publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2016-04-25 | Anisotropic transport and optical spectroscopy study on antiferromagentic triangular lattice EuCd_2As_2: an interplay between magnetism and charge transport properties | We present anisotropic transport and optical spectroscopy studies on
EuCd_2As_2. The measurements reveal that EuCd_2As_2 is a low carrier density
semimetal with moderate anisotropic resistivity ratio. The charge carriers
experience very strong scattering from Eu magnetic moments, resulting in a
Kondo-like increase of resistivity at low temperature. Below the
antiferromagnetic transition temperature at $T_N$= 9.5 K, the resistivity drops
sharply due to the reduced scattering from the ordered Eu moments.
Nevertheless, the anisotropic ratio of $\rho_c/\rho_{ab}$ keeps increasing,
suggesting that the antiferromagnetic coupling is along the c-axis. The optical
spectroscopy measurement further reveals, besides an overdamped reflectance
plasma edge at low energy, a strong coupling between phonon and electronic
continuum. Our study suggests that EuCd_2As_2 is a promising candidate
displaying intriguing interplay among charge, magnetism and the underlying
crystal lattice. | 1604.07114v2 |
2016-04-26 | Multiband effects and the possible Dirac states in LaAgSb$_2$ | Here we report the possible signature of Dirac fermions in the
magnetoresistance, Hall resistivity and magnetothermopower of LaAgSb$_2$. The
opposite sign between Hall resistivity and Seebeck coefficient indicates the
multiband effect. Electronic structure calculation reveals the existence of the
linear bands and the parabolic bands crossing the Fermi level. The large linear
magnetoresistance was attributed to the quantum limit of the possible Dirac
fermions or the breakdown of weak-field magnetotransport at the charge density
wave phase transition. Analysis of Hall resistivity using two-band model
reveals that Dirac holes which dominate the electronic transport have much
higher mobility and larger density than conventional electrons. Magnetic field
suppresses the apparent Hall carrier density, and also induces the sign change
of the Seebeck coefficient from negative to positive. These effects are
possibly attributed to the magnetic field suppression of the density of states
at the Fermi level originating from the quantum limit of the possible Dirac
holes. | 1604.07819v1 |
2016-04-27 | Superconductivity at 7.8 K in the ternary LaRu2As2 compound | Here we report the discovery of superconductivity in the ternary LaRu2As2
compound. The polycrystalline LaRu2As2 samples were synthesized by the
conventional solid state reaction method. Powder X-ray diffraction analysis
indicates that LaRu2As2 crystallizes in the ThCr2Si2-type crystal structure
with the space group I4/mmm (No. 139), and the refined lattice parameters are a
= 4.182(6) {\AA} and c = 10.590(3) {\AA}. The temperature dependent resistivity
measurement shows a clear superconducting transition with the onset Tc
(critical temperature) at 7.8 K, and zero resistivity happens at 6.8 K. The
upper critical field at zero temperature m0Hc2(0) was estimated to be 1.6 T
from the resistivity measurement. DC magnetic susceptibility measurement shows
a bulk superconducting Meissner transition at 7.0 K, and the isothermal
magnetization measurement indicates that LaRu2As2 is a type-II superconductor. | 1604.07958v1 |
2016-06-02 | First-principles calculation of the stabilities of lithium garnet compositions against hydration | A series of density functional electronic structure calculations were carried
out to better understand the crystallographic factors governing the stability
of LinA3B2O12 lithium garnet phases against hydration. The reaction studied is
H2O + LinA3B2O12 = LiOH + HnA3B2O12. Most of the compositions are stable
against pure water; the main driving force for instability in the atmosphere is
the reaction of lithium hydroxide with CO2 to make lithium carbonate. The
calculated hydration resistance scales with the Pauling bond valence on the
oxygen atom contributed by the coordinating A and B ions. In the unexchanged
Li-garnets, this bond valence must be balanced by lithium, so there is also a
good overall correlation of hydration stability with lithium stoichiometry (n):
hydration resistance increases in the order Li8-garnet < Li7-garnet <
Li6-garnet < Li5-garnet < Li3-garnet. Only Li3A3B2O12 garnets have proton
exchange energies sufficiently positive to overcome the decomposition energy of
lithium hydroxide into lithium carbonate + water; the n=3 garnets are predicted
to be stable to hydration under atmospheric conditions, in agreement with
observations (Galven et al. Chem. Mater. 2012 24, 3335-3345). At a given
lithium ion stoichiometry, hydration resistance is greater for A, B ions having
smaller ionic radii. | 1606.01807v1 |
2016-06-07 | The temperature dependence of FeRh's transport properties | The finite-temperature transport properties of FeRh compounds are
investigated by first-principles Density Functional Theory-based calculations.
The focus is on the behavior of the longitudinal resistivity with rising
temperature, which exhibits an abrupt decrease at the metamagnetic transition
point, $T = T_m$ between ferro- and antiferromagnetic phases. A detailed
electronic structure investigation for $T \geq 0$ K explains this feature and
demonstrates the important role of (i) the difference of the electronic
structure at the Fermi level between the two magnetically ordered states and
(ii) the different degree of thermally induced magnetic disorder in the
vicinity of $T_m$, giving different contributions to the resistivity. To
support these conclusions, we also describe the temperature dependence of the
spin-orbit induced anomalous Hall resistivity and Gilbert damping parameter.
For the various response quantities considered the impact of thermal lattice
vibrations and spin fluctuations on their temperature dependence is
investigated in detail. Comparison with corresponding experimental data finds
in general a very good agreement. | 1606.02072v1 |
2016-06-21 | Bad-Metal Relaxation Dynamics in a Fermi Lattice Gas | We report the discovery of phenomena consistent with bad-metal relaxation
dynamics in the metallic regime of an optical-lattice Hubbard model. The
transport lifetime induced by inter-particle scattering for a mass current of
atoms excited by stimulated Raman transitions is measured, and the
corresponding analog of resistivity is inferred. By exploring a range of
temperature, we demonstrate incompatibility with weak-scattering theory and a
key characteristic of bad metals: anomalous resistivity scaling consistent with
$T$-linear behavior. We also observe the onset of two behaviors---incoherent
transport and the approach to the Mott-Ioffe-Regel limit---associated with bad
metals. The interaction and temperature scaling of resistivity are verified to
be consistent with dynamic mean-field theory (DMFT) predictions of a bad metal,
which is associated with the reduction of quasiparticle weight by strong
interactions. | 1606.06669v5 |
2016-07-11 | The modification of the pore characteristics of activated carbon, for use in electrical double layer capacitors, through plasma processing | It was aimed to determine whether plasma processing could contribute to
enhanced capacitance and energy density of activated carbon electrode based
electrochemical capacitors, through the formation of additional surface
charges. While an increase of up to 35% of the gravimetric capacitance, along
with ~ 20% decrease in resistance, was obtained through optimal plasma
processing, increased plasma exposure yielded a drastic reduction (/increase)
in the capacitance (/resistance). It was also found that the capacitance and
resistance modulation was a sensitive function of sample processing as well as
electrochemical testing procedure. Considering the complexity of modeling
realistic porous matrices, a metric to parameterize the reach of an electrolyte
into the matrix has been posited. | 1607.03201v1 |
2016-07-15 | Chiral Phonons and Electrical Resistivity of Ferromagnetic Metals at Low Temperatures | Ferromagnetism is an exciting phase of matter exhibiting strongly correlated
electron behavior and a standard example of spontaneously broken rotational
symmetry: below the Curie temperature, atomic magnets in an isotropic
single-domain ferromagnetic metal align along a spontaneously chosen direction.
The scattering of conduction electrons from thermal perturbations to this spin
order, together with electron-electron collisions, mark the material electrical
behavior at low temperatures, where the resistivity varies mostly quadratically
with the temperature. Around liquid-helium temperatures however, an interesting
phenomenon occurs, giving rise to an extra \emph{linear} contribution to the
variation of the electrical resistivity with temperature, whose theoretical
explanation has encountered problems for a long time. Here I introduce a
spin-flip scattering mechanism of conduction electrons in ferromagnetic metals
arising from their interaction with the internal magnetic induction and
mediated by chiral modes of the crystal lattice vibrations carrying spin 1.
This mechanism is able to explain the above anomaly and give a good account of
the spin-lattice relaxation times of iron, cobalt and nickel at room
temperatures. | 1607.04585v2 |
2016-11-01 | Boundary conditions and heat resistance at the moving solid--liquid interface | Boundary conditions for the solid-liquid interface of the solidifying pure
melt have been derived. In the derivation the model of Gibbs interface is used.
The boundary conditions include both the state quantities of bulk phases are
taken at the interface and the quantities characterizing interfacial surface
such as the surface temperature and the surface heat flux. Introduction of the
surface temperature as an independent variable allows us to describe the
scattering energy at the interface. For the steady-state motion of the planar
interface the expression for the temperature discontinuity across the phase
boundary has been obtained. Effect of Kapitza resistance on the interface
velocity is considered. It is shown that heat resistance leads to non-linearity
in solidification kinetics, namely, in "velocity-undercooling" relationship.
The conditions of the steady--state motion of the planar interface has been
found. | 1611.00160v1 |
2017-06-01 | Edge transport in InAs and InAs/GaSb quantum wells | We investigate low-temperature transport through single InAs quantum wells
and broken-gap InAs/GaSb double quantum wells. Non-local measurements in the
regime beyond bulk pinch-off confirm the presence of edge conduction in InAs
quantum wells. The edge resistivity of 1-2 $\mathrm{k\Omega/\mu m}$ is of the
same order of magnitude as edge resistivities measured in the InAs/GaSb double
quantum well system. Measurements in tilted magnetic field suggests an
anisotropy of the conducting regions at the edges with a larger extent in the
plane of the sample than normal to it. Finger gate samples on both material
systems shine light on the length dependence of the edge resistance with the
intent to unravel the nature of edge conduction in InAs/GaSb coupled quantum
wells. | 1706.00320v1 |
2017-09-21 | Zero-Field Quantum Critical Point in Ce$_{0.91}$Yb$_{0.09}$CoIn$_5$ | We present results of specific heat, electrical resistance, and
magnetoresistivity measurements on single crystals of the heavy-fermion
superconducting alloy Ce$_{0.91}$Yb$_{0.09}$CoIn$_5$. Non-Fermi liquid to Fermi
liquid crossovers are clearly observed in the temperature dependence of the
Sommerfeld coefficient $\gamma$ and resistivity data. Furthermore, we show that
the Yb-doped sample with $x=0.09$ exhibits universality due to an underlying
quantum phase transition without an applied magnetic field by utilizing the
scaling analysis of $\gamma$. Fitting of the heat capacity and resistivity data
based on existing theoretical models indicates that the zero-field quantum
critical point is of antiferromagnetic origin. Finally, we found that at zero
magnetic field the system undergoes a third-order phase transition at the
temperature $T_{c3}\approx 7$ K. | 1709.07161v3 |
2017-12-01 | Titanium Contacts to Graphene: Process-Induced Variability in Electronic and Thermal Transport | Contact Resistance (RC) is a major limiting factor in the performance of
graphene devices. RC is sensitive to the quality of the interface and the
composition of the contact, which are affected by the graphene transfer process
and contact deposition conditions. In this work, a linear correlation is
observed between the composition of Ti contacts, characterized by X-ray
photoelectron spectroscopy, and the Ti/graphene (Gr) contact resistance
measured by the transfer length method. We find that contact composition is
tunable via deposition rate and base pressure. Reactor base pressure is found
to effect the resultant contact resistance. The effect of contact deposition
conditions on thermal transport measured by time-domain thermoreflectance is
also reported and interfaces with higher oxide composition appear to result in
a lower thermal boundary conductance. Possible origins of this thermal boundary
conductance change with oxide composition are discussed. | 1712.00331v1 |
2017-12-04 | Particle-hole symmetry reveals failed superconductivity in the metallic phase of two-dimensional superconducting films | Electrons confined to two dimensions display an unexpected diversity of
behaviors as they are cooled to absolute zero. Noninteracting electrons are
predicted to eventually "localize" into an insulating ground state, and it has
long been supposed that electron correlations stabilize only one other phase:
superconductivity. However, many two-dimensional (2D) superconducting materials
have shown surprising evidence for metallic behavior, where the electrical
resistivity saturates in the zero-temperature limit, the nature of this
unexpected metallic state remains under intense scrutiny. We report electrical
transport properties for two disordered 2D superconductors, indium oxide and
tantalum nitride, and observe a magnetic field-tuned transition from a true
superconductor to a metallic phase with saturated resistivity. This metallic
phase is characterized by a vanishing Hall resistivity, suggesting that it
retains particle-hole symmetry from the disrupted superconducting state. | 1712.00947v1 |
2018-01-15 | A study of electron and thermal transport in layered Titanium disulphide single crystals | We present a detailed study of thermal and electrical transport behavior of
single crystal Titanium disulphide flakes, which belongs to the two
dimensional, transition metal dichalcogenide class of materials. In-plane
Seebeck effect measurements revealed a typical metal-like linear temperature
dependence in the range of 85 - 285 K. Electrical transport measurements with
in-plane current geometry exhibited a nearly T^2 dependence of resistivity in
the range of 10 - 300 K. However, transport measurements along the out-of-plane
current geometry showed a transition in temperature dependence of resistivity
from T^2 to T^5 beyond 200 K. Interestingly, Au ion-irradiated TiS2 samples
showed a similar T 5 dependence of resistivity beyond 200 K, even in the
current-in-plane geometry. Micro- Raman measurements were performed to study
the phonon modes in both pristine and ion-irradiated TiS2 crystals. | 1801.04677v1 |
2018-02-23 | Possible charge-density-wave signatures in the anomalous resistivity of Li-intercalated multilayer MoS2 | We fabricate ion-gated field-effect transistors (iFET) on mechanically
exfoliated multilayer MoS$_2$. We encapsulate the flake by Al$_2$O$_3$, leaving
the device channel exposed at the edges only. A stable Li$^+$ intercalation in
the MoS$_2$ lattice is induced by gating the samples with a Li-based polymeric
electrolyte above $\sim$ 330 K and the doping state is fixed by quenching the
device to $\sim$ 300 K. This intercalation process induces the emergence of
anomalies in the temperature dependence of the sheet resistance and its first
derivative, which are typically associated with structural/electronic/magnetic
phase transitions. We suggest that these anomalies in the resistivity of
MoS$_2$ can be naturally interpreted as the signature of a transition to a
charge-density-wave phase induced by lithiation, in accordance with recent
theoretical calculations. | 1802.08449v2 |
2018-03-13 | Are thermal fluctuations the sole reason for finite longitudinal resistance in quantum anomalous Hall experiments? | In some recent experiments [A. J. Bestwick, et. al., Phys. Rev. Lett. 114,
187201 (2015), Cui-Zu Chang, et. al., Nat. Materials. 14, 473-477 (2015)] it
has been shown that in observations of the quantum anomalous Hall (QAH) effect
the longitudinal resistance $R_L$ increases as temperature $T$ increases, while
Hall resistance $R_H$ loses its quantization with increase in $T$. This
behavior was explained due to increased thermal fluctuations as $T$ increases.
We show that similar effects arise in QAH samples with quasi-helical edge modes
as disorder increases in presence of inelastic scattering or otherwise even at
temperature $T=0$. | 1803.04995v2 |
2018-03-21 | Bad metallic transport in a modified Hubbard model | Strongly correlated metals often display anomalous transport, including
$T$-linear resistivity above the Mott-Ioffe-Regel limit. We introduce a
tractable microscopic model for such bad metals, by supplementing the
well-known Hubbard model --- with hopping $t$ and on-site repulsion $U$ ---
with a `screened Coulomb' interaction between charge densities that decays
exponentially with spatial separation. This interaction entirely lifts the
extensive degeneracy in the spectrum of the $t=0$ Hubbard model, allowing us to
fully characterize the small $t$ electric, thermal and thermoelectric transport
in our strongly correlated model. Throughout the phase diagram we observe
$T$-linear resistivity above the Mott-Ioffe-Regel limit, together with strong
violation of the Weidemann-Franz law and a large thermopower that can undergo
sign change. At intermediate temperatures $t \ll k_B T \lesssim U$, the
approximate $T$-linear resistivity arises from a cancellation between the
nontrivial temperature dependence of both diffusivities and thermodynamic
susceptibilities, as observed in recent transport experiments on cold atomic
gases. | 1803.08054v3 |
2018-04-06 | Energy-Quality Scaling in Analog Mesh Computers | The recent push for post-Moore computer architectures has introduced a wide
variety of application-specific accelerators. One particular accelerator, the
resistance network analogue, has been well received due to its ability to
efficiently solve partial differential equations by eliminating the iterative
stages required by today's numerical solvers. However, in the ago of
programmable integrated circuits, the static nature of the resistance network
analogue, and other analog mesh computers like it, has relegated it to an
academic curiosity. Recent developments in materials, such as the memristor,
have made the resistance network analogue viable for inclusion in future
heterogeneous computer architectures. However, selection of an appropriate
sized mesh to be incorporated into a computer system requires that
energy-quality trade-offs are made regarding the problem size and required
resolution of the solution. This paper provides an in-depth study of the
scaling of analog mesh computer hardware, from the perspective of energy per
bit and required resolution, introduces a metric to aid in quantifying analog
mesh computers with different parameters, and introduces a method of
virtualization which enables an analog mesh computer of a fixed size to
approximate the calculations of a larger-sized mesh. | 1804.02389v2 |
2018-04-28 | Nonequilibrium Mean-Field Theory of Resistive Phase Transitions | We investigate the quantum mechanical origin of resistive phase transitions
in solids driven by a constant electric field in the vicinity of a
metal-insulator transition. We perform a nonequilibrium mean-field analysis of
a driven-dissipative anti-ferromagnet, which we solve analytically for the most
part. We find that the insulator-to-metal transition (IMT) and the
metal-to-insulator transition (MIT) proceed by two distinct electronic
mechanisms: Landau-Zener processes, and the destabilization of metallic state
by Joule heating, respectively. However, we show that both regimes can be
unified in a common effective thermal description, where the effective
temperature $T_{\rm eff}$ depends on the state of the system. This explains
recent experimental measurements in which the hot-electron temperature at the
IMT was found to match the equilibrium transition temperature. Our analytic
approach enables us to formulate testable predictions on the non-analytic
behavior of $I$-$V$ relation near the insulator-to-metal transition. Building
on these successes, we propose an effective Ginzburg-Landau theory which paves
the way to incorporating spatial fluctuations, and to bringing the theory
closer to a realistic description of the resistive switchings in correlated
materials. | 1804.10733v1 |
2018-09-24 | Fusion Between Frozen-Wave-Type Beams and Airy-Type Pulses: Diffraction-Dispersion-Attenuation Resistant Vortex Pulses in Absorbing Media | In this paper we perform a fusion between two important theoretical
methodologies, one related to the Frozen Wave beams, which are non-diffracting
beams whose longitudinal intensity pattern can be chosen a priori in an medium
(absorbing or not), and the other related to the Airy-Type pulses, which are
pulses resistant to dispersion effects in dispersive materials. As a result, a
new method emerges, capable of providing vortex pulses resistant to three
concomitant effects, i.e.: diffraction, dispersion and attenuation; while
concurrently the spatial variation of the wave intensity along its axis of
propagation can be engineered at will. The new approach can be seen as a
generalization of the Localized Waves theory in the paraxial regime and the new
pulses can have potential applications in different fields such as optics
communications, nonlinear optics, micromanipulation, and so on. | 1809.08740v1 |
2018-11-28 | Investigation of effective thermoelectric properties of composite with interfacial resistance using micromechanics-based homogenisation | We obtained the analytical expression for the effective thermoelectric
properties and dimensionless figure of merit of a composite with interfacial
electrical and thermal resistances using a micromechanics-based homogenisation.
For the first time, we derived the Eshelby tensor for a spherical inclusion as
a function of the interfacial resistances and obtained the solutions of the
effective Seebeck coefficient and the electrical and thermal conductivities of
a composite, which were validated against finite-element analysis (FEA). Our
analytical predictions well match the effective properties obtained from FEA
with an inclusion volume fraction up to 15%. Because the effective properties
were derived with the assumption of a small temperature difference, we discuss
a heuristic method for obtaining the effective properties in the case where a
thermoelectric composite is subjected to a large temperature difference. | 1811.11340v2 |
2019-05-13 | Quantum Oscillations of Electrical Resistivity in an Insulator | In metals, orbital motions of conduction electrons on the Fermi surface are
quantized in magnetic fields, which is manifested by quantum oscillations in
electrical resistivity. This Landau quantization is generally absent in
insulators. Here we report a notable exception in an insulator, ytterbium
dodecaboride (YbB12). Despite much larger than that of metals, the resistivity
of YbB12 exhibits profound quantum oscillations. This unconventional
oscillation is shown to arise from the insulating bulk, yet the temperature
dependence of their amplitude follows the conventional Fermi liquid theory of
metals. The large effective masses indicate the presence of Fermi surface
consisting of strongly correlated electrons. Our result reveals a mysterious
bipartite ground state of YbB12: it is both a charge insulator and a strongly
correlated metal. | 1905.05140v1 |
2019-09-27 | Magnetoresistance effects in the metallic antiferromagnet Mn$_2$Au | In antiferromagnetic spintronics, it is essential to separate the resistance
modifications of purely magnetic origin from other effects generated by current
pulses intended to switch the N\'eel vector. We investigate the
magnetoresistance effects resulting from magnetic field induced reorientations
of the staggered magnetization of epitaxial antiferromagnetic Mn2Au(001) thin
films. The samples were exposed to 60 T magnetic field pulses along different
crystallographic in-plane directions of Mn2Au(001), while their resistance was
measured. For the staggered magnetization aligned via a spin-flop transition
parallel to the easy [110]-direction, an ansiotropic magnetoresistance of -0.15
% was measured. In the case of a forced alignment of the staggered
magnetization parallel to the hard [100]-direction, evidence for a larger
anisotropic magnetoresistance effect was found. Furthermore, transient
resistance reductions of about 1 % were observed, which we associate with the
annihilation of antiferromagnetic domain walls by the magnetic field pulses. | 1909.12606v3 |
2020-03-22 | Monitoring of the formation of strontium molybdate intergrain tunneling barriers in strontium ferromolybdate | This work is a contribution to the understanding of the electrical
resistivity in strontium ferromolybdate (SFMO) ceramics. It demonstrates that
an appropriate thermal treatment leads to the formation of dielectric SrMoO4
shells at the surface of SFMO nanograins. In samples without SrMoO4 shells, the
sign of the temperature coefficient of resistance changes with increasing
temperature from negative at very low temperature to positive at higher
temperatures. Samples exhibiting a negative temperature coefficient contain
SrMoO4 shells and demonstrate a behavior of the resistivity that can be
described in terms of the fluctuation-induced tunneling model, and near room
temperature the conductivity mechanism converts to a variable-range hopping
one. The results of this work serve as a starting point for the understanding
of the low-field magnetoresistance which is very promising for spintronic
device application. | 2003.09997v1 |
2014-08-15 | Correlation between electrical and magnetic properties of phase separated manganites studied with a General Effective Medium model | We have performed electrical resistivity and DC magnetization measurements as
a function of temperature, on polycrystalline samples of phase separated
LaPrCaMnO. We have used the General Effective Medium Theory to obtain
theoretical resistivity vs. temperature curves corresponding to different fixed
ferromagnetic volume fraction values, assuming that the sample is a mixture of
typical metallic like and insulating manganites. By comparing this data with
our experimental resistivity curves we have obtained the relative ferromagnetic
volume fraction of our sample as a function of temperature. This result matches
with the corresponding magnetization data in excellent agreement, showing that
a mixed phase scenario is the key element to explain both the magnetic and
transport properties in the present compound. | 1408.3599v1 |
2014-08-28 | Room temperature giant baroresistance and magnetoresistance and its tunability in Pd doped FeRh | We report room temperature giant baro-resistance ($\approx$128\%) in
$Fe_{49}(Rh_{0.93}Pd_{0.07})_{51}$. With the application of external pressure
and magnetic field the temperature range of giant baro-resistance
($\approx$600\% at 5K and 19.9 kbar and 8 Tesla) and magnetoresistance
($\approx$-85\% at 5K and 8 tesla) can be tuned from 5 K to well above room
temperature. As the AFM state is stabilized at room temperature under external
pressure, it shows giant room temperature magnetoresistance ($\approx$-55\%)
with magnetic field. Due to coupled magnetic and latticel changes, the
isothermal change in room temperature resistivity with pressure (in the absence
of applied magnetic field) as well as magnetic field (under various constant
pressure) can be scaled together to a single curve when plotted as a function
of X = T + 12.8*H - 7.2*P. | 1408.6688v1 |
2017-01-18 | Iron-based superconductivity extended to the novel silicide LaFeSiH | We report the synthesis and characterization of the novel silicide LaFeSiH
displaying superconductivity with onset at 11 K. We find that this
pnictogen-free compound is isostructural to LaFeAsO, with a similar
low-temperature tetragonal to orthorhombic distortion. Using density functional
theory we show that this system is also a multiband metal in which the
orthorhombic distortion is likely related to single-stripe antiferromagnetic
order. Electrical resistivity and magnetic susceptibility measurements reveal
that these features occur side-by-side with superconductivity, which is
suppressed by external pressure. | 1701.05010v3 |
2017-03-09 | Oxygen migration during resistance switching and failure of hafnium oxide memristors | While the recent establishment of the role of thermophoresis/diffusion-driven
oxygen migration during resistance switching in metal oxide memristors provided
critical insights required for memristor modeling, extended investigations of
the role of oxygen migration during ageing and failure remain to be detailed.
Such detailing will enable failure-tolerant design, which can lead to enhanced
performance of memristor-based next-generation storage-class memory. Here we
directly observed lateral oxygen migration using in-situ synchrotron x-ray
absorption spectromicroscopy of HfOx memristors during initial resistance
switching, wear over millions of switching cycles, and eventual failure,
through which we determined potential physical causes of failure. Using this
information, we reengineered devices to mitigate three failure mechanisms, and
demonstrated an improvement in endurance of about three orders of magnitude. | 1703.03106v1 |
2018-10-09 | Electron scattering by short range defects and resistivity of graphene | The electron scattering by the short-range defects in the monolayer graphene
is considered in the framework of the flatland model. We analyze the effect of
this scattering on the electronic resistivity of the monolayer graphene (direct
problem) and develop a procedure for determination of the defect potential from
resistivity data (inverse problem). We use an approximation of the short-range
perturbation by the delta-shell potential that is reasonable since it
suppresses irrelevant short wavelength excitations. Our theoretical results
proved to be in a good agreement with experiment on suspended monolayer
graphene. It means that our model correctly describes essential features of the
physical problem under consideration. It gives possibility to consider the
inverse problem, i.e. on the basis of our results for direct problem to develop
a procedure for determination of parameters of the monolayer graphene sample
using experimental measurements for it. Thus the obtained results give new
important possibilities, which can be used in numerous applications. | 1810.03897v1 |
2018-10-16 | Studies of two-dimensional MoS2 on enhancing the electrical performance of ultrathin copper films | Copper nanowires are widely used as on-chip interconnects due to superior
conductivity. However, with aggressive Cu interconnect scaling, the diffusive
surface scattering of electrons drastically increases the electrical
resistivity. In this work, we studied the electrical performance of Cu thin
films on different materials. By comparing the thickness dependence of Cu films
resistivity on MoS2 and SiO2, we demonstrated that two-dimensional MoS2 can be
used to enhance the electrical performance of ultrathin Cu films due to a
partial specular surface scattering. By fitting the experimental data with the
theoretical Fuchs Sondheimer model, we obtained the specularity parameter at
the Cu MoS2 interface in the temperature range 2K to 300K. Furthermore, first
principle calculations based on the density functional theory indicates that
there are more localized states at the Cu amorphous SiO2 interface than the Cu
MoS2 interface which is responsible for the higher resistivity in the Cu SiO2
heterostructure due to more severe electron scattering. Our results suggest
that Cu MoS2 hybrid is a promising candidate structure for the future
generations of CMOS interconnects. | 1810.06772v1 |
2019-02-01 | Graph Resistance and Learning from Pairwise Comparisons | We consider the problem of learning the qualities of a collection of items by
performing noisy comparisons among them. Following the standard paradigm, we
assume there is a fixed "comparison graph" and every neighboring pair of items
in this graph is compared $k$ times according to the Bradley-Terry-Luce model
(where the probability than an item wins a comparison is proportional the item
quality). We are interested in how the relative error in quality estimation
scales with the comparison graph in the regime where $k$ is large. We prove
that, after a known transition period, the relevant graph-theoretic quantity is
the square root of the resistance of the comparison graph. Specifically, we
provide an algorithm that is minimax optimal. The algorithm has a relative
error decay that scales with the square root of the graph resistance, and
provide a matching lower bound (up to log factors). The performance guarantee
of our algorithm, both in terms of the graph and the skewness of the item
quality distribution, outperforms earlier results. | 1902.00141v2 |
2019-02-06 | AlGaN /GaN superlattice based p-channel field effect transistor (pFET) with TMAH treatment | To realize the full spectrum of advantages that the III-nitride materials
system offers, the demonstration of p-channel III-nitride based devices is
valuable. Authors report the first p-type field effect transistor (pFET) based
on an AlGaN/GaN superlattice (SL), grown using MOCVD. Magnesium was used as the
p-type dopant. A sheet resistance of 11.6 k{\Omega}/sq, and a contact
resistance of 14.9{\Omega}.mm was determined using transmission line
measurements (TLM) for a Mg doping of 1.5e19cm^-3 of Mg. Mobilities in the
range of 7-10 cm\^2/Vs and a total sheet charge density in the range of
1e13-6e13 cm-2 were measured using room temperature Hall effect measurements.
Without Tetramethylammonium hydroxide (TMAH) treatment, the fabricated pFETs
had a maximum drain-source current (IDS) of 3mA/mm and an On-Resistance (RON)
of 3.48 k{\Omega}.mm, and did not turn-off completely. With TMAH treatment
during fabrication, a maximum IDS of 4.5mA/mm, RON of 2.2k{\Omega}.mm, and five
orders of current modulation was demonstrated, which is the highest achieved
for a p-type transistor based on (Al,Ga)N. | 1902.02022v2 |
2019-02-26 | Au-Ge alloys for wide-range low-temperature on-chip thermometry | We present results of a Au-Ge alloy that is useful as a resistance-based
thermometer from room temperature down to at least \SI{0.2}{\kelvin}. Over a
wide range, the electrical resistivity of the alloy shows a logarithmic
temperature dependence, which simultaneously retains the sensitivity required
for practical thermometry while also maintaining a relatively modest and
easily-measurable value of resistivity. We characterize the sensitivity of the
alloy as a possible thermometer and show that it compares favorably to
commercially-available temperature sensors. We experimentally identify that the
characteristic logarithmic temperature dependence of the alloy stems from
Kondo-like behavior induced by the specific heat treatment it undergoes. | 1902.10111v2 |
2019-07-11 | DC Electrical Degradation of YSZ: Voltage Controlled Electrical Metallization of A Fast Ion Conducting Insulator | DC electrical degradation as a form of dielectric and resistance breakdown is
a common phenomenon in thin-film devices including resistance-switching memory.
To obtain design data and to probe the degradation mechanism, highly
accelerated lifetime tests (HALT) are often conducted at higher temperatures
with thicker samples. While the mechanism is well established in semiconducting
oxides such as perovskite titanates, it is not in stabilized zirconia and other
fast oxygen-ion conductors that have little electronic conductivity. Here we
model the mechanism by an oxygen-driven, transport-limited, metal-insulator
transition, which finds support in rich experimental observations - including
in situ videos and variable temperature studies - of yttria-stabilized
zirconia. They are contrasted with the findings in semiconducting titanates and
resistance memory, and provide new insight into ceramic processing with
extremely rapid heating and cooling such as flash sintering and melt
processing. | 1907.05479v2 |
2020-02-17 | Transport mechanism in amorphous molybdenum silicide thin films | Amorphous molybdenum silicide compounds have attracted significant interest
for potential device applications, particularly in single-photon detector. In
this work, the temperature-dependent resistance and magneto-resistance
behaviors were measured to reveal the charge transport mechanism, which is of
great importance for applications but is still insufficient. It is found that
Mott variable hopping conductivity dominates the transport of sputtered
amorphous molybdenum silicide thin films. Additionally, the observed
magneto-resistance crossover from negative to positive is ascribed to the
interference enhancement and the shrinkage of electron wave function, both of
which vary the probability of hopping between localized sites. | 2002.06884v3 |
2020-09-17 | Restored strange metal phase through suppression of charge density waves in underdoped YBa$_2$Cu$_3$O$_{7-δ}$ | The normal state of optimally doped cuprates is dominated by the "strange
metal" phase that shows a linear temperature ($T$) dependence of the
resistivity persisting down to the lowest $T$. For underdoped cuprates this
behavior is lost below the pseudogap temperature $T^*$, where Charge Density
Waves (CDW) together with other intertwined local orders characterize the
ground state. Here we show that the $T$-linear resistivity of highly strained,
ultrathin and underdoped YBa$_2$Cu$_3$O$_{7-\delta}$ films is restored when the
CDW amplitude, detected by Resonant Inelastic X-ray scattering, is suppressed.
This observation points towards an intimate connection between the onset of CDW
and the departure from $T$-linear resistivity in underdoped cuprates. Our
results illustrate the potential of using strain control to manipulate the
ground state of quantum materials. | 2009.08398v3 |
2007-10-03 | The effect of ozone oxidation on single-walled carbon nanotubes | Exposing single-walled carbon nanotubes to room temperature UV-generated
ozone leads to an irreversible increase in their electrical resistance. We
demonstrate that the increased resistance is due to ozone oxidation on the
sidewalls of the nanotubes rather than at the end caps. Raman and x-ray
photoelectron spectroscopy show an increase in the defect density due to the
oxidation of the nanotubes. Using ultraviolet photoelectron spectroscopy we
show that these defects represent the removal of pi-conjugated electron states
near the Fermi level, leading to the observed increase in electrical
resistance. Oxidation of carbon nanotubes is an important first step in many
chemical functionalization processes. Since the oxidation rate is controllable
with short exposures, UV-generated ozone offers the potential for use as a
low-thermal budget processing tool. | 0710.0803v1 |
2012-01-13 | Intermediate state switching dynamics in magnetic double layer nanopillars grown by molecular beam epitaxy | We observe a stable intermediate resistance switching state in the current
perpendicular to plane geometry for all Co/Cu/Co double layer nanopillar
junctions grown by molecular beam epitaxy. This novel state has a resistance
between the resistances of the parallel and antiparallel alignment of both
Co-layer magnetizations. The state, which originates from an additional
in-plane magnetic easy axis, can be reached by spin transfer torque switching
or by an external magnetic field. In addition to spin torque-induced coherent
small-angle spin wave modes we observe a broad microwave emission spectrum. The
latter is attributed to incoherent magnetic excitations that lead to a
switching between the intermediate state and the parallel or antiparallel
alignment of both ferromagnetic layers. We conclude that the additional
magnetic easy axis suppresses a stable trajectory of coherent large-angle
precession, which is not observed in our samples. | 1201.2752v1 |
2012-01-14 | Length dependence of the resistance in graphite: Influence of ballistic transport | Using a linear array of voltage electrodes with a separation of several
micrometers on a $20 $nm thick and 30 $\mu$m long multigraphene sample we show
that the measured resistance does not follow the usual length dependence
according to Ohm's law. The deviations can be quantitatively explained taking
into account Sharvin-Knudsen formula for ballistic transport. This allows us to
obtain without free parameters the mean free path of the carriers in the sample
at different temperatures. In agreement with recently reported values obtained
with a different experimental method, we obtain that the carrier mean free path
is of the order of $\sim 2 \mu$m with a mobility $\mu \sim 10^7
$cm$^{2}$V$^{-1}$s$^{-1}$. The results indicate that the usual Ohm's law is not
adequate to calculate the absolute resistivity of mesoscopic graphite samples. | 1201.3004v1 |
2012-01-14 | Temperature dependence of the thermal boundary resistivity of glass-embedded metal nanoparticles | The temperature dependence of the thermal boundary resistivity is
investigated in glass-embedded Ag particles of radius 4.5 nm, in the
temperature range from 300 to 70 K, using all-optical time-resolved
nanocalorimetry. The present results provide a benchmark for theories aiming at
explaining the thermal boundary resistivity at the interface between metal
nanoparticles and their environment, a topic of great relevance when tailoring
thermal energy delivery from nanoparticles as for applications in nanomedicine
and thermal management at the nanoscale | 1201.3034v1 |
2014-01-07 | Images of edge current in InAs/GaSb quantum wells | Quantum spin Hall devices with edges much longer than several microns do not
display ballistic transport: that is, their measured conductances are much less
than $e^2/h$ per edge. We imaged edge currents in InAs/GaSb quantum wells with
long edges and determined an effective edge resistance. Surprisingly, although
the effective edge resistance is much greater than $h/e^2$, it is independent
of temperature up to 30 K within experimental resolution. Known candidate
scattering mechanisms do not explain our observation of an effective edge
resistance that is large yet temperature-independent. | 1401.1531v2 |
2016-03-12 | Spin Hall Effect and Origins of Nonlocal Resistance in Adatom-Decorated Graphene | Recent experiments reporting unexpectedly large spin Hall effect (SHE) in
graphene decorated with adatoms have raised a fierce controversy. We apply
numerically exact Kubo and Landauer- Buttiker formulas to realistic models of
gold-decorated disordered graphene (including adatom clustering) to obtain the
spin Hall conductivity and spin Hall angle, as well as the nonlocal resistance
as a quantity accessible to experiments. Large spin Hall angles of 0.1 are
obtained at zero-temperature, but their dependence on adatom clustering differs
from the predictions of semiclassical transport theories. Furthermore, we find
multiple background contributions to the nonlocal resistance, some of which are
unrelated to SHE or any other spin-dependent origin, as well as a strong
suppression of SHE at room temperature. This motivates us to design a
multiterminal graphene geometry which suppresses these background contributions
and could, therefore, quantify the upper limit for spin current generation in
two-dimensional materials. | 1603.03870v3 |
2016-03-17 | Electrical Writing of Magnetic and Resistive Multistates in CoFe Films Deposited onto Pb[Zr$_x$Ti$_{1-x}$]O$_3$ | Electric control of magnetic properties is an important challenge for modern
magnetism and spintronic development. In particular, an ability to write
magnetic state electrically would be highly beneficial. Among other methods,
the use of electric field induced deformation of piezoelectric elements is a
promising low-energy approach for magnetization control. We investigate the
system of piezoelectric substrate Pb[Zr$_x$Ti$_{1-x}$]O$_3$ with CoFe
overlayers, extending the known reversible bistable electro-magnetic coupling
to surface and multistate operations, adding the initial state reset
possibility. Increasing the CoFe thickness improves the magnetoresistive
sensitivity, but at the expenses of decreasing the strain-mediated coupling,
with optimum magnetic thin film thickness of the order of 100 nm. The simplest
resistance strain gauge structure is realized and discussed as a multistate
memory cell demonstrating both resistive memory (RRAM) and magnetoresistive
memory (MRAM) functionalities in a single structure. | 1603.05476v1 |
2018-08-26 | Supercondutivity in SnSb with natural superlattice structure | We report the results of electrical resistivity, magnetic and thermodynamic
measurements on polycrystalline SnSb, whose structure consists of stacks of Sb
bilayers and Sn4Sb3 septuple layers along the c-axis. The material is found to
be a weakly coupled, fully gapped, type-II superconductor with a bulk Tc of
1.50 K, while showing a zero resistivity transition at a significantly higher
temperature of 2.48 K. The Sommerfeld coefficient and upper critical field,
obtained from specific heat measurements, are 2.29 mJ/mol K and 520 Oe,
respectively. Compositional inhomogeneity and strain effect at the grain
boundaries are proposed as possible origins for the difference in resistive and
bulk superconducting transitions.In addition, a comparison with the rock-salt
structure SnAs superconductor is presented. Our results provide the first clear
evidence of bulk superconductivity in a natural superlattice derived from a
topological semimetal. | 1808.08500v2 |
2019-03-03 | Scaling parameters in anomalous and nonlinear Hall effects depend on temperature | In the study of the anomalous Hall effect, the scaling relations between the
anomalous Hall and longitudinal resistivities play the central role. The
scaling parameters by definition are fixed as the scaling variable
(longitudinal resistivity) changes. Contrary to this paradigm, we unveil that
the electron-phonon scattering can result in apparent temperature-dependence of
scaling parameters when the longitudinal resistivity is tuned through
temperature. An experimental approach is proposed to observe this hitherto
unexpected temperature-dependence. We further show that this phenomenon also
exists in the nonlinear Hall effect in nonmagnetic inversion-breaking materials
and may help identify experimentally the presence of the side-jump contribution
besides the Berry-curvature dipole. | 1903.00810v5 |
2019-03-19 | Composition dependence of magnetoresistance in Fe$_{1-x}$Ni$_{x}$ alloys | Resistance of Fe$_{1-x}$Ni$_x$(x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.9)
has been measured using four probe method from 5K to 300K with and without a
longitudinal magnetic field of 8T. The zero field resistivity of x=0.1 and 0.9
alloys, predominant contribution to resistivity above near room temperature is
due to electron-phonon scattering, whereas for x=05 and 0.7 alloys
electron-magnon scattering is dominant. Alloys with x=0.1 and 0.9 exhibit
positive magnetoresistance(MR) from 5K to 300K. For x=0.5 and 0.7 alloys,
magnetoresistance changes sign from positive to negative with increase in
temperature. The temperature at which sign changes increase with Ni
concentration in the alloy. The field dependent magnetoresistance is positive
for x=0.1, 0.7 and 0.9 alloys whereas it is negative for x=0.5 alloy. MR
follows linear behaviour with field for x=0.1 alloy. MR of all other alloys
follow a second order polynomial in field. | 1903.08230v3 |
2019-03-26 | Controlled inter-state switching between quantized conductance states in resistive devices for multilevel memory | A detailed understanding of quantization conductance (QC), their correlation
with resistive switching phenomena and controlled manipulation of quantized
states is crucial for realizing atomic-scale multilevel memory elements. Here,
we demonstrate highly stable and reproducible quantized conductance states
(QC-states) in Al/Niobium oxide/Pt resistive switching devices. Three levels of
control over the QC-states, required for multilevel quantized state memories,
like, switching ON to different quantized states, switching OFF from quantized
states, and controlled inter-state switching among one QC states to another has
been demonstrated by imposing limiting conditions of stop-voltage and current
compliance. The well defined multiple QC-states along with a working principle
for switching among various states show promise for implementation of
multilevel memory devices. | 1903.10688v1 |
2019-12-11 | Current-induced fragmentation of antiferromagnetic domains | Electrical and optical pulsing allow for manipulating the order parameter and
magnetoresistance of antiferromagnets, opening novel prospects for digital and
analog data storage in spintronic devices. Recent experiments in CuMnAs have
demonstrated giant resistive switching signals in single-layer
antiferromagnetic films together with analog switching and relaxation
characteristics relevant for neuromorphic computing. Here we report
simultaneous electrical pulsing and scanning NV magnetometry of
antiferromagnetic domains in CuMnAs performed using a pump-probe scheme. We
observe a nano-scale fragmentation of the antiferromagnetic domains, which is
controlled by the current amplitude and independent on the current direction.
The fragmented antiferromagnetic state conserves a memory of the pristine
domain pattern, towards which it relaxes. Domain fragmentation coexists with
permanent switching due to the reorientation of the antiferromagnetic moments.
Our simultaneous imaging and resistance measurements show a correlation between
the antiferromagnetic domain fragmentation and the largest resistive switching
signals in CuMnAs. | 1912.05287v1 |
2019-12-12 | Aharonov-Bohm oscillations of four-probe resistance in topological quantum rings in silicene and bilayer graphene | We consider observation of Aharonov-Bohm oscillations in clean systems based
on the flow of topologically protected currents in silicene and bilayer
graphene. The chiral channels in these materials are defined by the flips of
the vertical electric field. The line of the flip confines chiral currents
flowing along it in the direction determined by the valley. We present an
electric field profile that forms a crossed ring to which four terminals can be
attached, and find that the conductance matrix elements oscillate in the
perpendicular magnetic field in spite of the absence of backscattering. We
propose a four-probe resistance measurement setup, and demonstrate that the
resistance oscillations have large visibility provided that the system is
prepared in such a way that a direct transfer of the chiral carriers between
the current probes is forbidden. | 1912.05876v2 |
2021-01-13 | Hinge Spin Polarization in Magnetic Topological Insulators Revealed by Resistance Switch | We report on the possibility to detect hinge spin polarization in magnetic
topological insulators by resistance measurements. By implementing a
three-dimensional model of magnetic topological insulators into a
multi-terminal device with ferromagnetic contacts near the top surface, local
spin features of the chiral edge modes are unveiled. We find local spin
polarization at the hinges that inverts sign between top and bottom surfaces.
At the opposite edge, the topological state with inverted spin polarization
propagates in the reverse direction. Large resistance switch between forward
and backward propagating states is obtained, driven by the matching between the
spin polarized hinges and the ferromagnetic contacts. This feature is general
to the ferromagnetic, antiferromagnetic and canted-antiferromagnetic phases,
and enables the design of spin-sensitive devices, with the possibility of
reversing the hinge spin polarization of the currents. | 2101.05293v2 |
2021-01-26 | Demystifying strange metal and violation of Luttinger theorem in a doped Mott insulator | Metallic states coined strange metal (SM), with robust linear-$T$
resistivity, have been widely observed in many quantum materials under strong
electron correlation, ranging from high-$T_{c}$ cuprate superconductor, organic
superconductor to twisted multilayer graphene and MoTe$_{2}$/WSe$_{2}$
superlattice. Despite decades of intensive studies, the mystery of strange
metal still defies any sensible theoretical explanation and has been the key
puzzle in modern condensed matter physics. Here, we solve a doped Mott
insulator model, which unambiguously exhibits SM phenomena accompanied with
quantum critical scaling in observables, e.g. resistivity, susceptibility and
specific heat. Closer look at SM reveals the breakdown of Landau's Fermi liquid
without any symmetry-breaking, i.e. the violation of Luttinger theorem.
Examining electron's self-energy extracted from numerical simulation provides
the explanation on the origin of linear-$T$ resistivity and suggests that the
long-overlooked static fluctuations in literature play an essential role in
non-Fermi liquid behaviors in correlated electron systems. | 2101.10611v3 |
2012-06-15 | A ferroelectric memristor | Memristors are continuously tunable resistors that emulate synapses.
Conceptualized in the 1970s, they traditionally operate by voltage-induced
displacements of matter, but the mechanism remains controversial. Purely
electronic memristors have recently emerged based on well-established physical
phenomena with albeit modest resistance changes. Here we demonstrate that
voltage-controlled domain configurations in ferroelectric tunnel barriers yield
memristive behaviour with resistance variations exceeding two orders of
magnitude and a 10 ns operation speed. Using models of ferroelectric-domain
nucleation and growth we explain the quasi-continuous resistance variations and
derive a simple analytical expression for the memristive effect. Our results
suggest new opportunities for ferroelectrics as the hardware basis of future
neuromorphic computational architectures. | 1206.3397v1 |
2015-04-30 | Study of the Negative Magneto-Resistance of Single Proton-Implanted Lithium-Doped ZnO Microwires | The magneto-transport properties of single proton-implanted ZnO and of
Li(7\%)-doped ZnO microwires have been studied. The as-grown microwires were
highly insulating and not magnetic. After proton implantation the Li(7\%) doped
ZnO microwires showed a non monotonous behavior of the negative
magneto-resistance (MR) at temperature above 150 K. This is in contrast to the
monotonous NMR observed below 50 K for proton-implanted ZnO. The observed
difference in the transport properties of the wires is related to the amount of
stable Zn vacancies created at the near surface region by the proton
implantation and Li doping. The magnetic field dependence of the resistance
might be explained by the formation of a magnetic/non magnetic heterostructure
in the wire after proton implantation. | 1504.08230v1 |
2015-07-29 | Integration of a 2D Periodic Nanopattern Into Thin Film Polycrystalline Silicon Solar Cells by Nanoimprint Lithography | The integration of two-dimensional (2D) periodic nanopattern defined by
nanoimprint lithography and dry etching into aluminum induced crystallization
(AIC) based polycrystalline silicon (Poly-Si) thin film solar cells is
investigated experimentally. Compared to the unpatterned cell an increase of 6%
in the light absorption has been achieved thanks to the nanopattern which, in
turn, increased the short circuit current from 20.6 mA/cm2 to 23.8 mA/cm2. The
efficiency, on the other hand, has limitedly increased from 6.4% to 6.7%. We
show using the transfer length method (TLM) that the surface topography
modification caused by the nanopattern has increased the sheet resistance of
the antireflection coating (ARC) layer as well as the contact resistance
between the ARC layer and the emitter front contacts. This, in turn, resulted
in increased series resistance of the nanopatterned cell which has translated
into a decreased fill factor, explaining the limited increase in efficiency. | 1507.08341v1 |
2019-06-03 | Observations of zero electrical resistance of Au-Ag thin films near room temperature | Recent observations of superconducting like transition at 286 K in Ag and Ag
nanostructures by Thapa et al. (arxiv: 1807.08572) have rekindled the hope for
room temperature superconductivity under ambient conditions. We also
investigated the electrical properties of Ag-Au nanostructure in the form of
thin film grown on SiO2/Si substrate by DC sputtering and observed signature of
zero resistance in the temperatures range of 243 K to 275 K. While the observed
electrical resistance of samples shows intriguing and perplexing behavior under
temperature cycling and external magnetic field; the large spatial
inhomogeneity present in thin film hampers the reproducibility indicating the
stability issues associated with superconducting like phase. | 1906.00708v1 |
2019-06-24 | Combination of informational storage and logical processing based on an all-oxide asymmetric multiferroic tunnel junction | Multiferroic tunnel junctions (MFTJs) have already been proved to be
promising candidates for application in spintronics devices. The coupling
between tunnel magnetoresistance (TMR) and tunnel electroresistance (TER) in
MFTJs can provide four distinct resistive states in a single memory cell. Here
we show that in an all-oxide asymmetric MFTJ of La0.7Sr0.3MnO3 /PbZr0.2Ti0.8O3
/La0.7Te0.3MnO3 (LSMO/PZT/LTMO) with p-type and n-type electrodes, the
intrinsic rectification is observed and can be modified by the ferroelectric
polarization of PZT. Owing to the combined TMR, TER and diode effects, two
different groups of four resistive states under opposite reading biases are
performed. With two parallel asymmetric junctions and the appropriate series
resistance, the coexistence of logic units and quaternary memory cells can be
realized in the same array devices. The asymmetric MFTJ structure enables more
possibilities for designing next generation of multi-states memory and logical
devices with higher storage density, lower energy consumption and significantly
increased integration level. | 1906.09993v1 |
2019-10-04 | Nonvolatile Multilevel States in Multiferroic Tunnel Junctions | Manipulation of tunneling spin-polarized electrons via a ferroelectric
interlayer sandwiched between two ferromagnetic electrodes, dubbed Multiferroic
Tunnel Junctions (MFTJs), can be achieved not only by the magnetic alignments
of two ferromagnets but also by the electric polarization of the ferroelectric
interlayer, providing great opportunities for next-generation multi-state
memory devices. Here we show that a La0.67Sr0.33MnO3
(LSMO)/PbZr0.2Ti0.8O3(PZT)/Co structured MFTJ device can exhibit multilevel
resistance states in the presence of gradually reversed ferroelectric domains
via tunneling electro-resistance and tunneling magnetoresistance, respectively.
The nonvolatile ferroelectric control in the MFTJ can be attributed to separate
contributions arising from two independent ferroelectric channels in the PZT
interlayer with opposite polarization. Our study shows the dominant role of
"mixed" ferroelectric states on achieving accumulative electrical modulation of
multilevel resistance states in MFTJs, paving the way for multifunctional
device applications. | 1910.02002v1 |
2020-06-02 | Ultra-fast Kinematic Vortices in Mesoscopic Superconductors: The Effect of the Self-Field | Within the framework of the generalized time-dependent Ginzburg-Landau
equations, we studied the influence of the magnetic self-field induced by the
currents inside a superconducting sample driven by an applied transport
current. The numerical simulations of the resistive state of the system show
that neither material inhomogeneity nor a normal contact smaller than the
sample width are required to produce an inhomogeneous current distribution
inside the sample, which leads to the emergence of a kinematic
vortex-antivortex pair (vortex street) solution. Further, we discuss the
behaviors of the kinematic vortex velocity, the annihilation rates of the
supercurrent, and the superconducting order parameters alongside the vortex
street solution. We prove that these two latter points explain the
characteristics of the resistive state of the system. They are the fundamental
basis to describe the peak of the current-resistance characteristic curve and
the location where the vortex-antivortex pair is formed. | 2006.01335v1 |
2020-07-09 | Coupling-independent, Real-time Wireless Resistive Sensing through Nonlinear PT-symmetry | We report the realization of coupling-independent, robust wireless sensing of
fully-passive resistive sensors. PT-symmetric operation obviates sweeping,
permitting real-time, single-point sensing. Self-oscillation is achieved
through a fast-settling nonlinearity whose voltage amplitude is proportional to
the sensor's resistance. These advances markedly simplify the reader. A dual
time-scale theoretical framework generalizes system analysis to arbitrary
operating conditions and a correction strategy reduces errors due to detuning
from PT-symmetric conditions by an order of magnitude. | 2007.05077v4 |
2020-07-29 | An electro-thermal computational study of conducting channels in dielectric thin films using self-consistent phase-field methodology: A view toward the physical origins of resistive switching | A large number of experimental studies suggest two-terminal resistive
switching devices made of a dielectric thin film sandwiched by a pair of
electrodes exhibit reversible multi-state switching behaviors; however coherent
understanding of physical and chemical origins of their electrical properties
needs to be further pursued to improve and customize the performance. In this
paper, phase-field methodology is used to study the formation and annihilation
of conductive channels resulting in reversible resistive switching behaviors
that can generally occur in any dielectric thin films. Our focus is on the
dynamical evolution of domains made of electrical charges under the influence
of spatially varying electric field and temperature resulting in distinctive
changes in electrical conductance. | 2007.15123v1 |
2020-08-24 | Peierls-type metal-insulator transition in carbon nanostructures | We report the observation of Peierls-type metal-insulator transition in
carbon nanostructures formed by chemical vapor deposition inside the pore
network of the ZSM-5 zeolite. The Raman spectrum of this nanocarbon@ZSM-5
indicates a clear signature of the radial breathing mode (RBM) for (3,0) carbon
nanotubes that can constitute the carbon network segments. Electrical transport
measurements on multiple few-micron-sized nanocarbon@ZSM-5 crystals showed
metallic temperature of resistance dependence down to 30 K, at which point the
resistance exhibited a sharp upturn that is accompanied by the opening of a
quasigap at the Fermi level as indicated by the differential resistance
measurements. Further Hall measurements have yielded both the sign of the
charge carrier and its density. The latter demonstrated excellent consistency
with the quasigap data. We employed first-principles calculations to verify
that there can indeed be softening of the phonon modes in the (3,0) carbon
nanotubes. | 2008.10160v1 |
2020-10-22 | Electrical and Thermal Transport Properties of the beta-Pyrochlore Oxide CsW2O6 | We report the electrical resistivity, thermoelectric power, and thermal
conductivity of single-crystalline and sintered samples of the 5d pyrochlore
oxide CsW2O6. The electrical resistivity of the single crystal is 3 mohm cm at
295 K and gradually increases with decreasing temperature above 215 K (Phase
I). The thermoelectric power of the single-crystalline and sintered samples
shows a constant value of approximately -60 uV K-1 in Phase I. These results
reflect that the electron conduction by W 5d electrons in Phase I is incoherent
and in the hopping regime, although a band gap does not open at the Fermi
level. The thermal conductivity in Phase I of both samples is considerably low,
which might be due to the rattling of Cs+ ions. In Phase II below 215 K, the
electrical resistivity and the absolute value of thermoelectric power of both
samples strongly increase with decreasing temperature, corresponding to a
transition to a semiconducting state with a band gap open at the Fermi level,
while the thermal conductivity in Phase II is smaller than that in Phase I. | 2010.11404v1 |
2020-11-11 | Elastic turbulence generates anomalous flow resistance in porous media | Diverse processes rely on the viscous flow of polymer solutions through
porous media. In many cases, the macroscopic flow resistance abruptly increases
above a threshold flow rate in a porous medium---but not in bulk solution. The
reason why has been a puzzle for over half a century. Here, by directly
visualizing the flow in a transparent 3D porous medium, we demonstrate that
this anomalous increase is due to the onset of an elastic instability. We
establish that the energy dissipated by the unstable flow fluctuations, which
vary across pores, generates the anomalous increase in flow resistance through
the entire medium. Thus, by linking the pore-scale onset of unstable flow to
macroscopic transport, our work provides generally-applicable guidelines for
predicting and controlling polymer solution flows. | 2011.06036v1 |
2021-02-08 | Double magnetic phase transitions and magnetotransport anomalies in a new compound Gd$_\textbf{2}$AgSi$_\textbf{3}$ | Dc and ac-magnetic susceptibility ($\chi$), specific heat ($C_\mathrm{P}$),
electrical resistivity ($\rho$) and magnetoresistance measurements performed on
the new polycrystalline compound $\mathrm{Gd_2AgSi_3}$, crystallizing in the
$\alpha$-$\mathrm{ThSi_2}$ tetragonal structure, are reported. Two magnetic
phase transitions were observed in dc and ac susceptibility, specific heat, and
resistivity measurements at temperatures $\mathrm{T_{N_1}} = 11$ K and
$\rm{T_{N_2}} = 20$ K, despite a single site occupied by Gd atom, which is an
indication of the complex magnetic behavior. $\mathrm{Gd_2AgSi_3}$ turns out to
be one of the rare Gd compound in which a minimum is observed in the
temperature dependence of resistivity in the paramagnetic state and also
negative magnetoresistance over a wide temperature range (above
$\rm{T_{N_2}}$), mimicking the behavior of exotic $\mathrm{Gd_2PdSi_3}$, in
this ternary family. The isothermal magnetic entropy and adiabatic temperature
changes reach a value of 9.5 J/kg-K and 7.5 K respectively for the field change
of 9 T. | 2102.04096v2 |
2021-04-23 | Ab initio inspection of thermophysical experiments for zirconium near melting | We present quantum molecular dynamics calculations of thermophysical
properties of solid and liquid zirconium in the vicinity of melting. An
overview of available experimental data is also presented. We focus on the
analysis of thermal expansion, molar enthalpy, resistivity and normal spectral
emissivity of solid and liquid Zr. Possible reasons of discrepancies between
the first-principle simulations and experiments are discussed. Our calculations
reveal a significant volume change on melting in agreement with electrostatic
levitation experiments. Meanwhile, we confirm a low value of enthalpy of fusion
obtained in some pulse-heating experiments. Electrical resistivity of solid and
liquid Zr is systematically underestimated in our simulations, however the
slope of resistivity temperature dependencies agrees with experiment. Our
calculations predict almost constant normal spectral emissivity in liquid Zr. | 2104.11521v2 |
2021-06-16 | Statistical Analysis of Contacts to Synthetic Monolayer MoS2 | Two-dimensional (2D) semiconductors are promising candidates for scaled
transistors because they are immune to mobility degradation at the monolayer
limit. However, sub-10 nm scaling of 2D semiconductors, such as MoS2, is
limited by the contact resistance. In this work, we show for the first time a
statistical study of Au contacts to chemical vapor deposited monolayer MoS2
using transmission line model (TLM) structures, before and after dielectric
encapsulation. We report contact resistance values as low as 330 ohm-um, which
is the lowest value reported to date. We further study the effect of Al2O3
encapsulation on variability in contact resistance and other device metrics.
Finally, we note some deviations in the TLM model for short-channel devices in
the back-gated configuration and discuss possible modifications to improve the
model accuracy. | 2106.08673v3 |
2021-06-19 | Dopant Precursor Adsorption into Single-Dimer Windows: Towards Guided Self-Assembly of Dopant Arrays on Si(100) | Atomically precise dopant arrays in Si are being pursued for solid-state
quantum computing applications. We propose a guided self-assembly process to
produce atomically precise arrays of single dopant atoms in lieu of
lithographic patterning. We leverage the self-assembled c(4x2) structure formed
on Br- and I-Si(100) and investigate molecular precursor adsorption into the
generated array of single-dimer window (SDW) adsorption sites with density
functional theory (DFT). The adsorption of several technologically relevant
dopant precursors (PH$_3$, BCl$_3$, AlCl$_3$, GaCl$_3$) into SDWs formed with
various resists (H, Cl, Br, I) are explored to identify the effects of steric
interactions. PH$_3$ adsorbed without barrier on all resists studied, while
BCl$_3$ exhibited the largest adsorption barrier, 0.34 eV, with an I resist.
Dense arrays of AlCl$_3$ were found to form within experimentally realizable
conditions demonstrating the potential for the proposed use of guided
self-assembly for atomically precise fabrication of dopant-based devices. | 2106.10556v1 |
2021-07-07 | Large Magneto-Electric Resistance in the Topological Dirac Semimetal alpha Sn | The spin-momentum locking of surface states in topological quantum materials
can produce a resistance that scales linearly with magnetic and electric
fields. Such a bilinear magneto-electric resistance (BMER) effect offers a
completely new approach for magnetic storage and magnetic field sensing
applications. The effects demonstrated so far, however, are relatively weak or
for low temperatures. Strong room-temperature BMER effects have now been found
in topological Dirac semimetal alpha-Sn thin films. The epitaxial alpha-Sn
films were grown by sputtering on silicon substrates. They showed BMER
responses that are 10^6 times larger than previously reported at room
temperature and also larger than that previously reported at low temperatures.
These results represent a major advance toward realistic BMER applications. The
data also made possible the first characterization of the three-dimensional,
Fermi-level spin texture of topological surface states in alpha-Sn. | 2107.03472v1 |
2021-10-21 | Magnetic critical behavior and anomalous Hall effect in 2H-Co$_{0.22}$TaS$_{2}$ single crystals | We report ferromagnetism in 2H-Co$_{0.22}$TaS$_2$ single crystals where Co
atoms are intercalated in the van der Waals gap, and a systematic study of its
magnetic critical behavior in the vicinity of $T_c \sim 28$ K. The obtained
critical exponents $\beta$ = 0.43(2), $\gamma$ = 1.15(1), and $\delta =
3.54(1)$ fulfill the Widom scaling relation $\delta = 1+\gamma/\beta$ and
follow the scaling equation. This indicates that the spin coupling in
2H-Co$_{0.22}$TaS$_2$ is of three-dimensional Hersenberg type coupled with
long-range magnetic interaction, and that the exchange interaction decays with
distance as $J(r)\approx r^{-4.69}$. 2H-Co$_{0.22}$TaS$_2$ exhibits a weak
temperature-dependent metallic behavior in resistivity and negative values of
thermopower with dominant electron-type carriers, in which obvious anomalies
were observed below $T_c$ as well as the anomalous Hall effect (AHE). The
linear scaling behavior between the modified anomalous Hall resistivity
$\rho_{xy}/\mu_0H$ and longitudinal resistivity $\rho_{xx}^2M/\mu_0H$ implies
that the origin of AHE in 2H-Co$_{0.22}$TaS$_2$ should be dominated by the
extrinsic side-jump mechanism. | 2110.11350v1 |
2022-01-21 | Anomalous metals: from "failed superconductor" to "failed insulator" | Resistivity saturation is found on both superconducting and insulating sides
of an "avoided" magnetic-field-tuned superconductor-to-insulator transition
(H-SIT) in a two-dimensional In/InO$_x$ composite, where the anomalous metallic
behaviors cut off conductivity or resistivity divergence in the
zero-temperature limit. The granular morphology of the material implies a
system of Josephson junctions (JJ) with a broad distribution of Josephson
coupling E$_J$ and charging energy E$_C$ , with a H-SIT determined by the
competition between E$_J$ and E$_C$ . By virtue of self-duality across the true
H-SIT, we invoke macroscopic quantum tunneling effects to explain the
temperature-independent resistance where the "failed superconductor" side is a
consequence of phase fluctuations and the "failed insulator" side results from
charge fluctuations. While true self-duality is lost in the avoided transition,
its vestiges are argued to persist, owing to the incipient duality of the
percolative nature of the dissipative path in the underlying random JJ system. | 2201.08801v1 |
2022-03-12 | Quantifying active and resistive stresses in adherent cells | To understand cell migration, it is crucial to gain knowledge on how cells
exert and integrate forces on/from their environment. A quantity of prime
interest for biophysicists interested in cell movements modeling is the
intracellular stresses. Up to now, three different methods have been proposed
to calculate it, they are all in the regime of the thin plate approximation.
Two are based on solving the mechanical equilibrium equation inside the cell
material (Monolayer Stress Microscopy, and Bayesian Inference Stress
Microscopy) and one is based on the continuity of displacement at the
cell/substrate interface (Intracellular Stress Microscopy). We show here using
3D FEM modeling that these techniques do not calculate the same quantities (as
was previously assumed), the first techniques calculate the sum of the active
and resistive stresses within the cell, whereas the last one only calculate the
resistive component. Combining these techniques should in principle permit to
get access to the active stress alone. | 2203.06475v2 |
2022-03-23 | Quantum oscillations and weak anisotropic resistivity in the chiral Fermion semimetal PdGa | We perform a detailed analysis of the magnetotransport and de Haas-van Alphen
(dHvA) oscillations in crystal PdGa which is predicted to be a typical chiral
Fermion semimetal from CoSi family holding a large Chern number. The
unsaturated quadratic magnetoresistance (MR) and nonlinear Hall resistivity
indicate that PdGa is a multi-band system without electron-hole compensation.
Angle-dependent resistivity in PdGa shows weak anisotropy with twofold or
threefold symmetry when the magnetic field rotates within the (1$\bar{1}$0) or
(111) plane perpendicular to the current. Nine or three frequencies are
extracted after the fast Fourier-transform analysis (FFT) of the dHvA
oscillations with B//[001] or B//[011], respectively, which is confirmed to be
consistent with the Fermi surfaces (FSs) obtained from first-principles
calculations with spin-orbit coupling (SOC) considered. | 2203.12772v1 |
2022-05-04 | Percolative Superconductivity in Electron-Doped Sr$_{1-x}$Eu$_{x}$CuO$_{2+y}$ Films | Electron-doped infinite-layer Sr$_{1-x}$Eu$_{x}$CuO$_{2+y}$ films over a wide
doping range have been prepared epitaxially on SrTiO$_3$(001) using reactive
molecular beam epitaxy. In-plane transport measurements of the single
crystalline samples reveal a dome-shaped nodeless superconducting phase
centered at $x$ $\sim$ 0.15, a Fermi-liquid behavior and pronounced upturn in
low temperature resistivity. We show that the resistivity upturn follows
square-root temperature dependence, suggesting the emergence of
superconductivity via a three-dimensional percolation process. The percolative
superconductivity is corroborated spectroscopically by imaging the electronic
phase separation between superconducting and metallic phases with
low-temperature scanning tunneling microscopy. Furthermore, we visualize
interstitial and apical oxygen anions that rapidly increase in number as $x>$
0.12, and elucidate their impacts on the superconductivity and normal-state
resistivity. | 2205.01844v1 |
2022-05-10 | Effect of substrate temperature on the optoelectronic properties of DC magnetron sputtered copper oxide films | Copper oxide thin films are deposited on quartz substrates by DC magnetron
sputtering and the effect of deposition temperature on their optoelectronic
properties is examined in detail. Scanning Electron Microscopy (SEM), X-ray
diffraction (XRD) analysis, Raman spectroscopy, UV-Vis spectroscopy, and
four-probe sheet resistance measurements are used to characterize the surface
morphology, structural, optical, and electrical properties respectively.
Deposition is carried out at room temperature and between 200 and 300 {\deg}C.
XRD analysis indicates that the oxide formed is primarily Cu$_2$O and the
absorption spectra show the films have a critical absorption edge at around 300
nm. The sheet resistance gradually decreases with increase in deposition
temperature thereby increasing the conductivity of these thin films. Also
observed is the increase in band gap from 2.20 eV for room temperature
deposition to 2.35 eV at 300 {\deg}C. The optical band gap and the variation of
sheet resistance with temperature shows that the microstructure plays a vital
role in their behavior. These transformation characteristics are of huge
technological importance having variety of applications including transparent
solar cell fabrication. | 2205.05615v1 |
2022-08-10 | Spin-carrier coupling induced ferromagnetism and giant resistivity peak in EuCd$_2$P$_2$ | EuCd$_2$P$_2$ is notable for its unconventional transport: upon cooling the
metallic resistivity changes slope and begins to increase, ultimately 100-fold,
before returning to its metallic value. Surprisingly, this giant peak occurs at
18K, well above the N\'{e}el temperature ($T_N$) of 11.5K. Using a suite of
sensitive probes of magnetism, including resonant x-ray scattering and
magneto-optical polarimetry, we have discovered that ferromagnetic order onsets
above $T_N$ in the temperature range of the resistivity peak. The observation
of inverted hysteresis in this regime shows that ferromagnetism is promoted by
coupling of localized spins and itinerant carriers. The resulting carrier
localization is confirmed by optical conductivity measurements. | 2208.05499v1 |
2022-10-04 | Time-domain impedance method for transient photovoltage analysis | In this work, we approximate the surface photovoltage (SPV) transients in
nm-sized ZnO films by the equivalent RC circuit model. The SPV rises in time in
time for about 90 mcs after the exciting light pulse at 275 nm is off at
different pulse widths ranging from 1.2 to 12 mcs. The key to this observation
is a considerable amount of defects in the films, which form a trap capacitance
in the equivalent circuit. The photogeneration of nonequilibrium electrons and
holes near the film surface is described by charging of a capacitance by the
current source whereas the rate of their spatial separation is determined by a
resistance. This resistance reflects an obstacle in the carrier movement while
another capacitance determines the charge separation distance. The
electron-hole recombination is account for a second resistance introduced into
the equivalent circuit. The resulting modeled SPV transient allows to reproduce
the observed experimental curve rather well. | 2210.07928v1 |
2022-10-17 | Multiscale modeling of resistive switching in gold nanogranular films | Metallic nanogranular films display a complex dynamical response to a
constant bias, showing up as atypical resistive switching mechanism which could
be used to create electrical components for neuromorphic applications. To model
such a phenomenon we use a multiscale approach blending together an ab initio
treatment of the electric current at the nanoscale, a molecular dynamical
approach dictating structural rearrangements, and a finite-element solution of
the heat equation for heat propagation in the sample. We also consider
structural changes due to electromigration which are modelled on the basis of
experimental observations on similar systems. Within such an approach, we
manage to describe some distinctive features of the resistive switching
occurring in nanogranular film and provide a physical interpretation at the
microscopic level. | 2210.09379v1 |
2022-10-27 | Green's Functions For Random Resistor Networks | We analyze random resistor networks through a study of lattice Green's
functions in arbitrary dimensions. We develop a systematic disorder
perturbation expansion to describe the weak disorder regime of such a system.
We use this formulation to compute ensemble averaged nodal voltages and bond
currents in a hierarchical fashion. We verify the validity of this expansion
with direct numerical simulations of a square lattice with resistances at each
bond exponentially distributed. Additionally, we construct a formalism to
recursively obtain the exact Green's functions for finitely many disordered
bonds. We provide explicit expressions for lattices with up to four disordered
bonds, which can be used to predict nodal voltage distributions for arbitrarily
large disorder strengths. Finally, we introduce a novel order parameter that
measures the overlap between the bond current and the optimal path (the path of
least resistance), for a given resistance configuration, which helps to
characterize the weak and strong disorder regimes of the system. | 2210.15562v3 |
2022-12-19 | Anisotropic resistance with a 90-degree twist in a ferromagnetic Weyl semimetal, Co2MnGa | Co$_2$MnGa is a ferromagnetic semimetal with Weyl nodal lines identified by
ARPES. We studied electrical transport in thin Co$_2$MnGa lamellae (10 $\times$
10 $\times$ 0.4-5 microns) cut from single-crystals using a focused ion beam.
These crystals exhibit an unexpected and highly unusual planar resistance
anisotropy ($\sim$10 times) with principal axes that rotate by 90 degrees
between the upper and lower faces. Using symmetry arguments and simulations, we
find that the observed resistance anisotropy resembles that of an isotropic
conductor with anisotropic surface states that are impeded from hybridization
with bulk states. The origin of these states awaits further experiments that
can correlate the surface bands with the observed 90$^\circ$-twist geometry. | 2212.09738v1 |
2022-12-29 | Stateful Logic using Phase Change Memory | Stateful logic is a digital processing-in-memory technique that could address
von Neumann memory bottleneck challenges while maintaining backward
compatibility with standard von Neumann architectures. In stateful logic,
memory cells are used to perform the logic operations without reading or moving
any data outside the memory array. Stateful logic has been previously
demonstrated using several resistive memory types, mostly by resistive RAM
(RRAM). Here we present a new method to design stateful logic using a different
resistive memory - phase change memory (PCM). We propose and experimentally
demonstrate four logic gate types (NOR, IMPLY, OR, NIMP) using commonly used
PCM materials. Our stateful logic circuits are different than previously
proposed circuits due to the different switching mechanism and functionality of
PCM compared to RRAM. Since the proposed stateful logic form a functionally
complete set, these gates enable sequential execution of any logic function
within the memory, paving the way to PCM-based digital processing-in-memory
systems. | 2212.14377v1 |
2023-03-15 | Two-fold anisotropic superconducting state in topological superconductor Sn$_4$Au | Here we report the anisotropic magnetotransport properties in the
superconducting state of Sn$_4$Au single crystal. Sn$_4$Au single crystal is
synthesized through an easy melt growth method. Superconducting properties are
evidenced by resistivity vs. temperature and DC magnetization measurements.
Isothermal magnetization measurements hint toward type-II superconductivity in
Sn$_4$Au. In-plane and out-of-plane resistivity measurements show anisotropic
behavior of the upper critical field at temperatures below superconducting
transition (T$_c$ = 2.3 K). The observed anisotropy is more elucidated in
resistivity measurements performed below Tc at different tilt angles. The
anisotropy parameter is found to be 1.26. The observed results show the
presence two-fold anisotropic superconducting state in Sn$_4$Au single crystal,
which may be induced due to the layered structure of synthesized Sn$_4$Au
single crystal. | 2303.08520v1 |
2023-03-28 | Effect of atomic anti-site disorder on the AMR in FeCo alloys | In order to understand the anti-site disorder effect on the anisotropic
magnetoresistance (AMR) effect in alloys, $\rm{Fe}_{50}Co_{50}$ alloys were
studied in this work using the fully relativistic spin-polarized screened (KKR)
method. The anti-site effect was modeled by interchanging Fe and Co atoms and
treated by the coherent potential approximation (CPA). We find that the
anti-site disorder broadens the spectral function and decreases the
conductivity. Our work emphasizes that the absolute variations of resistivity
under magnetic moment rotation are less affected by atomic disorders. The
annealing procedure improves the AMR by reduction of the total resistivity. At
the same time, we also find that the fourth-order term in the angular dependent
resistivity becomes weaker when the disorder increases, resulting from
increased scattering of the states around the band-crossing. | 2303.15726v1 |
2023-03-28 | Superconductivity in boron-doped carbon nanotube networks | By using the five Angstrom diameter pores of calcined zeolite as the
template, we have fabricated boron doped carbon nanotube networks via the
chemical vapor deposition method. Raman data indicate the network to comprise
segments of interconnected carbon nano tubes. Transport measurements showed a
superconducting transition initiating at 40K, with a sharp downturn around 20K
to a low resistance state at 2K, accompanied by a low resistance plateau in the
current voltage characteristic, fluctuating around zero resistance. Magnetic
measurements exhibited the Meissner effect characteristic of thin
superconducting wire networks in which the superconducting wire radius is much
smaller than the London penetration length. At low magnetic field, the negative
diamagnetic susceptibility was observed to persist beyond 200K. The transport
and magnetic data are reconciled on the basis of a physical model based on weak
links comprising short, one-dimensional superconducting nano tubes, that govern
the global transport behavior. | 2303.15980v1 |
2023-04-12 | Measuring a Soft Resistive Strain Sensor Array by Solving the Resistor Network Inverse Problem | Soft robotics is applicable to a variety of domains due to the adaptability
offered by the soft and compliant materials. To develop future intelligent soft
robots, soft sensors that can capture deformation with nearly infinite
degree-of-freedom are necessary. Soft sensor networks can address this problem,
however, measuring all sensor values throughout the body requires excessive
wiring and complex fabrication that may hinder robot performance. We circumvent
these challenges by developing a non-invasive measurement technique, which is
based on an algorithm that solves the inverse problem of resistor network, and
implement this algorithm on a soft resistive, strain sensor network. Our
algorithm works by iteratively computing the resistor values based on the
applied boundary voltage and current responses, and we analyze the
reconstruction error of the algorithm as a function of network size and
measurement error. We further develop electronics setup to implement our
algorithm on a stretchable resistive strain sensor network made of soft
conductive silicone, and show the response of the measured network to different
deformation modes. Our work opens a new path to address the challenge of
measuring many sensor values in soft sensors, and could be applied to soft
robotic sensor systems. | 2304.05828v1 |
2023-05-22 | Ion-selective scattering studied by the variable-energy electron irradiation of Ba$_{0.2}$K$_{0.8}$Fe$_2$As$_2$ superconductor | Low-temperature variable-energy electron irradiation was used to induce
non-magnetic disorder in a single crystal of hole-doped iron-based
superconductor, Ba$_{1-x}$K$_x$Fe$_2$As$_2$, $x=$0.80. To avoid systematic
errors, the beam energy was adjusted non-consequently for five values between
1.0 and 2.5 MeV, whence sample resistance was measured in-situ at 22 K. For all
energies, the resistivity raises linearly with the irradiation fluence
suggesting the creation of uncorrelated dilute point-like disorder (confirmed
by simulations). The rate of the resistivity increase peaks at energies below
1.5 MeV. Comparison with calculated partial cross-sections points to the
predominant creation of defects in the iron sublattice. Simultaneously,
superconducting $T_c$, measured separately between the irradiation runs, is
monotonically suppressed as expected since it depends on the total scattering
rate, hence total cross-section, which is a monotonically increasing function
of energy. Our work confirms experimentally an often-made assumption of the
dominant role of the iron sub-lattice in iron-based superconductors. | 2305.13217v1 |
2023-06-05 | Multilayer GZ/YSZ Thermal Barrier Coating from Suspension and Solution Precursor Plasma Spray | Gas turbines rely on thermal barrier coating (TBC) to thermally insulate the
nickel-based superalloys underneath during operation; however, current TBCs,
yttria stabilised zirconia (YSZ), limit the operating temperature and hence
efficiency. At an operating temperature above 1200{\deg}C, YSZ is susceptible
to failure due to phase instabilities and CMAS (Calcia-Magnesia-Alumina-Silica)
attack. Gadolinium zirconates (GZ) could overcome the drawback of YSZ,
complementing each other with the multi-layer approach. This study introduces a
novel approach utilising axial suspension plasma spray (ASPS) and axial
solution precursor plasma spray (ASPPS) to produce a double-layer and a
triple-layer TBCs with improved CMAS resistance. The former comprised
suspension plasma sprayed GZ and YSZ layers while the latter had an additional
dense layer deposited through a solution precursor to minimise the columnar
gaps that pre-existed in the SPS GZ layer, thus resisting CMAS infiltration.
Both coatings performed similarly in furnace cycling test (FCT) and burner rig
testing (BRT). In the CMAS test, triple-layer coating showed better CMAS
resistivity, as evidenced by the limited CMAS infiltration observed on the
surface. | 2306.02720v1 |
2024-01-31 | Effect of severe plastic deformation realized by rotary swaging on the mechanical properties and corrosion resistance of near-a-titanium alloy Ti-2.5Al-2.6Zr | The research aims to analyze the impact that severe plastic deformation
arising during Rotary Swaging has on mechanical properties and corrosion
resistance of a near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian industrial name
PT7M). The nature of corrosion decay in fine-grained alloys caused by hot salt
corrosion is known to vary from pit corrosion to intercrystalline corrosion at
the onset of recrystallization processes. Resistance to hot salt corrosion in a
fine-grained titanium alloy Ti-2.5Al-2.6Zr is shown to depend on the
structural-phase state of grain boundaries that varies during their migration
as a result of covering corrosive doping elements (aluminum, zirconium)
distributed in the crystal lattice of a titanium alloy. | 2401.17672v1 |
2024-03-17 | Observation of diamagnetic strange-metal phase in sulfur-copper codoped lead apatite | By codoping sulfur and copper into lead apatite, the crystal grains are
directionally stacked and the room-temperature resistivity is reduced from
insulating to $2\times10^{-5}~\Omega\cdot$m. The resistance-temperature curve
exhibits a nearly linear relationship at low temperature suggesting the
presence of strange-metal phase, and a second-order phase transition is then
observed at around 230~K during cooling the samples. A possible Meissner effect
is present in dc magnetic measurements. Further hydrothermal lead-free
synthesis results in smaller resistance and stronger diamagnetism,
demonstrating the essential component might be sulfur-substituted copper
apatite and the alkalis matter as well. A clear pathway towards
superconductivity in this material is subsequently benchmarked. | 2403.11126v3 |
2024-04-09 | Transport resistance strikes back: unveiling its impact on fill factor losses in organic solar cells | The fill factor ($FF$) is a critical parameter for solar cell efficiency, yet
its analytical description is challenging due to the interplay between
recombination and charge extraction processes. An often overlooked yet
significant factor contributing to $FF$ losses, beyond recombination, is the
influence of charge transport. In most state-of-the-art organic solar cells,
the primary limitation of the $FF$ arises not from recombination but rather
from low conductivity, highlighting the need for refined models to predict the
$FF$ accurately. Here, we extend the analytical model for transport resistance
to a more general case. Drawing from a large set of experimental
current-voltage and light intensity-dependent open-circuit voltage data, we
systematically incorporate crucial details previously omitted in the model.
Consequently, we introduce a straightforward set of equations to predict the
$FF$ of a solar cell, enabling the differentiation of losses attributed to
recombination and transport resistance. Our study provides valuable insights
into strategies for mitigating $FF$ losses based on the experimentally
validated analytical model, guiding the development of more efficient solar
cell designs and optimization strategies. | 2404.06190v1 |
2024-05-09 | Negative longitudinal resistance of monolayer graphene in the quantum Hall regime | In the quantum Hall regime the charge current is carried by ideal
one-dimensional edge channels where the backscattering is prohibited by
topology. This results in the constant potential along the edge of the Hall bar
leading to zero 4-terminal longitudinal resistance r_xx. Finite scattering
between the counter-propagating edge states, when the topological protection is
broken, commonly results in r_xx > 0. However, a local disorder, if allowing
intersection of the edge states, can result in a counter-intuitive scenario
when r_xx<0. In this work we report the observation and a systematic study of
such unconventional negative longitudinal resistance seen in an encapsulated
monolayer graphene Hall bar device measured in the quantum Hall regime. We
supplement our findings with the numerical calculations which allow us to
outline the conditions necessary for the appearance of negative r_xx and to
exclude the macroscopic disorder (contamination bubble) as the main origin of
it. | 2405.05515v2 |
2012-08-01 | Spin-fluctuations in Ti$_{60}$V$_{40}$ alloy and its influence on the superconductivity | We report experimental studies of the temperature and magnetic field
dependence of resistivity and dc magnetic susceptibility and the temperature
dependence of zero field heat capacity in a Ti$_{0.6}$V$_{0.4}$ alloy. The
temperature dependence of the normal state dc magnetic susceptibility in this
Ti$_{0.6}$V$_{0.4}$ alloy shows T$^2$lnT behavior. The temperature dependence
of resistivity follows a T$^2$ behaviour in the range 20-50 K. On the other
hand, a term $T^3$ lnT is needed in the expression containing the electronic
and lattice heat capacities to explain the temperature dependence of heat
capacity at temperatures where $T^2$ dependence of resistivity is observed.
Such temperature dependence of dc magnetic susceptibility, resistivity and heat
capacity are indications of the presence of spin-fluctuations in the system.
Further experimental evidence for the spin fluctuations is obtained in the form
of a negative value of T$^5$ term in the temperature dependence of resistivity.
The influence of spin-fluctuations on the superconducting properties of
Ti$_{0.6}$V$_{0.4}$ is discussed in detail. We show from our analysis of
resistivity and the susceptibility in normal and superconducting states that
the spin fluctuations present in Ti$_{0.6}$V$_{0.4}$ alloy are itinerant in
nature. There is some evidence of the existence of preformed Cooper-pairs in
the temperature range well above the superconducting transition temperature.
Our study indicates that the interesting correlations between spin-fluctuations
and superconductivity may actually be quite widespread amongst the
superconducting materials, and not necessarily be confined only to certain
classes of exotic compounds. | 1208.0181v3 |
2016-06-14 | On the multiferroic skyrmion-host GaV4S8 | The lacunar spinel GaV4S8 exhibits orbital ordering at 44 K and shows a
complex magnetic phase diagram below 12.7 K, which includes ferromagnetic and
cycloidal spin order. At low but finite external magnetic fields, N\'eel-type
skyrmions are formed in this material. Skyrmions are whirl-like spin vortices
that have received great theoretical interest because of their non-trivial spin
topology and that are also considered as basic entities for new data-storage
technologies. Interestingly, we found that the orbitally ordered phase shows
sizable ferroelectric polarization and that excess spin-driven polarizations
appear in all magnetic phases, including the skyrmion-lattice phase. Hence,
GaV4S8 shows simultaneous magnetic and polar order and belongs to the class of
multiferroics, materials that attracted enormous attention in recent years.
Here, we summarize the existing experimental information on the magnetic,
electronic, and dielectric properties of GaV4S8. By performing detailed
magnetic susceptibility, resistivity, specific heat, and dielectric
experiments, we complement the low-temperature phase diagram. Specifically, we
show that the low-temperature and low-field ground state of GaV4S8 seems to
have a more complex spin configuration than purely collinear ferromagnetic spin
order. In addition, at the structural Jahn-Teller transition the magnetic
exchange interaction changes from antiferromagnetic to ferromagnetic. We also
provide experimental evidence that the vanadium V4 clusters in GaV4S8 can be
regarded as molecular units with spin 1/2. However, at high temperatures
deviations in the susceptibility show up, indicating that either the magnetic
moments of the vanadium atoms fluctuate independently or excited states of the
V4 molecule become relevant. | 1606.04511v1 |
2016-10-24 | Self-aligned local electrolyte gating of 2D materials with nanoscale resolution | In the effort to make 2D materials-based devices smaller, faster, and more
efficient, it is important to control charge carrier at lengths approaching the
nanometer scale. Traditional gating techniques based on capacitive coupling
through a gate dielectric cannot generate strong and uniform electric fields at
this scale due to divergence of the fields in dielectrics. This field
divergence limits the gating strength, boundary sharpness, and pitch size of
periodic structures, and restricts possible geometries of local gates (due to
wire packaging), precluding certain device concepts, such as plasmonics and
transformation optics based on metamaterials. Here we present a new gating
concept based on a dielectric-free self-aligned electrolyte technique that
allows spatially modulating charges with nanometer resolution. We employ a
combination of a solid-polymer electrolyte gate and an ion-impenetrable
e-beam-defined resist mask to locally create excess charges on top of the gated
surface. Electrostatic simulations indicate high carrier density variations of
$\Delta n =10^{14}\text{cm}^{-2}$ across a length of 10 nm at the mask
boundaries on the surface of a 2D conductor, resulting in a sharp depletion
region and a strong in-plane electric field of $6\times10^8 \text{Vm}^{-1}$
across the so-created junction. We apply this technique to the 2D material
graphene to demonstrate the creation of tunable p-n junctions for
optoelectronic applications. We also demonstrate the spatial versatility and
self-aligned properties of this technique by introducing a novel graphene
thermopile photodetector. | 1610.07646v2 |
2020-09-22 | Half-Metal Spin-Gapless Semiconductor Junctions as a Route to the Ideal Diode | The ideal diode is a theoretical concept that completely conducts the
electric current under forward bias without any loss and that behaves like a
perfect insulator under reverse bias. However, real diodes have a junction
barrier that electrons have to overcome and thus they have a threshold voltage
$V_T$, which must be supplied to the diode to turn it on. This threshold
voltage gives rise to power dissipation in the form of heat and hence is an
undesirable feature. In this work, based on half-metallic magnets and
spin-gapless semiconductors we propose a diode concept that does not have a
junction barrier and the operation principle of which relies on the
spin-dependent transport properties of the HMM and SGS materials. We show that
the HMM and SGS materials form an Ohmic contact under any finite forward bias,
while for a reverse bias the current is blocked due to spin-dependent filtering
of the electrons. Thus, the HMM-SGS junctions act as a diode with zero
threshold voltage $V_T$, and linear $I-V$ characteristics as well as an
infinite on:off ratio at zero temperature. However, at finite temperatures,
non-spin-flip thermally excited high-energy electrons as well as low-energy
spin-flip excitations can give rise to a leakage current and thus reduce the
on:off ratio under a reverse bias. Furthermore, a zero threshold voltage allows
one to detect extremely weak signals and due to the Ohmic HMM-SGS contact, the
proposed diode has a much higher current drive capability and low resistance,
which is advantageous compared to conventional semiconductor diodes. We employ
the NEGF method combined with DFT to demonstrate the linear $I-V$
characteristics of the proposed diode based on two-dimensional half-metallic
Fe/MoS$_2$ and spin-gapless semiconducting VS$_2$ planar heterojunctions. | 2009.10463v1 |
2020-11-22 | Quasi-two-dimensional heterostructures (K$M_{1-x}$Te)(LaTe$_{3}$) ($M$ = Mn, Zn) with charge density waves | Layered heterostructure materials with two different functional building
blocks can teach us about emergent physical properties and phenomena arising
from interactions between the layers. We report the intergrowth compounds
KLa$M$$_{1-x}$Te$_{4}$ ($M$ = Mn, Zn; $x\approx$ 0.35) featuring two chemically
distinct alternating layers [LaTe$_3$] and [K$M$$_{1-x}$Te]. Their crystal
structures are incommensurate, determined by single X-ray diffraction for the
Mn compound and transmission electron microscope (TEM) study for the Zn
compound. KLaMn$_{1-x}$Te$_{4}$ crystallizes in the orthorhombic superspace
group $Pmnm$(01/2${\gamma}$)$s$00 with lattice parameters $a$ = 4.4815(3)
{\AA}, $b$ = 21.6649(16) {\AA} and $c$ = 4.5220(3) {\AA}. It exhibits charge
density wave (CDW) order at room temperature with a modulation wave vector
$\mathbf{q}$ = 1/2$\mathbf{b}$* + 0.3478$\mathbf{c}$* originating from
electronic instability of Te-square nets in [LaTe$_{3}$] layers. The Mn analog
exhibits a cluster spin glass behavior with spin freezing temperature
$T_{\mathrm{f}}$ $\approx$ 5 K attributed to disordered Mn vacancies and
competing magnetic interactions in the [Mn$_{1-x}$Te] layers. The Zn analog
also has charge density wave order at room temperature with a similar
$\mathbf{q}$-vector having the $\mathbf{c}$* component ~ 0.346 confirmed by
selected-area electron diffraction (SAED). Electron transfer from
[K$M_{1-x}$Te] to [LaTe$_{3}$] layers exists in KLa$M_{1-x}$Te$_{4}$, leading
to an enhanced electronic specific heat coefficient. The resistivities of
KLa$M_{1-x}$Te$_{4}$ ($M$ = Mn, Zn) exhibit metallic behavior at high
temperatures and an upturn at low temperatures, suggesting partial localization
of carriers in the [LaTe$_{3}$] layers with some degree of disorder associated
with the $M$ atom vacancies in the [$M_{1-x}$Te] layers. | 2011.11068v2 |
2021-06-09 | Fracture Mechanics-Based Quantitative Matching of Forensic Evidence Fragments | Fractured metal fragments with rough and irregular surfaces are often found
at crime scenes. Current forensic practice visually inspects the complex jagged
trajectory of fractured surfaces to recognize a ``match'' using comparative
microscopy and physical pattern analysis. We developed a novel computational
framework, utilizing the basic concepts of fracture mechanics and statistical
analysis to provide quantitative match analysis for match probability and error
rates. The framework employs the statistics of fracture surfaces to become
non-self-affine with unique roughness characteristics at relevant microscopic
length scale, dictated by the intrinsic material resistance to fracture and its
microstructure. At such a scale, which was found to be greater than two
grain-size or micro-feature-size, we establish that the material intrinsic
properties, microstructure, and exposure history to external forces on an
evidence fragment have the premise of uniqueness, which quantitatively
describes the microscopic features on the fracture surface for forensic
comparisons. The methodology utilizes 3D spectral analysis of overlapping
topological images of the fracture surface and classifies specimens with very
high accuracy using statistical learning. Cross correlations of image-pairs in
two frequency ranges are used to develop matrix variate statistical models for
the distributions among matching and non-matching pairs of images, and provides
a decision rule for identifying matches and determining error rates. A set of
thirty eight different fracture surfaces of steel articles were correctly
classified. The framework lays the foundations for forensic applications with
quantitative statistical comparison across a broad range of fractured materials
with diverse textures and mechanical properties. | 2106.04809v1 |
2021-06-16 | Role of surface termination in the metal-insulator transition of V$_2$O$_3$(0001) ultrathin films | Surface termination is known to play an important role in determining the
physical properties of materials. It is crucial to know how surface termination
affects the metal-insulator transition (MIT) of V$_2$O$_3$ films for both
fundamental understanding and its applications. By changing growth parameters,
we achieved a variety of surface terminations in V$_2$O$_3$ films that are
characterized by low energy electron diffraction (LEED) and photoemission
spectroscopy techniques. Depending upon the terminations, our results show MIT
can be partially or fully suppressed near the surface region due to the
different filling of the electrons at the surface and sub-surface layers and
change of screening length compared to the bulk. Across MIT, a strong
redistribution of spectral weight and its transfer from high-to-low binding
energy regime is observed in a wide-energy-scale. Our results show total
spectral weight in the low-energy regime is not conserved across MIT,
indicating a breakdown of `sum rules of spectral weight', a signature of a
strongly correlated system. Such change in spectral weight is possibly linked
to the change in hybridization, lattice volume ({\it i.e.,} effective carrier
density), and spin degree of freedom in the system that happens across MIT. We
find that MIT in this system is strongly correlation-driven where the
electron-electron interactions play a pivotal role. Moreover, our results
provide a better insight in understanding the electronic structure of strongly
correlated systems and highlight the importance of accounting surface effects
during interpretation of the physical property data mainly using surface
sensitive probes, such as surface resistivity. | 2106.08555v1 |
2022-03-24 | Influence of generated defects by Ar-implantation on the thermoelectric properties of ScN | Nowadays, making thermoelectric materials more efficient in energy conversion
is still a challenge. In this work, to reduce the thermal conductivity and thus
improve the overall thermoelectric performances, point and extended defects
were generated in epitaxial 111-ScN thin films by implantation using argon
ions. The films were investigated by structural, optical, electrical, and
thermoelectric characterization methods. The results demonstrated that argon
implantation leads to the formation of stable defects (up to 750 K operating
temperature) were identified as interstitial type defect clusters and so-called
argon-vacancy complexes. The insertion of those specific defects induces
acceptor-type deep levels in the bandgap yielding to a reduce of the free
carrier mobility. With a reduce electrical conductivity, the irradiated sample
exhibited higher Seebeck coefficient maintaining the power factor of the film.
The thermal conductivity is strongly reduced from 12 to 3 W.m-1.K-1 at 300 K,
showing the effect of defects in increasing phonon scattering. Subsequent high
temperature annealing, at 1573 K, leads to the progressive evolution of
defects: the initial clusters of interstitial evolved to the benefit of smaller
clusters and the formation of bubble. Thus, the number of free carriers, the
resistivity and the Seebeck coefficient are almost restored but the mobility of
the carriers remains low and a 30% drop in thermal conductivity is still
effective (8.5 W.m-1.K-1). This study shows that the control defect engineering
with defects introduced by irradiation using noble gases in a thermoelectric
coating can be an attractive method to enhance the figure of merit of
thermoelectric materials. | 2203.13227v4 |
2022-03-29 | Dose rate effects in radiation-induced changes to phenyl-based polymeric scintillators | Results on the effects of ionizing radiation on the signal produced by
plastic scintillating rods manufactured by Eljen Technology company are
presented for various matrix materials, dopant concentrations, fluors (EJ-200
and EJ-260), anti-oxidant concentrations, scintillator thickness, doses, and
dose rates. The light output before and after irradiation is measured using an
alpha source and a photomultiplier tube, and the light transmission by a
spectrophotometer. Assuming an exponential decrease in the light output with
dose, the change in light output is quantified using the exponential dose
constant $D$. The $D$ values are similar for primary and secondary doping
concentrations of 1 and 2 times, and for antioxidant concentrations of 0, 1,
and 2 times, the default manufacturer's concentration. The $D$ value depends
approximately linearly on the logarithm of the dose rate for dose rates between
2.2 Gy/hr and 70 Gy/hr for all materials. For EJ-200 polyvinyltoluene-based
(PVT) scintillator, the dose constant is approximately linear in the logarithm
of the dose rate up to 3400 Gy/hr, while for polystyrene-based (PS)
scintillator or for both materials with EJ-260 fluors, it remains constant or
decreases (depending on doping concentration) above about 100 Gy/hr. The
results from rods of varying thickness and from the different fluors suggest
damage to the initial light output is a larger effect than color center
formation for scintillator thickness $\leq1$ cm. For the blue scintillator
(EJ-200), the transmission measurements indicate damage to the fluors. We also
find that while PVT is more resistant to radiation damage than PS at dose rates
higher than about 100 Gy/hr for EJ-200 fluors, they show similar damage at
lower dose rates and for EJ-260 fluors. | 2203.15923v2 |
2022-04-11 | Thermal insulation and heat guiding using nanopatterned MoS2 | In the modern electronics overheating is one of the major reasons for device
failure. Overheating causes irreversible damage to circuit components and can
also lead to fire, explosions, and injuries. Accordingly, in the advent of 2D
material-based electronics, an understanding of their thermal properties in
addition to their electric ones is crucial to enable efficient transfer of
excess heat away from the electronic components. In this work we propose
structures based on free-standing, few-layer, nanopatterned MoS2 that insulate
and guide heat in the in-plane direction. We arrive at these designs via a
thorough study of the in-plane thermal conductivity as a function of thickness,
porosity, and temperature in both pristine and nanopatterned MoS2 membranes.
Two-laser Raman thermometry was employed to measure the thermal conductivities
of a set of free-standing MoS2 flakes with diameters greater than 20 um and
thicknesses from 5 to 40 nm, resulting in values from 30 to 85 W/mK,
respectively. After nanopatterning a square lattice of 100-nm diameter holes
with a focused ion beam we have obtained a greater than 10-fold reduction of
the thermal conductivities for the period of 500 nm and values below 1 W/mK for
the period of 300 nm. The results were supported by equilibrium molecular
dynamic simulations for both pristine and nanopatterned MoS2. The selective
patterning of certain areas results in extremely large difference in thermal
conductivities within the same material. Exploitation of this effect enabled
for the first time thermal insulation and heat guiding in the few-layer MoS2.
The patterned regions act as high thermal resistors: we obtained a thermal
resistance of 4x10-6 m2K/W with only four patterned lattice periods of 300 nm,
highlighting the significant potential of MoS2 for thermal management
applications. | 2204.04999v1 |
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