publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2021-06-15 | Charge Carrier Transport in Iron Pyrite Thin Films: Disorder Induced Variable Range Hopping | The origin of p-type conductivity and the mechanism responsible for low
carrier mobility was investigated in pyrite (FeS2) thin films. Temperature
dependent resistivity measurements were performed on polycrystalline and
nanostructured thin films prepared by three different methods. Films have a
high hole density and low mobility regardless of the method used for their
preparation. The charge transport mechanism is determined to be nearest
neighbour hopping (NNH) at near room temperature with Mott-type variable range
hopping (VRH) of holes via localized states occurring at lower temperatures.
Density functional theory (DFT) predicts that sulfur vacancy induced localized
defect states will be situated within the band gap with the charge remaining
localized around the defect. The data indicate that the electronic properties
including hopping transport in pyrite thin films can be correlated to sulfur
vacancy related defect. The results provide insights on electronic properties
of pyrite thin films and its implications for charge transport | 2106.08401v2 |
2021-06-24 | Epitaxial growth of Ruddlesden-Popper neodymium nickelates Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ (${n}$ = 1-5) | A series of Ruddlesden-Popper nickelates, Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ (${n}$
= 1-5), have been stabilized in thin film form using reactive molecular-beam
epitaxy. High crystalline quality has been verified by X-ray diffraction and
scanning transmission electron microscopy. X-ray photoelectron spectroscopy
indicates the ${n}$-dependent valence states of nickel in these compounds.
Metal-insulator transitions show clear ${n}$ dependence for intermediate
members (${n}$ = 3-5), and the low-temperature resistivities of which show
logarithmic dependence, resembling the Kondo-scattering as observed in the
parent compounds of superconducting infinite-layer nickelates. | 2106.12941v1 |
2021-07-28 | Narrow-gap semiconducting behavior in antiferromagnetic Eu$_{11}$InSb$_9$ | Here we investigate the thermodynamic and electronic properties of
Eu$_{11}$InSb$_9$ single crystals. Electrical transport data show that
Eu$_{11}$InSb$_9$ has a semiconducting ground state with a relatively narrow
band gap of $320$~meV. Magnetic susceptibility data reveal antiferromagnetic
order at low temperatures, whereas ferromagnetic interactions dominate at high
temperature. Specific heat, magnetic susceptibility, and electrical resistivity
measurements reveal three phase transitions at $T_{N1}=9.3$~K, $T_{N2} =8.3$~K,
and $T_{N3} =4.3$~K. Unlike Eu$_{5}$In$_{2}$Sb$_6$, a related
europium-containing Zintl compound, no colossal magnetoresistance (CMR) is
observed in Eu$_{11}$InSb$_9$. We attribute the absence of CMR to the smaller
carrier density and the larger distance between Eu ions and In-Sb polyhedra in
Eu$_{11}$InSb$_9$. Our results indicate that Eu$_{11}$InSb$_9$ has potential
applications as a thermoelectric material through doping or as a
long-wavelength detector due to its narrow gap. | 2107.13145v1 |
2021-08-04 | Theory of Huge Thermoelectric Effect Based on Magnon Drag Mechanism: Application to Thin-Film Heusler Alloy | To understand the unexpectedly high thermoelectric performance observed in
the thin-film Heusler alloy Fe$_2$V$_{0.8}$W$_{0.2}$Al, we study the magnon
drag effect, generated by the tungsten based impurity band, as a possible
source of this enhancement, in analogy to the phonon drag observed in FeSb$_2$.
Assuming that the thin-film Heusler alloy has a conduction band integrating
with the impurity band, originated by the tungsten substitution, we derive the
electrical conductivity $L_{11}$ based on the self-consistent t-matrix
approximation and the thermoelectric conductivity $L_{12}$ due to magnon drag,
based on the linear response theory, and estimate the temperature dependent
electrical resistivity, Seebeck coefficient and power factor. Finally, we
compare the theoretical results with the experimental results of the thin-film
Heusler alloy to show that the origin of the exceptional thermoelectric
properties is likely to be due to the magnon drag related with the
tungsten-based impurity band. | 2108.01880v1 |
2021-08-10 | Nature of electrons from oxygen vacancies and polar catastrophe at LaAlO3/SrTiO3 interfaces | The relative significance of quantum conductivity correction and magnetic
nature of electrons in understanding the intriguing low-temperature resistivity
minimum and negative magnetoresistance of the two-dimensional electron gas at
LaAlO3/SrTiO3 interfaces has been a long outstanding issue since its discovery.
Here we report a comparative magnetotransport study on amorphous and
oxygen-annealed crystalline LaAlO3/SrTiO3 heterostructures at a relatively
high-temperature range, where the orbital scattering is largely suppressed by
thermal fluctuations. Despite of a predominantly negative out-of-plane
magnetoresistance effect for both, the magnetotransport is isotropic for
amorphous LaAlO3/SrTiO3 while strongly anisotropic and well falls into a
two-dimensional quantum correction frame for annealed crystalline
LaAlO3/SrTiO3. These results clearly indicate that a large portion of electrons
from oxygen vacancies are localized at low temperatures, serving as magnetic
centers, while the electrons from the polar field are only weakly localized due
to constructive interference between time-reversed electron paths in the clean
limit and no signature of magnetic nature is visible. | 2108.04532v1 |
2021-08-19 | Chemomechanics: friend or foe of the "AND problem" of solid-state batteries? | Solid electrolytes are widely considered as the enabler of lithium metal
anodes for safe, durable, and high energy density rechargeable lithium-ion
batteries. Despite the promise, failure mechanisms associated with solid-state
batteries are not well-established, largely due to limited understanding of the
chemomechanical factors governing them. We focus on the recent developments in
understanding solid-state aspects including the effects of mechanical stresses,
constitutive relations, fracture, and void formation, and outline the gaps in
the literature. We also provide an overview of the manufacturing and processing
of solid-state batteries in relation to chemomechanics. The gaps identified
provide concrete directions towards the rational design and development of
failure-resistant solid-state batteries. | 2108.10150v2 |
2021-09-01 | Electrical switching of antiferromagnetic CoO | Pt across the Néel temperature | One of the most important challenges in antiferromagnetic spintronics is the
read-out of the N\'eel vector state. High current densities up to 10$^8$
Acm$^{-2}$ used in the electrical switching experiments cause notorious
difficulty in distinguishing between magnetic and thermal origins of the
electrical signals. To overcome this problem, we present a temperature
dependence study of the transverse resistance changes in the switching
experiment with CoO|Pt devices. We demonstrate the possibility to extract a
pattern of spin Hall magnetoresistance for current pulses density of $5 \times
10^7$ Acm$^{-2}$ that is present only below the N\'eel temperature and does not
follow a trend expected for thermal effects. This is the compelling evidence
for the magnetic origin of the signal, which is observed using purely
electrical techniques. We confirm these findings by complementary experiments
in an external magnetic field. Such an approach can allow determining the
optimal conditions for switching antiferromagnets and be very valuable when no
imaging techniques can be applied to verify the origin of the electrical
signal. | 2109.00293v2 |
2021-09-22 | Dynamic Behaviors and Training Effects in TiN/Ti/HfO$_x$/TiN Nanolayered Memristors with Controllable Quantized Conductance States: Implications for Quantum and Neuromorphic Computing Devices | Controllable quantized conductance states of TiN/Ti/HfO$_x$/TiN memristors
are realized with great precision through a pulse-mode reset procedure,
assisted with analytical differentiation of the condition of the set procedure,
which involves critical monitoring of the measured bias voltage. An intriguing
training effect that leads to faster switching of the states is also observed
during the operation. Detailed analyses on the low- and high-resistance states
under different compliance currents reveal a complete picture of the structural
evolution and dynamic behaviors of the conductive filament in the HfO$_x$
layer. This study provides a closer inspection on the quantum-level
manipulation of nanoscale atomic configurations in the memristors, which helps
to develop essential knowledge about the design and fabrication of the future
memristor-based quantum devices and neuromorphic computing devices. | 2109.10783v1 |
2021-09-27 | Strongly electron-correlated semimetal RuI$_3$ with a layered honeycomb structure | A polymorph of RuI$_3$ synthesized under high pressure was found to have a
two-layered honeycomb structure. The resistivity of RuI$_3$ exhibits a
semimetallic behavior, in contrast to insulating properties in
$\alpha$-RuCl$_3$. In addition, Pauli paramagnetic behavior was observed in the
temperature dependence of a magnetic susceptibility and a nuclear spin-lattice
relaxation rate 1/$T_1$. The band structure calculations indicate that
contribution of the I 5$p$ components to the low-energy $t_\mathrm{2g}$ bands
effectively decreases Coulomb repulsion, leading to semimetallic properties.
The physical properties also suggest strong electron correlations in RuI$_3$. | 2109.12864v2 |
2021-10-12 | Single-component superconducting state in UTe2 at 2 K | UTe2 is a newly-discovered unconventional superconductor wherein
multicomponent topological superconductivity is anticipated based on the
presence of two superconducting transitions and time-reversal symmetry breaking
in the superconducting state. The observation of two superconducting
transitions, however, remains controversial. Here we demonstrate that UTe2
single crystals displaying an optimal superconducting transition temperature at
2 K exhibit a single transition and remarkably high quality supported by their
small residual heat capacity in the superconducting state and large residual
resistance ratio. Our results shed light on the intrinsic superconducting
properties of UTe2 and bring into question whether UTe2 is a multicomponent
superconductor at ambient pressure. | 2110.06200v1 |
2021-10-13 | Large-Gap Quantum Spin Hall State and Temperature-Induced Lifshitz Transition in Bi4Br4 | Searching for new quantum spin Hall insulators with large fully opened energy
gap to overcome the thermal disturbance at room temperature has attracted
tremendous attention due to the one-dimensional (1D) spin-momentum locked
topological edge states serving as dissipationless channels for the practical
applications in low consumption electronics and high performance spintronics.
Here, we report the investigation of topological nature of monolayer Bi4Br4 by
the techniques of scanning tunneling microscopy and angle-resolved
photoemission spectroscopy (ARPES). The topological non-triviality of 1D edge
state integrals within the large bulk energy gap (~ 0.2 eV) is revealed by the
first-principle calculations. The ARPES measurements at different temperature
show a temperature-induced Lifshitz transition, corresponding to the
resistivity anomaly caused by the shift of chemical potential. The connection
between the emergency of superconductivity and the Lifshitz transition is
discussed. | 2110.06658v1 |
2021-11-09 | Weak antilocalization and Shubnikov-de Haas oscillations in CaCuSb single crystal | Quantum oscillations in both linear and Hall resistivities and weak
antilocalization (WAL) are barely observed in bulk single crystals. Here we
report the transport properties of a CaCuSb single crystal that crystallizes in
the hexagonal crystal structure. The magnetotransport studies reveal WAL and
Shubnikov-de Haas (SdH) quantum oscillations with a unique frequency at 314 T.
A cusp-like behavior in the low field regime of magnetotransport for J //
(ab)-plane and B // [0001] confirms the WAL in CaCuSb. Angular-dependent
normalized magnetoconductance and SdH oscillations studies reveal that the
observed phenomena originate from the 2D transport channels. The high magnetic
field (up to 45 T) experiments demonstrate plateau-like features in the Hall
measurements. The first-principles calculations unfold that CaCuSb is a
non-topological semimetal with dominant hole carries at the Fermi level. Our
study reveals that CaCuSb is a promising candidate to explore the quasi-2D
quantum transport phenomenon in the transition metal pnictide materials. | 2111.04996v1 |
2021-11-29 | High-Speed Light Focusing through Scattering Medium by Cooperatively Accelerated Genetic Algorithm | We develop an accelerated Genetic Algorithm (GA) system constructed by the
cooperation of field-programmable gate array (FPGA) and optimized parameters of
the GA. We found the enhanced decay of mutation rate makes convergence of the
GA much faster, enabling the parameter-induced acceleration of the GA.
Furthermore, the accelerated configuration of the GA is programmed in FPGA to
boost processing speed at the hardware level without external computation
devices. This system has ability to focus light through scattering medium
within 4 seconds with robust noise resistance and stable repetition
performance, which could be further reduced to millisecond level with advanced
board configuration. This study solves the long-term limitation of the GA, it
promotes the applications of the GA in dynamic scattering mediums, with the
capability to tackle wavefront shaping in biological material. | 2111.14916v1 |
2021-12-01 | Atomistic simulations of twin boundary effect on the crack growth behaviour in BCC Fe | In this paper, the effect of twin boundaries on the crack growth behaviour of
single crystal BCC Fe has been investigated using molecular dynamics
simulations. The growth of an atomically sharp crack with an orientation of
(111)$<$110$>$ (crack plane/crack front) has been studied under mode-I loading
at constant strain rate. In order to study the influence of twin boundaries on
the crack growth behaviour, single and multiple twin boundaries were introduced
perpendicular to crack growth direction. The results indicate that the
(111)$<$110$>$ crack in single crystal BCC Fe grows in brittle manner. However,
following the introduction of twin boundaries, a noticeable plastic deformation
has been observed at the crack tip. Further, increasing the number of twin
boundaries increased the amount of plastic deformation leading to better crack
resistance and high failure strains. Finally, an interesting relationship has
been observed between the crack growth rate and flow stress. | 2112.00354v1 |
2022-01-10 | Phase Boundary Segregation in Multicomponent Alloys: A Diffuse-Interface Thermodynamic Model | Microalloying elements tend to segregate to the matrix-precipitate phase
boundaries to reduce the interfacial energy. The segregation mechanism is
emerging as a novel design strategy for developing precipitation-hardened
alloys with significantly improved coarsening resistance for high temperature
applications. In this paper, we report a nanoscopic diffuse-interface
thermodynamic model that describes multicomponent segregation behavior in
two-phase substitutional alloys. Following classical approaches for grain
boundaries, we employ the regular solution thermodynamics to establish
segregation isotherms. We show that the model recovers the Guttmann
multicomponent isotherm describing local interfacial concentrations, and the
generalized Gibbs adsorption isotherm that governs the total solute excess and
interfacial energy. A variety of multicomponent segregation behaviors are
demonstrated for a model two-phase quaternary alloy. The nature of interfacial
parameters and the resulting analytic solutions make the model amenable for
parameterization and comparison with atomistic calculations and experimental
characterizations. | 2201.03117v1 |
2022-03-09 | Magnetotransport due to conductivity fluctuations in non-magnetic ZrTe2 nanoplates | Transition metal dichalcogenides with nontrivial band structures exhibit
various fascinating physical properties and have sparked intensively research
interest. Here, we performed systematic magnetotransport measurements on
mechanical exfoliation prepared ZrTe2 nanoplates. We revealed that the negative
longitudinal magnetoresistivity observed at high field region in the presence
of parallel electric and magnetic fields could stem from the conductivity
fluctuations due to the excess Zr in the nanoplates. In addition, the
parametric plot, the planar Hall resistivity as function of the in-plane
anisotropic magnetoresistivity, has an ellipse-shaped pattern with shifted
orbital center, which further strengthen the evidence for the conductivity
fluctuations. Our work provides some useful insights into transport phenomena
in topological materials. | 2203.04486v1 |
2022-03-11 | Ultrafast intrinsic optical-to-electrical conversion dynamics in graphene photodetector | Optical-to-electrical (O-E) conversion in graphene is a central phenomenon
for realizing anticipated ultrafast and low-power-consumption information
technologies. However, revealing its mechanism and intrinsic time scale require
uncharted terahertz (THz) electronics and device architectures. Here, we
succeeded in resolving O-E conversion processes in high-quality graphene by
on-chip electrical readout of ultrafast photothermoelectric current. By
suppressing the RC time constant using a resistive zinc oxide top gate, we
constructed a gate-tunable graphene photodetector with a bandwidth of up to 220
GHz. By measuring nonlocal photocurrent dynamics, we found that the
photocurrent extraction from the electrode is instantaneous without a
measurable carrier transit time across several-micrometer-long graphene,
following the Shockley-Ramo theorem. The time for photocurrent generation is
exceptionally tunable from immediate to > 4 ps, and its origin is identified as
Fermi-level-dependent intraband carrier-carrier scattering. Our results bridge
the gap between ultrafast optical science and device engineering, accelerating
ultrafast graphene optoelectronic applications. | 2203.05752v1 |
2022-03-14 | Little-Parks like oscillations in lightly doped cuprate superconductors | Understanding the rich and competing electronic orders in cuprate
superconductors may provide important insight into the mechanism of
high-temperature superconductivity. Here, by measuring Bi2Sr2CaCu2O8+x in the
extremely underdoped regime, we obtain evidence for a distinct type of
ordering, which manifests itself as resistance oscillations at low magnetic
fields (<10 T) and at temperatures around the superconducting transition. By
tuning the doping level p continuously, we reveal that these low-field
oscillations occur only when p<0.1. The oscillation amplitude increases with
decreasing p but the oscillation period stays almost constant. We show that
these low-field oscillations can be well described by assuming a periodic
superconducting structure with a mesh size of about 50 nm. Such a charge order,
which is distinctly different from the well-established charge density wave and
pair density wave, seems to be an unexpected piece of the puzzle on the
correlated physics in cuprates. | 2203.06971v1 |
2022-03-25 | Hydrodynamic Interactions Between Charged and Uncharged Brownian Colloids at a Fluid-Fluid Interface | Hypothesis: The collective dynamics and self-assembly of colloids floating at
a fluid/fluid interface is a balance between deterministic lateral interaction
forces, viscous resistance to colloid motion along the surface and thermal
(Brownian) fluctuations. As the colloid size decreases, thermal forces become
important and can affect the self assembly into ordered patterns and crystal
structures that are the starting point for various materials applications.
Numerics: Langevin dynamic simulations involving two particles straddling a
liquid/liquid interface with a high viscosity contrast are presented to
describe the lateral interfacial assembly of particles in Brownian and
non-Brownian dominated regimes. These simulations incorporate capillary
attraction, electrostatic repulsion, thermal fluctuations and HI between
particles (including the effect of the particle immersion depth). Simulation
results are presented for neutrally wetted particles which form a contact angle
of 90 degrees at the interface. Findings: Clustering, fractal growth and
particle ordering are observed at critically large values of the Pe numbers,
while smaller Pe numbers exhibit higher probabilities of yielding states in
which particles remain uncorrelated in space and more widely separated. | 2203.13925v2 |
2022-04-02 | Upscaling of a reaction-diffusion-convection problem with exploding non-linear drift | We study a reaction-diffusion-convection problem with nonlinear drift posed
in a domain with periodically arranged obstacles. The non-linearity in the
drift is linked to the hydrodynamic limit of a totally asymmetric simple
exclusion process (TASEP) governing a population of interacting particles
crossing a domain with obstacle. Because of the imposed large drift scaling,
this nonlinearity is expected to explode in the limit of a vanishing scaling
parameter. As main working techniques, we employ two-scale formal
homogenization asymptotics with drift to derive the corresponding upscaled
model equations as well as the structure of the effective transport tensors.
Finally, we use Schauder's fixed point theorem as well as monotonicity
arguments to study the weak solvability of the upscaled model posed in an
unbounded domain. This study wants to contribute with theoretical understanding
needed when designing thin composite materials that are resistant to high
velocity impacts. | 2204.00931v1 |
2022-06-01 | Charge density wave and superconductivity in 6R-TaS2 | The layered transition metal dichalcogenide compounds 1T-TaS2 and 4H-TaS2 are
well known for their exotic properties, which include charge density wave,
superconductivity, Mott transition, etc., and lately quantum spin liquid. Here,
we report the magnetic, transport and transmission electron microscopy study of
the charge density wave and superconductivity in 6R-TaS2 which is a relatively
less studied polymorph of this dichalcogenide TaS2. Our high temperature
electron microscopy reveals multiple charge density wave transitions between
room temperature and 650K. Magnetization, and the electrical resistivity
measurements in the temperature range of 2-400 K reveal that 6R-TaS2 undergoes
a charge density wave transition around 305 K and is followed by a transition
to a superconducting state around 3.5 K. The low temperature specific heat
measurement exhibits anomaly associated with the superconducting transition
around 2.4 K. The estimated Ginzburg Landau parameter suggests that this
compound lies at the extreme limit of type-II superconductivity. | 2206.00281v3 |
2022-06-03 | Effects of charge dopants in quantum spin Hall materials | Semiconductors' sensitivity to electrostatic gating and doping accounts for
their widespread use in information communication and new energy technologies.
It is demonstrated quantitatively and with no adjustable parameters that the
presence of paramagnetic acceptor dopants elucidates a variety of hitherto
puzzling properties of two-dimensional topological semiconductors at the
topological phase transition and in the regime of the quantum spin Hall effect.
The concepts of charge correlation, Coulomb gap, exchange interaction between
conducting electrons and holes localized on acceptors, strong coupling limit of
the Kondo effect, and bound magnetic polaron explain a short topological
protection length, high hole mobilities compared with electron mobilities, and
different temperature dependence of the spin Hall resistance in HgTe and
(Hg,Mn)Te quantum wells. | 2206.01613v3 |
2022-06-02 | Modeling Defect-Level Switching for Highly-Nonlinear and Hysteretic Electronic Devices | Many semiconductors feature defects with charge state transition levels that
can switch due to structure changes following defect ionization: we call this
defect-level switching (DLS). For example, DX centers in III-V compounds, and
oxygen vacancies in ZnO, can switch between deep and shallow donor
configurations, and these bistable dynamics are responsible for persistent
photoconductivity. We recently demonstrated highly-nonlinear, hysteretic,
two-terminal electronic devices using DLS in CdS [H. Yin, A. Kumar, J.M.
LeBeau, and R. Jaramillo, Phys. Rev. Applied 15, 014014 (2021).] The resulting
devices operate without mass transport, and in the opposite sense to most
resistive switches: they are in a high-conductivity state at equilibrium, and
switch to a low-conductivity state at forward bias. Although DLS uses the same
defect transitions that are responsible for persistent photoconductivity, DLS
devices operate without light and can be orders-of-magnitude faster due to
exponential tuning of transition rates with voltage. In this work we use theory
and numerical simulation to explore the design space of DLS devices,
emphasizing the tradeoff between speed and on/off ratio. Our results will be
useful to guide future applications of these unusual devices. | 2206.04108v1 |
2022-10-14 | The Electrical Property of Large Few Layer Graphene Flakes Obtained by Microwaves Assisted Exfoliation of Expanded Graphite | Few layer graphene (FLG) was synthesized by $\mu$-wave assisted exfoliation
of expanded graphite in toluene with an overall yield from c.a. 7% to 20%. A
significant difference in the absorption of $\mu$-waves by the expanded
graphite and toluene allowed a rapid heating of the medium. The number of FLG
sheets varies from 3 to 12, while the lateral size of the sheets exceeds few
$\mu$ms. The obtained FLG exhibits very low resistance with average value of
1.6 k$\Omega$ (500 $\Omega$ minimum) which is comparable to that of high
quality graphenes synthesized by CVD methods, and lower than numbers of
exfoliated graphenes. | 2210.07627v1 |
2022-10-26 | Superior damage tolerance of fish skins | Skin is the largest organ of many animals. Its protective function against
hostile environments and predatorial attack makes high mechanical strength a
vital characteristic. Here, we measured the mechanical properties of bass fish
skins and found that fish skins are highly ductile with a rupture strain of up
to 30-40% and a rupture strength of 10-15 MPa. The fish skins exhibit a
strain-stiffening behavior. Stretching can effectively eliminate the stress
concentrations near the pre-existing holes and edge notches, suggesting that
the skins are highly damage tolerant. Our measurement determined a
flaw-insensitivity length of several millimeters, which exceeds that of most
engineering materials. The strain-stiffening and damage tolerance of fish skins
are explained by an agent-based model of collagen network in which the
load-bearing collagen microfibers assembled from nanofibrils undergo
straightening and reorientation upon stretching. Our study inspires development
of artificial skins that are thin, flexible, but highly fracture-resistant and
widely applicable in soft robots. | 2210.14651v1 |
2022-10-29 | Magnetotransport Properties and Fermi Surface Topology of Nodal line Semimetal InBi | In the present study, we have discussed the up-turn behavior in the
resistivity pattern of the topological nodal line semimetal InBi. We argued
that such nature could be generalized with a mathematical model, that can be
applied to any compounds exhibiting similar behavior. The extremely high
magnetoresistance (XMR) has also been explained by the carrier compensation in
the compound, estimated from the Hall conductivity. Moreover, from the study of
Subhnikov-de Haas (SdH) oscillation and density functional theory (DFT), we
obtained the complete three-dimensional (3D) Fermi surface topology of the
compound InBi. A detailed understanding of carriers' behavior has been
discussed using those studies. We have also unfurled the topology of each
electron and hole pocket and its possible modulation with electron and hole
doping. | 2210.16527v1 |
2022-11-30 | Mixed Valence Pseudobrookite Al$_{1.75}$Ti$_{1.25}$O$_5$: High Temperature Phase Transitions, Magnetism and Resistivity | Dark blue single crystals of Al$_{1.75}^{3+}$ Ti$_{1.0}^{4+}$
Ti$_{0.25}^{3+}$O$_5$ were grown with a novel synthesis method based on the
reaction of a Ti3+/Ti4+ containing langbeinite melt and Al$_2$O$_3$. The
obtained needles crystallize in the pseudobrookite structure and undergo two
reversible phase transitions from orthorhombic Cmcm to C2/m first and
subsequently to C2 symmetry. Like the known aluminum titanate pseudobrookites,
anistropic thermal expansion is observed. The temperature evolution of the
crystal structure reveals some insights into the mechanism leading to the
decomposition of the Al$_{1.75}$Ti$_{1.25}$O$_5$ above 725$^\circ$C. The
magnetic and electrical properties are discussed and compared to other reported
aluminum titanate pseudobrookites. | 2211.17252v2 |
2022-12-14 | Study of the V$_2^0$ state in neutron-irradiated silicon using photon-absorption measurements | Pieces of $n$-type silicon with 3.5 k$\Omega \cdot $cm resistivity have been
irradiated by reactor neutrons to fluences of (1, 5 and 10) $\times 10^{16}$
cm$^{-2}$. Using light-transmission measurements, the absorption coefficients
have been determined for photon energies, $E_\gamma $, between 0.62 and 1.30 eV
for the samples as irradiated and after 15 min isochronal annealing with
temperatures between 80{\deg}C and 330{\deg}C. The radiation-induced absorption
coefficient, $\alpha_\mathit{irr}$, has been obtained by subtracting the
absorption coefficient for non-irradiated silicon. The $E_\gamma $-dependence
of $\alpha_\mathit{irr}$ shows a resonance peak, which is ascribed to the
neutral divacancy, V$_2^0$, sitting on a background, and $\alpha_\mathit{irr}
(E_\gamma )$ is fitted by a Breit-Wigner line shape on a parameterized
background. It is found that at an annealing temperature of 210{\deg}C the
V$_2^0$ intensity is reduced by a factor 2, and that at the meV level, the
position and the width of the fitted Breit-Wigner do not change with
irradiation dose and annealing. | 2212.07320v2 |
2023-01-18 | Schramm-Loewner evolution in 2d rigidity percolation | Amorphous solids may resist external deformation such as shear or compression
while they do not present any long-range translational order or symmetry at the
microscopic scale. Yet, it was recently discovered that, when they become
rigid, such materials acquire a high degree of symmetry hidden in the disorder
fluctuations: their microstructure becomes statistically conformally invariant.
In this Letter we exploit this finding to characterise the universality class
of central-force rigidity percolation (RP), using Schramm-Loewner Evolution
(SLE) theory. We provide numerical evidences that the interfaces of the
mechanically stable structures (rigid clusters), at the rigidification
transition, are consistently described by SLE$_\kappa$, showing that this
powerful framework can be applied to a mechanical percolation transition. Using
well-known relations between different SLE observables and the universal
diffusion constant $\kappa$, we obtain the estimation $\kappa\sim2.9$ for
central-force RP. This value is consistent, through relations coming from
conformal field theory, with previously measured values for the clusters'
fractal dimension $D_f$ and correlation length exponent $\nu$, providing new,
non-trivial relations between critical exponents for RP. These findings open
the way to a fine understanding of the microstructure in other important
classes of rigidity and jamming transitions. | 2301.07614v2 |
2023-01-26 | 3D-imaging of Printed Nanostructured Networks using High-resolution FIB-SEM Nanotomography | Networks of solution-processed nanomaterials are important for multiple
applications in electronics, sensing and energy storage/generation. While it is
known that network morphology plays a dominant role in determining the physical
properties of printed networks, it remains difficult to quantify network
structure. Here, we utilise FIB-SEM nanotomography to characterise the
morphology of nanostructured networks. Nanometer-resolution 3D-images were
obtained from printed networks of graphene nanosheets of various sizes, as well
as networks of WS2 nanosheets, silver nanosheets and silver nanowires.
Important morphological characteristics, including network porosity,
tortuosity, pore dimensions and nanosheet orientation were extracted and linked
to network resistivity. By extending this technique to interrogate the
structure and interfaces within vertical printed heterostacks, we demonstrate
the potential of this technique for device characterisation and optimisation. | 2301.11046v1 |
2023-03-08 | Optical rogue waves in spheroids of tumor cells | Rogue waves are intense and unexpected wavepackets ubiquitous in complex
systems. In optics, they are promising as robust and noise-resistant beams for
probing and manipulating the underlying material. Localizing large optical
power is crucial especially in biomedical systems, where, however, extremely
intense beams have not yet been observed. We here discover that tumor-cell
spheroids manifest optical rogue waves when illuminated by randomly modulated
laser beams. The intensity of light transmitted through bio-printed
three-dimensional tumor models follows a signature Weibull statistical
distribution, where extreme events correspond to spatially-localized optical
modes propagating within the cell network. Experiments varying the input beam
power and size indicate the rogue waves have a nonlinear origin. We show these
optical filaments form high-transmission channels with enhanced transmission.
They deliver large optical power through the tumor spheroid, which can be
exploited to achieve a local temperature increase controlled by the input wave
shape. Our findings shed new light on optical propagation in biological
aggregates and demonstrate how extreme event formation allows light
concentration in deep tissues, paving the way to using rogue waves in
biomedical applications such as light-activated therapies. | 2303.04553v1 |
2023-04-28 | Experimental observation of metallic states with different dimensionality in a quasi-1D charge density wave compound | TaTe$_4$ is a quasi-1D tetrachalcogenide that exhibits a CDW instability
caused by a periodic lattice distortion. Recently, pressure-induced
superconductivity has been achieved in this compound, revealing a competition
between these different ground states and making TaTe$_4$ very interesting for
fundamental studies. Although TaTe$_4$ exhibits CDW ordering below 475 K,
transport experiments have reported metallic behavior with a resistivity
plateau at temperatures lower than 10 K. In this paper, we study the electronic
structure of TaTe$_4$ using a combination of high-resolution angle-resolved
photoemission spectroscopy and density functional calculations. Our results
reveal the existence of the long-sought metallic states. These states exhibit
mixed dimensionality, while some of them might have potential topological
properties. | 2305.00053v1 |
2023-05-15 | Magnetic order and electronic transport properties in the Mn$_3$Al compound: the role of the structural state | Electronic transport and magnetic properties of bulk and rapid melt quenched
samples of the Mn$_3$Al Heusler alloy were studied. A correlation between the
magnetic and structural states was established. For a cast sample, there is no
ferromagnetic moment, and the behavior of the magnetic susceptibility (break at
low temperatures and the Curie-Weiss law with high values of the paramagnetic
Curie temperature) indicates a frustrated antiferromagnetic state. At the same
time, for a rapid melt quenched sample, a ferrimagnetic state is observed with
a moment close to compensation. The results of measurements of the electrical
resistivity and the Hall effect evidence as well in favor of the implementation
of these magnetic states. | 2305.08646v1 |
2023-06-01 | Native defect association in beta-Ga2O3 enables room-temperature p-type conductivity | The room temperature hole conductivity of the ultra wide bandgap
semiconductor beta Ga2O3 is a pre-requisite for developing the next-generation
electronic and optoelectronic devices based on this oxide. In this work,
high-quality p-type beta-Ga2O3 thin films grown on r-plane sapphire substrate
by metalorganic chemical vapor deposition (MOCVD) exhibit Rho = 50000Ohm.cm
resistivity at room temperature. A low activation energy of conductivity as
Ea2=170 meV was determined, associated to the oxygen - gallium native acceptor
defect complex. Further, taking advantage of cation (Zn) doping, the
conductivity of Ga2O3:Zn film was remarkably increased by three orders of
magnitude, showing a long-time stable room-temperature hole conductivity with
the conductivity activation energy of around 86 meV. | 2306.01115v1 |
2023-06-07 | Phase formation in hole- and electron-doped rare-earth nickelate single crystals | The recent discovery of superconductivity in hole-doped infinite-layer
nickelates has triggered a great interest in the synthesis of novel nickelate
phases, which have primarily been examined in thin film samples. Here, we
report the high-pressure optical floating zone (OFZ) growth of various
perovskite and perovskite-derived rare-earth nickelate single-crystals, and
investigate the effects of hole-, electron-, and self-doping. For hole-doping
with Ca and Sr, we observe phase separations during the growth process when a
substitution level of 8% is exceeded. A similar trend emerges for
electron-doping with Ce and Zr. Employing lower doping levels allows us to grow
sizeable crystals in the perovskite phase, which exhibit significantly
different electronic and magnetic properties than the undoped parent compounds,
such as a decreased resistivity and a suppressed magnetic response. Our
insights into the doping-dependent phase formation and the resulting properties
of the synthesized crystals reveal limitations and opportunities for the
exploration and manipulation of electronic states in rare-earth nickelates. | 2306.04157v1 |
2023-07-21 | Superexchange Interaction in Insulating EuZn$_{2}$P$_{2}$ | We report magnetic and transport properties of single-crystalline
EuZn$_{2}$P$_{2}$, which has trigonal CaAl$_2$Si$_2$-type crystal structure and
orders antiferromagnetically at $\approx$23~K. Easy $ab$-plane
magneto-crystalline anisotropy was confirmed from the magnetization isotherms,
measured with a magnetic field applied along different crystallographic
directions ($ab$-plane and $c$-axis). Positive Curie-Weiss temperature
indicates dominating ferromagnetic correlations. Electrical resistivity
displays insulating behavior with a band-gap of $\approx\,$0.177~eV, which
decreases to $\approx\,$0.13~eV upon application of a high magnetic field. We
explained the intriguing presence of magnetic interactions in an intermetallic
insulator by the mechanism of extended superexchange, with phosphorus as an
anion mediator, which is further supported by our analysis of the charge and
spin density distributions. We constructed the effective Heisenberg model, with
exchange parameters derived from the \textit{ab initio} DFT calculations, and
employed it in Monte-Carlo simulations, which correctly reproduced the
experimental value of N\'eel temperature. | 2307.11924v1 |
2023-08-04 | Learning to Shape by Grinding: Cutting-surface-aware Model-based Reinforcement Learning | Object shaping by grinding is a crucial industrial process in which a
rotating grinding belt removes material. Object-shape transition models are
essential to achieving automation by robots; however, learning such a complex
model that depends on process conditions is challenging because it requires a
significant amount of data, and the irreversible nature of the removal process
makes data collection expensive. This paper proposes a cutting-surface-aware
Model-Based Reinforcement Learning (MBRL) method for robotic grinding. Our
method employs a cutting-surface-aware model as the object's shape transition
model, which in turn is composed of a geometric cutting model and a
cutting-surface-deviation model, based on the assumption that the robot action
can specify the cutting surface made by the tool. Furthermore, according to the
grinding resistance theory, the cutting-surface-deviation model does not
require raw shape information, making the model's dimensions smaller and easier
to learn than a naive shape transition model directly mapping the shapes.
Through evaluation and comparison by simulation and real robot experiments, we
confirm that our MBRL method can achieve high data efficiency for learning
object shaping by grinding and also provide generalization capability for
initial and target shapes that differ from the training data. | 2308.02150v1 |
2023-08-16 | Growth of millimeter-sized high-quality CuFeSe$_2$ single crystals by the molten salt method and study of their semiconducting behavior | An eutectic AlCl$_3$/KCl molten salt method in a horizontal configuration was
employed to grow millimeter-sized and composition homogeneous CuFeSe$_2$ single
crystals due to the continuous growth process in a temperature gradient induced
solution convection. The typical as-grown CuFeSe$_2$ single crystals in cubic
forms are nearly 1.6$\times$1.2$\times$1.0 mm3 in size. The chemical
composition and homogeneity of the crystals was examined by both inductively
coupled plasma atomic emission spectroscopy and energy dispersive spectrometer
with Cu:Fe:Se = 0.96:1.00:1.99 consistent with the stoichiometric composition
of CuFeSe$_2$. The magnetic measurements suggest a ferrimagnetic or weak
ferromagnetic transition below T$_C$ = 146 K and the resistivity reveals a
semiconducting behavior and an abrupt increase below T$_C$. | 2308.08223v1 |
2023-08-25 | WSTac: Interactive Surface Perception based on Whisker-Inspired and Self-Illuminated Vision-Based Tactile Sensor | Modern Visual-Based Tactile Sensors (VBTSs) use cost-effective cameras to
track elastomer deformation, but struggle with ambient light interference.
Solutions typically involve using internal LEDs and blocking external light,
thus adding complexity. Creating a VBTS resistant to ambient light with just a
camera and an elastomer remains a challenge. In this work, we introduce WStac,
a self-illuminating VBTS comprising a mechanoluminescence (ML) whisker
elastomer, camera, and 3D printed parts. The ML whisker elastomer, inspired by
the touch sensitivity of vibrissae, offers both light isolation and high ML
intensity under stress, thereby removing the necessity for additional LED
modules. With the incorporation of machine learning, the sensor effectively
utilizes the dynamic contact variations of 25 whiskers to successfully perform
tasks like speed regression, directional identification, and texture
classification. Videos are available at: https://sites.google.com/view/wstac/. | 2308.13241v1 |
2023-09-03 | Validation of the Wiedemann-Franz Law in solid and molten tungsten above 2000 K through thermal conductivity measurements via steady state temperature differential radiometry | We measure the thermal conductivity of solid and molten tungsten using Steady
State Temperature Differential Radiometry. We demonstrate that the thermal
conductivity can be well described by application of Wiedemann-Franz Law to
electrical resistivity data, thus suggesting the validity of Wiedemann-Franz
Law to capture the electronic thermal conductivity of metals in their molten
phase. We further support this conclusion using ab initio molecular dynamics
simulations with a machine-learned potential. Our results show that at these
high temperatures, the vibrational contribution to thermal conductivity is
negligible compared to the electronic component. | 2309.01062v1 |
2023-10-05 | Demonstration of a monocrystalline GaAs-$β$-Ga$_2$O$_3$ p-n heterojunction | In this work, we report the fabrication and characterizations of a
monocrystalline GaAs/$\beta$-Ga$_2$O$_3$ p-n heterojunction by employing
semiconductor grafting technology. The heterojunction was created by lifting
off and transfer printing a p-type GaAs single crystal nanomembrane to an
Al$_2$O$_3$-coated n-type$\beta$-Ga$_2$O$_3$ epitaxial substrate. The resultant
heterojunction diodes exhibit remarkable performance metrics, including an
ideality factor of 1.23, a high rectification ratio of 8.04E9 at +/- 4V, and a
turn on voltage of 2.35 V. Furthermore, at +5 V, the diode displays a large
current density of 2500 A/cm$^2$ along with a low ON resistance of 2
m$\Omega\cdot$cm$^2$. | 2310.03886v1 |
2023-11-03 | Effects of Cr content on ion-irradiation hardening of FeCrAl ODS ferritic steels with 9 wt\% Al | FeCrAl ODS steels for accident tolerant fuel claddings are designed to bear
high-Cr and Al for enhancing oxidation resistance. In this study, we
investigated the effects of Cr content on ion-irradiation hardening of three
ODS ferritic steels with different Cr contents added with 9 wt\% Al, Fe12Cr9Al
(SP12), Fe15Cr9Al (SP13), and Fe18Cr9Al (SP14). The specimens were irradiated
with 6.4MeV Fe\textsuperscript{3+} at 300 \textdegree C to nominal 3 dpa. The
irradiation hardening was measured by nanoindentation method, and the Nix-Gao
plots were used to evaluate the bulk-equivalent hardness. The results showed
that the irradiation hardening decreased with increasing Cr content. The reason
is due to the growth of dislocation loops hindered by solute Cr atoms. TEM
observations showed both $\langle 100\rangle$ and $1/2\langle 111\rangle$
dislocation loops existed in the irradiated area. The irradiation hardening was
estimated by dispersed barrier hardening (DBH) model with dislocation loops. | 2311.01879v1 |
2023-11-11 | Evidence of Ordering in Cu-Ni Alloys from Experimental Electronic Entropy Measurements | Phase diagrams exhibiting extended solid-solution and lens-like melting are
often reproduced using ideal solutions, where ideal mixing considers a fully
random configurational entropy of mixing. In the field of irreversible
thermodynamics, experimental measurements of the composition variation of
high-temperature electronic transport and molten-state properties suggest
however a strong role for short-range atomic ordering in these systems. Herein,
measurements of the thermopower and resistivity are reported for Cu-Ni
solid-solutions as a function of temperature and composition. The electronic
transport properties were interpreted with an irreversible thermodynamic
framework, revealing a large electronic contribution to the entropy of mixing.
Through appeal to a cluster model for the configurational entropy that uses the
electronic contribution to inform the existence of ordered associates, we
rationalize such contribution of the electronic entropy with the notion of an
ideal entropy of mixing commonly used to model such systems. These results
suggest that the short range order (S.R.O.) of the atoms plays a significant
role in both the solid and molten states, even when there are no dominant
intermetallic compounds in these alloys. | 2311.06603v2 |
2023-11-12 | First-principles pressure dependent investigation of the physical properties of KB2H8: a prospective high-TC superconductor | Using the density functional theory (DFT) based first-principles
investigation, the structural, mechanical, hardness, elastic anisotropy,
optoelectronic, and thermal properties of cubic KB2H8 have been studied within
the uniform pressure range of 0 - 24 GPa. The calculated structural parameters
are in good agreement with the previous theoretical work. The compound KB2H8 is
found to be structurally and thermodynamically stable in the pressure range
from 8 GPa to 24 GPa. Single crystal elastic constants Cij and bulk elastic
moduli (B, G and Y) increase systematically with pressure from 8 GPa to 24 GPa.
In the stable phase, KB2H8 is moderately elastically anisotropic and ductile in
nature. The compound is highly machinable and fracture resistant. The Debye
temperature, melting temperature and thermal conductivity increases with
pressure. The results of electronic band structure calculations and optical
parameters at different pressures are consistent with each other. The compound
is optically isotropic. The compound KB2H8 has potential to be used as a very
efficient solar energy reflector. The electronic energy density of states at
the Fermi level decreases systematically with increasing pressure. The same
trend is found for the repulsive Coulomb pseudopotential. Possible relevance of
the studied properties to superconductivity has also been discussed in this
paper. | 2311.06709v1 |
2023-12-08 | Gate-controlled neuromorphic functional transition in an electrochemical graphene transistor | Neuromorphic devices have gained significant attention as potential building
blocks for the next generation of computing technologies owing to their ability
to emulate the functionalities of biological nervous systems. The essential
components in artificial neural network such as synapses and neurons are
predominantly implemented by dedicated devices with specific functionalities.
In this work, we present a gate-controlled transition of neuromorphic functions
between artificial neurons and synapses in monolayer graphene transistors that
can be employed as memtransistors or synaptic transistors as required. By
harnessing the reliability of reversible electrochemical reactions between C
atoms and hydrogen ions, the electric conductivity of graphene transistors can
be effectively manipulated, resulting in high on/off resistance ratio,
well-defined set/reset voltage, and prolonged retention time. Overall, the
on-demand switching of neuromorphic functions in a single graphene transistor
provides a promising opportunity to develop adaptive neural networks for the
upcoming era of artificial intelligence and machine learning. | 2312.04934v2 |
2023-12-20 | Collective dynamics and long-range order in thermal neuristor networks | In the pursuit of scalable and energy-efficient neuromorphic devices, recent
research has unveiled a novel category of spiking oscillators, termed "thermal
neuristors". These devices function via thermal interactions among neighboring
vanadium dioxide resistive memories, emulating biological neuronal behavior.
Here, we show that the collective dynamical behavior of networks of these
neurons showcases a rich phase structure, tunable by adjusting the thermal
coupling and input voltage. Notably, we identify phases exhibiting long-range
order that, however, does not arise from criticality, but rather from the time
non-local response of the system. In addition, we show that these thermal
neuristor arrays achieve high accuracy in image recognition and time series
prediction through reservoir computing, without leveraging long-range order.
Our findings highlight a crucial aspect of neuromorphic computing with possible
implications on the functioning of the brain: criticality may not be necessary
for the efficient performance of neuromorphic systems in certain computational
tasks. | 2312.12899v2 |
2024-01-30 | Momentum Matching for 2D-3D Heterogeneous Ohmic van der Waals Contact | Construction of ohmic contact is a long-standing challenge encountered by
two-dimensional (2D) device fabrication and integration. van der Waals
contacts, as a new solution for 2D contact construction, can effectively
eliminate issues, such as Fermi-level pining and formation of Schottky barrier.
Nevertheless, current research primarily considers energy band alignment, while
ignoring the transverse momentum conservation of charge carriers during the
quantum tunneling across the van der Waals contacts. In this study, by
comparing the IV characteristics and tunneling spectra of graphene-silicon
tunneling junctions with various interfacial transverse momentum distribution,
we demonstrate the importance of charge carrier momentum in constructing
high-performance 2D contact. Further, by conditioning the van der Waals
contacts and minimizing the momentum mismatch, we successfully enhanced the
quantum tunneling current with more than three orders of magnitude and obtain
ohmic-like contact. Our study provide and effective method for the construction
of direction 2D-3D contact with low resistance and can potentially benefit the
heterogeneous of integration of 2D materials in post-CMOS architectures. | 2401.17114v1 |
2024-02-11 | Langmuir-like model of dilute impurities in concentrated solid solutions | High-entropy alloys have drawn recent interest for their promising mechanical
properties and irradiation resistance. Various properties, namely transport
properties, are controlled by point defect concentration, which must be known
before performing atomistic simulations to compute transport coefficients. In
this work, we present a general Langmuir-like model for impurity concentration
in an arbitrarily complex solid solution and apply this model to generate
expressions for concentrations of vacancies and small interstitial atoms. We
then calculate the vacancy concentration as a function of temperature in the
equiatomic CoNiCrFeMn and FeAl alloys with modified embedded-atom-method
potentials for various chemical orderings, showing there is no clear
correlation between vacancy thermodynamics and chemical ordering in the
CoNiCrFeMn alloy but clear systematic patterns for FeAl. | 2402.07324v1 |
2024-02-28 | Strange metal in the doped Hubbard model via percolation | Many strongly correlated systems, including high-temperature superconductors
such as the cuprates, exhibit strange metallic behavior in certain parameter
regimes characterized by anomalous transport properties that are irreconcilable
with a Fermi-liquid-like description in terms of quasiparticles. The Hubbard
model is a standard theoretical starting point to examine the properties of
such systems and also exhibits non-Fermi-liquid behavior in simulations. Here
we analytically study the two-dimensional hole-doped Hubbard model, first
identifying a percolation transition that occurs in the low-energy sector at
critical hole doping $p_c\sim 0.19$. We then use the critical properties near
this transition to rewrite the Hubbard Hamiltonian in a way that motivates a
large-$N$ model with strange metallic properties. In particular, we show that
this model has the linear-in-$T$ resistivity and power-law optical conductivity
$\sim |\omega|^{-2/3}$ observed in the strange metal regime of cuprates,
suggesting potential relevance for describing this important class of
materials. | 2402.18626v2 |
2024-03-25 | Facile synthesis of micro-flower NiCo2O4 assembled by nanosheets efficient for electrocatalysis of water | Effective regulation of the morphology of transition metal spinel structures
is crucial for creating efficient and stable bifunctional catalysts for
electrocatalysis of water. In this work, micro-flower NiCo2O4 (F-NCO) assembled
by nanosheets via a chemical template method for the simultaneous promotion of
hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).
Electronic microscope analysis revealed that the thickness of the F-NCO
catalyst was only 2.7% of that of the NiCo2O4 bulk (B-NCO), and this ultrathin
lamellar structure was conducive to further exposure of the active site and
improved reaction kinetics. The F-NCO catalyst exhibited superior HER and OER
performance (10 = 236 and 310 mV) and robust long-term stability over the B-NCO
catalyst in 1.0 M KOH, with a 2.68-fold and 4.16-fold increase in active
surface area and a 0.42-fold and 0.61-fold decrease in charge transfer
resistance values, respectively. This micro-flower-structured electrode has
remarkable electrocatalytic property and long-term durability, providing a
novel insight for characterizing cost-effective and high-performance
bifunctional electrocatalysts. | 2403.17744v1 |
2024-04-30 | Aluminum nuclear demagnetization refrigerator for powerful continuous cooling | Many laboratories routinely cool samples to 10 mK, but relatively few can
cool condensed matter below 1 mK. Easy access to the microkelvin range would
propel fields such as quantum sensors and quantum materials. Such temperatures
are achieved with adiabatic nuclear demagnetization. Existing nuclear
demagnetization refrigerators (NDR) are "single-shot", and the recycling time
is incompatible with proposed sub-mK experiments. Furthermore, a high cooling
power is required to overcome the excess heat load of order nW on NDR
pre-cooled by cryogen-free dilution refrigerators. We report the performance of
an aluminum NDR designed for powerful cooling when part of a dual stage
continuous NDR (CNDR). Its thermal resistance is minimized to maximize the
cycling rate of the CNDR and consequently its cooling power. At the same time,
its susceptibility to eddy current heating is minimized. A CNDR based on two of
the aluminum NDR presented here would have a cooling power of approximately 40
nW at 560 $\mu$K. | 2404.19352v1 |
2024-05-10 | Effects of vortex and anti-vortex excitations in underdoped Bi-2223 bulk single crystals | To gain insights into mechanisms underlying superconducting transition in
copper oxide high-transition temperature ($T_c$) superconductors, we studied
transport properties of underdoped Bi$_2$Sr$_2$Ca$_2$Cu$_3$O$_{10+\delta}$
(Bi-2223) bulk single crystals. The power exponent $\alpha$ ($V \propto
I^{\alpha}$) reached 3 just below $T_c$, and the temperature dependence of
in-plane resistivity ($\rho_{ab}$) exhibited typical tailing behavior,
consistent with Kosterlitz--Thouless transition characteristics. Thus, with
increasing temperature, copper oxide high-$T_c$ superconductors undergo
transition to the normal state because of destruction of its phase
correlations, although a finite Cooper pair density exists at $T_c$. | 2405.06272v1 |
2024-05-15 | Unraveling impacts of polycrystalline microstructures on ionic conductivity of ceramic electrolytes by computational homogenization and machine learning | The ionic conductivity at the grain boundaries (GBs) in oxide ceramics is
typically several orders of magnitude lower than that within the grain
interior. This detrimental GB effect is the main bottleneck for designing
high-performance ceramic electrolytes intended for use in solid-state
Lithium-ion batteries, fuel cells, and electrolyzer cells. The macroscopic
ionic conductivity in oxide ceramics is essentially governed by the underlying
polycrystalline microstructures where GBs and grain morphology go hand in hand.
This provides the possibility to enhance the ion conductivity by microstructure
engineering. To this end, a thorough understanding of microstructure-property
correlation is highly desirable. In this work, we investigate numerous
polycrystalline microstructure samples with varying grain and grain boundary
features. Their macroscopic ionic conductivities are numerically evaluated by
the finite element homogenization method, whereby the GB resistance is
explicitly regarded. The influence of different microstructural features on the
effective ionic conductivity is systematically studied. The
microstructure-property relationships are revealed. Additionally, a graph
neural network-based machine learning model is constructed and trained. It can
accurately predict the effective ionic conductivity for a given polycrystalline
microstructure. This work provides crucial quantitative guidelines for
optimizing the ionic conducting performance of oxide ceramics by tailoring
microstructures. | 2405.09227v1 |
2024-05-20 | High-Mobility Carriers in Epitaxial IrO2 Films Grown using Hybrid Molecular Beam Epitaxy | Binary rutile oxides of 5d metals such as IrO2, stand out as a paradox due to
limited experimental studies despite the rich predicted quantum phenomena.
Here, we investigate the electrical transport properties of IrO2 by engineering
epitaxial thin films grown via hybrid molecular beam epitaxy. Our findings
reveal phonon-limited carrier transport and thickness-dependent anisotropic
in-plane resistance in IrO2 (110) films, the latter suggesting a complex
relationship between strain relaxation and orbital hybridization.
Magneto-transport measurements reveal a previously unobserved non-linear Hall
effect. A two-carrier analysis of this effect shows the presence of minority
carriers with mobility exceeding 3000 cm2/Vs at 1.8 K. These results point
towards emergent properties in 5d metal oxides that can be controlled using
dimensionality and epitaxial strain. | 2405.11716v1 |
2024-05-21 | A single crystal study of Kagome metals U$_2$Mn$_3$Ge and U$_2$Fe$_3$Ge | Single crystals of U$_2$Mn$_3$Ge and and U$_2$Fe$_3$Ge with a Kagome lattice
structure were synthesized using a high-temperature self-flux crystal growth
method. The physical properties of these crystals were characterized through
measurements of resistivity, magnetism, and specific heat. U$_2$Fe$_3$Ge
exhibits ferromagnetic ground state and Anomalous Hall Effect, and
U$_2$Mn$_3$Ge demonstrates a complex magnetic structure. Both compounds exhibit
large Sommerfeld coefficient, indicating coexistence of heavy Fermion behavior
with magnetism. Our results suggest that this U$_2$TM$_3$Ge (TM = Mn, Fe, Co)
family is a promising platform to investigate the interplay of magnetism, Kondo
physics and the Kagome lattice. | 2405.12905v1 |
2007-07-30 | Control of the Casimir force by the modification of dielectric properties with light | The experimental demonstration of the modification of the Casimir force
between a gold coated sphere and a single-crystal Si membrane by light pulses
is performed. The specially designed and fabricated Si membrane was irradiated
with 514 nm laser pulses of 5 ms width in high vacuum leading to a change of
the charge-carrier density. The difference in the Casimir force in the presence
and in the absence of laser radiation was measured by means of an atomic force
microscope as a function of separation at different powers of the absorbed
light. The total experimental error of the measured force differences at a
separation of 100 nm varies from 10 to 20% in different measurements. The
experimental results are compared with theoretical computations using the
Lifshitz theory at both zero and laboratory temperatures. The total theoretical
error determined mostly by the uncertainty in the concentration of charge
carriers when the light is incident is found to be about 14% at separations
less than 140 nm. The experimental data are consistent with the Lifshitz theory
at laboratory temperature, if the static dielectric permittivity of
high-resistivity Si in the absence of light is assumed to be finite. If the dc
conductivity of high-resistivity Si in the absence of light is included into
the model of dielectric response, the Lifshitz theory at nonzero temperature is
shown to be experimentally inconsistent at 95% confidence. The demonstrated
phenomenon of the modification of the Casimir force through a change of the
charge-carrier density is topical for applications of the Lifshitz theory to
real materials in fields ranging from nanotechnology and condensed matter
physics to the theory of fundamental interactions. | 0707.4390v1 |
2014-09-03 | The influence of the Al stabilizer layer thickness on the normal zone propagation velocity in high current superconductors | The stability of high-current superconductors is challenging in the design of
superconducting magnets. When the stability requirements are fulfilled, the
protection against a quench must still be considered. A main factor in the
design of quench protection systems is the resistance growth rate in the magnet
following a quench. The usual method for determining the resistance growth in
impregnated coils is to calculate the longitudinal velocity with which the
normal zone propagates in the conductor along the coil windings.
Here, we present a 2D numerical model for predicting the normal zone
propagation velocity in Al stabilized Rutherford NbTi cables with large cross
section. By solving two coupled differential equations under adiabatic
conditions, the model takes into account the thermal diffusion and the current
redistribution process following a quench. Both the temperature and magnetic
field dependencies of the superconductor and the metal cladding materials
properties are included. Unlike common normal zone propagation analyses, we
study the influence of the thickness of the cladding on the propagation
velocity for varying operating current and magnetic field.
To assist in the comprehension of the numerical results, we also introduce an
analytical formula for the longitudinal normal zone propagation. The analysis
distinguishes between low-current and high-current regimes of normal zone
propagation, depending on the ratio between the characteristic times of thermal
and magnetic diffusion. We show that above a certain thickness, the cladding
acts as a heat sink with a limited contribution to the acceleration of the
propagation velocity with respect to the cladding geometry. Both numerical and
analytical results show good agreement with experimental data. | 1409.1186v1 |
2020-01-10 | A barrier/seed system for electroless metallization on complex surfaces using (aminomethylaminoethyl)phenethyltrimethoxysilane self-assembled films | High frequency signals propagate along the edges of conductors. If the
conductors are electroplated, then the seed layer forms at least one edge, so
care must be taken to insure the electrical quality of these layers. In this
work, we study the initial quality of SAM-based seed layers that are compatible
with complex surfaces including through-silicon vias (TSVs), as are used in
via-last three-dimensional semiconductor device packaging. The conformal and
electrical quality of the seed metal is very important. Also important for a
multifunction seed layer is its ability as a barrier layer, which protects the
substrate from high temperature diffusion of the deposited metal. Thus, the
barrier layer must be robust enough to withstand diffusion, yet thin enough to
provide a conformal surface that allows metal seed layer deposition. Standard
barrier layer deposition methods such as evaporation or sputtering require
either a line of sight from the source or aspect ratios large enough to provide
scattering from the background gas within the structure to coat all surfaces.
Electrochemical and chemical vapor deposition provide alternatives, but
concerns arise about contamination and compatibility with radio frequency or
high-speed digital signals. We propose a barrier layer based on an aromatic
self-assembled monolayer (SAM) for use in electroless copper seed layer
deposition. The viability of the SAM barrier layer is determined by the quality
of the deposited copper seed film, judged quantitatively by thin film
resistivity and qualitatively by surface adhesion and morphological properties
such as cracks and bubbles. Insights to the origins of problems and an optimal
scheme are described. Extensions for use as a photolithographic resist layer
are suggested. Our SAM approach for TSV applications yields a 'smart' seed
layer that can be used with a 'simple,' scalloped, easy to fabricate, via hole. | 2001.03295v1 |
2022-04-04 | Exceptional fracture toughness of CrCoNi-based medium- and high-entropy alloys close to liquid helium temperatures | Medium- and high-entropy alloys based on the CrCoNi-system have been shown to
display outstanding strength, tensile ductility and fracture toughness
(damage-tolerance properties), especially at cryogenic temperatures. Here we
examine the JIc and (back-calculated) KJIc fracture toughness values of the
face-centered cubic, equiatomic CrCoNi and CrMnFeCoNi alloys at 20 K. At flow
stress values of ~1.5 GPa, crack-initiation KJIc toughnesses were found to be
exceptionally high, respectively 235 and 415 MPa(square-root)m for CrMnFeCoNi
and CrCoNi, with the latter displaying a crack-growth toughness Kss exceeding
540 MPa(square-root)m after 2.25 mm of stable cracking, which to our knowledge
is the highest such value ever reported. Characterization of the crack-tip
regions in CrCoNi by scanning electron and transmission electron microscopy
reveal deformation structures at 20 K that are quite distinct from those at
higher temperatures and involve heterogeneous nucleation, but restricted
growth, of stacking faults and fine nano-twins, together with transformation to
the hexagonal closed-packed phase. The coherent interfaces of these features
can promote both the arrest and transmission of dislocations to generate
respectively strength and ductility which strongly contributes to sustained
strain hardening. Indeed, we believe that these nominally single-phase,
concentrated solid-solution alloys develop their fracture resistance through a
progressive synergy of deformation mechanisms, including dislocation glide,
stacking-fault formation, nano-twinning and eventually in situ phase
transformation, all of which serve to extend continuous strain hardening which
simultaneously elevates strength and ductility (by delaying plastic
instability), leading to truly exceptional resistance to fracture. | 2204.01635v1 |
2023-10-16 | Electronic Transport and Fermi Surface Topology of Zintl phase Dirac Semimetal SrZn2Ge2 | We report a comprehensive study on the electronic transport properties of
SrZn$_2$Ge$_2$ single crystals. The in-plane electrical resistivity of the
compound exhibits linear temperature dependence for 80 K < T < 300 K, and T^2
dependence below 40 K, consistent with the Fermi liquid behavior. Both the
transverse and longitudinal magnetoresistance exhibit a crossover at critical
field B* from weak-field quadratic-like to high-field unsaturated linear field
dependence at low temperatures (T \leq 50 K). Possible sources of linear
magnetoresistance are discussed based on the Fermi surface topology, classical
and quantum transport models. The Hall resistivity data establish
SrZn$_2$Ge$_2$ as a multiband system with contributions from both the electrons
and holes. The Hall coefficient is observed to decrease with increasing
temperature and magnetic field, changing its sign from positive to negative.
The negative Hall coefficient observed at low temperatures in high fields and
at high temperatures over the entire field range suggests that the highly
mobile electron charge carriers dominate the electronic transport. Our
first-principles calculations show that nontrivial topological surface states
exist in SrZn$_2$Ge$_2$ within the bulk gap along the {\Gamma}-M path. Notably,
these surface states extend from the valence to conduction band with their
number varying based on the Sr and Ge termination plane. The Fermi surface of
the compound exhibits a distinct tetragonal petal-like structure, with one open
and several closed surfaces. Overall, these findings offer crucial insights
into the mechanisms underlying the electronic transport of the compound. | 2310.10621v2 |
2023-06-24 | High Strength Refractory AlHfNbTiV B2 High Entropy Alloys with High Fracture Strains | We demonstrate the development of a series of refractory high-entropy alloys
containing aluminum AlRHEAs in the ordered BCC-B2 phase by varying the aluminum
content within 10 to 25 atomic percent, with the goal of high strength and good
ductility synergy. The AlRHEAs obtained are found to show promising potential
for high-temperature applications. The incorporation of Al lowers the density
and promotes the long-range atomic ordering, which in turn stabilizes the B2
formation, and strengthens the material but usually deteriorates ductility.
Several B2 AlRHEAs that contain a combination of Ti, Hf, Nb, and V with
moderate to high Poisson ratios are investigated for high strength and
ductility. Furthermore, through statistical analysis, we identify a valley
around the valence electron concentration VEC of 6 where low ductility is
prominently observed. Machine-learning models are employed to screen the vast
compositional space of AlRHEA alloys to predict B2 formation and toughness
indicated by the yield strength and fracture strain. High prediction accuracies
are achieved. As the Al content decreases, the B2 atomic ordering decreases,
compression yield strengths decrease from 1500 MPa to 1200 MPa, and compression
fracture strains increase from 0.06 to over 0.5. Notably, Al10Hf20Nb22Ti33V15
retains a compression yield strength exceeding 800 MPa up to 700 C, tensile
yield strength of 1100 MPa, and fracture strain of 0.083. Our findings on
enhancing ductility in pure B2 alloys pave the way for further research on
Al-RHEA superalloys, striving to achieve high strength and ductility, reduced
density, and improved oxidation resistance. | 2306.14057v2 |
1998-04-04 | Ohmic Decay of Magnetic Fields due to non-spherical accretion in the Crusts of Neutron Stars | We consider magnetic field evolution of neutron stars during polar-cap
accretion. The size of the polar cap increases as the field decays, and is set
by the last open field line before the accretion disk. Below the polar cap we
find the temperature to be so high that electron-phonon scattering dominates
the resistivity. Outside the polar cap region, the temperature is such the
resistivity is dominated by temperature independent impurity scattering which
can be a few orders of magnitude larger than the electron- phonon resistivity.
The time-scale for field decay is therefore initially given by impurity
scattering dominated resistivity. When the field strength has been reduced to
$\sim 10^8 gauss$ the accretion is spherical and the time scale for field decay
is given by the smaller electron-phonon scattering resistivity. The field
strength is now reduced rapidly compared to before and this could be a reason
for there being no pulsars known with field strengths below $10^8 gauss$. We
also investigate the evolution of multipoles at the neutron star surface. We
find that contribution from higher-order multipoles are at most 30% to that of
the dipole mode. | 9804047v1 |
2000-01-10 | The Effect of Resistivity on the Nonlinear Stage of the Magnetorotational Instability in Accretion Disks | We present three-dimensional magnetohydrodynamic simulations of the nonlinear
evolution of the magnetorotational instability (MRI) with a non-zero Ohmic
resistivity. The properties of the saturated state depend on the initial
magnetic field configuration. In simulations with an initial uniform vertical
field, the MRI is able to support angular momentum transport even for large
resistivities through the quasi-periodic generation of axisymmetric radial
channel solutions rather than through the maintenance of anisotropic
turbulence. Simulations with zero net flux show that the angular momentum
transport and the amplitude of magnetic energy after saturation are
significantly reduced by finite resistivity, even at levels where the linear
modes are only slightly affected. This occurs at magnetic Reynolds numbers
expected in low, cool states of dwarf novae, these results suggest that finite
resistivity may account for the low and high angular momentum transport rates
inferred for these systems. | 0001164v1 |
1998-10-15 | The Quantized Hall Insulator: A New Insulator in Two-Dimensions | Quite generally, an insulator is theoretically defined by a vanishing
conductivity tensor at the absolute zero of temperature. In classical
insulators, such as band insulators, vanishing conductivities lead to diverging
resistivities. In other insulators, in particular when a high magnetic field
(B) is added, it is possible that while the magneto-resistance diverges, the
Hall resistance remains finite, which is known as a Hall insulator. In this
letter we demonstrate experimentally the existence of another, more exotic,
insulator. This insulator, which terminates the quantum Hall effect series in a
two-dimensional electron system, is characterized by a Hall resistance which is
approximately quantized in the quantum unit of resistance h/e^2. This insulator
is termed a quantized Hall insulator. In addition we show that for the same
sample, the insulating state preceding the QHE series, at low-B, is of the HI
kind. | 9810172v1 |
1999-03-05 | Comment on ``Evidence for Anisotropic State of Two-Dimensional Electrons in High Landau Levels'' | In a recent letter M. Lilly et al [PRL 82, 394 (1999)] have shown that a
highly anisotropic state can arise in certain two dimensional electron systems.
In the large square samples studied, resistances measured in the two
perpendicular directions are found to have a ratio that may be 60 or larger at
low temperature and at certain magnetic fields. In Hall bar measurements, the
anisotropy ratio is found to be much smaller (roughly 5). In this comment we
resolve this discrepancy by noting that the anisotropy of the underlying sheet
resistivities is correctly represented by Hall bar resistance measurements but
shows up exponentially enhanced in resistance measurements on square samples
due to simple geometric effects. We note, however, that the origin of this
underlying resistivity anisotropy remains unknown, and is not addressed here. | 9903086v3 |
1999-12-01 | Fractional-flux Little-Parks resistance oscillations in disordered superconducting Au$_{0.7}$In$_{0.3}$ cylinders | Resistance of disordered superconducting Au$_{0.7}$In$_{0.3}$ cylindrical
films was measured as a function of applied magnetic field. In the
high-temperature part of the superconducting transition regime, the resistance
oscillated with a period of $h/2e$ in the unit of the enclosed magnetic flux.
However, at lower temperatures, the resistance peaks split. We argue that this
splitting is due to the emergence of an oscillation with a period of $h/4e$,
half of the flux quantum for paired electrons. The possible physical origin of
the $h/4e$ resistance oscillation is discussed in the context of new minima in
the free energy of a disordered superconducting cylinder. | 9912003v3 |
2000-04-05 | Linear response conductance and magneto-resistance of ferromagnetic single-electron transistors | The current through ferromagnetic single-electron transistors (SET's) is
considered. Using path integrals the linear response conductance is formulated
as a function of the tunnel conductance vs. quantum conductance and the
temperature vs. Coulomb charging energy. The magneto-resistance of
ferromagnet-normal metal-ferromagnet (F-N-F) SET's is almost independent of the
Coulomb charging energy and is only reduced when the transport dwell time is
longer than the spin-flip relaxation time. In all-ferromagnetic (F-F-F) SET's
with negligible spin-flip relaxation time the magneto-resistance is calculated
analytically at high temperatures and numerically at low temperatures. The
F-F-F magneto-resistance is enhanced by higher order tunneling processes at low
temperatures in the 'off' state when the induced charges vanishes. In contrast,
in the 'on' state near resonance the magneto-resistance ratio is a
non-monotonic function of the inverse temperature. | 0004082v3 |
2001-09-10 | Transport properties of MgB2 | In this paper we present the resistivity, the Seebeck effect, and the thermal
conductivity measurements on a MgB2 sintered sample. Such transport properties
highlight the role of the junctions between the grains to a different extent.
In particular, the temperature dependence of resistivity may be explained with
the assumption that grain boundaries have a resistance, independent of
temperature, in series with the resistance of grains. Also the behaviour of the
Seebeck effect, as long as the scattering at the grain boundaries is elastic,
is not affected at all by granularity. Thus, the thermopower can be a useful
tool to provide information on the electronic structure. On the other hand, the
grain boundary resistance affects the thermal conductivity strongly, masking
the superconducting transition completely. | 0109174v2 |
2003-10-22 | Unconventional superconductivity and normal state properties of epsilon-iron at high pressure | Following the discovery of superconductivity in epsilon-iron, subsequent
experiments hinted at non-Fermi liquid behaviour of the normal phase and
sensitive dependence of the superconducting state on disorder, both signatures
of unconventional pairing. We report further resistive measurements under
pressure of samples of iron from multiple sources. The normal state resistivity
of epsilon-iron varied as rho_0+AT^{5/3} at low temperature over the entire
superconducting pressure domain. The superconductivity could be destroyed by
mechanical work, and was restored by annealing, demonstrating sensitivity to
the residual resistivity rho_0. There is a strong correlation between the rho_0
and A coefficients and the superconducting critical temperature T_c. Within the
partial resistive transition there was a significant current dependence, with
V(I)=a(I-I_0)+bI^2, with a >> b, possibly indicating flux-flow resistivity,
even in the absence of an externally applied magnetic field. | 0310519v1 |
2003-12-10 | Phase slips in superconducting films with constrictions | A system of two coplanar superconducting films seamlessly connected by a
bridge is studied. We observe two distinct resistive transitions as the
temperature is reduced. The first one, occurring in the films, shows some
properties of the Berezinskii-Kosterlitz-Thouless (BKT) transition. The second
apparent transition (which is in fact a crossover) is related to freezing out
of thermally activated phase slips (TAPS) localized on the bridge. We also
propose a powerful indirect experimental method allowing an extraction of the
sample's zero-bias resistance from high-current-bias measurements. Using direct
and indirect measurements, we determined the resistance $R(T)$ of the bridges
within a range of {\em eleven orders of magnitude}. Over such broad range, the
resistance follows a simple relation $R(T)=R_N \text{exp} [-(c/t)(1-t)^{3/2}]$,
where $c=\Delta F(0) / kT_c$ is the normalized free energy of a phase slip at
zero temperature, $t=T/T_c$ is normalized temperature, and $R_N$ is the normal
resistance of the bridge. | 0312268v2 |
2004-10-04 | The "normal" state of superconducting cuprates might really be normal after all | High magnetic field studies of cuprate superconductors revealed a non-BCS
temperature dependence of the upper critical field $H_{c2}(T)$ determined
resistively by several groups.
These determinations caused some doubts on the grounds of both the
contrasting effect of the magnetic field on the in-plane and out-of-plane
resistances reported for large Bi2212 sample and the large Nernst signal
\emph{well above} $T_{c}$.
Here we present both $\rho_{ab}(B)$ and $\rho_{c}(B)$ of tiny Bi2212 crystals
in magnetic fields up to 50 Tesla.
None of our measurements revealed a situation when on the field increase
$\rho_c$ reaches its maximum while $\rho_{ab}$ remains very small if not zero.
The resistive %upper critical fields estimated from the in-plane and
out-of-plane $H_{c2}(T)$ estimated from $\rho_{ab}(B)$ and $\rho_{c}(B)$ are
approximately the same. Our results support any theory of cuprates that
describes the state above the resistive phase transition as perfectly normal
with a zero off-diagonal order parameter. In particular, the anomalous Nernst
effect above the resistive phase transition in high-$T_{c}$ cuprates can be
described quantitatively as a normal state phenomenon in a model with itinerant
and localised fermions and/or charged bosons. | 0410075v1 |
2008-04-03 | Pressure-temperature Phase Diagram of Polycrystalline UCoGe Studied by Resistivity Measurement | Recently, coexistence of ferromagnetism (T_Curie = 2.8K) and
superconductivity (T_sc = 0.8K) has been reported in UCoGe, a compound close to
a ferromagnetic instability at ambient pressure P. Here we present resistivity
measurements under pressure on a UCoGe polycrystal. The phase diagram obtained
from resistivity measurements on a polycrystalline sample is found to be
qualitatively different to those of all other ferromagnetic superconductors. By
applying high pressure, ferromagnetism is suppressed at a rate of 1.4 K/GPa. No
indication of ferromagnetic order has been observed above P ~ 1GPa. The
resistive superconducting transition is, however, quite stable in temperature
and persists up to the highest measured pressure of about 2.4GPa.
Superconductivity would therefore appear also in the paramagnetic phase.
However, the appearance of superconductivity seems to change at a
characteristic pressure P* ~ 0.8GPa. Close to a ferromagnetic instability, the
homogeneity of the sample can influence strongly the electronic and magnetic
properties and therefore bulk phase transitions may differ from the
determination by resistivity measurements. | 0804.0500v1 |
2008-08-18 | Upper critical field, anisotropy, and superconducting properties of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ single crystals | The temperature dependent resistivity of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (x =
0.23, 0.25, 0.28 and 0.4) single crystals and the angle dependent resistivity
of superconducting Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystals were
measured in magnetic fields up to 9 T. The measurements of temperature
dependent resistivity for samples with different doping levels revealed very
high upper critical fields which increase with the transition temperature
monotonously, and a very low superconducting anisotropy ratio
$\Gamma=H_{c2}^{ab}/H_{c2}^c \approx$ 2. By scaling the resistivity in the
frame of the anisotropic Ginzburg-Landau theory, the angle dependent
resistivity of the Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ single crystal measured with
different magnetic fields at a certain temperature collapsed onto one curve. As
the only scaling parameter, the anisotropy $\Gamma$ was determined
alternatively for each temperature and was found to be between two and three. | 0808.2392v3 |
2009-04-28 | Complete pressure dependent phase diagrams for SrFe2As2 and BaFe2As2 | The temperature dependent electrical resistivity of single crystalline
SrFe2As2 and BaFe2As2 has been measured in a liquid medium, modified Bridgman
anvil cell for pressures in excess of 75 kbar. These data allow for the
determination of the pressure dependence of the higher temperature, structural
/ antiferromagnetic phase transitions as well as the lower temperature
superconducting phase transition. For both compounds the ambient pressure,
higher temperature structural / antiferromagnetic phase transition can be fully
suppressed with a dome-like region of zero resistivity found to be centered
about its critical pressure. Indeed, qualitatively, the temperature dependence
of the resistivity curves closest to the critical pressures are the closest to
linear, consistent with possible quantum criticality. For pressures
significantly higher than the critical pressure the zero resistivity state is
suppressed and the low temperature resistivity curves asymptotically approach a
universal, low temperature manifold. These results are consistent with the
hypothesis that correlations / fluctuations associated with the
ambient-pressure, high-temperature, tetragonal phase have to be brought to low
enough temperature to allow superconductivity, but if too fully suppressed can
lead to the loss of the superconducting state. | 0904.4488v1 |
2011-01-17 | The magnetoresistance and Hall effect in CeFeAsO: a high magnetic field study | The longitudinal electrical resistivity and the transverse Hall resistivity
of CeFeAsO are simultaneously measured up to a magnetic field of 45T using the
facilities of pulsed magnetic field at Los Alamos. Distinct behaviour is
observed in both the magnetoresistance Rxx({\mu}0H) and the Hall resistance
Rxy({\mu}0H) while crossing the structural phase transition at Ts \approx 150K.
At temperatures above Ts, little magnetoresistance is observed and the Hall
resistivity follows linear field dependence. Upon cooling down the system below
Ts, large magnetoresistance develops and the Hall resistivity deviates from the
linear field dependence. Furthermore, we found that the transition at Ts is
extremely robust against the external magnetic field. We argue that the
magnetic state in CeFeAsO is unlikely a conventional type of spin-density-wave
(SDW). | 1101.3170v1 |
2013-07-23 | Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells | We investigate experimentally transport in gated microsctructures containing
a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal
resistances using many contacts prove that in the depletion regime the current
is carried by the edge channels, as expected for a two-dimensional topological
insulator. However, high and non-quantized values of channel resistances show
that the topological protection length (i.e. the distance on which the carriers
in helical edge channels propagate without backscattering) is much shorter than
the channel length, which is ~100 micrometers. The weak temperature dependence
of the resistance and the presence of temperature dependent reproducible
quasi-periodic resistance fluctuations can be qualitatively explained by the
presence of charge puddles in the well, to which the electrons from the edge
channels are tunnel-coupled. | 1307.6115v3 |
2013-08-01 | Resistive Threshold Logic | We report a resistance based threshold logic family useful for mimicking
brain like large variable logic functions in VLSI. A universal Boolean logic
cell based on an analog resistive divider and threshold logic circuit is
presented. The resistive divider is implemented using memristors and provides
output voltage as a summation of weighted product of input voltages. The output
of resistive divider is converted into a binary value by a threshold operation
implemented by CMOS inverter and/or Opamp. An universal cell structure is
presented to decrease the overall implementation complexity and number of
components. When the number of input variables become very high, the proposed
cell offers advantages of smaller area and design simplicity in comparison with
CMOS based logic circuits. | 1308.0090v1 |
2014-02-03 | The Effect of Magnetic Fields, Temperature and Current on the Resistivity of Bi-2223 High Temperature Superconductors | The electrical resistivity of polycrystalline Bi2Sr2Ca2Cu3O10-x (Bi-2223) was
measured vs. applied magnetic fields up to 0.45 T, applied currents up to 1 A,
and temperature from liquid nitrogen temperature (LN2) to room temperature. In
the lowest temperature region, the only truly zero resistivity was observed
when the magnetic field was zero; otherwise, a quadratic dependence on the
magnetic field occurred. Hysteresis was noted at the higher currents. Current
vs. voltage curves in this region revealed a non-ohmic resistivity. In the
transition region to the mixed state, indications of negative resistivity and
suggestions of a phase change were observed. Arrhenius plots yielded activation
energies of around 0.05 eV/molecule. In the mixed state region up to the
transition temperature of ~110K, analysis implied that 4 superconducting
quantum states exist and that they are cooperatively filled by the
superconducting charge carriers. The occupation of the superconducting quantum
states is negatively affected by the applied magnetic field and by the applied
current. No effect on the polarity or direction of the magnetic field with
respect to the direction of the current was observed. | 1402.0436v1 |
2014-10-06 | Low Resistance Metal Contacts to MoS2 Devices with Nickel-Etched-Graphene Electrodes | We report an approach to achieve low-resistance contacts to MoS2 transistors
with the intrinsic performance of the MoS2 channel preserved. Through a dry
transfer technique and a metal-catalyzed graphene treatment process,
nickel-etched-graphene electrodes were fabricated on MoS2 that yield contact
resistance as low as 200 ohm-um. The substantial contact enhancement (~2 orders
of magnitude) as compared to pure nickel electrodes, is attributed to the much
smaller work function of nickel-graphene electrodes, together with the fact
that presence of zigzag edges in the treated graphene surface enhances
tunneling between nickel and graphene. To this end, the successful fabrication
of a clean graphene-MoS2 interface and a low resistance nickel-graphene
interface is critical for the experimentally measured low contact resistance.
The potential of using graphene as an electrode interlayer demonstrated in this
work paves the way towards achieving high performance next-generation
transistors. | 1410.1328v2 |
2017-06-14 | Kinetic theory of transport for inhomogeneous electron fluids | The interplay between electronic interactions and disorder is neglected in
the conventional Boltzmann theory of transport, yet can play an essential role
in determining the resistivity of unconventional metals. When quasiparticles
are long-lived, one can account for these intertwined effects by solving
spatially inhomogeneous Boltzmann equations. Assuming smooth disorder and
neglecting umklapp scattering, we solve these inhomogeneous kinetic equations
and compute the electrical resistivity across the ballistic-to-hydrodynamic
transition. An important consequence of electron-electron interactions is the
modification of the momentum relaxation time; this effect is ignored in the
conventional theory. We characterize precisely when interactions enhance the
momentum scattering rate, and when they decrease it. Our approach unifies
existing semiclassical theories of transport and reveals novel transport
mechanisms. In particular, we explain how the resistivity can be proportional
to the rate of momentum-conserving collisions. We compare this result with
existing transport mysteries, including the disorder-independent $T^2$
resistivity of many Fermi liquids, and the linear-in-$T$ "Planckian-limited"
resistivity of many strange metals. | 1706.04621v3 |
2017-10-11 | Zero-field quantum anomalous Hall metrology as a step towards a universal quantum standard unit system | In the quantum anomalous Hall effect, the edge states of a ferromagnetically
doped topological insulator exhibit quantized Hall resistance and
dissipationless transport at zero magnetic field. Up to now, however, the
resistance was experimentally assessed with standard transport measurement
techniques which are difficult to trace to the von-Klitzing constant R$_K$ with
high precision. Here, we present a metrologically comprehensive measurement,
including a full uncertainty budget, of the resistance quantization of V-doped
(Bi,Sb)$_2$Te$_3$ devices without external magnetic field. We established as a
new upper limit for a potential deviation of the quantized anomalous Hall
resistance from RK a value of 0.26 +- 0.22 ppm, the smallest and most precise
value reported to date. This provides another major step towards realization of
the zero-field quantum resistance standard which in combination with Josephson
effect will provide the universal quantum units standard in the future. | 1710.04090v1 |
2019-09-20 | Phenomenology of anomalous transport in disordered one-dimensional systems | We study anomalous transport arising in disordered one-dimensional spin
chains, specifically focusing on the subdiffusive transport typically found in
a phase preceding the many-body localization transition. Different types of
transport can be distinguished by the scaling of the average resistance with
the system's length. We address the following question: what is the
distribution of resistance over different disorder realizations, and how does
it differ between transport types? In particular, an often evoked so-called
Griffiths picture, that aims to explain slow transport as being due to rare
regions of high disorder, would predict that the diverging resistivity is due
to fat power-law tails in the resistance distribution. Studying many-particle
systems with and without interactions we do not find any clear signs of fat
tails. The data is compatible with distributions that decay faster than any
power law required by the fat tails scenario. Among the distributions
compatible with the data, a simple additivity argument suggests a Gaussian
distribution for a fractional power of the resistance. | 1909.09507v2 |
2019-06-29 | Ultra-Low Surface Resistance via Vacuum Heat Treatment of Superconducting Radiofrequency Cavities | We report on an effort to improve the performance of superconducting
radiofrequency cavities by the use of heat treatment in a temperature range
sufficient to dissociate the natural surface oxide. We find that the residual
resistance is significantly decreased, and we find an unexpected reduction in
the BCS resistance. Together these result in extremely high quality factor
values at relatively large accelerating fields Eacc ~20 MV/m: Q0 of 3-4x10^11
at <1.5 K and Q0 ~5x10^10 at 2.0 K. In one cavity, measurements of surface
resistance versus temperature showed an extremely small residual resistance of
just 0.63+/-0.06 nOhms at 16 MV/m. SIMS measurements confirm that the oxide was
significantly dissociated, but they also show the presence of nitrogen after
heat treatment. We also present studies of surface oxidation via exposure to
air and to water, as well as the effects of very light surface removal via HF
rinse. The possibilities for applications and the planned future development
are discussed. | 1907.00147v1 |
2012-03-21 | Magnetoplasmon resonance in 2D electron system driven into a zero-resistance state | We report on a remarkably strong, and a rather sharp, photoresistance peak
originating from a dimensional magnetoplasmon resonance (MPR) in a high
mobility GaAs/AlGaAs quantum well driven by microwave radiation into a
zero-resistance state (ZRS). The analysis of the MPR signalreveals a negative
background providing experimental evidence for the concept of absolute negative
resistance associated with the ZRS. When a system is further subject to a dc
field, the maxima of microwave-induced resistance oscillations decay away and a
system reveals a state with close-to-zero differential resistance. The MPR
peak, on the other hand, remains essentially unchanged, indicating surprisingly
robust Ohmic behavior under the MPR conditions. | 1203.4781v1 |
2015-04-21 | Radiation-induced resistance oscillations in a 2D hole gas: a demonstration of a universal effect | We report on a theoretical insight about the microwave-induced resistance
oscillations and zero resistance states when dealing with p-type semiconductors
and holes instead of electrons. We consider a high-mobility two-dimensional
hole gas hosted in a pure Ge/SiGe quantum well. Similarly to electrons we
obtain radiation-induce resistance oscillations and zero resistance states. We
analytically deduce a universal expression for the irradiated
magnetoresistance, explaining the origin of the minima positions and their
$1/4$ cycle phase shift. The outcome is that these phenomena are universal and
only depend on radiation and cyclotron frequencies. We also study the
possibility of having simultaneously two different carriers driven by
radiation: light and heavy holes. As a result the calculated magnetoresistance
reveals an interference profile due to the different effective masses of the
two types of carriers. | 1504.05564v2 |
2019-10-03 | Modeling of Electrical Resistivity of Soil Based on Geotechnical Properties | Determining the relationship between the electrical resistivity of soil and
its geotechnical properties is an important engineering problem. This study
aims to develop methodology for finding the best model that can be used to
predict the electrical resistivity of soil, based on knowing its geotechnical
properties. The research develops several linear models, three non-linear
models, and three artificial neural network models (ANN). These models are
applied to the experimental data set comprises 864 observations and five
variables. The results show that there are significant exponential negative
relationships between the electrical resistivity of soil and its geotechnical
properties. The most accurate prediction values are obtained using the ANN
model. The cross-validation analysis confirms the high precision of the
selected predictive model. This research is the first rigorous systematic
analysis and comparison of difference methodologies in ground electrical
resistivity studies. It provides practical guidelines and examples of design,
development and testing non-linear relationships in engineering intelligent
systems and applications. | 1910.01325v1 |
2019-10-16 | $T$-linear resistivity in models with local self-energy | A theoretical understanding of the enigmatic linear-in-temperature ($T$)
resistivity, ubiquitous in strongly correlated metallic systems, has been a
long sought-after goal. Furthermore, the slope of this robust $T$-linear
resistivity is also observed to stay constant through crossovers between
different temperature regimes: a phenomenon we dub "slope invariance".
Recently, several solvable models with $T$-linear resistivity have been
proposed, putting us in an opportune moment to compare their inner workings in
various explicit calculations. We consider two strongly correlated models with
local self-energies that demonstrate $T$-linearity: a lattice of coupled
Sachdev-Ye-Kitaev (SYK) models and the Hubbard model in single-site dynamical
mean-field theory (DMFT). We find that the two models achieve $T$-linearity
through distinct mechanisms at intermediate temperatures. However, we also find
that these mechanisms converge to an identical form at high temperatures.
Surprisingly, both models exhibit "slope invariance" across the two temperature
regimes. We thus not only reveal some of the diversity in the theoretical inner
workings that can lead to $T$-linear resistivity, but we also establish that
different mechanisms can result in "slope invarance". | 1910.07530v2 |
2020-05-28 | Contact resistance extraction of graphene FET technologies based on individual device characterization | Straightforward contact resistance extraction methods based on electrical
device characteristics are described and applied here to graphene field-effect
transistors from different technologies. The methods are an educated adaptation
of extraction procedures originally developed for conventional transistors by
exploiting the drift-diffusion-like transport in graphene devices under certain
bias conditions. In contrast to other available approaches for contact
resistance extraction of graphene transistors, the practical methods used here
do not require either the fabrication of dedicated test structures or internal
device phenomena characterization. The methodologies are evaluated with
simulation-based data and applied to fabricated devices. The extracted values
are close to the ones obtained with other more intricate methodologies.
Bias-dependent contact and channel resistances studies, bias-dependent
high-frequency performance studies and contact engineering studies are enhanced
and evaluated by the extracted contact resistance values. | 2005.13926v1 |
2021-10-29 | Influence of Device Geometry on Transport Properties of Topological Insulator Microflakes | In the transport studies of topological insulators, microflakes exfoliated
from bulk single crystals are often used because of the convenience in sample
preparation and the accessibility to high carrier mobilities. Here, based on
finite element analysis, we show that for the non-Hall-bar shaped topological
insulator samples, the measured four-point resistances can be substantially
modified by the sample geometry, bulk and surface resistivities, and magnetic
field. Geometry correction factors must be introduced for accurately converting
the four-point resistances to the longitudinal resistivity and Hall
resistivity. The magnetic field dependence of inhomogeneous current density
distribution can lead to pronounced positive magnetoresistance and nonlinear
Hall effect that would not exist in the samples of ideal Hall bar geometry. | 2110.15589v1 |
2022-04-14 | DC-coupled resistive silicon detectors for 4-D tracking | In this work, we introduce a new design concept: the DC-Coupled Resistive
Silicon Detectors, based on the LGAD technology. This new approach intends to
address a few known features of the first generation of AC-Coupled Resistive
Silicon Detectors (RSD). Our simulation exploits a fast hybrid approach based
on a combination of two packages, Weightfield2 and LTSpice. It demonstrates
that the key features of the RSD design are maintained, yielding excellent
timing and spatial resolutions: a few tens of ps and a few microns. In the
presentation, we will outline the optimization methodology and the results of
the simulation. We will present detailed studies on the effect of changing the
ratio between the n+ layer resistivity and the low-resistivity ring and on the
achievable temporal and spatial resolution. | 2204.07226v1 |
2022-10-19 | Vector graphics extraction and analysis of electrical resistance data in Nature volume 586, pages 373-377 (2020) | In this paper, I present an analysis of the electrical resistance graphs in
Nature volume 586, pages 373-377 (2020), which reported the discovery of room
temperature superconductivity in a carbonaceous sulfur hydride and was
subsequently retracted on September 26th, 2022. I show that, over a single
temperature interval, the electrical resistance data can be decomposed into at
least two signals of differing digital precision, thus raising questions
concerning the methods used to obtain the published data. Since the raw
data-files for the electrical resistance measurements have not been made
available, in order to perform this analysis, I have developed a set of python
scripts to extract the data-points with high precision from the internal
structure of the vector graphics image files. I describe the data extraction
method. Example code and the resulting electrical resistance vs temperature
data-files are made available in public repositories. | 2210.10766v1 |
2023-06-26 | Towards Optimal Effective Resistance Estimation | We provide new algorithms and conditional hardness for the problem of
estimating effective resistances in $n$-node $m$-edge undirected, expander
graphs. We provide an $\widetilde{O}(m\epsilon^{-1})$-time algorithm that
produces with high probability, an $\widetilde{O}(n\epsilon^{-1})$-bit sketch
from which the effective resistance between any pair of nodes can be estimated,
to $(1 \pm \epsilon)$-multiplicative accuracy, in $\widetilde{O}(1)$-time.
Consequently, we obtain an $\widetilde{O}(m\epsilon^{-1})$-time algorithm for
estimating the effective resistance of all edges in such graphs, improving (for
sparse graphs) on the previous fastest runtimes of
$\widetilde{O}(m\epsilon^{-3/2})$ [Chu et. al. 2018] and
$\widetilde{O}(n^2\epsilon^{-1})$ [Jambulapati, Sidford, 2018] for general
graphs and $\widetilde{O}(m + n\epsilon^{-2})$ for expanders [Li, Sachdeva
2022]. We complement this result by showing a conditional lower bound that a
broad set of algorithms for computing such estimates of the effective
resistances between all pairs of nodes require $\widetilde{\Omega}(n^2
\epsilon^{-1/2})$-time, improving upon the previous best such lower bound of
$\widetilde{\Omega}(n^2 \epsilon^{-1/13})$ [Musco et. al. 2017]. Further, we
leverage the tools underlying these results to obtain improved algorithms and
conditional hardness for more general problems of sketching the pseudoinverse
of positive semidefinite matrices and estimating functions of their
eigenvalues. | 2306.14820v1 |
2023-08-22 | Non-Hermitian topological ohmmeter | Measuring large electrical resistances forms an essential part of common
applications such as insulation testing, but suffers from a fundamental
problem: the larger the resistance, the less sensitive a canonical ohmmeter is.
Here we develop a conceptually different electronic sensor by exploiting the
topological properties of non-Hermitian matrices, whose eigenvalues can show an
exponential sensitivity to perturbations. The ohmmeter is realized in an
multi-terminal, linear electric circuit with a non-Hermitian conductance
matrix, where the target resistance plays the role of the perturbation. We
inject multiple currents and measure a single voltage in order to directly
obtain the value of the resistance. The relative accuracy of the device
increases exponentially with the number of terminals, and for large resistances
outperforms a standard measurement by over an order of magnitude. Our work
paves the way towards leveraging non-Hermitian conductance matrices in
high-precision sensing. | 2308.11367v1 |
2019-09-12 | Analysis of RF losses and material characterization of samples removed from a Nb3Sn-coated superconducting RF cavity | Nb3Sn (Tc ~ 18 K and Hsh ~ 400 mT) is a prospective material to replace Nb
(Tc ~ 9 K and Hsh ~ 200 mT) in SRF accelerator cavities for significant cost
reduction and performance enhancement. Because of its material properties,
Nb3Sn is best employed as a thin film (coating) inside an already built RF
cavity structure. A particular test cavity noted as C3C4 was a 1.5 GHz
single-cell Nb cavity, coated with Nb3Sn using Sn vapor diffusion process at
Jefferson Lab. Cold measurements of the coated cavity indicated the
superconducting transition temperature of about 18 K. Subsequent RF
measurements indicated field-dependent surface resistance both at 4.3 K and 2.0
K. After initial cold measurements, the cavity RF loss distribution was studied
with a thermometry mapping system. Loss regions were identified with
thermometry and were cut out for material analysis. The presence of
significantly thin patchy regions and other carbon-rich defects is associated
with strong local field-dependent surface resistance. This paper summarizes RF
and thermometry results correlated with material science findings. | 1909.05695v1 |
2020-02-27 | A simple approach to bulk bioinspired tough ceramics | The development of damage-resistant structural materials that can withstand
harsh environments is a major issue in materials science and engineering.
Bioinspired brick-and-mortar designs have recently demonstrated a range of
interesting mechanical properties in proof-of-concept studies. However,
reproducibility and scalability issues associated with the actual processing
routes have impeded further developments and industrialization of such
materials. Here we demonstrate a simple approach based on uniaxial pressing and
field assisted sintering of commercially available raw materials to process
bioinspired ceramic/ceramic composites of larger thickness than previous
approaches, with a sample thickness up to 1 cm. The ceramic composite retains
the strength typical of dense alumina ($430~\pm 30MPa$) while keeping the
excellent damage resistance demonstrated previously at the millimeter scale
with a crack initiation toughness of $6.6MPa.m^{1/2}$ and fracture toughness up
to $17.6 MPa.m^{1/2}$. These results validate the potential of these
all-ceramic composites, previously demonstrated at lab scale only, and could
enable their optimization, scale-up, and industrialization. | 2003.11898v1 |
2021-10-09 | Fracture Diodes: Directional asymmetry of fracture toughness | Toughness describes the ability of a material to resist fracture or crack
propagation. It is demonstrated here that fracture toughness of a material can
be asymmetric, i.e., the resistance of a medium to a crack propagating from
right to left can be significantly different from that to a crack propagating
from left to right. Such asymmetry is unknown in natural materials, but we show
that it can be built into artificial materials through the proper control of
microstructure. This paves the way for control of crack paths and direction,
where fracture -- when unavoidable -- can be guided through pre-designed paths
to minimize loss of critical components. | 2110.04613v1 |
2022-07-20 | Do thermoelectric generator modules degrade due to nickel diffusion | The paper shows by calculation that the diffusion of nickel even for 50 years
does not lead to degradation of thermoelectric generator modules. In the
process, we used the theory of composites to calculate the electrical contact
resistance, our own diffusion theory of electrical contact resistance, as well
as the method for approximating the temperature dependences of thermoelectric
material characteristics from the experimental data. When using the above
method, it was assumed that the main mechanism of scattering of free charge
carriers in a thermoelectric material is their scattering on the deformation
potential of acoustic phonons with a free path length independent of energy but
inversely proportional to temperature, and the main mechanism of phonon
scattering is phonon-phonon scattering with Umklapp, which is not affected by
the nickel impurity in the thermoelectric material. Thus, it was believed that
the role of nickel is reduced only to a change in the concentration of free
charge carriers in the material. | 2207.12122v1 |
2023-03-10 | Engineering heat transport across epitaxial lattice-mismatched van der Waals heterointerfaces | Artificially engineered 2D materials offer unique physical properties for
thermal management, surpassing naturally occurring materials. Here, using van
der Waals epitaxy, we demonstrate the ability to engineer extremely insulating
ultra-thin thermal metamaterials based on crystalline lattice-mismatched
Bi2Se3/MoSe2 superlattices and graphene/PdSe2 heterostructures with exceptional
thermal resistances (70-202 m^2K/GW) and ultralow cross-plane thermal
conductivities (0.01-0.07 Wm^-1K^-1) at room temperature, comparable to those
of amorphous materials. Experimental data obtained using frequency-domain
thermoreflectance and low-frequency Raman spectroscopy, supported by
tight-binding phonon calculations, reveal the impact of lattice mismatch,
phonon-interface scattering, size effects, temperature and interface thermal
resistance on cross-plane heat dissipation, uncovering different thermal
transport regimes and the dominant role of long-wavelength phonons. Our
findings provide essential insights into emerging synthesis and thermal
characterization methods and valuable guidance for the development of
large-area heteroepitaxial van der Waals films of dissimilar materials with
tailored thermal transport characteristics. | 2303.05808v1 |
2023-09-25 | Integrated bolometric photodetectors based on transparent conductive oxides from near- to mid-infrared wavelengths | On-chip photodetectors are essential components in optical communications as
they convert light into an electrical signal. Photobolometers are type of
photodetector that functions through a resistance change caused by electronic
temperature fluctuations upon light absorption. They are widely used in the
broad wavelength range from UV to MIR and can operate on a wide material
platform. In this work, I introduce a novel waveguide-integrated bolometer that
operates in a wide wavelength range from NIR to MIR on the standard material
platform with the transparent conductive oxides (TCOs) as the active material.
This material platform enables the construction of both modulators and
photodetectors using the same material, which is fully CMOS compatible and
easily integrated with passive on-chip components. The photobolometers proposed
here consist of a thin TCO layer placed inside the rib photonic waveguide to
enhance light absorption and then heat the electrons in the TCO to temperatures
above 1000 K. This rise in electron temperature leads to decreasing electron
mobility and consequential electrical resistance change. In consequence, a
responsivity exceeding 10 A/W can be attained with a mere few microwatts of
optical input power. Calculations suggest that further improvements can be
expected with lower doping of the TCO, thus opening new doors in on-chip
photodetectors. | 2309.14454v1 |
2023-10-04 | Current-driven magnetic resistance in van der Waals spin-filter antiferromagnetic tunnel junctions with MnBi$_2$Te$_4$ | The field of 2D magnetic materials has paved the way for the development of
spintronics and nanodevices with new functionalities. Utilizing
antiferromagnetic materials, in addition to layered van der Waals (vdW)
ferromagnetic materials, has garnered significant interest. In this work, we
present a theoretical investigation of the behavior of MnBi$_2$Te$_4$ devices
based on the non-equilibrium Green's function method. Our results show that the
current-voltage (I-V) characteristics can be influenced significantly by
controlling the length of the device and bias voltage and thus allow us to
manipulate the tunneling magneto-resistance (TMR) with an external bias
voltage. This can be further influenced by the presence of the boron nitride
layer which shows significantly enhanced TMR by selectively suppressing
specific spin channels for different magnetic configurations. By exploiting
this mechanism, the observed TMR value reaches up to 3690\%, which can be
attributed to the spin-polarized transmission channel and the projected local
density of states. Our findings on the influence of structural and magnetic
configurations on the spin-polarized transport properties and TMR ratios give
the potential implementation of antiferromagnetic vdW layered materials in
ultrathin spintronics. | 2310.02830v1 |
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