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2015-08-28 | Does a dissolution-precipitation mechanism explain concrete creep in moist environments? | Long-term creep (i.e., deformation under sustained load) is a significant
material response that needs to be accounted for in concrete structural design.
However, the nature and origin of creep remains poorly understood, and
controversial. Here, we propose that concrete creep at RH (relative humidity) >
50%, but fixed moisture-contents (i.e., basic creep), arises from a
dissolution-precipitation mechanism, active at nanoscale grain contacts, as is
often observed in a geological context, e.g., when rocks are exposed to
sustained loads, in moist environments. Based on micro-indentation and vertical
scanning interferometry experiments, and molecular dynamics simulations carried
out on calcium-silicate-hydrates (C-S-H's), the major binding phase in
concrete, of different compositions, we show that creep rates are well
correlated to dissolution rates - an observation which supports the
dissolution-precipitation mechanism as the origin of concrete creep. C-S-H
compositions featuring high resistance to dissolution, and hence creep are
identified - analysis of which, using topological constraint theory, indicates
that these compositions present limited relaxation modes on account of their
optimally connected (i.e., constrained) atomic networks. | 1508.07082v1 |
2015-09-11 | High thermoelectric performance and low thermal conductivity of densified LaOBiSSe | In this study, we examined the thermoelectric properties of the layered
bismuth-chalcogenide-based (BiCh2-based) compound LaOBiSSe, which is expected
to be a new candidate material for thermoelectric applications. Densified
samples were obtained with a hot-press method. The results of the X-ray
diffraction measurements showed that the samples obtained were weakly oriented.
This affected the resistivity (r) and Seebeck coefficient (S) of the samples
because they are dependent upon the orientation of the crystal structure. The
values obtained for the power factor (S2/r) when measured perpendicular to the
pressing direction (P1) were higher than that when measured parallel to the
pressing direction (P2). The thermal conductivity (k) of the samples was also
sensitive to the orientation. The values of k measured along P2 were lower than
that measured along P1. The highest figure-of-merit (approximately 0.36) was
obtained at around 650 K in both directions, i.e., P1 and P2. | 1509.03387v1 |
2016-04-22 | Thermoelectric Properties of Antiperovskite Calcium Oxides Ca3PbO and Ca3SnO | We report the thermoelectric properties of polycrystalline samples of
Ca3Pb1-xBixO (x = 0, 0.1, 0.2) and Ca3SnO, both crystallizing in a cubic
antiperovskite-type structure. The Ca3SnO sample shows metallic resistivity and
its thermoelectric power approaches 100 uV K-1 at room temperature, resulting
in the thermoelectric power factor of Ca3SnO being larger than that of
Ca3Pb1-xBixO. On the basis of Hall and Sommerfeld coefficients, the Ca3SnO
sample is found to be a p-type metal with a carrier density of ~1019 cm-3, a
mobility of ~80 cm2 V-1 s-1, both comparable to those in degenerated
semiconductors, and a moderately large hole carrier effective mass. The
coexistence of moderately high mobility and large effective mass observed in
Ca3SnO, as well as possible emergence of a mutivalley electronic structure with
a small band gap at low-symmetry points in k-space, suggests that the
antiperovskite Ca oxides have strong potential as a thermoelectric material. | 1604.06541v2 |
2016-04-26 | A Sinusoidally-Architected Helicoidal Biocomposite | A fibrous herringbone-modified helicoidal architecture is identified within
the exocuticle of an impact-resistant crustacean appendage. This previously
unreported composite microstructure, which features highly textured apatite
mineral templated by an alpha-chitin matrix, provides enhanced stress
redistribution and energy absorption over the traditional helicoidal design
under compressive loading. Nanoscale toughening mechanisms are also identified
using high load nanoindentation and in-situ TEM picoindentation. | 1604.07798v2 |
2016-05-04 | Atomically Thin Boron Nitride: Unique Properties and Applications | Atomically thin boron nitride (BN) is an important two-dimensional (2D)
nanomaterial, with many properties distinct from graphene. In this feature
article, these unique properties and associated applications often not possible
from graphene are outlined. The article starts with characterization and
identification of atomically thin BN. It is followed by demonstrating their
strong oxidation resistance at high temperatures and applications in protecting
metals from oxidation and corrosion. As flat insulators, BN nanosheets are
ideal dielectric substrates for surface enhanced Raman spectroscopy (SERS) and
electronic devices based on 2D heterostructures. The light emission of BN
nanosheets in the deep ultraviolet (DUV) and ultraviolet (UV) regions are also
included for its scientific and technological importance. The last part is
dedicated to synthesis, characterization, and optical properties of BN
nanoribbons, a special form of nanosheets. | 1605.01136v1 |
2016-05-06 | Superconducting gap structure of FeSe | The microscopic mechanism governing the zero-resistance flow of current in
some iron-based, high-temperature superconducting materials is not well
understood up to now. A central issue concerning the investigation of these
materials is their superconducting gap symmetry and structure. Here we present
a combined study of low-temperature specific heat and scanning tunnelling
microscopy measurements on single crystalline FeSe. The results reveal the
existence of at least two superconducting gaps which can be represented by a
phenomenological two-band model. The analysis of the specific heat suggests
significant anisotropy in the gap magnitude with deep gap minima. The tunneling
spectra display an overall "U"-shaped gap close to the Fermi level away as well
as on top of twin boundaries. These results are compatible with the anisotropic
nodeless models describing superconductivity in FeSe. | 1605.01908v2 |
2016-05-24 | Pressure-Induced Confined Metal from the Mott Insulator Sr3Ir2O7 | The spin-orbit Mott insulator Sr3Ir2O7 provides a fascinating playground to
explore insulator-metal transition driven by intertwined charge, spin, and
lattice degrees of freedom. Here, we report high pressure electric resistance
and resonant inelastic x ray scattering measurements on single crystal Sr3Ir2O7
up to 63 65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa,
showing metallicity in the ab plane but an insulating behavior along the c
axis. Such an unusual phenomenon resembles the strange metal phase in cuprate
superconductors. Since there is no sign of the collapse of spin orbit or
Coulomb interactions in x-ray measurements, this novel insulator metal
transition is potentially driven by a first-order structural change at nearby
pressures. Our discovery points to a new approach for synthesizing functional
materials. | 1605.07582v1 |
2016-11-08 | Valley Hall Effect and Nonlocal Transport in Strained Graphene | Graphene subject to high levels of shear strain leads to strong
pseudo-magnetic fields resulting in the emergence of Landau levels. Here we
show that, with modest levels of strain, graphene can also sustain a classical
valley hall effect (VHE) that can be detected in nonlocal transport
measurements. We provide a theory of the strain-induced VHE starting from the
quantum Boltzmann equation. This allows us to show that, averaging over
short-range impurity configurations destroys quantum coherence between valleys,
leaving the elastic scattering time and inter-valley scattering rate as the
only parameters characterizing the transport theory. Using the theory, we
compute the nonlocal resistance of a Hall bar device in the diffusive regime.
Our theory is also relevant for the study of moderate strain effects in the
(nonlocal) transport properties of other two-dimensional materials and van der
Walls heterostructures. | 1611.02382v2 |
2016-11-11 | Microfluidization of graphite and formulation of graphene-based conductive inks | We report the exfoliation of graphite in aqueous solutions under high shear
rate [$\sim10^8s^{-1}$] turbulent flow conditions, with a 100\% exfoliation
yield. The material is stabilized without centrifugation at concentrations up
to 100 g/L using carboxymethylcellulose sodium salt to formulate conductive
printable inks. The sheet resistance of blade coated films is
below$\sim2\Omega/\square$. This is a simple and scalable production route for
graphene-based conductive inks for large area printing in flexible electronics. | 1611.04467v1 |
2016-12-26 | Observation of quantum oscillations in FIB fabricated nanowires of topological insulator (Bi2Se3) | Since last few years, research based on topological insulators (TI) is in
great interests due to intrinsic exotic fundamental properties and future
potential applications such as quantum computers or spintronics. The
fabrication of TI nanodevices and study on their transport properties mostly
focused on high quality crystalline nanowires or nanoribbons. Here we report
robust approach of Bi2Se3 nanowire formation from deposited flakes using ion
beam milling method. The fabricated Bi2Se3 nanowire devices have been employed
to investigate the robustness of topological surface state (TSS) to gallium ion
doping and any deformation in the material due to fabrication tools. We report
the quantum oscillations in magnetoresistance curves under the parallel
magnetic field. The resistance versus magnetic field curves have been studied
and compared with Aharonov-Bohm (AB) interference effects which further
demonstrate the transport through TSS. The fabrication route and observed
electronic transport properties indicate clear quantum oscillations and can be
exploited further in studying the exotic electronic properties associated with
TI based nanodevices. | 1612.08353v1 |
2017-09-26 | SnAs-based layered superconductor NaSn2As2 | Superconductivity with exotic properties has often been discovered in
materials with a layered (two-dimensional) crystal structure. The low
dimensionality affects the electronic structure of materials, which could
realize a high transition temperature (Tc) and/or unconventional pairing
mechanisms. Here, we report the superconductivity in a layered tin arsenide
NaSn2As2. The crystal structure consists of (Sn2As2)2- bilayers, which is bound
by van-der-Waals forces, separated by Na+ ions. Measurements of electrical
resistivity and specific heat confirm the bulk nature of superconductivity of
NaSn2As2 with Tc of 1.3 K. Our results propose that the SnAs layers will be a
basic structure providing another universality class of a layered
superconducting family, and it provides a new platform for the physics and
chemistry of low-dimensional superconductors with lone pair electrons. | 1709.08899v2 |
2017-11-10 | Giant anisotropic magnetoresistance and planar Hall effect in the Dirac semimetal Cd3As2 | Anisotropic magnetoresistance is the change tendency of resistance of a
material on the mutual orientation of the electric current and the external
magnetic field. Here, we report experimental observations in the Dirac
semimetal Cd3As2 of giant anisotropic magnetoresistance and its transverse
version, called the planar Hall effect. The relative anisotropic
magnetoresistance is negative and up to -68% at 2 K and 10 T. The high
anisotropy and the minus sign in this isotropic and nonmagnetic material are
attributed to a field-dependent current along the magnetic field, which may be
induced by the Berry curvature of the band structure. This observation not only
reveals unusual physical phenomena in Weyl and Dirac semimetals, but also finds
additional transport signatures of Weyl and Dirac fermions other than negative
magnetoresistance. | 1711.03671v2 |
2017-11-15 | Revisiting the electron-doped SmFeAsO: enhanced superconductivity up to 58.6 K by Th and F codoping | In the iron-based high-Tc bulk superconductors, Tc above 50K was only
observed in the electron-doped 1111-type compounds. Here we revisit the
electron-doped SmFeAsO polycrystals to make a further investigation for the
highest T-c in these materials. To introduce more electron carriers and less
crystal lattice distortions, we study the Th and F codoping effects into the
Sm-O layers with heavy electron doping. Dozens of Sm1-x Th-x FeAsO1-y F-y
samples are synthesized through the solid state reaction method, and these
samples are carefully characterized by the structural, resistive, and magnetic
measurements. We find that the codoping of Th and F clearly enhances the
superconducting T-c more than the Th or F single-doped samples, with the
highest record T-c up to 58.6K when x= 0.2 and y= 0.225. Further element doping
causes more impurities and lattice distortions in the samples with a weakened
superconductivity. | 1711.05440v1 |
2018-01-19 | Observation of Meissner effect in potassium-doped \emph{p}-quinquephenyl} | The chain-like organic compounds with conjugated structure have the potential
to become high temperature superconductors. We examine this idea by choosing
p-quinquephenyl with five phenyl rings connected in para position. The dc
magnetic susceptibility measurements provide solid evidence for the presence of
Meissner effect when the compound is doped by potassium. The real part of the
ac susceptibility shows exactly same transition temperature as that in dc
magnetization, and the imaginary part of nearly zero value after transition
implies the realization of zero-resistivity. All these features support the
existence of superconductivity with a critical temperature of 7.3 K in this
material. The occurrence of bipolarons revealed by Raman spectra guarantees
potassium metal intercalated into p-quinquephenyl and suggests the important
role of this elementary excitation played on superconductivity. | 1801.06324v2 |
2018-01-19 | Pressure-induced superconductivity in palladium sulfide | An extended study on PdS is carried out with the measurements of the
resistivity, Hall coefficient, Raman scattering, and X-ray diffraction at high
pressures up to 42.3 GPa. With increasing pressure, superconductivity is
observed accompanying with a structural phase transition at around 19.5 GPa.
The coexistence of semiconducting and metallic phases observed at normal state
is examined by the Raman scattering and X-ray diffraction between 19.5 and 29.5
GPa. After that, only the metallic normal state maintains with an almost
constant superconducting transition temperature. The similar evolution between
the superconducting transition temperature and carrier concentration with
pressure supports the phonon-mediated superconductivity in this material. These
results highlight the important role of pressure played in inducing
superconductivity from these narrow band-gap semiconductors. | 1801.06330v1 |
2018-02-07 | Structure, magnetic and transport properties of epitaxial thin films of equiatomic CoFeMnGe quaternary Heusler alloy | Future spintronics requires the realization of thin film of half-metallic
ferromagnets having high Curie temperature and 100\% spin polarization at the
Fermi level for potential spintronics applications. In this paper, we report
the epitaxial thin films growth of half-metallic CoFeMnGe Heusler alloy on MgO
(001) substrate using pulsed laser deposition system, along with the study of
structural, magnetic and transport properties. The magnetic property
measurements of the thin film suggest a soft ferromagnetic state at room
temperature with an in-plane magnetic anisotropy and a Curie temperature well
above the room temperature. Anisotropic magnetoresistance (AMR) ratio and
temperature dependent electrical resistivity measurements of the thin film
indicate the compound to be half-metallic in nature and therefore suitable for
the fabrications of spintronics devices. | 1802.02413v1 |
2018-03-12 | Sub 20 meV Schottky barriers in metal/MoTe2 junctions | The newly emerging class of atomically-thin materials has shown a high
potential for the realisation of novel electronic and optoelectronic
components. Amongst this family, semiconducting transition metal
dichalcogenides (TMDCs) are of particular interest. While their band gaps are
compatible with those of conventional solid state devices, they present a wide
range of exciting new properties that is bound to become a crucial ingredient
in the future of electronics. To utilise these properties for the prospect of
electronics in general, and long-wavelength-based photodetectors in particular,
the Schottky barriers formed upon contact with a metal and the contact
resistance that arises at these interfaces have to be measured and controlled.
We present experimental evidence for the formation of Schottky barriers as low
as 10 meV between MoTe2 and metal electrodes. By varying the electrode work
functions, we demonstrate that Fermi level pinning due to metal induced gap
states at the interfaces occurs at 0.14 eV above the valence band maximum. In
this configuration, thermionic emission is observed for the first time at
temperatures between 40 K and 75 K. Finally, we discuss the ability to tune the
barrier height using a gate electrode. | 1803.04164v1 |
2018-04-09 | Dislocation-induced thermal transport anisotropy in single-crystal group-III nitride films | Dislocations, one-dimensional lattice imperfections, are common to
technologically important materials such as III-V semiconductors, and adversely
affect heat dissipation in e.g., nitride-based high-power electronic devices.
For decades, conventional models based on nonlinear elasticity theory have
predicted this thermal resistance is only appreciable when heat flux is
perpendicular to the dislocations. However, this dislocation-induced
anisotropic thermal transport has yet to be seen experimentally. In this study,
we measure strong thermal transport anisotropy governed by highly oriented
threading dislocation arrays along the cross-plane direction in micron-thick,
single-crystal indium nitride (InN) films. We find that the cross-plane thermal
conductivity is more than tenfold higher than the in-plane thermal conductivity
at 80 K when the dislocation density is on the order of ~3x10^10 cm^-2. This
large anisotropy is not predicted by the conventional models. With enhanced
understanding of dislocation-phonon interactions, our results open new regimes
for tailoring anisotropic thermal transport with line defects, and will
facilitate novel methods for directed heat dissipation in thermal management of
diverse device applications. | 1804.02825v1 |
2018-05-01 | Strongly correlated proton-doped perovskite nickelate memory devices | We demonstrate memory devices based on proton doping and re-distribution in
perovskite nickelates (RNiO3, {R=Sm,Nd}) that undergo filling-controlled Mott
transition. Switching speeds as high as 30 ns in two-terminal devices patterned
by electron-beam lithography is observed. The state switching speed reported
here are 300X greater than what has been noted with proton-driven resistance
switching to date. The ionic-electronic correlated oxide memory devices also
exhibit multi-state non-volatile switching. The results are of relevance to use
of quantum materials in emerging memory and neuromorphic computing. | 1805.00527v1 |
2018-06-21 | Strange metallicity in the doped Hubbard model | Strange or bad metallic transport, defined by its incompatibility with
conventional quasiparticle pictures, is a theme common to strongly correlated
materials and ubiquitous in many high temperature superconductors. The Hubbard
model represents a minimal starting point for modeling strongly correlated
systems. Here we demonstrate strange metallic transport in the doped
two-dimensional Hubbard model using determinantal quantum Monte Carlo
calculations. Over a wide range of doping, we observe resistivities exceeding
the Mott-Ioffe-Regel limit with linear temperature dependence. The temperatures
of our calculations extend to as low as 1/40 the non-interacting bandwidth,
placing our findings in the degenerate regime relevant to experimental
observations of strange metallicity. Our results provide a foundation for
connecting theories of strange metals to models of strongly correlated
materials. | 1806.08346v2 |
2018-09-13 | Superconductivity in LaPd2Bi2 with CaBe2Ge2-type structure | Here we report the synthesis and superconductivity of a novel ternary
compound LaPd2Bi2. Shiny plate-like single crystals of LaPd2Bi2 were first
synthesized by high-temperature solution method with PdBi flux. X-ray
diffraction analysis indicates that LaPd2Bi2 belongs to the primitive
tetragonal CaBe2Ge2-type structure with the space group P4/nmm (No. 129), and
the refined lattice parameters are a = 4.717(2) {\AA}, c = 9.957(3) {\AA}.
Electrical resistivity and magnetic susceptibility measurements reveal that
LaPd2Bi2 undergoes a superconducting transition at 2.83 K and exhibits the
characteristics of type-II superconductivity. The discovery of
superconductivity in LaPd2Bi2 with CaBe2Ge2-type structure may help to further
understand the possible relationship between the occurrence of
superconductivity and the crystal structures in 122-type materials. | 1809.04811v1 |
2019-05-08 | Miniature Multi-Level Optical Memristive Switch Using Phase Change Material | The optical memristive switches are electrically activated optical switches
that can memorize the current state. They can be used as optical latching
switches in which the switching state is changed only by applying an electrical
Write/Erase pulse and maintained without external power supply. We demonstrate
an optical memristive switch based on a silicon MMI structure covered with
nanoscale-size Ge2Sb2Te5 (GST) material on top. The phase change of GST is
triggered by resistive heating of the silicon layer beneath GST with an
electrical pulse. Experimental results reveal that the optical transmissivity
can be tuned in a controllable and repeatable manner with the maximum
transmission contrast exceeding 20 dB. Partial crystallization of GST is
obtained by controlling the width and amplitude of the electric pulses.
Crucially, we also demonstrate that both Erase and Write operations, to and
from any intermediate level, are possible with accurate control of the
electrical pulses. Our work marks a significant step forward towards realizing
photonic memristive switches without static power consumption, which are highly
demanded in high-density large-scale integrated photonics. | 1905.03163v1 |
2020-03-02 | Structural and Magnetic Properties of Molecular Beam Epitaxy Grown Chromium Selenide Thin Films | Chromium selenide thin films were grown epitaxially on Al${_2}$O${_3}$(0001)
and Si(111)-(7${\times}$7) substrates using molecular beam epitaxy (MBE). Sharp
streaks in reflection high-energy electron diffraction and triangular
structures in scanning tunneling microscopy indicate a flat smooth film growth
along the c-axis, and is very similar to that from a hexagonal surface. X-ray
diffraction pattern confirms the growth along the c-axis with c-axis lattice
constant of 17.39 {\AA}. The grown film is semiconducting, having a small band
gap of about 0.034 eV, as calculated from the temperature dependent
resistivity. Antiferromagnetic nature of the film with a N\'eel temperature of
about 40 K is estimated from the magnetic exchange bias measurements. A larger
out-of-plane exchange bias, along with a smaller in-plane exchange bias is
observed below 40 K. Exchange bias training effects are analyzed based on
different models and are observed to be following a modified power-law decay
behavior. | 2003.01199v1 |
2017-03-01 | Chemical and Lattice Stability of the Tin Sulfides | The tin sulfides represent a materials platform for earth-abundant
semiconductor technologies. We present a first-principles study of the five
known and proposed phases of SnS together with SnS2 and Sn2S3. Lattice-dynamics
techniques are used to evaluate the dynamical stability and
temperature-dependent thermodynamic free energy, and we also consider the
effect of dispersion forces on the energetics. The recently identified
{\pi}-cubic phase of SnS is found to be metastable with respect to the
well-known orthorhombic Pnma/Cmcm equilibrium. The Cmcm phase is a low-lying
saddle point between Pnma minima on the potential-energy surface, and is
observed as an average structure at high temperatures. Bulk rocksalt and
zincblende phases are found to be dynamically unstable, and we show that
whereas rocksalt SnS can potentially be stabilised under a reduction of the
lattice constant, the hypothetical zincblende phase proposed in several earlier
studies is extremely unlikely to form. We also investigate the stability of
Sn2S3 with respect to SnS and SnS2, and find that both dispersion forces and
vibrational contributions to the free energy are required to explain its
experimentally-observed resistance to decomposition. | 1703.00361v2 |
2017-03-11 | Sign reversal of magnetoresistance and p to n transition in Ni doped ZnO thin film | We report the magnetoresistance and nonlinear Hall effect studies over a wide
temperature range in pulsed laser deposited Ni0.07Zn0.93O thin film. Negative
and positive contributions to magnetoresistance at high and low temperatures
have been successfully modeled by the localized magnetic moment and two band
conduction process involving heavy and light hole subbands, respectively.
Nonlinearity in the Hall resistance also agrees well with the two channel
conduction model. A negative Hall voltage has been found for T $\gte 50 K$,
implying a dominant conduction mainly by electrons whereas positive Hall
voltage for T less than 50 K shows hole dominated conduction in this material.
Crossover in the sign of magnetoresistance from negative to positive reveals
the spin polarization of the charge carriers and hence the applicability of Ni
doped ZnO thin film for spintronic applications. | 1703.03942v1 |
2018-10-01 | Quantum transport in a compensated semimetal W2As3 with nontrivial Z2 indices | We report a topological semimetal W2As3 with a space group C2/m. Based on the
first-principles calculations, band crossings are partially gapped when
spin-orbit coupling is included. The Z2 indices at the electron filling are
[1;111], characterizing a strong topological insulator and topological surface
states. From the magnetotransport measurements, nearly quadratic field
dependence of magnetoresistance (MR) (B || [200]) at 3 K indicates an
electron-hole compensated compound whose longitudinal MR reaches 115 at 3 K and
15 T. In addition, multiband features are detected from the high-magnetic-field
Shubnikov-de Haas (SdH) oscillation, Hall resistivity, and band calculations. A
nontrivial pi Berry's phase is obtained, suggesting the topological feature of
this material. A two- band model can fit well the conductivity and Hall
coefficient. Our experiments manifest that the transport properties of W2As3
are in good agreement with the theoretical calculations. | 1810.00665v1 |
2019-07-05 | Giant enhancement of Piezo-resistance in ballistic graphene due to transverse electric fields | We investigate the longitudinal and transverse piezoresistance effect in
suspended graphene in the ballistic regime. Utilizing parametrized tight
binding Hamiltonian from ab initio calculations along with Landauer quantum
transport formalism, we devise a methodology to evaluate the piezoresistance
effect in 2D materials especially in graphene. We evaluate the longitudinal and
transverse gauge factor of graphene along armchair and zigzag directions in the
linear elastic limit ($0\%$-$10\%$). The longitudinal and transverse gauge
factors are identical along armchair and zigzag directions. Our model predicts
a significant variation ($\approx 1000\% $ change) in transverse gauge factor
compared to longitudinal gauge factor along with sign inversion. The calculated
value of longitudinal gauge factor is $\approx 0.3$ whereas the transverse
gauge factor is $\approx -3.3$. We rationalize our prediction using deformation
of Dirac cone and change in separation between transverse modes due to
longitudinal and transverse strain, leading to an inverse change in gauge
factor. The results obtained herein may serve as a template for high strain
piezoresistance effect of graphene in nano electromechanical systems. | 1907.02896v1 |
2020-04-23 | Experimental evidence of monolayer AlB$_2$ with symmetry-protected Dirac cones | Monolayer AlB$_2$ is composed of two atomic layers: honeycomb borophene and
triangular aluminum. In contrast with the bulk phase, monolayer AlB$_2$ is
predicted to be a superconductor with a high critical temperature. Here, we
demonstrate that monolayer AlB$_2$ can be synthesized on Al(111) via molecular
beam epitaxy. Our theoretical calculations revealed that the monolayer AlB$_2$
hosts several Dirac cones along the $\Gamma$--M and $\Gamma$--K directions;
these Dirac cones are protected by crystal symmetries and are thus resistant to
external perturbations. The extraordinary electronic structure of the monolayer
AlB$_2$ was confirmed via angle-resolved photoemission spectroscopy
measurements. These results are likely to stimulate further research interest
to explore the exotic properties arising from the interplay of Dirac fermions
and superconductivity in two-dimensional materials. | 2004.10916v1 |
2020-09-13 | Extreme softness of brain matter in simple shear | We show that porcine brain matter can be modelled accurately as a very soft
rubber-like material using the Mooney-Rivlin strain energy function, up to
strains as high as 60\%. This result followed from simple shear experiments
performed on small rectangular fresh samples ($2.5$ cm$^3$ and $1.1$ cm$^3$) at
quasi-static strain rates. They revealed a linear shear stress--shear strain
relationship ($R^2> 0.97 $), characteristic of Mooney-Rivlin materials at large
strains. We found that porcine brain matter is about 30 times less resistant to
shear forces than a silicone gel. We also verified experimentally that brain
matter exhibits the positive Poynting effect of nonlinear elasticity, and
numerically that the stress and strain fields remain mostly homogeneous
throughout the thickness of the samples in simple shear. | 2009.06102v1 |
2020-09-29 | Dimensional Crossover Tuned by Pressure in Layered Magnetic NiPS3 | Layered magnetic transition-metal thiophosphate NiPS3 has unique
two-dimensional (2D) magnetic properties and electronic behavior. The
electronic band structure and corresponding magnetic state are expected to
sensitive to the interlayer interaction, which can be tuned by external
pressure. Here, we report an insulator-metal transition accompanied with
magnetism collapse during the 2D-3D crossover in structure induced by
hydrostatic pressure. A two-stage phase transition from monoclinic (C2=m) to
trigonal (P-31m) lattice is identified by ab initio simulation and confirmed by
high-pressure XRD and Raman data, corresponding to a layer by layer slip
mechanism along the a-axis. Temperature dependence resistance measurements and
room temperature infrared spectroscopy show that the insulator-metal transition
occurs near 20 GPa as well as magnetism collapse, which is further confirmed by
low temperature Raman measurement and theoretical calculation. These results
establish a strong correlation among the structural change, electric transport,
and magnetic phase transition and expand our understandings about the layered
magnetic materials. | 2009.14051v1 |
2022-02-23 | The honeycomb and hyperhoneycomb polymorphs of IrI$_3$ | The synthesis of IrI$_3$ at high pressure in its layered honeycomb polymorph
is reported. Its crystal structure is refined by single crystal X-ray
diffraction. Faults in the honeycomb layer stacking are observed by single
crystal diffraction, synchrotron powder diffraction, and transmission electron
microscopy. A previously unreported hyperhoneycomb polymorph of IrI$_3$
($\beta$-IrI$_3$), is also described. Its structure in space group Fddd is
determined by single crystal XRD. Both materials are highly-resistive
diamagnetic semiconductors, consistent with a low spin d$^6$ configuration for
Ir(III). The two- and three-dimensional Ir arrays in these polymorphs of
IrI$_3$ are analogous to those found in the $\alpha$- and $\beta$- polymorphs
of Li$_2$IrO$_3$, although the Ir electron configurations are different. | 2202.11658v1 |
2014-01-10 | Ferroelectric-like SrTiO3 surface dipoles probed by graphene | The electrical transport properties of graphene are greatly influenced by its
environment. Owing to its high dielectric constant, strontium titanate (STO) is
expected to suppress the long-range charged impurity scattering and
consequently to enhance the mobility. However, the absence of such enhancement
has caused some controversies regarding the scattering mechanism. In graphene
devices transferred from SiO2 to STO using a newly developed technique, we
observe a moderate mobility enhancement near the Dirac point, which is the
point of charge neutrality achieved by adjusting the Fermi level. While bulk
STO is not known as a ferroelectric material, its surface was previously
reported to exhibit an outward displacement of oxygen atoms and
ferroelectric-like dipole moment. When placed on STO, graphene shows strong and
asymmetric hysteresis in resistivity, which is consistent with the dipole
picture associated with the oxygen displacement. The hysteretic response of the
surface dipole moment diminishes the polarizability, therefore weakens the
ability of STO to screen the Coulomb potential of the impurities. | 1401.2222v1 |
2017-05-01 | Large Thermoelectric Power Factor at Low Temperatures in One-Dimensional Telluride Ta4SiTe4 | We report the discovery of a very large thermoelectric power over -400 microV
K-1 in the whisker crystals of a one-dimensional telluride Ta4SiTe4, while
maintaining a low electrical resistivity of rho = 2 mohm cm, yielding a very
large power factor of P = 80 microW cm-1 K-2 at an optimum temperature of 130
K. This temperature is widely controlled from the cryogenic temperature of 50 K
to room temperature by chemical doping, resulting in the largest P of 170
microW cm-1 K-2 at 220-280 K. These P values far exceed those of the
Bi2Te3-Sb2Te3 alloys at around room temperature, offering an avenue for
realizing the practical-level thermoelectric cooling at low temperatures. The
coexistence of a one-dimensional electronic structure and a very small band gap
appearing in the vicinity of the Dirac semimetals probably causes the very
large power factors in Ta4SiTe4, indicating that the "one-dimensional Dirac
semimetal" is a promising way to find high-performance thermoelectric materials
for the low temperature applications. | 1705.00404v1 |
2017-08-25 | Spin torque control of antiferromagnetic moments in NiO | For a long time, there have been no efficient ways of controlling
antiferromagnets. Quite a strong magnetic field was required to manipulate the
magnetic moments because of a high molecular field and a small magnetic
susceptibility. It was also difficult to detect the orientation of the magnetic
moments since the net magnetic moment is effectively zero. For these reasons,
research on antiferromagnets has not been progressed as drastically as that on
ferromagnets which are the main materials in modern spintronic devices. Here we
show that the magnetic moments in NiO, a typical natural antiferromagnet, can
indeed be controlled by the spin torque with a relatively small electric
current density (~5 x 10^7 A/cm^2) and their orientation is detected by the
transverse resistance resulting from the spin Hall magnetoresistance . The
demonstrated techniques of controlling and detecting antiferromagnets would
outstandingly promote the methodologies in the recently emerged
"antiferromagnetic spintronics". Furthermore, our results essentially lead to a
spin torque antiferromagnetic memory. | 1708.07682v1 |
2019-03-13 | Hydrodynamic Phonon Transport: Past, Present, and Prospect | The hydrodynamic phonon transport was studied several decades ago for
verifying the quantum theory of lattice thermal transport. Recent prediction of
significant hydrodynamic phonon transport in graphitic materials shows its
practical importance for high thermal conductivity materials and brought a
renewed attention. As the study on this topic has been inactive to some extent
for several decades, we aim at providing a brief overview of the past studies
as well as very recent studies. The topics we discuss in this chapter include
the collective motion of phonons, several approaches to solve the
Peierls-Boltzmann transport equation for hydrodynamic phonon transport, the
role of normal scattering for thermal resistance, and the propagation of second
sound. Then, we close this chapter with our perspectives for the future studies
and the practical implication of hydrodynamic phonon transport. | 1903.05731v1 |
2019-04-12 | Synthesis of anti-perovskite-type carbides and nitrides from metal oxides and melamine | Four anti-perovskite-type compounds, ZnNNi3, ZnCNi3, SnNCo3, and SnCCo3, are
synthesised through reactions between ingredient metal oxides and organic
compound melamine (C3H6N6). ZnNNi3 and ZnCNi3 are selectively synthesised by
choosing different reaction temperatures and nominal oxide-to-melamine ratios.
SnNCo3 is synthesised for the first time by this melamine method. Resistivity,
magnetisation, and heat capacity measurements reveal that SnNCo3 is a
correlated metal with a high density of states at the Fermi level. Our results
demonstrate that this feasible synthetic route using melamine is useful in the
search for complex metal carbides and nitrides toward novel functional
materials. | 1904.06103v1 |
2019-12-23 | Hydride Vapor-Phase Epitaxy Reactor for Bulk GaN Growth | An HVPE reactor for the growth of bulk GaN crystals with a diameter of 50 mm
was developed. Growth rate non-uniformity of 1% was achieved using an
axisymmetric vertical gas injector with stagnation point flow.
Chemically-resistant refractory materials were used instead of quartz in the
reactor hot zone. High-capacity external gallium precursor sources were
developed for the non-stop growth of the bulk GaN layers. A load-lock vacuum
chamber and a dry in-situ growth chamber cleaning were implemented to improve
the growth process reproducibility. Freestanding GaN crystals with a diameter
of 50 mm were grown with the reactor. | 1912.11010v1 |
2012-03-27 | Shadow evaporation of epitaxial Al/Al2O3/Al tunnel junctions on sapphire utilizing an inorganic bilayer mask | This letter describes a new inorganic shadow mask that has been employed for
the evaporation of all-epitaxial Al/Al2O3/Al superconducting tunnel junctions.
Organic resists that are commonly used for shadow masks and other lift-off
processes are not compatible with ultra-high vacuum deposition systems, and
they can break down at even moderately elevated temperatures. The inorganic
mask described herein does not suffer these same shortcomings. It was
fabricated from a Ge/Nb bilayer, comprising suspended Nb bridges supported by
an undercut Ge sacrificial layer. Utilizing such a bilayer mask on C-plane
sapphire, the growth of epitaxial Al tunnel junctions was achieved using
molecular beam epitaxy. Crystalline Al2O3 was grown diffusively at 300 C in a
molecular oxygen background of 2.0 utorr, while amorphous oxide was grown at
room temperature and 25 mtorr. A variety of analysis techniques were employed
to evaluate the materials, and tunnel junction current-voltage characteristics
were measured at millikelvin temperatures. | 1203.6007v1 |
2012-06-14 | Conduction in jammed systems of tetrahedra | Control of transport processes in composite microstructures is critical to
the development of high performance functional materials for a variety of
energy storage applications. The fundamental process of conduction and its
control through the manipulation of granular composite attributes (e.g., grain
shape) are the subject of this work. We show that athermally jammed packings of
tetrahedra with ultra-short range order exhibit fundamentally different
pathways for conduction than those in dense sphere packings. Highly resistive
granular constrictions and few face-face contacts between grains result in
short-range distortions from the mean temperature field. As a consequence,
'granular' or differential effective medium theory predicts the conductivity of
this media within 10% at the jamming point; in contrast, strong enhancement of
transport near interparticle contacts in packed-sphere composites results in
conductivity divergence at the jamming onset. The results are expected to be
particularly relevant to the development of nanomaterials, where nanoparticle
building blocks can exhibit a variety of faceted shapes. | 1206.2990v1 |
2016-09-06 | Effect of morphology and defectiveness of graphene-related materials on the electrical and thermal conductivity of their polymer nanocomposites | In this work, electrically and thermally conductive poly (butylene
terephthalate) nanocomposites were prepared by in-situ ring-opening
polymerization of cyclic butylene terephthalate (CBT) in presence of a
tin-based catalyst. One type of graphite nanoplatelets (GNP) and two different
grades of reduced graphene oxide (rGO) were used. Furthermore, high temperature
annealing treatment under vacuum at 1700{\deg}C was carried out on both RGO to
reduce their defectiveness and study the correlation between the
electrical/thermal properties of the nanocomposites and the nanoflakes
structure/defectiveness. The morphology and quality of the nanomaterials were
investigated by means of electron microscopy, x-ray photoelectron spectroscopy,
thermogravimetry and Raman spectroscopy. Thermal, mechanical and electrical
properties of the nanocomposites were investigated by means of rheology,
dynamic mechanical thermal analysis, volumetric resistivity and thermal
conductivity measurements. Physical properties of nanocomposites were
correlated with the structure and defectiveness of nanoflakes, evidencing a
strong dependence of properties on nanoflakes structure and defectiveness. In
particular, a significant enhancement of both thermal and electrical
conductivities was demonstrated upon the reduction of nanoflakes defectiveness. | 1609.01581v2 |
2016-09-22 | Crystal structure and low-energy Einstein mode in ErV$_2$Al$_{20}$ intermetallic cage compound | Single crystals of a new ternary aluminide ErV$_2$Al$_{20}$ were grown using
a self-flux method. The crystal structure was determined by powder X-ray
diffraction measurements and Rietveld refinement, and physical properties were
studied by means of electrical resistivity, magnetic susceptibility and
specific heat measurements. These measurements reveal that ErV$_2$Al$_{20}$ is
a Curie-Weiss paramagnet down to 1.95 K with an effective magnetic moment
$\mu_{eff}$ = 9.27(1) $\mu_B$ and Curie-Weiss temperature $\Theta_{CW}$ =
-0.55(4) K. The heat capacity measurements show a broad anomaly at low
temperatures that is attributed to the presence of a low-energy Einstein mode
with characteristic temperature $\Theta_E$ = 44 K, approximately twice as high
as in the isostructural 'Einstein solid' VAl$_{10.1}$. | 1609.07161v1 |
2020-05-11 | Crystal Structure and Thermoelectric Transport Properties of As-Doped Layered Pnictogen Oxyselenides NdO0.8F0.2Sb1-xAsxSe2 | We report the synthesis and thermoelectric transport properties of As-doped
layered pnictogen oxyselenides NdO0.8F0.2Sb1-xAsxSe2 (x < 0.7), which are
predicted to show high-performance thermoelectric properties based on
first-principles calculation. The crystal structure of these compounds belongs
to the tetragonal P4/nmm space group (No. 129) at room temperature. The lattice
parameter c decreases with increasing x, while a remains almost unchanged among
the samples. Despite isovalent substitution of As for Sb, electrical
resistivity significantly rises with increasing x. Very low thermal
conductivity of less than 0.8 W/mK is observed at temperatures between 300 and
673 K for all the examined samples. For As-doped samples, the thermal
conductivity further decreases above 600 K. Temperature-dependent synchrotron
X-ray diffraction indicates that an anomaly also occurs in the c-axis length at
around 600 K, which may relate to the thermal transport properties. | 2005.04836v1 |
2020-05-17 | Paramagnetic resonance in La2NiMnO6 probed by impedance and lock-in detection techniques | We report the detection of paramagnetic resonance in the double perovskite
La2NiMnO6 at room temperature for microwave magnetic fields with frequencies, f
= 1 GHz to 5 GHz, using two cavity-less methods. We use an indirect impedance
method which makes use of a radio frequency impedance analyzer and a folded
copper strip coil for the frequency range f = 1 to 2.2 GHz. In this method,
when an applied dc magnetic field is swept, high-frequency resistance of the
strip coil exhibits a sharp peak and the reactance curve crosses zero
exhibiting resonance. A lock-in based broadband setup using a coplanar
waveguide for microwave excitation was used for f = 2 to 5 GHz The resonance
fields (Hr) obtained from both the techniques increase linearly with frequency
and a large spectroscopic g-factor, equal to 2.1284, which supports the
presence of Ni2+ cation with strong spin-orbit coupling. Line shape analysis
and analytical fitting were performed to characterize the material in terms of
its initial susceptibility and damping parameters. | 2005.08142v1 |
2020-05-19 | Molecular beam epitaxy growth of nonmagnetic Weyl semimetal LaAlGe thin film | Here, we report a detailed method of growing LaAlGe, a non-magnetic Weyl
semimetal, thin film on silicon(100) substrates by molecular beam epitaxy and
their structural and electrical characterizations. 50 nm thick LaAlGe films
were deposited and annealed for 16 hours in situ at a temperature 793 K.
As-grown high-quality films showed uniform surface topography and near ideal
stoichiometry with a body-centered tetragonal crystal structure.
Temperature-dependent longitudinal resistivity can be understood with dominant
interband s-d electron-phonon scattering in the temperature range 5-40 K. Hall
measurements confirmed the semimetallic nature of the films with electron
dominated charge carrier density near 7.15*10^21 cm^-3 at 5 K. | 2005.09695v1 |
2020-07-13 | One nanometer HfO$_2$-based ferroelectric tunnel junctions on silicon | In ferroelectric materials, spontaneous symmetry breaking leads to a
switchable electric polarization, which offers significant promise for
nonvolatile memories. In particular, ferroelectric tunnel junctions (FTJs) have
emerged as a new resistive switching memory which exploit
polarization-dependent tunnel current across a thin ferroelectric barrier. Here
we demonstrate FTJs with CMOS-compatible Zr-doped HfO$_2$ (Zr:HfO$_2$)
ferroelectric barriers of just 1 nm thickness, grown by atomic layer deposition
on silicon. These 1 nm Zr:HfO$_2$ tunnel junctions exhibit large
polarization-driven electroresistance (19000$\%$), the largest value reported
for HfO$_2$-based FTJs. In addition, due to just a 1 nm ferroelectric barrier,
these junctions provide large tunnel current (> 1 A/cm$^2$) at low read
voltage, orders of magnitude larger than reported thicker HfO$_2$-based FTJs.
Therefore, our proof-of-principle demonstration provides an approach to
simultaneously overcome three major drawbacks of prototypical FTJs: a
Si-compatible ultrathin ferroelectric, large electroresistance, and large read
current for high-speed operation. | 2007.06182v1 |
2020-08-03 | Energy gap tuning and gate-controlled topological phase transition in InAs/In$_{x}$Ga$_{1-x}$Sb composite quantum wells | We report transport measurements of strained InAs/In$_{x}$Ga$_{1-x}$Sb
composite quantum wells (CQWs) in the quantum spin Hall phase, focusing on the
control of the energy gap through structural parameters and an external
electric field. For highly strained CQWs with $x = 0.4$, we obtain a gap of 35
meV, an order of magnitude larger than that reported for binary InAs/GaSb CQWs.
Using a dual-gate configuration, we demonstrate an electrical-field-driven
topological phase transition, which manifests itself as a re-entrant behavior
of the energy gap. The sizeable energy gap and high bulk resistivity obtained
in both the topological and normal phases of a single device open the
possibility of electrical switching of the edge transport. | 2008.00664v1 |
2020-08-15 | Microwave AC voltage induced phase change in Sb$_2$Te$_3$ nanowires | Scaling information bits to ever smaller dimensions is a dominant drive for
information technology (IT). Nanostructured phase change material emerges as a
key player in the current green-IT endeavor with low power consumption,
functional modularity and promising scalability. In this work, we present the
demonstration of microwave AC voltage induced phase change phenomenon at 3 GHz
in single Sb$_2$Te$_3$ nanowires. The resistance change by a total of 6 - 7
orders of magnitude is evidenced by a transition from the crystalline metallic
to the amorphous semiconducting phase, which is cross-examined by temperature
dependent transport measurement and high-resolution electron microscopy
analysis. This discovery could potentially tailor multi-state information bit
encoding and discrimination along a single nanowire, rendering technology
advancement for neuro-inspired computing devices. | 2008.06666v1 |
2020-10-23 | Observation of photoelectric nonvolatile memory and oscillations in VO2 at room temperature | Vanadium dioxide (VO2) is a phase change material that can reversibly change
between high and low resistivity states through electronic and structural phase
transitions. Thus far, VO2 memory devices have essentially been volatile at
room temperature, and nonvolatile memory has required non-ambient surroundings
(e.g., elevated temperatures, electrolytes) and long write times. Here, we
report the first observation of optically addressable nonvolatile memory in VO2
at room temperature with a readout by voltage oscillations. The read and write
times had to be kept shorter than about 150 {\mu}s. The writing of the memory
and onset of the voltage oscillations had a minimum optical power threshold.
This discovery demonstrates the potential of VO2 for new computing devices and
architectures, such as artificial neurons and oscillatory neural networks. | 2010.12531v1 |
2020-11-17 | Effect of Surface Treatment on High-Temperature Oxidation Behavior of IN 713C | The effects of surface preparations on oxidation kinetics and oxide scale
morphology for the commercially available Ni-based superalloy IN 713C have been
investigated. The ground and polished samples were exposed in air at 800-1100C.
The ground specimens were found to demonstrate lower oxidation kinetics
compared to those after polishing. The grinding also affected the oxide scale
morphology, resulting in a protective alumina scale, while the polished samples
developed Ni-/Cr-rich mixed oxides on the surface. Better oxidation resistance
of the ground surfaces is related to a higher concentration of defects in the
nearsurface region introduced by cold working. These defects facilitate the
outward transport of the scaleforming element Al and thus are beneficial for
protective oxidation. The oxidation mechanism at lower temperatures was
introduced. The model based on the generalized Darken method and multiphase
approximation was proposed. | 2011.08910v1 |
2021-02-01 | Resistive transition of hydrogen-rich superconductors | Critical temperature, $T_c$, and the transition width, $\Delta$$T_c$, are two
primary parameters of the superconducting transition. The latter parameter
reflects the superconducting state disturbance originating from the
thermodynamic fluctuations, atomic disorder, applied magnetic field, the
presence of secondary crystalline phases, applied pressure, etc. Recently,
Hirsch and Marsiglio (2020 arXiv:2012.12796) performed an analysis of the
transition width in several near-room-temperature superconductors (NRTS) and
reported that the reduced transition width, $\Delta$$T_c$$/$$T_c$, in these
materials does not follow a conventional trend of transition width broadening
on applied magnetic field observed in low- and high-$T_c$ superconductors. Here
we present thorough mathematical analysis of the magnetoresistive data,
$\it{R(T,B)}$, for the high-entropy alloy $(ScZrNb)_{0.65}$$[RhPd]_{0.35}$ and
hydrogen-rich superconductors of Im-3m-$H_{3}S$, C2/m-$LaH_{10}$ and
P63/mmc-$CeH_9$. We found that the reduced transition width,
$\Delta$$T_c$$/$$T_c$, in these materials does follow a conventional broadening
trend on applied magnetic field. | 2102.00946v3 |
2021-02-10 | Evidence of damage in carbon fibre composite tiles joined to a metallic heat sink under high heat flux fatigue | The two years experience with Active Metal Casting flat bonds shows that this
technology is suitable for the heat fluxes expected in Tore Supra (10
MW/m${}^2$). Tests were pursued up to 3330 cycles, with elements still
functional. At higher heat fluxes, fatigue damage is observed, but the bond
resists remarkably well with no tile detachment. Examination of such
deliberately damaged bonds showed distributed cracking, proving the absence of
any weak link. The limitations to those higher heat fluxes are more related to
the design and the base materials than to the bond itself. | 2102.05316v1 |
2021-03-14 | Electron-beam Floating-zone Refined UCoGe | The interplay between unconventional superconductivity and quantum critical
ferromagnetism in the U-Ge compounds represents an open problem in strongly
correlated electron systems. Sample quality can have a strong influence on both
of these ordered states in the compound UCoGe, as is true for most
unconventional superconductors. We report results of a new approach at UCoGe
crystal growth using a floating-zone method with potential for improvements of
sample quality and size as compared with traditional means such as Czochralski
growth. Single crystals of the ferromagnetic superconductor UCoGe were produced
using an ultra-high vacuum electron-beam floating-zone refining technique.
Annealed single crystals show well-defined signatures of bulk ferromagnetism
and superconductivity at $T_c \sim$2.6 K and $T_s \sim$0.55 K, respectively, in
the resistivity and heat capacity. Scanning electron microscopy of samples with
different surface treatments shows evidence of an off-stoichiometric uranium
rich phase of UCoGe collected in cracks and voids that might be limiting sample
quality. | 2103.08000v1 |
2021-03-24 | Large Nernst effect and field enhanced transversal ZT in ZrTe5 | Thermoelectric materials can recover electrical energy from waste heat and
vice versa, which are of great significance in green energy harvesting and
solid state refrigerator. The thermoelectric figure of merit (zT) quantifies
the energy conversion efficiency, and a large Seebeck or Nernst effect is
crucial for the development of thermoelectric devices. Here we present a
significantly large Nernst thermopower in topological semimetal ZrTe5, which is
attributed to both strong Berry curvature and bipolar transport. The largest
in-plane S_xy (when B//b) approaches 1900 {\mu}V/K at T=100K and B=13T, and the
out-of-plane S_xz (when B//c) reaches 5000 {\mu}V/K. As a critical part of z_N
T, the linearly increased in-plane S_xy and resistivity \r{ho}_yy regard to B
induces an almost linear increasing transversal z_N T without saturate under
high fields. The maximum z_N T of 0.12 was obtained at B=13 T and T= 120K,
which significantly surmounts its longitudinal counterpart under the same
condition. | 2103.13069v1 |
2021-03-26 | Large Microwave Inductance of Granular Boron-Doped Diamond Superconducting Films | Boron-doped diamond granular thin films are known to exhibit
superconductivity with an optimal critical temperature of Tc = 7.2K. Here we
report the measured complex surface impedance of Boron-doped diamond films in
the microwave frequency range using a resonant technique. Experimentally
measured inductance values are in good agreement with estimates obtained from
the normal state sheet resistance of the material. The magnetic penetration
depth temperature dependence is consistent with that of a fully-gapped s-wave
superconductor. Boron-doped diamond films should find application where high
kinetic inductance is needed, such as microwave kinetic inductance detectors
and quantum impedance devices. | 2103.14738v3 |
2021-06-25 | An estimate for thermal diffusivity in highly irradiated tungsten using Molecular Dynamics simulation | The changing thermal conductivity of an irradiated material is among the
principal design considerations for any nuclear reactor, but at present few
models are capable of predicting these changes starting from an arbitrary
atomistic model. Here we present a simple model for computing the thermal
diffusivity of tungsten, based on the conductivity of the perfect crystal and
resistivity per Frenkel pair, and dividing a simulation into perfect and
athermal regions statistically. This is applied to highly irradiated
microstructures simulated with Molecular Dynamics. A comparison to experiment
shows that simulations closely track observed thermal diffusivity over a range
of doses from the dilute limit of a few Frenkel pairs to the high dose
saturation limit at 3 displacements per atom (dpa). | 2106.13666v2 |
2021-07-15 | Microstructure manipulation by laser-surface remelting of a full-Heusler compound to enhance thermoelectric properties | There is an increasing reckoning that the thermoelectric performance of a
material is dependent on its microstructure. However, the
microstructure-properties relationship often remains elusive, in part due to
the complexity of the hierarchy and scales of features that influence transport
properties. Here, we focus on the promising Heusler-Fe2VAl compound. We
directly correlate microstructure and local properties, using advanced scanning
electron microscopy methods including in-situ four-point-probe technique for
electron transport measurements. The local thermal conductivity is investigated
by scanning thermal microscopy. Finally, atom probe tomography provides
near-atomic scale compositional analysis. To locally manipulate the
microstructure, we use laser surface remelting. The rapid quenching creates a
complex microstructure with a high density of dislocations and small, elongated
grains. We hence showcase that laser surface remelting can be employed to
manipulate the microstructure to reduce the thermal conductivity and electrical
resistivity, leading to a demonstrated enhancement of the thermoelectric
performance at room temperature. | 2107.07327v1 |
2021-07-29 | Breakdown of the topological protection by cavity vacuum fields in the integer quantum Hall effect | The control of the electronic properties of materials via the vacuum fields
of cavity electromagnetic resonators is one of the emerging frontiers of
condensed matter physics. We show here that the enhancement of vacuum field
fluctuations in subwavelength split-ring resonators dramatically affects
arguably one of the most paradigmatic quantum protectorates, namely the quantum
Hall electron transport in high-mobility 2D electron gases. The observed
breakdown of the topological protection of the integer quantum Hall effect is
interpreted in terms of a long-range cavity-mediated electron hopping where the
anti-resonant terms of the light-matter coupling finally result into a finite
resistivity induced by the vacuum fluctuations. The present experimental
platform can be used for any 2D material and provides new ways to manipulate
electron phases in matter thanks to vacuum-field engineering | 2107.14145v1 |
2021-09-03 | Quantum anomalous Hall edge channels survive up to the Curie temperature | Achieving metrological precision of quantum anomalous Hall resistance
quantization at zero magnetic field so far remains limited to temperatures of
the order of 20 mK, while the Curie temperature in the involved material is as
high as 20 K. The reason for this discrepancy remains one of the biggest open
questions surrounding the effect, and is the focus of this article. Here we
show, through a careful analysis of the non-local voltages on a multi-terminal
Corbino geometry, that the chiral edge channels continue to exist without
applied magnetic field up to the Curie temperature of bulk ferromagnetism of
the magnetic topological insulator, and that thermally activated bulk
conductance is responsible for this quantization breakdown. Our results offer
important insights on the nature of the topological protection of these edge
channels, provide an encouraging sign for potential applications, and establish
the multi-terminal Corbino geometry as a powerful tool for the study of edge
channel transport in topological materials. | 2109.01463v1 |
2021-11-03 | Insulator-to-superconductor transition in quasi-one-dimensional HfS3 under pressure | Various transition metal trichalcogenides (TMTC) show the charge-density-wave
and superconductivity, which provide an ideal platform to study the correlation
between these two orderings and the mechanism of superconductivity. Currently,
almost all metallic TMTC compounds can show superconductivity either at ambient
pressure or at high pressure. However, most TMTC compounds are semiconductors
and even insulators. Does the superconductivity exist in any non-metal TMTC
compound? In this work, we managed to manipulate the electronic behavior of
highly insulating HfS3 in term of pressure. HfS3 underwent an
insulator-semiconductor transition near 17 GPa with a band gap reduce of ~1 eV.
The optical absorption and Raman measurement provide the consistent results,
suggesting the structural origin of the electronic transition. Upon further
compression, HfS3 becomes a superconductor. The superconducting transition was
initialized as early as 50.6 GPa and the zero-resistance is reached above 91.2
GPa. The superconducting behavior is further confirmed by both the magnetic
field effect and current effect. This work sheds the light that all TMTC may be
superconductors, and opens a new avenue to explore the abundant emergence
phenomena in TMTC material family. | 2111.02060v1 |
2021-11-16 | Ultrathin ferrimagnetic GdFeCo films with very low damping | Ferromagnetic materials dominate as the magnetically active element in
spintronic devices, but come with drawbacks such as large stray fields, and low
operational frequencies. Compensated ferrimagnets provide an alternative as
they combine the ultrafast magnetization dynamics of antiferromagnets with a
ferromagnet-like spin-orbit-torque (SOT) behavior. However to use ferrimagnets
in spintronic devices their advantageous properties must be retained also in
ultrathin films (t < 10 nm). In this study, ferrimagnetic Gdx(Fe87.5Co12.5)1-x
thin films in the thickness range t = 2-20 nm were grown on high resistance
Si(100) substrates and studied using broadband ferromagnetic resonance
measurements at room temperature. By tuning their stoichiometry, a nearly
compensated behavior is observed in 2 nm Gdx(Fe87.5Co12.5)1-x ultrathin films
for the first time, with an effective magnetization of Meff = 0.02 T and a low
effective Gilbert damping constant of {\alpha} = 0.0078, comparable to the
lowest values reported so far in 30 nm films. These results show great promise
for the development of ultrafast and energy efficient ferrimagnetic spintronic
devices. | 2111.08768v1 |
2021-12-06 | Sliding Ferroelectric Tunnel Junctions | Very recently, ferroelectric polarization in staggered bilayer hexagonal
boron nitride (BBN) and its novel sliding inversion mechanism was reported
experimentally (Science 2021, 372, 1458; 2021, 372, 1462), which paves a new
way to realize van der Waals (vdW) ferroelectric devices with new
functionalities. Here, we develop vdW sliding ferroelectric tunnel junctions
(FTJs) using the sliding ferroelectric BBN unit as ultrathin barriers and
explore their transport properties with different ferroelectric states and
metal contacts via the first principles. It is found that the electrode/BBN
contact electric field quenches the ferroelectricity in the staggered BBN,
resulting a very small tunnelling electroresistance (TER). Inserting
high-mobility 2D materials between Au and BN can restore the BBN
ferroelectricity, reaching a giant TER of ~10,000% in sliding FTJs. We finally
investigate the metal-contact and thickness effect on the tunnelling property
of sliding FTJs. The giant TER and multiple non-volatile resistance states in
vdW sliding FTJs show the promising applications in voltage-controlled
nano-memories with ultrahigh storage density. | 2112.02886v1 |
2022-06-06 | Enhancement of superconductivity on the verge of a structural instability in isovalently doped $β$-ThRh$_{1-x}$Ir$_{x}$Ge | $\beta$-ThRhGe, the high-temperature polymorph of ThRhGe, is isostructural to
the well-known ferromagnetic superconductor URhGe. However, contrary to URhGe,
$\beta$-ThRhGe is nonmagnetic and undergoes an incomplete structural phase
transition at 244 K, followed by a superconducting transition below 3.36 K.
Here we show that the isovalent substitution of Ir for Rh leads to a strong
enhancement of superconductivity by suppressing the structural transition. At
$x$ = 0.5, where the structural transition disappears, $T_{\rm c}$ reaches a
maximum of 6.88 K. The enhancement of superconductivity is linked to the
proximity to a structural quantum critical point at this Ir concentration, as
suggested by the analysis of thermodynamic as well as resistivity data. First
principles calculations indicate that the Ir doping has little effect on the
electronic band dispersion near the Fermi level. $\beta$-ThRh$_{1-x}$Ir$_{x}$Ge
thus provides an excellent platform to study the interplay between
superconductivity and structural quantum criticality in actinide-containing
compounds. | 2206.02364v1 |
2022-06-21 | HR-EBSD analysis of in situ stable crack growth at the micron scale | Understanding the local fracture resistance of microstructural features. such
as brittle inclusions, coatings, and interfaces at the microscale under complex
loading conditions is critical for microstructure-informed design of materials.
In this study, a novel approach has been formulated to decompose the J-integral
evaluation of the elastic energy release rate to the three-dimensional stress
intensity factors directly from experimental measurements of the elastic
deformation gradient tensors of the crack field by in situ high (angular)
resolution electron backscatter diffraction (HR-EBSD). An exemplar study is
presented of a quasi-static crack, inclined to the observed surface,
propagating on low index {hkl} planes in a (001) single crystal silicon wafer. | 2206.10243v2 |
2022-10-01 | Surface modulation of metal-organic frameworks for on-demand photochromism in the solid state | Organic photoswitchable molecules have struggled in solid state form to
fulfill their remarkable potential, in terms of photoswitching performance and
long-term stability when compared to their inorganic counterparts. We report
the concept of non-electron deficient host's surface with optimal porosity and
hydrophobicity, as a priori strategy to design photoefficient organic
solid-state photochromic materials with outstanding mechanical robustness. When
exposed to a light stimulus including natural sunlight, the photoswitchable
nanocomposite changes color promptly and reversibly, in a matter of seconds
along with excellent photo-fatigue resistance, which are on a par with
inorganic photochromes. Exemplars of commercially viable prototypes that are
optically clear, comprising smart windows, complex photochromic sculptures, and
self-erasing rewritable devices, were engineered by direct blending with
resilient polymers; particularly, the use of high-stiffness polymer (> 2 GPa)
is no longer an insurmountable challenge. Finally, photochromic films with
anticounterfeiting features could be manufactured through precision inkjet
printing of nanocrystals. | 2210.00241v1 |
2022-10-06 | Fracture behavior of MOF monoliths revealed by nanoindentation and nanoscratch | Monolithic metal-organic frameworks (MOFs) represent a promising solution for
the industrial implementation of this emerging class of multifunctional
materials, due to their structural stability. When compared to MOF powders,
monoliths exhibit other intriguing properties like hierarchical porosity, that
significantly improves volumetric adsorption capacity. The mechanical
characterization of MOF monoliths plays a pivotal role in their industrial
expansion, but so far, several key aspects remain unclear. In particular, the
fracture behavior of MOF monoliths has not been explored. In this work, we
studied the initiation and propagation of cracks in four prototypical MOF
monoliths, namely ZIF-8, HKUST-1, MIL-68 and MOF-808. We observed that shear
faults inside the contact area represent the main failure mechanism of MOF
monoliths and are the source of radial cracks. MIL-68 and MOF-808 showed a
remarkably high resistance to cracking, which can be ascribed to their
consolidated nanostructure. | 2210.03219v1 |
2022-10-26 | Thermoelectric properties in semimetals with inelastic electron-hole scattering | We present systematic theoretical results on thermoelectric effects in
semimetals based on the variational method of the linearized Boltzmann
equation. Inelastic electron-hole scattering is known to play an important role
in the unusual transport of semimetals, including the broad $T^2$ temperature
dependence of the electrical resistivity and the strong violation of the
Wiedemann-Franz law. By treating the inelastic electron-hole scattering more
precisely beyond the relaxation time approximation, we show that the Seebeck
coefficient when compensated depends on the screening length of the Coulomb
interaction as well as the Lorenz ratio (the ratio of thermal to electric
conductivity due to electrons divided by temperature). It is found that
deviations from the compensation condition significantly increase the Seebeck
coefficient, along with crucial suppressions of the Lorenz ratio. The result
indicates that uncompensated semimetals with the electron-hole scattering have
high thermoelectric efficiency when the phonon contribution to thermal
conductivity is suppressed. | 2210.14825v2 |
2023-01-10 | Depolarization Induced III-V Triatomic Layers with Tristable Polarization States | The integration of ferroelectrics that exhibit high dielectric,
piezoelectric, and thermal susceptibilities with the mainstream semiconductor
industry will enable novel device types for widespread applications, and yet
there are few silicon-compatible ferroelectrics suitable for device
downscaling. We demonstrate with first-principles calculations that the
enhanced depolarization field at the nanoscale can be utilized to soften
unswitchable wurtzite III-V semiconductors, resulting in ultrathin
two-dimensional (2D) sheets possessing reversible polarization states. A 2D
sheet of AlSb consisting of three atomic planes is identified to host both
ferroelectricity and antiferroelectricity, and the tristate switching is
accompanied by a metal-semiconductor transition. The thermodynamics stability
and potential synthesizability of the triatomic layer are corroborated with
phonon spectrum calculations, ab initio molecular dynamics, and
variable-composition evolutionary structure search. We propose a 2D AlSb-based
homojunction field effect transistor that supports three distinct and
nonvolatile resistance states. This new class of III-V semiconductor-derived 2D
materials with dual ferroelectricity and antiferroelectricity opens up the
possibility for nonvolatile multibit-based integrated nanoelectronics. | 2301.03876v1 |
2023-01-11 | Direct imaging of local atomic structures in zeolite using novel low-dose scanning transmission electron microscopy | Zeolites have been used in industrial applications such as catalysts, ion
exchangers, and molecular sieves because of their unique porous atomic
structures. However, the direct observation of zeolitic local atomic structures
via electron microscopy is difficult owing to their low resistance to electron
irradiation. Subsequently, the fundamental relationships between these
structures and their properties remain unclear. A novel low-electron-dose
imaging technique, optimum bright-field scanning transmission electron
microscopy (OBF STEM) has recently been developed. It reconstructs images with
a high signal-to-noise ratio and a dose efficiency approximately two orders of
magnitude higher than that of conventional methods. Herein, we performed
low-dose atomic-resolution OBF STEM observations of an FAU-type zeolite,
effectively visualizing all the atomic sites in its framework. Additionally,
the complex local atomic structure of the twin boundaries in the zeolite was
directly characterized. The results of this study facilitate the
characterization of the local atomic structures in many electron-beam-sensitive
materials. | 2301.04377v1 |
2023-04-25 | Simulations of Magnetization Reversal in FM/AFM Bilayers With THz Frequency Pulses | It is widely known that antiferromagnets (AFMs) display a high frequency
response in the terahertz (THz) range, which opens up the possibility for
ultrafast control of their magnetization for next generation data storage and
processing applications. However, because the magnetization of the different
sublattices cancel, their state is notoriously difficult to read. One way to
overcome this is to couple AFMs to ferromagnets - whose state is trivially read
via magneto-resistance sensors. Here we present conditions, using theoretical
modelling, that it is possible to switch the magnetization of an AFM/FM bilayer
using THz frequency pulses with moderate field amplitude and short durations,
achievable in experiments. Consistent switching is observed in the phase
diagrams for an order of magnitude increase in the interface coupling and a
tripling in the thickness of the FM layer. We demonstrate a range of reversal
paths that arise due to the combination of precession in the materials and the
THz-induced fields. Our analysis demonstrates that the AFM drives the switching
and results in a much higher frequency dynamics in the FM due to the exchange
coupling at the interface. The switching is shown to be robust over a broad
range of temperatures relevant for device applications. | 2304.12969v1 |
2023-05-24 | A new class of carbon stabilized austenitic steels resistant to hydrogen embrittlement | High strength steels are susceptible to H-induced failure, which is typically
caused by the presence of diffusible H in the microstructure. The diffusivity
of H in austenitic steels with fcc crystal structure is slow. The austenitic
steels are hence preferred for applications in the hydrogen-containing
atmospheres. However, the fcc structure of austenitic steels is often
stabilized by the addition of Ni, Mn or N, which are relatively expensive
alloying elements to use. Austenite can kinetically also be stabilized by using
C. Here, we present an approach applied to a commercial cold work tool steel,
where we use C to fully stabilize the fcc phase. This results in a
microstructure consisting of only austenite and an M7C3 carbide. An exposure to
H by cathodic hydrogen charging exhibited no significant influence on the
strength and ductility of the C stabilized austenitic steel. While this
material is only a prototype based on an existing alloy of different purpose,
it shows the potential for low-cost H-resistant steels based on C stabilized
austenite. | 2305.15290v3 |
2023-06-17 | Pseudogap behavior in charge density wave kagome material ScV$_6$Sn$_6$ revealed by magnetotransport measurements | Over the last few years, significant attention has been devoted to studying
the kagome materials AV$_3$Sb$_5$ (A = K, Rb, Cs) due to their unconventional
superconductivity and charge density wave (CDW) ordering. Recently
ScV$_6$Sn$_6$ was found to host a CDW below $\approx$90K, and, like
AV$_3$Sb$_5$, it contains a kagome lattice comprised only of V ions. Here we
present a comprehensive magnetotransport study on ScV$_6$Sn$_6$. We discovered
several anomalous transport phenomena above the CDW ordering temperature,
including insulating behavior in interlayer resistivity, a strongly
temperature-dependent Hall coefficient, and violation of Kohler's rule. All
these anomalies can be consistently explained by a progressive decrease in
carrier densities with decreasing temperature, suggesting the formation of a
pseudogap. Our findings suggest that high-temperature CDW fluctuations play a
significant role in determining the normal state electronic properties of
ScV$_6$Sn$_6$. | 2306.10230v1 |
2023-07-12 | Monolithic Selenium/Silicon Tandem Solar Cells | Selenium is experiencing renewed interest as a promising candidate for the
wide bandgap photoabsorber in tandem solar cells. However, despite the
potential of selenium-based tandems to surpass the theoretical efficiency limit
of single junction devices, such a device has never been demonstrated. In this
study, we present the first monolithically integrated selenium/silicon tandem
solar cell. Guided by device simulations, we investigate various
carrier-selective contact materials and achieve encouraging results, including
an open-circuit voltage of V$_\text{oc}$=1.68 V from suns-V$_\text{oc}$
measurements. The high open-circuit voltage positions selenium/silicon tandem
solar cells as serious contenders to the industrially dominant single junction
technologies. Furthermore, we quantify a pseudo fill factor of more than 80%
using injection-level-dependent open-circuit voltage measurements, indicating
that a significant fraction of the photovoltaic losses can be attributed to
parasitic series resistance. This work provides valuable insights into the key
challenges that need to be addressed for realizing higher efficiency
selenium/silicon tandem solar cells. | 2307.05996v1 |
2023-10-09 | Colossal c-axis response and lack of rotational symmetry breaking within the kagome plane of the CsV$_3$Sb$_5$ superconductor | The kagome materials AV4$_3$Sb$_5$ (A = K, Rb, Cs) host an intriguing
interplay between unconventional superconductivity and charge-density-waves.
Here, we investigate CsV$_3$Sb$_5$ by combining high-resolution
thermal-expansion, heat-capacity and electrical resistance under strain
measurements. We directly unveil that the superconducting and charge-ordered
states strongly compete, and that this competition is dramatically influenced
by tuning the crystallographic c-axis. In addition, we report the absence of
additional bulk phase transitions within the charge-ordered state, notably
associated with rotational symmetry-breaking within the kagome planes. This
suggests that any breaking of the C$_6$ invariance occurs via different
stacking of C$_6$-symmetric kagome patterns. Finally, we find that the
charge-density-wave phase exhibits an enhanced A$_{1g}$-symmetric
elastoresistance coefficient, whose large increase at low temperature is driven
by electronic degrees of freedom. | 2310.06102v1 |
2023-10-15 | Parabolic Vector Focus Wave Modes | Weber-type parabolic beams have a transverse intensity profile, which is
parabolically-shaped and can be flexibly controlled. On the other hand, this
type of beams belongs to the family of the so-called nondiffracting beams and
have properties, promising for applications where the shape of the beam is of
an importance. Vector electromagnetic theory has to be introduced in order to
fully describe optical beams inside a high numerical aperture system, where the
angles of the spatial spectra are large. We introduce here parabolic vector
focus wave modes (FWM), which are both resistant to diffraction and to material
dispersion. We employ here a spectral approach and investigate durations of
parabolic vector FWMs in the femtosecond region. Two cases of transverse
electric and transverse magnetic modes are introduced and both standing and
traveling types of waves are considered. We demonstrate how the angular
dispersion affects the pulse shape and its properties. Parabolic vector FWMs
are studied in a transparent dielectric media (sapphire), which is widely used
as laser processed material. | 2310.09896v1 |
2023-11-09 | Single-Atom Control of Arsenic Incorporation in Silicon for High-Yield Artificial Lattice Fabrication | Artificial lattices constructed from individual dopant atoms within a
semiconductor crystal hold promise to provide novel materials with tailored
electronic, magnetic, and optical properties. These custom engineered lattices
are anticipated to enable new, fundamental discoveries in condensed matter
physics and lead to the creation of new semiconductor technologies including
analog quantum simulators and universal solid-state quantum computers. In this
work, we report precise and repeatable, substitutional incorporation of single
arsenic atoms into a silicon lattice. We employ a combination of scanning
tunnelling microscopy hydrogen resist lithography and a detailed statistical
exploration of the chemistry of arsine on the hydrogen terminated silicon (001)
surface, to show that single arsenic dopants can be deterministically placed
within four silicon lattice sites and incorporated with 97$\pm$2% yield. These
findings bring us closer to the ultimate frontier in semiconductor technology:
the deterministic assembly of atomically precise dopant and qubit arrays at
arbitrarily large scales. | 2311.05752v1 |
2023-11-26 | Quantum oscillations in kagome metals (Ti, Zr, Hf)V6Sn6 at Van Hove filling | Kagome materials have recently drawn great attention due to the interplay
between nontrivial band topology, electron correlations, and Van Hove
singularities related many-body orders. Here we report three new vanadium-based
kagome metals, TiV6Sn6, ZrV6Sn6, and HfV6Sn6, and conduct a comprehensive
investigation of their structural, magnetic, and electrical transport
properties. All three compounds exhibit large unsaturated magnetoresistances
and multiband Hall effects at low temperatures, indicating the existence of
multiple highly mobile carriers. Both the diagonal and off-diagonal resistivity
show quantum oscillations with nontrivial Berry phases and high quantum
mobilities. First-principles calculations together with quantum oscillation
analyses suggest the Van Hove singularities at the M point for the three
compounds all located in close vicinity of the Fermi level, and there also
exist multiple topological nontrivial band crossings, including a nodal ring
and a massive Dirac cone. Our work extends the kagome AM6X6 family and paves
the way for searching possible Van Hove physics in the V kagome lattice. | 2311.15239v2 |
2023-12-14 | Long-Range Structural Order in a Hidden Phase of Ruddlesden-Popper Bilayer Nickelate La$_3$Ni$_2$O$_7$ | The recent discovery of superconductivity in Ruddlesden-Popper bilayer
nickelate, specifically La$_3$Ni$_2$O$_7$, has generated significant interest
in the exploration of high-temperature superconductivity within this material
family. In this study, we present the crystallographic and electrical
resistivity properties of two distinct Ruddlesden-Popper nickelates: the
bilayer La$_3$Ni$_2$O$_7$ (referred to as 2222-phase) and a previously
uncharacterized phase, La$_3$Ni$_2$O$_7$ (1313-phase). The 2222-phase is
characterized by a pseudo $F$-centered orthorhombic lattice, featuring bilayer
perovskite [LaNiO$_3$] layers interspaced by rock salt [LaO] layers, forming a
repeated ...2222... sequence. Intriguingly, the 1313-phase, which displays
semiconducting properties, crystallizes in the $Cmmm$ space group and exhibits
a pronounced predilection for a $C$-centered orthorhombic lattice. Within this
structure, the perovskite [LaNiO$_3$] layers exhibit a distinctive long-range
ordered arrangement, alternating between single- and trilayer configurations,
resulting in a ...1313... sequence. This report contributes to novel insights
into the crystallography and the structure-property relationship of
Ruddlesden-Popper nickelates, paving the way for further investigations into
their unique physical properties. | 2312.09200v2 |
2024-03-11 | Active Control of Bound States in the Continuum in Toroidal Metasurfaces | The remarkable properties of toroidal metasurfaces, featuring ultrahigh-Q
bound states in the continuum (BIC) resonances and nonradiating anapole modes,
have garnered significant attention. The active manipulation of toroidal
resonance characteristics offers substantial potential for advancing tunable
metasurfaces. Our study specifically explores the application of vanadium
dioxide, a widely used phase change material in active photonics and
room-temperature bolometric detectors, to control BIC resonances in toroidal
metasurfaces. The phase change transition of vanadium dioxide occurs in a
narrow temperature range providing a large variation in material resistivity.
Through heating thin film patches of vanadium dioxide integrated into a
metasurface comprising gold split-ring resonators on a sapphire substrate, we
achieve remarkable control over the amplitude and frequency of toroidal dipole
BIC resonances due to their high sensitivity to losses present in the system.
Breaking the symmetry of meta-atoms reveals enhanced tunability. The predicted
maximum change in the amplitude of toroidal dipole BIC resonances reaches 14 dB
with a temperature variation of approximately 10oC. The proposed tunable
metasurface holds promise for various applications, including active photonic
systems and room temperature bolometers. | 2403.06345v1 |
2024-04-11 | Hydrogen Trapping and Embrittlement in Metals -- A Review | Hydrogen embrittlement in metals (HE) is a serious challenge for the use of
high strength materials in engineering practice and a major barrier to the use
of hydrogen for global decarbonization. Here we describe the factors and
variables that determine HE susceptibility and provide an overview of the
latest understanding of HE mechanisms. We discuss hydrogen uptake and how it
can be managed. We summarize hydrogen trapping and the techniques used for its
characterization. We also review literature that argues that hydrogen trapping
can be used to decrease HE susceptibility. We discuss the future research that
is required to advance the understanding of HE and hydrogen trapping and to
develop HE-resistant alloys. | 2404.07736v1 |
1999-07-23 | Unconventional one-magnon scattering resistivity in half metals | Low-temperature resistivity of half-metals is investigated. To date it has
been discussed that the one-magnon scattering process in half-metals is
irrelevant for low-temperature resistivity, due to the fully spin-polarized
electronic structure at the ground state. If one takes into account the
non-rigid-band behavior of the minority band due to spin fluctuations at finite
temperatures, however, the unconventional one-magnon scattering process is
shown to be most relevant and gives T^3 dependence in resistivity. This
behavior may be used as a crucial test in the search for half-metallic
materials which are potentially important for applications. Comparison with
resistivity data of
La_1-x Sr_x MnO_3 as candidates for half-metals shows good agreement. | 9907363v2 |
2002-05-27 | Superconductivity of epsilon-Fe: complete resistive transition | Last year, iron was reported to become superconducting at temperatures below
2K and pressures between 15 and 30 GPa. The evidence presented was a weak
resistivity drop, suppressed by a magnetic field above 0.2 T, and a small
Meissner signal. However, a compelling demonstration, such as the occurrence of
zero resistance, was lacking. Here we report the measurement of a complete
resistive transition at 22.2 GPa with an onset slightly above 2 K in two very
pure samples of iron, of different origins. The superconductivity appears
unusually sensitive to disorder, developing only when the electronic mean free
path is above a threshold value, while the normal state resistivity is
characteristic of a nearly ferromagnetic metal. | 0205557v1 |
2002-06-08 | Diffusion theory of spin injection through resistive contacts | Insertion of a resistive contact between a ferromagnetic metal and a
semiconductor microstructure is of critical importance for achieving efficient
spin injection into a semiconductor. However, the equations of the diffusion
theory are rather cumbersome for the junctions including such contacts. A
technique based on deriving a system of self-consistent equations for the
coefficients of spin injection, "gamma", through different contacts are
developed. These equations are concise when written in the proper notations.
Moreover, the resistance of a two-contact junction can be expressed in terms of
"gamma"'s of both contacts. This equation makes calculating the spin valve
effect straightforward, allows to find an explicit expression for the junction
resistance and to prove that its nonequilibrium part is positive. Relation of
these parameters to different phenomena like spin-e.m.f. and the junction
transients is established. Comparative effect of the Coulomb screening on
different parameters is clarified. It is also shown that the spin
non-conservation in a contact can have a dramatic effect on the non-equilibrium
resistance of the junction. | 0206129v2 |
2002-08-13 | Resistance of multilayers with long length scale interfacial roughness | The resistance of multilayers with interface roughness on a length scale
which is large compared to the atomic spacing is computed in several cases via
the Boltzmann equation. This type of roughness is common in magnetic
multilayers. When the electronic mean free paths are small compared to the
layer thicknesses, the current flow is non-uniform, and the resistance
decreases in the Current-Perpendicular-to-Plane (CPP) configuration and
increases in the Current-In-Plane (CIP) configuration. For mean free paths much
longer than the layer thicknesses, the current flow is uniform, and the
resistance increases in both the CPP and CIP configurations due to enhanced
surface scattering. In both the CPP and CIP geometries, the giant
magnetoresistance can be either enhanced or reduced by the presence of long
length scale interface roughness depending on the parameters. Finally, the
changes in the CPP and CIP resistivities due to increasing interface roughness
are estimated using experimentally determined parameters. | 0208251v1 |
2004-02-13 | Superconducting Properties under Magnetic Field in Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O Single Crystal | We report the in-plane resistivity and magnetic susceptibility of the layered
cobalt oxide Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O single crystal. The
temperature dependence of the resistivity shows metallic behavior from room
temperature to the superconducting transition temperature $T_{c}$ of 4.5 K.
Sharp resistive transition, zero resistivity and almost perfect superconducting
volume fraction below $T_{c}$ indicate the good quality and the bulk
superconductivity of the single crystal. The upper critical field $H_{c2}$ and
the coherence length $\xi$ are obtained from the resistive transitions in
magnetic field parallel to the c-axis and the $ab$-plane. The anisotropy of
$\xi$, $\xi_{ab} / \xi_{c} =$ 12 nm/1.3 nm $\simeq$ 9.2, suggests that this
material is considered to be an anisotropic three dimensional superconductor.
In the field parallel to the $ab$-plane, $H_{c2}$ seems to be suppressed to the
value of Pauli paramagnetic limit. It may indicate the spin singlet
superconductivity in the cobalt oxide. | 0402355v1 |
2004-03-22 | Electrical Transport Across an Individual Magnetic Domain Wall in (Ga,Mn)As Microdevices | Recent studies demonstrate that an individual magnetic domain wall (DW) can
be trapped and reproducibly positioned within multiterminal (Ga,Mn)As
microdevices. The electrical resistance obtained from such measurements is
found to be measurably altered by the presence of this single entity. To
elucidate these observations we develop a simple model for the electrical
potential distribution along a multiterminal device in the presence of a single
DW. This is employed to calculate the effect of a single DW upon the
longitudinal and transverse resistance. The model provides very good agreement
with experimental observations, and serves to highlight important deviations
from simple theory. We show that measurements of transverse resistance along
the channel permits establishing the position and the shape of the DW contained
within it. An experimental scheme is developed that enables unambiguous
extraction of the intrinsic DW resistivity. This permits the intrinsic
contribution to be differentiated from resistivities originating from the bulk
and from magnetic anisotropy - effects that are generally manifested as large
backgrounds in the experiments. | 0403547v1 |
2004-07-30 | Occurrence of Hysteresis like behavior of resistance of $Sb_2 Te_3$ film in heating-cooling cycle | Experimental observations of a peculiar behavior observed on heating and
cooling ${\rm Sb_2Te_3}$ films at different heating and cooling rate are
detailed. The film regained its original resistance, forming a closed loop, on
the completion of the heating-cooling cycle which was reproducible for
identical conditions of heating and cooling. The area enclosed by the loop was
found to depend on (i) the thickness of the film, (ii) the heating rate, (iii)
the maximum temperature to which film was heated and (iv) the cooling rate. The
observations are explained on basis of model which considers the film to be a
resultant of parallel resistances. The film's finite thermal conductivity gives
rise to a temperature gradient along the thickness of the film, due to this and
the temperature coefficient of resistance, the parallel combination of
resistance changes with temperature. Difference in heating and cooling rates
give different temperature gradient, which explains the observed hysteresis. | 0407796v1 |
2004-08-03 | Non-Gaussian Resistance Fluctuations in Disordered Materials | We study the distribution of resistance fluctuations of conducting thin films
with different levels of internal disorder. The film is modeled as a resistor
network in a steady state determined by the competition between two biased
processes, breaking and recovery of the elementary resistors. The fluctuations
of the film resistance are calculated by Monte Carlo simulations which are
performed under different bias conditions, from the linear regime up to the
threshold for electrical breakdown. Depending on the value of the external
current, on the level of disorder and on the size of the system, the
distribution of the resistance fluctuations can exhibit significant deviations
from Gaussianity. As a general trend, a size dependent, non universal
distribution is found for systems with low and intermediate disorder. However,
for strongly disordered systems, close to the critical point of the
conductor-insulator transition, the non-Gaussianity persists when the size is
increased and the distribution of resistance fluctuations is well described by
the universal Bramwell-Holdsworth-Pinton distribution. | 0408057v1 |
2007-02-26 | Nonpolar resistance switching of metal/binary-transition-metal oxides/metal sandwiches: homogeneous/inhomogeneous transition of current distribution | Exotic features of a metal/oxide/metal (MOM) sandwich, which will be the
basis for a drastically innovative nonvolatile memory device, is brought to
light from a physical point of view. Here the insulator is one of the
ubiquitous and classic binary-transition-metal oxides (TMO), such as Fe2O3,
NiO, and CoO. The sandwich exhibits a resistance that reversibly switches
between two states: one is a highly resistive off-state and the other is a
conductive on-state. Several distinct features were universally observed in
these binary TMO sandwiches: namely, nonpolar switching, non-volatile threshold
switching, and current--voltage duality. From the systematic sample-size
dependence of the resistance in on- and off-states, we conclude that the
resistance switching is due to the homogeneous/inhomogeneous transition of the
current distribution at the interface. | 0702564v1 |
2007-11-02 | Effects of Ferromagnetic Magnetic Ordering and Phase Transition on the Resistivity of Spin Current | It has been shown experimentally a long time ago that the magnetic ordering
causes an anomalous behavior of the electron resistivity in ferromagnetic
crystals. Phenomenological explanations based on the interaction between
itinerant electron spins and lattice spins have been suggested to explain these
observations. We show by extensive Monte Carlo simulation that this behavior is
also observed for the resistivity of the spin current calculated as a function
of temperature ($T$) from low-$T$ ordered phase to high-$T$ paramagnetic phase
in a ferromagnet. We show in particular that across the critical region, the
spin resistivity undergoes a huge peak. The origin of this peak is shown to
stem from the formation of magnetic domains near the phase transition. The
behavior of the resistivity obtained here is compared to experiments and
theories. A good agreement is observed. | 0711.0298v1 |
2008-01-29 | Temperature Dependence of the Spin Resistivity in Ferromagnetic Thin Films | The magnetic phase transition is experimentally known to give rise to an
anomalous temperature-dependence of the electron resistivity in ferromagnetic
crystals. Phenomenological theories based on the interaction between itinerant
electron spins and lattice spins have been suggested to explain these
observations. In this paper, we show by extensive Monte Carlo (MC) simulation
the behavior of the resistivity of the spin current calculated as a function of
temperature ($T$) from low-$T$ ordered phase to high-$T$ paramagnetic phase in
a ferromagnetic film. We analyze in particular effects of film thickness,
surface interactions and different kinds of impurities on the spin resistivity
across the critical region. The origin of the resistivity peak near the phase
transition is shown to stem from the existence of magnetic domains in the
critical region. We also formulate in this paper a theory based on the
Boltzmann's equation in the relaxation-time approximation. This equation can be
solved using numerical data obtained by our simulations. We show that our
theory is in a good agreement with our MC results. Comparison with experiments
is discussed. | 0801.4444v1 |
2008-02-19 | Advanced resistivity model for arbitrary magnetization orientation applied to a series of compressive- to tensile-strained (Ga,Mn)As layers | The longitudinal and transverse resistivities of differently strained
(Ga,Mn)As layers are theoretically and experimentally studied as a function of
the magnetization orientation. The strain in the series of (Ga,Mn)As layers is
gradually varied from compressive to tensile using (In,Ga)As templates with
different In concentrations. Analytical expressions for the resistivities are
derived from a series expansion of the resistivity tensor with respect to the
direction cosines of the magnetization. In order to quantitatively model the
experimental data, terms up to the fourth order have to be included. The
expressions derived are generally valid for any single-crystalline cubic and
tetragonal ferromagnet and apply to arbitrary surface orientations and current
directions. The model phenomenologically incorporates the longitudinal and
transverse anisotropic magnetoresistance as well as the anomalous Hall effect.
The resistivity parameters obtained from a comparison between experiment and
theory are found to systematically vary with the strain in the layer. | 0802.2635v1 |
2008-07-28 | Current induced resistance change of magnetic tunnel junctions with ultra-thin MgO tunnel barriers | Ultra-thin magnetic tunnel junctions with low resistive MgO tunnel barriers
are prepared to examine their stability under large current stress. The devices
show magnetoresistance ratios of up to 110 % and an area resistance product of
down to 4.4 ohm micrometer squared. If a large current is applied, a reversible
resistance change is observed, which can be attributed to two different
processes during stressing and one relaxation process afterwards. Here, we
analyze the time dependence of the resistance and use a simple model to explain
the observed behavior. The explanation is further supported by numerical fits
to the data in order to quantify the timescales of the involved phenomena. | 0807.4422v1 |
2009-05-15 | First-principles analysis of spin-disorder resistivity of Fe and Ni | Spin-disorder resistivity of Fe and Ni and its temperature dependence are
analyzed using noncollinear density functional calculations within the
supercell method. Different models of thermal spin disorder are considered,
including the mean-field approximation and the nearest-neighbor Heisenberg
model. Spin-disorder resistivity is found to depend weakly on magnetic
short-range order. If the local moments are kept frozen at their
zero-temperature values, very good agreement with experiment is obtained for
Fe, but for Ni the resistivity at elevated temperatures is significantly
overestimated. Agreement with experiment for Fe is improved if the local
moments are iterated to self-consistency. The overestimation of the resistivity
for paramagnetic Ni is attributed to the reduction of the local moments down to
0.35 Bohr magnetons. Overall, the results suggest that low-energy spin
fluctuations in Fe and Ni are better viewed as classical rotations of local
moments rather than quantized spin fluctuations that would require an (S+1)/S
correction. | 0905.2606v1 |
2009-06-04 | Resistivity of Graphene Nanoribbon Interconnects | Graphene nanoribbon interconnects are fabricated, and the extracted
resistivity is compared to that of Cu. It is found that the average resistivity
at a given line-width (18nm<W<52nm) is about 3X that of a Cu wire, whereas the
best GNR has a resistivity comparable to that of Cu. The conductivity is found
to be limited by impurity scattering as well as LER scattering; as a result,
the best reported GNR resistivity is 3X the limit imposed by substrate phonon
scattering. This study reveals that even moderate-quality graphene nanowires
have the potential to outperform Cu for use as on-chip interconnects. | 0906.0924v1 |
2009-08-17 | Unipolar Resistance Switching in Amorphous High-k dielectrics Based on Correlated Barrier Hopping Theory | We have proposed a kind of nonvolatile resistive switching memory based on
amorphous LaLuO3, which has already been established as a promising candidate
of high-k gate dielectric employed in transistors. Well-developed unipolar
switching behaviors in amorphous LaLuO3 make it suited for not only logic but
memory applications using the conventional semiconductor or the emerging
nano/CMOS architectures. The conduction transition between high- and low-
resistance states is attributed to the change in the separation between oxygen
vacancy sites in the light of the correlated barrier hopping theory. The mean
migration distances of vacancies responsible for the resistive switching are
demonstrated in nanoscale, which could account for the ultrafast programming
speed of 6 ns. The origin of the distributions in switching parameters in
oxides can be well understood according to the switching principle.
Furthermore, an approach has also been developed to make the operation voltages
predictable for the practical applications of resistive memories. | 0908.2379v2 |
2010-05-21 | Highly anisotropic resistivities in the double-exchange model for strained manganites | The highly anisotropic resistivities in strained manganites are theoretically
studied using the two-orbital double-exchange model. At the nanoscale, the
anisotropic double-exchange and Jahn-Teller distortions are found to be
responsible for the robust anisotropic resistivities observed here via Monte
Carlo simulations. An unbalanced in the population of orbitals caused by strain
is responsible for these effects. In contrast, the anisotropic superexchange is
found to be irrelevant to explain our results. Our model study suggests that
highly anisotropic resistivities could be present in a wide range of strained
manganites, even without (sub)micrometer-scale phase separation. In addition,
our calculations also confirm the formation of anisotropic clusters in
phase-separated manganites, which magnifies the anisotropic resistivities. | 1005.3865v1 |
2010-06-28 | Random barrier double-well model for resistive switching in tunnel barriers | The resistive switching phenomenon in MgO-based tunnel junctions is
attributed to the effect of charged defects inside the barrier. The presence of
electron traps in the MgO barrier, that can be filled and emptied, locally
modifies the conductance of the barrier and leads to the resistive switching
effects. A double-well model for trapped electrons in MgO is introduced to
theoretically describe this phenomenon. Including the statistical distribution
of potential barrier heights for these traps leads to a power-law dependence of
the resistance as a function of time, under a constant bias voltage. This model
also predicts a power-law relation of the hysteresis as a function of the
voltage sweep frequency. Experimental transport results strongly support this
model and in particular confirm the expected power laws dependencies of
resistance. They moreover indicate that the exponent of these power laws varies
with temperature as theoretically predicted. | 1006.5329v2 |
2010-12-08 | Measuring sheet resistance of CIGS solar cell's window layer by spatially resolved electroluminescence imaging | A spatially resolved electroluminescence (EL) imaging experiment is developed
to measure the local sheet resistance of the window layer, directly on the
completed CIGS cell. Our method can be applied to the EL imaging studies that
are made in fundamental studies as well as in in-line process inspection (1-3).
The EL experiment consists in using solar cell as a light emitting device : a
voltage is applied to the cell and its luminescence is detected. We develop an
analytical and quantitative model to simulate the behavior of CIGS solar cells
based on the spread sheet resistance effect in the window layer. We determine
the repartition of the electric potential on the ZnO, for given cell's
characteristics such as sheet resistance and contact geometries. Knowing the
repartition of the potential, the EL intensity is estimated and the
experimental EL signal is fitted, which allows the determination of the window
layer sheet resistance. | 1012.1693v1 |
2011-02-11 | Pressure cycle of superconducting Cs0.8Fe2Se2: a transport study | We report measurements of the temperature and pressure dependence of the
electrical resistivity of single crystalline iron-based chalcogenide
Cs0.8Fe2Se2. In this material superconductivity Tc~30K develops from a normal
state with extremely large resistivity. At ambient pressure a large "hump" in
the resistivity is observed around 200K. Under pressure, the resistivity
decreases by two orders of magnitude, concomitant with a sudden Tc suppression
around p~8GPa. Even at 9GPa a metallic resistivity state is not recovered, and
the {\rho}(T) "hump" is still detected. A comparison of the data measured upon
increasing and decreasing the external pressure leads us to suggest that
superconductivity is not related to this hump. | 1102.2464v2 |
2011-12-06 | Tunable resistivity of individual magnetic domain walls | Despite the relevance of current-induced magnetic domain wall (DW) motion for
new spintronics applications, the exact details of the current-domain wall
interaction are not yet understood. A property intimately related to this
interaction is the intrinsic DW resistivity. Here, we investigate
experimentally how the resistivity inside a DW depends on the wall width D,
which is tuned using focused ion beam irradiation of Pt/Co/Pt strips. We
observe the nucleation of individual DWs with Kerr microscopy, and measure
resistance changes in real-time. A 1/D^2 dependence of DW resistivity is found,
compatible with Levy-Zhang theory. Also quantitative agreement with theory is
found by taking full account of the current flowing through each individual
layer inside the multilayer stack. | 1112.1239v1 |
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