publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2019-08-29 | Evidence for weak antilocalization-weak localization crossover and metal-insulator transition in CaCu$_{3}$Ru$_{4}$O$_{12}$ thin films | Artificial confinement of electrons by tailoring the layer thickness has
turned out to be a powerful tool to harness control over competing phases in
nano-layers of complex oxides. We investigate the effect of dimensionality on
transport properties of $d$-electron based heavy-fermion metal
CaCu$_{3}$Ru$_{4}$O$_{12}$. Transport behavior evolves from metallic to
localized regime upon reducing thickness and a metal insulator transition is
observed below 3 nm film thickness for which sheet resistance crosses $h/e^{2}
\sim 25~$k$\Omega$, the quantum resistance in 2D. Magnetotransport study
reveals a strong interplay between inelastic and spin-orbit scattering lengths
upon reducing thickness, which results in weak antilocalization (WAL) to weak
localization (WL) crossover in magnetoconductance. | 1908.11128v2 |
2021-01-17 | Surface-Wave Propagation on Non-Hermitian Metasurfaces with Extreme Anisotropy | Electromagnetic metasurfaces enable the advanced control of surface-wave
propagation by spatially tailoring the local surface reactance. Interestingly,
tailoring the surface resistance distribution in space provides new, largely
unexplored degrees of freedom. Here, we show that suitable spatial modulations
of the surface resistance between positive (i.e., loss) and negative (i.e.,
gain) values can induce peculiar dispersion effects, far beyond a mere
compensation. Taking inspiration from the parity-time symmetry concept in
quantum physics, we put forward and explore a class of non-Hermitian
metasurfaces that may exhibit extreme anisotropy mainly induced by the
gain-loss interplay. Via analytical modeling and full-wave numerical
simulations, we illustrate the associated phenomenon of surface-wave
canalization, explore nonlocal effects and possible departures from the ideal
conditions, and address the feasibility of the required constitutive
parameters. Our results suggest intriguing possibilities to dynamically
reconfigure the surface-wave propagation, and are of potential interest for
applications to imaging, sensing and communications. | 2101.06641v1 |
2012-06-11 | Multiorbital effects on the transport and the superconducting fluctuations in LiFeAs | The resistivity, Hall effect and transverse magnetoresistance (MR) have been
measured in low residual resistivity single crystals of LiFeAs. A comparison
with angle resolved photoemission spectroscopy and quantum oscillation data
implies that four carrier bands unevenly contribute to the transport. However
the scattering rates of the carriers all display the T^2 behavior expected for
a Fermi liquid. Near Tc low field deviations of the MR with respect to a H^2
variation permit us to extract the superconducting fluctuation contribution to
the conductivity. Though below Tc the anisotropy of superconductivity is rather
small, the superconducting fluctuations display a quasi ideal two-dimensional
behavior which persists up to 1.4 Tc. These results call for a refined
theoretical understanding of the multiband behavior of superconductivity in
this pnictide. | 1206.2278v2 |
2015-04-27 | Two types of nematicity in the phase diagram of the cuprate superconductor YBa$_2$Cu$_3$O$_y$ | Nematicity has emerged as a key feature of cuprate superconductors, but its
link to other fundamental properties such as superconductivity, charge order
and the pseudogap remains unclear. Here we use measurements of transport
anisotropy in YBa$_2$Cu$_3$O$_y$ to distinguish two types of nematicity. The
first is associated with short-range charge-density-wave modulations in a
doping region near $p = 0.12$. It is detected in the Nernst coefficient, but
not in the resistivity. The second type prevails at lower doping, where there
are spin modulations but no charge modulations. In this case, the onset of
in-plane anisotropy - detected in both the Nernst coefficient and the
resistivity - follows a line in the temperature-doping phase diagram that
tracks the pseudogap energy. We discuss two possible scenarios for the latter
nematicity. | 1504.06972v3 |
2015-06-29 | Magnetization and magneto-transport studies on Fe$_2$VAl$_{1-x}$Si$_x$ | We report on magnetoresistance, Hall and magnetization measurements of
Fe2VAl1-xSix Heusler compounds for x= 0.005, 0.015, 0.02. There is a systematic
change in the temperature coefficient of resistance (TCR) from negative to
positive as the Si composition is increased. The Hall co-efficient shows that
the carriers are electron like and the carrier density increases with Si
concentration. Resistance measurements under magnetic field indicate a
decreasing behavior under the application of magnetic field at low temperature
region (T< 60 K), suggesting the suppression of scattering by magnetic field.
Temperature and field dependent magnetization measurements did not show any
significant change apart from the fact that the presence of super paramagnetic
(SPM) cluster and its ordering at low temperatures. Arrott plot analysis of
magnetization versus field also indicates the magnetic ordering with applied
field below 60 K. | 1506.08516v1 |
2015-07-07 | Two-dimensional superconductor-insulator quantum phase transitions in an electron-doped cuprate | We use ionic liquid-assisted electric field effect to tune the carrier
density in an electron-doped cuprate ultrathin film and cause a two-dimensional
superconductor-insulator transition (SIT). The low upper critical field in this
system allows us to perform magnetic field (B)-induced SIT in the liquid-gated
superconducting film. Finite-size scaling analysis indicates that SITs induced
both by electric and magnetic field are quantum phase transitions and the
transitions are governed by percolation effects - quantum mechanical in the
former and classical in the latter case. Compared to the hole-doped cuprates,
the SITs in electron-doped system occur at critical sheet resistances (Rc) much
lower than the pair quantum resistance RQ=h/(2e)2=6.45 k{\Omega}, suggesting
the possible existence of fermionic excitations at finite temperature at the
insulating phase near SITs. | 1507.01668v1 |
2015-07-07 | S-wave Superconductivity in Optimally Doped SrTi$_{1-x}$Nb$_x$O$_3$ Unveiled by Electron Irradiation | We report on a study of electric resistivity and magnetic susceptibility
measurements in electron irradiated SrTi$_{0.987}$Nb$_{0.013}$O$_3$ single
crystals. Point-like defects, induced by electron irradiation, lead to an
almost threefold enhancement of the residual resistivity, but barely affect the
superconducting critical temperature ($T_c$). The pertinence of Anderson's
theorem provides strong evidence for a s-wave superconducting order parameter.
Stronger scattering leads to a reduction of the effective coherence length
($\xi$) and the deduced coherence length in the clean limit ($\xi_0$) is around
the BCS coherence length ($\xi_{BCS}$). Combined with thermal conductivity data
pointing to multiple nodeless gaps, the current results identify optimally
doped SrTi$_{1-x}$Nb$_x$O$_3$ as a multi-band s-wave superconductor. | 1507.01867v2 |
2015-07-15 | Depinning of Trapped Magnetic Flux in Bulk Niobium SRF Cavities | Trapped magnetic flux is known to be a significant contribution to the
residual resistance of superconducting radio frequency (SRF) cavities. The
additional losses depend strongly if the vortices are depinned by the RF. The
depinning is affected by the purity of the material, and the size of the
pinning centers, as well as the cavity operation frequency. One may define a
depinning frequency, above which significant depinning occurs. This publication
presents a derivation of the depinning frequency from experimental data. We
find a depinning frequency of 673 MHz for RRR 110 niobium. On this basis the
currently used model is extended to describe the trapped flux sensitivity as
function of residual resistance ratio (RRR) and operation frequency while also
accounting for the pinning center size and the treatment history of the cavity.
Moreover, the model offers an explanation for the significantly higher trapped
flux sensitivity reported for nitrogen doped and 120 C baked cavities. | 1507.04105v1 |
2016-09-08 | Pressure-induced topological phase transition in polar semiconductor BiTeBr | We performed X-ray diffraction and electrical resistivity measurement up to
pressures of 5 GPa and the first-principles calculations utilizing experimental
structural parameters to investigate the pressure-induced topological phase
transition in BiTeBr having a noncentrosymmetric layered structure (space group
P3m1). The P3m1 structure remains stable up to pressures of 5 GPa; the ratio of
lattice constants, c/a, has a minimum at pressures of 2.5 - 3 GPa. In the same
range, the temperature dependence of resistivity changes from metallic to
semiconducting at 3 GPa and has a plateau region between 50 and 150 K in the
semiconducting state. Meanwhile, the pressure variation of band structure shows
that the bulk band-gap energy closes at 2.9 GPa and re-opens at higher
pressures. Furthermore, according to the Wilson loop analysis, the topological
nature of electronic states in noncentrosymmetric BiTeBr at 0 and 5 GPa are
explicitly revealed to be trivial and non-trivial, respectively. These results
strongly suggest that pressure-induced topological phase transition in BiTeBr
occurs at the pressures of 2.9 GPa. | 1609.02274v1 |
2016-09-27 | Anomalous Feedback and Negative Domain Wall Resistance | Magnetic induction can be regarded as a negative feedback effect, where the
motive-force opposes the change of magnetic flux that generates the
motive-force. In artificial electromagnetics emerging from spintronics,
however, this is not necessarily the case. By studying the current-induced
domain wall dynamics in a cylindrical nanowire, we show that the spin
motive-force exerting on electrons can either oppose or support the applied
current that drives the domain wall. The switching into the anomalous feedback
regime occurs when the strength of the dissipative torque {\beta} is about
twice the value of the Gilbert damping constant {\alpha}. The anomalous
feedback manifests as a negative domain wall resistance, which has an analogy
with the water turbine. | 1609.08250v1 |
2018-07-19 | General theory of topological Hall effect in systems with chiral spin textures | We present a consistent theory of the topological Hall effect (THE) in 2D
magnetic systems with disordered array of chiral spin textures, such as
magnetic skyrmions. We focus on the scattering regime when the mean-free path
of itinerant electrons exceeds the spin texture size, and THE arises from the
asymmetric carrier scattering on individual chiral spin textures. We calculate
the resistivity tensor on the basis of the Boltzmann kinetic equation taking
into account the asymmetric scattering on skyrmions via the collision integral.
Our theory describes both the adiabatic regime, when THE arises from a spin
Hall effect and the non-adiabatic scattering when THE is due to purely charge
transverse currents. We analyze the dependence of THE resistivity on a chiral
spin texture structure,as well as on material parameters. We discuss the
crossover between spin and charge regimes of THE driven by the increase of
skyrmion size, the features of THE due to the variation of the Fermi energy,
and the exchange interaction strength; we comment on the sign and magnitude of
THE | 1807.07396v1 |
2018-12-21 | Thermoelectric transport in two-dimensional topological insulator state based on HgTe quantum well | The thermoelectric response of HgTe quantum wells in the state of
two-dimensional topological insulator (2D TI) has been studied experimentally.
Ambipolar thermopower, typical for an electron-hole system, has been observed
across the charge neutrality point, where the carrier type changes from
electrons to holes according to the resistance measurements. The hole-type
thermopower is much stronger than the electron-type one. The thermopower
linearly increases with temperature. We present a theoretical model which
accounts for both the edge and bulk contributions to the electrical
conductivity and thermoelectric effect in a 2D TI, including the effects of
edge to bulk leakage. The model, contrary to previous theoretical studies,
demonstrates that the 2D TI is not expected to show anomalies of thermopower
near the band conductivity threshold, which is consistent with our experimental
results. Based on the experimental data and theoretical analysis, we conclude
that the observed thermopower is mostly of the bulk origin, while the
resistance is determined by both the edge and bulk transport. | 1812.09226v1 |
2019-01-09 | Crystal structures and the sign reversal Hall resistivity in iron-based superconductors Lix(C3H10N2)0.32FeSe (0.15<x<0.4) | We report the crystal structure, superconductivity and normal state
properties of two iron-based materials, Li0.15(C3H10N2)0.32FeSe(P-4) and
Lix(C3H10N2)0.32FeSe(P4/nmm, 0.25<x<0.4) with superconducting transition
temperature from 40~46K. The determined crystal structures revealed a coupling
between Li concentration and the oritation of 1,2-Diaminopropane molecules
within the hyper expanded FeSe layers. Further fitting on resistivity in terms
of the Lawence-Doniach model suggests the two superconductors belong to the
quasi-two dimonsional system. With increasing temperature, a differences in
crystal structures and doping levels. First principle calculations revealed the
increase in FeSe layer diatance will restruct the Fermi surface and generate a
new hole pocket around Gamma point in the Brillouin Zone. Our findings support
that the increase in two dimensionalities will leads to a temperature induced
Lifshitz transition in electron doped FeSe superconductors. | 1901.02580v1 |
2019-01-18 | Tuning electric charge scattering in YBCO single crystals via irradiation with MeV electrons | Irradiation with electrons is an efficient approach to inducing a large
number of defects with a minimal impact on the material itself. Analysis of the
energy transfer from an accelerated particle smashing into the crystal lattice
shows that only electrons with MeV energies produce point defects in the form
of interstitial ions and vacancies that form perfect scattering centers. Here,
we investigate the changes in the resistive characteristics of YBCO single
crystals from the 1-2-3 system after several steps of low-temperature
irradiation with $0.5-2.5$\,MeV electrons and irradiation doses of up to
$8.8\times10^{18}$\,cm$^{-2}$. The penetration depth of such electrons is much
larger than the crystal thickness. We reveal that defects appearing in
consequence of such electron irradiation not only increase the residual
resistance, but they affect the phonon spectrum of the system and lower the
superconducting transition temperature linearly with increase of the
irradiation dose. Furthermore, the irradiation-induced defects are distributed
non-uniformly, that manifests itself via a broadening of the superconducting
transition. Interestingly, the excess conductivity remains almost unaffected
after such electron irradiation. | 1901.06293v1 |
2019-06-11 | Characterisation of Li in the surface film of a corrosion resistant Mg-Li(-Al-Y-Zr) alloy | The surface film formed upon Mg-Li(-Al-Y-Zr) following aqueous immersion and
air-exposure was investigated. This alloy (which contains 30.3 at. % Li)
possesses a bcc crystal structure and has been reported as being corrosion
resistant. It was determined that the principal components of the surface film
were Li2CO3 and Mg(OH)2 as characterised by grazing incidence X-ray diffraction
(GIXRD). The detection of hcp grains near the alloy surface was observed by
GIXRD and selected area electron diffraction (SAED). The spatial distribution
of Li and Mg in the surface film was characterised by electron energy loss
spectroscopy (EELS) and the distribution of other major elements in the alloy
was characterised by scanning transmission electron microscopy (STEM) and
energy dispersive X-ray spectroscopy (EDXS). It was observed that Li was
distributed throughout the alloy surface film and with an elevated
concentration in the so-called outer layer. | 1906.04508v1 |
2019-06-11 | Electrical Switching of Tristate Antiferromagnetic Néel Order in $α$-Fe$_{2}$O$_{3}$ Epitaxial Films | The ability to manipulate antiferromagnetic (AF) moments is a key requirement
for the emerging field of antiferromagnetic spintronics. Electrical switching
of bi-state AF moments has been demonstrated in metallic AFs, CuMnAs and
Mn$_2$Au. Recently, current-induced "saw-tooth" shaped Hall resistance was
reported in Pt/NiO bilayers, while its mechanism is under debate. Here, we
report the first demonstration of convincing, non-decaying, step-like
electrical switching of tri-state N\'eel order in Pt/$\alpha$-Fe$_2$O$_3$
bilayers. Our experimental data, together with Monte-Carlo simulations, reveal
the clear mechanism of the switching behavior of $\alpha$-Fe$_2$O$_3$ N\'eel
order among three stable states. We also show that the observed "saw-tooth"
Hall resistance is due to an artifact of Pt, not AF switching, while the
signature of AF switching is step-like Hall signals. This demonstration of
electrical control of magnetic moments in AF insulator (AFI) films will greatly
expand the scope of AF spintronics by leveraging the large family of AFIs. | 1906.04694v2 |
2019-10-01 | Valley Hall Effect and Non-Local Resistance in Locally Gapped Graphene | We report on the emergence of bulk, valley-polarized currents in
graphene-based devices, driven by spatially varying regions of broken
sublattice symmetry, and revealed by non-local resistance ($R_\mathrm{NL}$)
fingerprints. By using a combination of quantum transport formalisms, giving
access to bulk properties as well as multi-terminal device responses, the
presence of a non-uniform local bandgap is shown to give rise to
valley-dependent scattering and a finite Fermi surface contribution to the
valley Hall conductivity, related to characteristics of $R_\mathrm{NL}$. These
features are robust against disorder and provide a plausible interpretation of
controversial experiments in graphene/hBN superlattices. Our findings suggest
both an alternative mechanism for the generation of valley Hall effect in
graphene, and a route towards valley-dependent electron optics, by materials
and device engineering. | 1910.00489v2 |
2019-11-14 | Free-standing silicon shadow masks for transmon qubit fabrication | Nanofabrication techniques for superconducting qubits rely on resist-based
masks patterned by electron-beam or optical lithography. We have developed an
alternative nanofabrication technique based on free-standing silicon shadow
masks fabricated from silicon-on-insulator wafers. These silicon shadow masks
not only eliminate organic residues associated with resist-based lithography,
but also provide a pathway to better understand and control surface-dielectric
losses in superconducting qubits by decoupling mask fabrication from substrate
preparation. We have successfully fabricated aluminum 3D transmon
superconducting qubits with these shadow masks and found coherence quality
factors comparable to those fabricated with standard techniques. | 1911.05924v2 |
2019-11-21 | Experimental Realization of a Reconfigurable Electroacoustic Topological Insulator | A substantial challenge in guiding elastic waves is the presence of
reflection and scattering at sharp edges, defects, and disorders. Recently,
mechanical topological insulators have sought to overcome this challenge by
supporting back-scattering resistant wave transmission. In this Letter, we
propose and experimentally demonstrate the first \emph{reconfigurable
electroacoustic} topological insulator exhibiting an analog to the quantum
valley Hall effect (QVHE). Using programmable switches, this phononic structure
allows for rapid reconfiguration of domain walls and thus the ability to
control back-scattering resistant wave propagation along dynamic interfaces for
phonons lying in static and finite-frequency regimes. Accordingly, a
graphene-like Polyactic Acid (PLA) layer serves as the host medium, equipped
with periodically arranged and bonded piezoelectric patches, resulting in two
Dirac cones at the $K-$points. The PZT patches are then connected to negative
capacitance external circuits to break inversion symmetry and create nontrivial
topologically-protected bandgaps. As such, topologically protected interface
waves are demonstrated numerically and validated experimentally for different
predefined trajectories over a broad frequency range. | 1911.09608v1 |
2020-01-07 | Joule heating in the normal-superconductor phase transition in a magnetic field | Joule heating is a non-equilibrium dissipative process that occurs in a
normal metal when an electric current flows, in an amount proportional to the
metal's resistance. When it is induced by eddy currents resulting from a change
in magnetic flux, it is also proportional to the rate at which the magnetic
flux changes. Here we show that in the phase transformation between normal and
superconducting states of a metal in a magnetic field, the total amount of
Joule heating is determined by the thermodynamic properties of the system and
is independent of the resistivity of the normal metal. We also show that Joule
heating only occurs in the normal region of the material. The conventional
theory of superconductivity however predicts that Joule heating occurs also in
the superconducting region within a London penetration depth of the phase
boundary. This implies that there is a problem with the conventional theory of
superconductivity. | 2001.07509v2 |
2020-05-05 | Study of single crystalline SrAgSb and SrAuSb semimetals | Given renewed interest in the electronic properties of semimetallic compounds
with varying degrees of spin orbit coupling we have grown single crystals of
SrAgSb and SrAuSb, measured their temperature and field dependent electrical
resistivity and magnetization and performed density functional theory (DFT)
band structure calculations. Magnetization measurements are consistent with a
diamagnetic host with a small amount of local moment bearing impurities.
Although the residual resistivity ratio (RRR) for all samples studied was
relatively low, ranging between 2.4 and 3.4, the compounds had non-saturating
magnetoresistance (MR), reaching values of $\sim$ 17% and $\sim$ 70% at 4 K and
9 T for SrAgSb and SrAuSb respectively. Band structure calculations, using the
experimentally determined Wyckoff positions for the Sr, Ag/Au, and Sb atoms,
show that whereas SrAgSb is a topologically trivial, but compensated,
semimetal; SrAuSb is a topologically non-trivial, Dirac semimetal. | 2005.02323v1 |
2020-05-12 | Large anisotropic topological Hall effect in a hexagonal non-collinear magnet Fe5Sn3 | We report the observation of a large anisotropic topological Hall effect
(THE) in the hexagonal non-collinear magnet Fe5Sn3 single crystals. It is found
that the sign of the topological Hall resistivity is negative when a magnetic
field H perpendicular to the bc-plane (H\perp bc-plane), however, it changes
form negative to positive when H parallel to the c-axis (H\parallel c-axis).
The value of topological Hall resistivity increased with the increasing
temperature and reached approximately -2.12 \mu\Omega cm (H\perp bc-plane) and
0.5 \mu\Omega cm (H\parallel c-axis) at 350 K, respectively. Quantitative
analyses of the measured data suggest that the observed anisotropic THE may
originate from the opposite scalar spin chirality induced by the magnetic
fields perpendicular and parallel to the c-axis, respectively. | 2005.05709v1 |
2020-05-16 | Defect Level Switching for Highly-Nonlinear and Hysteretic Electronic Devices | Nonlinear and hysteretic electrical devices are needed for applications from
circuit protection to next-generation computing. Widely-studied devices for
resistive switching are based on mass transport, such as the drift of ions in
an electric field, and on collective phenomena, such as insulator-metal
transitions. We ask whether the large photoconductive response known in many
semiconductors can be stimulated in the dark and harnessed to design electrical
devices. We design and test devices based on photoconductive CdS, and our
results are consistent with the hypothesis that resistive switching arises from
point defects that switch between deep- and shallow-donor configurations:
defect level switching (DLS). This new electronic device design principle -
photoconductivity without photons - leverages decades of research on
photoconductivity and defect spectroscopy. It is easily generalized and will
enable the rational design of new nonlinear, hysteretic devices for future
electronics. | 2005.07935v1 |
2020-06-04 | Competition between ferromagnetic and antiferromagnetic states in Al8.5-xFe23Ge12.5+x (0<=x<=3) | Polycrystalline Al7+xFe23Ge14-x-type orthorhombic Al8.5-xFe23Ge12.5+x
(0<=x<=3) compounds were studied by X-ray diffraction measurement,
metallographic examination, and magnetization and electrical resistivity
measurements. The lattice parameters show anisotropic x dependences, reflecting
a lower symmetry of rather complex crystal structure. In the x=0 sample, a
ferromagnetic (FM) transition occurs at the Curie temperature TC of 255 K,
which is systematically reduced with increasing x and disappears at x=2.5 where
an antiferromagnetic (AFM) ground state is realized. The Neel temperature TN
seems to appear at x>=1, and grows to 143 K at x=3 with the increment of x. In
the intermediate range of x (1<=x<=2), a FM to AFM phase transition occurs
below TC. In the AFM phase, the electrical resistivity rho shows a Fermi
surface instability characterized by the upturn of rho below approximately TN.
The competition between the FM and AFM states would be ascribed to the
anisotropic x dependences of Fe-Fe bond lengths. | 2006.03152v1 |
2020-06-08 | Anisotropic physical properties and large critical current density in KCa${_2}$Fe${_4}$As${_4}$F${_2}$ single crystal | We present a systematic study of electrical resistivity, Hall coefficient,
magneto-optical imaging, magnetization, and STEM analyses of
KCa${_2}$Fe${_4}$As${_4}$F${_2}$ single crystals. Sharp diamagnetic transition
and magneto-optical imaging reveal homogeneity of single crystal and prominent
Bean-like penetrations of vortices. Large anisotropy of electrical resistivity,
with ${\rho _c / \rho _{ab}}$ > 100, and semiconductor-like ${\rho _c}$ suggest
that the electronic state is quasi two-dimensional. Hall effect measurements
indicate that KCa${_2}$Fe${_4}$As${_4}$F${_2}$ is a multiband system with holes
as main carriers. Magnetization measurements reveal significantly larger J$_c$
compared with that in other iron-based superconductors with different values of
J$_c$ depending on the direction of magnetic field. Origin of these J$_c$
characteristics is discussed based on microstructural observations using STEM.
In addition, further enhancement of J$_c$ in KCa${_2}$Fe${_4}$As${_4}$F${_2}$
for future application is demonstrated in terms of heavy-ion irradiation. | 2006.04478v1 |
2020-06-12 | Unraveling ferroelectric polarization and ionic contributions to electroresistance in epitaxial Hf0.5Zr0.5O2 tunnel junctions | Tunnel devices based on ferroelectric Hf0.5Zr0.5O2 (HZO) barriers hold great
promises for emerging data storage and computing technologies. The resistance
state of the device can be changed by a suitable writing voltage. However, the
microscopic mechanisms leading to the resistance change are an intricate
interplay between ferroelectric polarization controlled barrier properties and
defect-related transport mechanisms. Here is shown the fundamental role of the
microstructure of HZO films setting the balance between those contributions.
The oxide film presents coherent or incoherent grain boundaries, associated to
the existence of monoclinic and orthorhombic phases in HZO films, which are
dictated by the mismatch with the substrates for epitaxial growth. These grain
boundaries are the toggle that allows to obtain either large (up to 450 %) and
fully reversible genuine polarization controlled electroresistance when only
the orthorhombic phase is present or an irreversible and extremely large
(1000-100000 %) electroresistance when both phases coexist. | 2006.07093v1 |
2020-06-30 | 2D MoSe2 as a Promising Chemo-resistive Sensor for N2O Detection: A DFT Approach | We have investigated the impact of toxic N2O gas upon structural and
electronic properties of 2D MoSe2 monolayer using DFT approach. In this work,
as a result of N2O gas absorption, charge transfer, band gap and density of
states (DOS) are changed and these parameters are extracted as electronic
properties of 2D MoSe2 monolayer nano-gas sensor. Moreover, the band gap is
tunable upon the N2O gas absorption for pristine and adsorbed MoSe2 in both Top
Mo (Top Se) structures. Also, the spin up and down states in the DOS results
considerable magnetic moment altering the magnetic property of the 2D MoSe2
monolayer. Later, the desorption property of the 2D MoSe2 monolayer towards the
target N2O gas molecule at three different temperature are calculated. Thus,
the paper concludes with outcomes of the structural and electronic properties
aligning its behavior as a chemo-resistive nano-gas sensor and showing it as a
potential applicant for sensing of toxic N2O gas molecule. The nature of toxic
N2O gas molecule is not explored till date using 2D monolayer, thus, in this
work it is estimated through simulated results and the experimental
verification is awaited. | 2006.16698v2 |
2020-07-09 | Magnetoresistance scaling, disorder, `hot spots' and the origin of $T$-linear resistivity in BaFe$_2$(As$_{1-x}$P$_x$)$_2$ | The scaling of $H$-linear magnetoresistance in field and temperature was
measured in under-doped (x = 0.19) and optimally-doped
(x=0.31)~BaFe$_2$(As$_{1-x}$P$_x$)$_2$. We analyze the data based on an orbital
model in the presence of strongly anisotropic quasiparticle spectra and
scattering time due to antiferromagnetism. The magnetoresistance is dominated
by the properties of small regions of the Fermi surface called `hot spots'
where antiferromagnetic excitations induce a large quasiparticle scattering
rate. Approximate temperature-magnetic field scaling relations are derived and
shown to be consistent with the experimental data. We argue that these results
link the origin of linear-in-temperature resistivity to hot spots arising from
an antiferromagnetic critical point, and magnetoresistance measurements provide
a route to quantify this link. | 2007.04970v1 |
2020-07-28 | A Novel Compact Si-B-N Barrier on Mg-Li Alloys via Plasma Treatment | Mg-Li alloys have attracted much attention due to their superior properties.
However, it is a great challenge to improve their inferior oxidation and
corrosion resistance. We report a novel Si-B-N ceramic film deposited on the
Mg-9.6Li alloy surface as an effective barrier against oxidation and corrosion.
The films were deposited by using plasma enhanced chemical vapor deposition
from a N2-B2H6-SiH4 gas mixtures, showing compact structure and adhesive
attachment to the alloy surface. The barrier revealed excellent protection
against oxidation in humid air for 500 days, and no observable changes were
found in immersion test of the 3.5 wt.% NaCl solution for 10 min. The superior
oxidation and corrosion resistance are attributed to the excellent material
property of Si-B-N coatings with compact structure via plasma treatment.
Moreover, it is found that moderate proportion of B_2 H_6 in the source gas
mixture is beneficial to the protection of alloys, where the hydrogen release
reaction nearly disappeared and no bubbles were generated on the surface in the
immersion test. | 2007.14170v1 |
2020-08-13 | Resistivity saturation in Kondo insulators | Resistivities of heavy-fermion insulators typically saturate below a
characteristic temperature $T^*$. For some, metallic surface states,
potentially from a non-trivial bulk topology, are a likely source of residual
conduction. Here, we establish an alternative mechanism: At low temperature, in
addition to the charge gap, the scattering rate turns into a relevant energy
scale, invalidating the semiclassical Boltzmann picture. Finite lifetimes of
intrinsic carriers limit conduction, impose the existence of a crossover $T^*$,
and control - now on par with the gap - the quantum regime emerging below it.
We showcase the mechanism with realistic many-body simulations and elucidate
how the saturation regime of the Kondo insulator Ce$_3$Bi$_4$Pt$_3$, for which
residual conduction is a bulk property, evolves under external pressure and
varying disorder. Using a phenomenological formula we derived for the quantum
regime, we also unriddle the ill-understood bulk conductivity of SmB$_6$ -
demonstrating that our mechanism is widely applicable to correlated narrow-gap
semiconductors. | 2008.05846v1 |
2020-08-21 | Growth and anisotropy evaluation of NbBiCh$_3$ (Ch = S, Se) misfit-layered superconducting single crystals | NbBiCh$_3$ (Ch = S, Se) misfit-layered superconducting single crystals were
successfully grown using a CsCl/KCl flux for the first time. The obtained
crystals had a well-developed habit parallel to the c-plane with a typical
width of 1-2 mm and thickness of 10-40 um. The superconducting transition
temperatures with zero resistivity of NbBiS$_3$ single crystals obtained from
the nominal composition of Nb0.9Bi1.2S3 was 0.31 K, and that value of the
NbBiSe$_3$ single crystals grown from the stoichiometry composition
(NbBiSe$_3$) was 2.3 K. Sharp decreases in electric resistivity and magnetic
susceptibility at approximately 3 K suggested a possible superconducting
transition temperature of NbBiSe$_3$. The normal-state anisotropy values of
grown NbBiS$_3$ and NbBiSe$_3$ single crystals were 2.2-2.4 and 1.5-1.6,
respectively. | 2008.09322v1 |
2020-08-27 | Core-structure and lattice resistance of twinning dislocations in fcc metals | Metals with fcc structure may exhibit deformation twinning under specific
conditions, which is an interesting but somewhat elusive aspect of their
deformation behavior. It is well acknowledged that the phenomenon occurs
through the activities of twinning partial dislocations. However, the lack of a
comprehensive understanding of their fundamental properties obstructs the
development of detailed multiscale models of crystal plasticity in the fcc
metals. Here we explore the core-structures and lattice friction of twinning
partials through atomistically informed numerical modeling. To this end, we
choose four fcc crystals with widely differing stacking fault energies. Using
the semi-discrete variational Peierls Nabarro model, we compute the core-widths
and Peierls stresses of edge and screw twinning dislocations. Apart from the
conventional layer-by-layer model of twin nucleation, the recently proposed
alternate-shear model has also been examined. In the latter case, a negative
stable fault energy has been observed, which is large enough to overcome the
Peierls barrier. This study also highlights the significance of incorporating
the surface correction, the absence of which leads to an overestimation of the
intrinsic lattice resistance of the twinning dislocations. | 2008.11937v1 |
2020-10-11 | Electrical properties of thermal oxide scales on pure iron in liquid lead-bismuth eutectic | The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic
(LBE) at 200 oC is studied using electrochemical impedance spectroscopy. The
structures and resistance of oxide grown on iron oxidized in air at different
temperatures and durations are compared. The results show that the resistance
of the oxide film increases with increasing oxidizing temperature, due to the
formation of a thicker scale and fewer defects. At the same temperature (600
oC), increasing the oxidation time can also reduce the defect concentration in
the oxide film and improve the impedance of the oxide scale in LBE. | 2010.05372v1 |
2020-10-14 | Competing spin modulations in a magnetically frustrated semimetal EuCuSb | The competing magnetic ground states of the itinerant magnet EuCuSb, which
has a hexagonal layered structure, were studied via magnetization, resistivity,
and neutron diffraction measurements on single-crystal samples. EuCuSb has a
three-dimensional semimetallic band structure as confirmed by band calculation
and angle-resolved photoelectron spectroscopy, consistent with the nearly
isotropic metallic conductivity in the paramagnetic state. However, below the
antiferromagnetic transition temperature of TN1 (8.5 K), the resistivity,
especially along the hexagonal axis, increases significantly. This implies the
emergence of anisotropic magnetic ordering coupled to the conducting electrons.
Neutron diffraction measurements show that the Eu spins, which order
ferromagnetically within each layer, are collinearly modulated
(up-up-down-down) along the hexagonal axis below TN1, followed by the partial
emergence of helical spin modulation below TN2 (6 K). Based on the observation
of anomalous magnetoresistance with hysteretic behavior, we discuss the
competing nature of the ground state inherent in a frustrated Heisenberg-like
spin system with a centrosymmetric structure. | 2010.06841v1 |
2020-10-20 | Strange metals as ersatz Fermi liquids | A long standing mystery of fundamental importance in correlated electron
physics is to understand strange non-Fermi liquid metals that are seen in
diverse quantum materials. A striking experimental feature of these metals is a
resistivity that is linear in temperature ($T$). In this paper we ask what it
takes to obtain such non-Fermi liquid physics down to zero temperature in a
translation invariant metal. If in addition the full frequency ($\omega$)
dependent conductivity satisfies $\omega/T$ scaling, we argue that the
$T$-linear resistivity must come from the intrinsic physics of the low energy
fixed point. Combining with earlier arguments that compressible translation
invariant metals are `ersatz Fermi liquids' with an infinite number of emergent
conserved quantities, we obtain powerful and practical conclusions. We show
that there is necessarily a diverging susceptibility for an operator that is
odd under inversion/time reversal symmetries, and has zero crystal momentum. We
discuss a few other experimental consequences of our arguments, as well as
potential loopholes which necessarily imply other exotic phenomena. | 2010.10523v3 |
2020-11-06 | Molecular Dynamic Study of Local Interfacial Thermal Resistance of Solid-Liquid and Solid-Solid Interfaces: Water and Nanotextured Surface | Degradation in performances of air conditioners and refrigerators is caused
by a frost formation and adhesion on the surface. In the present study, by
means of the classical molecular dynamics simulation, we investigate how and
how much the nanotextured surface characteristics, such as surface wettability
and geometry, influenced the interfacial thermal resistance (ITR) between the
solid wall and the water/ice. The ITR of the interfacial region was comparable
in both the water and the ice states. As the nanostructure gaps became
narrower, the ITR of the interfacial region decreased. The local ITR had a weak
negative correlation with the local H2O molecule density regardless of the
phase of the H2O molecules. The local ITR decreased as the local density
increased. The greater amount of the thermal energy was transferred through the
material interface by means of the intermolecular interaction when more the H2O
molecules were located in the proximity area, which was closer to the Pt solid
wall than the first adsorption layer peak. When the H2O molecules were in the
crystal form on the solid wall, the proximity molecules decreased, and then the
local ITR significantly increased. | 2011.03184v2 |
2020-11-10 | Thickness induced metal to insulator charge transport and unusual hydrogen response in granular palladium nanofilms | This work reports a systematic study of the evolution of charge transport
mechanism in granular ultra-thin films of palladium of thickness varying
between 6nm and 2nm. While the films with thickness > 4nm exhibit metallic
behaviour, that at 3nm thickness undergoes a metal-insulator transition at
19.5K. In contrast, the 2nm thick film remained insulating at all temperatures.
with transport following Mott's variable range hopping. At room temperature,
while the thicker film exhibit resistance decrease on H$_2$ exposure. the
insulating film showed an anomalous initial resistance increase before
switching to a subsequent decrease. The nanostructure dependent transport and
the ensuing H$_2$ response is modeled on a percolation model, which also
explores the relevance of film thickness as a macroscopic control parameter to
engineer the desired system response in granular metal films. | 2011.05123v1 |
2020-11-23 | From hidden metal-insulator transition to Planckian-like dissipation by tuning disorder in a nickelate | Heavily oxygen deficient NdNiO$_3$ (NNO) films, which are insulating due to
electron localization, contain pristine regions that undergo a hidden
metal-insulator transition. Increasing oxygen content increases the
connectivity of the metallic regions and the metal-insulator transition is
first revealed, upon reaching the percolation threshold, by the presence of
hysteresis. Only upon further oxygenation is the global metallic state (with a
change in the resistivity slope) eventually achieved. It is shown that
sufficient oxygenation leads to linear temperature dependence of resistivity in
the metallic state, with a scattering rate directly proportional to
temperature. Despite the known difficulties to establish the proportionality
constant, the experiments are consistent with a relationship 1/$\tau$= $\alpha
k_B T/\hbar$, with $\alpha$ not far from unity. These results could provide
experimental support for recent theoretical predictions of disorder in a
two-fluid model as a possible origin of Planckian dissipation. | 2011.11535v2 |
2020-11-26 | All-MOCVD-Grown Gallium Nitride Diodes with Ultra-Low Resistance Tunnel Junctions | We carefully investigate three important effects including postgrowth
activation annealing, delta ({\delta}) dose and p+-GaN layer thickness and
experimentally demonstrate their influence on the electrical properties of GaN
p-n homojunction diodes with a tunnel junction (TJ)-based p-contact. The p-n
diodes and TJ structures were monolithically grown by metalorganic chemical
vapor deposition (MOCVD) in a single growth step. By optimizing the annealing
time and temperature for magnesium (Mg) activation and introducing
{\delta}-doses for both donors and acceptors at TJ interfaces, a significant
improvement in electrical properties is achieved. For the continuously-grown,
all-MOCVD GaN homojunction TJs, ultra-low forward voltage penalties of 158 mV
and 490 mV are obtained at current densities of 20 A/cm2 and 100 A/cm2,
respectively. The p-n diode with an engineered TJ shows a record-low normalized
differential resistance of 1.6 x 10-4 {\Omega}-cm2 at 5 kA/cm2. | 2011.13431v1 |
2020-12-29 | Efficient partitioning of surface Green's function: toward ab initio contact resistance study | In this work, we propose an efficient computational scheme for
first-principle quantum transport simulations to evaluate the open-boundary
conditions. Its partitioning differentiates from conventional methods in that
the contact self-energy matrices are constructed on smaller building blocks,
principal layers (PL), while conventionally it was restricted to have the same
lateral dimensions of the adjoining atoms in a channel region. Here, we obtain
the properties of bulk electrodes through non-equilibrium Green's function
(NEGF) approach with significant improvements in the computational efficiency
without sacrificing the accuracy of results. To exemplify the merits of the
proposed method we investigate the carrier density dependency of contact
resistances in silicon nanowire devices connected to bulk metallic contacts. | 2012.14903v1 |
2020-12-30 | Anomalous thermal transport and violation of Wiedemann-Franz law in the critical regime of a charge density wave transition | ErTe$_3$ is studied as a model system to explore thermal transport in a
layered charge density wave (CDW) material. We present data from thermal
diffusivity, resistivity, and specific heat measurements: There is a sharp
decrease in thermal conductivity both parallel and perpendicular to the primary
CDW at the CDW transition temperature. At the same time, the resistivity
changes more gradually. Correspondingly, while well above and below $T_c$, a
consistent description of the thermal transport applies with essentially
independent electron and phonon contributions (estimated using the Wiedemann
Franz law), in the critical regime no such description is possible; the
observed behavior corresponds to a strongly coupled electron-phonon critical
`soup.' | 2012.15048v1 |
2021-02-05 | A Colossal Electroresistance response, accompanied by metal-insulator transition, in a mixed-valent vanadate | Colossal electroresistance (CER) in manganites, i.e., a large change in
electrical resistance under the influence of either an applied electric field
or an applied electric current, has often been described as complimentary to
the colossal magnetoresistance (CMR) effect. Mixed valent vanadates with active
t2g and empty eg orbitals, unlike manganites, have not naturally been discussed
in this context, as double exchange based CMR is not realizable in them.
However, presence of coupled spin and orbital degrees of freedom,
metal-insulator transition (MIT) accompanied by orbital order-disorder
transition, etc., anyway make the vanadates an exciting group of materials.
Here we probe a Fe-doped hollandite lead vanadate PbFe1.75V4.25O11 (PFVO),
which exhibits a clear MIT as a function of temperature. Most importantly, a
giant fall in the resistivity, indicative of a CER, as well as a systematic
shift in the MIT towards higher temperature are observed as a function of
applied electric current. Detailed structural, magnetic, thermodynamic and
transport studies point towards a complex interplay between orbital
order/disorder effect, MIT and double exchange in this system. | 2102.03128v1 |
2021-02-02 | Fabrication of astronomical x-ray reflection gratings using thermally activated selective topography equilibration | Thermally activated selective topography equilibration (TASTE) enables the
creation of 3D structures in resist using grayscale electron-beam lithography
followed by a thermal treatment to induce a selective polymer reflow. A blazed
grating topography can be created by reflowing repeating staircase patterns in
resist into wedge-like structures. Motivated by astronomical applications, such
patterns with periodicities 840 nm and 400 nm have been fabricated in 130
nm-thick PMMA using TASTE to provide a base for X-ray reflection gratings. A
path forward to integrate this alternative blazing technique into grating
fabrication recipes is discussed. | 2102.12359v1 |
2021-03-04 | Uncovering Thermal and Electrical Properties of Sb2Te3/GeTe Superlattice Films | Superlattice-like phase change memory (SL-PCM) promises lower switching
current than conventional PCM based on Ge2Sb2Te5 (GST). However, a fundamental
understanding of SL-PCM requires detailed characterization of the interfaces
within such a SL. Here, we explore the electrical and thermal transport of SLs
with deposited Sb2Te3 and GeTe alternating layers of various thicknesses. We
find up to ~4X reduction of the effective cross-plane thermal conductivity of
the SL stack (as-deposited polycrystalline) compared to polycrystalline GST
(as-deposited amorphous and later annealed) due to the thermal interface
resistances within the SL. Thermal measurements with varying periods of our SLs
show a signature of phonon coherence with a transition from wave-like to
particle-like phonon transport, further described by our modeling. Electrical
resistivity measurements of such SLs reveal strong anisotropy (~2000X) between
the in-plane and cross-plane directions due to the weakly interacting van der
Waals gaps. This work uncovers electro-thermal transport in SLs based on Sb2Te3
and GeTe, for improved design of low-power PCM. | 2103.02867v3 |
2021-04-01 | Unconventional satellite resistance peaks in moiré superlattice of h-BN/ AB-stacked tetralayer-graphene heterostructure | Most studies on moir\'e superlattices formed from a stack of h-BN and
graphene have focused on single layer graphene; graphene with multiple layers
is less understood. Here, we show that a moir\'e superlattice of multilayer
graphene shows new features arising from the anisotropic Fermi surface affected
by the superlattice structure. The moir\'e superlattice of a h-BN/AB-stacked
tetralayer graphene heterostructure exhibited resistivity peaks showing a
complicated dependence on the perpendicular electric field. The peaks were not
due to secondary Dirac cones forming, but rather opening of the energy gap due
to folding of the anisotropic Fermi surface. In addition, superlattice peaks
resulted from mixing of light- and heavy-mass bilayer-like bands via the
superlattice potential. The gaps did not open on the boundary of the
superlattice Brillouin zone, but rather opened inside it, which reflected the
anisotropy of the Fermi surface of multilayer graphene. | 2104.00261v1 |
2021-07-07 | Structural and WAL analysis of Topological single-crystal SnSb2Te4 | Here, we report successful single crystal growth of SnSb2Te4 using the
self-flux method. Unidirectional crystal growth is confirmed through X Ray
Diffraction (XRD) pattern taken on mechanically cleaved crystal flake while the
rietveld refined Powder XRD (PXRD) pattern confirms the phase purity of the
grown crystal. Scanning Electron Microscopy (SEM) image and Energy Dispersive
X-Ray analysis (EDAX) confirm crystalline morphology and exact stoichiometry of
constituent elements. Vibrational Modes observed in Raman spectra also confirm
the formation of the SnSb2Te4 phase. DC resistivity measurements confirm the
metallic character of the grown crystal. Magneto-transport measurements up to
5T show a nonsaturating low magneto-resistance percentage. V type cusp and
Hikami Larkin Nagaoka (HLN) fitting at lower field confirms the Weak
Anti-localization (WAL) effect in SnSb2Te4. Density Functional Theory (DFT)
calculations were showing topological non-trivial electronic band structure. It
is the first-ever report on MR study and WAL analysis of SnSb2Te4 single
crystal. | 2107.03014v1 |
2021-07-13 | First-principles study of the crystal structure, electronic structure, and transport properties of NiTe$_2$ under pressure | Recent experiments showed the distinct observations on the transition metal
ditelluride NiTe$_2$ under pressure: one reported a superconducting phase
transition at 12 GPa, whereas another observed a sign reversal of Hall
resistivity at 16 GPa without the appearance of superconductivity. To clarify
the controversial experimental phenomena, we have carried out first-principles
electronic structure calculations on the compressed NiTe$_2$ with structure
searching and optimization. Our calculations show that the pressure can
transform NiTe$_2$ from a layered P-3m1 phase to a cubic Pa-3 phase at $\sim$10
GPa. Meanwhile, both the P-3m1 and Pa-3 phases possess nontrivial topological
properties. The calculated superconducting $T_c$'s for these two phases based
on the electron-phonon coupling theory both approach 0 K. Further magnetic
transport calculations reveal that the sign of Hall resistance for the Pa-3
phase is sensitive to the pressure and the charge doping, in contrast to the
case of the P-3m1 phase. Our theoretical predictions on the compressed NiTe$_2$
wait for careful experimental examinations. | 2107.05922v1 |
2021-07-14 | A fast-converging scheme for the Phonon Boltzmann equation with dual relaxation times | Callaway's dual relaxation times model, which takes into account the normal
and resistive scatterings of phonon, is used to describe the heat conduction in
materials like graphene. For steady-state problems, the Callaway model is
usually solved by the conventional iterative scheme (CIS), which is efficient
in the ballistic regime, but inefficient in the diffusive/hydrodynamic regime.
In this paper, a general synthetic iterative scheme (GSIS) is proposed to
expedite the convergence to steady-state solutions. First, macroscopic
synthetic equations are designed to guide the evolution of equilibrium
distribution functions for normal and resistive scatterings, so that fast
convergence can be achieved even in the diffusive/hydrodynamic regime. Second,
the Fourier stability analysis is conducted to find the convergence rate for
both CIS and GSIS, which rigorously proves the efficiency of GSIS over CIS.
Finally, several numerical simulations are carried out to demonstrate the
accuracy and efficiency of GSIS, where up to three orders of magnitude of
convergence acceleration is achieved. | 2107.06688v1 |
2021-07-26 | Statistical analysis of spin switching in coupled spin-crossover molecules | We study the switching behavior of two spin-crossover molecules residing in a
nanojunction device consisting of two closely spaced gold electrodes. The spin
states are monitored through a real-time measurement of the resistance of the
junction. A statistical analysis of the resistance values, the occupation
probabilities, and the lifetimes of the respective spin states shows that the
two spin-crossover molecules are coupled to each other. We extract the
parameters for a minimal model describing the two coupled spin-crossover
molecules. Finally, we use the time dependence of factorial cumulants to
demonstrate that the measured data indicates the presence of interactions
between the two spin-crossover molecules. | 2107.11935v1 |
2021-09-29 | Physical and one-dimensional properties of single crystalline La$_{5}$AgPb$_{3}$ | We report here the properties of single crystals of La$_{5}$AgPb$_{3}$, which
is a member of the $R_5MX_3$ ($R$ = rare earth, $M$ = transition metal or main
group element, $X$ = Pb, Sn, Sb, In, Bi) family of chain-like compounds.
Measurements of the electrical resistivity, specific heat and magnetic
susceptibility are compared to the results of density functional calculations,
finding that La$_{5}$AgPb$_{3}$ is a non-magnetic metal with moderate
correlations. The analysis of the electrical resistivity and specific heat
measurements highlight the importance of lattice vibrations in the material,
while the calculated electron density suggests the presence of localized La and
well-hybridized Ag atoms that extend along the c-axis in the La$_{5}$AgPb$_{3}$
structure. The temperature dependence of the magnetic susceptibility is
consistent with a possible one-dimensional character of La$_{5}$AgPb$_{3}$,
where the strength of correlations is much weaker than in one-dimensional
conductors that have been previously reported. | 2109.14716v1 |
2021-10-20 | Anomalous Hall effect from gapped nodal line in Co2FeGe Heusler compound | Full Heusler compounds with Cobalt as a primary element show anomalous
transport properties owing to the Weyl fermions and broken time-reversal
symmetry. We present here the study of anomalous Hall effect (AHE) in Co2FeGe
Heusler compound. The experiment reveals anomalous Hall conductivity (AHC) 100
S/cm at room temperature with an intrinsic contribution of 78 S/cm . The
analysis of anomalous Hall resistivity suggests the scattering independent
intrinsic mechanism dominates the overall behaviour of anomalous Hall
resistivity. The first principles calculation reveals that the Berry curvature
originated by gapped nodal line near EF is the main source of AHE in Co2FeGe
Heusler compound. The theoretically calculated AHC is in agreement with the
experiment. | 2110.10677v1 |
2021-11-06 | GdV6Sn6: a Multi-carrier Metal with Non-magnetic 3d-electron Kagome Bands and 4f-electron Magnetism | Electronic properties of the single crystal of GdV6Sn6, where non-magnetic
V-kagome layers are separated by magnetic Gd-triangular lattice, are
investigated. GdV6Sn6 exhibits unique magnetotransport properties at
low-temperature such as non-linear Hall resistivity and increase of resistance
R in magnetic field H as R ~ H^0.75 up to 56 T with Shubnikov-De Haas
oscillations. Investigation of the non-magnetic analogue YV6Sn6 and the first
principles calculations reveal these properties are relevant to the bands
arising from the V-kagome layer. A magnetic transition at 5 K in GdV6Sn6
modifies the transport properties, pointing to a coupling between Gd-spins on
the triangular lattice and carriers in the V-kagome layer. | 2111.03806v1 |
2021-11-14 | Modelling photothermal induced resonance microscopy: the role of interface thermal resistances | Infrared (IR) nanospectroscopy by photothermal induced resonance (PTIR) is a
novel experimental technique that combines the nanoscale resolution granted by
atomic force microscopy (AFM) and the chemical labelling made possible by IR
absorption spectroscopy. While the technique has developed enormously over the
last decade from an experimental point of view, the theoretical modelling of
the signal still varies significantly throughout the literature and misses a
solid benchmark. Here, we report an analysis focused on the electromagnetic and
thermal simulations of a PTIR experiment. Thanks to a control experiment where
the signal is acquired as a function of the thickness of a polymer film and for
different tip geometries, we find clear evidence that the interface thermal
resistances play a key role in the determination of the measured signal and
should therefore always be accounted for by any quantitative modelling. | 2111.07303v1 |
2021-12-01 | Immobilization of the rare earth fraction in lanthanide phosphates LnPO4. Radiation and hydrolytic resistance of the matrix | Radiation and hydrolytic resistance of
Eu0.054Gd0.014Y0.05La0.111Ce0.2515Pr0.094Nd0.3665Sm0.059PO4 with monazite
structure has been studied. The powders were obtained by deposition from
solutions. Ceramic specimens with relative density ~97% were obtained by Spark
Plasma Sintering (heating rate Vh = 50 {\deg}C/min, sintering temperature Ts =
1070 {\deg}C, sintering time ts = 18 min). Irradiation by accelerated electrons
up to dose of 10^9 Ge was found not to result in a destruction of the target
phase. After the irradiation, an increasing of the leaching rate by an order of
magnitude (up to ~10^{-8} g/(cm2*day)) and a reduction of the mechanical
properties by 32% as compared to the non-irradiated ceramic specimen were
observed. | 2112.00844v1 |
2021-12-24 | Measured potential profile in a quantum anomalous Hall system suggests bulk-dominated current flow | Ideally, quantum anomalous Hall systems should display zero longitudinal
resistance. Yet in experimental quantum anomalous Hall systems elevated
temperature can make the longitudinal resistance finite, indicating dissipative
flow of electrons. Here, we show that the measured potentials at multiple
locations within a device at elevated temperature are well-described by
solution of Laplace's equation, assuming spatially-uniform conductivity,
suggesting non-equilibrium current flows through the two-dimensional bulk.
Extrapolation suggests that at even lower temperatures current may still flow
primarily through the bulk rather than, as had been assumed, through edge
modes. An argument for bulk current flow previously applied to quantum Hall
systems supports this picture. | 2112.13123v3 |
2022-01-24 | Nonconventional Quantized Hall Resistances Obtained with $ν= 2$ Equilibration in Epitaxial Graphene $p-n$ Junctions | We have demonstrated the millimeter-scale fabrication of monolayer epitaxial
graphene $p-n$ junction devices using simple ultraviolet photolithography,
thereby significantly reducing device processing time compared to that of
electron beam lithography typically used for obtaining sharp junctions. This
work presents measurements yielding nonconventional, fractional multiples of
the typical quantized Hall resistance at $\nu=2$ ($R_H\approx 12906 {\Omega}$)
that take the form: $\frac{a}{b}R_H$. Here, $a$ and $b$ have been observed to
take on values such 1, 2, 3, and 5 to form various coefficients of $R_H$.
Additionally, we provide a framework for exploring future device configurations
using the LTspice circuit simulator as a guide to understand the abundance of
available fractions one may be able to measure. These results support the
potential for drastically simplifying device processing time and may be used
for many other two-dimensional materials. | 2201.09791v1 |
2022-03-11 | Toward accurate polarization estimation in nanoscopic systems | The nanoscopic characterization of ferroelectric thin films is crucial from
their device application point of view. Standard characterization techniques
are based on detecting the nanoscopic charge compensation current (switching
current) caused by the polarization reversal in the ferroelectric. Owing to
various surface and bulk limited mechanisms, leakage currents commonly appear
during such measurements, which are frequently subtracted using the device I-V
characteristic by employing positive-up-negative-down (PUND) measurement
scheme. By performing nanoscopic switching current measurements on a commonly
used ferroelectric, BiFeO3, we show that such characterization methods may be
prone to large errors in the polarization estimation on ferro-resistive
samples, due to current background subtraction issues. Especially, when
ferro-resistive behavior is associated with the polarization reversal of the
ferroelectric thin film, background current subtraction is not accurate due to
the mismatch of the I-V characteristics for the two polarization states. We
show instead that removing the background current by an asymmetric least
squares subtraction method, though not perfect, gives a much better estimation
of the ferroelectric properties of the sample under study. | 2203.06157v1 |
2022-05-11 | Self-heating Effect in Silicon-Photomultipliers | The main effect of radiation damage in a Silicon-Photolumtiplier (SiPM) is a
dramatic increase in the dark current. The power dissipated, if not properly
cooled, heats the SiPM, whose performance parameters depend on temperature.
Heating studies were performed with a KETEK SiPM, glued on an Al$_2$O$_3$
substrate, which is either directly connected to the temperature-controlled
chuck of a probe station, or through layers of material with well-known thermal
resistance. The SiPM is illuminated by a LED operated in DC-mode. The SiPM
current is measured and used to determine the steady-state temperature as a
function of power dissipated in the multiplication region of the SiPM and
thermal resistance, as well as the time dependencies for heating and cooling.
This information can be used to correct the parameters determined for
radiation-damaged SiPM for the effects of self-heating. The method can also be
employed for packaged SiPMs with unknown thermal contact to a heat sink. The
results presented in this paper are preliminary. | 2205.05504v2 |
2022-05-31 | A Novel Readout Scheme for Muon Tomography Application in Material Identification | This work reports a cost-effective, multi-parameter readout and
data-acquisition system for a muon scattering tomography system based on
Resistive Plate Chambers (RPCs). Initial test measurements with a prototype
Resistive Plate Chamber were performed using a low-cost FPGA coupled to the
NINO ASIC for the event selection and handling data. The Time over-Threshold
(TOT) property of NINO ASICs has been used to achieve better position
information and achieve precise tracking capability. In our test setup, we try
to build an imaging setup using a single RPC and lead block, which covers some
areas of RPC. A glass RPC of dimension 30cm x 30cm, filled with a gas mixture
of 95% Freon and 5% Isobutane, equipped with two orthogonal panels of readout
strips of width 3 cm and pitch 3.2 cm, has been operated. | 2205.15966v1 |
2022-06-04 | How to recognize the universal aspects of Mott criticality? | In this paper we critically discuss several examples of two-dimensional
electronic systems displaying interaction-driven metal-insulator transitions of
the Mott (or Wigner--Mott) type, including dilute two-dimension electron gases
(2DEG) in semiconductors, Mott organic materials, as well as the recently
discovered transition-metal dichalcogenide (TMD) moir\'e bilayers. Remarkably
similar behavior is found in all these systems, which is starting to paint a
robust picture of Mott criticality. Most notable, on the metallic side a
resistivity maximum is observed whose temperature scale vanishes at the
transition. We compare the available experimental data on these systems to
three existing theoretical scenarios: spinon theory, Dynamical Mean Field
Theory (DMFT) and percolation theory. We show that the DMFT and percolation
pictures for Mott criticality can be distinguished by studying the origins of
the resistivity maxima using an analysis of the dielectric response. | 2206.02055v2 |
2022-06-28 | Negative Differential Resistance in Spin-Crossover Molecular Devices | We demonstrate, based on low-temperature scanning tunneling microscopy (STM)
and spectroscopy, a pronounced negative differential resistance (NDR) in
spin-crossover (SCO) molecular devices, where a Fe$^{\text{II}}$ SCO molecule
is deposited on surfaces. The STM measurements reveal that the NDR is robust
with respect to substrate materials, temperature, and the number of SCO layers.
This indicates that the NDR is intrinsically related to the electronic
structure of the SCO molecule. Experimental results are supported by density
functional theory (DFT) with non-equilibrium Green's functions (NEGF)
calculations and a generic theoretical model. While the DFT+NEGF calculations
reproduce NDR for a special atomically-sharp STM tip, the effect is attributed
to the energy-dependent tip density of states rather than the molecule itself.
We, therefore, propose a Coulomb blockade model involving three molecular
orbitals with very different spatial localization as suggested by the molecular
electronic structure. | 2206.13767v2 |
2022-07-26 | Understanding the Mechanism of the Performance Improvement in Nitrogen-doped Niobium Superconducting Radio Frequency Cavity | Niobium superconducting radiofrequency cavities enable applications in modern
accelerators and quantum computers. However, the surface resistance
significantly deteriorates the cavities performance. Nitrogen doping surface
treatment can consistently increase cavity performance by reducing surface
resistance, but the improvement mechanism is not fully understood. Herein, we
employed transmission electron microscopy and spectroscopy to uncover the
structural and chemical differences of the Nb-air interface between the
non-doped and nitrogen-doped cavities. The results indicate that nitrogen
doping passivates the Nb surface by introducing a compressive strain close to
the Nb/air interface, which impedes the oxygen diffusion and hydrogen atoms and
reduces surface oxide thickness. | 2207.13171v1 |
2022-08-31 | Possible origin of extremely large magnetoresistance in the topological insulator CaBi2 single crystal | CaBi2 has been experimentally found to be a superconductor with a transition
temperature of 2 K and identified as a topological insulator via spin- and
angle-resolved photoemission spectroscopy, which makes it a possible platform
to study the interplay between superconductivity and topology. But the detailed
transport properties for CaBi2 single crystal remain unexplored in experiments.
Here, we systematically studied the magneto-transport properties of CaBi2
single crystal grown by a flux method. CaBi2 shows a magnetic-field-induced
upturn behavior with a plateau in resistivity at low temperature. An extremely
large and non-saturating magnetoresistance up to ~15000% at 3 K and 12 T was
achieved. The possible reason for the magnetic field and temperature dependence
of resistivity and extremely large magnetoresistance at low temperature was
discussed by adopting the Kohler's scaling law, which can be understood by the
compensation effect confirmed by the Hall Effect measurement. | 2208.14595v1 |
2022-09-16 | Ferroelectricity and resistive switching in BaTiO$_3$ thin films with liquid electrolyte top contact for bioelectronic devices | We investigate ferroelectric- and resistive switching behavior in 18-nm-thick
epitaxial BaTiO$_3$ (BTO) films in a model
electrolyte-ferroelectric-semiconductor (EFS) configuration. The system is
explored for its potential as a ferroelectric microelectrode in bioelectronics.
The BTO films are grown by pulsed laser deposition (PLD) on semiconducting
Nb-doped (0.5 wt\%) SrTiO$_{3}$ (Nb:STO) single crystal substrates. The
ferroelectric properties of the bare BTO films are demonstrated by
piezoresponse force microscopy (PFM) measurements. Cyclic voltammetry (CV)
measurements in EFS configuration, with phosphate buffered saline (PBS) acting
as the liquid electrolyte top contact, indicate characteristic ferroelectric
switching peaks in the bipolar current-voltage loop. The ferroelectric nature
of the observed switching peaks is confirmed by analyzing the current response
of the EFS devices to unipolar voltage signals. Moreover, electrochemical
impedance spectroscopy (EIS) measurements indicate bipolar resisitive switching
behavior of the EFS devices, which is controlled by the remanent polarization
state of the BTO layer. Our results represent a constitutive step towards the
realization of neuroprosthetic implants and hybrid neurocomputational systems
based on ferroelectric microelectrodes. | 2209.08020v1 |
2022-09-21 | Colossal Spontaneous Hall Effect and Emergent Magnetism in KTaO$_3$ Two-Dimensional Electron Gases | There has been intense recent interest in the two-dimensional electron gases
(2DEGs) that form at the surfaces and interfaces of KTaO$_3$ (KTO), with the
discovery of superconductivity at temperatures significantly higher than those
of similar 2DEGs based on SrTiO$_3$ (STO). Here we demonstrate that KTO 2DEGs
fabricated under conditions that suppress the superconductivity show a large
spontaneous Hall effect at low temperatures. The transverse response is
asymmetric in an applied perpendicular magnetic field and becomes hysteretic at
millikelvin temperatures. The hysteresis is due to long range magnetic order
arising from local Ta$^{4+}$ moments. However, the most striking features of
the data are the asymmetry of the transverse response and the large spontaneous
transverse resistance at zero field, which can be a significant fraction of the
longitudinal resistance and depends on crystal orientation. Both effects are
due to the presence of a dominant contribution to the transverse response that
is symmetric in perpendicular field, suggesting that its origin is topological
in nature. We argue that this contribution arises from Berry curvature dipoles
coupled with nonequilibrium conditions induced by the measuring current. | 2209.10534v2 |
2022-09-30 | Remote Surface Optical Phonon Scattering in Ferroelectric Ba$_{0.6}$Sr$_{0.4}$TiO$_{3}$ Gated Graphene | We report the effect of remote surface optical (RSO) phonon scattering on
carrier mobility in monolayer graphene gated by ferroelectric oxide. We
fabricate monolayer graphene transistors back-gated by epitaxial (001)
Ba$_{0.6}$Sr$_{0.4}$TiO$_{3}$ films, with field effect mobility up to 23,000
cm$^{2}$V$^{-1}$s$^{-1}$ achieved. Switching the ferroelectric polarization
induces nonvolatile modulation of resistance and quantum Hall effect in
graphene at low temperatures. Ellipsometry spectroscopy studies reveal four
pairs of optical phonon modes in Ba$_{0.6}$Sr$_{0.4}$TiO$_{3}$, from which we
extract the RSO phonon frequencies. The temperature dependence of resistivity
in graphene can be well accounted for by considering the scattering from the
intrinsic longitudinal acoustic phonon and the RSO phonon, with the latter
dominated by the mode at 35.8 meV. Our study reveals the room temperature
mobility limit of ferroelectric-gated graphene transistors imposed by RSO
phonon scattering. | 2209.15527v1 |
2022-10-06 | Kinetically Decoupled Electrical and Structural Phase Transitions in VO2 | Vanadium dioxide (VO2) has drawn significant attention for its near room
temperature insulator to metal transition and associated structural phase
transition. The underlying Physics behind the temperature induced insulator to
metal and concomitant structural phase transition in VO2 is yet to be fully
understood. We have investigated the kinetics of the above phase transition
behaviors of VO2 with the help of resistivity measurements and Raman
spectroscopy. Resistance thermal hysteresis scaling and relaxation measurements
across the temperature induced insulator to metal transition reveal the unusual
behaviour of this first-order phase transition, whereas Raman relaxation
measurements show that the temperature induced structural phase transition in
VO2 follows usual behaviour and is consistent with mean field prediction. At
higher temperature sweeping rates decoupling of insulator to metal transition
and structural phase transition have been confirmed. The observed anomalous
first order phase transition behavior in VO2 is attributed to the
unconventional quasi particle dynamics, i.e. significantly lowered electronic
thermal conductivity across insulator to metal transition, which is confirmed
by ultrafast optical pump-probe time domain thermoreflectance measurements. | 2210.02691v1 |
2022-11-06 | Triclinic BiFeO3: A room-temperature multiferroic phase with enhanced magnetism and resistivity | The magnetic and transport properties of BiFeO3/La2NiMnO6 (BFO/LNMO)
composite have been investigated both experimentally and theoretically. Unlike
the normal rhombohedral (R3c) phase, BFO in the composites is crystallized in
the triclinic phase (P1). Interestingly, the composites demonstrate a
significant enhancement in the magnetization, magnetoelectric coupling and show
higher resistivity than that of the regular BFO (R3c). As LNMO has its Curie
temperature at 280 K, the room temperature and above room temperature magnetic
contribution in the composites is expected to be from the triclinic BFO phase.
Experimentally observed enhancement in magnetization is validated using
classical Monte Carlo simulation and density functional theory (DFT)
calculations. The calculations reveal higher magnetic moments in triclinic BFO
as compared to the rhombohedral BFO. Overall, this study reveals triclinic BFO
as the promising room temperature multiferroic phase which is helpful to
optimize the multiferroicity of BFO and achieve wider applications in future. | 2211.03123v3 |
2022-11-11 | Synthesis and physical properties of uranium thin-film hydrides UH2 and \b{eta}-UH3 | Formation of thin uranium hydrides films, UH2 and \b{eta}-UH3, synthesized by
a reactive dc sputtering of uranium metal, was explored using variable
deposition conditions. Obtained stable oxygen-free hydride films were studied
by a variety of methods, both in situ (photoelectron spectroscopy - XPS), and
ex-situ (x-ray diffraction - XRD, transmission electron microscopy - TEM),
electrical resistivity, and magnetometry). Both types of hydrides are
ferromagnetic, the Curie temperatures of UH2 and \b{eta}-UH3 are approx. 120
and 170 K, respectively. Ferromagnetism in the thin films is robust and does
not depend on structure details while electrical resistivity data reflect
disorder in both types of hydrides. | 2211.06144v1 |
2023-01-03 | Supercurrent in Bi$_4$Te$_3$ Topological Material-Based Three-Terminal Junctions | In an in-situ prepared three-terminal Josephson junction based on the
topological insulator Bi$_4$Te$_3$ and the superconductor Nb the transport
properties are studied. The differential resistance maps as a function of two
bias currents reveal extended areas of Josephson supercurrent including
coupling effects between adjacent superconducting electrodes. The observed
dynamics for the coupling of the junctions is interpreted using a numerical
simulation of a similar geometry based on a resistively and capacitively
shunted Josephson junction model. The temperature dependency indicates that the
device behaves similar to prior experiments with single Josephson junctions
comprising topological insulators weak links. Irradiating radio frequencies to
the junction we find a spectrum of integer Shapiro steps and an additional
fractional step, which is interpreted by a skewed current-phase relationship.
In a perpendicular magnetic field we observe Fraunhofer-like interference
patterns of the switching currents. | 2301.01115v1 |
2023-01-06 | Berry curvature induced valley Hall effect in non-encapsulated hBN/Bilayer graphene heterostructure aligned with near-zero twist angle | Valley Hall effect has been observed in asymmetric single-layer and bilayer
graphene systems. In single-layer graphene systems, asymmetry is introduced by
aligning graphene with hexagonal boron nitride (hBN) with a near-zero twist
angle, breaking the sub-lattice symmetry. Although a similar approach has been
used in bilayer graphene to break the layer symmetry and thereby observe the
valley Hall effect, the bilayer graphene was sandwiched with hBN on both sides
in those studies. This study looks at a much simpler, non-encapsulated
structure where hBN is present only at the top of graphene. The
crystallographic axes of both hBN and bilayer graphene are aligned. A clear
signature of the valley Hall effect through non-local resistance measurement
($R_{\rm{NL}}$) was observed. The observed non-local resistance could be
manipulated by applying a displacement field across the heterostructure.
Furthermore, the electronic band structure and Berry curvature calculations
validate the experimental observations. | 2301.02358v2 |
2023-01-29 | Anisotropic magnetic and magnetotransport properties in morphologically distinct Nd0.6Sr0.4MnO3 thin films | We investigate the magnetic and magnetotransport properties of nanostructured
Nd0.6Sr0.4MnO3 (NSMO) thin films grown on (100) oriented SrTiO3 (STO)
substrates. The thin films fabricated using the pulsed laser deposition
technique have been found to possess two distinct surface morphologies:
granular and nano rod type. Magnetization measurements have revealed that the
films with rod-type morphology exhibit improved in-plane magnetic anisotropy.
Magnetotransport studies have revealed that the granular thin films display a
characteristic butterfly-shaped low-field magneto-resistive (LFMR) behavior.
Furthermore, we investigate the anisotropic magneto-resistive (AMR) phenomenon
in the samples and we find that morphology greatly affects AMR. Thin films with
rod-type morphology show an enhanced AMR %. Such morphology dependent
tunability in magnetoresistance properties over a wide temperature range is
potentially interesting for developing oxide-based sensors and devices. | 2301.12406v1 |
2023-02-10 | Electrical characterization of the azimuthal anisotropy of $(\mathrm{Ni}_x\mathrm{Co}_{1-x})\mathrm{B}$-based ferromagnetic nanotubes | We report on the structural, electric and magnetic properties of
$(\mathrm{Ni}_x\mathrm{Co}_{1-x})\mathrm{B}$ ferromagnetic nanotubes,
displaying azimuthal magnetization. The tubes are fabricated using electroless
plating in polycarbonate porous templates, with lengths several tens of
micrometers, diameters from 100nm to 500nm and wall thicknesses from 10nm to
80nm. The resistivity is $\sim 1.5\times10^{-6}\mathrm{\Omega/m}$, and the
anisotropic magnetoresistance~(AMR) of 0.2-0.3%, one order of magnitude
larger~(resp. smaller) than in the bulk material, which we attribute to the
resistance at grain boundaries. We determined the azimuthal anisotropy field
from M(H) AMR loops of single tubes contacted electrically. Its magnitude is
around 10mT, and tends to increase with the tube wall thickness, as well as the
Co content. However, surprisingly it does not dependent much on the diameter
nor on the curvature. | 2302.05246v1 |
2023-02-14 | Microscopic mechanism of tunable thermal conductivity in carbon nanotube-geopolymer nanocomposites | Geopolymer has been considered as a green and low-carbon material with great
potential application due to its simple synthesis process, environmental
protection, excellent mechanical properties, good chemical resistance and
durability. In this work, the molecular dynamics simulation is employed to
investigate the effect of the size, content and distribution of carbon
nanotubes on the thermal conductivity of geopolymer nanocomposites, and the
microscopic mechanism is analyzed by the phonon density of states, phonon
participation ratio and spectral thermal conductivity, etc. The results show
that there is a significant size effect in geopolymer nanocomposites system due
to the carbon nanotubes. In addition, when the content of carbon nanotubes is
16.5%, the thermal conductivity in carbon nanotubes vertical axial direction
(4.85 W/(mk)) increases 125.6% compared with the system without carbon
nanotubes (2.15 W/(mk)). However, the thermal conductivity in carbon nanotubes
vertical axial direction (1.25 W/(mk)) decreases 41.9%, which is mainly due to
the interfacial thermal resistance and phonon scattering at the interfaces. The
above results provide theoretical guidance for the tunable thermal conductivity
in carbon nanotube-geopolymer nanocomposites. | 2302.07195v1 |
2023-02-18 | Fractional Marcus-Hush-Chidsey-Yakopcic current-voltage model for redox-based resistive memory devices | We propose a circuit-level model combining the Marcus-Hush-Chidsey electron
current equation and the Yakopcic equation for the state variable for
describing resistive switching memory devices of the structure metal-ionic
conductor-metal. We extend the dynamics of the state variable originally
described by a first-order time derivative by introducing a fractional
derivative with an arbitrary order between zero and one. We show that the
extended model fits with great fidelity the current-voltage characteristic data
obtained on a Si electrochemical metallization memory device with Ag-Cu alloy. | 2302.09407v2 |
2023-03-01 | Electronic Transport Studies of Ag-doped Bi2Se3 Topological Insulator | The structural, magnetotransport, and angle-resolved photoemission
spectroscopy (ARPES) of Ag-doped Bi2Se3 single crystals are presented.
Temperature dependent resistivity exhibits metallic behavior with a slope
change above 200 K for Ag-doped Bi2Se3. The magnetoresistance shows positive
quadratic dependence at low fields satisfying Kohler's rule. Hall resistivity
measurement shows that electrons are dominant charge carriers. Furthermore,
these results agree well with the ARPES spectra observed at T = 20 K, where the
Fermi level lies inside the bulk conduction band. The Dirac point of the
topological surface states is shifted toward higher binding energy (~ 0.12 eV)
for Ag-doped samples as compared to pristine Bi2Se3. | 2303.00296v1 |
2023-02-21 | Electronic Transport in the Silicon Carbide Semiconductor in Phase 3C | In this work we study, theoretically, electronic mobility of the silicon
carbide semiconductor in the 3C phase, named 3C-SiC. 3C-SiC has shown great
potential for applications in extreme conditions. Thus, the study of the
electronic mobility of this semiconductor is of great interest. In this work
were theoretically deduced: drift velocity, displacement and mobility of the
charge carriers in the n-type doped 3C-SiC semiconductor, subjected to a
constant electric field. The dependence of these transport properties as a
function of the intensity of the electric field and temperature was analyzed.
For this, a differential equation of motion was used with a source term (low
intensity electric fields) and a term of resistance to movement (electrical
resistance). | 2303.09457v1 |
2023-03-19 | The fluidic memristor: collective phenomena in elastohydrodynamic networks | Fluid flow networks are ubiquitous and can be found in a broad range of
contexts, from human-made systems such as water supply networks to living
systems like animal and plant vasculature. In many cases, the elements forming
these networks exhibit a highly non-linear pressure-flow relationship. Although
we understand how these elements work individually, their collective behavior
remains poorly understood. In this work, we combine experiments, theory, and
numerical simulations to understand the main mechanisms underlying the
collective behavior of soft flow networks with elements that exhibit negative
differential resistance. Strikingly, our theoretical analysis and experiments
reveal that a minimal network of nonlinear resistors, which we have termed a
`fluidic memristor', displays history-dependent resistance. This new class of
element can be understood as a collection of hysteresis loops that allows this
fluidic system to store information. Our work provides insights that may inform
new applications of fluid flow networks in soft materials science, biomedical
settings, and soft robotics, and may also motivate new understanding of the
flow networks involved in animal and plant physiology. | 2303.10777v1 |
2023-03-20 | Engineering Higher-Order Dirac and Weyl Semimetallic phase in 3D Topolectrical Circuits | We propose a 3D topolectrical (TE) network that can be tuned to realize
various higher-order topological gapless and chiral phases. We first study a
higher-order Dirac semimetal phase that exhibits a hinge-like Fermi arc linking
the Dirac points. This circuit can be extended to host highly tunable first-
and second-order Weyl semimetal phases by introducing a non-reciprocal
resistive coupling in the x-y plane that breaks time reversal symmetry. The
first- and second-order Weyl points are connected by zero-admittance surface
and hinge states, respectively. We also study the emergence of first- and
second-order chiral modes induced by resistive couplings between similar nodes
in the z-direction. These modes respectively occur in the midgap of the surface
and hinge admittance bands in our circuit model without the need for any
external magnetic field. | 2303.10911v2 |
2023-03-20 | Electronic and magnetic properties of Lu and LuH$_2$ | Clarifying the electronic and magnetic properties of lutetium, lutetium
dihydride, and lutetium oxide is very helpful to understand the emergent
phenomena in lutetium-based compounds (such as room-temperature
superconductivity). However, this kind of study is still scarce at present.
Here, we report on the electronic and magnetic properties of lutetium metals,
lutetium dihydride powders, and lutetium oxide powders. Crystal structures and
chemical compositions of these samples were characterized by X-ray diffraction
and X-ray photoemission spectroscopy, respectively. Electrical transport
measurements show that the resistance of lutetium has a linear behavior
depending on temperature, whereas the resistance of lutetium dihydride powders
is independent of temperature. More interestingly,
paramagnetism-ferromagnetism-spin glass transitions were observed at near 240
and 200 K, respectively, in lutetium metals. Our work uncovered the complex
magnetic properties of Lu-based compounds. | 2303.11063v2 |
2023-04-22 | A Deep Neural Network Deployment Based on Resistive Memory Accelerator Simulation | The objective of this study is to illustrate the process of training a Deep
Neural Network (DNN) within a Resistive RAM (ReRAM) Crossbar-based simulation
environment using CrossSim, an Application Programming Interface (API)
developed for this purpose. The CrossSim API is designed to simulate neural
networks while taking into account factors that may affect the accuracy of
solutions during training on non-linear and noisy ReRAM devices. ReRAM-based
neural cores that serve as memory accelerators for digital cores on a chip can
significantly reduce energy consumption by minimizing data transfers between
the processor and SRAM and DRAM. CrossSim employs lookup tables obtained from
experimentally derived datasets of real fabricated ReRAM devices to digitally
reproduce noisy weight updates to the neural network. The CrossSim directory
comprises eight device configurations that operate at different temperatures
and are made of various materials. This study aims to analyse the results of
training a Neural Network on the Breast Cancer Wisconsin (Diagnostic) dataset
using CrossSim, plotting the innercore weight updates and average training and
validation loss to investigate the outcomes of all the devices. | 2304.11337v1 |
2023-05-16 | The kinetic theory of ultra-subsonic fermion systems and applications to flat band magic angle twisted bilayer graphene | The only kinematically-allowed phonon-scattering events for bands of subsonic
fermions ($v_F < v_p$) are interband transitions, leading to different low-$T$
transport physics than in the typical supersonic case. We apply a kinetic
theory of phonon-limited transport to a generic two-band system of subsonic
fermions, deriving formulae for relaxation times and resistivity that are
accurate in the limit of close bands and small $v_F/v_p$. We predict regimes of
$\rho \propto T$, $\rho \propto T^2$, and perfect conductivity. Our theory
predicts linear-in-$T$ resistivity down to a crossover temperature that is
suppressed from its supersonic analogue by a factor of $v_F/v_p$, offering a
new explanation for low-$T$ "strange metal" behavior observed in flat band
systems. | 2305.09120v1 |
2023-05-31 | Supercurrent through a single transverse mode in nanowire Josephson junctions | Hybrid superconductor-semiconductor materials are fueling research in
mesoscopic physics and quantum technology. Recently demonstrated smooth
$\beta$-Sn superconductor shells, due to the increased induced gap, are
expanding the available parameter space to new regimes. Fabricated on
quasiballistic InSb nanowires, with careful control over the hybrid interface,
Sn shells yield critical current-normal resistance products exceeding
temperature by at least an order of magnitude even when nanowire resistance is
of order 10k$\Omega$. In this regime Cooper pairs travel through a purely 1D
quantum wire for at least part of their trajectory. Here, we focus on the
evolution of supercurrent in magnetic field parallel to the nanowire. Long
decay up to fields of 1T is observed. At the same time, the decay for higher
occupied subbands is notably faster in some devices but not in others. We
analyze this using a tight-binding numerical model that includes the Zeeman,
orbital and spin-orbit effects. When the first subband is spin polarized, we
observe a dramatic suppression of supercurrent, which is also confirmed by the
model and suggests an absence of significant triplet supercurrent generation. | 2306.00146v1 |
2023-06-26 | Origin of magnetic ordering in half-Heusler RuMnGa | The half-Heusler alloy RuMnGa having valence electron count (VEC) 18 has
recently been theoretically proposed to exhibit compensated ferrimagnetic
(CFiM) character instead of the expected nonmagnetic ground state. On the other
hand, a preliminary experimental study proposed ferromagnetic (FM) ordering. As
no half-Heusler system with VEC 18 is known to exhibit magnetic ordering, we
have investigated the details of crystal structure and magnetic properties of
RuMnGa using a combination of experimental tools, viz., x-ray and neutron
diffraction techniques, dc and ac susceptibility, isothermal magnetisation,
heat capacity, resistivity and neutron depolarisation measurements. Rietveld
refinements of x-ray and neutron diffraction data suggest single phase nature
of the compound with elemental composition RuMn$_{0.86}$Ga$_{1.14}$. We have
shown that the system exhibits FM-type ordering owing to the inherent presence
of this minor off-stoichiometry, showing very low magnetic moment. The system
also exhibits reentrant canonical spin-glass behaviour, which is rarely
observed in half-Heusler alloys. The temperature coefficient of resistivity
changes its sign from negative to positive and further to negative as the
temperature decreases. | 2306.14836v1 |
2023-07-02 | Giant coercivity, resistivity upturn, and anomalous Hall effect in ferrimagnetic FeTb | Despite the blooming interest, the transition-metal rare-earth ferrimagnets
have not been comprehensively understood in terms of their coercivity and
transport properties. Here, we report a systematic study of the magnetic and
transport properties of ferrimagnetic FeTb alloy by varying the layer thickness
and temperature. The FeTb is tuned from the Tb-dominated regime to the
Fe-dominated regime via the layer thickness, without varying the composition.
The coercivity closely follows the $1/\cos\theta_H$ scaling (where $\theta_H$
is the polar angle of the external magnetic field) and increases
quasi-exponentially upon cooling (exceeding 90 kOe at low temperatures),
revealing that the nature of the coercivity is the thermally-assisted domain
wall depinning field. The resistivity exhibits a quasi-linear upturn upon
cooling possibly due to thermal vibrations of the structure factor of the
amorphous alloy. The existing scaling laws of the anomalous Hall effect in the
literature break down for the amorphous FeTb that are either Fe- or
Tb-dominated. These findings should advance the understanding of the
transition-metal-rare-earth ferrimagnets and the associated ferrimagnetic
phenomena in spintronics. | 2307.00475v1 |
2023-07-19 | Observation of large intrinsic anomalous Hall conductivity in polycrystalline Mn$_3$Sn films | We report the observation of anomalous Hall effect in Mn$_3$Sn
polycrystalline thin films deposited on Pt coated Al$_2$O$_3$ substrate with a
large anomalous Hall conductivity of 65($\Omega$cm)$^{-1}$ at 3K. The Hall and
magnetic measurements show a very small hysteresis owing to a weak
ferromagnetic moment in this material. The longitudinal resistivity decreases
sufficiently for the thin films as compared to the polycrystalline bulk sample
used as the target for the film deposition. The anomalous Hall resistivity and
conductivity decreases almost linearly with the increase in the temperature. A
negative magnetoresistance is observed for all the measured temperatures with
the negative decrease in the magnitude with the increase in temperature. | 2307.09808v1 |
2023-10-27 | A diamond anvil microassembly for Joule heating and electrical measurements up to 150 GPa and 4000 K | When diamond anvil cell (DAC) sample chambers are outfitted with both thermal
insulation and electrodes, two cutting-edge experimental methods are enabled:
Joule heating with spectroradiometric temperature measurement, and electrical
resistance measurements of samples heated to thousands of kelvin. The accuracy
of temperature and resistance measurements, however, often suffers from poor
control of the shape and location of the sample, electrodes, and thermal
insulation. Here, we present a recipe for the reproducible and precise
fabrication of DAC sample, electrodes, and thermal insulation using a
three-layer microassembly. The microassembly contains two potassium chloride
thermal insulation layers, four electrical leads, a sample, and a buttressing
layer made of polycrystalline alumina. The sample, innermost electrodes, and
buttress layer are fabricated by focused-ion-beam milling. Three iron samples
are presented as proof of concept. Each is successfully compressed and pulsed
Joule heated while maintaining a four-point probe configuration. The highest
pressure-temperature condition achieved is $\sim 150$ GPa and $\sim 4000$ K. | 2310.18176v1 |
2023-11-02 | Disentangling transport mechanisms in a correlated oxide by photoinduced charge injection | We present a novel heterostructured approach to disentangle the mechanism of
electrical transport of the strongly correlated PrNiO3, by placing the
nickelate under the photoconductor CdS. This enables the injection of carriers
into PrNiO3 in a controlled way, which can be used to interrogate its intrinsic
transport mechanism. We find a non-volatile resistance decrease when
illuminating the system at temperatures below the PrNiO3 metal-insulator
transition. The photoinduced change becomes more volatile as the temperature
increases. These data help understand the intrinsic transport properties of the
nickelate-CdS bilayer. Together with data from a bare PrNiO3 film, we find that
the transport mechanism includes a combination of mechanisms including both
thermal activation and variable range hopping. At low temperatures without
photoinduced carriers the transport is governed by hopping, while at higher
temperatures and intense illumination the activation mechanism becomes
relevant. This work shows a new way to optically control the low-temperature
resistance of PrNiO3. | 2311.00904v1 |
2023-11-13 | Metallic conductivity on Na-deficient structural domain walls in the spin-orbit Mott insulator Na$_2$IrO$_3$ | Honeycomb Na$_2$IrO$_3$ is a prototype spin-orbit Mott insulator and Kitaev
magnet. We report a combined structural and electrical resistivity study of
Na$_2$IrO$_3$ single crystals. Laue back-scattering diffraction indicates
twinning with $\pm 120^\circ$ rotation around the $c^*$-axis while scanning
electron microscopy displays nanothin lines parallel to all three b-axis
orientations of twin domains. Energy dispersive x-ray analysis line-scans
across such domain walls indicate no change of the Ir signal intensity, i.e.
intact honeycomb layers, while the Na intensity is reduced down to $\sim 2/3$
of its original value at the domain walls, implying significant hole doping.
Utilizing focused-ion-beam micro-sectioning, the temperature dependence of the
electrical resistance of individual domain walls is studied. It demonstrates
the tuning through the metal-insulator transition into a correlated-metal
ground state by increasing hole doping. | 2311.07275v1 |
2023-11-30 | Electrical resistance associated with the scattering of optically oriented electrons in n-GaAs | In a bulk GaAs crystal, an unusual magnetoresistance effect, which takes
place when a spin-polarized current flows through the sample, was detected.
Under conditions of optical pumping of electron spins, an external magnetic
field directed along the electric current and perpendicular to the oriented
spins decreases the resistance of the material. The phenomenon is due to the
spin-dependent scattering of electrons by neutral donors. It was found that the
sign of the magnetoresistance does not depend on the sign of the exciting light
circular polarization, the effect is even with respect to the sign of the spin
polarization of the carriers, which indicates a correlation between the spins
of optically oriented free electrons and electrons localized on donors. | 2311.18713v1 |
2023-12-01 | Comparative study of Kondo effect in Vanadium dichalcogenides VX$_2$ (X=Se & Te) | We report on the electrical transport, magnetotransport, and magnetic
properties studies on the transition metal dichalcogenides VSe$_2$ and VTe$_2$
and draw a comprehensive comparison between them. We observe Kondo effect in
both systems induced by the exchange interaction between localized moments and
conduction electrons at low temperature, resulting into resistance upturn at 6
K for VSe$_2$ and 17 K for VTe$_2$. From the field dependent resistance
measurements we find that the data is fitted best with modified Hamann equation
corrected by the quantum Brillouin function for VSe$_2$, while the data is
fitted best with modified Hamann equation corrected by the classical Langevin
function for VTe$_2$. Interestingly, we observe a contrasting magnetoresistance
(MR) property between these systems across the Kondo temperature. That means,
negative MR is found in both systems in the Kondo state. In the normal state MR
is positive for VSe$_2$, while it is negligible for VTe$_2$. In addition, both
systems show weak ferromagnetism at low temperature due to intercalated V
atoms. | 2312.09258v1 |
2023-12-28 | Memristive behavior of functionalized graphene quantum dot and polyaniline nanocomposites | Zero-dimensional graphene quantum dots (GQD) dispersed in conducting polymer
matrix display a striking range of optical, mechanical, and thermoelectric
properties which can be utilized to design next-generation sensors and low-cost
thermoelectric. This exotic electrical property in GQDs is achieved by
exploiting the concentration of the GQDs and by tailoring the functionalization
of the GQDs. However, despite extensive investigation, the nonlinear
resistivity behavior leading to memristive like characteristic has not been
explored much. Here, we report electrical characterisation of nitrogen
functionalized GQD (NGQD) embedded in a polyaniline (PANI) matrix. We observe a
strong dependence of the resistance on current and voltage history, the
magnitude of which depends on the NGQD concentration and temperature. We
explain this memristive property using a phenomenological model of the
alignment of PANI rods with a corresponding charge accumulation arising from
the NGQD on its surface. The NGQD-PANI system is unique in its ability to
matrix offers a unique pathway to design neuromorphic logic and synaptic
architectures with crucial advantages over existing systems. | 2312.16759v1 |
2024-01-04 | Anomalous upper critical field in the quasicrystal superconductor Ta$_{1.6}$Te | Superconductivity in quasicrystals poses a new challenge in condensed matter
physics. We measured the resistance and ac magnetic susceptibility of a
Ta$_{1.6}$Te dodecagonal quasicrystal, which is superconducting below $T_c
\sim$ 1 K. We show that the upper critical field increases linearly with a
large slope of $-$4.4 T/K with decreasing temperature down to 0.04 K, with no
tendency to level off. The extrapolated zero-temperature critical field exceeds
the Pauli limit by a factor of 2.3. We also observed flux-flow resistance with
thermally activated behavior and an irreversibility field that is distinct from
the upper critical field. We discuss these peculiarities in terms of the
nonuniform superconducting gap and spin--orbit interaction in quasicrystal
structures. | 2401.02079v1 |
2024-01-07 | Advancing Noise-Resilient Twist Angle Characterization in Bilayer Graphene through Raman Spectroscopy via GAN-CNN Modeling | In this study, we introduce an innovative methodology for robust twist angle
identification in bilayer graphene using Raman spectroscopy, featuring the
integration of generative adversarial network and convolutional neural network
(GAN-CNN). Our proposed approach showcases remarkable resistance to noise
interference, particularly in ultra-low Signal-to-Noise Ratio (SNR) conditions.
We demonstrate the GAN-CNN model's robust learning capability, even when SNR
reaches minimal levels. The model's exceptional noise resilience negates the
necessity for preprocessing steps, facilitating accurate classification, and
substantially reducing computational expenses. Empirical results reveal the
model's prowess, achieving heightened accuracy in twist angle identification.
Specifically, our GAN-CNN model achieves a test accuracy exceeding 99.9% and a
recall accuracy of 99.9%, relying on an augmented dataset containing 4209
spectra. This work not only contributes to the evolution of noise-resistant
spectral analysis methodologies but also provides crucial insights into the
application of advanced deep learning techniques for bilayer graphene
characterization through Raman spectroscopy. The findings presented herein have
broader implications for enhancing the precision and efficiency of material
characterization methodologies, laying the foundation for future advancements
in the field. | 2401.03371v1 |
2024-01-10 | Superconductivity in Ternary Zirconium Telluride Zr6MTe2 with 3d Transition Metals | We report the synthesis, electronic properties, and electronic states of
Zr6MTe2 (M = Cr, Mn, Fe, and Co), which is isostructural to a recently
discovered superconductor family Sc6MTe2. Based on the electrical resistivity
and heat capacity data measured at low temperatures, Zr6FeTe2 is found to show
bulk superconductivity below Tc = 0.76 K. Zr6CoTe2 also exhibited zero
resistivity due to superconductivity below 0.13 K. In contrast, Zr6+dMn1-dTe2
does not show superconductivity but instead exhibits strong magnetism, which
most likely prevents the formation of superconductivity in this material. The
electronic properties and electronic states of Zr6MTe2 are discussed in
comparison with those of Sc6MTe2. | 2401.04870v1 |
2024-01-25 | Non-zero crossing current-voltage characteristics of interface-type resistive switching devices | A number of memristive devices, mainly ReRAMs, have been reported to exhibit
a unique non-zero crossing hysteresis attributed to the interplay of resistive
and not yet fully understood `capacitive', and `inductive' effects. This work
exploits a kinetic simulation model based on the stochastic cloud-in-a-cell
method to capture these effects. The model, applied to Au/BiFeO$_{3}$/Pt/Ti
interface-type devices, incorporates vacancy transport and capacitive
contributions. The resulting nonlinear response, characterized by hysteresis,
is analyzed in detail, providing an in-depth physical understanding of the
virtual effects. Capacitive effects are modeled across different layers,
revealing their significant role in shaping the non-zero crossing hysteresis
behavior. Results from kinetic simulations demonstrate the impact of
frequency-dependent impedance on the non-zero crossing phenomenon. This model
provides insights into the effects of various device material properties, such
as Schottky barrier height, device area and oxide layer on the non-zero
crossing point. | 2401.14507v1 |
2024-01-27 | Electronic structure and physical properties of candidate topological material GdAgGe | We grew needle-shaped single crystals of GdAgGe, which crystallizes in a
noncentrosymmetric hexagonal crystal structure with space group
P$\overline{6}$2$m$ (189). The magnetic susceptibility data for $H \perp c$
reveal two pronounced antiferromagnetic transitions at $T_{N1}$ = 20 K and
$T_{N2}$ = 14.5 K. The magnetic susceptibility anomalies are less prominent for
$H \parallel c$. The transition at $T_{N1}$ is accompanied by a pronounced heat
capacity anomaly confirming the bulk nature of the magnetic transition. Below
$T_{N1}$, the electrical resistivity data follows a $T^{3/2}$ dependence. In
the magnetically ordered state, GdAgGe shows positive transverse
magnetoresistance, which increases with decreasing temperature and increasing
field, reaching a value of $\sim$ 27% at 9 T and 10 K. The Hall resistivity
data and electronic band structure calculations suggest that both the hole and
electron charge carriers contribute to the transport properties. The electronic
band structure displays linear band crossings near the Fermi level. The
calculations reveal that GdAgGe has a nodal line with drumhead surface states
coupled with a nonzero Berry phase, making it a nontrivial nodal-line
semimetal. | 2401.15464v1 |
2024-02-29 | First-principles electron-phonon interactions and electronic transport in large-angle twisted bilayer graphene | Twisted bilayer graphene (tBLG) has emerged as an exciting platform for novel
condensed matter physics. However, electron-phonon ($e$-ph) interactions in
tBLG and their effects on electronic transport are not completely understood.
Here we show first-principles calculations of $e$-ph interactions and
resistivity in commensurate tBLG with large twist angles of 13.2 and 21.8
degrees. These calculations overcome key technical barriers, including large
unit cells of up to 76 atoms, Brillouin-zone folding of the $e$-ph
interactions, and unstable lattice vibrations due to the AA-stacked domains. We
show that $e$-ph interactions due to layer-breathing (LB) phonons enhance
intervalley scattering in large-angle tBLG. This interaction effectively
couples the two layers, which are otherwise electronically decoupled at such
large twist angles. As a result, the phonon-limited resistivity in tBLG
deviates from the temperature-linear trend characteristic of monolayer graphene
and tBLG near the magic angle. Taken together, our work quantifies $e$-ph
interactions and scattering mechanisms in tBLG, revealing subtle interlayer
coupling effects at large twist angles. | 2402.19453v1 |
2024-03-04 | Tuning charge density wave of kagome metal ScV6Sn6 | Compounds with a kagome lattice exhibit intriguing properties and the charge
density wave (CDW) adds an additional layer of interest to research on them. In
this study, we investigate the temperature and magnetic field dependent
electrical properties under a chemical substitution and hydrostatic pressure of
ScV6Sn6, a non-magnetic charge density wave (CDW) compound. Substituting 5 % Cr
at the V site or applying 1.5 GPa of pressure shifts the CDW to 50 K from 92 K.
This shift is attributed to the movement of the imaginary phonon band, as
revealed by the phonon dispersion relation. The longitudinal and Hall
resistivities respond differently under these stimuli. The magnetoresistance
(MR) maintains its quasilinear behavior under pressure, but it becomes
quadratic after Cr substitution. The anomalous Hall-like behavior of the parent
compound persists up to the respective CDW transition under pressure, after
which it sharply declines. In contrast, the longitudinal and Hall resistivities
of Cr substituted compounds follow a two-band model and originates from the
multi carrier effect. These results clearly highlight the role of phonon
contributions in the CDW transition and call for further investigation into the
origin of the anomalous Hall-like behavior in the parent compound. | 2403.02463v1 |
2024-03-05 | A Reduced-Order Resistive Force Model for Robotic Foot-Mud Interactions | Legged robots are well-suited for broad exploration tasks in complex
environments with yielding terrain. Understanding robotic foot-terrain
interactions is critical for safe locomotion and walking efficiency for legged
robots. This paper presents a reduced-order resistive-force model for
robotic-foot/mud interactions. We focus on vertical robot locomotion on mud and
propose a visco-elasto-plastic analog to model the foot/mud interaction forces.
Dynamic behaviors such as mud visco-elasticity, withdrawing cohesive suction,
and yielding are explicitly discussed with the proposed model. Besides
comparing with dry/wet granular materials, mud intrusion experiments are
conducted to validate the force model. The dependency of the model parameter on
water content and foot velocity is also studied to reveal in-depth model
properties under various conditions. The proposed force model potentially
provides an enabling tool for legged robot locomotion and control on muddy
terrain. | 2403.02617v1 |
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