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2023-07-31 | Ferroelectricity in tetragonal ZrO$_2$ thin films | We report on the crystal structure and ferroelectric properties of epitaxial
ZrO$_2$ films ranging from 7 to 42 nm thickness grown on
La$_{0.67}$Sr$_{0.33}$MnO$_3$-buffered (110)-oriented SrTiO$_3$ substrate. By
employing X-ray diffraction, we confirm a tetragonal phase at all investigated
thicknesses, with slight in-plane strain due to the substrate in the thinnest
films. Further confirmation of the tetragonal phase was obtained through
Infrared absorption spectroscopy with synchrotron light, performed on ZrO$_2$
membrane transferred onto a high resistive Silicon substrate. Up to a thickness
of 31 nm, the ZrO$_2$ epitaxial films exhibit ferroelectric behavior, at
variance with the antiferroelectric behavior reported previously for the
tetragonal phase in polycrystalline films. However, the ferroelectricity is
found here to diminish with increasing film thickness, with a polarization of
about 13 $\mu$C.cm$^{-2}$ and down to 1 $\mu$C.cm$^{-2}$ for 7 nm and 31
nm-thick ZrO$_2$ films, respectively. This highlights the role of thickness
reduction, substrate strain, and surface effects in promoting polarization in
the tetragonal ZrO$_2$ thin films. These findings provide new insights into the
ferroelectric properties and structure of ZrO$_2$ thin films, and open up new
directions to investigate the origin of ferroelectricity in ZrO$_2$ and to
optimize this material for future applications. | 2307.16492v1 |
2023-08-16 | Automated Semiconductor Defect Inspection in Scanning Electron Microscope Images: a Systematic Review | A growing need exists for efficient and accurate methods for detecting
defects in semiconductor materials and devices. These defects can have a
detrimental impact on the efficiency of the manufacturing process, because they
cause critical failures and wafer-yield limitations. As nodes and patterns get
smaller, even high-resolution imaging techniques such as Scanning Electron
Microscopy (SEM) produce noisy images due to operating close to sensitivity
levels and due to varying physical properties of different underlayers or
resist materials. This inherent noise is one of the main challenges for defect
inspection. One promising approach is the use of machine learning algorithms,
which can be trained to accurately classify and locate defects in semiconductor
samples. Recently, convolutional neural networks have proved to be particularly
useful in this regard. This systematic review provides a comprehensive overview
of the state of automated semiconductor defect inspection on SEM images,
including the most recent innovations and developments. 38 publications were
selected on this topic, indexed in IEEE Xplore and SPIE databases. For each of
these, the application, methodology, dataset, results, limitations and future
work were summarized. A comprehensive overview and analysis of their methods is
provided. Finally, promising avenues for future work in the field of SEM-based
defect inspection are suggested. | 2308.08376v2 |
2023-10-05 | Spin-orbit torques and spin Hall magnetoresistance generated by twin-free and amorphous Bi0.9Sb0.1 topological insulator films | Topological insulators have attracted great interest as generators of
spin-orbit torques (SOTs) in spintronic devices.
Bi\textsubscript{1-x}Sb\textsubscript{x} is a prominent topological insulator
that has a high charge-to-spin conversion efficiency. However, the origin and
magnitude of the SOTs induced by current-injection in
Bi\textsubscript{1-x}Sb\textsubscript{x} remain controversial. Here we report
the investigation of the SOTs and spin Hall magnetoresistance resulting from
charge-to-spin conversion in twin-free epitaxial layers of
Bi\textsubscript{0.9}Sb\textsubscript{0.1}(0001) coupled to FeCo, and compare
it with that of amorphous Bi\textsubscript{0.9}Sb\textsubscript{0.1}. We find a
large charge-to-spin conversion efficiency of 1 in the first case and less than
0.1 in the second, confirming crystalline
Bi\textsubscript{0.9}Sb\textsubscript{0.1} as a strong spin injector material.
The SOTs and spin Hall magnetoresistance are independent of the direction of
the electric current, indicating that charge-to-spin conversion in
single-crystal Bi\textsubscript{0.9}Sb\textsubscript{0.1}(0001) is isotropic
despite the strong anisotropy of the topological surface states. Further, we
find that the damping-like SOT has a non-monotonic temperature dependence with
a minimum at 20~K. By correlating the SOT with resistivity and weak
antilocalization measurements, we conclude that charge-spin conversion occurs
via thermally-excited holes from the bulk states above 20~K, and conduction
through the isotropic surface states with increasing spin polarization due to
decreasing electron-electron scattering below 20~K. | 2310.03487v1 |
2023-12-09 | Extended Kohler's Rule of Magnetoresistance in TaCo$_2$Te$_2$ | TaCo$_2$Te$_2$ is recently reported to be an air-stable, high mobility Van
der Waals material with probable magnetic order. Here we investigate the
scaling behavior of its magnetoresistance. We measured both the longitudinal
($\rho_{xx}$) and Hall ($\rho_{xy}$) magnetoresistivities of TaCo$_2$Te$_2$
crystals in magnetic fields parallel to the c-axis and found that the
magnetoresistance violates the Kohler's rule $MR \sim f[H/\rho_0]$ while
obeying the extended Kohler's rule $MR \sim f[H/(n_T\rho_0)]$, where $MR \sim
[\rho_{xx}(H)-\rho_0]/\rho_0$, $H$ is the magnetic field, $n_T$ is a thermal
factor, $\rho_{xx}(H)$ and $\rho_0$ are the resistivities at $H$ and zero
field, respectively. While deviating from those of the densities of electrons
($n_e$) and holes ($n_h$) obtained from the two-band model analysis of the
magnetoconductivities, the temperature dependence of $n_T$ is close to that of
the Hall carrier densities $n_H$ calculated from the slopes of $\rho_{xy}(H)$
curves at low magnetic fields, providing a new way to obtain the thermal factor
in the extended Kohler's rule. | 2312.05624v1 |
2023-12-16 | Electronic phase transition, vibrational properties and structural stability of single and two polyyne chains under external electric field | Search for one dimensional (1D) van der Waals materials has become an urgent
need to meet the demand as building blocks for high performance, miniaturized,
lightweight device applications. Polyyne, a 1D atomic chain of carbon is the
thinnest and strongest allotrope of carbon, showing promising applications in
new generation low dimensional devices due to the presence of a band gap. A
system of two carbon chains held together by van der Waals interaction has been
theoretically postulated and shows band gap tunability under structural changes
which finds applications in the realms of resistive switching and spintronics.
In this study, we use first principles Density Functional Theory (DFT) to show
a sharp semiconductor to metal transition along with the emergence of an
asymmetry in the spin polarized density of states for single and two polyyne
chains under a transverse electric field. The thermodynamic stability of the
system has been substantiated through the utilization of Ab Initio Molecular
Dynamics (AIMD) simulations, phonon dispersion curve analyses, and formation
energy calculations. Furthermore, in addition to its dynamic stability
assessment, phonon calculations have served to identify Raman active
vibrational modes which offers an invaluable non-destructive experimental
avenue for discerning electronic phase transitions in response to an applied
electric field. Our study presents a predictive framework for the prospective
utilization of one and two polyyne chains in forthcoming flexible
nano-electronic and spintronic devices. The future prospects of the system are
contingent upon advancements in nano-electronics fabrication techniques and the
precise construction of circuitry for harnessing spin-related applications. | 2312.10335v1 |
2024-02-06 | Observation of the double quantum spin Hall phase in moiré WSe2 | Quantum spin Hall (QSH) insulators are a topologically protected phase of
matter in two dimensions that can support non-dissipative spin transport. A
hallmark of the phase is a pair of helical edge states surrounding an
insulating bulk. A higher (even) number of helical edge state pairs is usually
not possible in real materials because spin mixing would gap out the edge
states. Multiple pairs of helical edge states have been proposed in materials
with spin conservation symmetry and high spin Chern bands, but remained
experimentally elusive. Here, we demonstrate a QSH phase with one and two pairs
of helical edge states in twisted bilayer WSe2 at moir\'e hole filling factor
{\nu}= 2 and 4, respectively. We observe nearly quantized conductance or
resistance plateaus of h/({\nu}e^2 ) at {\nu} = 2 and 4 while the bulk is
insulating. The conductance is nearly independent of out-of-plane magnetic
field and decreases under an in-plane magnetic field. We also observe nonlocal
transport, which is sensitive only to the in-plane magnetic field. The results
agree with quantum transport of helical edge states protected by Ising spin
conservation symmetry and open a promising platform for low-power spintronics. | 2402.04196v1 |
2024-02-13 | Coarse-Graining in Space versus Time | Understanding the structure and dynamics of liquids is pivotal for the study
of larger spatiotemporal processes, particularly for glass-forming materials at
low temperatures. The so-called thermodynamic scaling relation, validated for
many molecular systems through experiments, offers an efficient means to
explore a vast range of time scales along a one-dimensional phase diagram.
Isomorph theory provides a theoretical framework for thermodynamic scaling
based on strong virial-potential energy correlations, but this approach is most
successful for simple point particles. In particular, isomorph theory has
resisted extension to complex molecular liquids due to the existence of
high-frequency intramolecular interactions. To elucidate the microscopic origin
of density scaling for molecular systems, we employ two distinct approaches for
coarse-graining in space or in time. The former eliminates fast degrees of
freedom by reducing a molecule to a center-of-mass-level description, while the
latter involves temporally averaged fluctuations or correlation functions over
the characteristic time scale. We show that both approaches yield a consistent
density scaling coefficient for ortho-terphenyl, which is moreover in agreement
with the experimental value. Building upon these findings, we derive the
density scaling relationship exhibiting a single-parameter phase diagram from
fully atomistic simulations. Our results unravel the microscopic nature
underlying thermodynamic scaling and shed light on the role of coarse-graining
for assessing the slow fluctuations in molecular systems, ultimately enabling
the extension of systematic bottom-up approaches to larger and more complex
molecular liquids that are experimentally challenging to probe. | 2402.08675v1 |
2024-02-27 | Design principles of nonlinear optical materials for Terahertz lasers | We have investigated both inter-band and intra-band second order nonlinear
optical conductivity based on the velocity correlation formalism and the
spectral expansion technique. We propose a scenario in which the second order
intra-band process is nonzero while the inter-band process is zero. This occurs
for a band structure with momentum asymmetry in the Brillouin zone. Very
low-energy photons are blocked by the Pauli exclusion principle from
participating in the inter-band process; however, they are permitted to
participate in the intra-band process, with the band smeared by some impurity
scattering. We establish a connection between the inter-band nonlinear optical
conductivity in the velocity gauge and the shift vector in the length gauge for
a two-band model. Using a quasiclassical kinetic approach, we demonstrate the
importance of intra-band transitions in high harmonic generations for the
single tilted Dirac cone model and hexagonal warping model. We confirm that the
Kramers-Kronig relations break down for the limit case of ($\omega$, $-\omega$)
in the nonlinear optical conductivity. Finally, we calculate the
superconducting transition temperature of NbN and the dielectric function of
AlN, and the resistance of the NbN/AlN junction. The natural non-linearity of
the Josephson junction brings a Josephson plasma with frequency in the
Terahertz region. | 2402.17126v1 |
2024-03-25 | Multi-Objective Quality-Diversity for Crystal Structure Prediction | Crystal structures are indispensable across various domains, from batteries
to solar cells, and extensive research has been dedicated to predicting their
properties based on their atomic configurations. However, prevailing Crystal
Structure Prediction methods focus on identifying the most stable solutions
that lie at the global minimum of the energy function. This approach overlooks
other potentially interesting materials that lie in neighbouring local minima
and have different material properties such as conductivity or resistance to
deformation. By contrast, Quality-Diversity algorithms provide a promising
avenue for Crystal Structure Prediction as they aim to find a collection of
high-performing solutions that have diverse characteristics. However, it may
also be valuable to optimise for the stability of crystal structures alongside
other objectives such as magnetism or thermoelectric efficiency. Therefore, in
this work, we harness the power of Multi-Objective Quality-Diversity algorithms
in order to find crystal structures which have diverse features and achieve
different trade-offs of objectives. We analyse our approach on 5 crystal
systems and demonstrate that it is not only able to re-discover known real-life
structures, but also find promising new ones. Moreover, we propose a method for
illuminating the objective space to gain an understanding of what trade-offs
can be achieved. | 2403.17164v1 |
2002-08-26 | Magnetized Accretion-Ejection Structures: 2.5D MHD simulations of continuous Ideal Jet launching from resistive accretion disks | We present numerical magnetohydrodynamic (MHD) simulations of a magnetized
accretion disk launching trans-Alfvenic jets. These simulations, performed in a
2.5 dimensional time-dependent polytropic resistive MHD framework, model a
resistive accretion disk threaded by an initial vertical magnetic field. The
resistivity is only important inside the disk, and is prescribed as eta =
alpha_m V_AH exp(-2Z^2/H^2), where V_A stands for Alfven speed, H is the disk
scale height and the coefficient alpha_m is smaller than unity. By performing
the simulations over several tens of dynamical disk timescales, we show that
the launching of a collimated outflow occurs self-consistently and the ejection
of matter is continuous and quasi-stationary. These are the first ever
simulations of resistive accretion disks launching non-transient ideal MHD
jets. Roughly 15% of accreted mass is persistently ejected. This outflow is
safely characterized as a jet since the flow becomes super-fastmagnetosonic,
well-collimated and reaches a quasi-stationary state. We present a complete
illustration and explanation of the `accretion-ejection' mechanism that leads
to jet formation from a magnetized accretion disk. In particular, the magnetic
torque inside the disk brakes the matter azimuthally and allows for accretion,
while it is responsible for an effective magneto-centrifugal acceleration in
the jet. As such, the magnetic field channels the disk angular momentum and
powers the jet acceleration and collimation. The jet originates from the inner
disk region where equipartition between thermal and magnetic forces is
achieved. A hollow, super-fastmagnetosonic shell of dense material is the
natural outcome of the inwards advection of a primordial field. | 0208459v1 |
2006-02-17 | Coupling losses and transverse resistivity of multifilament YBCO coated superconductors | We studied the magnetization losses of four different types of filamentary
YBCO coated conductors. A 10 mm wide YBCO coated conductor was subdivided into
20 filaments by laser cutting. The separation of coupling loss from the total
is possible because the energy loss per cycle in samples with electrically
insulated filaments has a very small frequency dependence. We measured the
frequency dependence of the total losses in the frequency range between 0.1 Hz
and 500 Hz. The coupling loss was obtained from the total by subtracting the
hysteresis loss. The latter was measured at low frequencies since only
hysteresis loss is non-negligible at frequencies below 1 Hz. The transverse
resistivity was determined from the coupling losses; it was assumed that the
sample length is equal to half of the twist pitch. The values of transverse
resistivity deduced from the loss data were compared with those obtained by the
four-point measurements with current flowing perpendicular to the filaments.
Preliminary results indicate that the current method of laser ablation creates
electrical contacts between the superconducting filaments and the substrate.
This was also confirmed by the Hall probe mapping of the magnetic field in the
vicinity of the tape. The measured transverse resistivity was close to the
resistivity of the substrate (Hastelloy). | 0602422v1 |
2007-02-21 | Electrical current-driven pinhole formation and insulator-metal transition in tunnel junctions | Current Induced Resistance Switching (CIS) was recently observed in thin
tunnel junctions (TJs) with ferromagnetic (FM) electrodes and attributed to
electromigration of metallic atoms in nanoconstrictions in the insulating
barrier. The CIS effect is here studied in TJs with two thin (20 \AA)
non-magnetic (NM) Ta electrodes inserted above and below the insulating
barrier. We observe resistance (R) switching for positive applied electrical
current (flowing from the bottom to the top lead), characterized by a
continuous resistance decrease and associated with current-driven displacement
of metallic ions from the bottom electrode into the barrier (thin barrier
state). For negative currents, displaced ions return into their initial
positions in the electrode and the electrical resistance gradually increases
(thick barrier state). We measured the temperature (T) dependence of the
electrical resistance of both thin- and thick-barrier states ($R_b$ and R$_B$
respectively). Experiments showed a weaker R(T) variation when the tunnel
junction is in the $R_b$ state, associated with a smaller tunnel contribution.
By applying large enough electrical currents we induced large irreversible
R-decreases in the studied TJs, associated with barrier degradation. We then
monitored the evolution of the R(T) dependence for different stages of barrier
degradation. In particular, we observed a smooth transition from tunnel- to
metallic-dominated transport. The initial degradation-stages are related to
irreversible barrier thickness decreases (without the formation of pinholes).
Only for later barrier degradation stages do we have the appearance of metallic
paths between the two electrodes that, however, do not lead to metallic
dominated transport for small enough pinhole radius. | 0702501v2 |
2008-12-15 | Nanomechanical detection of antibiotic-mucopeptide binding in a model for superbug drug resistance | The alarming growth of the antibiotic-resistant superbugs
methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant
Enterococcus (VRE) is driving the development of new technologies to
investigate antibiotics and their modes of action. We report the label-free
detection of vancomycin binding to bacterial cell wall precursor analogues
(mucopeptides) on cantilever arrays, with 10 nM sensitivity and at clinically
relevant concentrations in blood serum. Differential measurements quantified
binding constants for vancomycin-sensitive and vancomycin-resistant mucopeptide
analogues. Moreover, by systematically modifying the mucopeptide density we
gain new insights into the origin of surface stress. We propose that stress is
a product of a local chemical binding factor and a geometrical factor
describing the mechanical connectivity of regions affected by local binding in
terms of a percolation process. Our findings place BioMEMS devices in a new
class of percolative systems. The percolation concept will underpin the design
of devices and coatings to significantly lower the drug detection limit and may
also impact on our understanding of antibiotic drug action in bacteria. | 0812.2728v1 |
2010-05-19 | Resistance in Superconductors | In this pedagogical review, we discuss how electrical resistance can arise in
superconductors. Starting with the idea of the superconducting order parameter
as a condensate wave function, we introduce vortices as topological excitations
with quantized phase winding, and we show how phase slips occur when vortices
cross the sample. Superconductors exhibit non-zero electrical resistance under
circumstances where phase slips occur at a finite rate. For one-dimensional
superconductors or Josephson junctions, phase slips can occur at isolated
points in space-time. Phase slip rates may be controlled by thermal activation
over a free-energy barrier, or in some circumstances, at low temperatures, by
quantum tunneling through a barrier. We present an overview of several
phenomena involving vortices that have direct implications for the electrical
resistance of superconductors, including the Berezinskii-Kosterlitz-Thouless
transition for vortex-proliferation in thin films, and the effects of vortex
pinning in bulk type II superconductors on the non-linear resistivity of these
materials in an applied magnetic field. We discuss how quantum fluctuations can
cause phase slips and review the non-trivial role of dissipation on such
fluctuations. We present a basic picture of the superconductor-to-insulator
quantum phase transitions in films, wires, and Josephson junctions. We point
out related problems in superfluid helium films and systems of ultra-cold
trapped atoms. While our emphasis is on theoretical concepts, we also briefly
describe experimental results, and we underline some of the open questions. | 1005.3347v1 |
2013-06-28 | Impact of sintering temperature on room temperature magneto-resistive and magneto-caloric properties of Pr2/3Sr1/3MnO3 | Magneto-resistive and magneto-caloric properties of polycrystalline
Pr2/3Sr1/3MnO3 have been studied as a function of sintering temperature (Ts)
between 1260-1450{\deg}C. Reitveld refinement of their X-ray diffraction (XRD)
patterns confirms their single phase crystalline structure with orthorhombic
Pbnm space group. The point of maximum value of temperature coefficient of
resistance (TCRmax) and Curie temperature (Tc) decreased slightly with Ts.
Magneto-resistance (MR) and magnetic entropy ({\Delta}SM) increased markedly
with sintering temperature. This could be attributed to the observed sharpness
of both the magnetic and resistive transitions due to better grain
connectivity. Optimum results are obtained for the sample with Ts =
1400{\deg}C. MR at Tc of the same is found to be as large as 32% at 1T and 58%
at 5T magnetic fields. The maximum entropy change ({\Delta}SMmax) near its Tc
is 2.3Jkg-1K-1 and 7.8 Jkg-1K-1 upon 1T and 5T fields change respectively.
These characteristics [MR (32% 1T, 58% 5T) and reasonable change in magnetic
entropy (7.8Jkg-1K-1, 5T)] generate possibility that the optimized compound can
be used as a potential magnetic refrigerant close to room temperature. | 1306.6792v2 |
2014-11-15 | Shock-waves and commutation speed of memristors | Progress of silicon based technology is nearing its physical limit, as
minimum feature size of components is reaching a mere 10 nm. The resistive
switching behaviour of transition metal oxides and the associated memristor
device is emerging as a competitive technology for next generation electronics.
Significant progress has already been made in the past decade and devices are
beginning to hit the market; however, it has been mainly the result of
empirical trial and error. Hence, gaining theoretical insight is of essence. In
the present work we report the striking result of a connection between the
resistive switching and {\em shock wave} formation, a classic topic of
non-linear dynamics. We argue that the profile of oxygen vacancies that migrate
during the commutation forms a shock wave that propagates through a highly
resistive region of the device. We validate the scenario by means of model
simulations and experiments in a manganese-oxide based memristor device. The
shock wave scenario brings unprecedented physical insight and enables to
rationalize the process of oxygen-vacancy-driven resistive change with direct
implications for a key technological aspect -- the commutation speed. | 1411.4198v3 |
2015-09-29 | Extraordinary Hall resistance and unconventional magnetoresistance in Pt/LaCoO3 hybrids | We report an investigation of transverse Hall resistance and longitudinal
resistance on Pt thin films sputtered on epitaxial LaCoO$_3$ (LCO)
ferromagnetic insulator films. The LaCoO$_3$ films were deposited on several
single crystalline substrates [LaAlO$_3$ (LAO), (La,Sr)(Al,Ta)O$_3$ (LSAT), and
SrTiO$_3$ (STO)] with (001) orientation. The physical properties of LaCoO$_3$
films were characterized by the measurements of magnetic and transport
properties. The LaCoO$_3$ films undergo a paramagnetic to ferromagnetic (FM)
transition at Curie temperatures ranging from 40 K to 85 K, below which the
Pt/LCO hybrids exhibit significant extraordinary Hall resistance (EHR) up to 50
m$\Omega$ and unconventional magnetoresistance (UCMR) ratio
$\Delta$$\rho$/$\rho_0$ about $1.2 \times 10^{-4}$, accompanied by the
conventional magnetoresistance (CMR). The observed spin transport properties
share some common features as well as some unique characteristics when compared
with well-studied Y$_3$Fe$_5$O$_{12}$-based Pt thin films. Our findings call
for new theories since the extraordinary Hall resistance and magnetoresistance
cannot be consistently explained by the existing theories. | 1509.08691v1 |
2016-02-24 | Contact resistances in trigate and FinFET devices in a Non-Equilibrium Green's Functions approach | We compute the contact resistances $R_{\rm c}$ in trigate and FinFET devices
with widths and heights in the 4 to 24 nm range using a Non-Equilibrium Green's
Functions approach. Electron-phonon, surface roughness and Coulomb scattering
are taken into account. We show that $R_{\rm c}$ represents a significant part
of the total resistance of devices with sub-30 nm gate lengths. The analysis of
the quasi-Fermi level profile reveals that the spacers between the heavily
doped source/drain and the gate are major contributors to the contact
resistance. The conductance is indeed limited by the poor electrostatic control
over the carrier density under the spacers. We then disentangle the ballistic
and diffusive components of $R_{\rm c}$, and analyze the impact of different
design parameters (cross section and doping profile in the contacts) on the
electrical performances of the devices. The contact resistance and variability
rapidly increase when the cross sectional area of the channel goes below
$\simeq 50$ nm$^2$. We also highlight the role of the charges trapped at the
interface between silicon and the spacer material. | 1602.07545v1 |
2017-10-26 | Effect of air confinement on thermal contact resistance in nanoscale heat transfer | We report herein the pressure dependent thermal contact resistance (Rc)
between Wollaston wire thermal probe and samples which is evaluated within the
framework of an analytical model. This work presents heat transfer between the
Wollaston wire thermal probe and samples at nanoscale for different air
pressure ranging from 1 Pa to 10e5 Pa. We make use of a scanning thermal
microscopy (SThM) for the thermal analysis of two samples, fused silica (SiO2)
and Titanium (Ti), with different thermal conductivities. The thermal probe's
output voltage difference (deltaV) between out-off contact output voltage (Voc)
and in-contact output voltage (Vic) was recorded. The result shows that the
heat transfer increases with the increasing air pressure and it is found higher
for higher thermal conductive material. We also propose an analytical model
based on the normalized output voltage difference to extract the probe-sample
thermal contact resistance. The obtained Rc values in the range of ~1.8e7 K/W
to ~14.3e7 K/W validate the presented analytical model. Further analysis
reveals that the thermal contact resistance between the probe and sample
decreases with increasing air pressure. Such behavior is interpreted by the
contribution of heat transfer through confined air on thermal contact
resistance. In addition, the signature of Rc is also evidenced in the context
of thermal mismatch behavior which is studied by using acoustic mismatch model
(AMM) and diffuse mismatch model (DMM). | 1710.09501v1 |
2017-11-08 | Surface impedance and optimum surface resistance of a superconductor with imperfect surface | We calculate a low-frequency surface impedance of a dirty, s-wave
superconductor with an imperfect surface incorporating either a thin layer with
a reduced pairing constant or a thin, proximity-coupled normal layer. Such
structures model realistic surfaces of superconducting materials which can
contain oxide layers, absorbed impurities or nonstoichiometric composition. We
solved the Usadel equations self-consistently and obtained spatial
distributions of the order parameter and the quasiparticle density of states
which then were used to calculate a low-frequency surface resistance $R_s(T)$
and the magnetic penetration depth $\lambda(T)$ as functions of temperature in
the limit of local London electrodynamics. It is shown that the imperfect
surface in a single-band s-wave superconductor results in a non-exponential
temperature dependence of $Z(T)$ at $T\ll T_c$ which can mimic the behavior of
multiband or d-wave superconductors. The imperfect surface and the broadening
of the gap peaks in the quasiparticle density of states $N(\epsilon)$ in the
bulk give rise to a weakly temperature-dependent residual surface resistance.
We show that the surface resistance can be optimized and even reduced below its
value for an ideal surface by engineering $N(\epsilon)$ at the surface using
pairbreaking mechanisms, particularly, by incorporating a small density of
magnetic impurities or by tuning the thickness and conductivity of the normal
layer and its contact resistance. The results of this work address the limit of
$R_s$ in superconductors at $T\ll T_c$, and the ways of engineering the optimal
density of states by surface nano-structuring and impurities to reduce losses
in superconducting micro-resonators, thin film strip lines, and radio frequency
cavities for particle accelerators. | 1711.03077v1 |
2018-02-15 | Parallel magnetic field suppresses dissipation in superconducting nanostrips | The motion of Abrikosov vortices in type-II superconductors results in a
finite resistance in the presence of an applied electric current. Elimination
or reduction of the resistance via immobilization of vortices is the "holy
grail" of superconductivity research. Common wisdom dictates that an increase
in the magnetic field escalates the loss of energy since the number of vortices
increases. Here we show that this is no longer true if the magnetic field and
the current are applied parallel to each other.Our experimental studies on the
resistive behavior of a superconducting Mo$_{0.79}$Ge$_{0.21}$ nanostrip reveal
the emergence of a dissipative state with increasing magnetic field, followed
by a pronounced resistance drop, signifying a reentrance to the superconducting
state. Large-scale simulations of the 3D time-dependent Ginzburg-Landau model
indicate that the intermediate resistive state is due to an unwinding of
twisted vortices. When the magnetic field increases, this instability is
suppressed due to a better accommodation of the vortex lattice to the pinning
configuration. Our findings show that magnetic field and geometrical
confinement can suppress the dissipation induced by vortex motion and thus
radically improve the performance of superconducting materials. | 1802.05673v1 |
2018-05-22 | Structural properties and anisotropic electronic transport in SrIrO3 films | Perovskite SrIrO3 (SIO) films epitaxially deposited with a thickness of about
60 nm on various substrate materials display nearly strain-relieved state.
Films grown on orthorhombic (110) DyScO3 (DSO) are found to display untwinned
bulk-like orthorhombic structure. However, film deposition on cubic (001)
SrTiO3 induces a twinned growth of SIO. Resistance measurements on the SIO
films reveal only weak temperature dependence, where the resistance R increases
with decreasing temperature T. Hall measurements show dominant electron-like
transport throughout the temperature range from 2 K to 300 K. At 2 K, the
electron concentration and resistivity for SIO on STO amount to ne = 1.4*10^20
cm-3 and 1 mohmcm. Interestingly, the film resistance of untwinned SIO on DSO
along the [1-10] and the [001] direction differs by up to 25% indicating
pronounced anisotropic electronic transport. The anisotropy of the resistance
increases with decreasing T and displays a distinct maximum around 86 K. The
specific T-dependence is similar to that of the structural anisotropy
sqrt(a2+b2)/c of bulk SIO. Therefore, anisotropic electronic transport in SIO
is very likely induced by the orthorhombic distortion. Consequently, for
twinned SIO films on STO anisotropy vanishes nearly completely. The
experimental results show that structural changes are very likely responsible
for the observed anisotropic electronic transport. The strong sensitivity of
the electronic transport in SIO films may be explained in terms of the narrow
electron-like bands in SIO caused by spin-orbit-coupling and orthorhombic
distortion. | 1805.08473v2 |
2022-02-24 | Thermal spreading resistance of GaN HEMTs with heat source heating studied by hybrid Monte Carlo-diffusion simulations | Exact assessment of thermal spreading resistance is of great importance to
the thermal management of electronic devices, especially when completely
considering the heat conduction process from the nanoscale heat source to the
macroscopic scale heat sink. The existing simulation methods are either based
on convectional Fourier's law or limited to small system sizes, making it
difficult to accurately and efficiently study the cross-scale heat transfer. In
this paper, a hybrid phonon Monte Carlo-diffusion method that couples phonon
Monte Carlo (MC) method with Fourier's law by dividing the computational domain
is adopted to analyze thermal spreading resistance in ballistic-diffusive
regime. Compared with phonon MC simulation, the junction temperature of the
hybrid method has the same precision, while the time costs could be reduced up
to 2 orders of magnitude at most. Furthermore, the simulation results indicate
that the heating scheme has a remarkable impact on phonon transport. The
thermal resistance of the heat source (HS) scheme can be larger than that of
the heat flux (HF) scheme, which is opposite from the prediction of Fourier's
law. In the HS scheme, the enhanced phonon-boundary scattering counteracts the
broadening of the heat source, leading to a stronger ballistic effect as the
heat source thickness decreases. The conclusion is verified by a
one-dimensional thermal resistance model. This work has opened up an
opportunity for the fast and extensive thermal modeling of cross-scale heat
transfer in electronic devices and highlighted the influence of heating
schemes. | 2202.13770v1 |
2007-10-10 | Strong Reduction of the Field-Dependent Microwave Surface Resistance in YBCO with BaZrO_3 Inclusions | We present measurements of the magnetic field dependent microwave surface
resistance in laser-ablated YBa$_2$Cu$_3$O$_{7-\delta}$ films on SrTiO$_3$
substrates. BaZrO$_3$ crystallites were included in the films using composite
targets containing BaZrO$_3$ inclusions with mean grain size smaller than 1
$\mu$m. X-ray diffraction showed single epitaxial relationship between
BaZrO$_3$ and YBa$_2$Cu$_3$O$_{7-\delta}$. The effective surface resistance was
measured at 47.7 GHz for 60$< T <$90 K and 0$< \mu_0H <$0.8 T. The magnetic
field had a very different effect on pristine YBa$_2$Cu$_3$O$_{7-\delta}$ and
YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$, while for $\mu_0H=$0 only a reduction of
$T_c$ in the YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ film was observed,
consistent with dc measurements. At low enough $T$, in moderate fields
YBa$_2$Cu$_3$O$_{7-\delta}$/BaZrO$_3$ exhibited an intrinsic thin film
resistance lower than the pure film. The results clearly indicate that
BaZrO$_3$ inclusions determine a strong reduction of the field-dependent
surface resistance. From the analysis of the data in the framework of simple
models for the microwave surface impedance in the mixed state we argue that
BaZrO$_3$ inclusions determine very steep pinning potentials. | 0710.1953v1 |
2018-07-19 | Theoretical study of scattering in graphene ribbons in the presence of structural and atomistic edge roughness | We investigate the diffusive electron-transport properties of charge-doped
graphene ribbons and nanoribbons with imperfect edges. We consider different
regimes of edge scattering, ranging from wide graphene ribbons with (partially)
diffusive edge scattering to ribbons with large width variations and
nanoribbons with atomistic edge roughness. For the latter, we introduce an
approach based on pseudopotentials, allowing for an atomistic treatment of the
band structure and the scattering potential, on the self-consistent solution of
the Boltzmann transport equation within the relaxation-time approximation and
taking into account the edge-roughness properties and statistics. The resulting
resistivity depends strongly on the ribbon orientation, with zigzag (armchair)
ribbons showing the smallest (largest) resistivity and intermediate ribbon
orientations exhibiting intermediate resistivity values. The results also show
clear resistivity peaks, corresponding to peaks in the density of states due to
the confinement-induced subband quantization, except for armchair-edge ribbons
that show a very strong width dependence because of their claromatic behavior.
Furthermore, we identify a strong interplay between the relative position of
the two valleys of graphene along the transport direction, the correlation
profile of the atomistic edge roughness, and the chiral valley modes, leading
to a peculiar strongly suppressed resistivity regime, most pronounced for the
zigzag orientation. | 1807.07263v2 |
2020-10-07 | Correlation of uniaxial magnetic anisotropy axes and principal resistivities in polycrystalline ferromagnetic films | In the present study, we demonstrate the measurement of resistivity tensor
($\rho$) along the magnetic axes of a polycrystalline film of ferromagnetic
permalloy (Py). To this end, conventional Hall-bar and a more recent extended
van der Pauw methods were utilized for determining 2D $\rho$ in the film plane.
The samples were prepared by normal incidence sputter deposition within an
in-situ magnetic field to induce in-plane uniaxial magnetic anisotropy in the
film. Since $\rho$ might be affected by the internal magnetization of the film,
we performed measurements by rotation of a saturating magnetic field in the
film plane. Both methods indicate that the average resistivity is lower along
the easy axis of the film compared to the hard axis. Since X-ray diffraction
results indicated no dominating texture in the film, we concluded that there is
a correlation between uniaxial magnetic axes and principal resistivity axes.
This is an important finding that allows determining the direction of magnetic
anisotropy axes without magnetometry. The results also verify atomic or pair
ordering to be the origin of uniaxial magnetic anisotropy in the Py since
resistivity is sensitive to the level of order in solids. The extended van der
Pauw utilized here can be easily performed on the as-received samples which is
of practical interest. | 2010.03554v3 |
2020-12-31 | DC Resistance Degradation of SrTiO$_3$: The Role of Virtual-Cathode Needles and Oxygen Bubbles | This study of highly accelerated lifetime tests of SrTiO$_3$, a model
semiconducting oxide, is motivated by the interest in reliable multilayer
ceramic capacitors and resistance-switching thin-film devices. Our analytical
solution to oxygen-vacancy migration under a DC voltage -- the cause of
resistance degradation in SrTiO$_3$ -- agrees with previous numerical
solutions. However, all solutions fail to explain why degradation kinetics
feature a very strong voltage dependence, which we attribute to the nucleation
and growth of cathode-initiated fast-conducting needles. While they have no
color contrast in SrTiO$_3$ single crystals and are nominally invisible,
needles presence in DC-degraded samples -- in silicone oil and in air -- was
unambiguously revealed by in-situ hot-stage photography. Observations in
silicone oil and thermodynamic considerations of voltage boundary conditions
further revealed a cooccurrence of copious oxygen bubbling and the onset of
final accelerating degradation, suggesting sudden oxygen loss is a precursor of
final failure. Remarkably, both undoped and Fe-doped SrTiO$_3$ can emit
electroluminescence at higher current densities, thus providing a vivid
indicator of resistance degradation and a metal-to-insulator resistance
transition during cooling. The implications of these findings to thin ceramic
and thin film SrTiO$_3$ devices are discussed, along with connections to
similar findings in likewise degraded fast-ion yttria-stabilized zirconia. | 2012.15777v1 |
2021-04-12 | Temperature-linear Resistivity in Twisted Double Bilayer Graphene | We report an experimental study of carrier density (n), displacement field
(D) and twist angle ({\theta}) dependence of temperature (T)-linear resistivity
in twisted double bilayer graphene (TDBG). For a large twist angle
({\theta}>1.5{\deg}) where correlated insulating states are absent, we observe
a T-linear resistivity (with the slope of the order ~10{\Omega}/K) over a wide
range of carrier density and its slope decreases with increasing of n, in
agreement with acoustic phonon scattering model semi-quantitatively. The slope
of T-linear resistivity is non-monotonically dependent on the displacement
field with a single peak structure. For device with {\theta}~1.23{\deg} at
which correlated states emerge, the slope of T-linear resistivity is found
maximum (~100{\Omega}/K) at the boundary of the halo structure where phase
transition occurs, with signatures of continuous phase transition, Planckian
dissipation, and the diverging effective mass; these observations are in line
with quantum critical behaviors, which might be due to the symmetry-breaking
instability at the critical points. Our results shed new light on correlated
physics in TDBG and other twisted moir\'e systems. | 2104.05406v3 |
2022-01-06 | Coulomb drag in metal monochalcogenides double-layer structures with Mexican-hat band dispersions | We theoretically study the Coulomb drag resistivity and plasmon modes
behavior for a system composed of two parallel p-type doped GaS monolayers with
Mexican-hat valence energy band using the Boltzmann transport theory formalism.
We investigate the effect of temperature,$\ T$, carrier density,$\ p$, and
layer separation,$\ d$, on the plasmon modes and drag resistivity within the
energy-independent scattering time approximation. Our results show that the
density dependence of plasmon modes can be approximated by$\ p^{0.5}$. Also,
the calculations suggest a$\ d^{0.2}$ and a$\ d^{0.1}$ dependencies for the
acoustic and optical plasmon energies, respectively. Interestingly, we obtain
that the behavior of drag resistivity in the double-layer metal
monochalcogenides swings between the behavior of a double-quantum well system
with parabolic dispersion and that of a double-quantum wire structure with a
large carrier density of states. In particular, the transresistivity value
reduces exponentially with increasing the distance between layers. Furthermore,
the drag resistivity changes as$\ T^{2}/p^{4}$ ($\ T^{2.8}/p^{4.5}$) at low
(intermediate) temperatures. Finally, we compare the drag resistivity as a
function of temperature for GaS with other Mexican-hat materials including GaSe
and InSe and find that it adopts higher values when the metal monochalcogenide
has smaller Mexican-hat height. | 2201.02077v1 |
2023-02-14 | Acoustic phonon contribution to the resistivity of twisted bilayer graphene | We calculate the contribution to the doping ($n$) and temperature ($T$)
dependence of the electrical resistivity of twisted bilayer graphene (TBLG) due
to scattering by acoustic phonons. Our calculation retains the full
Bistritzer-MacDonald (BM) band structure, with a focus on understanding the
role of the complicated geometric features present in the BM band structure on
electronic transport theory. We find that the band geometry plays an important
role in determining the resistivity, giving an intricate dependence on both $n$
and $T$ that mirrors features in the band structure and complicates the
Bloch-Gr\"{u}neisen (BG) crossover. Our calculations predict pronounced
departures from the standard simplistic expectation of a linear $T$-dependence
above the BG crossover. In particular, we are able to explain the presence of
the resistance peaks that have been observed in experiment, as well as
quantitatively predict the temperatures at which they occur. Our calculated
theoretical results are germane to an ongoing debate over the existence of a
strange metal state in TBLG by providing a quantitatively accurate theory for
the TBLG resistivity at finite temperatures. | 2302.07275v3 |
2023-04-21 | Star-Mesh Quantized Hall Array Resistance Devices | Advances in the development of graphene-based technology have enabled
improvements in DC resistance metrology. Devices made from epitaxially grown
graphene have replaced the GaAs-based counterparts, leading to an easier and
more accessible realization of the ohm. By optimizing the scale of the growth,
it has become possible to fabricate quantized Hall array resistance standards
(QHARS) with nominal values between 1 k{\Omega} and 1.29 M{\Omega}. One of
these QHARS device designs accommodates a value of about 1.01 M{\Omega}, which
made it an ideal candidate to pursue a proof-of-concept that graphene-based
QHARS devices are suitable for forming wye-delta resistance networks. In this
work, the 1.01 M{\Omega} array output nearly 20.6 M{\Omega} due to the
wye-delta transformation, which itself is a special case of star-mesh
transformations. These mathematical equivalence principles allow one to extend
the QHR to the 100 M{\Omega} and 10 G{\Omega} resistance levels with fewer
array elements than would be necessary for a single array with many more
elements in series. The 1.01 M{\Omega} device shows promise that the wye-delta
transformation can shorten the calibration chain, and, more importantly,
provide a chain with a more direct line to the quantum SI. | 2304.11243v1 |
2023-06-12 | Symmetric, off-diagonal, resistance from rotational symmetry breaking in graphene-WSe$_2$ heterostructure: prediction for a large magic angle in a Moire system | We show that any two-dimensional system with a non-zero \textit{symmetric}
off-diagonal component of the resistance matrix, $R_{xy}=R_{yx} \neq 0$, must
have the in-plane rotational symmetry broken down to $C_2$. Such a resistance
response is Ohmic, and is different from the Hall response which is the
\textit{anti-symmetric} part of the resistance tensor, $R_{xy}=-R_{yx}$, is
rotationally symmetric in the 2D plane, and requires broken time-reversal
symmetry. We show how a minute amount of strain due to lattice mismatch - less
than $1 \%$ - can produce a vastly exaggerated symmetric off-diagonal response
- $\frac{R_{xy}}{R_{xx}} \sim 20\%$ - because of the momentum matching
constraints in a Moire system. Our results help explain an important new
transport experiment on graphene-WSe$_2$ heterostructures, as well as are
relevant for other experimental systems with rotational symmetry breaking, such
as nematic systems and Kagome charge density waves. Additionally, our work
predicts an example of a `magic' angle, $\theta\sim 27^0$, in a Moire system
which is a significant fraction of $\pi$. Our prediction that the anomalous
resistance anisotropy occurs at a large value of magic angle, in contrast to
known examples of magic angle transport anomalies that are small fractions of
$\pi$, can be experimentally tested in graphene-WSe$_2$ heterostructures. | 2306.06840v2 |
2024-03-04 | Electric field induced resistive switching in M$^{3+}_x$V$_{1-x}$O$_2$ (M$^{3+}$= Ga$^{3+}$, Al$^{3+}$) single crystals at temperatures below the T $\to$ M2 phase transition | The phase diagram of VO$_2$ strained or doped with several trivalent ions
consists of four phases; in order of increasing temperatures, three (M1, T and
M2) are insulating while the fourth (R), above ~340 K, is metallic. These
phases and the three phase transitions have been thoroughly investigated for
about half a century by a wide variety of techniques, including electronic
transport. While an upwards jump of the resistance of up to a factor of 2 was
observed at the T-M2 transition and a drop of several orders of magnitude was
observed at the M2$\to$R one, resistive switching at the M1$\to$T transition
remained elusive over all these years. Here we report on the investigation of
Ga- and Al-doped VO$_2$ single crystals, following the rather surprising
appearance of a small and steep drop of a factor of ~ 0.12 in the resistance of
Ga-doped VO$_2$ single crystals detected by pulsed and DC I-V measurements
carried out at room temperature, below the T$\to$M2 phase transition. Similar
results were obtained also from measurements on Al-doped VO2 single crystals.
Raman spectra of Ga-, and Al-doped crystals resolved their structures as
function of temperature. The accumulated results of the measurements on Ga-,
and Al-doped single crystals provide evidence for identifying the resistive
switching at T$_{\rm RS}$<T$_{\rm T\to M2}$ with the M1$\to$T transition. | 2403.01808v2 |
2017-07-27 | Experimental study of electron and phonon dynamics in nanoscale materials by ultrafast laser time-domain spectroscopy | With the rapid advances in the development of nanotechnology, nowadays, the
sizes of elementary unit, i.e. transistor, of micro- and nanoelectronic devices
are well deep into nanoscale. For the pursuit of cheaper and faster nanoscale
electronic devices, the size of transistors keeps scaling down. As the
miniaturization of the nanoelectronic devices, the electrical resistivity
increases dramatically, resulting rapid growth in the heat generation. The heat
generation and limited thermal dissipation in nanoscale materials have become a
critical problem in the development of the next generation nanoelectronic
devices. Copper (Cu) is widely used conducting material in nanoelectronic
devices, and the electron-phonon scattering is the dominant contributor to the
resistivity in Cu nanowires at room temperature. Meanwhile, phonons are the
main carriers of heat in insulators, intrinsic and lightly doped
semiconductors. The thermal transport is an ensemble of phonon transport, which
strongly depends on the phonon frequency. In addition, the phonon transport in
nanoscale materials can behave fundamentally different than in bulk materials,
because of the spatial confinement. However, the size effect on electron-phonon
scattering and frequency dependent phonon transport in nanoscale materials
remain largely unexplored, due to the lack of suitable experimental techniques.
This thesis is mainly focusing on the study of carrier dynamics and acoustic
phonon transport in nanoscale materials. | 1707.08698v2 |
2002-10-17 | New heat treatment to prepare high quality polycrystalline and single crystal MgB2 in single process | We report here on a new heat treatment to prepare both dense polycrystalline
and single crystal MgB2 high quality samples in one single process. Resistivity
measurements for polycrystalline part of the sample gives a residual
resistivity ratio RRR=16.6 and a very low normal state resistivity rho(40K)=
0.28 microOhmcm. Both SEM and SQUID study on polycrystals reveal the high
quality, dense character and well coupling of grain boundaries. On the other
hand, the high quality single crystals have a unique shape that resembles the
hexagonal crystal structure. SQUID measurements reveals very weak flux pinning
character implying our single crystals to be very clean. In this study, we
conclude that heat treatment is playing a major rule on the characteristics of
both polycrystalline and single crystal MgB2. Samples are thoroughly
characterized by x-ray, resistivity, dc SQUID and SEM. | 0210384v1 |
2010-05-03 | Overview of the DHCAL Project | We review the status and plans of the Digital Hadron Calorimeter with
Resistive Plate Chambers project. | 1005.0412v1 |
2010-08-26 | Simulation of Edge Localised Modes using BOUT++ | The BOUT++ code is used to simulate ELMs in a shifted circle equilibrium.
Reduced ideal MHD simulations are first benchmarked against the linear ideal
MHD code ELITE, showing good agreement. Diamagnetic drift effects are included
finding the expected suppression of high toroidal mode number modes. Nonlinear
simulations are performed, making the assumption that the anomalous kinematic
electron viscosity is comparable to the anomalous electron thermal diffusivity.
This allows simulations with realistically high Lundquist numbers S = 1e8,
finding ELM sizes of 5-10% of the pedestal stored thermal energy. Scans show a
strong dependence of the ELM size resistivity at low Lundquist numbers, with
higher resistivity leading to more violent eruptions. At high Lundquist numbers
relevant to high-performance discharges, ELM size is independent of resistivity
as hyper-resistivity becomes the dominant dissipative effect. | 1008.4554v1 |
2021-05-24 | Ageing studies of Multi-Strip Multi-Gap Resistive Plate Counters based on low resistivity glass electrodes in high irradiation dose | Detailed tests and analysis of ageing effects of high irradiation dose on
Multi-Strip Multi-Gap Resistive Plate Counters based on low resistivity glass
electrodes were performed. MSMGRPC efficiency and cluster size before
irradiation are measured and compared with their values after irradiation in a
high irradiation dose accessed at a multi-purpose irradiation facility of
IFIN-HH based on $^{60}$Co source. The composition and properties of the
deposited layers on the glass electrodes, studied based on a multitude of
analysis methods, i.e. SEM, XPS, foil-ERDA, RBS, AFM and THz-TDS, are
presented. | 2105.12214v2 |
2021-11-23 | Superconducting aluminum heat switch with 3 n$Ω$ equivalent resistance | Superconducting heat switches with extremely low normal state resistances are
needed for constructing continuous nuclear demagnetization refrigerators with
high cooling power. Aluminum is a suitable superconductor for the heat switch
because of its high Debye temperature and its commercial availability in high
purity. We have constructed a high quality Al heat switch whose design is
significantly different than that of previous heat switches. In order to join
the Al to Cu with low contact resistance, we plasma etched the Al to remove its
oxide layer then immediately deposited Au without breaking the vacuum of the
e-beam evaporator. In the normal state of the heat switch, we measured a
thermal conductance of $8 T$ W/K$^2$ which is equivalent to an electrical
resistance of 3 n$\Omega$ according to the Wiedemann-Franz law. In the
superconducting state we measured a thermal conductance that is $2\times10^6$
times lower than that of the normal state at 50 mK. | 2111.11896v2 |
2023-02-18 | Search for universal minimum drag resistance underwater vehicle hull using CFD | In Autonomous Underwater Vehicles (AUVs) design, hull resistance is an
important factor in determining the power requirements and range of vehicle and
consequently affect battery size, weight, and volume requirement of the design.
In this paper, we leverage on AI-based optimization algorithm along with
Computational Fluid Dynamics (CFD) simulation to study the optimal hull design
that minimizing the resistance. By running the CFD-based optimization at
different operating velocities and turbulence intensity, we want to
study/search the possibility of a universal design that will provide least
resistance/near-optimal design across all operating conditions (operating
velocity) and environmental conditions (turbulence intensity). Early result
demonstrated that the optimal design found at low velocity and low turbulence
condition performs very poor at high velocity and high turbulence conditions.
However, a design that is optimal at high velocity and high turbulence
conditions performs near-optimal across many considered velocity and turbulence
conditions. | 2302.09441v2 |
2019-11-22 | Radiation Damage Studies on Titanium Alloys as High Intensity Proton Accelerator Beam Window Materials | A high-strength dual alpha+beta phase titanium alloy Ti-6Al-4V is utilized as
a material for beam windows in several accelerator target facilities. However,
relatively little is known about how material properties of this alloy are
affected by high-intensity proton beam irradiation. With plans to upgrade
neutrino facilities at J-PARC and Fermilab to over 1 MW beam power, the
radiation damage in the window material will reach a few displacements per atom
(dpa) per year, significantly above the ~0.3 dpa level of existing data. The
RaDIATE collaboration has conducted a high intensity proton beam irradiation of
various target and window material specimens at BLIP facility, including a
variety of titanium alloys. Post-Irradiation Examination of the specimens in
the 1st capsule, irradiated at up to 0.25 dpa, is in progress. Tensile tests in
a hot cell at PNNL exhibited a clear signature of radiation hardening and loss
of ductility for Ti-6Al-4V, while Ti-3Al-2.5V, with less beta phase, exhibited
less severe hardening. Microstructural investigations will follow to study the
cause of the difference in tensile behavior between these alloys. High-cycle
fatigue (HCF) performance is critical to the lifetime estimation of beam
windows exposed to a periodic thermal stress from a pulsed proton beam. The 1st
HCF data on irradiated titanium alloys are to be obtained by a conventional
bend fatigue test at Fermilab and by an ultrasonic mesoscale fatigue test at
Culham Laboratory. Specimens in the 2nd capsule, irradiated at up to ~1 dpa,
cover typical titanium alloy grades, including possible radiation-resistant
candidates. These systematic studies on the effects of radiation damage of
titanium alloys are intended to enable us to predict realistic lifetimes of
current beam windows made of Ti-6Al-4V and to extend the lifetime by choosing a
more radiation and thermal shock tolerant alloy. | 1911.10198v1 |
2023-09-26 | The $p_0$-Laplace "Signature" for Quasilinear Inverse Problems | This paper refers to an imaging problem in the presence of nonlinear
materials. Specifically, the problem we address falls within the framework of
Electrical Resistance Tomography and involves two different materials, one or
both of which are nonlinear. Tomography with nonlinear materials in the early
stages of developments, although breakthroughs are expected in the
not-too-distant future. The original contribution this work makes is that the
nonlinear problem can be approximated by a weighted $p_0$-Laplace problem. From
the perspective of tomography, this is a significant result because it
highlights the central role played by the $p_0$-Laplacian in inverse problems
with nonlinear materials. Moreover, when $p_0=2$, this result allows all the
imaging methods and algorithms developed for linear materials to be brought
into the arena of problems with nonlinear materials. The main result of this
work is that for "small" Dirichlet data, (i) one material can be replaced by a
perfect electric conductor and (ii) the other material can be replaced by a
material giving rise to a weighted $p_0$-Laplace problem. | 2309.15865v2 |
1996-11-30 | Exchange coupling and current-perpendicular-to-plane giant magneto-resistance of magnetic trilayers. Rigorous results within a tight-binding single-band model | It is shown that the current-perpendicular-to-plane giant magneto-resistance
(CPP-GMR) oscillations, in the ballistic regime, are strongly correlated with
those of the exchange coupling (J). Both the GMR and J are treated on equal
footing within a rigorously solvable tight-binding single-band model. The
strong correlation consists in sharing asymptotically the same period,
determined by the spacer Fermi surface, and oscillating with varying spacer
thickness predominantly in opposite phases. | 9612008v1 |
1998-09-30 | Thickness dependent magnetotransport in ultra-thin manganite films | To understand the near-interface magnetism in manganites, uniform, ultra-thin
films of La_{0.67}Sr_{0.33}MnO_3 were grown epitaxially on single crystal (001)
LaAlO_3 and (110) NdGaO_3 substrates. The temperature and magnetic field
dependent film resistance is used to probe the film's structural and magnetic
properties. A surface and/or interface related dead-layer is inferred from the
thickness dependent resistance and magnetoresistance. The total thickness of
the dead layer is estimated to be $\sim 30 \AA$ for films on NdGaO_3 and $\sim
50 \AA$ for films on LaAlO_3. | 9809414v1 |
1999-10-14 | Giant 1/f noise in perovskite manganites: evidence of the percolation threshold | We discovered an unprecedented magnitude of the 1/f noise near the Curie
temperature Tc in low-Tc manganites. The scaling behavior of the 1/f noise and
the resistance provides strong evidence of the percolation nature of the
ferromagnetic transition in the polycrystalline samples. The step-like changes
of the resistance with temperature, observed for single crystals, suggest that
the size of the ferromagnetic domains depends on the size of crystallites. | 9910220v1 |
2000-01-12 | Anomalous Hopping Exponents of Ultrathin Films of Metals | The temperature dependence of the resistance R(T) of ultrathin
quench-condensed films of Ag, Bi, Pb and Pd has been investigated. In the most
resistive films, R(T)=Roexp(To/T)^x, where x=0.75. Surprisingly, the exponent x
was found to be constant for a wide range of Ro and To in all four materials,
possibly implying a consistent underlying conduction mechanism. The results are
discussed in terms of several different models of hopping conduction. | 0001162v1 |
2000-07-03 | The mean free path for electron conduction in metallic fullerenes | We calculate the electrical resistivity due to electron-phonon scattering for
a model of A3C60 (A= K, Rb), using an essentially exact quantum Monte-Carlo
calculation. In agreement with experiment, we obtain exceptionally large
metallic resistivities at large temperatures T. This illustrates that the
apparent mean free path can be much shorter than the separation of the
molecules. An interpretation of this result is given. The calculation also
explains the linear behavior in T at small T. | 0007024v1 |
2000-09-04 | Observation of anomalous single-magnon scattering in half-metallic ferromagnets by chemical pressure control | Temperature variation of resistivity and specific heat have been measured for
prototypical half-metallic ferromagnets,
R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have
found variation of the temperature scalings in the resistivity from
T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in
terms of the anomalous single-magnon scattering (AMS) process in the
half-metallic system. | 0009035v1 |
2000-10-25 | Ca0.85Sm0.15MnO3: A mixed antiferromagnet with unusual properties | We investigated electrical and magnetic properties of the electron-doped
manganites Ca1-xSmxMnO3 (0<x<0.2). Our results indicate the possibility of
phase separation in electron doped manganites. The compounds with x = 0.13-0.15
show unusual difference between zero-field cooled and field-cooled
resistivities which are not observed in lower compositions. Our results suggest
that electronic phase separation alone is insufficient to understand the origin
of the resistivity irreversibilities. | 0010384v1 |
2001-08-21 | Metals with Small Electron Mean-Free Path: Saturation versus Escalation of Resistivity | Resistivity of metals is commonly observed either to 'escalate' beyond the
Ioffe-Regel limit (mean free path l equal to lattice constant a) or to
'saturate' at this point. It is argued that neither behavior is
well-understood, and that 'escalation' is not necessarily more mysterious than
'saturation.' | 0108343v2 |
2002-02-18 | Conductivity Oscillations in Current-Induced Metastable States in Low-Doped Manganite Single Crystals | Deterministic oscillations of current-induced metastable resistivity in
changing voltage have been detected in La$_{0.82}$Ca$_{0.18}$MnO$_3$ single
crystals. At low temperatures, below the Curie point, application of specific
bias procedures switches the crystal into metastable resistivity state
characterized by appearance of pronounced reproducible and random structures in
the voltage dependence of the differential conductivity. In certain bias range
equally spaced broad conductivity peaks have been observed. The oscillating
conductivity has been tentatively ascribed to resonances in a quantum well
within the double tunnel barrier of intrinsic weak-links associated with
twin-like defect boundaries. | 0202284v1 |
2002-02-20 | Universal transport in 2D granular superconductors | The transport properties of quench condensed granular superconductors are
presented and analyzed. These systems exhibit transitions from insulating to
superconducting behavior as a function of inter-grain spacing.
Superconductivity is characterized by broad transitions in which the resistance
drops exponentially with reducing temperature. The slope of the log R versus T
curves turns out to be universaly dependent on the normal state film resistance
for all measured granular systems. It does not depend on the material, critical
temperature, geometry, or experimental set-up. We discuss possible physical
scenarios to explain these findings. | 0202342v1 |
2002-05-22 | Universal angular magnetoresistance and spin torque in ferromagnetic/normal metal hybrids | The electrical resistance of ferromagnetic/normal-metal (F/N)
heterostructures depends on the nature of the junctions which may be tunnel
barriers, point contacts, or intermetallic interfaces. For all junction types,
the resistance of disordered F/N/F perpendicular spin valves as a function of
the angle between magnetization vectors is shown to obey a simple universal
law. The spin-current induced magnetization torque can be measured by the
angular magnetoresistance of these spin valves. The results are generalized to
arbitrary magnetoelectronic circuits. | 0205453v1 |
2002-08-22 | A scheme for electrical detection of spin resonance signal from a single electron trap | We study a scheme for electrical detection of the spin resonance (ESR) of a
single electron trapped near a Field Effect Transistor (FET) conduction
channel. In this scheme, the resonant Rabi oscillations of the trapped electron
spin cause a modification of the average occupancy of a shallow trap, which can
be detected through the change in the FET channel resistivity. We show that the
dependence of the channel resistivity on the frequency of the rf field can have
either peak or dip at the Larmor frequency of the electron spin in the trap. | 0208438v1 |
2003-02-20 | Electron scattering near an itinerant to localized electronic transition | We report an unconventional temperature dependence of the resistivity in
several strongly correlated systems approaching a localized to itinerant
electronic transition from the itinerant electron side. The observed
resistivity, proportioanl to T^(3/2)over the entire range of materials
discussed, cannot be explained within the framework of existing theories. We
propose a model in which the scattering of the conduction electrons by locally
cooperative bond-length fluctuations in a matrix of vibronic and Fermi-liquid
electrons can account for the experimental data. | 0302426v1 |
2003-03-10 | New collective zero-resistance states in GaAs/AlGaAs heterostructures | Exponentially small resistance in crossed static magnetic and microwave
fields occurs in ultrapure two dimensional electron gases (2DEG), while in less
pure systems the magnetoresistance oscillates but is always positive. A
non-perturbative theory of self-organization explains the new collective states
in terms of open orbits. There are analogies to many other anomalous physical
phenomena, as well as to scaling and evolutionary principles of biophysics. | 0303181v1 |
2003-04-04 | Co-ordination between Rashba spin-orbital interaction and space charge effect and enhanced spin injection into semiconductors | We consider the effect of the Rashba spin-orbital interaction and space
charge in a ferromagnet-insulator/semiconductor/insulator-ferromagnet junction
where the spin current is severely affected by the doping, band structure and
charge screening in the semiconductor. In diffusion region, if the the
resistance of the tunneling barriers is comparable to the semiconductor
resistance, the magnetoresistance of this junction can be greatly enhanced
under appropriate doping by the co-ordination between the Rashba effect and
screened Coulomb interaction in the nonequilibrium transport processes within
Hartree approximation. | 0304117v1 |
2003-07-17 | Electron interaction with domain walls in antiferromagnetically coupled multilayers | For antiferromagnetically coupled Fe/Cr multilayers the low field
contribution to the resistivity, which is caused by the domain walls, is
strongly enhanced at low temperatures. The low temperature resistivity varies
according to a power law with the exponent about 0.7 to 1. This behavior can
not be explained assuming ballistic electron transport through the domain
walls. It is necessary to invoke the suppression of anti-localization effects
(positive quantum correction to conductivity) by the nonuniform gauge fields
caused by the domain walls. | 0307414v1 |
2004-01-16 | Break-Junction Tunneling Spectroscopy for Doped Semiconductors in the Hopping Regime | We present a theory for tunneling spectroscopy in a break-junction
semiconductor device for materials in which the electronic conduction mechanism
is hopping transport. Starting from the conventional expression for the hopping
current we develop an expression for the break-junction tunnel current for the
case in which the tunnel resistance is much larger than the effective
single-hop resistances. We argue that percolation like methods are inadequate
for this case and discuss in detail the interplay of the relevant scales that
control the possibility to extract spectroscopic information from the
characteristic of the device. | 0401282v1 |
2004-02-05 | Resistivity model for both paramagnetic and ferromagnetic phases | The resistivity, $\rho$ as a function of temperature and ionization energy
(doping) and magnetization respectively is derived with further confinements
from spin-disorder scattering. The computed $T_{crossover}$ below $T_C$ and
carrier density in Ga$_{1-x}$Mn$_x$As system are 8-12 K and 10$^{19}$
cm$^{-3}$, remarkably identical with the experimental values of 10-12 K and
10$^{18}-10^{20}$ cm$^{-3}$ respectively. | 0402153v5 |
2004-05-26 | The steady state in noncollinear magnetic multilayers | There are at least two different putative steady state solutions for current
across noncollinear magnetic multilayers; one has a discontinuity in the spin
current at the interface the other is continuous. We compare the resistance of
the two and find the solution with the continuous spin currents is lower. By
using the entropic principle we can state that this solution is a better
estimate of the resistance for a noncollinear magnetic | 0405624v1 |
2004-06-09 | Negative Magnetoresistance in (In,Mn)As | The magnetotransport properties of an In0.95Mn0.05As thin film grown by
metal-organic vapor phase epitaxy were measured. Resistivity was measured over
the temperature range of 5 to 300 K. The resistivity decreased with increasing
temperature from 90 ohm-cm to 0.05 ohm-cm. The field dependence of the low
temperature magnetoresistance was measured. A negative magnetoresistance was
observed below 17 K with a hysteresis in the magnetoresistance observed at 5 K.
The magnetoresistance as a function of applied field was described by the
Khosla-Fischer model for spin scattering of carriers in an impurity band. | 0406230v1 |
2004-06-21 | Large negative magnetoresistance in thiospinel CuCrZrS4 | We report on large negative magnetoresistance observed in ferromagnetic
thiospinel compound CuCrZrS$_{4}$. Electrical resistivity increased with
decreasing temperature according to the form proportional to
$\textrm{exp}(T_{0}/T)^{1/2} $, derived from variable range hopping with strong
electron-electron interaction. Resistivity under magnetic fields was expressed
by the same form with the characteristic temperature T0 decreasing with
increasing magnetic field. Magnetoresistance ratio $\rho (T,0)/\rho(T,H)$ is
1.5 at 100 K for H=90 kOe and increases divergently with decreasing temperature
reaching 80 at 16 K. Results of magnetization measurements are also presented.
Possible mechanism of the large magnetoresistance is discussed. | 0406459v1 |
2004-08-27 | Disorder-Induced Resistive Anomaly Near Ferromagnetic Phase Transitions | We show that the resistivity rho(T) of disordered ferromagnets near, and
above, the Curie temperature T_c generically exhibits a stronger anomaly than
the scaling-based Fisher-Langer prediction. Treating transport beyond the
Boltzmann description, we find that within mean-field theory, d\rho/dT exhibits
a |T-T_c|^{-1/2} singularity near T_c. Our results, being solely due to
impurities, are relevant to ferromagnets with low T_c, such as SrRuO3 or
diluted magnetic semiconductors, whose mobility near T_c is limited by
disorder. | 0408602v2 |
2004-10-07 | Negative differential thermal resistance and thermal transistor | We report on the first model of a thermal transistor to control heat flow.
Like its electronic counterpart, our thermal transistor is a three-terminal
device with the important feature that the current through the two terminals
can be controlled by small changes in the temperature or in the current through
the third terminal. This control feature allows us to switch the device between
"off" (insulating) and "on" (conducting) states or to amplify a small current.
The thermal transistor model is possible because of the negative differential
thermal resistance. | 0410172v2 |
2004-11-23 | Current perpendicular to plane Giant Magnetoresistance (GMR) in laminated nanostructures | We theoretically studied spin dependent electron transport
perpendicular-to-plain (CPP) in magnetic laminated multilayered structures by
using Kubo formalism. We took into account not only bulk scattering, but the
interface resistance due to both specular and diffuse reflection and also spin
conserving and spin-flip processes. It was shown that spin-flip scattering at
interfaces substantially reduces the value of GMR. This can explain the
experimental observations that the CPP GMR ratio for laminated structures only
slightly increases as compared to non-laminated ones despite lamination induces
a significant increase in CPP resistance. | 0411571v1 |
2004-12-08 | Ageing effects around the glass and melting transitions in poly(dimethylsiloxane) visualized by resistance measurements | The process of ageing in rubbers requires monitoring over long periods (days
to years). To do so in non-conducting rubbers, small amounts of carbon-black
particles were dispersed in a fractal network through the rubber matrix, to
make the rubber conducting without modifying its properties. Continuous
monitoring of the resistance reveals the structural changes around the glass
and melting transitions and especially details about the hysteresis and ageing
processes. We illustrate the method for the semicrystalline polymer
poly(dimethylsiloxane) (PDMS). | 0412187v1 |
2005-04-19 | Enhancement of low field magnetoresistance at room temperature in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Al$_{2}$O$_{3}$ nanocomposite | Magnetotransport properties in a nanocrystalline
La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/micron sized Al$_{2}$O$_{3}$ granular composite
with different concentrations of Al$_{2}$O$_{3}$ have been studied. The
resistivity curves in absence of magnetic field and the various transport
mechanisms which might account for the upturn in resistivity at low
temperature, has been discussed. Enhancement of low field magnetoresistance at
room temperature with the introduction of Al$_{2}$O$_{3}$ has been observed. | 0504469v1 |
2005-09-09 | Negative differential resistance in single crystal La_{2}CuO_{4} at low temperature | A current-controlled negative differential resistance has been revealed in
the I-V characteristics of single crystal La$_{2}$CuO$_{4+\delta}$ in the low
temperature region. The non-linear behavior of conductivity is accompanied by a
transition from positive to negative magnetoresistance when the current is
growing. Possible reasons for the effect observed are discussed. | 0509247v1 |
2005-11-02 | Current-induced vortex displacement and annihilation in a single Permalloy disk | The induced motion of a magnetic vortex in a micron-sized ferromagnetic disk
due to the DC current injection is studied by measuring planar Hall effect. The
DC current injection is found to induce the spin torque that sweeps the vortex
out of the disk at the critical current while bias magnetic field are applied.
The current-induced vortex core displacement deduced from the change in planar
Hall resistance is quantitatively consistent with theoretical prediction. Peak
structures similar to those originated from spin wave excitations are observed
in the differential planar Hall resistance curve. | 0511040v1 |
2006-01-20 | Domain-wall resistance in ferromagnetic (Ga,Mn)As | A series of microstructures designed to pin domain-walls (DWs) in (Ga,Mn)As
with perpendicular magnetic anisotropy has been employed to determine extrinsic
and intrinsic contributions to DW resistance. The former is explained
quantitatively as resulting from a polarity change in the Hall electric field
at DW. The latter is one order of magnitude greater than a term brought about
by anisotropic magnetoresistance and is shown to be consistent with
disorder-induced misstracing of the carrier spins subject to spatially varying
magnetization. | 0601464v1 |
2006-01-25 | Single-ion Kondo behavior of a novel Kondo lattice, CeNi9Si4 | The compound, CeNi9Si4 has been recently reported to be an unusual Kondo
lattice with a large Ce-Ce separation, with a breakdown of Kadowaki-Woods
relationship governing low temperature electrical resistivity and
heat-capacity. Here we report the results of magnetic susceptibility,
heat-capacity and electrical resistivity of the solid solution,
Ce(1-x)La(x)Ni9Si4 to understand the Kondo behavior of this compound. The
results establish that the observed properties of Ce in this compound are
single-ionic in character. | 0601577v1 |
2006-05-12 | Large domain wall resistance in self-organised manganite film | The electrical resistance of magnetic domain walls in ferromagnetic metallic
manganites can be enhanced to 10-12 Ohm.m2 by patterning nanoconstrictions [J.
Appl. Phys. 89, 6955 (2001)]. We show equally large enhancements in a phase
separated La0.60Ca0.40MnO3 manganite film without recourse to nanopatterning.
The domain walls were measured in the current-perpendicular-to-the-plane (CPP)
geometry between ferromagnetic metallic La0.70Ca0.30MnO3 electrodes patterned
like magnetic tunnel junctions. | 0605341v2 |
2006-06-18 | Cotunneling and one-dimensional localization in individual single-wall carbon nanotubes | We report on the temperature dependence of the intrinsic resistance of long
individual disordered single-wall carbon nanotubes. The resistance grows
dramatically as the temperature is reduced, and the functional form is
consistent with an activated behavior. These results are described by Coulomb
blockade along a series of quantum dots. We occasionally observe a kink in the
activated behavior that reflects the change of the activation energy as the
temperature range is changed. This is attributed to charge hopping events
between non-adjacent quantum dots, which is possible through cotunneling
processes. | 0606473v1 |
2006-10-10 | Nanofabrication of spin-transfer torque devices by a PMMA mask one step process: GMR versus single layer devices | We present a method to prepare magnetic spin torque devices of low specific
resistance in a one step lithography process. The quality of the pillar devices
is demonstrated for a standard magnetic double layer device. For single layer
devices, we found hysteretic switching and a more complex dynamical excitation
pattern in higher fields. A simple model to explain the resistance spikes is
presented. | 0610277v1 |
2006-11-27 | Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing | We have observed that submicron sized Al--AlO{$_x$}--Al tunnel junctions can
be stabilized completely by annealing them in vacuum at temperatures between
$350^{\circ}$C and $450^{\circ}$C. In addition, low temperature
characterization of the samples after the annealing treatment showed a marked
improvement of the tunneling characteristics due to disappearance of unwanted
resonances in the current. Charging energy, tunneling resistance, barrier
thickness and height all increase after the treatment. The superconducting gap
is not affected, but supercurrent is reduced in accordance with the increase of
tunneling resistance. | 0611664v1 |
2007-01-17 | Theory of Spin Transport Across Domain-Walls in (Ga,Mn)As | We present results of numerical calculations of domain-wall resistance in the
ferromagnetic semiconductor (Ga,Mn)As. We employ Landauer-Buttiker formalism
and the tight binding method. Taking into account the full valence band
structure we predict the magnitude of the domain-wall resistance without
disorder and compare it to experimental values. Next we add disorder to the
model and study numerically both small and large disorder regime. | 0701398v1 |
2007-06-01 | Treatment of electron viscosity in quantum conductance | In a recent paper Sai {\it et al.} [1] identified a correction $R^{dyn}$ to
the DC conductance of nanoscale junctions arising from dynamical
exchange-correlation ($XC$) effects within time-dependent density functional
theory. This quantity contributes to the total resistance through
$R=R_{s}+R^{dyn}$ where $R_{s}$ is the resistance evaluated in the absence of
dynamical $XC$ effects. In this Comment we show that the numerical estimation
of $R^{dyn}$ in example systems of the type they considered should be
considerably reduced, once a more appropriate form for the shear electron
viscosity $\eta$ is used. | 0706.0140v1 |
2007-07-05 | Observation of a uniform temperature dependence in the electrical resistance across the structural phase transition in thin film vanadium oxide ($VO_{2}$) | An electrical study of thin $VO_{2}$ films in the vicinity of the structural
phase transition at $68^{0}C$ shows (a) that the electrical resistance $R$
follows $log (R)$ $\propto$ $-T$ over the $T$-range, $20 < T < 80 ^{0}C$
covering both sides of the structural transition, and (b) a history dependent
hysteresis loop in $R$ upon thermal cycling. These features are attributed here
to transport through a granular network. | 0707.0885v1 |
2007-08-07 | Nonlinear screening and ballistic transport in a graphene p-n junction | We study the charge density distribution, the electric field profile, and the
resistance of an electrostatically created lateral p-n junction in graphene. We
show that the electric field at the interface of the electron and hole regions
is strongly enhanced due to limited screening capacity of Dirac quasiparticles.
Accordingly, the junction resistance is lower than estimated in previous
literature. | 0708.0892v2 |
2007-08-22 | Voltage and temperature dependencies of conductivity in gated graphene | The resistivity of gated graphene is studied taking into account electron and
hole scattering by short- and long-range structural imperfections the
characteristics of disorder were taken from the scanning tunneling microscopy
data and by acoustic phonons. The calculations are based on the quasiclassical
kinetic equation with the normalization condition fixed by surface charge. The
gate-voltage and temperature effects on the resistance peak, which is centered
at the point of intrinsic conductivity, are found to be in agreement with the
transport measurements. | 0708.2976v2 |
2007-09-12 | Design issues of a variable thermal resistance | Some years ago we have proposed a thermal mount with electronically variable
thermal resistance [1]. In this earlier work the feasibility of such a
structure has been demonstrated. Now we intend to realize this mount in a
maturated form, suitable to the everyday use in the practice of package thermal
qualification and modeling. The design of such a device raises a number of new
questions and problems. The present paper is dealing with these problems and
the possible solutions. | 0709.1836v1 |
2007-11-29 | Quantum size effects in solitary wires of bismuth | We have performed four-probe electrical transport measurements on solitary
highly crystalline wires of semimetallic bismuth with aspect ratios up to 60 at
room and at cryogenic temperatures. By proper choice of the substrate material
and the film deposition parameters, lithographic wires with lateral dimensions
of down to one single grain, $\sim 250$ nm, were fabricated. The electrical
resistance of each wire was measured against its thickness through successive
reactive ion etching of the self-same wire. Quantum size effects revealed
themselves as regular oscillations in the electrical resistance. Some evidence
for the semimetal-to-semiconductor phase transition has been detected. The
measured data are discussed within the framework of the existing theoretical
models. | 0711.4816v1 |
2008-02-15 | Non-intrinsic superconductivity in InN epilayers: role of Indium Oxide | In recent years there have been reports of anomalous electrical resistivity
and the presence of superconductivity in semiconducting InN layers. By a
careful correlation of the temperature dependence of resistivity and magnetic
susceptibility with structural information from highresolution x-ray
diffraction measurements we show that superconductivity is not intrinsic to InN
and is seen only in samples that show traces of oxygen impurity. We hence
believe that InN is not intrinsically a superconducting semiconductor. | 0802.2126v1 |
2008-03-26 | Quasi-Two-Dimensional Extraordinary Hall Effect | Quasi-two-dimensional transport is investigated in a system consisting of one
ferromagnetic layer placed between two insulating layers. Using the mechanism
of skew-scattering to describe the Extraordinary Hall Effect (EHE) and
calculating the conductivity tensor, we compare the quasi- two-dimensional Hall
resistance with the resistance of a massive sample. In this study a new
mechanism of EHE (geometric mechanism of EHE) due to non-ideal interfaces and
volume defects is also proposed. | 0803.3649v2 |
2008-04-17 | Conductivity behavior of La$_{0.75}$Ca$_{0.25}$MnO$_{3}$ in vicinity of ferromagnetic-paramagnetic transition studied with single current pulses | Temperature and current dependences of resistivity of bulk
La$_{0.75}$Ca$_{0.25}$MnO$_{3}$ sample grown by the floating-zone method were
studied using single ramp pulses of current. It is found that near the Curie
temperature $T_C$ the sample resistance depends substantially on current
magnitude. The observed features can be determined by inhomogeneous Joule
overheating due to mixed phase state of manganites near the
ferromagnetic-paramagnetic transition and percolation character of this
transition. | 0804.2806v1 |
2008-05-13 | Temperature dependent transport in suspended graphene | The resistivity of ultra-clean suspended graphene is strongly temperature
dependent for 5K<T<240K. At T~5K transport is near-ballistic in a device of
~2um dimension and a mobility ~170,000 cm^2/Vs. At large carrier density,
n>0.5*10^11 cm^-2, the resistivity increases with increasing T and is linear
above 50K, suggesting carrier scattering from acoustic phonons. At T=240K the
mobility is ~120,000 cm^2/Vs, higher than in any known semiconductor. At the
charge neutral point we observe a non-universal conductivity that decreases
with decreasing T, consistent with a density inhomogeneity <10^8 cm^-2. | 0805.1830v1 |
2008-06-20 | Effective Resistance Mismatch and Magnetoresistance of a CPP-GMR system with Current-Confined-Paths | We theoretically study the magnetoresistance of a CPP-GMR system with current
confined paths (CCP) in the framework of Valet-Fert theory. The continuity
equations for charge and spin currents are numerically solved with the
three-dimensional CCP geometry by use of finite element method. It is confirmed
that the MR ratio is enhanced by the CCP structure, which is consistent with
the experimental results. Moreover, we find that there exists a certain contact
width which maximize the MR ratio. We show that the contact width which
maximize the MR ratio is well described by the effective resistance matching. | 0806.3314v1 |
2008-06-26 | Negative differential resistance in molecular junctions: The effect of the electrodes electronic structure | We have carried out calculations of electron transport through a
metal-molecule-metal junction with metal nanoclusters taking the part of
electrodes. We show that negative differential resistance peaks could appear in
the current-voltage curves. The peaks arise due to narrow features in the
electron density of states of the metal clusters. The proposed analysis is
based on the ab initio computations of the relevant wave functions and energies
within the framework of the density functional theory using NRLMOL software
package. | 0806.4397v2 |
2008-10-07 | Huge anisotropic magneto-resistance in iridium atomic chains | We analyze in this article the magneto-resistance ratio of finite and
infinite iridium and platinum chains. Our calculations, that are based on a
combination of non equilibrium Green function techniques and density functional
theory, include a fully self-consistent treatment of non-collinear magnetism
and of the spin-orbit interaction. They indicate that, in addition to having an
extremely large magnetic anisotropy that may overcome the super-paramagnetic
limit, infinite and also realistic finite-length iridium chains show sizeable
anisotropic magnetoresistance ratios. We therefore propose iridium
nanostructures as promising candidates for nanospintronics logic devices. | 0810.1170v1 |
2008-10-22 | Itinerant Ferromagnetism in the electronic localization limit | We present Hall effect, $R_{xy}(H)$, and magnetoresistance, $R_{xx}(H)$,
measurements of ultrathin films of Ni, Co and Fe with thicknesses varying
between 0.2-8 nm and resistances between 1 M$\Omega$ - 100 $\Omega.$ Both
measurements show that films having resistance above a critical value, $R_{C}$,
(thickness below a critical value, $d_{C}$) show no signs for ferromagnetism.
Ferromagnetism appears only for films with $R<R_{C}$, where $R_{C}$ is material
dependent. We raise the possibility that the reason for the absence of
spontaneous magnetization is suppression of itinerant ferromagnetism by
electronic disorder in the strong localization regime. | 0810.4081v2 |
2008-11-06 | Connectivity and Critical Currents in Polycrystalline MgB2 | Current transport in polycrystalline magnesium diboride is highly non-uniform
(percolative) due to the presence of secondary phases and also due to the
intrinsic anisotropy of the material. The influence of secondary phases on the
transport properties of MgB2 was investigated. Bulk samples were prepared from
a mixture of MgB2 and MgO powders by the ex-situ technique in order to vary the
MgO content systematically. The samples were characterized by resistive and
magnetization measurements. The reduced MgB2 fraction is modeled by a reduced
effective cross section (connectivity), which was assessed directly by the
experiments. The presence of MgO also increases the percolation threshold,
which reduces the zero resistivity (or irreversibility) field. | 0811.0986v1 |
2008-12-02 | Independent magnetization behavior of a ferromagnetic metal/semiconductor hybrid system | We report the discovery of an effect where two ferromagnetic materials, one
semiconductor ((Ga,Mn)As) and one metal (permalloy), can be directly deposited
on each other and still switch their magnetization independently. We use this
independent magnetization behavior to create various resistance states
dependent on the magnetization direction of the individual layers. At zero
magnetic field a two layer device can reach up to four non-volatile resistance
states. | 0812.0455v1 |
2009-03-31 | Proper Scaling of the Anomalous Hall Effect | Working with epitaxial films of Fe, we succeeded in independent control of
different scattering processes in the anomalous Hall effect. The result
appropriately accounted for the role of phonons, thereby clearly exposing the
fundamental flaws of the standard plot of the anomalous Hall resistivity versus
longitudinal resistivity. A new scaling has been thus established that allows
an unambiguous identification of the intrinsic Berry curvature mechanism as
well as the extrinsic skew scattering and side-jump mechanisms of the anomalous
Hall effect. | 0903.5360v1 |
2009-04-08 | Negative differential resistance in nanoscale transport in the Coulomb blockade | Motivated by recent experiments, we have studied transport behavior of
coupled quantum dot systems in the Coulomb blockade regime using the master
(rate) equation approach. We explore how electron-electron interactions in a
donor-acceptor system, resembling weakly coupled quantum dots with varying
charging energy, can modify the systems response to an external bias, taking it
from normal Coulomb blockade behavior to negative differential resistance (NDR)
in the curent-voltage characteristics. | 0904.1335v1 |
2009-05-18 | On the origin of the electric carrier concentration in graphite | We investigate the dependence of the electrical resistivity of $\sim 60 $nm
thick single crystalline graphite samples on the defect concentration produced
by proton irradiation at very low fluences. We show that the resistivity
decreases few percent at room temperature after inducing defects at
concentrations as low as $\sim 0.1 $ppm due to the increase in the carrier
density, in agreement with theoretical estimates. The overall results indicate
that the carrier densities measured in graphite are not intrinsic but related
to defects and impurities. | 0905.2945v2 |
2009-06-18 | Temperature-dependent resistivity of ferromagnetic GaMnAs: Interplay between impurity scattering and many-body effects | The static conductivity of the dilute magnetic semiconductor GaMnAs is
calculated using the memory function formalism and time-dependent
density-functional theory to account for impurity scattering and to treat
Hartree and exchange interactions within the hole gas. We find that the Coulomb
scattering off the charged impurities alone is not sufficient to explain the
experimentally observed drop in resistivity below the ferromagnetic transition
temperature: the often overlooked scattering off the fluctuations of localized
spins is shown to play a significant role. | 0906.3526v1 |
2009-09-11 | Kinetic Friction by a Small Number of Intervening Inelastic Particles between Rough Surfaces | We investigate a mechanism of the appearance of kinetic friction in granular
materials. We consider a small number of intervening inelastic particles
between two rough surfaces as one of the simplest dynamical models to study
granular friction. The resistance force applied to the upper surface is
numerically calculated. We find that the resistance force F(t) is scaled as
F'(vt) for a small pulling velocity v. The time average F_0=<F(t)> in the limit
v->0 is not zero owing to the mutual collisions between the intervening
particles. The nonzero F_0 implies the appearance of kinetic friction in this
simple dynamical system. | 0909.2132v1 |
2009-10-13 | Superconductivity of FeSe0.5Te0.5 Thin Films Grown by Pulsed Laser Deposition | FeSe0.5Te0.5 thin films with PbO-type structure are successfully grown on
MgO(100) and LaSrAlO4(001) substrates from FeSe0.5Te0.5 or FeSe0.5Te0.75
polycrystalline targets by pulsed-laser deposition. The film deposited on the
MgO substrate (film thickness ~ 55 nm) shows superconductivity at 10.6 K
(onset) and 9.2 K (zero resistivity). On the other hand, the film deposited on
the LaSrAlO4 substrate (film thickness ~ 250 nm) exhibits superconductivity at
5.4 K (onset) and 2.7 K (zero resistivity). This suggests the strong influence
of substrate materials and/or the c-axis length to superconducting properties
of FeSe0.5Te0.5 thin films. | 0910.2301v1 |
2010-01-25 | Evidence for effective thermal boundary resistance from magnon/phonon disequilibrium | We use the time-resolved magneto-optical Kerr effect (TRMOKE) to measure the
local temperature and heat flow dynamics in ferromagnetic SrRuO3 thin films.
After heating by a pump pulse, the film temperature decays exponentially,
indicating that the heat flow out of the film is limited by the film/substrate
interface. We show that this behavior is consistent with an effective boundary
resistance resulting from disequilibrium between the spin and phonon
temperatures in the film. | 1001.4557v1 |
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