systems
are also studied using solutions to the Boltzmann transport equation (BTE).
Interestingly, the resistivity of $(1 \bar{1}00)$ surfaces exhibits a
significant size effect even in the absence of surface steps. When
monolayer-high steps are spaced $\sim 10$ nm apart, the resistivity is shown to
increase due to scattering from the steps. However, only a small increase was
found which cannot explain the large effect seen in recent experiments with Ru
thin films. This highlights the need for further elucidation of the resistivity
size effect. Theoretical analysis suggest that films made from materials with a
relatively large ballistic conductance per area like Ru should exhibit a
reduced resistivity size effect. This result points to Ru as a promising
interconnect material. Finally, because a very efficient algorithm for
computing resistivity based on the kernel polynomial method (KPM) is used, the
approach fulfills a need for realistic models that can span length scales
directly relevant to experimental results. The calculations described here
include films approaching $5$ nm in thickness, with in-plane distances up to
$\sim 160$ nm and $3.8\times10^{5}$ atomic sites. | 2108.09424v7 |
2018-11-14 | Linear-in-T resistivity in dilute metals: A Fermi liquid perspective | We consider a short-range deformation potential scattering model of
electron-acoustic phonon interaction to calculate the resistivity of an ideal
metal as a function of temperature (T) and electron density (n). We consider
both 3D metals and 2D metals, and focus on the dilute limit, i.e., low
effective metallic carrier density of the system. The main findings are: (1) a
phonon scattering induced linear-in-T resistivity could persist to arbitrarily
low T in the dilute limit independent of the Debye temperature ($T_D$) although
eventually the low-T resistivity turns over to the expected Bloch-Gruneisen
(BG) behavior with $T^5$ ($T^4$) dependence, in 3D (2D) respectively; (2)
because of low values of n, the phonon-induced resistivity could be very high
in the system; (3) the resistivity shows an intrinsic saturation effect at very
high temperatures (for $T>T_D$), and in fact, decreases with increasing T above
a high crossover temperature with this crossover being dependent on both $T_D$
and n in a non-universal manner. We also provide high-T linear-in-T resistivity
results for 2D and 3D Dirac materials. Our work brings out the universal
features of phonon-induced transport in dilute metals, and we comment on
possible implications of our results for strange metals, emphasizing that the
mere observation of a linear-in-T metallic resistivity at low temperatures or a
very high metallic resistivity at high temperatures is not necessarily a reason
to invoke an underlying quantum critical strange metal behavior. We discuss the
temperature variation of the effective transport scattering rate showing that
the scattering rate could be below or above $k_BT$, and in particular, purely
coincidentally, the calculated scattering rate happens to be $k_BT$ in normal
metals with no implications for the so-called Planckian behavior. | 1811.05862v2 |
2012-04-10 | Challenges for RPCs and resistive micropattern detectors in the next few years | Nowadays RPCs are in a booming phase: they are successfully used in many
experiments, including LHC; there are ambitious plans to use them in several
upgrade detectors and in some new experiments as well as in various
applications. The aim of this paper is to highlight the main challenges which
the RPC community may face in the next few years and which were addressed in
talks presented at this conference. Examples could be: new and difficult
requirements from experiments (and their upgrades) and applications,
optimization and improvements of the existing traditional detector designs,
improvement of their characteristics (timing /rate performance, aging, dark
current and so on), implementation of new more sensitive electronics,
investigation of new materials, development of large- area detectors. We will
also review the fast and very promising developments of another type of
resistive electrode gaseous detector -micropattern detectors having at least
one of their electrodes made of resistive materials. These innovative detectors
combine in one design the best features of RPC (spark protection) and
micropattern detectors (high granularity-high position resolution). | 1204.2144v1 |
2021-01-28 | Magnetic Field Effects on the Transport Properties of High-Tc Cuprates | Starting from a recently proposed comprehensive theory for the high-Tc
superconductivity in cuprates, we derive a general analytic expression for the
planar resistivity, in the presence of an applied external magnetic field
$\textbf{H}$ and explore its consequences in the different phases of these
materials. As an initial probe of our result, we show it compares very well
with experimental data for the resistivity of LSCO at different values of the
applied field. We also apply our result to Bi2201 and show that the
magnetoresistivity in the strange metal phase of this material, exhibits the
$H^2$ to $H$ crossover, as we move from the weak to the strong field regime.
Yet, despite of that, the magnetoresistivity does not present a quadrature
scaling. Remarkably, the resistivity H-field derivative does scale as a
function of $\frac{H}{T}$, in complete agreement with recent magneto-transport
measurements made in the strange metal phase of cuprates \cite{Hussey2020}. We,
finally, address the issue of the $T$-power-law dependence of the resistivity
of overdoped cuprates and compare our results with experimental data for
Tl2201. We show that this provides a simple method to determine whether the
quantum critical point associated to the pseudogap temperature $T^*(x)$ belongs
to the SC dome or not. | 2101.11969v1 |
2022-09-08 | Dominance of Electron-Magnon Scattering in Itinerant Ferromagnet Fe3GeTe2 | Fe3GeTe2 is a 2-dimensional van der Waals material exhibiting itinerant
ferromagnetism upto 230 K. Here, we study aspects of scattering mechanism in
Fe3Ge2Te2 single crystals via resistivity, magneto-transport and Hall effect
measurements. The quadratic temperature dependence of electrical resistivity
below the Curie temperature hints towards the dominance of electron-magnon
scattering. A non-saturating positive magnetoresistance (MR) is observed at low
temperatures when the magnetic field is applied parallel to the sample plane.
The linear negative MR at high fields for T < TC corroborates to the
suppression in magnon population due to the damping of spin waves. In the high
temperature regime T > TC,MR can be described by the scattering from spin
fluctuations using the model described by Khosla and Fischer. Isothermal Hall
resistivity curves unveil the presence of anomalous Hall resistivity.
Correlation between MR and side jump mechanism further reveals that the
electron-magnon scattering is responsible for the side jump contribution to the
anomalous Hall effect. Our results provide a clear understanding of the role of
electron-magnon scattering on anomalous Hall effect that rules out its origin
to be the topological band structure. | 2209.03555v1 |
2014-12-01 | Novel experimental design for high pressure - high temperature electrical resistance measurements in a 'Paris-Edinburgh' large volume press | We present a novel experimental design for high sensitivity measurements of
the electrical resistance of samples at high pressures (0-6GPa) and high
temperatures (300-1000K) in a 'Paris-Edinburgh' type large volume press.
Uniquely, the electrical measurements are carried out directly on a small
sample, thus greatly increasing the sensitivity of the measurement. The
sensitivity to even minor changes in electrical resistance can be used to
clearly identify phase transitions in material samples. Electrical resistance
measurements are relatively simple and rapid to execute and the efficacy of the
present experimental design is demonstrated by measuring the electrical
resistance of Pb, Sn and Bi across a wide domain of temperature-pressure phase
space and employing it to identify the loci of phase transitions. Based on
these results, the phase diagrams of these elements are reconstructed to high
accuracy and found to be in excellent agreement with previous studies. In
particular, by mapping the locations of several well-studied reference points
in the phase diagram of Sn and Bi, it is demonstrated that a standard
calibration exists for the temperature and pressure, thus eliminating the need
for direct or indirect temperature and pressure measurements. The present
technique will allow simple and accurate mapping of phase diagrams under
extreme conditions and may be of particular importance in advancing studies of
liquid state anomalies. | 1412.0613v2 |
2010-05-13 | Gravitational-wave spin-down and stalling lower limits on the electrical resistivity of the accreted mountain in a millisecond pulsar | The electrical resistivity of the accreted mountain in a millisecond pulsar
is limited by the observed spin-down rate of binary radio millisecond pulsars
(BRMSPs) and the spins and X-ray fluxes of accreting millisecond pulsars
(AMSPs). We find $\eta \ge 10^{-28}\,\mathrm{s}\,
(\tau_\mathrm{SD}/1\,\mathrm{Gyr})^{-0.8}$ (where $\tau_\mathrm{SD}$ is the
spin-down age) for BRMSPs and $\eta \ge
10^{-25}\,\mathrm{s}\,(\dot{M}_\mathrm{a}/\dot{M}_\mathrm{E})^{0.6}$ (where
$\dot{M}_\mathrm{a}$ and $\dot{M}_\mathrm{E}$ are the actual and Eddington
accretion rates) for AMSPs. These limits are inferred assuming that the
mountain attains a steady state, where matter diffuses resistively across
magnetic flux surfaces but is replenished at an equal rate by infalling
material. The mountain then relaxes further resistively after accretion ceases.
The BRMSP spin-down limit approaches the theoretical electron-impurity
resistivity at temperatures $\ga 10^5$ K for an impurity concentration of $\sim
0.1$, while the AMSP stalling limit falls two orders of magnitude below the
theoretical electron-phonon resistivity for temperatures above $10^8$ K. Hence
BRMSP observations are already challenging theoretical resistivity calculations
in a useful way. Next-generation gravitational-wave interferometers will
constrain $\eta$ at a level that will be competitive with electromagnetic
observations. | 1005.2257v1 |
2017-01-23 | Crystal Growth and Magneto-transport of Bi2Se3 Single crystals | In this letter, we report growth and characterization of bulk Bi2Se3 single
crystals. The studied Bi2Se3 crystals are grown by self flux method through
solid state reaction from high temperature (950C) melt of constituent elements
and slow cooling (2C/hour). The resultant crystals are shiny and grown in [00l]
direction, as evidenced from surface XRD. Detailed Reitveld analysis of PXRD
(powder x-ray diffraction) of the crystals showed that these are crystallized
in rhombohedral crystal structure with space group of R3m (D5) and the lattice
parameters are a = 4.14(2)A, b = 4.14 (2) A and c = 28.7010(7) A. Temperature
versus resistivity (R-T) plots revealed metallic conduction down to 2K, with
typical room temperature resistivity (R300K) of around 0.53 mohm-cm and
residual resistivity of 0.12 mohm-cm. Resistivity under magnetic field ]
measurements exhibited large +Ve magneto resistance right from 2K to 200K.
Isothermal magneto resistance [RH] measurements at 2K, 100K and 200K exhibited
magneto resistance (MR) of up to 240, 130 and 60 percent respectively at 14
Tesla. Further the MR plots are non saturating and linear with field at all
temperature. At 2K the MR plots showed clear quantum oscillations at above say
10 Tesla applied field. Also the Kohler plots i.e., were seen consolidating on
one plot. Interestingly, the studied Bi2Se3 single crystal exhibited the
Shubnikov-de Haas oscillations (SdH) at 2K under different applied magnetic
fields ranging from 4Tesla to 14 Tesla | 1701.06280v2 |
2020-06-24 | Conductive filament evolution dynamics revealed by cryogenic (1.5 K) multilevel switching of CMOS-compatible Al2O3/TiO2 resistive memories | This study demonstrates multilevel switching at 1.5 K of Al2O3/TiO2-x
resistive memory devices fabricated with CMOS-compatible processes and
materials. The I-V characteristics exhibit a negative differential resistance
(NDR) effect due to a Joule-heating-induced metal-insulator transition of the
Ti4O7 conductive filament. Carrier transport analysis of all multilevel
switching I-V curves show that while the insulating regime follows the space
charge limited current (SCLC) model for all resistance states, the conduction
in the metallic regime is dominated by SCLC and trap-assisted tunneling (TAT)
for low- and high-resistance states respectively. A non-monotonic conductance
evolution is observed in the insulating regime, as opposed to the continuous
and gradual conductance increase and decrease obtained in the metallic regime
during the multilevel SET and RESET operations. Cryogenic transport analysis
coupled to an analytical model accounting for the
metal-insulator-transition-induced NDR effects and the resistance states of the
device provide new insights on the conductive filament evolution dynamics and
resistive switching mechanisms. Our findings suggest that the non-monotonic
conductance evolution in the insulating regime is due to the combined effects
of longitudinal and radial variations of the Ti4O7 conductive filament during
the switching. This behavior results from the interplay between temperature-
and field-dependent geometrical and physical characteristics of the filament. | 2006.13394v1 |
2002-04-23 | Effects of stoichiometry, purity, etching and distilling on resistance of MgB2 pellets and wire segments | We present a study of the effects of non-stoichiometry, boron purity, wire
diameter and post-synthesis treatment (etching and Mg distilling) on the
temperature dependent resistance and resistivity of sintered MgB2 pellets and
wire segments. Whereas the residual resistivity ratio (RRR) varies between RRR
\~ 4 to RRR > 20 for different boron purity, it is only moderately affected by
non-stoichiometry (from 20% Mg deficiency to 20% Mg excess) and is apparently
independent of wire diameter and presence of Mg metal traces on the wire
surface. The obtained set of data indicates that RRR values in excess of 20 and
residual resistivities as low as rho{0} ~ 0.4 mu Ohm cm are intrinsic material
properties of high purity MgB2. | 0204510v1 |
2007-01-19 | Resistance Anomaly in Disordered Superconducting Films | We report on a resistance anomaly in disordered superconducting films
containing arrays of irregularly distributed nanoscale holes. At high driving
currents, peaks appear in the resistance as a function of temperature, with
peak values up to 2% above the classic normal-state resistance. We attribute
the observed resistance anomaly to dissipation-induced granularity which
enhances the contributions from fluctuation-induced reduction of the density of
states of the quasiparticles. The granular feature of a disordered
superconducting film originates from the inhomogeneous temperature distribution
caused by the variation of the local dissipation and/or heat transfer. | 0701483v1 |
2007-07-28 | Giant Magneto-impedance in stress-annealed Finemet/Copper/Finemet based trilayer structures | The resistive and reactive components of magneto-impedance (MI) for
Finemet/Copper/Finemet sandwiched structures based on stress-annealed
nanocrystalline Fe75Si15B6Cu1Nb3 ribbons as functions of different fields
(longitudinal and perpendicular) and frequencies have been measured and
analyzed. Maximum magneto-resistance and magneto-inductance ratios of 700% and
450% have been obtained in 30-600 kHz frequency range respectively. These large
magneto-resistance and magneto-inductive ratios are a direct consequence of the
large effective relative permeability due to the closed magnetic flux path in
the trilayer structure. The influence of perpendicular bias fields (Hper) in
the Longitudinal Magneto-impedance (LMI) configuration greatly improves the MI
ratios and sensitivities. The maximum MI ratio for the resistive part increases
to as large as 2500% for Hper ~ 1 Oe. The sensitivity of the magneto-resistance
increases from 48%/Oe to 288%/Oe at 600 kHz frequency with the application of
Hper ~ 30 Oe. Such high increase in MI ratios and sensitivities with
perpendicular bias fields are due to the formation the favourable (transverse)
domain structures. | 0707.4229v1 |
2010-04-12 | Systematic Investigation of the Intrinsic Channel Properties and Contact Resistance of Monolayer and Multilayer Graphene FET | The intrinsic channel properties of monolayer and multilayer graphene were
systematically investigated as a function of layer number by the exclusion of
contact resistance using four-probe measurements. We show that the continuous
change in normalized sheet resistivity from graphite to a bilayer graphene is
governed by one unique property, i.e., the band overlap, which markedly
increases from 1 meV for a bilayer graphene to 11 meV for eight layers and
eventually reaches 40 meV for graphite. The monolayer graphene, however, showed
a deviation in temperature dependence due to a peculiar linear dispersion.
Additionally, contact resistivity was extracted for the case of typical Cr/Au
electrodes. The observed high contact resistivity, which varies by three orders
of magnitude (from ~103 to 106 Ohm micron), might significantly mask the
outstanding performance of the monolayer graphene channel, suggesting its
importance in future research. | 1004.2074v1 |
2010-09-02 | Kondo and charge fluctuation resistivity due to Anderson impurities in graphene | Motivated by experiments on ion irradiated graphene, we compute the
resistivity of graphene with dilute impurities. In the local moment regime we
employ the perturbation theory up to third order in the exchange coupling to
determine the behavior at high temperatures within the Kondo model. Resistivity
due to charge fluctuations is obtained within the mean field approach on the
Anderson impurity model. Due to the linear spectrum of the graphene the Kondo
behavior is shown to depend on the gate voltage applied. The location of the
impurity on the graphene sheet is an important variable determining its effect
on the Kondo scale and resistivity. Our results show that for chemical
potential nearby the node the charge fluctuations is responsible for the
observed temperature dependence of resistivity while away from the node the
spin fluctuations take over. Quantitative agreement with experimental data is
achieved if the energy of the impurity level varies linearly with the chemical
potential. | 1009.0551v3 |
2017-10-05 | Electric field Control of Exchange Bias by Resistive Switching | We demonstrated an electric field controlled exchange bias (EB) effect
accompanied with unipolar resistive switching behavior in the
Si/SiO2/Pt/Co/NiO/Pt device. By applying certain voltages, the device displays
obvious EB in high-resistance-state while negligible EB in
low-resistance-state. Conductive filaments forming and rupture in the NiO layer
but near the Co-NiO interface are considered to play dominant roles in
determining the combined resistive switching and EB phenomena. This work paves
a new way for designing multifunctional and nonvolatile magnetic-electrical
random access memory devices. | 1710.01865v1 |
2018-06-11 | Conductivity and Resistivity of Dirac Electrons in Single-Component Molecular Conductor [Pd(dddt)_2] | Dirac electrons, which have been found in the single-component molecular
conductor [Pd(dddt)_2] under pressure, are examined by calculating the
conductivity and resistivity in terms of a tight-binding model for several
pressures of P GPa, which give a nodal line semimetal or insulator. The
temperature (T) dependence of the conductivity shows that the conductivity
increases linearly under pressure at low T due to the Dirac cone but stays
almost constant at high T. Further, at lower pressures, the conductivity is
suppressed due to an unconventional gap, which is examined by calculating the
resistivity. The resistivity exhibits a pseudogap-like behavior even in the
case described by the Dirac cone. Such behavior originates from a novel role of
the nodal line semimetal followed by a pseudogap that is different from a band
gap. The present result reasonably explains the resistivity observed in the
experiment. | 1806.03819v2 |
2019-05-29 | Intrinsic resistance peaks in AB-stacked multilayer graphene with odd number of layers | The intrinsic resistance peak (ridge) structures were recently found to
appear in the carrier density dependence plot of the resistance of the
AB-stacked multilayer graphene with even numbers of layers.The ridges are due
to topological changes in the Fermi surface. Here, these structures were
studied in AB-stacked multilayer graphene with odd numbers of layers (5 and 7
layers) by performing experiments using encapsulated high-quality graphene
samples equipped with top and bottom gate electrodes.The intrinsic resistance
peaks that appeared on maps plotted with respect to the carrier density and
perpendicular electric field showed particular patterns depending on graphene's
crystallographic structure, and were qualitatively different from those of
graphene with even numbers of layers. Numerical calculations of the dispersion
relation and semi-classical resistivity using information based on the Landau
level structure determined by the magnetoresistance oscillations, revealed that
the difference stemmed from the even-odd layer number effect on the electronic
band structure. | 1905.12193v2 |
2014-08-01 | Resistive switching in ultra-thin La0.7Sr0.3MnO3 / SrRuO3 superlattices | Superlattices may play an important role in next generation electronic and
spintronic devices if the key-challenge of the reading and writing data can be
solved. This challenge emerges from the coupling of low dimensional individual
layers with macroscopic world. Here we report the study of the resistive
switching characteristics of a of hybrid structure made out of a superlattice
with ultrathin layers of two ferromagnetic metallic oxides, La0.7Sr0.3MnO3
(LSMO) and SrRuO3 (SRO). Bipolar resistive switching memory effects are
measured on these LSMO/SRO superlattices, and the observed switching is
explainable by ohmic and space charge-limited conduction laws. It is evident
from the endurance characteristics that the on/off memory window of the cell is
greater than 14, which indicates that this cell can reliably distinguish the
stored information between high and low resistance states. The findings may
pave a way to the construction of devices based on nonvolatile resistive memory
effects. | 1408.0103v1 |
2019-07-19 | Niobium nitride thin films for very low temperature resistive thermometry | We investigate thin film resistive thermometry based on
metal-to-insulator-transition (niobium nitride) materials down to very low
temperature. The variation of the NbN thermometer resistance have been
calibrated versus temperature and magnetic field. High sensitivity in
tempertaure variation detection is demonstrated through efficient temperature
coefficient of resistance. The nitrogen content of the niobium nitride thin
films can be tuned to adjust the optimal working temperature range. In the
present experiment, we show the versatility of the NbN thin film technology
through applications in very different low temperature use-cases. We
demonstrate that thin film resistive thermometry can be extended to
temperatures below 30 mK with low electrical impedance. | 1907.08443v1 |
2018-07-23 | Coexistence of Diamagnetism and Vanishingly Small Electrical Resistance at Ambient Temperature and Pressure in Nanostructures | The great practical utility has motivated extensive efforts to discover
ultra-low resistance electrical conductors and superconductors in ambience.
Here we report the observation of vanishingly small electrical resistance at
the ambient temperature and pressure conditions in films and pellets of a
nanostructured material that is composed of silver particles embedded into a
gold matrix. Upon cooling below a sample-specific temperature scale ($T_{C}$)
as high as $286$ K, the film resistance drops below $\sim 2\mu\Omega$, being
limited by measurement uncertainty. The corresponding resistivity ($\sim
10^{-12}$ $\Omega$.m) is at least four orders of magnitude below that of
elemental noble metals, such as gold, silver or copper. Furthermore, the
samples become strongly diamagnetic below $T_{C}$, with volume susceptibilities
as low as -0.056. We additionally describe methods to tune $T_{C}$ to
temperatures much higher than room temperature. | 1807.08572v3 |
2022-11-22 | Contact Resistance Study of Various Metal Electrodes with CVD Graphene | In this study, the contact resistance of various metals to chemical vapour
deposited (CVD) monolayer graphene is investigated. Transfer length method
(TLM) structures with varying widths and separation between contacts have been
fabricated and electrically characterized in ambient air and vacuum condition.
Electrical contacts are made with five metals: gold, nickel, nickel/gold,
palladium and platinum/gold. The lowest value of 92 {\Omega}{\mu}m is observed
for the contact resistance between graphene and gold, extracted from back-gated
devices at an applied back-gate bias of -40 V. Measurements carried out under
vacuum show larger contact resistance values when compared with measurements
carried out in ambient conditions. Post processing annealing at 450{\deg}C for
1 hour in argon-95% / hydrogen-5% atmosphere results in lowering the contact
resistance value which is attributed to the enhancement of the adhesion between
metal and graphene. The results presented in this work provide an overview for
potential contact engineering for high performance graphene-based electronic
devices. | 2211.12415v1 |
2023-03-06 | Quantum Acoustics Spawns Planckian Resistivity | Strange metals exhibit universal linear-in-temperature resistivity described
by a Planckian scattering rate, the origin of which remains elusive. By
employing a novel approach inspired by quantum optics, we arrive at the
coherent state limit of lattice vibrations: quantum acoustics. Utilizing this
nonperturbative framework, we demonstrate that lattice vibrations are active
drivers in the Planckian resistivity phenomenon, challenging prevailing
theories. Treating charge carriers as quantum wave packets negotiating the
dynamic acoustic field, competition ensues between localization and
delocalization, settling on the conjectured universal quantum bound of
diffusion and capturing the enigmatic $T$-linear resistivity over hundreds of
degrees. Our research not only elucidates the critical role of phonons in
Planckian resistivity but also redefines their significance in the broader
landscape of high-temperature superconductivity and condensed matter physics. | 2303.06077v3 |
2011-04-11 | DOS-limited contact resistance in graphene FETs | Graphene has attracted much attention as one of promising candidates of
future high-speed transistor materials because of its high carrier mobility of
more than 10,000 cm2 V-1 s-1. Up to this point, we have focused on the contact
properties as performance killers, as a very small density of states in
graphene might suppress the current injection from metal to graphene. This
paper systematically reviews the metal/graphene contact properties and
discusses the present status and future requirements of the specific contact
resistivity. | 1104.1818v1 |
2006-07-28 | Contact effects in polymer field-effect transistors | Contact resistances often contribute significantly to the overall device
resistance in organic field-effect transistors (OFETs). Understanding charge
injection at the metal-organic interface is critical to optimizing OFET device
performance. We have performed a series of experiments using bottom-contact
poly(3-hexylthiophene) (P3HT) OFETs in the shallow channel limit to examine the
injection process. When contacts are ohmic we find that contact resistivity is
inversely proportional to carrier mobility, consistent with diffusion-limited
injection. However, data from devices with other electrode materials indicate
that this simple picture is inadequate to describe contacts with significant
barriers. A generalized transmission line method allows the analysis of
nonohmic contacts, and we find reasonable agreement with a model for injection
that accounts for the hopping nature of conduction in the polymer. Variation of
the (unintentional) dopant concentration in the P3HT can significantly alter
the injection process via changes in metal-organic band alignment. At very low
doping levels, transport suggests the formation of a barrier at the Au/P3HT
interface, while Pt/P3HT contacts remain ohmic with comparatively low
resistance. We recently observed that self-assembled monolayers on the metal
source/drain electrodes can significantly decrease contact resistance and
maintain ohmic conduction under conditions that would result in nonohmic, high
resistance contacts to untreated electrodes. Finally, we discuss measurements
on extremely short channel devices, in the initial steps toward examining
transport through individual polymer chains. | 0607744v1 |
2008-11-21 | Tuning the Correlation Decay in the Resistance Fluctuations of Multi-Species Networks | A new network model is proposed to describe the $1/f^\alpha$ resistance noise
in disordered materials for a wide range of $\alpha$ values ($0< \alpha < 2$).
More precisely, we have considered the resistance fluctuations of a thin
resistor with granular structure in different stationary states: from nearly
equilibrium up to far from equilibrium conditions. This system has been
modelled as a network made by different species of resistors, distinguished by
their resistances, temperature coefficients and by the energies associated with
thermally activated processes of breaking and recovery. The correlation
behavior of the resistance fluctuations is analyzed as a function of the
temperature and applied current, in both the frequency and time domains. For
the noise frequency exponent, the model provides $0< \alpha < 1$ at low
currents, in the Ohmic regime, with $\alpha$ decreasing inversely with the
temperature, and $1< \alpha <2$ at high currents, in the non-Ohmic regime.
Since the threshold current associated with the onset of nonlinearity also
depends on the temperature, the proposed model qualitatively accounts for the
complicate behavior of $\alpha$ versus temperature and current observed in many
experiments. Correspondingly, in the time domain, the auto-correlation function
of the resistance fluctuations displays a variety of behaviors which are tuned
by the external conditions. | 0811.3565v2 |
2023-07-01 | The near room-temperature upsurge of electrical resistivity in Lu-H-N is not superconductivity, but a metal-to-poor-conductor transition | Since the discovery of superconductivity in mercury at 4 K in 1911, searching
for materials with superconductivity at higher temperatures towards practical
conditions has been a primary enduring goal. The recent report of
room-temperature superconductivity at near-ambient pressure in nitrogen-doped
lutetium hydride (Lu-H-N) by Dasenbrock-Gammon et al. (Hereafter referred as
D-G) seems a great step approaching the ultimate goal. Specifically, they
claimed evidence of superconductivity on Lu-H-N with a maximum Tc of 294 K at 1
GPa. However, the failure to observe the drastic temperature-dependent
resistance change above 200 K in high-pressure synthesized Lu-H-N compounds, a
prerequisite for superconductivity, by researchers worldwide in all independent
follow-up studies casts a heavy shadow on the authenticity of the claims. The
sober questions are: what is the sample that produces the sharp resistance jump
near room temperature? What are the reasons for the non-reproducibility of
others who follow the D-G method of synthesis and the inscrutable low success
rate (35%) in synthesizing the right sample even for the authors in Ref. 1?
What causes the observed sharp resistance jump? Here, with a well-controlled
experiment protocol, we repeatedly reproduced the near room-temperature sudden
change of electrical resistance in the Lu-H-N sample, and we could
quantitatively compare its behavior with the initial pure Lu in a normal
metallic state. These results enable us to scrutinize the origin for the
near-room temperature sharp resistance change, which is attributed to a
metal-to-poor-conductor transition rather than superconductivity. | 2307.00201v1 |
2020-01-17 | Magnetic, magnetoelastic and corrosion resistant properties of (Fe-Ni) based metallic glasses for structural health monitoring applications | We have performed a study of the magnetic, magnetoelastic, and corrosion
resistance properties of seven different composition magnetoelastic-resonant
platforms. For some applications, such as structural health monitoring, these
materials must have not only good magnetomechanical properties, but also a high
corrosion resistance. In the fabricated metallic glasses of composition
Fe(73-x)NixCr5Si10B12, the Fe/Ni ratio was varied (Fe + Ni = 73% at.) thus
changing the magnetic and magnetoelastic properties. A small amount of chromium
(Cr5) was added in order to achieve the desired good corrosion resistance. As
expected, all the studied properties change with the composition of the
samples. Alloys containing a higher amount of Ni than Fe do not show magnetic
behavior at room temperature, while iron-rich alloys have demonstrated not only
good magnetic properties, but also good magnetoelastic ones, with
magnetoelastic coupling coefficient as high as 0.41 for x=0 in the
Fe73Ni0Cr5Si10B12 (the sample containing only Fe but not Ni). Concerning
corrosion resistance, we have found a continuous degradation of these
properties as the Ni content increases in the composition. Thus, the corrosion
potential decreases monotonously from 46.74 mV for the x=0 composition,
Fe73Ni0Cr5Si10B12 to -239.47 mV for the x=73 composition Fe0Ni73Cr5Si10B12. | 2001.06283v1 |
2014-05-08 | Controlling boron redistribution in CoFeB/MgO magnetic tunnel junctions during annealing by variation of cap layer materials and MgO deposition methods | Magnetic tunnel junctions with crystalline MgO tunnel barrier and amorphous
CoFeB electrodes received much attention due to their high tunnel magneto
resistance ratio at room temperature. One important parameter for achieving
high tunnel magneto resistance ratios is to control the boron diffusion from
the electrodes especially during post growth annealing. By high resolution
transmission electron microscopy and electron energy loss spectroscopy
techniques we show that the cap layer material adjacent to the electrodes and
the MgO deposition method are crucial to control boron redistribution. It is
pointed out, that Ta cap layers acts as sinks for boron during annealing in
contrast to Ru layers. Furthermore, radio frequency sputtered MgO tunneling
barriers contain a rather high concentraion of boron in trigonal
[BO$_3$]$^{3-}$ - environment after annealing in contrast to electron beam
evaporated MgO which is virtually free from any boron. Our data further
indicate that neither boron nor oxygen-vacancy-related gap states in the bulk
of MgO barriers affect spin polarized transport for tunnel magneto resistance
ratios at the level of 200%. | 1405.1907v1 |
2021-10-20 | Materials and possible mechanisms of extremely large magnetoresistance: A review | Magnetoresistance (MR) is a characteristic that the resistance of a substance
changes with the external magnetic field, reflecting various physical origins
and microstructures of the substance. A large MR, namely a huge response to a
low external field, has always been a useful functional feature in industrial
technology and a core goal pursued by physicists and materials scientists.
Conventional large MR materials are mainly manganites, whose colossal MR (CMR)
can be as high as -90%. The dominant mechanism is attributed to spin
configuration aligned by the external field, which reduces magnetic scattering
and thus resistance. In recent years, some new systems have shown an extremely
large unsaturated MR (XMR). Unlike ordinary metals, the positive MR of these
systems can reach 103-108% and is persistent under super high magnetic fields.
The XMR materials are mainly metals or semimetals, distributed in high-mobility
topological or non-topological systems, and some are magnetic, which suggests a
wide range of application scenarios. Various mechanisms have been proposed for
the potential physical origin of XMR, including electron-hole compensation,
steep band, ultrahigh mobility, high residual resistance ratio, topological
fermions, etc. It turns out that some mechanisms play a leading role in certain
systems, while more are far from clearly defined. In addition, the researches
on XMR are largely overlapped or closely correlated with other recently rising
physics and materials researches, such as topological matters and
two-dimensional (2D) materials, which makes elucidating the mechanism of XMR
even more important. Moreover, the disclosed novel properties will lay a broad
and solid foundation for the design and development of functional devices. In
this review, we will discuss several aspects in the following order: ... | 2110.10454v1 |
2024-05-09 | Extreme high lattice-misfit superalloys with regular cubic L12 particles and excellent creep resistance | In novel Co and CoNi based superalloys, the creep resistance is limited at
high temperatures due to low lattice misfit and solvus temperature. In this
study, we combined the advantages of Co-Ti (high lattice misfit and solvus
temperature) and Co-Al based superalloys (cuboidal precipitates) by using Ti to
substitute Al in alloys of Co-30Ni-(12.5-x)Al-xTi-2.5Mo-2.5W (at.%)
composition. With high Ti content, the alloys obtained extreme high lattice
misfit (bigger than 1.3 %) and solvus temperature (bigger than 1150 degree).
During aging at 900 degree, alloys with high Ti/Al ratio exhibited a lower
gamma prime precipitate coarsening rate resulting from their lower gamma prime
and gamma interfacial energy and higher lattice misfit. In addition, high Ti/Al
ratio brought higher gamma prime volume fraction and excellent mechanical
properties, such as higher yield stress and better creep resistance. However,
at high temperature of 1100 degree, the cubic gamma prime phase was decomposed
into deleterious Eta phase with D024 structure if the Ti/Al ratio exceeded 1.
Based on this, we outreached new alloys design with a high content of Cr and Ta
and appropriate Ti/Al ratio, i.e., Ti/Al ratio is smaller than 1. The newly
designed alloys still have high solvus temperature (bigger than 1200 degree)
and exhibit high lattice misfit (bigger than 1.2 %) as Co-12Ti (at.%)
superalloys but more regular cubic gamma prime precipitates and significantly
better creep resistance than superalloys Co-9Al-9W and Co-9Al-9W-2Ti at 850 and
950 degree. Nevertheless, compared with creep resistance of Ni based
superalloys, our newly designed alloys still need to be further improved,
especially in the 1000 and 1050 degree range. | 2405.05851v1 |
2019-01-28 | Strong damping-like spin-orbit torque and tunable Dzyaloshinskii-Moriya interaction generated by low-resistivity Pd$_{1-x}$Pt$_x$ alloys | Despite their great promise for providing a pathway for very efficient and
fast manipulation of magnetization at the nanoscale, spin-orbit torque (SOT)
operations are currently energy inefficient due to a low damping-like SOT
efficiency per unit current bias, and/or the very high resistivity of the spin
Hall materials. Here, we report an advantageous spin Hall material, Pd1-xPtx,
which combines a low resistivity with a giant spin Hall effect as evidenced
through the use of three independent SOT ferromagnetic detectors. The optimal
Pd0.25Pt0.75 alloy has a giant internal spin Hall ratio of >0.47 (damping-like
SOT efficiency of ~ 0.26 for all three ferromagnets) and a low resistivity of
~57.5 {\mu}{\Omega} cm at 4 nm thickness. Moreover, we find the
Dzyaloshinskii-Moriya interaction (DMI), the key ingredient for the
manipulation of chiral spin arrangements (e.g. magnetic skyrmions and chiral
domain walls), is considerably strong at the Pd1-xPtx/Fe0.6Co0.2B0.2 interface
when compared to that at Ta/Fe0.6Co0.2B0.2 or W/Fe0.6Co0.2B0.2 interfaces and
can be tuned by a factor of 5 through control of the interfacial spin-orbital
coupling via the heavy metal composition. This work establishes a very
effective spin current generator that combines a notably high energy efficiency
with a very strong and tunable DMI for advanced chiral spintronics and spin
torque applications. | 1901.09954v1 |
2014-10-29 | Contact Research Strategy for Emerging Molybdenum Disulfide and Other Two-Dimensional Field-effect Transistors | Layered two-dimensional (2D) semiconducting transition metal dichalcogenides
(TMD) have been widely isolated, synthesized, and characterized recently.
Numerous 2D materials are identified as the potential candidates as channel
materials for future thin film technology due to their high mobility and the
exhibiting bandgaps. While many TMD filed-effect transistors (FETs) have been
widely demonstrated along with a significant progress to clearly understand the
device physics, large contact resistance at metal/semiconductor interface still
remain a challenge. From 2D device research point of view, how to minimize the
Schottky barrier effects on contacts thus reduce the contact resistance of
metals on 2D materials is very critical for the further development of the
field. Here, we present a review of contact research on molybdenum disulfide
and other TMD FETs from the fundamental understanding of metal-semiconductor
interfaces on 2D materials. A clear contact research strategy on 2D
semiconducting materials is developed for future high-performance 2D FETs with
aggressively scaled dimensions. | 1410.8201v1 |
2023-06-29 | Speeding up high-throughput characterization of materials libraries by active learning: autonomous electrical resistance measurements | High-throughput experimentation enables efficient search space exploration
for the discovery and optimization of new materials. However, large search
spaces of, e.g., compositionally complex materials, require decreasing
characterization times significantly. Here, an autonomous measurement algorithm
was developed, which leverages active learning based on a Gaussian process
model capable of iteratively scanning a materials library based on the highest
uncertainty. The algorithm is applied to a four-point probe electrical
resistance measurement device, frequently used to obtain indications for
regions of interest in materials libraries. Ten materials libraries with
different complexities of composition and property trends are analyzed to
validate the model. By stopping the process before the entire library is
characterized and predicting the remaining measurement areas, the measurement
efficiency can be improved drastically. As robustness is essential for
autonomous measurements, intrinsic outlier handling is built into the model and
a dynamic stopping criterion based on the mean predicted covariance is
proposed. A measurement time reduction of about 70-90% was observed while still
ensuring an accuracy of above 90%. | 2306.17277v1 |
2013-03-29 | An operational window for radiation-resistant materials based on sequentially healing grain interiors and boundaries | Design of nuclear materials with high radiation-tolerance has great
significance1, especially for the next generation of nuclear energy systems2,3.
Response of nano- and poly-crystals to irradiation depends on the radiation
temperature, dose-rate and grain size4-13. However the dependencies had been
studied and interpreted individually, and thus severely lacking is the ability
to predict radiation performance of materials in extreme environments. Here we
propose an operational window for radiation-resistant materials, which is based
on a perspective of interactions among irradiation-induced interstitials,
vacancies, and grain boundaries. Using atomic simulations, we find that healing
grain boundaries needs much longer time than healing grain interiors. Not been
noticed before, this finding suggests priority should be thereafter given to
recovery of the grain boundary itself. This large disparity in healing time is
reflected in the spectra of defects-recombination energy barriers by the
presence of one high-barrier peak in addition to the peak of low barriers. The
insight gained from the study instigates new avenues for examining the role of
grain boundaries in healing the material. In particular, we sketch out the
radiation-endurance window in the parameter space of temperature, dose-rate and
grain size. The window helps evaluate material performance and develop
resistant materials against radiation damage. | 1303.7316v1 |
2004-09-08 | Magnetic and electronic phase transformations in (Sm0.65Sr0.35)MnO3 induced by temperature and magnetic field | Temperature (4.2-260 K) and magnetic field (0-50 kOe) dependencies of the dc
electrical resistance, dc magnetization, and ac magnetic susceptibility of
(Sm0.65Sr0.35)MnO3 prepared from high purity components have been studied. | 0409213v1 |
2015-11-19 | High performance sensors based on resistance fluctuations of single layer graphene transistors | One of the most interesting predicted applications of graphene monolayer
based devices is as high quality sensors. In this letter we show, through
systematic experiments, a chemical vapor sensor based on the measurement of low
frequency resistance fluctuations of single layer graphene
field-effect-transistor (SLG-FET) devices. The sensor has extremely high
sensitivity, very high specificity, high fidelity and fast response times. The
performance of the device using this scheme of measurement (which uses
resistance fluctuations as the detection parameter) is more than two orders of
magnitude better than a detection scheme where changes in the average value of
the resistance is monitored. We propose a number-density fluctuation based
model to explain the superior characteristics of noise measurement based
detection scheme presented in this article. | 1511.06213v1 |
2014-08-19 | Aluminium-oxide wires for superconducting high kinetic inductance circuits | We investigate thin films of conducting aluminium-oxide, also known as
granular aluminium, as a material for superconducting high quality, high
kinetic inductance circuits. The films are deposited by an optimised reactive
DC magnetron sputter process and characterised using microwave measurement
techniques at milli-Kelvin temperatures. We show that, by precise control of
the reactive sputter conditions, a high room temperature sheet resistance and
therefore high kinetic inductance at low temperatures can be obtained. For a
coplanar waveguide resonator with 1.5\,k$\Omega$ sheet resistance and a kinetic
inductance fraction close to unity, we measure a quality factor in the order of
700\,000 at 20\,mK. Furthermore, we observe a sheet resistance reduction by
gentle heat treatment in air. This behaviour is exploited to study the kinetic
inductance change using the microwave response of a coplanar wave guide
resonator. We find the correlation between the kinetic inductance and the sheet
resistance to be in good agreement with theoretical expectations. | 1408.4347v3 |
2013-05-05 | Resistance of High-Temperature Cuprate Superconductors | Cuprate superconductors have many different atoms per unit cell. A large
fraction of cells (5-25%) must be modified ("doped") before the material
superconducts. Thus it is not surprising that there is little consensus on the
superconducting mechanism, despite almost 200,000 papers. Most astonishing is
that for the simplest electrical property, the resistance, "despite sustained
theoretical efforts over the past two decades, its origin and its relation to
the superconducting mechanism remain a profound, unsolved mystery." Currently,
model parameters used to fit normal state properties are experiment specific
and vary arbitrarily from one doping to the other. Here, we provide a
quantitative explanation for the temperature and doping dependence of the
resistivity, Hall effect, and magnetoresistance in one self-consistent model by
showing that cuprates are intrinsically inhomogeneous with a percolating
metallic region and insulating regions. Using simple counting of dopant-induced
plaquettes, we show that the superconducting pairing and resistivity are due to
phonons. | 1305.1058v1 |
2013-12-18 | Cyclic electric field stress on bipolar resistive switching devices | We have studied the effects of accumulating cyclic electrical pulses of
increasing amplitude on the non-volatile resistance state of interfaces made by
sputtering a metal (Au, Pt) on top of the surface of a cuprate superconductor
YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO). We have analyzed the influence of the
number of applied pulses $N$ on the relative amplitude of the remnant
resistance change between the high ($R_H$) and the low ($R_L$) state
[$\alpha=(R_{H}-R_{L})/R_{L}$] at different temperatures ($T$). We show that
the critical voltage ($V_c$) needed to produce a resistive switching (RS, i.e.
$\alpha >0$) decreases with increasing $N$ or $T$. We also find a power law
relation between the voltage of the pulses and the number of pulses
$N_{\alpha_0}$ required to produce a RS of $\alpha=\alpha_0$. This relation
remains very similar to the Basquin equation used to describe the
stress-fatigue lifetime curves in mechanical tests. This points out to the
similarity between the physics of the RS, associated with the diffusion of
oxygen vacancies induced by electrical pulses, and the propagation of defects
in materials subjected to repeated mechanical stress. | 1312.5338v1 |
2014-06-13 | Subcoercive and multilevel ferroelastic remnant states with resistive readout | Ferroelectric devices use their electric polarization ferroic order as the
switching and storage physical quantity for memory applications. However,
additional built-in physical quantities and memory paradigms are requested for
applications. We propose here to take advantage of the multiferroic properties
of ferroelectrics, using ferroelasticity to create a remnant strain, persisting
after stressing the material by converse piezoelectricity means. While large
electric fields are needed to switch the polarization, here writing occurs at
subcoercive much lower field values, which can efficiently imprint multiple
remnant strain states. A proof-of-principle device, with the simplest and
non-optimized resistance strain detection design, is shown here to exhibit
13-memory states of high reproducibility and reliability. The related
advantages in lower power consumption and limited device fatigue make our
approach relevant for applications. | 1406.3457v1 |
2023-03-08 | Encoding multistate charge order and chirality in endotaxial heterostructures | High-density phase change memory (PCM) storage is proposed for materials with
multiple intermediate resistance states, which have been observed in
1$T$-TaS$_2$ due to charge density wave (CDW) phase transitions. However, the
metastability responsible for this behavior makes the presence of multistate
switching unpredictable in TaS$_2$ devices. Here, we demonstrate the
fabrication of nanothick verti-lateral $H$-TaS$_2$/1$T$-TaS$_2$
heterostructures in which the number of endotaxial metallic $H$-TaS$_2$
monolayers dictates the number of resistance transitions in 1$T$-TaS$_2$
lamellae near room temperature. Further, we also observe optically active
heterochirality in the CDW superlattice structure, which is modulated in
concert with the resistivity steps, and we show how strain engineering can be
used to nucleate these polytype conversions. This work positions the principle
of endotaxial heterostructures as a promising conceptual framework for
reliable, non-volatile, and multi-level switching of structure, chirality, and
resistance. | 2303.04387v3 |
2021-05-13 | Interaction Effects and Viscous Magneto-Transport in a Strongly Correlated 2D Hole System | Fermi liquid theory has been a foundation in understanding the electronic
properties of materials. For weakly interacting two-dimensional (2D) electron
or hole systems, electron-electron interactions are known to introduce quantum
corrections to the Drude conductivity in the FL theory, giving rise to
temperature dependent conductivity and magneto-resistance. Here we study the
magneto-transport in a strongly interacting 2D hole system over a broad range
of temperatures ($T$ = 0.09 to $>$1K) and densities $p=1.98-0.99\times10^{10}$
cm$^{-2}$ where the ratio between Coulomb energy and Fermi energy $r_s$ = 20 -
30. We show that while the system exhibits a negative parabolic
magneto-resistance at low temperatures ($\lesssim$ 0.4K) characteristic of an
interacting FL, the FL interaction corrections represent an insignificant
fraction of the total conductivity. Surprisingly, a positive magneto-resistance
emerges at high temperatures and grows with increasing temperature even in the
regime $T \sim E_F$, close to the Fermi temperature. This unusual positive
magneto-resistance at high temperatures is attributed to the collective viscous
transport of 2D hole fluid in the hydrodynamic regime where holes scatter
frequently with each other. These findings highlight the collective transport
in a strongly interacting 2D system in the $r_s\gg 1$ regime and the
hydrodynamic transport induced magneto-resistance opens up possibilities to new
routes of magneto-resistance at high temperatures. | 2105.06502v1 |
2015-04-29 | Gate-Tunable Tunneling Resistance in Graphene/Topological Insulator Vertical Junctions | Graphene-based vertical heterostructures, particularly stacks incorporated
with other layered materials, are promising for nanoelectronics. The stacking
of two model Dirac materials, graphene and topological insulator, can
considerably enlarge the family of van der Waals heterostructures. Despite well
understanding of the two individual materials, the electron transport
properties of a combined vertical heterojunction are still unknown. Here we
show the experimental realization of a vertical heterojunction between Bi2Se3
nanoplate and monolayer graphene. At low temperatures, the electron transport
through the vertical heterojunction is dominated by the tunneling process,
which can be effectively tuned by gate voltage to alter the density of states
near the Fermi surface. In the presence of a magnetic field, quantum
oscillations are observed due to the quantized Landau levels in both graphene
and the two-dimensional surface states of Bi2Se3. Furthermore, we observe an
exotic gate-tunable tunneling resistance under high magnetic field, which
displays resistance maxima when the underlying graphene becomes a quantum Hall
insulator. | 1504.07780v3 |
2022-03-31 | Towards automated design of corrosion resistant alloy coatings with an autonomous scanning droplet cell | We present an autonomous scanning droplet cell platform designed for
on-demand alloy electrodeposition and real-time electrochemical
characterization for investigating the corrosion-resistance properties of
multicomponent alloys. Automation and machine learning are currently driving
rapid innovation in high throughput and autonomous materials design and
discovery. We present two alloy design case studies: one focusing on a
multi-objective corrosion resistant alloy optimization, and a case study
highlighting the complexity of the multimodal characterization needed to
provide insight into the underlying structural and chemical factors that drive
observed material behavior. This motivates a close coupling between autonomous
research platforms and scientific machine learning methodology that blends
mechanistic physical models and black box machine learning models. This
emerging research area presents new opportunities to accelerate materials
synthesis, evaluation, and hence discovery and design. | 2203.17049v1 |
2019-06-10 | Quantum oscillation of thermal conductivity and violation of Weidemann-Franz law in TaAs$_2$ and NbAs$_2$ | We report a study of thermal conductivity and resistivity at ultra-low
temperatures and in high magnetic fields for semi-metal materials TaAs$_2$ and
NbAs$_2$ by using single crystal samples. The thermal conductivity is strongly
suppressed in magnetic fields, having good correspondence with the large
positive magnetoresistance, which indicates a dominant electronic contribution
to thermal conductivity. In addition, not only the resistivity but also the
thermal conductivity display clear quantum oscillations behavior at subKelvin
temperatures and in magnetic fields up to 14 T. The most striking phenomenon is
that the thermal conductivity show a $T^4$ behavior at very low temperatures,
while the resistivity show a $T$-independent behavior. This indicates a strong
violation of the Weidemann-Franz law and points to a non-Feimi liquid state of
these materials. | 1906.03961v3 |
2022-01-09 | Resistivity testing of palladium dilution limits in CoPd alloys for hydrogen storage | Palladium satisfies most of the requirements for an effective hydrogen
storage material with two major drawbacks: it has a relatively low gravimetric
hydrogen density and is prohibitively expensive for large-scale applications.
Pd-based alloys should be considered as possible alternatives to a pure Pd. The
question is how much one can dilute the Pd concentration in a variety of
candidate materials while preserving hydrogen absorption capability. We
demonstrate that the resistivity measurements of thin-film alloy samples can be
used for a qualitative high-throughput screening and study of the
hydrogen-absorbing properties over the entire range of palladium
concentrations. Contrary to palladium-rich alloys where additional hydrogen
scattering indicates a degree of hydrogen content, the diluted alloy films
respond by a decrease of resistance due to their thickness expansion. Evidence
of significant hydrogen absorption was found in thin CoPd films diluted to just
20% of Pd. | 2201.02974v1 |
2023-05-26 | Ferroelectricity driven-resistive switching and Schottky barrier modulation at CoPt/MgZnO interface for non-volatile memories | Ferroelectric memristors have attracted much attention as a type of
nonvolatile resistance switching memories in neuromorphic computing, image
recognition, and information storage. Their resistance switching mechanisms
have been studied several times in perovskite and complicated materials
systems. It was interpreted as the modulation of carrier transport by
polarization control over Schottky barriers. Here, we experimentally report the
isothermal resistive switching across a CoPt/MgZnO Schottky barrier using a
simple binary semiconductor. The crystal and texture properties showed
high-quality and single-crystal Co$_{0.30}$Pt$_{0.70}$/Mg$_{0.20}$Zn$_{0.80}$O
hetero-junctions. The resistive switching was examined by an electric-field
cooling method that exhibited a ferroelectric T$_C$ of MgZnO close to the bulk
value. The resistive switching across CoPt/MgZnO Schottky barrier was
accompanied by a change in the Schottky barrier height of 26.5 meV due to an
interfacial charge increase and/or orbital hybridization induced reversal of
MgZnO polarization. The magnitude of the reversed polarization was estimated to
be a reasonable value of 3.0 (8.25) $\mu$ C/cm$^2$ at 300 K (2 K). These
findings demonstrated the utilities of CoPt/MgZnO interface as a potential
candidate for ferroelectric memristors and can be extended to probe the
resistive switching of other hexagonal ferroelectric materials. | 2305.16563v3 |
2016-08-04 | Bulk Superconductivity Induced by In-plane Chemical Pressure Effect in Eu0.5La0.5FBiS2-xSex | We have investigated Se substitution effect to superconductivity of an
optimally-doped BiS2-based superconductor Eu0.5La0.5FBiS2. Eu0.5La0.5FBiS2-xSex
samples with x = 0-1 were synthesized. With increasing x, in-plane chemical
pressure is enhanced. For x = 0.6, 0.8, and 1, superconducting transitions with
a large shielding volume fraction are observed in magnetic susceptibility
measurements, and the highest Tc is 3.8 K for x = 0.8. From low-temperature
electrical resistivity measurements, a zero-resistivity state is observed for
all the samples, and the highest Tc is observed for x = 0.8. With increasing Se
concentration, characteristics of electrical resistivity changes from
semiconducting-like to metallic, suggesting that the emergence of bulk
superconductivity is linked with the enhanced metallicity. A superconductivity
phase diagram of the Eu0.5La0.5FBiS2-xSex superconductor is established.
Temperature dependences of electrical resistivity show an anomalous two-step
transition under high magnetic fields. Hence, the resistivity data are analyzed
with assuming in-plane anisotropy of upper critical field. | 1608.01470v2 |
2018-11-03 | Carbon nanotube/metal corrosion issues for nanotube coatings and inclusions in a matrix | Corrosion is an inevitable phenomenon that is inherent in metals and even
though there has been significant research on this subject, no ideal protection
has been discovered to fully prevent corrosion. However, methods such as using
protective coatings, and modifying the structure or composition of the material
have been used to slow down gradual corrosion and fortunately they proved to be
quite beneficial. The research focus has shifted to integrating novel materials
and structures to improve the corrosion resistance of composites. Carbon
nanotubes (CNTs) are an attractive and promising filler due to their chemical
inertness and high mechanical, electrical, and thermal properties. CNTs can
fill the gaps of metals and polymer-based composites by forming a passive layer
on metals and promoting sacrificial protection in zinc rich polymer (ZRP)
coatings, and can therefore function as an anti-corrosion filler. This paper
reviews the research that has been performed to better understand the influence
of CNTs on corrosion resistance in composites. Accordingly, in metal matrix
composites (MMCs), most of the work has been carried out on electrodeposited
coatings, namely Ni-based-CNT composites, which show improved corrosion
resistance by CNT addition. On the other hand, there are a few papers that have
studied the corrosion resistance of Mg-based-CNT composites and their corrosion
results contradict those obtained from other metal-CNT composites. For ZRPs or
polymer-based coatings there are a few papers that studied the effect of CNTs
on the corrosion of said composites. It is believed that CNTs can strengthen
the adhesion between the coating and the substrate and facilitate sacrificial
protection by Zn particles by forming a conductive network, hence the improved
corrosion resistance. | 1812.03815v1 |
1997-04-29 | Normal state c-axis resistivity of high T_c cuprate superconductors | It is shown that a strong intraplanar incoherent scattering can effectively
block the interplanar coherent tunneling between the weakly coupled planes of
the highly anisotropic but clean (intrinsic) materials such as the optimally
doped high-T_c layered cuprate superconductors. The calculated normal-state
C-axis resistivity \rho_c(T) then follows the metal-like temperature dependence
of the ab-plane resistivity \rho_{ab}(T) at high temperatures. At low enough
temperatures, however, \rho_c(T) exhibits a non-metal like upturn even as
\rho_{ab}(T) remains metallic. Moreover, in the metallic regime, \rho_c(T) is
not limited by the maximum metallic resistivity of Mott-Ioffe-Regel. This
correlation between the intrinsic \rho_c(T) and \rho_{ab}(T) is observed in the
normal state of the high-T_c stoichiometric cuprates. | 9704242v1 |
1997-09-24 | Radiation Induced Damage in GaAs Particle Detectors | The motivation for investigating the use of GaAs as a material for detecting
particles in experiments for High Energy Physics (HEP) arose from its perceived
resistance to radiation damage. This is a vital requirement for detector
materials that are to be used in experiments at future accelerators where the
radiation environments would exclude all but the most radiation resistant of
detector types. | 9709034v1 |
2017-07-05 | Effects of Temperature and Near Ultraviolet Light on Current-Voltage Characteristics of Colemanite | We investigate current-voltage (I-V) characteristics of the ferroelectric
material colemanite at room temperature, at a high temperature, and also under
the influence of near ultraviolet light. We demonstrate that all three I-V
plots exhibit hysteresis effects, and these new results shed new light on the
resistance of colemanite. These novel properties are explained on the basis of
its microstructure indicating potential applications in devices with negative
resistance as well as in photovoltaic devices. | 1707.01194v1 |
2023-08-23 | Verification of Wiedemann-Franz law in silver with moderate residual resistivity ratio | Electrical and thermal transport were studied in a vacuum-annealed
polycrystalline silver wire with residual resistivity ratio 200-400, in the
temperature range 0.1-1.2K and in magnetic fields up to 5T. Both at zero field
and at 5T the wire exhibits the Wiedemann-Franz law with the fundamental Lorenz
number, contrary to an earlier report [Gloos, K. et al, Cryogenics 30, 14
(1990)]. Our result demonstrates that silver is an excellent material for
thermal links in ultra-low-temperature experiments operating at high magnetic
fields. | 2308.12349v1 |
2016-02-02 | Coexistence of magneto-resistance and -capacitance tunability in Sm2Ga2Fe2O9 | We propose that charge gradient resulting in the coexisting
magneto-resistance and-capacitance tunability in material systems. We have
experimentally observed coexisting of tunable magneto-resistance and
-capacitance in Sm2Ga2Fe2O9. Our model fits well with the experimental result. | 1602.01136v1 |
2013-03-06 | Nonlinear Surface Resistance of YBa2Cu3O7-x Superconducting Thin Films on MgO Substrates in Dielectric Resonator at Ultra High Frequencies | The nonlinear surface resistance Rs of the YBa2Cu3O7-x superconducting thin
films on the MgO substrates was researched in the Hakki-Coleman dielectric
resonator at the microwave signal powers from -18 dBm to +30 dBm at the ultra
high frequency of 25 GHz in the range of temperatures from 12 K to 85 K. The
dependences of the surface resistance on the temperature RS(T) in the
YBa2Cu3O7-x superconducting thin films at the microwaves were measured. The
dependence of the surface resistance on the microwave power RS(P) in the
YBa2Cu3O7-x superconducting thin films at the microwaves were found at the two
temperatures T = 25 K and T = 50 K. The full expression for the estimation of
the measurements accuracy of the surface resistance RS was derived, and the
measurements accuracy was set at 1 %. The physical mechanisms, which can be
used to explain the experimental results, were discussed. It is shown that the
surface resistance Rs can nonlinearly increase as a result of the transition by
the sub-surface layer of the HTS thin film in a mixed state with the Abricosov
and Josephson magnetic vortices generation at an increase of the microwave
signal power P above the magnitude of 8 dBm. It is assumed that some additional
energy losses have place, because of the microwave power dissipation on the
normal metal cores of the magnetic vortices. | 1303.1276v2 |
2019-12-13 | Picosecond Multilevel Resistive Switching in Tantalum Oxide Thin Films | The increasing demand for high-density data storage leads to an increasing
interest in novel memory concepts with high scalability and the opportunity of
storing multiple bits in one cell. A promising candidate is the redox-based
resistive switch repositing the information in form of different resistance
states. For reliable programming, the underlying physical parameters need to be
understood. We reveal that the programmable resistance states are linked to
internal series resistances and the fundamental nonlinear switching kinetics.
The switching kinetics of Ta$_{2}$O$_{5}$-based cells was investigated in a
wide range over 15 orders of magnitude from 250 ps to 10$^{5}$ s. We found
strong evidence for a switching speed of 10 ps which is consistent with analog
electronic circuit simulations. On all time scales, multi-bit data storage
capabilities were demonstrated. The elucidated link between fundamental
material properties and multi-bit data storage paves the way for designing
resistive switches for memory and neuromorphic applications. | 2002.00700v1 |
2014-03-05 | Strong Oxidation Resistance of Atomically Thin Boron Nitride Nanosheets | Investigation on oxidation resistance of two-dimensional (2D) materials is
critical for many of their applications, because 2D materials could have higher
oxidation kinetics than their bulk counterparts due to predominant surface
atoms and structural distortions. In this study, the oxidation behavior of
high-quality boron nitride (BN) nanosheets of 1-4 layer thick has been examined
by heating in air. Atomic force microscopy and Raman spectroscopy analyses
reveal that monolayer BN nanosheets can sustain up to 850 {\deg}C and the
starting temperature of oxygen doping/oxidation of BN nanosheets only slightly
increases with the increase of nanosheet layer and depends on heating
conditions. Elongated etch lines are found on the oxidized monolayer BN
nanosheets, suggesting that the BN nanosheets are first cut along the
chemisorbed oxygen chains and then the oxidative etching grows perpendicularly
to these cut lines. The stronger oxidation resistance of BN nanosheets suggests
that they are more preferable for high-temperature applications than graphene. | 1403.1002v1 |
2016-08-30 | Design and Demonstration of Ultra Wide Bandgap AlGaN Tunnel Junctions | Ultra violet light emitting diodes (UV LEDs) face critical limitations in
both the injection efficiency and light extraction efficiency due to the
resistive and absorbing p-type contact layers. In this work, we investigate the
design and application of polarization engineered tunnel junctions for
ultra-wide bandgap AlGaN (Al mole fraction higher than 50%) materials towards
highly efficient UV LEDs. We demonstrate that polarization-induced 3D charge is
beneficial in reducing tunneling barriers especially for high composition AlGaN
tunnel junctions. The design of graded tunnel junction structures could lead to
low tunneling resistance below 10-3 Ohm cm2 and low voltage consumption below 1
V (at 1 kA/cm2) for high composition AlGaN tunnel junctions. Experimental
demonstration of 292 nm emission was achieved through non-equilibrium hole
injection into wide bandgap materials with bandgap energy larger than 4.7 eV,
and detailed modeling of tunnel junctions shows that they can be engineered to
have low resistance, and can enable efficient emitters in the UV-C wavelength
range. | 1608.08653v1 |
2010-02-10 | Strain, magnetic anisotropy, and anisotropic magnetoresistance in (Ga,Mn)As on high-index substrates: application to (113)A-oriented layers | Based on a detailed theoretical examination of the lattice distortion in
high-index epilayers in terms of continuum mechanics, expressions are deduced
that allow the calculation and experimental determination of the strain tensor
for (hhl)-oriented (Ga,Mn)As layers. Analytical expressions are derived for the
strain-dependent free-energy density and for the resistivity tensor for
monoclinic and orthorhombic crystal symmetry, phenomenologically describing the
magnetic anisotropy (MA) and anisotropic magnetoresistance (AMR) by appropriate
anisotropy and resistivity parameters, respectively. Applying the results to
(113)A orientation with monoclinic crystal symmetry, the expressions are used
to determine the strain tensor and the shear angle of a series of
(113)A-oriented (Ga,Mn)As layers by high-resolution x-ray diffraction and to
probe the MA and AMR at 4.2 K by means of angle-dependent magnetotransport.
Whereas the transverse resistivity parameters are nearly unaffected by the
magnetic field, the parameters describing the longitudinal resistivity are
strongly field dependent. | 1002.2179v2 |
2011-08-08 | Beam screen issues | In the High Energy LHC (HE-LHC), a beam energy of about 16.5 TeV is currently
contemplated. The beam screen issues linked to the use of 20 T dipole magnets
instead of 8.33 T are discussed, with a particular emphasis on two mechanisms,
the magneto-resistance and the anomalous skin effect, assuming the nominal
machine and beam parameters. The magneto-resistance effect always leads to an
increase of the material resistivity (as the mean free path in the presence of
a transverse magnetic field becomes smaller). As concerns the anomalous skin
effect, the anomalous increase of surface resistance of metals at low
temperatures and high frequencies is attributed to the long mean free path of
the conduction electrons: when the skin depth becomes much smaller than the
mean free path, only a fraction of the conduction electrons moving almost
parallel to the metal surface is effective in carrying the current and the
classical theory breaks down. | 1108.1643v1 |
2012-04-15 | A Structural Phase Transition in Ca3Co4O9 Associated with Enhanced High Temperature Thermoelectric Properties | Temperature dependent electrical resistivity, crystal structure and heat
capacity measurements reveal a resistivity drop and metal to semiconductor
transition corresponding to first order structural phase transition near 400 K
in Ca3Co4O9. The lattice parameter c varies smoothly with increasing
temperature, while anomalies in the a, b1 and b2 lattice parameters occur at ~
400 K. Both Ca2CoO3 and CoO2 layers become distorted above ~ 400 K associated
with the metal to semiconductor transport behavior change. Resistivity and heat
capacity measurements as a function of temperature under magnetic field
indicates low spin contribution to this transition. Reduced resistivity
associated with this first order phase transition from metallic to
semiconducting behavior enhances the thermoelectric properties at high
temperatures and points to the metal to semiconductor transition as a mechanism
for improved ZT in high temperature thermoelectric oxides. | 1204.3231v1 |
2015-10-07 | Fabrication and Characterisation of Oil-Free Large High Pressure Laminate Resistive Plate Chamber | A large (240 cm $\times$ 120 cm $\times$ 0.2 cm) oil-free High Pressure
Laminate (HPL), commonly referred as "bakelite", Resistive Plate Chamber (RPC)
has been developed at VECC-Kolkata using locally available P-302 OLTC grade
HPL. The chamber has been operated in streamer mode using Argon, Freon(R134a)
and Iso-butane in a ratio of 34:57:9 by volume. The electrodes and glue samples
have been characterised by measuring their electrical parameters like bulk
resistivity and surface resistivity. The performance of the chamber has been
studied by measuring the efficiency, its uniformity and stability in detection
of cosmic muons. Timing measurement has been performed at a central location of
the chamber. The chamber showed an efficiency $>$95$\%$ and time resolution
($\sigma$), at the point of measurement, $\sim$0.83 ns at 9000V. Details of the
material characterisation, fabrication procedure and performance studies have
been discussed. | 1510.02028v4 |
2016-11-22 | CSAR 62 as negative-tone resist for high-contrast e-beam lithography at temperatures between 4 K and room temperature | The temperature dependence of the electron-beam sensitive resist CSAR 62 is
investigated in its negative-tone regime. The writing temperatures span a wide
range from 4 K to room temperature with the focus on the liquid helium
temperature regime. The importance of low temperature studies is motivated by
the application of CSAR 62 for deterministic nanophotonic device processing by
means of in-situ electron-beam lithography. At low temperature, CSAR 62
exhibits a high contrast of 10.5 and a resolution of 49 nm. The etch stability
is almost temperature independent and it is found that CSAR 62 does not suffer
from peeling which limits the low temperature application of the standard
electron-beam resist PMMA. As such, CSAR 62 is a very promising negative-tone
resist for in-situ electron-beam lithography of high quality nanostructures at
low temperature. | 1611.07266v1 |
2017-07-24 | Advancement in the understanding of the field and frequency dependent microwave surface resistance of niobium | The radio-frequency surface resistance of niobium resonators is incredibly
reduced when nitrogen impurities are dissolved as interstitial in the material,
conferring ultra-high Q-factors at medium values of accelerating field. This
effect has been observed in both high and low temperature nitrogen treatments.
As a matter of fact, the peculiar anti Q-slope observed in nitrogen doped
cavities, i.e. the decreasing of the Q-factor with the increasing of the
radio-frequency field, come from the decreasing of the BCS surface resistance
component as a function of the field. Such peculiar behavior has been
considered consequence of the interstitial nitrogen present in the niobium
lattice after the doping treatment. The study here presented show the field
dependence of the BCS surface resistance of cavities with different resonant
frequencies, such as: 650 MHz, 1.3 GHz, 2.6 GHz and 3.9 GHz, and processed with
different state-of-the-art surface treatments. These findings show for the
first time that the anti Q-slope might be seen at high frequency even for clean
Niobium cavities, revealing useful suggestion on the physics underneath the
anti Q-slope effect. | 1707.07582v1 |
2022-09-29 | Magnetic properties, electrical resistivity, and hardness of high-entropy alloys FeCoNiPd and FeCoNiPt | We report the magnetic properties, electrical resistivity, and Vickers
microhardness of as-cast and annealed high-entropy alloys (HEAs) FeCoNiPd and
FeCoNiPt with the face-centered cubic structure. The heat treatment at 800
$^{\circ}$C does not largely affect the physical properties in each HEA. The
values of the Curie temperature and the saturation moment at 50 K are 955 K and
1.458 $\mu_\mathrm{B}$/f.u. for the annealed FeCoNiPd, and 851 K and 1.456
$\mu_\mathrm{B}$/f.u. for the annealed FeCoNiPt, respectively. Each HEA is a
soft ferromagnet and shows metallic resistivity. The electronic structure
calculations of both HEAs support the ferromagnetic ground states. The
comparisons between experimental and theoretical values are made for the Curie
temperature, the saturation moment, and the residual resistivity. The Vickers
microhardness of annealed FeCoNiPd and FeCoNiPt are both 188 HV. The hardness
vs. valence electron count (VEC) per atom plot of these HEAs does not largely
deviate from an expected universal relation forming a broad peak at
VEC$\sim$6.8. This study would give some hints on designing a soft
ferromagnetic HEA with high hardness. | 2209.14506v1 |
2018-11-29 | Logarithmic Upturn in Low-Temperature Electronic Transport as a Signature of d-Wave Order in Cuprate Superconductors | In cuprate superconductors, high magnetic fields have been used extensively
to suppress superconductivity and expose the underlying normal state. Early
measurements revealed insulating-like behavior in underdoped material versus
temperature $T$, in which resistivity increases on cooling with a puzzling
$\log(1/T)$ form. We instead use microwave measurements of flux-flow
resistivity in YBa$_2$Cu$_3$O$_{6+y}$ and Tl$_2$Ba$_2$CuO$_{6+\delta}$ to study
charge transport deep inside the superconducting phase, in the low temperature
and low field regime. Here, the transition from metallic low-temperature
resistivity ($d\rho/dT>0$) to a $\log(1/T)$ upturn persists throughout the
superconducting doping range, including a regime at high carrier dopings in
which the field-revealed normal-state resistivity is Fermi-liquid-like. The
$\log(1/T)$ form is thus likely a signature of $d$-wave superconducting order,
and the field-revealed normal state's $\log(1/T)$ resistivity may indicate the
free-flux-flow regime of a phase-disordered $d$-wave superconductor. | 1811.12348v1 |
2019-05-31 | Pressure-Induced Structural Phase Transition and a Special Amorphization Phase of Two-Dimensional Ferromagnetic Semiconductor Cr2Ge2Te6 | Layered transition-metal trichalcogenides have become one of the research
frontiers as two-dimensional magnets and candidate materials used for
phase-change memory devices. Herein we report the high-pressure synchrotron
X-ray diffraction and resistivity measurements on Cr2Ge2Te6 (CGT) single
crystal by using diamond anvil cell techniques, which reveal a mixture of
crystalline-to-crystalline and crystalline-to-amorphous transitions taking
place concurrently at 18.3-29.2 GPa. The polymorphic transition could be
interpreted by atomic layer reconstruction and the amorphization could be
understood in connection with randomly flipping atoms into van der Waals gaps.
The amorphous (AM) phase is quenchable to ambient conditions. The electrical
resistance of CGT shows a bouncing point at ~ 18 GPa, consistent with the
polymorphism phase transition. Interestingly, the high-pressure AM phase
exhibits metallic resistance with the magnitude comparable to that of
high-pressure crystalline phases, whereas the resistance of the AM phase at
ambient pressure fails to exceed that of the crystalline phase, indicating that
the AM phase of CGT appeared under high pressure is quite unique and similar
behavior has never been observed in other phase-change materials. The results
definitely would have significant implications for the design of new functional
materials. | 1905.13603v1 |
2018-08-23 | Evidence for superconductivity above 260 K in lanthanum superhydride at megabar pressures | Recent predictions and experimental observations of high Tc superconductivity
in hydrogen-rich materials at very high pressures are driving the search for
superconductivity in the vicinity of room temperature. We have developed a
novel preparation technique that is optimally suited for megabar pressure
syntheses of superhydrides using pulsed laser heating while maintaining the
integrity of sample-probe contacts for electrical transport measurements to 200
GPa. We detail the synthesis and characterization, including four-probe
electrical transport measurements, of lanthanum superhydride samples that
display a significant drop in resistivity on cooling beginning around 260 K and
pressures of 190 GPa. Additional measurements on two additional samples
synthesized the same way show resistance drops beginning as high as 280 K at
these pressures. The loss of resistance at these high temperatures is not
observed in control experiments on pure La as well as in partially transformed
samples at these pressures, and x-ray diffraction as a function of temperature
on the superhydride reveal no structural changes on cooling. We infer that the
resistance drop is a signature of the predicted room-temperature
superconductivity in LaH10, in good agreement with density functional structure
search and BCS theory calculations. | 1808.07695v3 |