publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2018-03-20 | HPL-GEM: Controlling High Pressure Laminates bulk resistivity with GEMs | We succeeded in modifying and controlling the electrical resistance of a
standard High Pressure Laminate (HPL) panel through the use of a Gas Electron
Multiplier (GEM) foil that has been embedded into the bulk of the HPL plate
itself. Electrical characterizations were made and preliminary data show that
this HPL-GEM embedded system can easily vary its bulk resistance by more than
one order of magnitude. Data show that the bulk resistance change is
exponential with the applied voltage to the embedded GEM. | 1803.07675v1 |
2024-02-22 | Auxiliary Calculations for Graphene-Based Quantum Hall Arrays Using Partially Recursive Star-Mesh Transformations | A previous mathematical approach adopted for optimizing the number of total
device elements required for obtaining high effective quantized resistances in
graphene-based quantum Hall array devices (QHARS) has been further explored
with partial recursion patterns. Designs would assume the use of epitaxial
graphene elements, whose quantized Hall resistance at the {\nu}=2 plateau (R_H
\approx 12906.4 \Ohm) becomes the building block for larger effective,
quantized resistances. Auxiliary calculations suggest the importance of
applying full recursions at least once to maximize the reduction of total QHARS
elements needed for high resistances. | 2402.14520v1 |
2005-03-31 | Tuning Negative Differential Resistance in a Molecular Film | We have observed tunable negative differential resistance (NDR) in scanning
tunneling spectroscopy measurements of a double layer of C60 molecules on a
metallic surface. Using a simple model we show that the observed NDR behavior
is explained by voltage-dependent changes in the tunneling barrier height. | 0503765v1 |
2006-10-10 | Residual resistivity due to wedge disclination dipoles in metals with rotational plasticity | The residual resistivity $\rho $ in metals caused by wedge disclination
dipoles is studied in the framework of the Drude formula. It is shown that
$\rho\sim L^{-p}$ with $p=3$ for biaxial and $p=2$ for uniaxial dipoles ($L$ is
a size of dipole arm) | 0610258v1 |
2006-10-26 | Two years later--lessons from vortex dynamics in super media | Two years ago the reasons for resistance to the fundamental vortex dynamics
in super media emerged in 1990's were analyzed (cond-mat/0407007). Five
"mistakes" were identified to explain this resistance. Given the current
tremendous interest in vortex dynamics, it would be desirable to provide a
progress report: A survey of literature reveals that 3 out 5 "mistakes" has in
fact been confirmed by other researchers. | 0610753v1 |
2008-12-16 | Electrical properties of vanadium oxide subject to hydrogen plasma treatment | The effect of doping with hydrogen on the electrical properties of vanadium
oxide is studied. For vanadium oxide films, subject to cold hydrogen plasma
treatment, the temperature dependence of resistance with a maximum at T ~ 100 K
is observed. Also, the dependence of the a.c. resistance on frequency is
studied. A strategy for fabrication new superconducting materials is discussed. | 0812.2973v1 |
2011-02-07 | Direct correlation between strengthening mechanisms and electrical noise in strained copper wires | We have measured the resistance noise of copper metallic wires during a
tensile stress. The time variation of the main resistance is continuous up to
the wire breakdown, but its fluctuations reveal the intermittent and
heterogeneous character of plastic flow. We show in particular direct
correlations between strengthening mechanisms and noise spectra
characteristics. | 1102.1253v1 |
2011-09-05 | Mesoscopic Thermovoltage Measurement Design | Quantitative thermoelectric measurements in the mesoscopic regime require
accurate knowledge of temperature, thermovoltage, and device energy scales. We
consider the effect of a finite load resistance on thermovoltage measurements
of InAs/InP heterostructure nanowires. Load resistance and ac attenuation
distort the measured thermovoltage therefore complicating the evaluation of
device performance. Understanding these effects improves experimental design
and data interpretation. | 1109.1009v1 |
2016-07-20 | MegaOhm Extraordinary Hall effect in oxidized CoFeB | We report on development of controllably oxidized CoFeB ferromagnetic films
demonstrating the extraordinary Hall effect (EHE) resistivity exceeding 1 Ohmcm
and magnetic field sensitivity up to 10^6 Ohm/T. Such EHE resistivity is four
orders of magnitude higher than previously observed in ferromagnetic materials,
while sensitivity is two orders larger than the best of semiconductors | 1607.05923v1 |
1995-12-18 | Anisotropic Localization Effect in Layered Materials | We investigate localization properties in the highly anisotropic and
intrinsically disordered layered material, which is analogous to high-Tc
cuprates. By varying the anisotropy of the system which is parameterized by the
interlayer hopping $tp$, we find a crossover from two-dimensional (2D) to
three-dimensional (3D) behavior at a critical hopping amplitude $tp_c$, where a
mobility edge starts to appear. We show that below the mobility edge,
anisotropic localization effect may exist for a finite size system, when the
$ab$-plane localization length is longer than the system size and the $c$-axis
localization length is shorter than the system size. Nevertheless, we argue
that such anisotropic localization can not account for the ``semiconductor''
like behavior of the $c$-axis resistivity of high $\Tc$ cuprates. | 9512133v1 |
2008-03-20 | Graphene-Based Liquid Crystal Device | Graphene is only one atom thick, optically transparent, chemically inert and
an excellent conductor. These properties seem to make this material an
excellent candidate for applications in various photonic devices that require
conducting but transparent thin films. In this letter we demonstrate liquid
crystal devices with electrodes made of graphene which show excellent
performance with a high contrast ratio. We also discuss the advantages of
graphene compared to conventionally-used metal oxides in terms of low
resistivity, high transparency and chemical stability. | 0803.3031v1 |
2008-10-02 | Carrier doping to pseudo-low-dimensional compound La2RuO5 | Hole carrier doping has been tried to pseudo-low-dimensional material La2RuO5
by substituting La3+ with Cd2+. Single phased samples of La2-xCdxRuO5 with x up
to 0.5 have been successfully obtained and also high pressure O2 annealing has
been performed to the x=0.5 sample. Although the formal ionic state of Ru is
expected to increase from 4+ (at x=0) to 4.5+ (at x=0.5), the magnetic and
electrical properties show no significant changes in as-sintered samples. In
contrast, high pressure O2 annealed x=0.5 samples show a little reduction of
electrical resistivity and the decrease of thermoelectric power at 260 K. From
these results, it can be speculated that the doped carriers are mostly
compensated by oxygen deficiency in as-sintered samples. | 0810.0350v1 |
2008-12-15 | High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La2-xSrxNiO4-δ(x = 1 and 1.4) | Oxygen nonstoichiometry, electrical conductivity and thermal expansion of La2
xSrxNiO4-\delta phases with high levels of strontium substitution (1 =< x =<
1.4) have been investigated in air and oxygen atmosphere in the temperature
range 20-1050 degrees C. These phases retain the K2NiF4-type structure of
La2NiO4 (tetragonal, space group I4/mmm). The oxygen vacancy fraction was
determined independently from thermogravimetric and neutron diffraction
experiments, and is found to increase considerably on heating. The electrical
resistivity, thermal expansion and cell parameters with temperature show
peculiar variations with temperature, and differ notably from
La2NiO4$\pm$\delta in this respect. These variations are tentatively correlated
with the evolution of nickel oxidation state, which crosses from a Ni3+/Ni4+ to
a Ni2+/Ni3+ equilibrium on heating. | 0812.2747v1 |
2009-12-08 | The Deposition of High-Quality HfO2 on Graphene and the Effect of Remote Oxide Phonon Scattering | We demonstrate the atomic layer deposition of high-quality HfO2 film on
graphene and report the magnitude of remote oxide phonon (ROP) scattering in
dual-oxide graphene transistors. Top gates with 30 nm HfO2 oxide layer exhibit
excellent doping capacity of greater than 1.5x10^(13)/cm^(2). The carrier
mobility in HfO2-covered graphene reaches 20,000 cm^(2)/Vs at low temperature,
which is the highest among oxide-covered graphene and compares to that of
pristine samples. The temperature-dependent resistivity exhibits the effect of
ROP scattering from both the SiO2 substrate and the HfO2 over-layer. At room
temperature, surface phonon modes of the HfO2 film centered at 54 meV dominate
and limit the carrier mobility to ~20,000 cm^(2)/Vs. Our results highlight the
important choice of oxide in graphene devices. | 0912.1378v2 |
2013-12-21 | Near-Field Microwave Magnetic Nanoscopy of Superconducting Radio Frequency Cavity Materials | A localized measurement of the RF critical field on superconducting radio
frequency (SRF) cavity materials is a key step to identify specific defects
that produce quenches of SRF cavities. Two new measurements are performed to
demonstrate these capabilities with a novel near-field scanning probe microwave
microscope. The first is a third harmonic nonlinear measurement on a high
Residual- Resistance-Ratio bulk Nb sample showing strong localized nonlinear
response for the first time, with surface RF magnetic field $B_{surface} \sim
10^{2}$ $mT$. The second is a raster scanned harmonic response image on a high
quality $MgB_{2}$ thin film demonstrating a quench defect-free surface over
large areas. | 1312.6257v1 |
2014-11-14 | Characterization of TiAlSiON Coatings Deposited by Plasma Enhanced Magnetron Sputtering: XRD, XPS, and DFT Studies | The results of characterization of TiAlSiON hard coatings deposited on
ferric-chromium AISI 430 stainless steel by plasma enhanced magnetron
sputtering are presented. The coating with maximum hardness (of 45 GPa) was
obtained at the following optimal values of elemental concentrations: Si ~5
at.%, Al ~15 at.%, and Ti ~27 at.%. The elastic modulus of the coating was 590
GPa. The reading of gaseous mixture (Ar-N2) pressure was 1*10-3 Torr and the
reading of partial pressure of oxygen (O2) was 1*10-5 Torr. The X-ray
diffraction (XRD) measurements showed the presence of Ti(Al)N. High-energy
resolved XPS spectra of core levels revealed the formation of Ti-N, Ti-O-N,
Si-N and Al-O-N bonds. Comparison of XPS valence band spectra with specially
performed density functional theory calculations for two ordered and few
disordered TiN1-xOx (0 =< x <= 1) demonstrates that a Ti(Al)OxNy phase is
formed on the surface of AISI430 steel upon the plasma enhanced magnetron
sputtering, which provides this material with a good combination of high
hardness and improved oxidation resistance. | 1411.3859v1 |
2015-05-25 | Cluster spin-glass ground state in quasi-one-dimensional KCr$_{3}$As$_{3}$ | We report structural and physical properties of a new quasi-one-dimensional
Cr-based compound, KCr$_{3}$As$_{3}$, which is prepared by potassium
deintercalation from the superconductive K$_{2}$Cr$_{3}$As$_{3}$.
KCr$_{3}$As$_{3}$ adopts the TlFe$_{3}$Te$_{3}$-type structure with space group
$P6_{3}$/$m$ (No. 176). The high-temperature magnetic susceptibility obeys the
Curie-Weiss law with an effective magnetic moment of 0.68
$\mu_{\mathrm{B}}$/Cr. Below 56 K the susceptibility deviates from the
high-temperature Curie-Weiss behavior, coinciding with the rapid increase in
resistivity, which suggests formation of spin clusters. The short-range spin
correlations are also supported by the specific-heat data. The title material
does not exhibit bulk superconductivity; instead, it shows a cluster spin-glass
state below $\sim$ 5 K. | 1505.06525v1 |
2017-12-29 | Structural transformations in porous glasses under mechanical loading. II. Compression | The role of porous structure and glass density in response to compressive
deformation of amorphous materials is investigated via molecular dynamics
simulations. The disordered, porous structures were prepared by quenching a
high-temperature binary mixture below the glass transition into the phase
coexistence region. With decreasing average glass density, the pore morphology
in quiescent samples varies from a random distribution of compact voids to a
porous network embedded in a continuous glass phase. We find that during
compressive loading at constant volume, the porous structure is linearly
transformed in the elastic regime and the elastic modulus follows a power-law
increase as a function of the average glass density. Upon further compression,
pores deform significantly and coalesce into large voids leading to formation
of domains with nearly homogeneous glass phase, which provides an enhanced
resistance to deformation at high strain. | 1712.10265v1 |
2018-02-07 | Stability of boron-doped graphene/copper interface: DFT, XPS and OSEE studies | Two different types of boron-doped graphene/copper interfaces synthesized
using two different flow rates of Ar through the bubbler containing the boron
source were studied. X-ray photoelectron spectra (XPS) and optically stimulated
electron emission (OSEE) measurements have demonstrated that boron-doped
graphene coating provides a high corrosion resistivity of Cu-substrate with the
light traces of the oxidation of carbon cover. The density functional theory
calculations suggest that for the case of substitutional (graphitic)
boron-defect only the oxidation near boron impurity is energetically favorable
and creation of the vacancies that can induce the oxidation of copper substrate
is energetically unfavorable. In the case of non-graphitic boron defects
oxidation of the area, a nearby impurity is metastable that not only prevent
oxidation but makes boron-doped graphene. Modeling of oxygen reduction reaction
demonstrates high catalytic performance of these materials. | 1802.02345v1 |
2018-06-11 | Uncovering electron scattering mechanisms in NiFeCoCrMn derived concentrated solid solution and high entropy alloys | Whilst it has long been known that disorder profoundly affects transport
properties, recent measurements on a series of solid solution 3d-transition
metal alloys reveal two orders of magnitude variations in the residual
resistivity. Using ab-initio methods, we demonstrate that, while the carrier
density of all alloys is as high as in normal metals, the electron
mean-free-path can vary from ~10 {\AA} (strong scattering limit) to ~10$^3$
{\AA} (weak scattering limit). Here, we delineate the underlying electron
scattering mechanisms responsible for this disparate behavior. While spin
dependent site-diagonal disorder is always dominant, for alloys containing only
Fe, Co, and Ni the majority spin channel experiences negligible disorder
scattering, thereby providing a short circuit, while for Cr/Mn containing
alloys both spin channels experience strong disorder scattering due to an
electron filling effect. Unexpectedly, other scattering mechanisms (e.g.
displacement scattering) are found to be relatively weak in most cases. | 1806.03785v2 |
2018-11-26 | Engineering Large Anisotropic Magnetoresistance in La0.7Sr0.3MnO3 Films at Room Temperature | The magnetoresistance (MR) effect is widely employed in technologies that
pervade our world from magnetic reading heads to sensors. Diverse contributions
to MR, such as anisotropic, giant, tunnel, colossal, and spin-Hall, are
revealed in materials depending on the specific system and measuring
configuration. Half-metallic manganites hold promise for spintronic
applications but the complexity of competing interactions has not permitted the
understanding and control of their magnetotransport properties to enable the
realization of their technological potential. Here we report on the ability to
induce a dominant switchable magnetoresistance in La0.7Sr0.3MnO3 epitaxial
films, at room temperature (RT). By engineering an extrinsic magnetic
anisotropy, we show a large enhancement of anisotropic magnetoresistance (AMR)
which leads to, at RT, signal changes much larger than the other contributions
such as the colossal magnetoresistance (CMR). The dominant extrinsic AMR
exhibits large variation in the resistance in low field region, showing high
sensitivity to applied low magnetic fields. These findings have a strong impact
on the real applications of manganite based devices for the high-resolution low
field magnetic sensors or spintronics. | 1811.10301v1 |
2017-03-23 | Unconventional Large Linear Magnetoresistance in Cu$_{2-x}$Te | We report a large linear magnetoresistance in Cu$_{2-x}$Te, reaching
$\Delta\rho/\rho(0)$ = 250\% at 2 K in a 9 T field. This is observed for
samples with $x$ in the range 0.13 to 0.22, and the results are comparable to
the effects observed in Ag$_2 X$ materials, although in this case the results
appear for a much wider range of bulk carrier density. Examining the magnitude
vs. crossover field from low-field quadratic to high-field linear behavior, we
show that models based on classical transport behavior best explain the
observed results. The effects are traced to misdirected currents due to
topologically inverted behavior in this system, such that stable surface states
provide the high mobility transport channels. The resistivity also crosses over
to a $T^2$ dependence in the temperature range where the large linear MR
appears, an indicator of electron-electron interaction effects within the
surface states. Thus this is an example of a system in which these interactions
dominate the low-temperature behavior of the surface states. | 1703.07945v1 |
2019-02-14 | One-dimensional edge contacts to a monolayer semiconductor | Integration of electrical contacts into van der Waals (vdW) heterostructures
is critical for realizing electronic and optoelectronic functionalities.
However, to date no scalable methodology for gaining electrical access to
buried monolayer two-dimensional (2D) semiconductors exists. Here we report
viable edge contact formation to hexagonal boron nitride (hBN) encapsulated
monolayer MoS$_2$. By combining reactive ion etching, in situ Ar$^+$ sputtering
and annealing, we achieve a relatively low edge contact resistance, high
mobility (up to ~30 cm$^2$/Vs) and high on-current density (>50 uA/um at
V$_{\rm DS}$ = 3V), comparable to top contacts. Furthermore, the atomically
smooth hBN environment also preserves the intrinsic MoS$_2$ channel quality
during fabrication, leading to a steep subthreshold swing of 116 mV/dec with a
negligible hysteresis. Hence, edge contacts are highly promising for
large-scale practical implementation of encapsulated heterostructure devices,
especially those involving air sensitive materials, and can be arbitrarily
narrow, which opens the door to further shrinkage of 2D device footprint. | 1902.05506v3 |
2019-02-20 | Vortex pinning and flux flow microwave studies of coated conductors | Demanding microwave applications in a magnetic field require the material
optimization not only in zero-field but, more important, in the in-field flux
motion dominated regime. However, the effect of artificial pinning centers
(APC) remains unclear at high frequency. Moreover, in coated conductors the
evaluation of the high frequency material properties is difficult due to the
complicated electromagnetic problem of a thin superconducting film on a
buffered metal substrate. In this paper we present an experimental study at 48
GHz of 150-200 nm YBa$_2$Cu$_3$O$_{7-x}$ coated conductors, with and without
APCs, on buffered Ni-5at%W tapes. By properly addressing the electromagnetic
problem of the extraction of the superconductor parameters from the measured
overall surface impedance $Z$, we are able to extract and to comment on the
London penetration depth, the flux flow resistivity and the pinning constant,
highlighting the effect of artificial pinning centers in these samples. | 1902.07589v1 |
2020-02-25 | Shear thickening and jamming of dense suspensions: the "roll" of friction | Particle-based simulations of discontinuous shear thickening (DST) and shear
jamming (SJ) suspensions are used to study the role of stress-activated
constraints, with an emphasis on resistance to gear-like rolling. Rolling
friction decreases the volume fraction required for DST and SJ, in quantitative
agreement with real-life suspensions with adhesive surface chemistries and
"rough" particle shapes. It sets a distinct structure of the frictional force
network compared to only sliding friction, and from a dynamical perspective
leads to an increase in the velocity correlation length, in part responsible
for the increased viscosity. The physics of rolling friction is thus a key
element in achieving a comprehensive understanding of strongly shear-thickening
materials. | 2002.10996v2 |
2020-09-16 | Superconductivity in CuAl2-type Co0.2Ni0.1Cu0.1Rh0.3Ir0.3Zr2 with a high-entropy-alloy transition metal site | Research on high-entropy-alloy (HEA) superconductors is a growing field in
material science. In this study, we explored new HEA-type superconductors and
discovered a CuAl2-type superconductor Co0.2Ni0.1Cu0.1Rh0.3Ir0.3Zr2 with a
HEA-type transition metal site. A superconducting transition was observed at
8.0 K after electrical resistivity, magnetization, and specific heat
measurements. The bulk characteristics of the superconductivity were confirmed
through the specific heat measurements. The discovery of superconductivity in
HEA-type Co0.2Ni0.1Cu0.1Rh0.3Ir0.3Zr2 will provide a novel pathway to explore
new HEA-type superconductors and investigate the relationship between the
mixing entropy and superconductivity of HEA-type compounds. | 2009.07548v3 |
2017-05-17 | High Thermoelectric Figure of Merit by Resonant Dopant in Half-Heusler Alloys | Half-Heusler alloys have been one of the benchmark high temperature
thermoelectric materials owing to their thermal stability and promising figure
of merit ZT. Simonson et al. early showed that small amounts of vanadium doped
in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change
with the increased density of states near the Fermi level. We herein report a
systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta)
as prospective resonant dopants in enhancing the ZT of n-type half-Heusler
alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase
the Seebeck coefficient in the temperature range 300-1000 K, consistent with a
resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as
evident by the systematic decrease in electrical resistivity and Seebeck
coefficient. The combination of enhanced Seebeck coefficient due to the
presence of V resonant states and the reduced thermal conductivity has led to a
state-of-the-art ZT of 1.3 near 850 K in n-type
(Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys. | 1705.06100v1 |
2019-03-12 | Superconductivity behavior in epitaxial TiN films points at surface magnetic disorder | We analyze the evolution of the normal and superconducting electronic
properties in epitaxial TiN films, characterized by high Ioffe-Regel parameter
values, as a function of the film thickness. As the film thickness decreases,
we observe an increase of in the residual resistivity, which becomes dominated
by diffusive surface scattering for $d\leq20\,$nm. At the same time, a
substantial thickness-dependent reduction of the superconducting critical
temperature is observed compared to the bulk TiN value. In such a high quality
material films, this effect can be explained by a weak magnetic disorder
residing in the surface layer with a characteristic magnetic defect density of
$\sim10^{12}\,\mathrm{cm}^{-2}$. Our results suggest that surface magnetic
disorder is generally present in oxidized TiN films. | 1903.05009v3 |
2019-12-30 | Pinning Dislocations in Colloidal Crystals with Active Particles that Seek Stacking Faults | There is growing interest in functional, adaptive devices built from
colloidal subunits of micron size or smaller. A colloidal material with dynamic
mechanical properties could facilitate such microrobotic machines. Here we
study via computer simulation how active interstitial particles in small
quantities can be used to modify the bulk mechanical properties of a colloidal
crystal. Passive interstitial particles are known to pin dislocations in
metals, thereby increasing resistance to plastic deformation. We extend this
tactic by employing anisotropic active interstitials that travel
super-diffusively and bind strongly to stacking faults associated with partial
dislocations. We find that: 1) interstitials that are effective at reducing
plasticity compromise between strong binding to stacking faults and high
mobility in the crystal bulk. 2) Reorientation of active interstitials in the
crystal depends upon rotational transitions between high-symmetry crystal
directions. 3) The addition of certain active interstitial shapes at
concentrations as low as $60$ per million host particles ($0.006\%$) can create
a shear threshold for dislocation migration. | 1912.12792v1 |
2015-06-16 | Correlation of Crystal Quality and Extreme Magnetoresistance of WTe$_2$ | High quality single crystals of WTe$_2$ were grown using a Te flux followed
by a cleaning step involving self-vapor transport. The method is reproducible
and yields consistently higher quality single crystals than are typically
obtained via halide assisted vapor transport methods. Magnetoresistance
(MR)values at 9 Tesla and 2 Kelvin as high as 1.75 million \%, nearly an order
of magnitude higher than previously reported for this material, were obtained
on crystals with residual resistivity ratio (RRR) of approximately 1250. The MR
follows a near B$^2$ law (B = 1.95(1)) and, assuming a semiclassical model, the
average carrier mobility for the highest quality crystal was found to be
~167,000 cm$^2$/Vs at 2 K. A correlation of RRR, MR ratio and average carrier
mobility ($\mu_{avg}$) is found with the cooling rate during the flux growth. | 1506.04823v1 |
2018-12-18 | The role of β-titanium ligaments in the deformation of dual phase titanium alloys | Multiphase titanium alloys are critical materials in high value engineering
components, for instance in aero engines. Microstructural complexity is
exploited through interface engineering during mechanical processing to realise
significant improvements in fatigue and fracture resistance and strength. In
this work, we explore the role of select interfaces using in-situ
micromechanical testing with concurrent observations from high angular
resolution electron backscatter diffraction (HR-EBSD). Our results are
supported with post mortem transmission electron microscopy (TEM). Using
micro-pillar compression, we performed in-depth analysis of the role of select
{\beta}-titanium (body centred cubic) ligaments which separate neighbouring
{\alpha}-titanium (hexagonal close packed) regions and inhibit the dislocation
motion and impact strength during mechanical deformation. These results shed
light on the strengthening mechanisms and those that can lead to strain
localisation during fatigue and failure. | 1812.07250v2 |
2019-10-14 | Investigation of nitrogen polar p-type doped GaN/AlxGa(1-x)N superlattices for applications in wide-bandgap p-type field effect transistors | In this study the MOCVD growth and electrical properties of N-polar
modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet
charge density and mobility were studied as a function of the concentration of
the p-type dopant Mg in the SL and the number of SL periods. Room temperature
Hall measurements were carried out to determine the hole mobility and the sheet
charge density. While the hole density increased with increasing number of SL
periods, the hole mobility was largely unaffected.Hole mobilities as high as
18cm2/Vs at a simultaneous high hole density of 6.5e13 cm-2 were observed for
N-polar SLs with a Mg modulation doping of 7.5e18 cm-3. For comparable
uniformly doped Ga-polar SL samples, a mobility of 11cm2/Vs was measured.
Lowest sheet resistance in the GaN/AlGaN materials system of 5kOhm/sq is also
reported. Test-structure transistors were also fabricated to investigate the
applicability of these SL structures, with planar device resulting in a current
of 5mA/mm, and a FinFET structure resulting in a current of over 100mA/mm. | 1910.06421v1 |
2019-11-27 | Enhancement of the electronic thermoelectric properties of bulk strained silicon-germanium alloys using the scattering relaxation times from first principles | We use first-principles electronic structure methods to calculate the
electronic thermoelectric properties (i.e. due to electronic transport only) of
single-crystalline bulk $n$-type silicon-germanium alloys vs Ge composition,
temperature, doping concentration and strain. We find excellent agreement to
available experiments for the resistivity, mobility and Seebeck coefficient.
These results are combined with the experimental lattice thermal conductivity
to calculate the thermoelectric figure of merit $ZT$, finding very good
agreement with experiment. We predict that 3% tensile hydrostatic strain
enhances the $n$-type $ZT$ by 50% at carrier concentrations of $n=10^{20}$
cm$^{-3}$ and temperature of $T=1200K$. These enhancements occur at different
alloy compositions due to different effects: at 50% Ge composition the
enhancements are achieved by a strain induced decrease in the Lorenz number,
while the power factor remains unchanged. These characteristics are important
for highly doped and high temperature materials, in which up to 50% of the heat
is carried by electrons. At 70% Ge the increase in $ZT$ is due to a large
increase in electrical conductivity produced by populating the high mobility
$\Gamma$ conduction band valley, lowered in energy by strain. | 1911.12149v1 |
2020-10-01 | High magnetic field spin-valley-split Shubnikov-de Haas oscillations in a WSe$_2$ monolayer | We study Shubnikov-de Haas oscillations in a p-type WSe$_2$ monolayer under
very high magnetic field. The oscillation pattern is complex due to a large
spin and valley splitting, in the non-fully-resolved Landau level regime. Our
experimental data can be reproduced with a model in which the main parameter is
the ratio between the Zeeman energy and the cyclotron energy. The model takes
into account the Landau levels from both valleys with the same Gaussian
broadening, which allows to predict the relative amplitude of the resistance
oscillation originating from each valley. The Zeeman energy is found to be
several times larger than the cyclotron energy. It translates into a large and
increasing effective Land\'e factor as the hole density decreases, in the
continuity of the values reported in the literature at lower carrier density. | 2010.00510v1 |
2020-11-27 | High-pressure effects on superconducting properties and crystal structure of Bi-based layered superconductor La2O2Bi3Ag0.6Sn0.4S6 | The effects of pressure on the superconducting properties of a Bi-based
layered superconductor La2O2Bi3Ag0.6Sn0.4S6, which possesses a four-layer-type
conducting layer, have been studied through the electrical resistance and
magnetic susceptibility measurements. The crystal structure under pressure was
examined using synchrotron X-ray diffraction at SPring-8. In the low-pressure
regime, bulk superconductivity with a transition temperature Tc of ~ 4.5 K was
induced by pressure, which was achieved by in-plane chemical pressure effect
owing to the compression of the tetragonal structure. In the high-pressure
regime above 6.4 GPa, a structural symmetry lowering was observed, and
superconducting transitions with a Tc ~ 8 K were observed. Our results suggest
the possible commonality on the factor essential for Tc in Bi-based
superconductors with two-layer-type and four-layer-type conducting layers. | 2011.13532v1 |
2021-02-01 | Liquefaction-induced Plasticity from Entropy-boosted Amorphous Ceramics | Ceramics are easy to break, and very few generic mechanisms are available for
improving their mechanical properties, e.g., the 1975-discovered anti-fracture
mechanism is strictly limited to zirconia and hafnia. Here we report a general
mechanism for achieving high plasticity through liquefaction of ceramics. We
further disclose the general material design strategies to achieve this
difficult task through entropy-boosted amorphous ceramics (EBACs), enabling
fracture-resistant properties that can withstand severe plastic deformation
(e.g., over 95%, deformed to a thickness of a few nanometers) while maintaining
high hardness and reduced modulus. The findings reported here open a new route
to ductile ceramics and many applications. | 2102.00802v1 |
2021-02-13 | Mechanical Performance of 3D Printed Interpenetrating Phase Composites with Spinodal Topologies | The mechanical response of interpenetrating phase composites (IPCs) with
stochastic spinodal topologies is investigated experimentally and numerically.
Model polymeric systems are fabricated by Polyjet multi-material printing, with
the reinforcing phase taking the topology of a spinodal shell, and the
remaining volume filled by a softer matrix. We show that spinodal shell IPCs
have comparable compressive strength and stiffness to IPCs with two
well-established periodic reinforcements, the Schwarz P triply periodic minimal
surface (TPMS) and the octet truss-lattice, while exhibiting far less
catastrophic failure and greater damage resistance, particularly at high volume
fraction of reinforcing phase. The combination of high stiffness and strength
and a long flat plateau after yielding makes spinodal shell IPCs a promising
candidate for energy absorption and impact protection applications, where the
lack of material softening upon large compressive strains can prevent sudden
collapse. Importantly, in contrast with all IPCs with periodic reinforcements,
spinodal shell IPCs are amenable to scalable manufacturing via self-assembly
techniques. | 2102.06707v1 |
2021-07-22 | Anomalous High-Field Magnetotransport in CaFeAsF due to the Quantum Hall Effect | CaFeAsF is an iron-based superconductor parent compound whose Fermi surface
is quasi-two dimensional, composed of Dirac-electron and Schr\"odinger-hole
cylinders elongated along the $c$ axis. We measured the longitudinal and Hall
resistivities in CaFeAsF with the electrical current in the $ab$ plane in
magnetic fields up to 45 T applied along the $c$ axis and obtained the
corresponding conductivities via tensor inversion. We found that both the
longitudinal and Hall conductivities approached zero above $\sim$40 T as the
temperature was lowered to 0.4 K. Our analysis indicates that the Landau-level
filling factor is $\nu$ = 2 for both electrons and holes at these high field
strengths, resulting in a total filling factor $\nu$ = $\nu_{hole} -
\nu_{electron}$ = 0. We therefore argue that the $\nu$ = 0 quantum Hall state
emerges under these conditions. | 2107.10460v4 |
2022-01-08 | Atomic disorder and Berry phase driven anomalous Hall effect in Co2FeAl Heusler compound | Co2-based Heusler compounds are the promising materials for the spintronics
application due to their high Curie temperature, large spin-polarization, large
magnetization density, and exotic transport properties. In the present
manuscript, we report the anomalous Hall effect (AHE) in a polycrystalline
Co2FeAl Heusler compound using combined experimental and theoretical studies.
The Rietveld analysis of high-resolution synchrotron x-ray diffraction data
reveals a large degree (~50 %) of antisite disorder between Fe and Al atoms.
The analysis of anomalous transport data provides the experimental anomalous
Hall conductivity (AHC) about 227 S/cm at 2 K with an intrinsic contribution of
155 S/cm, which has nearly constant variation with temperature. The detailed
scaling analysis of anomalous Hall resistivity suggests that the AHE in Co2FeAl
is governed by the Berry phase driven intrinsic mechanism. Our theoretical
calculations reveal that the disorder present in Co2FeAl compound enhances the
Berry curvature induced intrinsic AHC. | 2201.02864v1 |
2022-07-15 | High power density energy harvesting devices based on the anomalous Nernst effect of Co/Pt magnetic multilayers | The anomalous Nernst effect (ANE) is a thermomagnetic phenomenon with
potential applications in thermal energy harvesting. While many recent works
studied the approaches to increase the ANE coefficient of materials, relatively
little effort was devoted to increasing the power supplied by the effect. Here
we demonstrate a nanofabricated device with record power density generated by
the ANE. To accomplish this, we fabricate micrometer-sized devices in which the
thermal gradient is three orders of magnitude higher than conventional
macroscopic devices. In addition, we use Co/Pt multilayers, a system
characterized by a high ANE thermopower (~1 microV/K), low electrical
resistivity, and perpendicular magnetic anisotropy. These innovations allow us
to obtain power densities of around 13 W/cm3. We believe that this design may
find uses in harvesting wasted energy in e.g. electronic devices. | 2207.07526v2 |
2023-02-20 | A High Throughput Aqueous Passivation Testing Methodology for Compositionally Complex Alloys using Scanning Droplet Cell | Compositionally complex alloy systems containing more than five principal
elements allow exploring a wide range of compositions, processing, and
structural variables with the hope for identifying unique properties. Such
opportunities also apply to designing materials for improved corrosion
resistance, regulated by a self-healing passive film. Such a rich landscape in
reactivity and protectivity demands the search for high-throughput experimental
testing workflows to uncover key metrics, indicative of superior properties. In
this communication, one such methodology is demonstrated for evaluating
passivation performance of a combinatorial library of
Al0.7-x-yCoxCryFe0.15Ni0.15 thin film alloys in deaerated 0.1 mol/L H2SO4(aq),
using a scanning droplet cell. | 2302.09804v4 |
2023-09-29 | Transforming Materials Discovery for Artificial Photosynthesis: High-Throughput Screening of Earth-Abundant Semiconductors | We present a highly efficient workflow for designing semiconductor structures
with specific physical properties, which can be utilized for a range of
applications, including photocatalytic water splitting. Our algorithm generates
candidate structures composed of earth-abundant elements that exhibit optimal
light-trapping, high efficiency in \ce{H2} and/or \ce{O2} production, and
resistance to reduction and oxidation in aqueous media. To achieve this, we use
an ionic translation model trained on the Inorganic Crystal Structure Database
(ICSD) to predict over thirty thousand undiscovered semiconductor compositions.
These predictions are then screened for redox stability under Hydrogen
Evolution Reaction (HER) or Oxygen Evolution Reaction (OER) conditions before
generating thermodynamically stable crystal structures and calculating accurate
band gap values for the compounds. Our approach results in the identification
of dozens of promising semiconductor candidates with ideal properties for
artificial photosynthesis, offering a significant advancement toward the
conversion of sunlight into chemical fuels. | 2310.00118v1 |
2023-10-28 | Ultralong-term high-density data storage with atomic defects in SiC | There is an urgent need to increase the global data storage capacity, as
current approaches lag behind the exponential growth of data generation driven
by the Internet, social media and cloud technologies. In addition to increasing
storage density, new solutions should provide long-term data archiving that
goes far beyond traditional magnetic memory, optical disks and solid-state
drives. Here, we propose a concept of energy-efficient, ultralong, high-density
data archiving based on optically active atomic-size defects in a radiation
resistance material, silicon carbide (SiC). The information is written in these
defects by focused ion beams and read using photoluminescence or
cathodoluminescence. The temperature-dependent deactivation of these defects
suggests a retention time minimum over a few generations under ambient
conditions. With near-infrared laser excitation, grayscale encoding and
multi-layer data storage, the areal density corresponds to that of Blu-ray
discs. Furthermore, we demonstrate that the areal density limitation of
conventional optical data storage media due to the light diffraction can be
overcome by focused electron-beam excitation. | 2310.18843v1 |
2003-04-30 | Pulsed Laser Deposition of epitaxial titanium diboride thin films | Epitaxial titanium diboride thin films have been deposited on sapphire
substrates by Pulsed Laser Ablation technique. Structural properties of the
films have been studied during the growth by Reflection High Energy Electron
Diffraction (RHEED) and ex-situ by means of X-ray diffraction techniques; both
kinds of measurements indicate a good crystallographic orientation of the TiB2
film both in plane and along the c axis. A flat surface has been observed by
Atomic Force Microscopy imaging. Electrical resistivity at room temperature
resulted to be five times higher than the value reported for single crystals.
The films resulted to be also very stable at high temperature, which is very
promising for using this material as a buffer layer in the growth of magnesium
diboride thin films. | 0304680v1 |
2016-02-19 | Magnetic anisotropy of large floating-zone-grown single-crystals of SrRuO3 | SrRuO3 is a highly interesting material due to its anomalous-metal properties
related with ferromagnetism and its relevance as conductive perovskite layer or
substrate in heterostructure devices. We have used optical floating zone
technique in an infrared image furnace to grow large single crystals of SrRuO3
with volumes attaining several hundred mm3. Crystals obtained for optimized
growth parameters exhibit a high ferromagnetic Curie temperature of 165 K and a
low-temperature magnetization of 1.6 muB at a magnetic field of 6 T. The high
quality of the crystals is further documented by large residual resistance
ratios of 75 and by crystal structure and chemical analyzes. With these
crystals the magnetic anisotropy could be determined. | 1602.06171v2 |
2014-08-11 | High spin polarization in CoFeMnGe quaternary Heusler alloy | We report the structure, magnetic property and spin polarization of CoFeMnGe
equiatomic quaternary Heusler alloy. The alloy was found to exist in the L21
structure with considerable amount of DO3 disorder. Thermal analysis result
indicated the Curie temperature is about 711K without any other phase
transformation up to melting temperature. The magnetization value was close to
that predicted by the Slater-Pauling curve. Current spin polarization of P =
0.70 {plus/minus}0.1 was deduced using point contact Andreev reflection (PCAR)
measurements. Half-metallic trend in the resistivity has also been observed in
the temperature range of 5 K to 300 K. Considering the high spin polarization
and Curie temperature, this material appears to be promising for spintronic
applications. | 1408.2408v2 |
2019-04-01 | Quantum transport in high-quality shallow InSb quantum wells | InSb is one of the promising candidates to realize a topological state
through proximity induced superconductivity in a material with strong
spin-orbit interactions. In two-dimensional systems, thin barriers are needed
to allow strong coupling between superconductors and semiconductors. However,
it is still challenging to obtain a high-quality InSb two-dimensional electron
gas in quantum wells close to the surface. Here we report on a molecular beam
epitaxy grown heterostructure of InSb quantum wells with substrate-side
Si-doping and ultra-thin InAlSb (5 nm, 25 nm, and 50 nm) barriers to the
surface. We demonstrate that the carrier densities in these quantum wells are
gate-tunable and electron mobilities up to 350,000 $\rm{cm^2(Vs)^{-1}}$ are
extracted from magneto-transport measurements. Furthermore, from
temperature-dependent magneto-resistance measurements, we extract an effective
mass of 0.02 $m_0$ and find a Zeeman splitting compatible with the expected
g-factor. | 1904.00828v2 |
2021-06-28 | Topological Anderson Insulator in cation-disordered Cu2ZnSnS4 | Abstract: Using ab initio calculations supported by experimental transport
measurements, we present the first credible candidate for the realization of a
disorder-induced Topological Anderson Insulator in a real material system. High
energy reactive ball-milling produces a polymorph of Cu2ZnSnS4 with high cation
disorder, which shows an inverted ordering of bands at the Brillouin zone
center, in contrast to its ordered phase. Adiabatic continuity arguments
establish that this disordered Cu2ZnSnS4 can be connected to the closely
related Cu2ZnSnSe4, previously predicted to be a 3D topological insulator. Band
structure calculations with a slab geometry reveal the presence of robust
surface states, while impedance spectroscopy coupled with resistivity
measurements point to the surface-dominated transport which such states would
imply; thus making a strong case in favor of a novel topological phase. As
such, this study opens up a window to understanding and potentially exploiting
topological behavior in a rich class of easily-synthesized multinary,
disordered compounds. | 2106.14714v1 |
2023-12-11 | Impersonating a Superconductor: High-Pressure BaCoO$_3$, an Insulating Ferromagnet | We report the high-pressure synthesis (6 GPa, 1200 $^{\circ}$C) and ambient
pressure characterization of hexagonal HP-BaCoO$_3$. The material (with the 2H
crystal structure) has a short intrachain Co-Co distance of about 2.07
$\text{\r{A}}$. Our magnetization investigation revealed robust diamagnetic
behavior below approximately 130 K when exposed to weak applied magnetic fields
(10 Oe) and a distinct half-levitation phenomenon below that temperature, such
as is often observed for superconductors. Its field-dependent magnetization
profile, however, unveils the characteristics of ferromagnetism, marked by a
substantial magnetic retentivity of 0.22(1) ${\mu}_B$/Co at a temperature of 2
K. Electrical resistivity measurements indicate that HP-BaCoO$_3$ is a
ferromagnetic insulator, not a superconductor. | 2312.14955v1 |
2022-10-03 | The impact of resistive electric fields on particle acceleration in reconnection layers | In the context of particle acceleration in high-energy astrophysical
environments featuring magnetic reconnection, the importance of the resistive
term of the electric field compared to the convective one is still under
debate. In this work, we present a quantitative analysis through 2D
magnetohydrodynamic numerical simulations of tearing-unstable current sheets
coupled to a test-particles approach, performed with the PLUTO code. We find
that the resistive field plays a significant role in the early-stage
energization of high-energy particles. Indeed, these particles are firstly
accelerated due to the resistive electric field when they cross an X-point,
created during the fragmentation of the current sheet. If this preliminary
particle acceleration mechanism dominated by the resistive field is neglected,
particles cannot reach the same high energies. Our results support therefore
the conclusion that the resistive field is not only non-negligible but it does
actually play an important role in the particle acceleration mechanism. | 2210.01113v1 |
2024-01-31 | Investigation of Microstructure and Corrosion Resistance of Ti-Al-V Titanium Alloys Obtained by Spark Plasma Sintering | The research results of the microstructure and corrosion resistance of Ti and
Ti-Al-V Russian industrial titanium alloys obtained by spark plasma sintering
(SPS) are described. Investigations of the microstructure, phase composition,
hardness, tensile strength, electrochemical corrosion resistance and hot salt
corrosion of Ti-Al-V titanium alloy specimens were carried out. It was shown
that the alloy specimens have a uniform highly dense microstructure and high
hardness values. The studied alloys also have high resistance to
electrochemical corrosion during tests in acidic aqueous solution causing the
intergranular corrosion as well as high resistance to the hot salt corrosion.
The assumption that the high hardness of the alloys as well as the differences
in the corrosion resistance of the central and lateral parts of the specimens
are due to the diffusion of carbon from the graphite mold into the specimen
surface was suggested. | 2401.17941v1 |
2003-02-01 | High-Temperature Hall Effect in Ga(1-x)Mn(x)As | The temperature dependence of the Hall coefficient of a series of
ferromagnetic Ga(1-x)Mn(x)As samples is measured in the temperature range 80K <
T < 500K. We model the Hall coefficient assuming a magnetic susceptibility
given by the Curie-Weiss law, a spontaneous Hall coefficient proportional to
rho_xx^2(T), and including a constant diamagnetic contribution in the
susceptibility. For all low resistivity samples this model provides excellent
fits to the measured data up to T=380K and allows extraction of the hole
concentration (p). The calculated p are compared to alternative methods of
determining hole densities in these materials: pulsed high magnetic field (up
to 55 Tesla) technique at low temperatures (less than the Curie temperature),
and electrochemical capacitance- voltage profiling. We find that the Anomalous
Hall Effect (AHE) contribution to rho_xy is substantial even well above the
Curie temperature. Measurements of the Hall effect in this temperature regime
can be used as a testing ground for theoretical descriptions of transport in
these materials. We find that our data are consistent with recently published
theories of the AHE, but they are inconsistent with theoretical models
previously used to describe the AHE in conventional magnetic materials. | 0302013v2 |
2007-06-15 | Growth mechanisms and structure of fullerene-like carbon-based thin films: superelastic materials for tribological applications | In this chapter we review our findings on the bonding structure and growth
mechanisms of carbon-based thin solid films with fullerene-like (FL)
microstructure. The so-called FL arrangements arise from the curvature and
cross-linking of basal planes in graphitic-like structures, partially
resembling that of molecular fullerenes. This three-dimensional superstructure
takes advantage of the strength of planar pi bonds in sp2 hybrids and confers
the material interesting mechanical properties, such as high hardness, high
elastic recovery, low-friction and wear-resistance. These properties can be
tailored by controlling the curvature, size and connectivity of the FL
arrangements, making these materials promising coatings for tribological
applications. We have focused our interest mostly on carbon nitride (CNx) since
nitrogen promotes the formation of FL arrangements at low substrate
temperatures and they are emerging over pure carbon coatings in tribological
applications such as protective overcoats in magnetic hard disks. We address
structural issues such as origin of plane curvature, nature of the
cross-linking sites and sp2 clustering, together with growth mechanisms based
on the role of film-forming precursors, chemical re-sputtering or concurrent
ion assistance during growth. | 0706.2258v1 |
2013-07-08 | Significant ZT Enhancement in p-type Ti(Co,Fe)Sb-InSb Nanocomposites via a Synergistic High Mobility Electron Injection Energy filtering and Boundary Scattering Approach | It has been demonstrated that InSb nanoinclusions, which are formed in situ,
can simultaneously improve all three individual thermoelectric properties of
the n-type half Heusler compound (Ti,Zr,Hf)(Co,Ni)Sb [Xie et al., Acta Mater.
58, 4795 (2010)]. In the work presented herein, we have adopted the same
approach to the p-type half Heusler compound Ti(Co,Fe)Sb. The results of
resistivity, Seebeck coefficient, thermal conductivity, and Hall coefficient
measurements indicate that the combined high mobility electron injection, low
energy electron filtering, and boundary scattering, again, lead to a
simultaneous improvement of all three individual thermoelectric properties:
enhanced Seebeck coefficient and electrical conductivity as well as reduced
lattice thermal conductivity. A figure of merit of ZT=0.33 was attained at 900
K for the sample containing 1 atomic percent InSb nanoinclusions, a 450 percent
improvement over the nanoinclusion-free sample. This represents a rare case
that the same nanostructuring approach successfully works for both p-type and
n-type thermoelectric materials of the same class, hence pointing to a
promising materials design route for higher performance half-Heusler materials
in the future and hopefully will realize similar improvement in TE devices
based on such half Heusler alloys. | 1307.2160v1 |
2018-06-21 | Planar Hall effect in type II Dirac semimetal VAl$_{3}$ | The study of electronic properties in topological systems is one of the most
fascinating topics in condensed matter physics, which has generated enormous
interests in recent times. New materials are frequently being proposed and
investigated to identify their non-trivial band structure. While sophisticated
techniques such as angle-resolved photoemission spectroscopy have become
popular to map the energy-momentum relation, the transport experiments lack any
direct confirmation of Dirac and Weyl fermions in a system. From band structure
calculations, VAl$_{3}$ has been proposed to be a type II topological Dirac
semimetal. This material represents a large family of isostructural compounds,
all having similar electronic band structure and is an ideal system to explore
the rich physics of Lorentz symmetry violating Dirac fermions. In this work, we
present a detailed analysis on the magnetotransport properties of VAl$_{3}$. A
large, non-saturating magnetoresistance has been observed. Hall resistivity
reveals the presence of two types of charge carriers with high mobility. Our
measurements show a large planar Hall effect in this material, which is robust
and can be easily detectable up to high temperature. This phenomenon originates
from the relativistic chiral anomaly and non-trivial Berry curvature, which
validates the theoretical prediction of the Dirac semimetal phase in VAl$_{3}$. | 1806.08287v1 |
2017-08-17 | Separation of Electron and Hole Dynamics in the Semimetal LaSb | We report investigations on the magnetotransport in LaSb, which exhibits
extremely large magnetoresistance (XMR). Foremost, we demonstrate that the
resistivity plateau can be explained without invoking topological protection.
We then determine the Fermi surface from Shubnikov - de Haas (SdH) quantum
oscillation measurements and find good agreement with the bulk Fermi pockets
derived from first principle calculations. Using a semiclassical theory and the
experimentally determined Fermi pocket anisotropies, we quantitatively describe
the orbital magnetoresistance, including its angle dependence. We show that the
origin of XMR in LaSb lies in its high mobility with diminishing Hall effect,
where the high mobility leads to a strong magnetic field dependence of the
longitudinal magnetoconductance. Unlike a one-band material, when a system has
two or more bands (Fermi pockets) with electron and hole carriers, the added
conductance arising from the Hall effect is reduced, hence revealing the latent
XMR enabled by the longitudinal magnetoconductance. With diminishing Hall
effect, the magnetoresistivity is simply the inverse of the longitudinal
magnetoconductivity, enabling the differentiation of the electron and hole
contributions to the XMR, which varies with the strength and orientation of the
magnetic field. This work demonstrates a convenient way to separate the
dynamics of the charge carriers and to uncover the origin of XMR in multi-band
materials with anisotropic Fermi surfaces. Our approach can be readily applied
to other XMR materials. | 1708.05416v2 |
2019-01-21 | Solid-State Thermal Energy Storage Using Reversible Martensitic Transformations | The identification and use of reversible Martensitic transformations,
typically described as shape memory transformations, as a new class of
solid-solid phase change material is experimentally demonstrated here for the
first time. To prove this claim, time-domain thermoreflectance,
frequency-domain thermoreflectance, and differential scanning calorimetry
studies were conducted on commercial NiTi alloys to quantify thermal
conductivity and latent heat. Additional Joule-heating experiments demonstrate
successful temperature leveling during transient heating and cooling in a
simulated environment. Compared to standard solid-solid materials and
solid-liquid paraffin, these experimental results show that shape memory alloys
provide up to a two order of magnitude higher Figure of Merit. Beyond these
novel experimental results, a comprehensive review of >75 binary NiTi and
NiTi-based ternary and quaternary alloys in the literature shows that shape
memory alloys can be tuned in a wide range of transformation temperatures (from
-50 to 330{deg}C), latent heats (from 9.1 to 35.1 J/g), and thermal
conductivities (from 15.6 to 28 W/mK). This can be accomplished by changing the
Ni and Ti balance, introducing trace elements, and/or by thermomechanical
processing. Combining excellent corrosion resistance, formability, high
strength and ductility, high thermal performance, and tunability, SMAs
represent an exceptional phase change material that circumvents many of the
scientific and engineering challenges hindering progress in this field. | 1901.06990v1 |
2020-11-30 | Discovery of carbon-based strongest and hardest amorphous material | Carbon is likely the most fascinating element of the periodic table because
of the diversity of its allotropes stemming from its variable (sp, sp2, and
sp3) bonding motifs. Exploration of new forms of carbon has been an eternal
theme of contemporary scientific research. Here we report on novel amorphous
carbon phases containing high fraction of sp3 bonded atoms recovered after
compressing fullerene C60 to previously unexplored high pressure and
temperature. The synthesized carbons are the hardest and strongest amorphous
materials known to date, capable of scratching diamond crystal and approaching
its strength which is evidenced by complimentary mechanical tests.
Photoluminescence and absorption spectra of the materials demonstrate they are
semiconductors with tunable bandgaps in the range of 1.5-2.2 eV, comparable to
that of amorphous silicon. A remarkable combination of the outstanding
mechanical and electronic properties makes this class of amorphous carbons an
excellent candidate for photovoltaic applications demanding ultrahigh strength
and wear resistance. | 2011.14819v2 |
2021-12-20 | Ultrafast Multi-Shot Ablation and Defect Generation in Monolayer Transition Metal Dichalcogenides | Transition metal dichalcogenides are known to possess large optical
nonlinearities and driving these materials at high intensities is desirable for
many applications. Understanding their optical responses under repetitive
intense excitation is essential to improve the performance limit of these
strong-field devices and to achieve efficient laser patterning. Here, we report
the incubation study of monolayer MoS${}_{2}$ and WS${}_{2}$ induced by 160 fs,
800 nm pulses in air to examine how their ablation threshold scales with the
number of admitted laser pulses. Both materials were shown to outperform
graphene and most bulk materials; specifically, MoS${}_{2}$ is as resistant to
radiation degradation as the best of the bulk thin films with a record fast
saturation. Our modeling provides convincing evidence that the small reduction
in threshold and fast saturation of MoS${}_{2}$ originates in its excellent
bonding integrity against radiation-induced softening. Sub-ablation damages, in
the forms of vacancies, lattice disorder, and nano-voids, were revealed by
transmission electron microscopy, photoluminescence, Raman, and second harmonic
generation studies, which were attributed to the observed incubation. For the
first time, a sub-ablation damage threshold is identified for monolayer
MoS${}_{2}$ to be 78% of single-shot ablation threshold, below which
MoS${}_{2}$ remains intact for many laser pulses. Our results firmly establish
MoS${}_{2}$ as a robust material for strong-field devices and for
high-throughput laser patterning. | 2112.10743v1 |
2024-03-19 | Electrical transport crossover and large magnetoresistance in selenium deficient van der Waals HfSe2-x | Transition metal dichalcogenides have received much attention in the past
decade not only due to the new fundamental physics, but also due to the
emergent applications in these materials. Currently chalcogenide deficiencies
in TMDs are commonly believed either during the high temperature growth
procedure or in the nanofabrication process resulting significant changes of
their reported physical properties in the literature. Here we perform a
systematic study involving pristine stochiometric HfSe2, Se deficient HfSe1.9
and HfSe1.8. Stochiometric HfSe2 transport results show semiconducting behavior
with a gap of 1.1eV. Annealing HfSe2 under high vacuum at room temperature
causes the Se loss resulting in HfSe1.9, which shows unconventionally large
magnetoresistivity following the extended Kohler's rule at low temperatures
below 50 K. Moreover, a clear electrical resistivity crossover, mimicking the
metal-insulator transition, is observed in the HfSe1.9 single crystal. Further
increasing the degree of deficiency in HfSe1.8 results in complete metallic
electrical transport at all temperatures down to 2K. Such a drastic difference
in the transport behaviors of stoichiometric and Se-deficient HfSe2 further
emphasizes that defect control and engineering could be an effective method
that could be used to tailor the electronic structure of 2D materials,
potentially unlock new states of matter, or even discover new materials. | 2403.12430v1 |
2018-09-27 | Granular aluminum: A superconducting material for high impedance quantum circuits | Superconducting quantum information processing machines are predominantly
based on microwave circuits with relatively low characteristic impedance, of
about 100 Ohm, and small anharmonicity, which can limit their coherence and
logic gate fidelity. A promising alternative are circuits based on so-called
superinductors, with characteristic impedances exceeding the resistance quantum
$R_Q = 6.4$ k$\Omega$. However, previous implementations of superinductors,
consisting of mesoscopic Josephson junction arrays, can introduce unintended
nonlinearity or parasitic resonant modes in the qubit vicinity, degrading its
coherence. Here we present a fluxonium qubit design using a granular aluminum
(grAl) superinductor strip. Granular aluminum is a particularly attractive
material, as it self-assembles into an effective junction array with a
remarkably high kinetic inductance, and its fabrication can be in-situ
integrated with standard aluminum circuit processing. The measured qubit
coherence time $T_2^R$ up to 30 $\mu$s illustrates the potential of grAl for
applications ranging from protected qubit designs to quantum limited amplifiers
and detectors. | 1809.10646v1 |
2012-11-29 | Effects of Resistivity on Magnetized Core-Collapse Supernovae | We studied roles of a turbulent resistivity in the core-collapse of a
strongly magnetized massive star, carrying out 2D-resistive-MHD simulations.
The three cases with different initial strengths of magnetic field and rotation
are investigated; 1. strongly magnetized rotating core; 2.moderately magnetized
rotating core; 3. very strongly magnetized non-rotating core. In each case,
both an ideal-MHD model and resistive-MHD models are computed. As a result of
computations, each model shows a matter eruption helped by a magnetic
acceleration (and also by a centrifugal acceleration in the rotating cases). We
found that a resistivity attenuates the explosion in case~1 and 2, while it
enhances the explosion in case~3. We also found that in the rotating cases,
main mechanisms for the amplification of a magnetic field in the post-bounce
phase are an outward advection of magnetic field and a winding of poloidal
magnetic field-lines by differential rotation, which are somewhat dampened down
with the presence of a resistivity. Although the magnetorotational instability
seems to occur in the rotating models, it will play only a minor role in a
magnetic field amplification. Another impact of resistivity is that on the
aspect ratio. In the rotating cases, a large aspect ratio of the ejected
matters, $> 2.5$, attained in a ideal-MHD model is reduced to some extent in a
resistive model. These results indicate that a resistivity possibly plays an
important role in the dynamics of strongly magnetized supernovae. | 1211.6817v2 |
2019-04-18 | Scaling-up atomically thin coplanar semiconductor-metal circuitry via phase engineered chemical assembly | Two-dimensional (2D) layered semiconductors, with their ultimate atomic
thickness, have shown promise to scale down transistors for modern integrated
circuitry. However, the electrical contacts that connect these materials with
external bulky metals are usually unsatisfactory, which limits the transistor
performance. Recently, contacting 2D semiconductors using coplanar 2D
conductors has shown promise in reducing the problematic high resistance
contacts. However, many of these methods are not ideal for scaled production.
Here, we report on the large-scale, spatially controlled chemical assembly of
the integrated 2H-MoTe2 field-effect transistors (FETs) with coplanar metallic
1T' MoTe2 contacts via phase engineered approaches. We demonstrate that the
heterophase FETs exhibit ohmic contact behavior with low contact resistance,
resulting from the coplanar seamless contact between 2H and 1T' MoTe2 confirmed
by transmission electron microscopy characterizations. The average mobility of
the heterophase FETs was measured to be as high as 23 cm2 V-1 s-1 (comparable
with those of exfoliated single crystals), due to the large 2H MoTe2
single-crystalline domain (486{\mu}m). By developing a patterned growth method,
we realize the 1T' MoTe2 gated heterophase FET array whose components of
channel, gate, and contacts are all 2D materials. Finally, we transfer the
heterophase device array onto a flexible substrate and demonstrate the
near-infrared photoresponse with high photoresponsivity (~1.02 A/W). Our study
provides a basis for the large-scale application of phase-engineered coplanar
MoTe2 semiconductors-meter structure in advanced electronics and
optoelectronics. | 1904.08545v1 |
2023-09-27 | High-Resolution Full-field Structural Microscopy of the Voltage Induced Filament Formation in Neuromorphic Devices | Neuromorphic functionalities in memristive devices are commonly associated
with the ability to electrically create local conductive pathways by resistive
switching. The archetypal correlated material, VO2, has been intensively
studied for its complex electronic and structural phase transition as well as
its filament formation under applied voltages. Local structural studies of the
filament behavior are often limited due to time-consuming rastering which makes
impractical many experiments aimed at investigating large spatial areas or
temporal dynamics associated with the electrical triggering of the phase
transition. Utilizing Dark Field X-ray Microscopy (DFXM), a novel full-field
x-ray imaging technique, we study this complex filament formation process
in-operando in VO2 devices from a structural perspective. We show that prior to
filament formation, there is a significant gain of the metallic rutile phase
beneath the metal electrodes that define the device. We observed that the
filament formation follows a preferential path determined by the nucleation
sites within the device. These nucleation sites are predisposed to the phase
transition and can persistently maintain the high-temperature rutile phase even
after returning to room temperature, which can enable a novel training/learning
mechanism. Filament formation also appears to follow a preferential path
determined by a nucleation site within the device which is predisposed to the
rutile transition even after returning to room temperature. Finally, we found
that small isolated low-temperature phase clusters can be present inside the
high-temperature filaments indicating that the filament structure is not
uniform. Our results provide a unique perspective on the electrically induced
filament formation in metal-insulator transition materials, which further the
basic understanding of this resistive switching. | 2309.15712v1 |
2020-12-23 | Separated transport relaxation scales and interband scattering in SrRuO$_3$, CaRuO$_3$, and Sr$_2$RuO$_4$ thin films | The anomalous charge transport observed in some strongly correlated metals
raises questions as to the universal applicability of Landau Fermi liquid
theory. The coherence temperature $T_{FL}$ for normal metals is usually taken
to be the temperature below which $T^2$ is observed in the resistivity. Below
this temperature, a Fermi liquid with well-defined quasiparticles is expected.
However, metallic ruthenates in the Ruddlesden-Popper family, frequently show
non-Drude low-energy optical conductivity and unusual $\omega/T$ scaling,
despite the frequent observation of $T^2$ dc resistivity. Herein we report
time-domain THz spectroscopy measurements of several different high-quality
metallic ruthenate thin films and show that the optical conductivity can be
interpreted in more conventional terms. In all materials, the conductivity has
a two-Drude peak lineshape at low temperature and a crossover to a one-Drude
peak lineshape at higher temperatures. The two-component low-temperature
conductivity is indicative of two well-separated current relaxation rates for
different conduction channels. We discuss three particular possibilities for
the separation of rates: (a) Strongly energy-dependent inelastic scattering;
(b) an almost-conserved pseudomomentum operator that overlaps with the current,
giving rise to the narrower Drude peak; (c) the presence of multiple conduction
channels that undergoes a crossover to stronger interband scattering at higher
temperatures. None of these scenarios require the existence of exotic
quasiparticles. The results may give insight into the possible significance of
Hund's coupling in determining interband coupling in these materials. Our
results also show a route towards understanding the violation of Matthiessen's
rule in this class of materials and deviations from the "Gurzhi" scaling
relations in Fermi liquids. | 2012.12800v1 |
2016-05-09 | An analytical model for the influence of contact resistance on thermoelectric efficiency | An analytical model is presented that can account for both electrical and hot
and cold thermal contact resistances when calculating the efficiency of a
thermoelectric generator. The model is compared to a numerical model of a
thermoelectric leg, for 16 different thermoelectric materials, as well as the
analytical models of Ebling et. al. (2010) and Min \& Rowe (1992). The model
presented here is shown to accurately calculate the efficiency for all systems
and all contact resistances considered, with an average difference in
efficiency between the numerical model and the analytical model of
$-0.07\pm0.35$ pp. This makes the model more accurate than previously published
models. The maximum absolute difference in efficiency between the analytical
model and the numerical model is 1.14 pp for all materials and all contact
resistances considered. | 1605.03565v1 |
2017-12-22 | Magnetoresistance in YBi and LuBi semimetals due to nearly perfect carrier compensation | Monobismuthides of yttrium and lutetium are shown as new representatives of
materials which exhibit extreme magnetoresistance and magnetic-field-induced
resistivity plateau. At low temperatures and in magnetic field of 9T the
magnetoresistance attains the order of magnitude of 10,000% and 1,000%, on YBi
and LuBi, respectively. Our thorough examination of electron transport
properties of both compounds show that observed features are the consequence of
nearly perfect carrier compensation rather than of possible nontrivial topology
of electronic states. The field-induced plateau of electrical resistivity can
be explained with Kohler scaling. Anisotropic multi-band model of electronic
transport describes very well the magnetic field dependence of electrical
resistivity and Hall resistivity. Data obtained from the Shubnikov-de Haas
oscillations analysis also confirm that Fermi surface of each compound contains
almost equal amounts of holes and electrons. First-principle calculations of
electronic band structure are in a very good agreement with the experimental
data. | 1712.08433v3 |
2020-05-07 | Origin of the Significant Impact of Ta on the Creep Resistance of FeCrNi Alloys | Heat resistant FeCrNi alloys are widely used in the petrochemical industry
because they exhibit a unique combination of creep and oxidation resistance at
temperatures exceeding 900$^\circ$C. Their creep properties are often optimized
by micro-additions of carbide forming elements. In the present work, the
influence of Ta micro-additions has been experimentally investigated both on
as-cast and aged microstructures to understand the origin of the significant
impact of this element on the creep resistance. Calculations with thermocal
software were also carried out to support experimental data. It is shown that a
small addition of Ta is beneficial as it increases the volume fraction of
stable MC carbides. We demonstrate also that additions of Ta may have a
dramatic effect on the thermal stability of microstructures. This is attributed
to a smaller equilibrium volume fraction of M23C6 and more pronounced
heterogeneous precipitation at MC/matrix interfaces. The influence on the creep
properties in then discussed. | 2005.03309v1 |
2022-10-07 | Radiation-resistant aluminium alloy for space missions in the extreme environment of the solar system | Future human-based exploration of our solar system requires the invention of
materials that can resist harsh environments. Age-hardenable aluminium alloys
would be attractive candidates for structural components in long-distance
spacecrafts, but their radiation resistance to solar energetic particles is
insufficient. Common hardening phases dissolve and displacement damage occurs
in the alloy matrix, which strongly degrades properties. Here we present an
alloy where hardening is achieved by T-phase, featuring a giant unit cell and
highly-negative enthalpy of formation. The phase shows record radiation
survivability and can stabilize an ultrafine-grained structure upon temperature
and radiation in the alloy, therby successfully preventing displacement damage
to occur. Such concept can be considered ideal for the next-generation space
materials and the design of radiation resistant alloy. | 2210.03397v3 |
2022-11-22 | Optical properties and corrosion resistance of Ti2AlC, Ti3AlC2, and Cr2AlC as candidates for Concentrated Solar Power receivers | New generation concentrated solar power (CSP) plants require new solar
receiver materials with selective optical properties and excellent corrosion
resistance against molten salts. MAX phases are promising materials for CSP
applications due to their optical properties and resistance to thermal shocks.
Herein, we report a solar absorptance >/= 0.5 and a thermal emittance of
0.17-0.31 between 600 and 1500 K for Cr2AlC, Ti2AlC, and Ti3AlC2. These
compositions were also exposed to solar salt corrosion at 600{\deg}C for up to
4 weeks. Cr2AlC exhibited superior corrosion resistance due to the formation of
a protective nanometric layer. | 2211.12251v2 |
2020-01-16 | Social Engineering Resistant 2FA | Attackers increasingly, and with high success rates, use social engineering
techniques to circumvent second factor authentication (2FA) technologies,
compromise user accounts and sidestep fraud detection technologies. We
introduce a social engineering resistant approach that we term device-aware
2FA, to replace the use of traditional security codes. | 2001.06075v1 |
2019-01-12 | Surface impedance measurements on Nb$_{3}$Sn at high magnetic fields | Nb$_{3}$Sn is a superconductor of great relevance for perspective RF
applications. We present for the first time surface impedance $Z_s$
measurements at 15 GHz and low RF field amplitude on Nb$_{3}$Sn in high
magnetic fields up to 12 T, with the aim of increasing the knowledge of
Nb$_{3}$Sn behavior in such conditions. $Z_s$ is a fundamental material
parameter that directly gives useful information about the dissipative and
reactive phenomena when the superconductor is subjected to high-frequency
excitations. Therefore, we present an analysis of the measured $Z_s$ with the
aim of extracting interesting data about pinning in Nb$_{3}$Sn at high
frequencies. From $Z_s$ we extract the vortex motion complex resistivity to
obtain the $r$-parameter and the depinning frequency $\nu_p$ in high magnetic
fields. The comparison of the results with the literature shows that the
measured $\nu_p$ on bulk Nb$_{3}$Sn is several times greater than that of pure
Nb. This demonstrates how Nb$_{3}$Sn can be a good candidate for RF
technological applications, also in high magnetic fields. | 1901.03819v1 |
2020-08-25 | Observation of High Harmonics of the Cyclotron Resonance in Microwave Transmission of a High-Mobility Two-Dimensional Electron System | We report an observation of magnetooscillations of the microwave power
transmitted through the high mobility two-dimensional electron system hosted by
a GaAs quantum well. The oscillations reflect an enhanced absorption of
radiation at high harmonics of the cyclotron resonance and follow
simultaneously measured microwave-induced resistance oscillations (MIRO) in the
dc transport. While the relative amplitude (up to 1%) of the transmittance
oscillations appears to be small, they represent a significant (>50%)
modulation of the absorption coefficient. The analysis of obtained results
demonstrates that the low-B decay, magnitude, and polarization dependence of
the transmittance oscillations accurately follow the theory describing
photon-assisted scattering between distant disorder-broadened Landau levels.
The extracted sample parameters reasonably well describe the concurrently
measured MIRO. Our results provide an insight into the MIRO polarization
immunity problem and pave the way to probe diverse high-frequency transport
properties of high-mobility systems using precise transmission measurements. | 2008.11114v1 |
2021-09-20 | Giant anomalous Nernst signal in the antiferromagnet YbMnBi2 | Searching for a high anomalous Nernst effect (ANE) is crucial for
thermoelectric energy conversion applications because the associated unique
transverse geometry facilitates module fabrication. Topological ferromagnets
with large Berry curvatures show high ANEs; however, they face drawbacks such
as strong magnetic disturbances and low mobility due to high magnetization.
Herein, we demonstrate that YbMnBi2, a canted antiferromagnet, has a large ANE
conductivity of ~10 Am-1K-1 that surpasses the common high values (i.e. 3-5
Am-1K-1) observed so far in ferromagnets. The canted spin structure of Mn
guarantees a nonzero Berry curvature but generates only a weak magnetization
three orders of magnitude lower than that of general ferromagnets. The heavy Bi
with a large spin-orbit coupling enables a high ANE and low thermal
conductivity, whereas its highly dispersive px/y orbitals ensure low
resistivity. The high anomalous transverse thermoelectric performance and
extremely small magnetization makes YbMnBi2 an excellent candidate for
transverse thermoelectrics. | 2109.09382v1 |
2022-02-09 | Low energy switching of phase change materials using a 2D thermal boundary layer | The switchable optical and electrical properties of phase change materials
(PCMs) are finding new applications beyond data storage in reconfigurable
photonic devices. However, high power heat pulses are needed to melt-quench the
material from crystalline to amorphous. This is especially true in silicon
photonics, where the high thermal conductivity of the waveguide material makes
heating the PCM energy inefficient. Here, we improve the energy efficiency of
the laser-induced phase transitions by inserting a layer of two-dimensional
(2D) material, either MoS2 or WS2, between the silica or silicon and the PCM.
The 2D material reduces the required laser power by at least 40% during the
amorphization (RESET) process, depending on the substrate. Thermal simulations
confirm that both MoS2 and WS2 2D layers act as a thermal barrier, which
efficiently confines energy within the PCM layer. Remarkably, the thermal
insulation effect of the 2D layer is equivalent to a ~100 nm layer of SiO2. The
high thermal boundary resistance induced by the van der Waals (vdW)-bonded
layers limits the thermal diffusion through the layer interfaces. Hence, 2D
materials with stable vdW interfaces can be used to improve the thermal
efficiency of PCM-tuned Si photonic devices. Furthermore, our waveguide
simulations show that the 2D layer does not affect the propagating mode in the
Si waveguide, thus this simple additional thin film produces a substantial
energy efficiency improvement without degrading the optical performance of the
waveguide. Our findings pave the way for energy-efficient laser-induced
structural phase transitions in PCM-based reconfigurable photonic devices. | 2202.04699v1 |
2008-06-27 | Electron pockets in the Fermi surface of hole-doped high-Tc superconductors | High-temperature superconductivity occurs as copper oxides are chemically
tuned to have a carrier concentration intermediate between their metallic state
at high doping and their insulating state at zero doping. The underlying
evolution of the electron system in the absence of superconductivity is still
unclear and a question of central importance is whether it involves any
intermediate phase with broken symmetry. The Fermi surface of underdoped
YBa2Cu3Oy and YBa2Cu4O8 was recently shown to include small pockets in contrast
with the large cylinder characteristic of the overdoped regime1, pointing to a
topological change in the Fermi surface. Here we report the observation of a
negative Hall resistance in the magnetic field-induced normal state of
YBa2Cu3Oy and YBa2Cu4O8, which reveals that these pockets are electron-like. We
propose that electron pockets arise most likely from a reconstruction of the
Fermi surface caused by the onset of a density-wave phase, as is thought to
occur in the electron-doped materials near the onset of antiferromagnetic order
Comparison with materials of the La2CuO4 family that exhibit spin/charge
density-wave order suggests that a Fermi surface reconstruction also occurs in
those materials, pointing to a generic property of high-Tc superconductors. | 0806.4621v1 |
2008-11-19 | Elucidation of the origins of HTSC transport behaviour and quantum oscillations | A detailed exposition is made of recent transport and 'quantum oscillation'
results from HTSC systems covering the full range from overdoped to underdoped
material. This now very extensive and high quality data set is interpreted here
within the framework developed by the author of local pairs and boson-fermion
resonance, arising in the context of negative-U behaviour in an inhomogeneous
electronic environment. The strong inhomogeneity comes with the mixed-valent
condition of these materials, which when underdoped lie in close proximity to
the Mott-Anderson transition. The observed intense scattering is presented as
resulting from pair formation and electron-boson collisions in the resonant
crossover circumstance. The high level of scattering brings the systems to
incoherence in the pseudogapped state, p < pc (= 0.183). In a high magnetic
field the striped partition of the inhomogeneous charge distribution is much
strengthened and regularized. Magnetization and resistance oscillations, of
period dictated by the favoured positioning of the square fluxon array within
the real space environment of the diagonal 2D charge striping array, are
demonstrated to be responsible for the recently reported behaviour hitherto
widely attributed to the quantum oscillation response of a much more standard
Fermi liquid condition. A detailed analysis embracing all the experimental data
serves to indicate that in the given conditions of very high field, low
temperature, 2D-striped, underdoped, d-wave superconducting, HTSC material the
flux quantum becomes doubled to h/e. | 0811.3096v2 |
2011-11-04 | Local Structure of the Superconductor K0.8Fe1.6+xSe2: Evidence of Large Structural Disorder | The local structure of superconducting single crystals of K0.8Fe1.6+xSe2 with
Tc = 32.6 K was studied by x-ray absorption spectroscopy. Near-edge spectra
reveal that the average valence of Fe is 2+. The room temperature structure
about the Fe, K and Se sites was examined by iron, selenium and potassium
K-edge measurements. The structure about the Se and Fe sites shows a high
degree of order in the nearest neighbor Fe-Se bonds. On the other hand, the
combined Se and K local structure measurements reveal a very high level of
structural disorder in the K layers. Temperature dependent measurements at the
Fe sites show that the Fe-Se atomic correlation follows that of the Fe-As
correlation in the superconductor LaFeAsO0.89F0.11 - having the same effective
Einstein temperature (stiffness). In K0.8Fe1.6+xSe2, the nearest neighbor Fe-Fe
bonds has a lower Einstein temperature and higher structural disorder than in
LaFeAsO0.89F0.11. The moderate Fe site and high K site structural disorder is
consistent with the high normal state resistivity seen in this class of
materials. For higher shells, an enhancement of the second nearest neighbor
Fe-Fe interaction is found just below Tc and suggests that correlations between
Fe magnetic ion pairs beyond the first neighbor are important in models of
magnetic order and superconductivity in these materials. | 1111.1026v1 |
2017-02-14 | Pressure-induced metallization and superconducting phase in ReS2 | Among the family of TMDs, ReS2 takes a special position, which crystalizes in
a unique distorted low-symmetry structure at ambient conditions. The interlayer
interaction in ReS2 is rather weak, thus its bulk properties are similar to
that of monolayer. However, how does compression change its structure and
electronic properties is unknown so far. Here using ab initio crystal structure
searching techniques, we explore the high-pressure phase transitions of ReS2
extensively and predict two new high-pressure phases. The ambient pressure
phase transforms to a "distorted-1T" structure at very low pressure and then to
a tetragonal I41/amd structure at around 90 GPa. The "distorted-1T" structure
undergoes a semiconductor-metal transition (SMT) at around 70 GPa with a band
overlap mechanism. Electron-phonon calculations suggest that the I41/amd
structure is superconducting and has a critical superconducting temperature of
about 2 K at 100 GPa. We further perform high-pressure electrical resistance
measurements up to 102 GPa. Our experiments confirm the SMT and the
superconducting phase transition of ReS2 under high pressure. These
experimental results are in good agreement with our theoretical predictions. | 1702.04061v1 |
2018-05-04 | Silicon Oxide Electron-Emitting Nanodiodes | Electrically driven on-chip electron sources that do not need to be heated
have been long pursued because the current thermionic electron sources show the
problems of high power consumption, slow temporal response, bulky size, etc.,
but their realization remains challenging. Here we show that a nanogap formed
by two electrodes on a silicon oxide substrate functions as an
electron-emitting nanodiode after the silicon oxide in the nanogap is
electrically switched to a high-resistance conducting state. A nanodiode based
on graphene electrodes can be turned on by a voltage of ~7 V in ~100 ns and
show an emission current of up to several microamperes, corresponding to an
emission density of ~10^6 A cm^-2 and emission efficiency as high as 16.6%. We
attribute the electron emission to be generated from a metal-insulator-metal
tunneling diode on the substrate surface formed by the rupture of conducting
filaments in silicon oxide. An array of 100 nanodiodes exhibits a global
emission density of 5 A cm^-2 and stable emission with negligible current
degradation over tens of hours under modest vacuum. The combined advantages of
a low operating voltage, fast temporal response, high emission density and
efficiency, convenient fabrication and integration, and stable emission in
modest vacuum make silicon oxide electron-emitting nanodiodes a promising
on-chip alternative to thermionic emission sources. | 1805.01602v1 |
2019-11-04 | Enhanced upper critical field in Co-doped Ba122 superconductors by lattice defect tuning | Nanoscale defects in superconductors play a dominant role in enhancing
superconducting properties through electron scattering, modulation of coherence
length, and correlation with quantized magnetic flux. For iron-based
superconductors (IBSCs) that are expected to be employed in high-field magnetic
applications, a fundamental question is whether such defects develop an upper
critical field (Hc2) similar to that of conventional BCS-type superconductors.
Herein, we report the first demonstration of a significantly improved Hc2 in a
122-phase IBSC by introducing defects through high-energy milling. Co-doped
Ba122 polycrystalline bulk samples (Ba(Fe,Co)2As2) were prepared by sintering
powder which was partially mechanically alloyed through high-energy milling. A
remarkable increase in full-width at half maximum of X-ray powder diffraction
peaks, anomalous shrinkage in the a-axis, and elongation in the c-axis were
observed. When lattice defects are introduced into the grains, semiconductor
behavior of the electric resistivity at low temperature (T < 100 K), slight
decrease in transition temperature (Tc), upturn of Hc2(T) near Tc, and a large
increase in Hc2(T) slope were observed. The slope of Hc2(T) increased
approximately by 50%, i.e., from 4 to 6 T/K, and exceeded that of single
crystals and thin films. Defect engineering through high-energy milling is
expected to facilitate new methods for the designing and tuning of Hc2 in
122-phase IBSCs. | 1911.01080v1 |
2019-11-07 | Chemical manipulation of hydrogen induced high p-type and n-type conductivity in Ga2O3 | Advancement of optoelectronic and high-power devices is tied to the
development of wide band gap materials with excellent transport properties.
However, bipolar doping (n-type and p-type doping) and realizing high carrier
density while maintaining good mobility have been big challenges in wide band
gap materials. Here P-type and n-type conductivity was introduced in
beta-Ga2O3, an ultra-wide band gap oxide, by controlling hydrogen incorporation
in the lattice without further doping. Hydrogen induced a 9-order of magnitude
increase of n-type conductivity with donor ionization energy of 20 meV and
resistivity of 10-4 Ohm.cm. The conductivity was switched to p-type with
acceptor ionization energy of 42 meV by altering hydrogen incorporation in the
lattice. Density functional theory calculations were used to examine hydrogen
location in the Ga2O3 lattice and identified a new donor type as the source of
this remarkable n-type conductivity. Positron annihilation spectroscopy
confirmed this finding and the interpretation of the results. This work
illustrates a new approach that allows a tunable and reversible way of
modifying the conductivity of semiconductors and it is expected to have
profound implications on semiconductor field. At the same time it demonstrates
for the first time p-type and remarkable n-type conductivity in Ga2O3 which
should usher in the development of Ga2O3 devices and advance optoelectronics
and high-power devices | 1911.02717v1 |
2021-03-01 | Absence of magnetic evidence for superconductivity in hydrides under high pressure | It is generally believed that magnetization measurements on sulfur hydride
under high pressure performed in 2015 [1] provided "final convincing evidence
of superconductivity" [2] in that material, in agreement with theoretical
predictions [3,4]. Supported by this precedent, drops in resistance that were
later observed in several other hydrides under high pressure [2,5] have been
generally accepted as evidence of superconductivity without corroborating
evidence from magnetic measurements. In this paper we challenge the original
interpretation that the magnetic measurements on sulfur hydride performed in
2015 were evidence of superconductivity. We point out that a large paramagnetic
contribution to the magnetic susceptibility was detected below Tc and argue
that its temperature dependence rules out the possibility that it would be a
background signal; instead the temperature dependence indicates that the
paramagnetic behavior originated in the sample. We discuss possible
explanations for this remarkable behavior and conclude that standard
superconductors would not show such behavior. We also survey all the other
published data from magnetic measurements on this class of materials and
conclude that they do not provide strong evidence for superconductivity.
Consequently, we call into question the generally accepted view that
conventional superconductivity in hydrogen-rich materials at high temperature
and pressure is a reality, and discuss the implications if it is not. | 2103.00701v3 |
2021-08-15 | High power Figure-of-Merit, 10.6-kV AlGaN/GaN lateral Schottky barrier diode with single channel and sub-100-μm anode-to-cathode spacing | GaN-based lateral Schottky diodes (SBDs) have attracted great attention for
high-power applications due to its combined high electron mobility and large
critical breakdown field. However, the breakdown voltage (BV) of the SBDs are
far from exploiting the material advantages of GaN at present, limiting the
desire to use GaN for ultra-high voltage (UHV) applications. Then, a golden
question is whether the excellent properties of GaN-based materials can be
practically used in the UHV field? Here we demonstrate UHV AlGaN/GaN SBDs on
sapphire with a BV of 10.6 kV, a specific on-resistance of 25.8 m{\Omega}.cm2,
yielding a power figure of merit of more than 3.8 GW/cm2. These devices are
designed with single channel and 85-{\mu}m anode-to-cathode spacing, without
other additional electric field management, demonstrating its great potential
for the UHV application in power electronics. | 2108.06679v1 |
2023-11-14 | A New Look at Calcium Digermanide CaGe$_2$: A High-Performing Semimetal Transparent Conducting Material for Ge Optoelectronics | Following a recently manifested guide of how to team up infrared transparency
and high electrical conductivity within semimetal materials [C. Cui $et$ $al.$
Prog. Mater. Sci. 2023, 136, 101112], we evaluate an applicability of the
calcium digermanide (CaGe$_2$) thin film electrodes for the advanced Ge-based
optical devices. Rigorous growth experiments were conducted to define the
optimal annealing treatment and thickness of the Ca-Ge mixture for producing
stable CaGe$_2$ layers with high figure of merit (FOM) as transparent
conducting material. Ab-initio electronic band structure calculations and
optical modeling confirmed CaGe$_2$ semimetal nature, which is responsible for
a demonstrated high FOM. To test CaGe$_2$ electrodes under actual conditions, a
planar Ge photodetector (PD) with metal-semiconductor-metal structure was
fabricated, where CaGe$_2$/Ge interface acts as Schottky barrier. The resulting
Ge PD with semimetal electrodes outperformed commercially available Ge devices
in terms of both photoresponse magnitude and operated spectral range. Moreover,
by using femtosecond-laser projection lithography, a mesh CaGe$_2$ electrode
with the relative broadband transmittance of 90\% and sheet resistance of 20
$\Omega$/sq. was demonstrated, which further enhanced Ge PD photoresponse.
Thus, obtained results suggest that CaGe$_2$ thin films have a great potential
in numerous applications promoting the era of advanced Ge optoelectronics. | 2311.07903v1 |
2023-12-14 | Unlocking High Performance, Ultra-Low Power Van der Waals Transistors: Towards Back-End-of-Line In-Sensor Machine Vision Applications | Recent reports on machine learning (ML) and machine vision (MV) devices have
demonstrated the potentials of 2D materials and devices. Yet, scalable 2D
devices are being challenged by contact resistance and Fermi Level Pinning
(FLP), power consumption, and low-cost CMOS compatible lithography processes.
To enable CMOS+2D, it is essential to find a proper lithography strategy that
can fulfill these requirements. Here, we explore modified van der Waals (vdW)
deposition lithography and demonstrate a relatively new class of
van-der-Waals-Field-Effect-Transistors (vdW-FETs) based on 2D materials. This
lithography strategy enables us to unlock high performance devices evident by
high current on-off ratio (Ion/Ioff), high turn-on current density (Ion), and
weak Fermi Level Pinning (FLP). We utilize this approach to demonstrate a
gate-tunable near-ideal diode using MoS2/WSe2 heterojunction with an ideality
factor of ~1.65 and current rectification of 102. We finally demonstrate a
highly sensitive, scalable, and ultra-low power phototransistor using MoS2/
WSe2 vdW-FET for Back-End-of-Line (BEOL) integration. Our phototransistor
exhibits the highest gate-tunable photoresponsivity achieved to date for white
light detection with ultra-low power dissipation, enabling ultra-sensitive,
ultra-fast, and efficient optoelectronic applications such as in-sensor
neuromorphic machine vision. Our approach shows the great potential of modified
vdW deposition lithography for back-end-of-line CMOS+2D applications. | 2312.08634v1 |
2006-08-31 | Systematic study of disorder induced by neutron irradiation in MgB2 thin films | The effects of neutron irradiation on normal state and superconducting
properties of epitaxial magnesium diboride thin films are studied up to
fluences of 1020 cm-2. All the properties of the films change systematically
upon irradiation. Critical temperature is suppressed and, at the highest
fluence, no superconducting transition is observed down to 1.8 K. Residual
resistivity progressively increases from 1 to 190 microohmcm; c axis expands
and then saturates at the highest damage level. We discuss the mechanism of
damage through the comparison with other damage procedures. The normal state
magnetoresistivity of selected samples measured up to high fields (28 and 45T)
allows to determine unambiguously the scattering rates in each band; the
crossover between the clean and dirty limit in each sample can be monitored.
This set of samples, with controlled amount of disorder, is suitable to study
the puzzling problem of critical field in magnesium diboride thin films. The
measured critical field values are extremely high (of the order of 50T in the
parallel direction at low fluences) and turns out to be rather independent on
the experimental resistivity, at least at low fluences. A simple model to
explain this phenomenology is presented. | 0608706v2 |
2001-11-30 | Effects of Bulk and Surface Conductivity on the Performance of CdZnTe Pixel Detectors | We studied the effects of bulk and surface conductivity on the performance of
high-resistivity CdZnTe (CZT) pixel detectors with Pt contacts. We emphasize
the difference in mechanisms of the bulk and surface conductivity as indicated
by their different temperature behaviors. In addition, the existence of a thin
(10-100 A) oxide layer on the surface of CZT, formed during the fabrication
process, affects both bulk and surface leakage currents. We demonstrate that
the measured I-V dependencies of bulk current can be explained by considering
the CZT detector as a metal-semiconductor-metal system with two back-to-back
Schottky-barrier contacts. The high surface leakage current is apparently due
to the presence of a low-resistivity surface layer that has characteristics
which differ considerably from those of the bulk material. This surface layer
has a profound effect on the charge collection efficiency in detectors with
multi-contact geometry; some fraction of the electric field lines originated on
the cathode intersects the surface areas between the pixel contacts where the
charge produced by an ionizing particle gets trapped. To overcome this effect
we place a grid of thin electrodes between the pixel contacts; when the grid is
negatively biased, the strong electric field in the gaps between the pixels
forces the electrons landing on the surface to move toward the contacts,
preventing the charge loss. We have investigated these effects by using CZT
pixel detectors indium bump bonded to a custom-built VLSI readout chip. | 0112001v1 |
2008-10-23 | Thermopower across the pseudogap critical point of La(1.6-x)Nd(0.4)Sr(x)CuO(4): Evidence for a quantum critical point in a hole-doped high-Tc superconductor | The thermopower S of the high-Tc superconductor La(1.6-x)Nd(0.4)Sr(x)CuO(4)
was measured as a function of temperature T near its pseudogap critical point,
the critical hole doping p* where the pseudogap temperature T* goes to zero.
Just above p*, S/T varies as ln(1/T) over a decade of temperature. Below p*,
S/T undergoes a large increase below T*. As with the temperature dependence of
the resistivity, which is linear just above p* and undergoes a large upturn
below T*, these are typical signatures of a quantum phase transition. This
suggests that p* is a quantum critical point below which some order sets in,
causing a reconstruction of the Fermi surface, whose fluctuations are
presumably responsible for the linear-T resistivity and logarithmic
thermopower. We discuss the possibility that this order is the "stripe" order
known to exist in this material. | 0810.4280v2 |
2009-09-23 | Zooming on the Quantum Critical Point in Nd-LSCO | Recent studies of the high-Tc superconductor La_(1.6-x)Nd_(0.4)Sr_(x)CuO_(4)
(Nd-LSCO) have found a linear-T in-plane resistivity rho_(ab) and a logarithmic
temperature dependence of the thermopower S / T at a hole doping p = 0.24, and
a Fermi-surface reconstruction just below p = 0.24 [1, 2]. These are typical
signatures of a quantum critical point (QCP). Here we report data on the c-axis
resistivity rho_(c)(T) of Nd-LSCO measured as a function of temperature near
this QCP, in a magnetic field large enough to entirely suppress
superconductivity. Like rho_(ab), rho_(c) shows an upturn at low temperature, a
signature of Fermi surface reconstruction caused by stripe order. Tracking the
height of the upturn as it decreases with doping enables us to pin down the
precise location of the QCP where stripe order ends, at p* = 0.235 +- 0.005. We
propose that the temperature T_(rho) below which the upturn begins marks the
onset of the pseudogap phase, found to be roughly twice as high as the stripe
ordering temperature in this material. | 0909.4218v1 |
2009-12-30 | 30 inch Roll-Based Production of High-Quality Graphene Films for Flexible Transparent Electrodes | We report that 30-inch scale multiple roll-to-roll transfer and wet chemical
doping considerably enhance the electrical properties of the graphene films
grown on roll-type Cu substrates by chemical vapor deposition. The resulting
graphene films shows a sheet resistance as low as ~30 Ohm/sq at ~90 %
transparency which is superior to commercial transparent electrodes such as
indium tin oxides (ITO). The monolayer of graphene shows sheet resistances as
low as ~125 Ohm/sq with 97.4% optical transmittance and half-integer quantum
Hall effect, indicating the high-quality of these graphene films. As a
practical application, we also fabricated a touch screen panel device based on
the graphene transparent electrodes, showing extraordinary mechanical and
electrical performances. | 0912.5485v3 |
2013-10-03 | Aharonov-Bohm resistance magneto-oscillations on single-nanohole graphite and graphene structures | Graphene is a stable single atomic layer material exhibiting two-dimensional
electron gas of massless Dirac fermions of high mobility. One of the intriguing
properties of graphene is a possibility of realization of the Tamm-type edge
states. These states differ from the usual surface states caused by defects,
impurities and other imperfections at the edge of the system, as well as they
differ from the magnetic edge states caused by skipping cyclotron orbits. The
Tamm states result from breaking of periodic crystal potential at the edge,
they can exist even at zero magnetic field and form a conducting band. Until
recently those states have been observed in graphene only by local STM
technique and there were no direct experiments on their contribution to
transport measurements. Here we present the experiments on Aharonov-Bohm (AB)
oscillations of resistance in a single-nanohole graphite and graphene
structures, it indicates the presence of conducting edge states cycling around
nanohole. An estimation show the penetration depth of the edge states to be as
short as about 2 nm. The oscillations persist up to temperature T=115 K and the
T-range of their existence increases with a decrease of the nanohole diameter.
The proposed mechanism of the AB oscillations based on the resonant intervalley
backscattering of the Dirac fermions by the nanohole via the Tamm states. The
experimental results are consistent with such a scenario. Our findings show a
way towards interference devices operating at high temperatures on the edge
states in graphene | 1310.0991v1 |
2014-02-27 | Spin-charge interplay in antiferromagnetic La$_{2-x}$Sr$_{x}$CuO$_{4}$ studied by the muons, neutrons, and ARPES techniques | Exploring whether a spin density wave (SDW) is responsible for the charge
excitations gap in the high-temperature superconducting cuprates is difficult,
since the region of the phase diagram where the magnetic properties are clearly
exposed is different from the region where the band dispersion is visible. On
the one hand, long range magnetic order disappears as doping approaches 2% from
below, hindering our ability to perform elastic neutron scattering (ENS). On
the other hand, cuprates become insulating at low temperature when the doping
approaches 2% from above, thus restricting angle-resolved photoemission
spectroscopy (ARPES). In fact, ARPES data for samples with doping lower than 3%
are rare and missing the quasiparticle peaks in the energy distribution curves
(EDCs). The main problem is the high resistivity of extremely underdoped
samples, which is detrimental to ARPES due to charging effects. Nevertheless,
the resistivity of La$_{2-x}$Sr$_{x}$CuO$_{4}$ as a function of temperature, at
2% doping, has a broad minimum around 100K. This minimum opens a window for
both experiments. By preparing a series of LSCO single crystals with $\sim
$0.2-0.3% doping steps around 2%, we managed to find one to which both
techniques apply. This allows us to explore the cross talk between the magnetic
and electronic properties of the material. | 1402.6936v1 |
2014-05-21 | High Mobility WSe2 p- and n-Type Field Effect Transistors Contacted by Highly Doped Graphene for Low-Resistance Contacts | We report the fabrication of both n-type and p-type WSe2 field effect
transistors with hexagonal boron nitride passivated channels and ionic-liquid
(IL)-gated graphene contacts. Our transport measurements reveal intrinsic
channel properties including a metal-insulator transition at a characteristic
conductivity close to the quantum conductance e2/h, a high ON/OFF ratio of >107
at 170 K, and large electron and hole mobility of ~200 cm2V-1s-1 at 160 K.
Decreasing the temperature to 77 K increases mobility of electrons to ~330
cm2V-1s-1 and that of holes to ~270 cm2V-1s-1. We attribute our ability to
observe the intrinsic, phonon limited conduction in both the electron and hole
channels to the drastic reduction of the Schottky barriers between the channel
and the graphene contact electrodes using IL gating. We elucidate this process
by studying a Schottky diode consisting of a single graphene/WSe2 Schottky
junction. Our results indicate the possibility to utilize chemically or
electrostatically highly doped graphene for versatile, flexible and transparent
low-resistance Ohmic contacts to a wide range of quasi-2D semiconductors.
KEYWORDS: MoS2, WSe2, field-effect transistors, graphene, Schottky barrier,
ionic-liquid gate | 1405.5437v1 |
2015-01-07 | Angle dependence of the orbital magnetoresistance in bismuth | We present an extensive study of angle-dependent transverse magnetoresistance
in bismuth, with a magnetic field perpendicular to the applied electric current
and rotating in three distinct crystallographic planes. The observed angular
oscillations are confronted with the expectations of semi-classic transport
theory for a multi-valley system with anisotropic mobility and the agreement
allows us to quantify the components of the mobility tensor for both electrons
and holes. A quadratic temperature dependence is resolved. As Hartman argued
long ago, this indicates that inelastic resistivity in bismuth is dominated by
carrier-carrier scattering. At low temperature and high magnetic field, the
threefold symmetry of the lattice is suddenly lost. Specifically, a $2\pi/3$
rotation of magnetic field around the trigonal axis modifies the amplitude of
the magneto-resistance below a field-dependent temperature. By following the
evolution of this anomaly as a function of temperature and magnetic field, we
mapped the boundary in the (field, temperature) plane separating two electronic
states. In the less-symmetric state, confined to low temperature and high
magnetic field, the three Dirac valleys cease to be rotationally invariant. We
discuss the possible origins of this spontaneous valley polarization, including
a valley-nematic scenario. | 1501.01584v2 |
2015-02-26 | First principles design of divacancy defected graphene nanoribbon based rectifying and negative differential resistance device | We have elaborately studied the electronic structure of 555-777 divacancy
(DV) defected armchair edged graphene nanoribbon (AGNR) and transport
properties of AGNR based two-terminal device constructed with one defected
electrode and one N doped electrode, by using density functional theory and
non-equilibrium Green's function based approach. The introduction of 555-777 DV
defect into AGNRs, results in a shifting of the {\pi} and {\pi}* bands towards
the higher energy value which indicates a shifting of the Fermi level towards
the lower energy. Formation of a potential barrier, very similar to that of
conventional p-n junction, has been observed across the junction of defected
and N doped AGNR. The prominent asymmetric feature of the current in the
positive and negative bias indicates the diode like property of the device with
high rectifying efficiency within wide range of bias voltages. The device also
shows robust negative differential resistance (NDR) with very high
peak-to-valley ratio. The analysis of the shifting of the energy states of the
electrodes and the modification of the transmission function with applied bias
provides an insight into the nonlinearity and asymmetry observed in the I-V
characteristics. Variation of the transport properties on the width of the
ribbon has also been discussed. | 1502.07465v1 |
2016-06-07 | Superconductivity and Charge Density Wave in ZrTe$_{3-x}$Se$_{x}$ | Charge density wave (CDW), the periodic modulation of the electronic charge
density, will open a gap on the Fermi surface that commonly leads to decreased
or vanishing conductivity. On the other hand superconductivity, a commonly
believed competing order, features a Fermi surface gap that results in infinite
conductivity. Here we report that superconductivity emerges upon Se doping in
CDW conductor ZrTe$_{3}$ when the long range CDW order is gradually suppressed.
Superconducting critical temperature $T_c(x)$ in ZrTe$_{3-x}$Se$_x$
(${0\leq}x\leq0.1$) increases up to 4 K plateau for
$0.04$$\leq$$x$$\leq$$0.07$. Further increase in Se content results in
diminishing $T_{c}$ and filametary superconductivity. The CDW modes from Raman
spectra are observed in $x$ = 0.04 and 0.1 crystals, where signature of
ZrTe$_{3}$ CDW order in resistivity vanishes. The electronic-scattering for
high $T_{c}$ crystals is dominated by local CDW fluctuations at high
temperures, the resistivity is linear up to highest measured $T=300K$ and
contributes to substantial in-plane anisotropy. | 1606.02284v1 |
2016-07-15 | Effect of interface on mid-infrared photothermal response of MoS2 thin film grown by pulsed laser deposition | Here we report mid infrared (mid-IR) photothermal response of multi layer
MoS2 thin film grown on crystalline (p-type silicon and c-axis oriented single
crystal sapphire) and amorphous substrates (Si/SiO2 and Si/SiN) by pulsed laser
deposition (PLD) technique. The photothermal response of the MoS2 films was
measured as changes in the resistance of MoS2 films when irradiated with mid IR
(7 to 8.2 {\mu}m) source. We show that it is possible to enhance the
temperature coefficient of resistance (TCR) of the MoS2 thin film by
controlling the interface through proper choice of substrate and growth
conditions. The thin films grown by PLD were characterized using XRD, Raman,
AFM, XPS and TEM. High-resolution transmission electron microscopy (HRTEM)
images show that the MoS2 films grow on sapphire substrate in a layer-by-layer
manner with misfit dislocations. Layer growth morphology is disrupted when
grown on substrates with diamond cubic structure such as silicon due to growth
twin formation. The growth morphology is very different on amorphous substrates
such as Si/SiO2 or Si/SiN. The MoS2 film grown on silicon shows a very high TCR
(-2.9% K-1), mid IR sensitivity (delR/R=5.2 %) and responsivity (8.7 V/W) as
compared to films on other substrates. | 1607.04682v1 |
2016-11-10 | Pressure-induced quantum phase transition in the itinerant ferromagnet UCoGa | In this paper, we report the results of a high pressure study of the
itinerant 5f-electron ferromagnet UCoGa. The work is focused on probing the
expected ferromagnet-to-paramagnet quantum phase transition induced by high
pressure and on the general features of the P-T(-H) phase diagram. Diamond
anvil cells were employed to measure the magnetization and electrical
resistivity under pressures up to ~ 10 GPa.At ambient pressure, UCoGa exhibits
collinear ferromagnetic ordering of uranium magnetic moments {\mu}U ~ 0.74
{\mu}B (at 2 K) aligned along the c-axis of the hexagonal crystal structure
below Curie temperature TC = 48K. With the application of pressure, gradual
decrease of both, TC and the saturated magnetic moment, has been observed up to
pressures ~ 6 GPa. This is followed by a sharp drop of magnetic moment and a
sudden disappearance of the magnetic order at the pressure of 6.5 GPa,
suggesting a first-order phase transition, as expected for a clean system. The
low temperature power law dependence of the electrical resistivity shows
distinct anomalies around the ~ 6 GPa, consistent with the pressure evolution
of the magnetic moment and the ordering temperature. The tricritical point of
the UCoGa phase diagram is located at approximately ~ 30 K and ~ 6 GPa. | 1611.03276v1 |
2016-11-14 | Two-carrier analyses of the transport properties of black phosphorus under pressure | We report on the electronic transport properties of black phosphorus and
analyze them using a two-carrier model in a wide range of pressure up to 2.5
GPa. In semiconducting state at 0.29 GPa, the remarkable non-linear behavior in
the Hall resistance is reasonably reproduced by assuming the coexistence of two
kinds of hole with different densities and mobilities. On the other hand,
two-carrier analyses of the magnetotransport properties above 1.01 GPa suggest
the coexistence of high mobility electron and hole carriers that have almost
the same densities, i.e., nearly compensated semimetallic nature of black
phosphorus. In the semimetallic state, analyses of both the two-carrier model
and quantum oscillations indicate a systematic increase in the carrier
densities as pressure increases. An observed sign inversion of Hall resistivity
at low magnetic fields suggests the existence of high mobility electrons
(\sim105 cm2 V-1 s-1) that is roughly ten times larger than that of holes, in
the semimetallic black phosphorus. We conclude that the extremely large
positive magnetoresistance that has been observed in semimetallic state cannot
be reproduced by a conventional two-carrier model. | 1611.04277v2 |
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