publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2015-01-07 | Semimetallic transport properties of epitaxially stabilized perovskite CaIrO3 films | We report on the synthesis and transport properties of perovskite (Pv) CaIrO3
thin films. The Pv phase of CaIrO3 was stabilized by epitaxial growth on
SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and LaAlO3 substrates with strong tensile,
weak tensile, and compressive strains, respectively. The resistivity of these
films showed a poorly metallic behavior. The Hall resistivity exhibited a sign
change as a function of temperature and a nonlinear magnetic-field dependence,
which clearly indicated the coexistence of electrons and holes and hence
supported that Pv CaIrO3 films are semimetallic. The observed robustness of the
semimetallic ground state against tensile and compressive strains is consistent
with the presence of symmetry-protected Dirac points (nodes) around the Fermi
level that prohibits the system from becoming a band insulator. | 1501.01433v1 |
2015-02-13 | Surface state reconstruction in ion-damaged SmB_6 | We have used ion-irradiation to damage the (001) surfaces of SmB_6 single
crystals to varying depths, and have measured the resistivity as a function of
temperature for each depth of damage. We observe a reduction in the residual
resistivity with increasing depth of damage. Our data are consistent with a
model in which the surface state is not destroyed by the ion-irradiation, but
instead the damaged layer is poorly conducting and the initial surface state is
reconstructed below the damage. This behavior is consistent with a surface
state that is topologically protected. | 1502.04103v1 |
2015-02-19 | Occurrence of flat bands in strongly correlated Fermi systems and high-$T_c$ superconductivity of electron-doped compounds | We consider a class of strongly correlated Fermi systems that exhibit an
interaction-induced flat band pinned to the Fermi surface, and generalize the
Landau strategy to accommodate a flat band and apply the more comprehensive
theory to electron systems of solids. The non-Fermi-liquid behavior that
emerges is compared with relevant experimental data on heavy-fermion metals and
electron-doped high-$T_c$ compounds. We elucidate how heavy-fermion metals have
extremely low superconducting transition temperature $T_c$, its maximum reached
in the heavy-fermion metal CeCoIn$_5$ does not exceed 2.3 K, and explain the
enhancement of $T_c$ observed in high-$T_c$ superconductors. We show that the
coefficient $A_1$ of the $T$-linear resistivity scales with $T_c$, in agreement
with the experimental behavior uncovered in the electron-doped materials. We
have also constructed schematic temperature-doping phase diagram of the copper
oxide superconductor $\rm La_{2-x}Ce_xCuO_4$ and explained the doping
dependence of its resistivity. | 1502.05659v2 |
2015-03-05 | Optical study of phase transitions in single-crystalline RuP | RuP single crystals of MnP-type orthorhombic structure were synthesized by
the Sn flux method. Temperature-dependent x-ray diffraction measurements reveal
that the compound experiences two structural phase transitions, which are
further confirmed by enormous anomalies shown in temperature-dependent
resistivity and magnetic susceptibility. Particularly, the resistivity drops
monotonically upon temperature cooling below the second transition, indicating
that the material shows metallic behavior, in sharp contrast with the
insulating ground state of polycrystalline samples. Optical conductivity
measurements were also performed in order to unravel the mechanism of these two
transitions. The measurement revealed a sudden reconstruction of band structure
over a broad energy scale and a significant removal of conducting carriers
below the first phase transition, while a charge-density-wave-like energy gap
opens below the second phase transition. | 1503.01544v1 |
2015-03-25 | Nature of magnetotransport in metal/insulating-ferromagnet heterostructures: Spin Hall magnetoresistance or magnetic proximity effect | We study the anomalous Hall-like effect (AHLE) and the effective anisotropic
magnetoresistance (EAMR) in antiferromagnetic {\gamma} -IrMn3/Y3Fe5O12(YIG) and
Pt/YIG heterostructures. For {\gamma} -IrMn3/YIG, the EAMR and the AHLE
resistivity change sign with temperature due to the competition between the
spin Hall magnetoresistance (SMR) and the magnetic proximity effect (MPE)
induced by the interfacial antiferromagnetic uncompensated magnetic moment. In
contrast, for Pt/YIG the AHLE resistivity changes sign with temperature whereas
no sign change is observed in the EAMR. This is because the MPE and the SMR
play a dominant role in the AHLE and the EAMR, respectively. As new types of
galvanomagnetic property, the AHLE and the EAMR have proved vital in
disentangling the MPE and the SMR in metal/insulating-ferromagnet
heterostructures. | 1503.07388v2 |
2015-03-31 | Persistence of two-dimensional topological insulator state in wide HgTe quantum well | Our experimental studies of electron transport in wide (14 nm) HgTe quantum
wells confirm persistence of a two-dimensional topological insulator state
reported previously for narrower wells, where it was justified theoretically.
Comparison of local and nonlocal resistance measurements indicate edge state
transport in the samples of about 1 mm size at temperatures below 1 K.
Temperature dependence of the resistances suggests an insulating gap of the
order of a few meV. In samples with sizes smaller than 10 $\mu$m a
quasiballistic transport via the edge states is observed. | 1503.08978v1 |
2015-05-19 | Frequency-Independent Response of Self-Complementary Checkerboard Screens | This research resolves a long-standing problem on the electromagnetic
response of self-complementary metallic screens with checkerboardlike geometry.
Although Babinet's principle implies that they show a frequency-independent
response, this unusual characteristic has not been observed yet due to the
singularities of the metallic point contacts in the checkerboard geometry. We
overcome this difficulty by replacing the point contacts with resistive sheets.
The proposed structure is prepared and characterized by terahertz time-domain
spectroscopy. It is experimentally confirmed that the resistive checkerboard
structures exhibit a flat transmission spectrum over 0.1--1.1 THz. It is also
demonstrated that self-complementarity can eliminate even the
frequency-dependent transmission characteristics of resonant metamaterials. | 1505.04874v2 |
2015-05-22 | Greedy Biomarker Discovery in the Genome with Applications to Antimicrobial Resistance | The Set Covering Machine (SCM) is a greedy learning algorithm that produces
sparse classifiers. We extend the SCM for datasets that contain a huge number
of features. The whole genetic material of living organisms is an example of
such a case, where the number of feature exceeds 10^7. Three human pathogens
were used to evaluate the performance of the SCM at predicting antimicrobial
resistance. Our results show that the SCM compares favorably in terms of
sparsity and accuracy against L1 and L2 regularized Support Vector Machines and
CART decision trees. Moreover, the SCM was the only algorithm that could
consider the full feature space. For all other algorithms, the latter had to be
filtered as a preprocessing step. | 1505.06249v1 |
2015-09-07 | Optimization of Spatial Dose Distribution for Controlling Sidewall Shape in Electron-beam Lithography | Electron-beam (e-beam) lithography is widely employed in fabrication of 2-D
patterns and 3-D structures. A certain type or shape of the sidewall in the
remaining resist profile may be desired in an application, e.g., an undercut
for lift-off and a vertical sidewall for etching, or required for a device.
Also, as the feature size is decreased well below a micron, a small variation
of the sidewall slope can lead to a significant (relative) CD error in certain
layers of resist. Therefore, it is important to understand effects of spatial
dose distribution on sidewall shape and be able to achieve the desired shape.
In this study, via simulation, the relationship among the total dose, spatial
distribution of dose, developing time and sidewall shape, and performance of
the method developed to optimize the dose distribution for a target sidewall
shape have been analyzed. The simulation results have been verified through
experiments. | 1509.04694v1 |
2015-10-05 | Magnetic oscillations of the anomalous Hall conductivity | It is known that the Shubnikov--de Haas oscillations can be observed in the
Hall resistivity, although their amplitude is much weaker than the amplitude of
the diagonal resistivity oscillations. Employing a model of two-dimensional
massive Dirac fermions that exhibits anomalous Hall effect, we demonstrate that
the amplitude of the Shubnikov--de Haas oscillations of the anomalous Hall
conductivity is the same as that of the diagonal conductivity. We argue that
the oscillations of the anomalous Hall conductivity can be observed by studying
the valley Hall effect in graphene superlattices and the spin Hall effect in
the low-buckled Dirac materials. | 1510.01360v2 |
2015-10-12 | Weak ferromagnetism in non-centrosymmetric BiPd 4K superconductor | We report synthesis of non-centrosymmetric BiPd single crystal by self flux
method. The BiPd single crystal is crystallized in monoclinic structure with
the P21 space group. Detailed SEM (Scanning Electron Microscopy) results show
that the crystals are formed in slab like morphology with homogenous
distribution of Bi and Pd. The magnetic susceptibility measurement confirmed
that the BiPd compound is superconducting below 4K. Further, BiPd exhibits weak
ferromagnetism near the superconducting transition temperature in isothermal
magnetization (MH) measurements. The temperature dependent electrical
resistivity also confirmed that the BiPd single crystal is superconducting at
Tc=4K. Magneto transport measurements showed that the estimated Hc2(0) value is
around 7.0kOe. We also obtained a sharp peak in heat capacity Cp(T)
measurements at below 4K due to superconducting ordering. The normalized
specific-heat jump, DC/{\gamma}Tc, is 1.52, suggesting the BiPd to be an
intermediate BCS coupled superconductor. The pressure dependent electrical
resistivity shows the Tc decreases with increasing applied pressure and the
obtained dTc/dP is -0.62K/Gpa. | 1510.03217v2 |
2015-11-25 | Andreev reflection at the edge of a two-dimentional semimetal | We investigate electron transport through the interface between a niobium
superconductor and the edge of a two-dimensional semimetal, realized in a 20~nm
wide HgTe quantum well. Experimentally, we observe that typical behavior of a
single Andreev contact is complicated by both a pronounced zero-bias resistance
anomaly and shallow subgap resistance oscillations with $1/n$ periodicity.
These results are demonstrated to be independent of the superconducting
material and should be regarded as specific to a 2D semimetal in a proximity
with a superconductor. We interpret these effects to originate from the
Andreev-like correlated process at the edge of a two-dimensional semimetal. | 1511.08085v1 |
2015-12-12 | Low Temperature Structural and Transport Studies of La0.175Pr0.45Ca0.375MnO3 | The temperature (T) dependent x-ray diffraction (XRD) and resistivity
measurements of La0.175Pr0.45Ca0.375MnO3 (LPCMO) have been performed down to 2K
to understand the structural and transport properties. From room temperature
down to 220K, LPCMO exists in orthorhombic phase with Pnma structure and at
220K, it transforms to charge ordered (CO) monoclinic phase with P21/m
structure and remains as it is down to 2K. The CO phase is evident from the
occurrence of weak but well defined superlattice peaks in the XRD pattern. This
structural transformation is of first order in nature as evident from the phase
coexistence across the transition region. These results thus clearly illustrate
that LPCMO undergoes a first order structural phase transition from charge
disordered orthorhombic phase to CO monoclinic phase at 220K, consistent with
temperature dependent resistivity results. Our structural analysis of T
dependent XRD data using Rietveld refinement infers that below 220K, LPCMO
forms commensurate CO monoclinic P21/m structure with four times structural
modulation. | 1512.03890v1 |
2015-12-17 | A self-consistent spin-diffusion model for micromagnetics | We propose a three-dimensional micromagnetic model that dynamically solves
the Landau-Lifshitz-Gilbert equation coupled to the full spin-diffusion
equation. In contrast to previous methods, we solve for the magnetization
dynamics and the electric potential in a self-consistent fashion. This
treatment allows for an accurate description of magnetization dependent
resistance changes. Moreover, the presented algorithm describes both spin
accumulation due to smooth magnetization transitions and due to material
interfaces as in multilayer structures. The model and its finite-element
implementation are validated by current driven motion of a magnetic vortex
structure. In a second experiment, the resistivity of a magnetic multilayer
structure in dependence of the tilting angle of the magnetization in the
different layers is investigated. Both examples show good agreement with
reference simulations and experiments respectively. | 1512.05519v4 |
2015-12-18 | Antiferromagnetism and superconductivity in the half-Heusler semimetal HoPdBi | We observed the coexistence of superconductivity and antiferromagnetic order
in the single-crystalline ternary pnictide HoPdBi, a plausible topological
semimetal. The compound orders antiferromagnetically at $T_N =$1.9 K and
exhibits superconductivity below $T_c =$0.7 K, which was confirmed by magnetic,
electrical transport and specific heat measurements. The specific heat shows
anomalies corresponding to antiferromagnetic ordering transition and
crystalline field effect, but not to superconducting transition. Single-crystal
neutron diffraction indicates that the antiferromagnetic structure is
characterized by the (1/2, 1/2, 1/2) propagation vector. Temperature variation
of the electrical resistivity reveals two parallel conducting channels of
semiconducting and metallic character. In weak magnetic fields, the
magnetoresistance exhibits weak antilocalization effect, while in strong fields
and temperatures below 50 K it is large and negative. At temperatures below 7 K
Shubnikov-de Haas oscillations with two frequencies appear in the resistivity.
These oscillations have non-trivial Berry phase, which is a distinguished
feature of Dirac fermions. | 1512.05972v1 |
2016-02-08 | Phase separated behavior in Yttrium doped CaMnO3 | The effect of electron doping on the structural, transport, and magnetic
properties of Mn (IV) - rich Ca1-xYxMnO3 (x < 0.2) samples have been
investigated using neutron diffraction, neutron depolarization, magnetization
and resistivity techniques. The temperature dependence of resistivity follows
the small polaron model and the activation energy exhibits a minimum for x=0.1
sample. A phase separated magnetic ground state consisting of ferromagnetic
domains (~7microns) embedded in G-type antiferromagnetic matrix is observed in
the sample, x = 0.1. The transition to the long range magnetically ordered
state in this sample is preceded by a Griffiths phase. On lowering temperature
below 300K a structural transition from orthorhombic structure (Pnma) to a
monoclinic structure (P21/m) is observed in the case of x=0.2 sample. The
ferromagnetic behavior in this case is suppressed and the antiferromagnetic
ordering is described by coexisting C-type and G-type magnetic structures
corresponding to the monoclinic and orthorhombic phases, respectively.< | 1602.02479v1 |
2016-02-08 | Scaling behavior of temperature-dependent thermopower in CeAu2Si2 under pressure | We report a combined study of in-plane resistivity and thermopower of the
pressure-induced heavy fermion superconductor CeAu2Si2 up to 27.8 GPa. It is
found that thermopower follows a scaling behavior in T/T* almost up to the
magnetic critical pressure pc ~ 22 GPa. By comparing with resistivity results,
we show that the magnitude and characteristic temperature dependence of
thermopower in this pressure range are governed by the Kondo coupling and
crystal-field splitting, respectively. Below pc, the superconducting transition
is preceded by a large negative thermopower minimum, suggesting a close
relationship between the two phenomena. Furthermore, thermopower of a variety
of Ce-based Kondo-lattices with different crystal structures follows the same
scaling relation up to T/T* ~ 2. | 1602.02498v2 |
2016-02-22 | Quantum Oscillations at Integer and Fractional Landau Level Indices in ZrTe5 | A three-dimensional (3D) Dirac semimetal (DS) is an analogue of graphene, but
with linear energy dispersion in all (three) momentum directions.3D DSs have
been a fertile playground in discovering novel quantum particles, for example
Weyl fermions, in solid state systems.Many 3D DSs (e.g., ZrTe5) were
theoretically predicted. We report here the results from the studies of
aberration-corrected scanning transmission electron microscopy and low
temperature magneto-transport measurements in exfoliated ZrTe5 thin
flakes.Several unique results were observed. First, an
anomalous-Hall-effect-like behavior was observed around zero magnetic field
(B).Second, a non-trivial Berry's phase of \pi\ was obtained from the Landau
level fan diagram of the Shubnikov-de Haas oscillations in the longitudinal
resistivity. Third, the longitudinal resistivity shows linear B field
dependence in the quantum limit. Most surprisingly, quantum oscillations were
observed at fractional Landau level indices N = 2/3 and 2/5, demonstrating
strong electron-electron interactions effects in ZrTe5. | 1602.06824v3 |
2016-02-26 | Eigenanalysis of morphological diversity in silicon random nanostructures formed via resist collapse | This paper demonstrates eigenanalysis to quantitatively reveal the diversity
and capacity of identities offered by the morphological diversity in silicon
nanostructures formed via random collapse of resist. The analysis suggests that
approximately 10^115 possible identities are provided per 0.18-um^2 area of
nanostructures, indicating that nanoscale morphological signatures will be
extremely useful for future information security applications where securing
identities is critical. The eigenanalysis provides an intuitive physical
picture and quantitative characterization of the diversity of structural
fluctuations while unifying measurement stability concerns, which will be
widely applicable to other materials, devices, and system architectures. | 1602.08205v2 |
2016-04-29 | Ca$_3$Ir$_4$Sn$_{13}$: A weakly correlated nodeless superconductor | We report detailed Seebeck coefficient, Hall resistivity as well as specific
heat measurement on Ca$_3$Ir$_4$Sn$_{13}$ single crystals. The Seebeck
coefficient exhibits a peak corresponding to the anomaly in resistivity at
$T^*$, and the carrier density is suppressed significantly below $T^*$. This
indicates a significant Fermi surface reconstruction and the opening of the
charge density wave gap at the supperlattice transition. The magnetic field
induced enhancement of the residual specific heat coefficient $\gamma(H)$
exhibits a nearly linear dependence on magnetic field, indicating a nodeless
gap. In the temperature range close to $T_c$ the Seebeck coefficient can be
described well by the diffusion model. The zero-temperature extrapolated
thermoelectric power is very small, implying large normalized Fermi
temperature. Consequently the ratio $\frac{T_c}{T_F}$ is very small. Our
results indicate that Ca$_3$Ir$_4$Sn$_{13}$ is a weakly correlated nodeless
superconductor. | 1604.08948v1 |
2016-06-06 | First-principles calculation of the stabilities of LMP/LAMP lithium superionic conductors against sodium-ion exchange in seawater | Electronic structure calculations carried out to estimate the free energies
of Na(aq)+ exchange for lithium in LiM2(PO4)3 (LMP, M=Si4+,Ge4+,Ti4+,Sn4+,Zr4+)
and Li1+xAlxM2-x(PO4)3 (LAMP; M=Ge4+,Ti4+, between 0 and 0.5) compounds in
seawater. The calculations show that resistance to sodium-ion exchange
increases with decreasing cell volume. For the pure LMP compounds, only the
hypothetical LiSi2(PO4)3 is predicted to be stable against sodium ion exchange
in aqueous solution. The calculations indicate that increasing the extent of
Al3+ substitution for M4+ in the LAMP compounds increases the resistance to
exchange, and that both LAGP and LATP can be stabilized against sodium exchange
for x greater than or equal to approximately 0.5 Li1+xAlxM2-x(PO4)3. | 1606.02177v1 |
2016-06-09 | Giant Linear Magneto-resistance in Nonmagnetic PtBi2 | We synthesized nonmagnetic PtBi$_2$ single crystals and observed a giant
linear magneto-resistance (MR) up to 684\% under a magnetic field $\mu_0H$ = 15
T at $T$ = 2 K. The linear MR decreases with increasing temperature, but it is
still as large as 61\% under $\mu_0H$ of 15 T at room temperature. Such a giant
linear MR is unlikely to be described by the quantum model as the quantum
condition is not satisfied. Instead, we found that the slope of MR scales with
the Hall mobility, and it can be well explained by a classical disorder model. | 1606.02847v1 |
2016-07-13 | Tuning the electronic and the crystalline structure of LaBi by pressure | Extreme magnetoresistance (XMR) in topological semimetals is a recent
discovery which attracts attention due to its robust appearance in a growing
number of materials. To search for a relation between XMR and
superconductivity, we study the effect of pressure on LaBi taking advantage of
its simple structure and simple composition. By increasing pressure we observe
the disappearance of XMR followed by the appearance of superconductivity at
P=3.5 GPa.The suppression of XMR is correlated with increasing zero-field
resistance instead of decreasing in-field resistance. At higher pressures, P=11
GPa, we find a structural transition from the face center cubic lattice to a
primitive tetragonal lattice in agreement with theoretical predictions. We
discuss the relationship between extreme magnetoresistance, superconductivity,
and structural transition in LaBi. | 1607.03560v1 |
2016-07-20 | Performance of Topological Insulator Interconnects | The poor performance of copper interconnects at the nanometer scale calls for
new material solutions for continued scaling of integrated circuits. We propose
the use of three dimensional time-reversal-invariant topological insulators
(TIs), which host backscattering-protected surface states, for this purpose.
Using semiclassical methods, we demonstrate that nanoscale TI interconnects
have a resistance 1-3 orders of magnitude lower than copper interconnects and
graphene nanoribbons at the nanometer scale. We use the nonequilibrium Green
function (NEGF) formalism to measure the change in conductance of nanoscale TI
and metal interconnects caused by the presence of impurity disorder. We show
that metal interconnects suffer a resistance increase, relative to the clean
limit, in excess of 500% due to disorder while the TI's surface states increase
less than 35% in the same regime. | 1607.06131v2 |
2016-08-03 | Prominent metallic surface conduction and the singular magnetic response of topological Dirac fermion in three-dimensional topological insulator Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$ | We report semiconductor to metal-like crossover in temperature dependence of
resistivity ($\rho$) due to the switching of charge transport from bulk to
surface channel in three-dimensional topological insulator
Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$. Unlike earlier studies, a much
sharper drop in $\rho$($T$) is observed below the crossover temperature due to
the dominant surface conduction. Remarkably, the resistivity of the conducting
surface channel follows a rarely observable $T^2$ dependence at low temperature
as predicted theoretically for a two-dimensional Fermi liquid system. The field
dependence of magnetization shows a cusp-like paramagnetic peak in the
susceptibility ($\chi$) at zero field over the diamagnetic background. The peak
is found to be robust against temperature and decays linearly with field from
its zero-field value. This unique behavior of $\chi$ is associated with the
spin-momentum locked topological surface state of
Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$. The reconstruction of surface state
with time is clearly reflected through the reduction of peak height with the
age of the sample. | 1608.01203v2 |
2016-08-11 | Magnetoresistance generated from charge-spin conversion by anomalous Hall effect in metallic ferromagnetic/nonmagnetic bilayers | A theoretical formulation of magnetoresistance effect in a metallic
ferromagnetic/nonmagnetic bilayer originated from the charge-spin conversion by
the anomalous Hall effect is presented. Analytical expressions of the
longitudinal and transverse resistivities in both nonmagnet and ferromagnet are
obtained by solving the spin diffusion equation. The magnetoresistance
generated from charge-spin conversion purely caused by the anomalous Hall
effect in the ferromagnet is found to be proportional to the square of the spin
polarizations in the ferromagnet and has fixed sign. We also find additional
magnetoresistances in both nonmagnet and ferromagnet arising from the mixing of
the spin Hall and anomalous Hall effects. The sign of this mixing resistance
depends on those of the spin Hall angle in the nonmagnet and the spin
polarizations of the ferromagnet. | 1608.03359v2 |
2016-08-12 | Growth of ultra thin vanadium dioxide thin films using magnetron sputtering | In this work, the results of fabricating ultra thin VO$_2$ films on the
technologically relevant amorphous SiO$_2$ surface using reactive DC magnetron
sputtering are presented. Results indicate that a post deposition anneal in low
partial pressures of oxygen is an effective way at stabilizing the
VO$_2$(M$_{1}$) phase on the SiO$_2$ surface. VO$_2$ films with a thickness of
42nm show a continuous microstructure, and undergo a resistivity change of more
than a factor of 200 as the temperature of the film increases above 72$^{o}C$.
The film shows hysteresis in the metal-insulator transition temperature upon
heating and cooling with a width of approximately 8$^o$C. The resistivity of
the low temperature semiconducting phase is found to be thermally activated
with an activation energy 0.16$\pm$0.03 $ev$. Stress measurements using X-ray
diffraction indicate that the ultra thin VO$_2$ film has a large tensile stress
of 2.0$\pm$0.2 $GPa$. This value agrees well with the calculated thermal stress
due to differential thermal expansion between the VO$_2$ thin film and silicon
substrate. The stress leads to a shift of the metal-insulator transition
temperature by approximately 4$^{o}C$. | 1608.03911v1 |
2016-08-31 | Spin polarization ratios of resistivity and density of states estimated from anisotropic magnetoresistance ratio for nearly half-metallic ferromagnets | We derive a simple relational expression between the spin polarization ratio
of resistivity, $P_\rho$, and the anisotropic magnetoresistance ratio $\Delta
\rho/\rho$, and that between the spin polarization ratio of the density of
states at the Fermi energy, $P_{\rm DOS}$, and $\Delta \rho/\rho$ for nearly
half-metallic ferromagnets. We find that $P_\rho$ and $P_{\rm DOS}$ increase
with increasing $|\Delta \rho/\rho|$ from 0 to a maximum value. In addition, we
roughly estimate $P_\rho$ and $P_{\rm DOS}$ for a Co$_2$FeGa$_{0.5}$Ge$_{0.5}$
Heusler alloy by substituting its experimentally observed $\Delta \rho/\rho$
into the respective expressions. | 1608.08888v1 |
2016-10-17 | Anomalous Hall effect of ferromagnetic Fe3Sn2 single crystal with geometrically frustrated kagome lattice | The anomalous Hall effect is investigated for ferromagnetic Fe3Sn2 single
crystal with geometrically frustrated kagome bilayer of Fe. The scaling
behavior between anomalous Hall resistivity rho_{xy}^{A} and longitudinal
resistivity rho_{xx} is quadratic and further analysis implies that the AHE in
Fe3Sn2 single crystal should be dominated by the intrinsic Karplus-Luttinger
mechanism rather than extrinsic skew-scattering or side-jump mechanisms.
Moreover, there is a sudden jump of anomalous Hall conductivity sigma_{xy}^{A}
appearing at about 100 K where the spin-reorientation transition from the c
axis to the ab plane is completed. This change of sigma_{xy}^{A} might be
related to the evolution of Fermi surface induced by the spin-reorientation
transition. | 1610.04970v1 |
2016-11-11 | MgGa2O4 spinel barrier for magnetic tunnel junctions: coherent tunneling and low barrier height | Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel
junctions (MTJs) were fabricated by magnetron sputtering. Tunnel
magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was
observed, suggesting a TMR enhancement by the coherent tunneling effect in the
MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good
lattice matching with the Fe layers owing to slight tetragonal lattice
distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance
and current-voltage characteristics revealed that the barrier height of the
MgGa2O4 barrier is much lower than that in an MgAl2O4 barrier. This study
demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a
large TMR ratio at a low resistance area product. | 1611.03606v1 |
2016-11-28 | Doping of metal-organic frameworks towards resistive sensing | Coordination polymerization leads to various metal-organic frameworks (MOFs)
in which symmetrical metal nodes exposed to nano voids lead to unique physical
properties and chemical functionalities. One of the challenges towards their
applications as porous materials is to make MOFs optimally conductive to be
used as electronic components. Here, we demonstrate that Co-MOF-74, a honeycomb
nano{framework with one{dimensionally arranged cobalt atoms advances its
physical properties by accommodating Tetracyanochinodimethan (TCNQ), an
acceptor molecule. Strong intermolecular charge transfer narrows the optical
band gap down to 1.5 eV of divalent TCNQ and enhances the electrical
conduction, which allows the MOF to be utilized for resistive gas- and
photo-sensing. Our result provides insight into electronic interactions in
doped MOFs and paves the way towards their electronic applications. | 1611.09138v1 |
2016-12-02 | Stokes paradox in electronic Fermi liquids | The Stokes paradox is the statement that in a viscous two dimensional fluid,
the "linear response" problem of fluid flow around an obstacle is ill-posed. We
present a simple consequence of this paradox in the hydrodynamic regime of a
Fermi liquid of electrons in two-dimensional metals. Using hydrodynamics and
kinetic theory, we estimate the contribution of a single cylindrical obstacle
to the global electrical resistance of a material, within linear response.
Momentum relaxation, present in any realistic electron liquid, resolves the
classical paradox. Nonetheless, this paradox imprints itself in the resistance,
which can be parametrically larger than predicted by Ohmic transport theory. We
find a remarkably rich set of behaviors, depending on whether or not the
quasiparticle dynamics in the Fermi liquid should be treated as diffusive,
hydrodynamic or ballistic on the length scale of the obstacle. We argue that
all three types of behavior are observable in present day experiments. | 1612.00856v2 |
2017-02-08 | Ironwood Meta Key Agreement and Authentication Protocol | Number theoretic public-key solutions, currently used in many applications
worldwide, will be subject to various quantum attacks, making them less
attractive for longer-term use. Certain group theoretic constructs are now
showing promise in providing quantum-resistant cryptographic primitives, and
may provide suitable alternatives for those looking to address known quantum
attacks. In this paper, we introduce a new protocol called a Meta Key Agreement
and Authentication Protocol (MKAAP) that has some characteristics of a
public-key solution and some of a shared-key solution. Specifically it has the
deployment benefits of a public-key system, allowing two entities that have
never met before to authenticate without requiring real-time access to a
third-party, but does require secure provisioning of key material from a
trusted key distribution system (similar to a symmetric system) prior to
deployment. We then describe a specific MKAAP instance, the Ironwood MKAAP,
discuss its security, and show how it resists certain quantum attacks such as
Shor's algorithm or Grover's quantum search algorithm. We also show Ironwood
implemented on several ``internet of things'' (IoT devices), measure its
performance, and show how it performs significantly better than ECC using fewer
device resources. | 1702.02450v2 |
2017-06-08 | Scale-invariant large nonlocality in polycrystalline graphene | The observation of large nonlocal resistances near the Dirac point in
graphene has been related to a variety of intrinsic Hall effects, where the
spin or valley degrees of freedom are controlled by symmetry breaking
mechanisms. Engineering strong spin or valley Hall signals on scalable graphene
devices could stimulate further practical developments of spin- and
valleytronics. Here we report on scale-invariant nonlocal transport in
large-scale chemical vapour deposition graphene under an applied external
magnetic field. Contrary to previously reported Zeeman spin Hall effect, our
results are explained by field-induced spin-filtered edge states whose
sensitivity to grain boundaries manifests in the nonlocal resistance. This
phenomenon, related to the emergence of the quantum Hall regime, persists up to
the millimeter scale, showing that polycrystalline morphology can be imprinted
in nonlocal transport. This suggests that topological Hall effects in
large-scale graphene materials are highly sensitive to the underlying
structural morphology, limiting practical realizations. | 1706.02539v2 |
2017-09-01 | Reproducibility and off-stoichiometry issues in nickelate thin films grown by pulsed laser deposition | Rare-earth nickelates are strongly correlated oxides displaying a
metal-to-insulator transition at a temperature tunable by the rare-earth ionic
radius. In PrNiO$_3$ and NdNiO$_3$, the transition is very sharp and shows an
hysteretic behavior akin to a first-order transition. Both the temperature at
which the transition occurs and the associated resistivity change are extremely
sensitive to doping and therefore to off-stoichiometry issues that may arise
during thin film growth. Here we report that strong deviations in the transport
properties of NdNiO$_3$ films can arise in films grown consecutively under
nominally identical conditions by pulsed laser deposition; some samples show a
well-developed transition with a resistivity change of up to five orders of
magnitude while others are metallic down to low temperatures. Through a
detailed analysis of \textit{in-situ} X-ray photoelectron spectroscopy data, we
relate this behavior to large levels of cationic off-stoichoimetry that also
translate in changes in the Ni valence and bandwidth. Finally, we demonstrate
that this lack of reproducibility can be remarkably alleviated by using
single-phase NdNiO$_3$ targets. | 1709.00240v1 |
2017-09-05 | Temperature Dependent n-p Transition of 3 Dimensional Dirac Semimetal Na$_3$Bi Thin Film | We study the temperature dependence ($77$ K - $475$ K) of the longitudinal
resistivity and Hall coefficient of thin films (thickness $20$ nm) of three
dimensional topological Dirac semimetal Na$_3$Bi grown via molecular beam
epitaxy (MBE). The temperature-dependent Hall coefficient is electron-like at
low temperature, but transitions to hole-like transport around $200$ K. We
develop a model of a Dirac band with electron-hole asymmetry in Fermi velocity
and mobility (assumed proportional to the square of Fermi velocity) which
explains well the magnitude and temperature dependence of the Hall resistivity.
We find that the hole mobility is about $7$ times larger than the electron
mobility. In addition, we find that the electron mobility decreases
significantly with increasing temperature, suggesting electron-phonon
scattering strongly limits the room temperature mobility. | 1709.01209v1 |
2017-09-05 | Superconducting and normal-state properties of the noncentrosymmetric superconductor Re6Zr | We systematically investigate the normal and superconducting properties of
non-centrosymmetric Re$_{6}$Zr using magnetization, heat capacity, and
electrical resistivity measurements. Resistivity measurements indicate
Re$_{6}$Zr has poor metallic behavior and is dominated by disorder. Re$_6$Zr
undergoes a superconducting transition at $T_{\mathrm{c}} =
\left(6.75\pm0.05\right)$ K. Magnetization measurements give a lower critical
field, $\mu_{0}H_{\mathrm{c1}} = \left(10.3 \pm 0.1\right)$ mT. The
Werthamer-Helfand-Hohenberg model is used to approximate the upper critical
field $\mu_{0}H_{\mathrm{c2}} = \left(11.2 \pm 0.2\right)$ T which is close to
the Pauli limiting field of 12.35 T and which could indicate singlet-triplet
mixing. However, low-temperature specific-heat data suggest that Re$_{6}$Zr is
an isotropic, fully gapped s-wave superconductor with enhanced electron-phonon
coupling. Unusual flux pinning resulting in a peak effect is observed in the
magnetization data, indicating an unconventional vortex state. | 1709.01328v1 |
2017-09-11 | Tuning electrical properties of silicon dioxide through intrinsic nano-patterns | The inherent network of nanopores and voids in silicon dioxide (SiO2) is
generally undesirable for aspects of film quality, electrical insulation and
dielectric performance. However, if we view these pores as natural
nano-patterns embedded in a dielectric matrix then that opens up new vistas for
exploration. The nano-pattern platform can be used to tailor electrical,
optical, magnetic and mechanical properties of the carrier film. In this
article we report the tunable electrical properties of thermal SiO2 thin-film
achieved through utilization of the metal-nanopore network where the pores are
filled with metallic Titanium (Ti). Without any intentional chemical doping, we
have shown that the electrical resistivity of the oxide film can be controlled
through physical filling up of the intrinsic oxide nanopores with Ti. The
electrical resistance of the composite film remains constant even after
complete removal of the metal from the film surface except the pores. Careful
morphological, electrical and structural analyses are carried out to establish
that the presence of Ti in the nanopores play a crucial role in the observed
conductive nature of the nanoporous film. | 1709.03259v1 |
2017-09-14 | Towards Universal Non-Volatile Resistance Switching in Non-metallic Monolayer Atomic Sheets | Here, we report the intriguing observation of stable non-volatile resistance
switching (NVRS) in single-layer atomic sheets sandwiched between metal
electrodes. NVRS is observed in the prototypical semiconducting (MX2, M=Mo, W;
and X=S, Se) transitional metal dichalcogenides (TMDs), and insulating
hexagonal boron nitride (h-BN), which alludes to the universality of this
phenomenon in non-metallic 2D monolayers, and features forming-free switching.
This observation of NVRS phenomenon, widely attributed to ionic diffusion,
filament and interfacial redox in bulk oxides and electrolytes, inspires new
studies on defects, ion transport and energetics at the sharp interfaces
between atomically-thin sheets and conducting electrodes. From a contemporary
perspective, switching is all the more unexpected in monolayers since leakage
current is a fundamental limit in ultra-thin oxides. Emerging device concepts
in non-volatile flexible memory fabrics, and brain-inspired (neuromorphic)
computing could benefit substantially from the pervasive NVRS effect and the
associated wide materials and engineering co-design opportunity.
Experimentally, a 50 GHz radio-frequency (RF) monolayer switch is demonstrated,
which opens up a new application for electronic zero-static power RF switching
technology. | 1709.04592v1 |
2017-11-06 | Negative to Positive Magnetoresistance transition in Functionalization of Carbon nanotube and Polyaniline Composite | Electrical resistivity and magnetoresistance(MR) in polyaniline(PANI) with
carbon nanotube(CNT) and functionalized carbon nanotube(fCNT) composites have
been studied for different weight percentage down to the temperature 4.2K and
up to magnetic field 5T. Resistivity increases significantly in composite at
low temperature due to functionalization of CNT compare to only CNT.
Interestingly transition from negative to positive magnetoresistance has been
observed for 10wt% of composite as the effect of disorder is more in fCNT/PANI.
This result depicts that the MR has strong dependency on disorder in the
composite system. The transition of MR has been explained in the basis of
polaron-bipolaron model. The long range Coulomb interaction between two
polarons screened by disorder in the composite of fCNT/PANI, increases the
effective on-site Coulomb repulsion energy to form bipolaron which leads to
change the sign of MR from negative to positive. | 1711.01957v2 |
2017-11-27 | Effect of RF Sputtering Process Parameters on Silicon Nitride Thin Film Deposition | The objective of this work was to study the RF sputtering process parameters
optimisation for deposition of Silicon Nitride thin films. The process
parameters chosen to be varied were deposition power, deposition duration, flow
rate of argon and flow rate of nitrogen. The parameters were varied at three
levels according to Taguchi L9 orthogonal array. Surface topology, film
composition, coating thickness, coating resistivity and refractive index were
determined using SEM, XRD, profilometer, Semiconductor device analyser and UV
spectrometer respectively. The measured film thickness values ranged from
127.8nm to 908.3nm with deposition rate varying from 1.47nm/min to a maximum
value of 10.1nm/min. The resistivity of the film varied between 1.53x1013ohm-m
to 7.85 x1013ohm-m. Refractive index of the film was calculated to be between
1.84 to 2.08. From the results, it was seen that film properties tend to be
poor when there is no nitrogen flow and tend to improve with small input of
nitrogen. Also, SEM images indicated amorphous structure of silicon nitride
which was confirmed by XRD pattern. | 1711.09556v2 |
2017-12-29 | Non-stoichiometry effects on the extreme magnetoresistance in Weyl semimetal WTe2 | Non-stoichiometry effect on the extreme magnetoresistance is systematically
investigated for the Weyl semimetal WTe2. Magnetoresistance and Hall
resistivity are measured for the as-grown samples with a slight difference in
Te vacancies and the annealed samples with increased Te vacancies. The fittings
to a two-carrier model show that the magnetoresistance is strongly dependent on
the residual resistivity ratio (i.e., the degree of non-stoichiometry), which
is eventually understood in terms of electron doping which not only breaks the
balance between electron-type and hole-type carrier densities but also reduces
the average carrier mobility. Thus, compensation effect and ultrahigh mobility
are probably the main driving force of the extreme magnetoresistance in WTe2. | 1712.10200v2 |
2018-03-03 | Giant Planar Hall Effect in the Dirac Semimetal ZrTe5 | Recently, giant planar Hall effect originating from chiral anomaly has been
predicted in nonmagnetic Dirac/Weyl semimetals. ZrTe5 is considered to be an
intriguing Dirac semimetal at the boundary of weak topological insulators and
strong topological insulators, though this claim still remains controversial.
Here, we report the observation in ZrTe5 of the giant planar Hall resistivity
that shows two different magnetic-field dependences as predicted by theory and
a maximum at the Lifshitz transition temperature. We found that the giant
planar Hall resistivity fades out with decreasing the thickness of ZrTe5
nanoplates, which may be ascribed to the vanishing of the 3D nature of the
samples. In addition, we have observed a nontrivial Berry phase,
chiral-anomaly-induced negative longitudinal magnetoresistance, and a giant
in-plane anisotropic magnetoresistance in these ZrTe5 nanoplates. All the
experimental observations demonstrated coherently that ZrTe5 is a Dirac
semimetal. | 1803.01213v2 |
2018-03-18 | Bulk transport properties of Bismuth selenide thin films approaching the two-dimensional limit | We have investigated the transport properties of topological insulator Bi2Se3
thin films grown using magnetron sputtering with an emphasis on understanding
the behavior as a function of thickness. We show that thickness has a strong
influence on all aspects of transport as the two-dimensional limit is
approached. Bulk resistivity and Hall mobility show disproportionately large
changes below 6 quintuple layer which we directly correlate to an increase in
the bulk band gap of few-layer Bi2Se3, an effect that is concomitant with
surface gap opening. A tendency to crossover from a metallic to an insulating
behavior in temperature-dependent resistivity measurements in ultra-thin Bi2Se3
is also consistent with an increase in the bulk band gap along with enhanced
disorder at the film-substrate interface. Our work highlights that the
properties of few-layer Bi2Se3 are tunable that may be attractive for a variety
of device applications in areas such as optoelectronics, nanoelectronics and
spintronics. | 1803.06593v1 |
2018-03-30 | Growth of Thin Oxidation-Resistive Crystalline Si Nanostructures on Graphene | We report the growth of Si nanostructures, either as thin films or
nanoparticles, on graphene substrates. The Si nanostructures are shown to be
single crystalline, air stable and oxidation resistive, as indicated by the
observation of a single crystalline Si Raman mode at around 520 cm-1, a STM
image of an ordered surface structure under ambient condition, and a Schottky
junction with graphite. Ultra-thin silicon regions exhibit silicene-like
behavior, including a Raman mode at around 550 cm-1, a triangular lattice
structure in STM that has distinctly different lattice spacing from that of
either graphene or thicker Si, and metallic conductivity of up to 500 times
higher than that of graphite. This work suggests a bottom-up approach to
forming a Si nanostructure array on a large scale patterned graphene substrate
for fabricating nanoscale Si electronic devices. | 1804.00072v1 |
2018-03-31 | Quantum Wires and Waveguides Formed in Graphene by Strain | Confinement of electrons in graphene to make devices has proven to be a
challenging task. Electrostatic methods fail because of Klein tunneling, while
etching into nanoribbons requires extreme control of edge terminations, and
bottom-up approaches are limited in size to a few nanometers. Fortunately, its
mechanical flexibility raises the possibility of using strain to alter
graphene's properties and create novel straintronic devices. Here, we report
transport studies of nanowires created by linearly-shaped strained regions
resulting from individual folds formed by layer transfer onto hexagonal boron
nitride. Conductance measurements across the folds reveal Coulomb blockade
signatures, indicating confined charges within these structures, which act as
quantum dots. Along folds, we observe sharp features in traverse resistivity
measurements, attributed to an amplification of the dot conductance modulations
by a resistance bridge incorporating the device. Our data indicates ballistic
transport up to ~1 um along the folds. Calculations using the Dirac model
including strain are consistent with measured bound state energies and predict
the existence of valley-polarized currents. Our results show that graphene
folds can act as straintronic quantum wires. | 1804.00207v1 |
2018-04-05 | Two-Stage Proximity-Induced Gap-Opening in Topological Insulator - Insulating Ferromagnet (Bi$_x$Sb$_{1-x}$)$_2$Te$_3$ - EuS Bilayers | To further investigate the interplay between ferromagnetism and topological
insulators, thin films of the low-carrier topological insulator
(Bi$_x$Sb$_{1-x}$)$_2$Te$_3$ were deposited on the insulating ferromagnet EuS
(100) in situ. AC susceptibility indicates magnetic anomalies between
$T\approx30~\mathrm{K}$ and $T\approx60~\mathrm{K}$, well above the Curie
temperature $T_C \approx 15~\mathrm{K}$ of EuS. When the Fermi level is close
to the Dirac point and the surface state dominates the electric conduction,
sharp increases in resistance with decreasing temperatures were observed
concurrently with the magnetic anomalies. Positive-negative magnetoresistance
crossovers were observed at the Curie temperature, which seem only to appear
when the sheet resistance exceeds the Mott-Ioffe-Regel limit $h/e^2$. A
two-stage gap-opening process due to magnetic proximity is proposed. | 1804.02061v2 |
2018-04-16 | Structural and magnetic properties of CeZnAl$_3$ single crystals | We have synthesized single crystals of CeZnAl$_3$, which is a new member of
the family of the Ce-based intermetallics Ce$TX_3$ ($T$ = transition metal,
$X$= Si, Ge, Al), crystallizing in the non-centrosymmetric tetragonal
BaNiSn$_3$-type structure. Magnetization, specific heat and resistivity
measurements all show that CeZnAl$_3$ orders magnetically below around 4.4 K.
Furthermore, magnetization measurements exhibit a hysteresis loop at low
temperatures and fields, indicating the presence of a ferromagnetic component
in the magnetic state. This points to a different nature of the magnetism in
CeZnAl$_3$ compared to the other isostructural Ce$T$Al$_3$ compounds.
Resistivity measurements under pressures up to 1.8 GPa show a moderate
suppression of the ordering temperature with pressure, suggesting that
measurements to higher pressures are required to look for quantum critical
behavior. | 1804.05477v1 |
2018-05-11 | Unveiling the mechanisms of the spin Hall effect in Ta | Spin-to-charge current interconversions are widely exploited for the
generation and detection of pure spin currents and are key ingredients for
future spintronic devices including spin-orbit torques and spin-orbit logic
circuits. In case of the spin Hall effect, different mechanisms contribute to
the phenomenon and determining the leading contribution is peremptory for
achieving the largest conversion efficiencies. Here, we experimentally
demonstrate the dominance of the intrinsic mechanism of the spin Hall effect in
highly-resistive Ta. We obtain an intrinsic spin Hall conductivity for
$\beta$-Ta of -820$\pm$120 ($\hbar$/e) $\Omega^{-1}cm^{-1}$ from spin
absorption experiments in a large set of lateral spin valve devices. The
predominance of the intrinsic mechanism in Ta allows us to linearly enhance the
spin Hall angle by tuning the resistivity of Ta, reaching up to -35$\pm$3%, the
largest reported value for a pure metal. | 1805.04475v1 |
2018-06-04 | Nodeless superconductivity in the SnAs-based van der Waals type superconductor NaSn2As2 | We grew the single crystals of the SnAs-based van der Waals (vdW)-type
superconductor NaSn$_2$As$_2$ and systematically measured its resistivity,
specific heat, and ultralow-temperature thermal conductivity. The
superconducting transition temperature $T_c$ = 1.60 K of our single crystal is
0.3 K higher than that previously reported. A weak but intrinsic anomaly
situated at 193 K is observed in both resistivity and specific heat, which
likely arises from a charge-density-wave (CDW) instability.
Ultralow-temperature thermal conductivity measurements reveal a fully-gapped
superconducting state with a negligible residual linear term in zero magnetic
field, and the field dependence of $\kappa_0 / T$ further suggests
NaSn$_2$As$_2$ is an $s$-wave superconductor. | 1806.01141v1 |
2018-06-20 | Heat transport in pristine and polycrystalline single-layer hexagonal boron nitride | We use a phase field crystal model to generate large-scale bicrystalline and
polycrystalline single-layer hexagonal boron nitride (h-BN) samples and employ
molecular dynamics (MD) simulations with the Tersoff many-body potential to
study their heat transport properties. The Kapitza thermal resistance across
individual h-BN grain boundaries is calculated using the inhomogeneous
nonequilibrium MD method. The resistance displays strong dependence on the tilt
angle, the line tension and the defect density of the grain boundaries. We also
calculate the thermal conductivity of pristine h-BN and polycrystalline h-BN
with different grain sizes using an efficient homogeneous nonequilibrium MD
method. The in-plane and the out-of-plane (flexural) phonons exhibit different
grain size scalings of the thermal conductivity in polycrystalline h-BN and the
extracted Kapitza conductance is close to that of large-tilt-angle grain
boundaries in bicrystals. | 1806.07936v2 |
2018-09-17 | Phase transformations and compatibility in helical structures | We systematically study phase transformations from one helical structure to
another. Motivated in part by recent work that relates the presence of
compatible interfaces with properties such as the hysteresis and reversibility
of a phase transformation [35, 33, 12, 28], we give necessary and sufficient
conditions on the structural parameters of two helical phases such that they
are compatible. We show that, locally, four types of compatible interface are
possible: vertical, horizontal, helical and elliptical. We discuss the mobility
of these interfaces and give examples of systems of interfaces that are mobile
and could be used to fully transform a helical structure from one phase to
another.
These results provide a basis for the tuning of helical structural parameters
so as to achieve compatibility of phases. In the case of transformations in
crystals, this kind of tuning has led to materials with exceptionally low
hysteresis and dramatically improved resistance to transformational fatigue.
Compatible helical transformations with low hysteresis and fatigue resistance
would exhibit an unusual shape memory effect involving both twist and
extension, and may have potential applications as new artificial muscles and
actuators. | 1809.06282v2 |
2019-05-01 | Hydrodynamic Coulomb drag and bounds on diffusion | We study Coulomb drag between an active layer with a clean electron liquid
and a passive layer with a pinned electron lattice in the regime of fast
intralayer equilibration. Such a two-fluid system offers an experimentally
realizable way to disentangle the fast rate of intralayer electron-electron
interactions from the much slower rate of momentum transfer between both
layers. We identify an intermediate temperature range above the Fermi energy of
the electron fluid but below the Debye energy of the electronic crystal where
the hydrodynamic drag resistivity is directly proportional to a fast
electron-electron scattering rate. The results are compatible with the
conjectured scenario for strong electron-electron interactions which poses that
a linear temperature dependence of resistivity originates from a "Planckian"
electron relaxation time $\tau_{eq}\sim \hbar/k_BT$. We compare this to the
better known semiclassical case, where the diffusion constant is found to be
not proportional to the microscopic timescale. | 1905.00317v2 |
2019-05-03 | Supersonic flow and negative local resistance in hydrodynamic Dirac electron nozzles | In clean Dirac electron systems such as graphene, electron-electron
interactions can dominate over other relaxation mechanisms such as phonon or
impurity scattering. It has been predicted that in this limit, collective
electron dynamics can be described by hydrodynamic equations. The prerequisites
for electron liquids are already fulfilled in current experiments and hints of
electron hydrodynamics have been identified in transport measurements. Here, we
show that a nozzle geometry, implemented for example in a graphene sample, can
cause a transition from subsonic to supersonic flow and provides an interesting
probe for the hydrodynamic regime of Dirac electrons. In particular, we predict
two distinct transport features that can be seen in the experimentally
measurable voltage characteristics on the exit side of the nozzle: a pronounced
negative local resistance, and an abrupt change of the electrostatic potential
induced by an electron shock wave. Our results pave the way for an experimental
identification of supersonic hydrodynamic electron flow and for the
experimental study of electron shock waves. | 1905.01247v2 |
2019-05-21 | Thermal Boundary Resistance Measurement and Analysis Across SiC/SiO2 Interface | Silicon Carbide (SiC) is a typical material for third-generation
semiconductor. The thermal boundary resistance (TBR) of 4H-SiC/SiO2 interface,
was investigated by both experimental measurements and theoretical
calculations. The structure of 4H-SiC/SiO2 was characterized by using
transmission electron microscopy and X-ray diffraction. The TBR is measured as
8.11*10-8 m2K/W by 3-omega method. Furthermore, the diffuse mismatch model was
employed to predict the TBR of different interfaces which is in good agreement
with measurements. Heat transport behavior based on phonon scattering
perspective was also discussed to understand the variations of TBR across
different interfaces. Besides, the intrinsic thermal conductivity of SiO2 thin
films (200~1,500 nm in thickness) on 4H-SiC substrates was measured by 3 omega
procedure, as 1.42 W/mK at room temperature. It is believed the presented
results could provide useful insights on the thermal management and heat
dissipation for SiC devices. | 1905.08570v1 |
2019-05-29 | The effect of atomic structure on the electrical response of aluminium oxide tunnel junctions | Many nanoelectronic devices rely on thin dielectric barriers through which
electrons tunnel. For instance, aluminium oxide barriers are used as Josephson
junctions in superconducting electronics. The reproducibility and drift of
circuit parameters in these junctions are affected by the uniformity,
morphology, and composition of the oxide barriers. To improve these circuits
the effect of the atomic structure on the electrical response of aluminium
oxide barriers must be understood. We create three-dimensional atomistic models
of aluminium oxide tunnel junctions and simulate their electronic transport
properties with the non-equilibrium Green's function formalism. Increasing the
oxide density is found to produce an exponential increase in the junction
resistance. In highly oxygen-deficient junctions we observe metallic channels
which decrease the resistance significantly. Computing the charge and current
density within the junction shows how variation in the local potential
landscape can create channels which dominate conduction. An atomistic approach
provides a better understanding of these transport processes and guides the
design of junctions for nanoelectronics applications. | 1905.12214v1 |
2019-09-06 | Structural, Surface Morphology and Magneto-Transport properties of Self Flux Grown Eu Doped Bi2Se3 Single Crystal | Here, we report the effect of europium (Eu) doping in Bi2Se3 topological
insulator (TI) by using different characterization techniques viz. X-ray
diffraction (XRD), scanning electron microscopy (SEM) coupled with energy
dispersive X-ray analysis (EDXA) and magneto-transport measurements.
Temperature dependent electrical resistivity curves revealed a metallic
behaviour both in the presence and absence of applied magnetic field.
Magneto-transport measurements showed a decrease in the magneto-resistance (MR)
value of the Eu0.1Bi1.9Se3 sample (32% at 5K) in comparison to the pure Bi2Se3
sample (80% at 5K). For, Eu0.1Bi1.9Se3 sample, a complex crossover between WL
and WAL phenomenon was observed at lower applied magnetic fields, whereas the
same was absent in case of the pristine one. Further, HLN (Hikami Larkin
Nagaoka) fitted magneto-conductivity (MC) analysis revealed a competing weak
anti localization (WAL) and weak localization (WL) behaviour. Summarily, in the
present work we study the structural, surface morphology and magneto-transport
properties of as grown Eu0.1Bi1.9Se3 single crystals. | 1909.02713v1 |
2019-09-12 | Magneto-transport and Shubnikov-de Haas oscillations in the layered ternary telluride Ta3SiTe6 topological semimetal | Topological semimetals characterize a novel class of quantum materials
hosting Dirac/Weyl fermions. The important features of topological fermions can
be exhibited by quantum oscillations. Here we report the magnetoresistance and
Shubnikov-de Haas (SdH) quantum oscillation of longitudinal resistance in the
single crystal of topological semimetal Ta3SiTe6 with the magnetic field up to
38 T. Periodic amplitude of the oscillations reveals related information about
the Fermi surface. The fast Fourier transformation spectra represent a single
oscillatory frequency. The analysis of the oscillations shows the Fermi pocket
with a cross-section area of 0.13 angstrom power minus 2. Combining
magneto-transport measurements and the first-principles calculation, we find
that these oscillations come from the hole pocket. Hall resistivity and the SdH
oscillations recommend that Ta3SiTe6 is a hole dominated system. | 1909.05564v1 |
2019-09-17 | A Thermal Resistance Network Model for Heat Conduction of Amorphous Polymers | Thermal conductivities (TCs) of the vast majority of amorphous polymers are
in a very narrow range, 0.1 $\sim$ 0.5 Wm$^{-1}$K$^{-1}$, although single
polymer chains possess TC of orders-of-magnitude higher. Entanglement of
polymer chains plays an important role in determining the TC of bulk polymers.
We propose a thermal resistance network (TRN) model for TC in amorphous
polymers taking into account the entanglement of molecular chains. Our model
explains well the physical origin of universally low TC observed in amorphous
polymers. The empirical formulae of pressure and temperature dependence of TC
can be successfully reproduced from our model not only in solid polymers but
also in polymer melts. We further quantitatively explain the anisotropic TC in
oriented polymers. | 1909.07607v1 |
2019-09-17 | A "road-map" of Nickelate superconductivity | We comment on the electronic structure of Nickelate system $Nd Ni O_2$ which
shows superconductivity on doping. The doped system $Nd_{0.8}Sr_{0.2}NiO_2$
shows (most probably unconventional) superconductivity with transition
temperatures ranging from $9~K$ to $15~K$\cite{dang}. The resistivity of the
parent compound $Nd NiO_2$ shows a minimum at around 60K, and an up-turn at
lower temperatures. In the current understanding it is thought to be
originating from a Kondo like coupling between mobile d-states of the $Nd~5d$
bands and un-paired electrons in $Ni 3d_{x^2-y^2}-O2p$ hybrid orbitals of
$Ni^{1+}$ and $O^{2-}$ions. In this note we offer alternative possibilities of
the observed resistance minimum in $LaNiO_2$. We attempt to construct a
"road-map" of various possibilities to comprehend the observed behaviour and
suggest further experiments to prove or disprove a given explanation. We also
compare and contrast Nickelates with Cuprates. Comparison points towards
unconventional superconductivity in Nickelates. | 1909.07688v1 |
2019-09-23 | Nanostructured La0.5Ba0.5CoO3 as cathode for solid oxide fuel cells | A simple method has been used to synthesize nanostructured La0.5Ba0.5CoO3
(LBCO) powders, by confining chemical precursors into the pores of
polycarbonate filters. The proposed method allows us to obtain powders formed
by crystallites of different sizes, it is scalable and does not involve the use
of sophisticated deposition techniques. The area specific polarization
resistance of symmetrical cells was studied to analyze the electrochemical
behavior of the LBCO nanostructures as cathodes for Solid-Oxide Fuel Cells. We
show that the performance is improved by reducing the size of the crystallites,
obtaining area specific resistance values of 0.2 Wcm2 at 700C, comparable with
newly developed cathodes using novel deposition techniques. | 1909.10611v1 |
2020-03-31 | In-situ grown single crystal aluminum as a non-alloyed ohmic contact to n-ZnSe by molecular beam epitaxy (MBE) | Novel ohmic contacts to n-ZnSe are demonstrated using single crystal Al films
deposited on epitaxially grown ZnSe (100) by molecular beam epitaxy (MBE).
Electron Backscatter Diffraction (EBSD) confirmed the single crystalline
structure of the Al films. The (110)-oriented Al layer was rotated rotated
45$^\circ$ relative to substrate to match the ZnSe (100) lattice constant. The
as-grown Al-ZnSe contact exhibited nearly ideal ohmic characteristics over a
large doping range of n-ZnSe without any additional treatment. The contact
resistances are in a range of 10$^{-3}$ $\Omega$-cm$^{2}$ for even lightly
doped ZnSe ($\sim$10$^{17}$ cm$^{-3}$). Leaky Schottky behavior in lightly
doped ZnSe samples suggested Al-ZnSe formed a low barrier height, Schottky
limit contact. In-situ grown Al could act as a simple metal contact to n-ZnSe
regardless of carrier concentration with lower resistance compared to other
reported contacts in literatures. The reported novel metallization method could
greatly simplify the ZnSe-based device fabrication complexity as well as lower
the cost | 2003.14411v2 |
2014-08-16 | Control of InGaAs facets using metal modulation epitaxy (MME) | Control of faceting during epitaxy is critical for nanoscale devices. This
work identifies the origins of gaps and different facets during regrowth of
InGaAs adjacent to patterned features. Molecular beam epitaxy (MBE) near SiO2
or SiNx led to gaps, roughness, or polycrystalline growth, but metal modulated
epitaxy (MME) produced smooth and gap-free "rising tide" (001) growth filling
up to the mask. The resulting self-aligned FETs were dominated by FET channel
resistance rather than source-drain access resistance. Higher As fluxes led
first to conformal growth, then pronounced {111} facets sloping up away from
the mask. | 1408.3714v1 |
2014-08-20 | Fluctuation Effects on the Transport Properties of Unitary Fermi Gases | In this letter, we investigate the fluctuation effects on the transport
properties of unitary Fermi gases in the vicinity of the superfluid transition
temperature $T_c$. Based on the time-dependent Ginzburg-Landau formalism of the
BEC-BCS crossover, we investigate both the residual resistivity below $T_c$
induced by phase slips and the paraconductivity above $T_c$ due to pair
fluctuations. These two effects have been well studied in the weak coupling BCS
superconductor, and here we generalize them to the unitary regime of ultracold
Fermi gases. We find that while the residual resistivity below $T_c$ increases
as one approaches the unitary limit, consistent with recent experiments, the
paraconductivity exhibits non-monotonic behavior. Our results can be verified
with the recently developed transport apparatus using mesoscopic channels. | 1408.4557v1 |
2017-01-11 | Morphology and mechanical properties of nanocrystalline Cu/Ag alloy | Hybrid Monte Carlo (MC)/molecular dynamics (MD) simulations are conducted to
study the microstructures of nanocrystalline (nc) Cu/Ag alloys with various Ag
concentrations. When the Ag concentration is below 50 Ag atoms/nm!, an increase
in Ag concentration leads to a gradual growth of monolayer grain boundary (GB)
complexions into nanolayer complexions. Above the concentration of 50 Ag
atoms/nm!, wetting layers with a bulk crystalline phase are observed. The
effects of Ag on mechanical properties and deformation mechanisms of nc Cu/Ag
alloys are investigated in MD simulations of uniaxial tension. GB sliding
resistance is found to first increase and then decrease with an increase in Ag
concentration. Surprisingly, we also find that the dislocation density
decreases monotonically with an increase in Ag concentration, which suggests
that the grain interiors are softened by the introduction of Ag dopants at GBs.
In addition, there is a critical Ag concentration that maximizes flow stress of
nc Cu/Ag alloys. The flow stress, GB sliding resistance, and the intragranular
dislocation densities become less sensitive to Ag dopants when the grain
diameter increases from 5nm to 40nm. | 1701.03013v1 |
2017-01-15 | Heat generation due to spin transport in spin valves | Using a macroscopic approach, we studied theoretically the heat generation
due to spin transport in a typical spin valve with nonmagnetic spacer layer of
finite thickness. Our analysis shows that the spin-dependent heat generation
can also be caused by another mechanism, the spin-conserving scattering in the
presence of spin accumulation gradient, in addition to the well-known spin-flip
scattering. The two mechanisms have equal contributions in semi-infinite
layers, such as the ferromagnetic layers of the spin valve. However, in the
nonmagnetic layer of a thickness much smaller than its spin-diffusion length,
the spin-dependent heat generation is dominated by the spin-flip scattering in
the antiparallel configuration, and by the spin-conserving scattering in the
parallel configuration. We also proved that the spin-dependent heat generation
cannot be interpreted as the Joule heating of the spin-coupled interface
resistance in each individual layer. An effective resistance is proposed as an
alternative so that the heat generation can still be described simply by
applying Joule's law to an equivalent circuit. | 1701.03984v1 |
2017-01-17 | Conditions for $T^2$ resistivity from electron-electron scattering | Many complex oxides (including titanates, nickelates and cuprates) show a
regime in which resistivity follows a power law in temperature ($\rho\propto
T^2$). By analogy to a similar phenomenon observed in some metals at low
temperature, this has often been attributed to electron-electron (Baber)
scattering. We show that Baber scattering results in a $T^2$ power law only
under several crucial assumptions which may not hold for complex oxides. We
illustrate this with sodium metal ($\rho_\text{el-el}\propto T^2$) and
strontium titanate ($\rho_\text{el-el}\not\propto T^2$). We conclude that an
observation of $\rho\propto T^2$ is not sufficient evidence for
electron-electron scattering. | 1701.04744v1 |
2017-01-30 | Negative differential resistance and magnetoresistance in zigzag borophene nanoribbons | We investigate the transport properties of pristine zigzag-edged borophene
nanoribbons (ZBNRs) of different widths, using the fist-principles
calculations. We choose ZBNRs with widths of 5 and 6 as odd and even widths.
The differences of the quantum transport properties are found, where even-N
BNRs and odd-N BNRs have different current-voltage relationships. Moreover, the
negative differential resistance (NDR) can be observed within certain bias
range in 5-ZBNR, while 6-ZBNR behaves as metal whose current rises with the
increase of the voltage. The spin filter effect of 36% can be revealed when the
two electrodes have opposite magnetization direction. Furthermore, the
magnetoresistance effect appears to be in even-N ZBNRs, and the maximum value
can reach 70%. | 1701.08501v1 |
2017-01-27 | Dynamics of a capacitive electret-based microcantilever for energy harvesting | In this paper, a novel electret-based capacitive energy harvesting device has
been developed according to out-of-plane gap closing scheme. The device is
composed of a micro cantilever and a substrate which form a variable capacitor
and is in series with a resistance. An electret material is used to provide the
bias voltage which is needed in capacitive energy harvesters in order to
scavenge energy from ambient vibration. The ambient vibration is applied to the
system as a harmonic base excitation. The motion equations and the
corresponding boundary conditions are derived using Hamilton's principle based
on Euler-Bernoulli beam theory and the Kirchhoff's voltage law is employed to
couple the mechanical and electrical fields. The equations of motion are
discretized using Galerkin procedure and integrated numerically over time.
Pull-in instability of the system is investigated in both static and dynamic
cases. The effect of various parameters on the behavior of the device is
studied. The maximum theoretical harvested power is resistance in the order of
1 micro-watt. | 1701.08843v1 |
2017-03-07 | Possible devil's staircase in the Kondo lattice CeSbSe | The temperature ($T$) - magnetic field ($H$) phase diagram for the tetragonal
layered compound CeSbSe, is determined from magnetization, specific heat, and
electrical resistivity measurements. This system exhibits complex magnetic
ordering at $T_{\rm{M}}$ $=$ 3 K and the application of a magnetic field
results in a cascade of magnetically ordered states for $H$ $\lesssim$ 1.8 T
which are characterized by fractional integer size steps: i.e., a possible
Devil's staircase is observed. Electrical transport measurements show a weak
temperature dependence and large residual resistivity which suggest a small
charge carrier density and strong scattering from the $f$-moments. These
features reveal Kondo lattice behavior where the $f$-moments are incompletely
screened, resulting in a fine balanced magnetic interaction between different
Ce neighbors that is mediated by the RKKY interaction. This produces the nearly
degenerate magnetically ordered states that are accessed under an applied
magnetic field. | 1703.02204v3 |
2017-03-07 | Strong Electron-Phonon Interaction and Colossal Magnetoresistance in EuTiO$_3$ | At low temperatures, EuTiO$_3$ system has very large resistivities and
exhibits colossal magnetoresistance. Based on a first principle calculation and
the dynamical mean-field theory for small polaron we have calculated the
transport properties of EuTiO$_3$. It is found that due to electron-phonon
interaction the conduction band may form a tiny subband which is close to the
Fermi level. The tiny subband is responsible for the large resistivity.
Besides, EuTiO$_3$ is a weak antiferromagnetic material and its magnetization
would slightly shift the subband via exchange interaction between conduction
electrons and magnetic atoms. Since the subband is close to the Fermi level, a
slight shift of its position gives colossal magnetoresistance. | 1703.02238v4 |
2018-10-06 | Impact of Angular Deviation from Coincidence Site Lattice Grain Boundaries on Hydrogen Segregation and Diffusion in Alpha-iron | Coincidence Site Lattice (CSL) grain boundaries (GBs) are believed to be
low-energy, resistant to intergranular fracture, as well as to hydrogen
embrittlement. Nevertheless, the behavior of CSL-GBs are generally confused
with their angular deviations. In the current study, the effect of angular
deviation from the perfect sigma3 (111) [1-10] GBs in Alpha-iron on the
hydrogen diffusion and the susceptibility of the GB to hydrogen embrittlement
is investigated through molecular static and dynamics simulations. By utilizing
Rice-Wang model it is shown that the ideal GB shows the highest resistance to
decohesion below the hydrogen saturation limit. Finally, the hydrogen
diffusivity along the ideal GB is observed to be the highest. | 1810.02988v1 |
2018-10-07 | Thermal properties of NbN single-photon detectors | We investigate thermal properties of a NbN single-photon detector capable of
unit internal detection efficiency. Using an independent calibration of the
coupling losses we determine the absolute optical power absorbed by the NbN
film and, via a resistive superconductor thermometry, the thermal resistance
Z(T) of the NbN film in dependence of temperature. In principle, this approach
permits a simultaneous measurement of the electron-phonon and phonon-escape
contributions to the energy relaxation, which in our case is ambiguous for
their similar temperature dependencies. We analyze the Z(T) within the
two-temperature model and impose an upper bound on the ratio of electron and
phonon heat capacities in NbN, which is surprisingly close to a recent
theoretical lower bound for the same quantity in similar devices. | 1810.03134v2 |
2018-10-16 | Quantitative and systematic analysis of bias dependence of spin accumulation voltage in a non-degenerate Si spin valve | Spin accumulation voltages in a non-degenerate Si spin valve are discussed
quantitatively as a function of electric bias current using systematic
experiments and model calculations. As an open question in semiconductor
spintronics, the origin of the deviation of spin accumulation voltages measured
experimentally in a non-degenerate Si spin valve is clarified from that
obtained by model calculation using the spin drift diffusion equation including
the effect of the spin-dependent interfacial resistance of tunneling barriers.
Unlike the case of metallic spin valves, the bias dependence of the
resistance-area product for a ferromagnet/MgO/Si interface, resulting in the
reappearance of the conductance mismatch, plays a central role to induce the
deviation. | 1810.06879v1 |
2019-02-19 | Nanoelectromechanical resonators from high-T$_c$ superconducting crystals of Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_{8+δ}$ | In this report, we present nanoelectromechanical resonators fabricated with
thin exfoliated crystals of a high-T$_c$ cuprate superconductor
Bi$_2$Sr$_2$Ca$_1$Cu$_2$O$_{8+\delta}$. The mechanical readout is performed by
capacitively coupling their motion to a coplanar waveguide microwave cavity
fabricated with a superconducting alloy of molybdenum-rhenium. We demonstrate
mechanical frequency tunability with external dc-bias voltage, and quality
factors up to 36600. Our spectroscopic and time-domain measurements show that
mechanical dissipation in these systems is limited by the contact resistance
arising from resistive outer layers. The temperature dependence of dissipation
indicates the presence of tunneling states, further suggesting that their
intrinsic performance could be as good as other two-dimensional atomic crystals
such as graphene. | 1902.06896v1 |
2020-02-10 | Structural and magneto-transport studies of iron intercalated Bi2Se3 single crystals | A detailed investigation on the structural and magneto-transport properties
of iron intercalated Bi2Se3 single crystals have been presented. The x-ray
diffraction and Raman studies confirm the intercalation of Fe in the van der
Waals gaps between the layers. The electrical resistivity of the compounds
decreases upon intercalation, and Hall resistivity shows the enhancement of the
charge carriers upon intercalation. The magnetoresistance shows the
non-saturating linear behavior at higher magnetic field and low temperature.
Intercalation of Fe increases the onset of the linear magnetoresistance
behavior, indicating the reduction in quantum effects. The Kohler scaling
employed on the magnetoresistance data indicates single scattering process for
all these compounds in the measured temperature range of 3- 300 K. | 2002.03609v2 |
2020-02-20 | Tunable correlation-driven symmetry breaking in twisted double bilayer graphene | A variety of correlated phases have recently emerged in select twisted van
der Waals (vdW) heterostructures owing to their flat electronic dispersions. In
particular, heterostructures of twisted double bilayer graphene (tDBG) manifest
electric field-tunable correlated insulating (CI) states at all quarter
fillings of the conduction band, accompanied by nearby states featuring
signatures suggestive of superconductivity. Here, we report electrical
transport measurements of tDBG in which we elucidate the fundamental role of
spontaneous symmetry breaking within its correlated phase diagram. We observe
abrupt resistivity drops upon lowering the temperature in the correlated
metallic phases neighboring the CI states, along with associated nonlinear
$I$-$V$ characteristics. Despite qualitative similarities to superconductivity,
concomitant reversals in the sign of the Hall coefficient instead point to
spontaneous symmetry breaking as the origin of the abrupt resistivity drops,
while Joule heating appears to underlie the nonlinear transport. Our results
suggest that similar mechanisms are likely relevant across a broader class of
semiconducting flat band vdW heterostructures. | 2002.08904v1 |
2020-03-31 | Efficiency Increase in Multijunction Monochromatic Photovoltaic Devices Due to Luminescent Coupling | We present a multijunction detailed balance model that includes the effects
of luminescent coupling, light trapping and nonradiative recombination,
suitable for treatment of multijunction solar cells and photonic power
converters -- photovoltaic devices designed to convert narrow-band light. The
model includes both specular and Lambertian reflections using a ray-optic
formalism and treats nonradiative processes using an internal radiative
efficiency. Using this model, we calculate and optimize the efficiency of
multijunction photonic power converters for a range of material qualities and
light-trapping schemes. Multijunction devices allow increased voltage with
lower current, decreasing series resistance losses. We show that efficiency
increases significantly with increased number of junctions, even without series
resistance, when the device has an absorbing substrate. Such an increase does
not occur when the device has a back reflector. We explain this effect using a
simplified model, which illustrates the origin of the decreased radiative
losses in multijunction devices on substrates. | 2004.00081v1 |
2020-04-15 | Theory for Non-Fermi Liquid Temperature Dependence in Resistivity of Ce_xLa_{1-x} Cu_{5.62} Au_{0.38} (x=0.02-0.10) on the Local Quantum Valence Criticality of Ce Impurities | It was reported by Shiino et al in J. Phys. Soc. Jpn. 86, 123705 (2017) that
Ce_xLa_{1-x} Cu_{5.62} Au_{0.38} (x=0.02-0.10) exhibits a new type of quantum
criticality in both magnetic and thermal properties, which is the same as that
observed in a series of materials exhibiting quantum critical valence
fluctuations (QCVF), such as \beta-YbAlB_4, Yb_{15}Al_{34}Au_{51}, and so on.
However, the temperature (T) dependence in the resistivity rho(T) for T<0.5K is
quite anomalous, i.e., \rho(T)\propto (const.-T^{n}) with n \simeq 0.75 at
x=0.05. We find that this anomalous exponent is given by n=2(1-\zeta), with
zeta being the weakly temperature dependent (0.5 \lsim \zeta \lsim 0.7)
critical exponent for the QCVF.The observed critical exponent n\simeq 0.75 at
x=0.05 is reproduced by choosing \zeta\simeq 0.63 which is consistent with the
divergent behavior observed in the uniform magnetic susceptibility \chi\propto
T^{-\zeta} with \zeta\simeq 0.67 at x=0.02. | 2004.06869v1 |
2020-04-20 | Anomalous pressure dependence of the electronic transport and anisotropy in SrIrO3 films | Iridate oxides display exotic physical properties that arise from the
interplay between a large spin-orbit coupling and electron correlations. Here,
we present a comprehensive study of the effects of hydrostatic pressure on the
electronic transport properties of SrIrO3 (SIO), a system that has recently
attracted a lot of attention as potential correlated Dirac semimetal. Our
investigations on untwinned thin films of SIO reveal that the electrical
resistivity of this material is intrinsically anisotropic and controlled by the
orthorhombic distortion of the perovskite unit cell. These effects provide
another evidence for the strong coupling between the electronic and lattice
degrees of freedom in this class of compounds. Upon increasing pressure, a
systematic increase of the transport anisotropies is observed. The anomalous
pressure-induced changes of the resistivity cannot be accounted for by the
pressure dependence of the density of the electron charge carriers, as inferred
from Hall effect measurements. Moreover, pressure-induced rotations of the IrO6
octahedra likely occur within the distorted perovskite unit cell and affect
electron mobility of this system. | 2004.09116v1 |
2022-02-07 | Time-correlation functions for odd Langevin systems | We investigate the statistical properties of fluctuations in active systems
that are governed by non-symmetric responses. Both an underdamped Langevin
system with an odd resistance tensor and an overdamped Langevin system with an
odd elastic tensor are studied. For a system in thermal equilibrium, the
time-correlation functions should satisfy time-reversal symmetry and the
anti-symmetric parts of the correlation functions should vanish. For the odd
Langevin systems, however, we find that the anti-symmetric parts of the
time-correlation functions can exist and that they are proportional to either
the odd resistance coefficient or the odd elastic constant. This means that the
time-reversal invariance of the correlation functions is broken due to the
presence of odd responses in active systems. Using the short-time asymptotic
expressions of the time-correlation functions, one can estimate an odd elastic
constant of an active material such as an enzyme or a motor protein. | 2202.03225v3 |
2022-02-24 | Resistivity anisotropy from the multiorbital Boltzmann equation in nematic FeSe | We compute the resistivity anisotropy in the nematic phase of FeSe from the
static solution of the multiorbital Boltzmann equation. By introducing disorder
at the level of the microscopic multiorbital model we show that even elastic
scattering by localized impurities may lead to non-trivial anisotropic
renormalization of the electronic velocities, challenging the usual
understanding of transport based only on cold- and hot-spots effects. Our model
takes into account both the $xz/yz$ and the recently proposed $xy$ nematic
ordering. We show that the latter one has a crucial role in order to reproduce
the experimentally-measured anisotropy, providing a direct fingerprint of the
different nematic scenarios on the bulk transport property of FeSe. | 2202.12070v2 |
2007-10-05 | Strain-induced insulator state in La_0.7Sr_0.3CoO_3 | We report on the observation of a strain-induced insulator state in
ferromagnetic La_0.7Sr_0.3CoO_3 films. Tensile strain above 1% is found to
enhance the resistivity by several orders of magnitude. Reversible strain of
0.15% applied using a piezoelectric substrate triggers huge resistance
modulations, including a change by a factor of 10 in the paramagnetic regime at
300 K. However, below the ferromagnetic ordering temperature, the magnetization
data indicate weak dependence on strain for the spin state of the Co ions. We
interpret the changes observed in the transport properties in terms of a
strain-induced splitting of the Co e_g levels and reduced double exchange,
combined with a percolation-type conduction in an electronic cluster state. | 0710.1306v1 |
2012-01-10 | Giant resistance change across the phase transition in spin crossover molecules | The electronic origin of a large resistance change in nanoscale junctions
incorporating spin crossover molecules is demonstrated theoretically by using a
combination of density functional theory and the non-equilibrium Green's
functions method for quantum transport. At the spin crossover phase transition
there is a drastic change in the electronic gap between the frontier molecular
orbitals. As a consequence, when the molecule is incorporated in a two terminal
device, the current increases by up to four orders of magnitude in response to
the spin change. This is equivalent to a magnetoresistance effect in excess of
3,000 %. Since the typical phase transition critical temperature for spin
crossover compounds can be extended to well above room temperature, spin
crossover molecules appear as the ideal candidate for implementing spin devices
at the molecular level. | 1201.2028v2 |
2014-01-08 | The features of contact resistivity behavior at helium temperatures for InP- and GaAs-based ohmic contacts | Contact resistivity rc of InP and GaAs based ohmic contacts was measured in
the 4.2/300 K temperature range. Nonmonotonic dependences rc(T), with a minimum
at temperature 50 K (150 K) for InP (GaAs) based contacts were obtained. The
results can be explained within the framework of the mechanism of current flow
through metal shunts (associated with dislocations) penetrating into the
semiconductor bulk, with allowance being made for electron freeze-out at helium
temperatures. Contact ohmicity in the 4.2/30K temperature range is due to
accumulation band bending near shunt ends at the metal/semiconductor interface. | 1401.1658v1 |
2016-03-16 | Mathematical Modeling of CRISPR-CAS system effects on biofilm formation | Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), linked
with CRISPR associated (CAS) genes, play a profound role in the interactions
between phage and their bacterial hosts. It is now well understood that
CRISPR-CAS systems can confer adaptive immunity against bacteriophage
infections. However, the possibility of failure of CRISPR immunity may lead to
a productive infection by the phage (cell lysis) or lysogeny. Recently,
CRISPR-CAS genes have been implicated in changes to group behaviour, including
biofilm formation, of the bacterium Pseudomonas aeruginosa when lysogenized.
For lysogens with a CRISPR system, another recent experimental study suggests
that bacteriophage re-infection of previously lysogenized bacteria may lead to
cell death. Thus CRISPR immunity can have complex effects on phage-host-lysogen
interactions, particularly in a biofilm. In this contribution, we develop and
analyse a series of models to elucidate and disentangle these interactions.
From a therapeutic standpoint, CRISPR immunity increases biofilm resistance to
phage therapy. Our models predict that lysogens may be able to displace
CRISPR-immune bacteria in a biofilm, and thus suggest strategies to eliminate
phage resistant biofilms. | 1603.05311v1 |
2017-04-10 | Experimental determination of phonon thermal conductivity and Lorenz ratio of single crystal bismuth telluride | We use a magnetothermal resistance method to measure the lattice thermal
conductivity of a single crystal of Bi$_2$Te$_3$ from 5 to 60 K. We apply a
large transverse magnetic field to suppress the electronic thermal conduction
while measuring thermal conductivity and electrical resistivity. The lattice
thermal conductivity is then calculated by extrapolating the thermal
conductivity versus electrical conductivity curve to a zero electrical
conductivity value. Our results show that the measured phonon thermal
conductivity follows the $e^{({\Delta}_{min}/T)}$ temperature dependence and
the Lorenz ratio corresponds to the modified Sommerfeld value in the
intermediate temperature range. Our low-temperature experimental data and
analysis on Bi$_2$Te$_3$ are an important compliment to previous measurements
of Goldsmid [14] and theoretical calculations by Broido $\textit{et al.}$ [21]
at higher temperature 100 - 300 K. | 1704.03029v1 |
2017-04-12 | Metal-Insulator Transition in Ga doped ZnO via Controlled Thickness | We report thickness dependent metal insulator transition in Ga doped ZnO
(Ga:ZnO) thin films grown by pulsed laser deposition technique. From the
electrical transport measurements, we find that while the thinnest film
exhibits a resistivity of 0.05 $\Omega$-cm, lying in the insulating regime, the
thickest has resistivity of $6.6\times10^{-4}\Omega$-cm which shows metallic
type of conduction. Our analysis reveals that the Mott's variable range hopping
(VRH) model governs the insulating behavior in the thinner Ga:ZnO whereas the
2D weak localization phenomena is appropriate to explain the electron transport
in the thicker Ga:ZnO. Magnetoresistance study further confirms the presence of
strong localization in 6 nm film while weak localization is observed in 20 nm
and above thicker films. From the density functional calculations, it is found
that due to surface reconstruction and Ga doping, strong crystalline disorder
sets in very thin films to introduce localized states and thereby, restricts
the donor electron mobility. | 1704.03846v1 |
2017-04-24 | Spin injection into silicon detected by broadband ferromagnetic resonance spectroscopy | We studied the spin injection in a NiFe(Py)/Si system using broadband
ferromagnetic resonance spectroscopy. The Gilbert damping parameter of the Py
layer on top of the Si channel was determined as a function of the Si doping
concentration and Py layer thickness. For fixed Py thickness we observed an
increase of the Gilbert damping parameter with decreasing resistivity of the Si
channel. For a fixed Si doping concentration we measured an increasing Gilbert
damping parameter for decreasing Py layer thickness. No increase of the Gilbert
damping parameter was found Py/Si samples with an insulating interlayer. We
attribute our observations to an enhanced spin injection into the
low-resistivity Si by spin pumping. | 1704.07006v1 |
2017-05-27 | Magnetic and magnetotransport properties of ThCr2Si2-type Ce2O2Bi composed of conducting Bi2- square net and magnetic Ce-O layer | ThCr2Si2-type Ce2O2Bi epitaxial thin films were grown by recently developed
multilayer solid phase epitaxy. The ionic state of Ce was confirmed to be 3+ by
x-ray photoelectron spectroscopy, corresponding to the electronic configuration
of [Xe]4f1. Electrical resistivity showed the nonmonotonic temperature
dependence with a sharp resistivity maximum, concomitant with a magnetization
kink at 10 K, suggesting antiferromagnetic transition. In addition,
magnetoresistance showed a large angular-dependent magnetoresistance. These
results imply that carrier transport in the Bi2- square net could be influenced
by magnetic ordering in the Ce-O layer owing to its unique layered structure
[Bi2-/(Ce2O2)2+], particularly in the form of epitaxial thin films. | 1705.09774v1 |
2017-07-03 | Inverse spin Hall effect in Nd doped SrTiO3 | Conversion of spin to charge current was observed in SrTiO3 doped with Nd
(Nd:STO), which exhibited a metallic behavior even with low concentration
doping. The obvious variation of DC voltages for Py/Nd:STO, obtained by
inverting the spin diffusion direction, demonstrated that the detected signals
contained the contribution from the inverse spin Hall effect (ISHE) induced by
the spin dependent scattering from Nd impurities with strong spin-orbit
interaction. The DC voltages of the ISHE for Nd:STO were measured at different
microwave frequency and power, which revealed that spin currents were
successfully injected into doped STO layer by spin pumping. The linear relation
between the ISHE resistivity and the resistivity induced by impurities implied
that the skew scattering was the dominant contribution in this case, and the
spin Hall angle was estimated to be 0.17%. This work demonstrated that
extrinsic spin dependent scattering in oxides can be used in spintroics besides
that in heavy elements doped metals. | 1707.00444v1 |
2017-07-27 | Chiral transport along magnetic domain walls in the quantum anomalous Hall effect | The recent prediction, and subsequent discovery, of the quantum anomalous
Hall (QAH) effect in thin films of the three-dimensional ferromagnetic
topological insulator (MTI) (Cr$_y$Bi$_x$Sb$_{1-x-y}$)$_2$Te$_3$ has opened new
possibilities for chiral-edge-state-based devices in zero external magnetic
field. Like the $\nu=1$ quantum Hall system, the QAH system is predicted to
have a single chiral edge mode circulating along the boundary of the film.
Backscattering of the chiral edge mode should be suppressed, as recently
verified by the observation of well-quantized Hall resistivities $\rho_{yx} =
\pm h/e^2$, along with longitudinal resistivities as low as a few ohms.
Dissipationless 1D conduction is also expected along magnetic domain walls.
Here, we intentionally create a magnetic domain wall in a MTI and study
electrical transport along the domain wall. We present the first observation of
chiral transport along domain walls, in agreement with theoretical predictions.
We present further evidence that two modes equilibrate and co-propagate along
the length of the domain wall. | 1707.08677v1 |
2018-08-20 | Theory of bilinear magneto-electric resistance from topological-insulator surface states | We theoretically investigate a new kind of nonlinear magnetoresistance on the
surface of three-dimensional topological insulators (TIs). At variance with the
unidirectional magnetoresistance (UMR) effect in magnetic bilayers, this
nonlinear magnetoresistance does not rely on a conducting ferromagnetic layer
and scales linearly with both the applied electric and magnetic fields; for
this reason, we name it bilinear magneto-electric resistance (BMER). We show
that the sign and the magnitude of the BMER depends sensitively on the
orientation of the current with respect to the magnetic field as well as the
crystallographic axes -- a property that can be utilized to map out the spin
texture of the topological surface states via simple transport measurement,
alternative to the angle-resolved photoemission spectroscopy (ARPES). | 1808.06339v1 |
2018-08-28 | Impact of antiferromagnetic order on Landau level splitting of quasi-two-dimensional Dirac fermions in EuMnBi$_2$ | We report spin-split Landau levels of quasi-two-dimensional Dirac fermions in
a layered antiferromagnet EuMnBi$_2$, as revealed by interlayer resistivity
measurements in a tilted magnetic field up to $\sim$35 T. The amplitude of
Shubnikov-de Haas (SdH) oscillation in interlayer resistivity is strongly
modulated by changing the tilt angle of the field, i.e., the
Zeeman-to-cyclotron energy ratio. The effective $g$ factor estimated from the
tilt angle, where the SdH oscillation exhibits a phase inversion, differs by
approximately 50% between two antiferromagnetic phases. This observation
signifies a marked impact of the magnetic order of Eu sublattice on the
Dirac-like band structure. The origin may be sought in strong exchange coupling
with the local Eu moments, as verified by the first-principles calculation. | 1808.09424v1 |
2018-08-31 | Absence of superconductivity in pulsed laser deposited Au/Ag modulated nanostructured thin films | We have grown Au/Ag modulated nanostructured thin films by pulsed laser
deposition using metallic targets. The growths performed at room temperature
involved deposition of alternate layers of the two metals with larger thickness
of Au and much lower thickness of Ag (two cases) on crystalline silicon (100)
and quartz substrates. However, the characterization revealed that
nanostructured configuration is realized in the film. We characterized the
films by x-ray diffraction (XRD), Field emission scanning electron microscopy
(FESEM) with energy dispersive analysis of x-rays (EDAX), magnetization (M-T)
and resistivity (Rho-T) measurements. The magnetization and resistivity
measurements confirm that there is no signature of superconducting transition
within the temperature range of 5K to 300K studied in these films. | 1808.10699v1 |
2019-03-02 | Turning ZrTe5 into semiconductor through atomic intercalation | In this work, we use the liquid ammonia method to successfully intercalate
potassium atoms into ZrTe5 single crystal, and find a transition from semimetal
to semiconductor at low temperature in the intercalated ZrTe5. The resistance
anomalous peak is gradually suppressed and finally disappears with increasing
potassium concentration. Whilst, the according sign reversal is always observed
in the Hall resistance measurement. We tentatively attribute the
semimetal-semiconductor transition to the lattice expansion induced by atomic
intercalation and thereby a larger energy band gap. | 1903.00644v1 |
2019-03-23 | An In-situ Annealing effect of Graphene-Graphene Interlayer Conduction | An interlayer distance modulation in twisted bilayer graphene is reported.
This is achieved by an in-situ annealing technique. The transformation of
systematic vacuum and hydrogen annealing effects in twisted bilayer CVD
graphene on SiO2 surface is reported based on experimental results. Incoherent
interlayer conduction is observed in the twisted bilayer device. In-situ
annealing efficiently removes the residues in the graphene-to-graphene
interface and enhances the interlayer conduction. We demonstrate
graphene-to-graphene interlayer resistance modulated by an order of magnetite
at 5 K. We also report on the behavior of molecular hydrogen on graphene
interlayer using the gate voltage-dependent resistance as a function of
temperature at atmospheric pressure. It was observed that interlayer conduction
in hydrogen/argon gas ambient is reduced. Results imply that modulation in the
interlayer distance of graphene-to-graphene junction, as determined by the
transport measurement investigation. Overall this result leads to the
possibility of making electrically tunable devices using twisted bilayer
graphene. | 1903.09899v2 |
2019-04-05 | Effect of density on microwave-induced resistance oscillations in back-gated GaAs quantum wells | We report on microwave-induced resistance oscillations (MIROs) in a
tunable-density 30-nm-wide GaAs/AlGaAs quantum well. We find that the MIRO
amplitude increases dramatically with carrier density. Our analysis shows that
the anticipated increase in the effective microwave power and quantum lifetime
with density is not sufficient to explain the observed growth of the amplitude.
We further observe that the fundamental oscillation extrema move towards
cyclotron resonance with increasing density, which also contradicts theoretical
predictions. These findings reveal that the density dependence is not properly
captured by existing theories, calling for further studies. | 1904.03140v1 |
2019-04-18 | Determining Phonon Mean Free Path Spectrum by Ballistic Phonon Resistance within a Nanoslot-Patterned Thin Film | At micro- to nano-scales, classical size effects in heat conduction play an
important role in suppressing the thermal transport process. Such effects occur
when the characteristic lengths become commensurate to the mean free paths
(MFPs) of heat carriers that are mainly phonons for nonmetallic crystals.
Beyond existing experimental efforts on thin films using laser-induced thermal
gratings, this work provides the complete theoretical analysis for a new
approach to extract the effective phonon MFP distribution for the in-plane heat
conduction within a thin film or flake-like sample. In this approach, nanoslots
are patterned on a suspended thin film. Phonons will transport ballistically
through the neck region between adjacent nanoslots if the phonon MFPs are much
longer than the neck width. The associated "ballistic thermal resistance" for
varied neck dimensions can then be used to reconstruct the phonon MFP
distribution within the film. The technique can be further extended to
two-dimensional materials when the relaxation time approximation is reasonably
accurate. | 1904.08956v2 |
2019-08-23 | Anomalous Kerr Effect in SrRuO$_3$ Thin Films | We study the magneto-optical Kerr effect (MOKE) in SrRuO$_3$ thin films,
uncovering wide regimes of wavelength, temperature, and magnetic field where
the Kerr rotation is not simply proportional to the magnetization but instead
displays two-component behavior. One component of the MOKE signal tracks the
average magnetization, while the second "anomalous" component bears a
resemblance to anomalies in the Hall resistivity which have been previously
reported in skyrmion materials. We present a theory showing that the MOKE
anomalies arise from the non-monotonic relation between the Kerr angle and the
magnetization, when we average over magnetic domains which proliferate near the
coercive field. Our results suggest that inhomogeneous domain formation, rather
than skyrmions, may provide a common origin for the observed MOKE and Hall
resistivity anomalies. | 1908.08974v2 |
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