publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2005-11-19 | Transport, thermal and magnetic properties of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_2O_{10-δ}, a magnetic superconductor | Resistivity, thermoelectric power, heat capacity and magnetization for
samples of RuSr_2(Gd_{1.5}Ce_{0.5})Cu_{2}O_{10-\delta} were investigated in the
temperature range 1.8-300 K with a magnetic field up to 8 T. The resistive
transitions to the superconducting state are found to be determined by the
inhomogeneous (granular) structure, characterized by the intragranular, T_{c0},
and intergranular, T_{cg}, transition temperatures. Heat capacity, C(T), shows
a jump at the superconducting transition temperature T_{c0}\approx 37.5 K. A
Schottky-like anomaly is found in C(T) below 20 K. This low temperature anomaly
can be attributed to splitting of the ground term $^{8}S_{7/2}$ of paramagnetic
Gd^{3+} ions by internal and external magnetic fields. | 0511489v1 |
2007-03-28 | Comparison between experiment and calculated band structures for DyN and SmN | We investigate the electronic band structure of two of the rare-earth
nitrides, DyN and SmN. Resistivity measurements imply that both materials have
a semiconducting ground state, and both show resistivity anomalies coinciding
with the magnetic transition, despite the different magnetic states in DyN and
SmN. X-ray absorption and emission measurements are in excellent agreement with
LSDA+U calculations, although for SmN the calculations predict a zero band gap. | 0703740v3 |
2007-04-24 | Impedance spectroscopy of epitaxial multiferroic thin films | Temperature dependent impedance spectroscopy enables the many contributions
to the dielectric and resistive properties of condensed matter to be
deconvoluted and characterized separately. We have achieved this for
multiferroic epitaxial thin films of BiFeO3 (BFO) and BiMnO3 (BMO), key
examples of materials with strong magneto-electric coupling. We demonstrate
that the true film capacitance of the epitaxial layers is similar to that of
the electrode interface, making analysis of capacitance as a function of film
thickness necessary to achieve deconvolution. We modeled non-Debye impedance
response using Gaussian distributions of relaxation times and reveal that
conventional resistivity measurements on multiferroic layers may be dominated
by interface effects. Thermally activated charge transport models yielded
activation energies of 0.60 eV +- 0.05 eV (BFO) and 0.25 eV +- 0.03 eV (BMO),
which is consistent with conduction dominated by oxygen vacancies (BFO) and
electron hopping (BMO). The intrinsic film dielectric constants were determined
to be 320 +- 75 (BFO) and 450 +- 100 (BMO). | 0704.3262v1 |
2007-08-09 | Carbon nanotube array vias for interconnect applications | The material and electrical properties of the CNT single vias and array vias
grown by microwave plasma-enhanced chemical vapor deposition were investigated.
The diameters of multiwall carbon nanotubes (MWNTs) grown on the bottom
electrode of Ta decrease with increasing pretreatment power and substrate
temperature while the effects of the growth power and methane flow ratio are
insignificant The decrease of CNT diameters leads to the decrease of the CNT
via diode devices. The increase of growth power enhances the CNT graphitization
degree and thue the conductivity of CNT via diode devices. In the same via
region, the MWNT diode resistances of the array vias are lower than those of
the single vias. The MWNT diode resistances on the bottom electrode of titanium
are lower than those on the bottom electrode of tantalum. It may be attributed
to the smaller tube diameters on the bottom electrode of Ti and the work
function difference between Ta and Ti films with respect to the work function
of CNTs. | 0708.1298v1 |
2007-08-14 | Suspension of Nanoparticles in SU-8 and Characterization of Nanocomposite Properties | Gold nanospheres, single wall carbon nanotubes (SWNT), and diamonoids were
phyically incorporated into the negative photoresist SU-8. the mixtures were
spin cast onto silicon or aluminium coated silicon wafers. ASTM standard D638
tensile specimens were lithographically patterned in the materials and then
released from the substrate using Microchem'Omnicoat or an anodic metal
dissolution process. the residual stresses, elastic moduli, and viscosity of
the SU-8. Resistivity measurements of SU-8/SWNT nanocomposites were also
investigates. We found the effective modulus and viscosity of the SU-8 test
specimens decreases with the addition of diamantane and SWNTs. Additionally,
the SU-8/SWNT nanocomposites showed changes in resistivity with increased
strain, suggesting a gauge factor for the 1 wt% SU-8/SWNT nanocomposite of
approximately 2-4. | 0708.1822v1 |
2007-12-07 | Field Tuned Superconductor to Insulator Transitions in an Amorphous Film with an Imposed Multiply Connected Geometry | We have observed multiple magnetic field driven superconductor to insulator
transitions (SIT) in amorphous Bi films perforated with a nano-honeycomb (NHC)
array of holes. The period of the magneto-resistance, H=H_M=h/2eS where S is
the area of a unit cell of holes, indicates the field driven transitions are
boson dominated. The field-dependent resistance follows
R(T)=R_0(H)exp(T_0(H)/T) on both sides of the transition so that the evolution
between these states is controlled by the vanishing of T_0 to0. We compare our
results to the thickness driven transition in NHC films and the field driven
transitions in unpatterned Bi films, other materials, and Josephson junction
arrays. Our results suggest a structural source for similar behavior found in
some materials and that despite the clear bosonic nature of the SITs,
quasiparticle degrees of freedom likely also play an important part in the
evolution of the SIT. | 0712.1076v1 |
2008-07-02 | Nano Imprint Lithography on Silica Sol-gels: a simple route to sequential patterning | Since the pioneering work of S.Y. Chou et al.[1] Nano Imprint Lithography
(NIL) has emerged as a promising technique for surface patterning, opening for
numerous applications ranging from nanophotonics[2] to microfluidics[3]. NIL
basically consists in the stamping of deformable surfaces or films. Preferred
materials are thermoplastics[4] and UV curable resists[5]. So far, most papers
report on single imprinting methods for which the same surface is imprinted
only once. In the present paper, we report the imprinting of square silica
structures from simple line gratings and demonstrate how the specific
thermo-rheological behavior of ICSG resists can be harnessed to form complex
structures by sequential imprinting at low pressures. | 0807.0378v1 |
2009-01-09 | Stability of a Charged Particle Beam in a Resistive Plasma Channel | A self-focusing of a coasting relativistic beam in a plasma channel that is
confined by an external magnetic field is studied as a means of reconditioning
the beam emerging from a beam injector [a radio frequency quadrupole (RFQ)] for
a linac. A detailed study of the beam stability in the self-focused beam has
been carried out. In order to explain beam filaments and the resistive hose
instability in a unified way, we treat all the azimuthal modes in the
derivation of the dispersion relation in a finite plasma channel that exhibit
many unstable modes, which are classified by Weinberg's scheme [Steven
Weinberg, J. Math. 8, 614 (1967)]. | 0901.1167v2 |
2009-07-21 | Anomalous transport properties of the halfmetallic ferromagnets Co2TiSi, Co2TiGe, and Co2TiSn | In this work the theoretical and experimental investigations of Co2TiZ (Z =
Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is
predicted for all three compounds with only two bands crossing the Fermi energy
in the majority channel. The magnetic moments fulfill the Slater-Pauling rule
and the Curie temperatures are well above room temperature. All compounds show
a metallic like resistivity for low temperatures up to their Curie temperature,
above the resistivity changes to semiconducting like behavior. A large negative
magnetoresistance of 55% is observed for Co2TiSn at room temperature in an
applied magnetic field of 4T which is comparable to the large negative
magnetoresistances of the manganites. The Seebeck coefficients are negative for
all three compounds and reach their maximum values at their respective Curie
temperatures and stay almost constant up to 950 K. The highest value achieved
is -52muV/K m for Co2TiSn which is large for a metal. The combination of
half-metallicity and the constant large Seebeck coefficient over a wide
temperature range makes these compounds interesting materials for
thermoelectric applications and further spincaloric investigations. | 0907.3562v1 |
2009-08-27 | A low field technique for measuring magnetic and magneto-resistance anisotropy coefficients applied to (Ga,Mn)As | We demonstrate a simple, low cost, magneto-transport method for rapidly
characterizing the magnetic anisotropy and anisotropic magneto-resistance (AMR)
of ferromagnetic devices with uniaxial magnetic anisotropy. This transport
technique is the analogue of magnetic susceptibility measurements of bulk
material but is applicable to very small samples with low total moment. The
technique is used to characterize devices fabricated from the dilute magnetic
semiconductor (Ga,Mn)As. The technique allows us to probe the behavior of the
parameters close to the Curie temperature, in the limit of the applied magnetic
field tending to zero. This avoids the complications arising from the presence
of paramagnetism. | 0908.3960v1 |
2010-01-20 | Robust charge and magnetic order under electric field and current in the multiferroic LuFe(2)O(4) | We performed elastic neutron scattering measurements on the charge- and
magnetically-ordered multiferroic material LuFe(2)O(4). An external electric
field along the [001] direction with strength up to 20 kV/cm applied at low
temperature (~100 K) does not affect either the charge or magnetic structure.
At higher temperatures (~360 K), before the transition to three-dimensional
charge-ordered state, the resistivity of the sample is low, and an electric
current was applied instead. A reduction of the charge and magnetic peak
intensities occurs when the sample is cooled under a constant electric current.
However, after calibrating the real sample temperature using its own
resistance-temperature curve, we show that the actual sample temperature is
higher than the thermometer readings, and the "intensity reduction" is entirely
due to internal sample heating by the applied current. Our results suggest that
the charge and magnetic orders in LuFe(2)O(4) are unaffected by the application
of external electric field/current, and previously observed electric
field/current effects can be naturally explained by internal sample heating. | 1001.3611v2 |
2010-10-07 | Compensation-dependence of magnetic and electrical properties in Ga1-xMnxP | We demonstrate the control of the hole concentration in Ga1-xMnxP over a wide
range by introducing compensating vacancies. The resulting evolution of the
Curie temperature from 51 K to 7.5 K is remarkably similar to that observed in
Ga1-xMnxAs despite the dramatically different character of hole transport
between the two material systems. The highly localized nature of holes in
Ga1-xMnxP is reflected in the accompanying increase in resistivity by many
orders of magnitude. Based on variable-temperature resistivity data we present
a general picture for hole conduction in which variable-range hopping is the
dominant transport mechanism in the presence of compensation. | 1010.1368v2 |
2011-02-04 | Low-Frequency Current Fluctuations in Graphene-like Exfoliated Thin-Films of Topological Insulators | We report on the low-frequency current fluctuations and electronic noise in
thin-films made of bismuth selenide topological insulators. The films were
prepared via the graphene-like mechanical exfoliation and used as the current
conducting channels in the four- and two-contact devices. Analysis of the
resistance dependence on the film thickness indicates that the surface
contribution to conductance is dominant in our samples. It was established that
the current fluctuations have the noise spectrum close to the pure 1/f in the
frequency range from 1 to 10 kHz (f is the frequency). The relative noise
amplitude S/I^2 for the examined films was increasing from ~5x10^-8 to 5x10^-6
(1/Hz) as the resistance of the channels varied from ~10^3 to 10^5 Ohms. The
obtained noise data is important for understanding electron transport through
the surface and volume of topological insulators, and proposed applications of
this class of materials. | 1102.0961v1 |
2011-05-04 | Sondheimer Oscillation as a Fingerprint of Surface Dirac Fermions | Topological states of matter challenge the paradigm of symmetry breaking,
characterized by gapless boundary modes and protected by the topological
property of the ground state. Recently, angle-resolved photoemission
spectroscopy (ARPES) has revealed that semiconductors of Bi$_{2}$Se$_{3}$ and
Bi$_{2}$Te$_{3}$ belong to such a class of materials. Here, we present
undisputable evidence for the existence of gapless surface Dirac fermions from
transport in Bi$_{2}$Te$_{3}$. We observe Sondheimer oscillation in
magnetoresistance (MR). This oscillation originates from the quantization of
motion due to the confinement of electrons within the surface layer. Based on
Sondheimer's transport theory, we determine the thickness of the surface state
from the oscillation data. In addition, we uncover the topological nature of
the surface state, fitting consistently both the non-oscillatory part of MR and
the Hall resistance.
The side-jump contribution turns out to dominate around 1 T in Hall
resistance while the Berry-curvature effect dominates in 3 T $\sim$ 4 T. | 1105.0731v1 |
2011-07-05 | Evidence for filamentary superconductivity nucleated at antiphase domain walls in antiferromagnetic CaFe$_2$As$_2$ | Resistivity, magnetization and microscopic $^{75}$As nuclear magnetic
resonance (NMR) measurements in the antiferromagnetically ordered state of the
iron-based superconductor parent material CaFe$_2$As$_2$ exhibit anomalous
features that are consistent with the collective freezing of domain walls.
Below $T^*\approx 10$ K, the resistivity exhibits a peak and downturn, the bulk
magnetization exhibits a sharp increase, and $^{75}$As NMR measurements reveal
the presence of slow fluctuations of the hyperfine field. These features in
both the charge and spin response are strongly field dependent, are fully
suppressed by $H^*\approx 15$ T, and suggest the presence of filamentary
superconductivity nucleated at the antiphase domain walls in this material. | 1107.0904v2 |
2011-08-22 | Ferromagnetic Quantum Criticality in the Quasi-One-Dimensional Heavy Fermion Metal YbNi4P2 | We present a new Kondo-lattice system, YbNi4P2, which is a clean
heavy-fermion metal with a severely reduced ferromagnetic ordering temperature
at T_C=0.17K, evidenced by distinct anomalies in susceptibility, specific-heat,
and resistivity measurements. The ferromagnetic nature of the transition, with
only a small ordered moment of ~0.05mu_B, is established by a diverging
susceptibility at T_C with huge absolute values in the ferromagnetically
ordered state, severely reduced by small magnetic fields. Furthermore, YbNi4P2
is a stoichiometric system with a quasi-one-dimensional crystal and electronic
structure and strong correlation effects which dominate the low temperature
properties. This is reflected by a stronger-than-logarithmically diverging
Sommerfeld coefficient and a linear-in-T resistivity above T_C which cannot be
explained by any current theoretical predictions. These exciting
characteristics are unique among all correlated electron systems and make this
an interesting material for further in-depth investigations. | 1108.4274v1 |
2012-10-18 | Observation of a Large Photo-response in a Single Nanowire (Diameter ~30 nm) of Charge Transfer Complex Cu:TCNQ | We report for the first time large photoresponse in a single NW of the charge
transfer complex Cu:TCNQ. We fabricate a metal-semiconductor-metal device with
a single NW and focus ion beam deposited Pt. We observe large photocurrent even
at zero bias. The spectral dependence of the photoresponse follows the main
absorption at ~ 405 nm which has the primarily responsible for photogenerated
carriers. We have quantitatively analyzed the bias dependent photocurrent by a
model of two back to back Schottky diodes connected by a series resistance. The
observation shows that the large photoresponse of the device primarily occurs
due to the reduction of the barrier at the contact regions due to illumination
along with the photoconductive contribution. There is also a bias driven
reduction of the nanowire resistance that is a unique feature for the material. | 1210.5207v1 |
2013-01-16 | Huge field-effect surface charge injection and conductance modulation in metallic thin films by electrochemical gating | The field-effect technique, popular thanks to its application in common
field-effect transistors, is here applied to metallic thin films by using as a
dielectric a novel polymer electrolyte solution. The maximum injected surface
charge, determined by a suitable modification of a classic method of
electrochemistry called double-step chronocoulometry, reached some units in
10^15 charges/cm^2. At room temperature, relative variations of resistance up
to 8%, 1.9% and 1.6% were observed in the case of gold, silver and copper,
respectively and, if the films are thick enough (> 25 nm), results can be
nicely explained within a free-electron model with parallel resistive channels.
The huge charge injections achieved make this particular field-effect technique
very promising for a vast variety of materials such as unconventional
superconductors, graphene and 2D-like materials. | 1301.3769v1 |
2013-02-05 | Scaling of Non-Saturating MR and quantum oscillations in pristine and ion-implanted HOPG | A wide variety of resistive and field dependent behaviors have been
previously observed in both doped and non-doped Highly Oriented Pyrolytic
Graphite (HOPG). We find HOPG samples to vary significantly in their
temperature dependent resistances, even between portions taken from the same
sample, yet they exhibit consistent non-saturating magnetoresistance (MR). The
scaling behavior of the MR is shown to be characteristic of a model based on
the Hall effect in granular materials. In addition to the large, field-linear
MR, all samples exhibit Shubnikov-de Haas (SdH) oscillations. Additional
samples were doped via ion-implantation by boron and phosphorous, but show no
signs of superconductivity nor any systematic change in their magnetoresistive
behavior. Analysis of the SdH data gives a 2D carrier density in agreement with
previous results, and a large mean-free path relative to crystallite size, even
in samples with thin ion-implanted surface layers. | 1302.1229v1 |
2013-02-07 | Thermoelectromotive force of hafnium at plastic deformation in regime of creep at temperature of 300 K | The thermoelectromotive force and electrical resistivity of the
polycrystalline hafnium (Hf) with the grain size of 10 {\mu}m during the
process of plastic deformation in the regime of creep at the temperature of 300
K are precisely measured. It is shown that the thermoelectromotive force
depends on the deformation mechanism nature, because of the changing magnitude
of the electrons scattering on the different structural defects in the hafnium
crystal lattice at the deformation process. The main research conclusion is
that the method of thermoelectromotive force measurements is more informative,
comparing to the method of electric resistivity measurements in the process of
accurate characterization of the hafnium. | 1302.1784v1 |
2013-03-11 | Nanobatteries in redox-based resistive switches require extension of memristor theory | Redox-based nanoionic resistive memory cells (ReRAMs) are one of the most
promising emerging nano-devices for future information technology with
applications for memory, logic and neuromorphic computing. Recently, the
serendipitous discovery of the link between ReRAMs and memristors and
memristive devices has further intensified the research in this field. Here we
show on both a theoretical and an experimental level that nanoionic-type
memristive elements are inherently controlled by non-equilibrium states
resulting in a nanobattery. As a result the memristor theory must be extended
to fit the observed non zerocrossing I-V characteristics. The initial
electromotive force of the nanobattery depends on the chemistry and the
transport properties of the materials system but can also be introduced during
ReRAM cell operations. The emf has a strong impact on the dynamic behaviour of
nanoscale memories, and thus, its control is one of the key factors for future
device development and accurate modelling. | 1303.2589v1 |
2013-07-02 | Non-volatile ferroelastic switching of the Verwey transition and resistivity of epitaxial Fe3O4/PMN-PT (011) | A central goal of electronics based on correlated materials or 'Mottronics'
is the ability to switch between distinct collective states with a control
voltage. Small changes in structure and charge density near a transition can
tip the balance between competing phases, leading to dramatic changes in
electronic and magnetic properties. In this work, we demonstrate that an
electric field induced two-step ferroelastic switching pathway in (011)
oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) substrates can be used to
tune the Verwey metal-insulator transition in epitaxial Fe3O4 films in a stable
and reversible manner. We also observe robust non-volatile resistance switching
in Fe3O4 up to room temperature, driven by ferroelastic strain. These results
provides a framework for realizing non-volatile and reversible tuning of order
parameters coupled to lattice-strain in epitaxial oxide heterostructures over a
broad range of temperatures, with potential device applications. | 1307.0838v1 |
2014-06-01 | Effect of carrier concentration on magnetism and magnetic order in the pyrochlore iridates | We present resistivity, magnetization, and zero field muon spin relaxation
($\mu$SR) data for the pyrochlore iridate materials
Nd$_{2-x}$Ca$_{x}$Ir$_{2}$O$_{7}$ ($x = 0, 0.06$, and $0.10$) and
Sm$_2$Ir$_2$O$_7$. While Nd$_{2}$Ir$_{2}$O$_{7}$ (Nd227) is weakly conducting,
Sm$_{2}$Ir$_{2}$O$_{7}$ (Sm227) has slowly diverging resistivity at low
temperature. Nd227 and Sm227 exhibit magnetic anomalies at $T_{M} = 105 K$ and
$137 K$, respectively. However, zero-field $\mu$SR measurements show that
long-range magnetic order of the Ir$^{4+}$ sublattice sets in at much lower
temperatures ($T_{LRO} \sim 8 K$ for Nd227 and $70 K$ for Sm227); both
materials show heavily damped muon precession with a characteristic frequency
near 9 MHz. The magnetic anomaly at $T_{M}$ in Nd227 is not significantly
affected by the introduction of hole carriers by Ca-substitution in the
conducting Nd$_{2-x}$Ca$_{x}$Ir$_{2}$O$_{7}$ samples, but the muon precession
is fully suppressed for both. | 1406.0194v1 |
2014-10-07 | Thickness Scaling Effect on Interfacial Barrier and Electrical Contact to Two-Dimensional MoS2 Layers | Understanding the interfacial electrical properties between metallic
electrodes and low dimensional semiconductors is essential for both fundamental
science and practical applications. Here we report the observation of thickness
reduction induced crossover of electrical contact at Au/MoS2 interfaces. For
MoS2 thicker than 5 layers, the contact resistivity slightly decreases with
reducing MoS2 thickness. By contrast, the contact resistivity sharply increases
with reducing MoS2 thickness below 5 layers, mainly governed by the quantum
confinement effect. It is found that the interfacial potential barrier can be
finely tailored from 0.3 to 0.6 eV by merely varying MoS2 thickness. A full
evolution diagram of energy level alignment is also drawn to elucidate the
thickness scaling effect. The finding of tailoring interfacial properties with
channel thickness represents a useful approach controlling the
metal/semiconductor interfaces which may result in conceptually innovative
functionalities. | 1410.1943v2 |
2015-03-04 | Observation of the chiral anomaly induced negative magneto-resistance in 3D Weyl semi-metal TaAs | Weyl semi-metal is the three dimensional analog of graphene. According to the
quantum field theory, the appearance of Weyl points near the Fermi level will
cause novel transport phenomena related to chiral anomaly. In the present
paper, we report the first experimental evidence for the long-anticipated
negative magneto-resistance generated by the chiral anomaly in a newly
predicted time-reversal invariant Weyl semi-metal material TaAs. Clear
Shubnikov de Haas oscillations (SdH) have been detected starting from very weak
magnetic field. Analysis of the SdH peaks gives the Berry phase accumulated
along the cyclotron orbits to be {\pi}, indicating the existence of Weyl
points. | 1503.01304v1 |
2015-03-12 | Shubnikov-de Haas oscillations, weak antilocalization effect and large linear magnetoresistance in the putative topological superconductor LuPdBi | We present electronic transport and magnetic properties of single crystals of
semimetallic half-Heusler phase LuPdBi, having theoretically predicted band
inversion requisite for nontrivial topological properties. The compound
exhibits superconductivity below a critical temperature $T_{\rm c}=1.8\,$K,
with a zero-temperature upper critical field $B_{\rm c2}\approx2.3\,$T.
Although superconducting state is clearly reflected in the electrical
resistivity and magnetic susceptibility data, no corresponding anomaly can be
seen in the specific heat. Temperature dependence of the electrical resistivity
suggests existence of two parallel conduction channels: metallic and
semiconducting, with the latter making negligible contribution at low
temperatures. The magnetoresistance is huge and clearly shows a weak
antilocalization effect in small magnetic fields. Above about 1.5 T, the
magnetoresistance becomes linear and does not saturate in fields up to 9 T. The
linear magnetoresistance is observed up to room temperature. Below 10 K, it is
accompanied by Shubnikov-de Haas oscillations. Their analysis reveals charge
carriers with effective mass of $0.06\,m_e$ and a Berry phase very close to
$\pi$, expected for Dirac-fermion surface states, thus corroborating
topological nature of the material. | 1503.03697v1 |
2015-11-17 | Microstructure, mechanical properties and corrosion of friction stir welded 6061 Aluminum Alloy | The microstructure, mechanical properties, and corrosion behavior of friction
stir welded (FSW) AA6061 aluminum alloys were investigated. Dynamic
recrystallized structures were observed and grain sizes of nugget zone (NZ),
thermomechanically-affected zone (TMAZ), heat-affected zone (HAZ), and base
material (BM) were different. Hardness test indicated that the minimum and
maximum hardness values wereobtained in the HAZ and BM, respectively. Tensile
results showed that fracture occurred in the relatively weak regions in between
TMAZ and HAZ. Polarization tests illustrated that the FSW process improved the
corrosion resistance of AA6061-AA6061 and the HAZ had better corrosion
resistance than other regions. Raman characterizations revealed that aluminum
hydroxide was the main corrosion product formed on Al after immersion
experiments. Intergranular attack was observed in the NZ and downside by
scanning electron microscopy. | 1511.05507v1 |
2015-11-20 | Transmission conditions for thin curvilinear close to circular heat-resistant interphases in composite ceramics | This paper considers the problem of heat transfer in a composite ceramic
material where the structural elements are bonded to the matrix via a thin heat
resistant adhesive layer. The layer has the form of a circular ring or close to
it. Using an asymptotic approach, the interphase is modeled by an infinitesimal
imperfect interface, preserving the main features of the temperature fields
around the interphase, and allowing a significant simplification where FEM
analysis is concerned. The nonlinear transmission conditions that accompany
such an imperfect interface are evaluated, and their accuracy is verified by
means of dedicated analytical examples as well as carefully designed FEM
simulations. The interphases of various geometries are analysed, with an
emphasis on the influence of the curvature of their boundaries on the accuracy
of the evaluated conditions. Numerical results demonstrate the benefits of the
approach and its limitations. | 1511.06630v2 |
2015-11-29 | Ultrafast electron-phonon-magnon interactions at noble metal-ferromagnet interfaces | Ultrafast optical excitation of gold-cobalt bilayers triggers the nontrivial
interplay between the electronic, acoustic, and magnetic degrees of freedom.
Laser-heated electrons generated at the gold-air interface diffuse through the
layer of gold and strongly overheat the lattice in cobalt resulting in the
emission of ultrashort acoustic pulses and generation of exchange-coupled
magnons. Time-resolved optical measurements allow for extracting the thermal
boundary (Kapitza) resistances at metal/metal interfaces and the hot electron
diffusion length in ferromagnetic materials. Both the experimental data and the
analytical treatment of the two-temperature model reveal the role of the
Kapitza resistance in transient lattice overheating. | 1511.09060v3 |
2016-04-05 | Gap state charge induced spin-dependent negative differential resistance in tunnel junctions | We propose and demonstrate through first-principles calculation a new
spin-dependent negative differential resistance (NDR) mechanism in magnetic
tunnel junctions (MTJ) with cubic cation disordered crystals (CCDC) AlO$_x$ or
Mg$_{1-x}$Al$_x$O as barrier materials. The CCDC is a class of insulators whose
band gap can be changed by cation doping. The gap becomes arched in an
ultrathin layer due to the space charge formed from metal-induced gap states.
With an appropriate combination of an arched gap and a bias voltage, NDR can be
produced in either spin channel. This mechanism is applicable to 2D and 3D
ultrathin junctions with a sufficiently small band gap that forms a large space
charge. It provides a new way of controlling the spin-dependent transport in
spintronic devices by an electric field. A generalized Simmons formula for
tunneling current through junction with an arched gap is derived to show the
general conditions under which ultrathin junctions may exhibit NDR. | 1604.01364v1 |
2016-05-12 | Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures | We report a systematic study on the thermoelectric performance of spin
Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of
device geometries: a spin Hall thermopile and spin Seebeck multilayer
structures. The spin Hall thermopile increases the sensitivity of the spin
Seebeck effect, while the increase in the sample internal resistance has a
detrimental effect on the output power. We found that the spin Seebeck
multilayers can overcome this limitation since the multilayers exhibit the
enhancement of the thermoelectric voltage and the reduction of the internal
resistance simultaneously, therefore resulting in significant power
enhancement. This result demonstrates that the multilayer structures are useful
for improving the thermoelectric performance of the spin Seebeck effect. | 1605.03752v1 |
2016-06-15 | Response of Carbon Nanotube (CNT) Ply Subjected to a Pulsed Magnetic Field | In this study, the possible deformation of a single Carbon Nanotube (CNT) ply
subjected to a pulsed magnetic field was investigated. In all tests the
capacitor bank was charged to 6kJ of energy. A Photon Doppler Velocimetry (PDV)
system was used to measure velocity or displacement of the CNT ply during the
experiments. The resistance of the CNT ply was measured using four-point probe
technique before and after the experiments. Preliminary results show that the
single CNT plies do not permanently deform in response to the pulsed magnetic
fields. However, they can be displaced, either by themselves a small amount
(0.6mm) or by a large amount using a driver material. Also, the resistance of
the CNT plies may increase or decrease depends on the lay-out (i.e., yarn) and
current flow directions. | 1606.04893v2 |
2016-07-28 | A 3D dislocation dynamics analysis of the size effect on the strength of [111] LiF micropillars at 300K and 600K | The mechanical behavior in compression of [111] LiF micropillars with
diameters in the range 0.5 $\mu$m to 2.0 $\mu$m was analyzed by means of
discrete dislocation dynamics at ambient and elevated temperature. The
dislocation velocity was obtained from the Peach-Koehler force acting on the
dislocation segments from a thermally-activated model that accounted for the
influence of temperature on the lattice resistance. A size effect of the type
"smaller is stronger" was predicted by the simulations, which was in
quantitative agreement with previous experimental results by the authors
\cite{SWC14}. The contribution of the different physical deformation mechanisms
to the size effect (namely, nucleation of dislocations, dislocation exhaustion
and forest hardening) could be ascertained from the simulations and the
dominant deformation mode could be assessed as a function of the specimen size
and temperature. These results shed light into the complex interaction among
size, lattice resistance and dislocation mobility in the mechanical behavior of
$\mu$m-sized single crystals. | 1607.08642v1 |
2016-11-20 | Uniform Benchmarking of Low Voltage Van Der Waals FETs | Monolayer MoS2, MoSe2, MoTe2, WS2, WSe2, and black phosphorous field effect
transistors (FETs) operating in the low-voltage (LV) regime (0.3V) with
geometries from the 2019 and 2028 nodes of the 2013 International Technology
Roadmap for Semiconductors (ITRS) are benchmarked along with an ultra-thin-body
Si FET. Current can increase or decrease with scaling, and the trend is
strongly correlated with the effective mass. For LV operation at the 2028 node,
an effective mass of ~0.4 m0, corresponding to that of WSe2, gives the maximum
drive current. The short 6 nm gate length combined with LV operation is
forgiving in its requirements for material quality and contact resistances. In
this LV regime, device and circuit performance are competitive using currently
measured values for mobilities and contact resistances for the monolayer
two-dimensional materials. | 1611.06480v1 |
2016-12-28 | In-plane anisotropy of transport coefficients in the electronic nematic states: Universal origin of the nematicity in Fe-based superconductors | The origin of the electronic nematicity and its remarkable
material-dependence are famous longstanding unsolved issues in Fe-based
superconductors. To attack these issues, we focus on the in-plane anisotropy of
the resistivity: In the nematic state in FeSe, the relation $\rho_x>\rho_y$
holds, where $\rho_{x(y)}$ is the resistivity along the longer (shorter) Fe-Fe
axis. In contrast, the opposite anisotropy $\rho_x<\rho_y$ is realized in other
undoped Fe-based superconductors. Such nontrivial material dependence is
naturally explained in terms of the strongly orbital-dependent inelastic
quasiparticle scattering realized in the orbital-ordered state. The opposite
anisotropy between FeSe ($\rho_x>\rho_y$) and other undoped compounds
($\rho_x<\rho_y$) reflects the difference in the number of hole-pockets. We
also explain the large in-plane anisotropy of the thermoelectric power in the
nematic state. | 1612.08841v1 |
2017-02-03 | Evolution of structure, magnetism and electronic transport in doped pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$ | The interplay between spin-orbit coupling (SOC) and electron correlation
($U$) is considered for many exotic phenomena in iridium oxides. We have
investigated the evolution of structural, magnetic and electronic properties in
pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$ where the substitution of Ru
has been aimed to tune this interplay. The Ru substitution does not introduce
any structural phase transition, however, we do observe an evolution of lattice
parameters with the doping level $x$. X-ray photoemission spectroscopy (XPS)
study indicates Ru adopts charge state of Ru$^{4+}$ and replaces the Ir$^{4+}$
accordingly. Magnetization data reveal both the onset of magnetic
irreversibility and the magnetic moment decreases with progressive substitution
of Ru. These materials show non-equilibrium low temperature magnetic state as
revealed by magnetic relaxation data. Interestingly, we find magnetic
relaxation rate increases with substitution of Ru. The electrical resistivity
shows an insulating behavior in whole temperature range, however, resistivity
decreases with substitution of Ru. Nature of electronic conduction has been
found to follow power-law behavior for all the materials. | 1702.01023v1 |
2017-02-25 | Compressive mechanical response of graphene foams and their thermal resistance with copper interfaces | We report compressive mechanical response of graphene foams (GFs) and the
thermal resistance ($R_{TIM}$) between copper (Cu) and GFs, where GFs were
prepared by the chemical vapor deposition (CVD) method. We observe that Young's
modulus ($E_{GF}$) and compressive strength ($\sigma_{GF}$) of GFs have a power
law dependence on increasing density ($\rho_{GF}$) of GFs. The maximum
efficiency of absorbed energy ($\eta_{max}$) for all GFs during the compression
is larger than ~0.39. We also find that a GF with a higher $\rho_{GF}$ shows a
larger $\eta_{max}$. In addition, we observe that the measured $R_{TIM}$ of
Cu/GFs at room temperature with a contact pressure of 0.25 MP applied increases
from ~50 to ~90 $mm^2K/W$ when $\rho_{GF}$ increases from 4.7 to 31.9
$mg/cm^3$. | 1702.07816v1 |
2017-11-22 | Structural properties of Fe/Cu magnetic multilayers: a Monte Carlo approach | Using atomistic Monte Carlo simulations, we investigated the impact of the
interface on the structural properties of iron and copper (Fe/Cu) magnetic
multilayers grown by Vorono\"i diagram. Interest in magnetic multilayers has
recently emerged as they are shown to be promising candidates for magnetic
storage media, magneto-resistive sensors, and personalized medical treatment.
As these artificial materials show large differences in properties compared to
conventional ones, many experimental and theoretical works have been dedicated
on shedding light on these differences and tremendous results have emerged.
However, little is known how the interfaces influence the structure of the
layers around them. By a numerical approach, we show that the structure of each
layer depends on its thickness and the interface morphology. The Fe and Cu
layers can adopt either the body-centered-cubic (bcc) or face-centered-cubic
(fcc) structure, while the interface can assume amorphous, bcc, fcc, or a
mixture of bcc and fcc structures depending on the layer thicknesses. These
results are in good agreement with the experiments. They could be helpful in
understanding effects such as giant magneto-resistance from the structural
viewpoint. | 1711.08508v1 |
2017-11-24 | Inter-layer and Intra-layer Heat Transfer in Bilayer/Monolayer Graphene van der Waals Heterostructure: Is There a Kapitza Resistance Analogous? | Van der Waals heterostructures have exhibited interesting physical
properties. In this paper, heat transfer in hybrid coplanar bilayer/monolayer
(BL-ML) graphene, as a model layered van der Waals heterostructure, was studied
using non-equilibrium molecular dynamics (MD) simulations. Temperature profile
and inter- and intra-layer heat fluxes of the BL-ML graphene indicated that,
there is no fully developed thermal equilibrium between layers and the drop in
average temperature profile at the step-like BL-ML interface is not
attributable to the effect of Kapitza resistance. By increasing the length of
the system up to 1 $\mu$m in the studied MD simulations, the thermally
non-equilibrium region was reduced to a small area near the step-like
interface. All MD results were compared to a continuum model and a good match
was observed between the two approaches. Our results provide a useful
understanding of heat transfer in nano- and micro-scale layered 2D materials
and van der Waals heterostructures. | 1711.09127v1 |
2018-04-20 | Comparative study of the compensated semi-metals LaBi and LuBi : A first-principles approach | We have investigated the electronic structures of LaBi and LuBi, employing
the full-potential all electron method as implemented in Wien2k. Using this, we
have studied in detail both the bulk and the surface states of these materials.
From our band structure calculations we find that LuBi, like LaBi, is a
compensated semi-metal with almost equal and sizable electron and hole pockets.
In analogy with experimental evidence in LaBi, we thus predict that LuBi will
also be a candidate for extremely large magneto-resistance (XMR), which should
be of immense technological interest. Our calculations reveal that LaBi,
despite being gapless in the bulk spectrum, displays the characteristic
features of a $\mathbb{Z}_{2}$ topological semi-metal, resulting in gapless
Dirac cones on the surface, whereas LuBi only shows avoided band inversion in
the bulk and is thus a conventional compensated semi-metal with extremely large
magneto-resistance. | 1804.07652v1 |
2014-08-02 | Destroyed quantum Hall effect in graphene with [0001] tilt grain boundaries | The reason why the half-integer quantum Hall effect (QHE) is suppressed in
graphene grown by chemical vapor deposition (CVD) is unclear. We propose that
it might be connected to extended defects in the material and present results
for the quantum Hall effect in graphene with [0001] tilt grain boundaries
connecting opposite sides of Hall bar devices. Such grain boundaries contain
5-7 ring complexes that host defect states that hybridize to form bands with
varying degree of metallicity depending on grain boundary defect density. In a
magnetic field, edge states on opposite sides of the Hall bar can be connected
by the defect states along the grain boundary. This destroys Hall resistance
quantization and leads to non-zero longitudinal resistance. Anderson disorder
can partly recover quantization, where current instead flows along returning
paths along the grain boundary depending on defect density in the grain
boundary and on disorder strength. Since grain sizes in graphene made by
chemical vapor deposition are usually small, this may help explain why the
quantum Hall effect is usually poorly developed in devices made of this
material. | 1408.0394v1 |
2019-02-21 | Correlation in transport coefficients of hole-doped CuRhO$_2$ single crystals | To clarify the origin of the nontrivial thermoelectric properties observed in
the delafossite oxide CuRhO$_2$ polycrystals, we have performed the systematic
transport measurements on the single-crystalline CuRhO$_2$ samples. In the
parent compound, we find a pronounced peak structure due to a phonon-drag
effect in the temperature dependence of the Seebeck coefficient, which is also
confirmed by the size effect experiments. In the Mg-substituted crystals, in
contrast to the results of the polycrystals, both the resistivity and the
Seebeck coefficient decrease with increasing Mg content $y$. In particular, the
coefficient $A$ for the $T^2$ term of the resistivity and the $T$-linear
coefficient for the Seebeck coefficient at low temperatures are well described
within a simple relationship expected for metals, which is also applicable to
the correlated materials with low carrier densities. | 1902.08301v1 |
2020-04-14 | Temperature overshoot as the cause of physical changes in resistive switching devices during electro-formation | Resistive switching devices based on transition metal oxides require
formation of a conductive filament in order for the device to be able to
switch. Such filaments have been proposed to form by the reduction of the oxide
due to application of the electric field, but this report seeks to rebut that
interpretation. Frequently reported physical changes during electro-formation
include delamination of electrodes, crystallization of functional oxide,
intermixing of electrode and oxide materials, and extensive loss of oxygen
presumably to the ambient. Here we show that most of these effects are not
inherent to the formation and switching processes and instead are due to an
experimental artifact: the discharge of parasitic capacitances in the forming
circuit. Discharge of typical BNC cables can raise the temperature of the
filament to between 2,000 and 5,000 K resulting in extensive physical changes.
Discharge and associated effects mentioned above can be eliminated using an
on-chip load element without affecting the ability to switch. | 2004.06571v1 |
2020-09-04 | Effective Thermal Conductivity of SrBi$_4$Ti$_4$O$_{15}$-La$_{0.7}$Sr$_{0.3}$MnO$_3$ Oxide composite: Role of Particle Size and Interface Thermal Resistance | We present a novel approach to reduce the thermal conductivity ($\kappa$) in
thermoelectric composite materials using acoustic impedance mismatch and the
Debye model. Also, the correlation between interface thermal resistance
(R$_{int}$) and the particle size of the dispersed phase on the k of the
composite is discussed. In particular, the $\kappa$ of an oxide composite which
consists of a natural superlattice Aurivillius phase (SrBi$_4$Ti$_4$O$_{15}$)
as a matrix and perovskite (La$_{0.7}$Sr$_{0.3}$MnO$_3$) as a dispersed phase
is investigated. A significant reduction in the $\kappa$ of composite, even
lower than the $\kappa$ of the matrix when the particle size of
La$_{0.7}$Sr$_{0.3}$MnO$_3$ is smaller than the Kapitza radius (a$_K$) is
observed, depicting that R$_{int}$ dominates for particle size lower than a$_K$
due to increased surface to volume ratio. The obtained results have the
potential to provide new directions for engineering composite thermoelectric
systems with desired thermal conductivity and promising in the field of energy
harvesting. | 2009.02218v1 |
2022-02-25 | Low-Temperature Thermal Conductivity of CeRh$_{2}$As$_{2}$ | CeRh$_2$As$_2$ is a rare unconventional superconductor ($T_c=0.26$ K)
characterized by two adjacent superconducting phases for a magnetic field $H
\parallel c$-axis of the tetragonal crystal structure. Antiferromagnetic order,
quadrupole-density-wave order ($T_0 = 0.4$ K) and the proximity of this
material to a quantum-critical point have also been reported: The coexistence
of these phenomena with superconductivity is currently under discussion. Here,
we present thermal conductivity and electrical resistivity measurements on a
single crystal of CeRh$_2$As$_2$ between 60 mK and 200 K and in magnetic fields
($H \parallel c$) up to 8 T. Our measurements at low $T$ verify the
Wiedemann-Franz law within the error bars. The $T$ dependence of the thermal
conductivity $\kappa(T)$ shows a pronounced drop below $T_c$ which is also
field dependent and thus interpreted as the signature of superconductivity.
However, the large residual resistivity and the lack of sharp anomalies in
$\kappa(T)$ at the expected transition temperatures clearly indicate that
samples of much higher purity are required to gain more information about the
superconducting gap structure. | 2202.12667v1 |
2016-03-07 | Pressure-resistant intermediate valence in Kondo insulator SmB6 | Resonant x-ray emission spectroscopy (RXES) was used to determine the
pressure dependence of the f-electron occupancy in the Kondo insulator SmB6.
Applied pressure reduces the f-occupancy, but surprisingly, the material
maintains a significant divalent character up to a pressure of at least 35 GPa.
Thus, the closure of the resistive activation energy gap and onset of magnetic
order are not driven by stabilization of an integer valent state. Over the
entire pressure range, the material maintains a remarkably stable intermediate
valence that can in principle support a nontrivial band structure. | 1603.02207v1 |
2017-04-01 | Small-signal model for 2D-material based field-effect transistors targeting radio-frequency applications: the importance of considering non-reciprocal capacitances | A small-signal equivalent circuit of 2D-material based field-effect
transistors is presented. Charge conservation and non-reciprocal capacitances
have been assumed so the model can be used to make reliable predictions at both
device and circuit levels. In this context, explicit and exact analytical
expressions of the main radio-frequency figures of merit of these devices are
given. Moreover, a direct parameter extraction methodology is provided based on
S-parameter measurements. In addition to the intrinsic capacitances,
transconductance and output conductance, our approach allows extracting the
series combination of drain/source metal contact and access resistances.
Accounting for these extrinsic resistances is of upmost importance when dealing
with low dimensional field-effect transistors. | 1704.00181v2 |
2017-04-05 | An open-source platform to study uniaxial stress effects on nanoscale devices | We present an automatic measurement platform that enables the
characterization of nanodevices by electrical transport and optical
spectroscopy as a function of uniaxial stress. We provide insights into and
detailed descriptions of the mechanical device, the substrate design and
fabrication, and the instrument control software, which is provided under
open-source license. The capability of the platform is demonstrated by
characterizing the piezo-resistance of an InAs nanowire device using a
combination of electrical transport and Raman spectroscopy. The advantages of
this measurement platform are highlighted by comparison with state-of-the-art
piezo-resistance measurements in InAs nanowires. We envision that the
systematic application of this methodology will provide new insights into the
physics of nanoscale devices and novel materials for electronics, and thus
contribute to the assessment of the potential of strain as a technology booster
for nanoscale electronics. | 1704.01394v1 |
2017-08-09 | Contact-Induced Semiconductor-to-Metal Transition in Single-Layer WS$_2$ | Low-resistance ohmic contacts are a challenge for electronic devices based on
two-dimensional materials. We show that an atomically precise junction between
a two-dimensional semiconductor and a metallic contact can lead to a
semiconductor-to-metal transition in the two-dimensional material--a finding
which points the way to a possible method of achieving low-resistance
junctions. Specifically, single-layer WS$_2$ undergoes a semiconductor-to-metal
transition when epitaxially grown on Ag(111), while it remains a direct band
gap semiconductor on Au(111). The metallicity of the single layer on Ag(111) is
established by lineshape analysis of core level photoemission spectra.
Angle-resolved photoemission spectroscopy locates the metallic states near the
Q point of the WS$_2$ Brillouin zone. Density functional theory calculations
show that the metallic states arise from hybridization between Ag bulk bands
and the local conduction band minimum of WS$_2$ near the Q point. | 1708.02799v1 |
2019-08-26 | Local electrodynamics of a disordered conductor model system measured with a microwave impedance microscope | We study the electrodynamic impedance of percolating conductors with a
pre-defined network topology using a scanning microwave impedance microscope
(sMIM) at GHz frequencies. For a given percolation number we observe strong
spatial variations across a sample which correlate with the connected regions
(clusters) in the network when the resistivity is low such as in Aluminum. For
the more resistive material NbTiN the impedance becomes dominated by the local
structure of the percolating network (connectivity). The results can
qualitatively be understood and reproduced with a network current spreading
model based on the pseudo-inverse Laplacian of the underlying network graph. | 1908.09810v1 |
2019-11-30 | Structural relaxation in amorphous materials under cyclic tension-compression loading | The process of structural relaxation in disordered solids subjected to
repeated tension-compression loading is studied using molecular dynamics
simulations. The binary glass is prepared by rapid cooling well below the glass
transition temperature and then periodically strained at constant volume. We
find that the amorphous system is relocated to progressively lower potential
energy states during hundreds of cycles, and the energy levels become deeper
upon approaching critical strain amplitude from below. The decrease in
potential energy is associated with collective nonaffine rearrangements of
atoms, and their rescaled probability distribution becomes independent of the
cycle number at sufficiently large time intervals. It is also shown that
yielding during startup shear deformation occurs at larger values of the stress
overshoot in samples that were cyclically loaded at higher strain amplitudes.
These results might be useful for mechanical processing of amorphous alloys in
order to reduce their energy and increase chemical resistivity and resistance
to crystallization. | 1912.00221v1 |
2021-01-04 | Twin Mechanical Metamaterials | By mimicking the geometrical relation of nano-twin crystals, we propose novel
architected twin mechanical metamaterials (TMMs), which can impede local
shearing band formation under external loading, thus avoiding global
catastrophic failure. The effects of twin-space and twin angle on the
mechanical performance of TMMs were also explored, such as: energy absorption,
strength, and crack propagation resistance. The results showed that the twin
topology design can not only significantly improve the energy-absorption
efficiency but also remarkably improve the crack-propagation resistances of
stretching-dominant mechanical metamaterials. We also studied the effect of
twin-space and twin angle on the tensile strength of TMMs. This study is the
first to report on the inverse Hall-Petch effect of TMMs. Our findings open an
avenue for the design and fabrication of advanced materials with exceptionally
tuneable mechanical properties. | 2101.00927v1 |
2012-06-04 | Optimal Condition for Strong Terahertz Radiation from Intrinsic Josephson Junctions | In order to enhance the radiation power in terahertz band based on the
intrinsic Josephson junctions of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ single
crystal, we investigate a long cylindrical sample embedded in a dielectric
material. Tuning the dielectric constant, the radiation power has a maximum
which is achieved when it equals the dissipation caused by Josephson plasma.
This yields the optimal dielectric constant of wrapping material in terms of
the properties of BSCCO single crystal. The maximal radiation power is found
proportional to the product of the typical superconducting current squared and
the typical normal resistance, or the gap energy squared divided by the typical
normal resistance, which offers a guideline for choosing superconductor as a
source of strong radiation. By introducing an anti-reflection layer, we can
build a compact device with the BSCCO cylinder and two wrapping dielectric
layers with finite thicknesses. | 1206.0516v1 |
2012-06-15 | Breakdown of the interlayer coherence in twisted bilayer graphene | Coherent motion of the electrons in the Bloch states is one of the
fundamental concepts of the charge conduction in solid state physics. In
layered materials, however, such a condition often breaks down for the
interlayer conduction, when the interlayer coupling is significantly reduced by
e.g. large interlayer separation. We report that complete suppression of
coherent conduction is realized even in an atomic length scale of layer
separation in twisted bilayer graphene. The interlayer resistivity of twisted
bilayer graphene is much higher than the c-axis resistivity of Bernal-stacked
graphite, and exhibits strong dependence on temperature as well as on external
electric fields. These results suggest that the graphene layers are
significantly decoupled by rotation and incoherent conduction is a main
transport channel between the layers of twisted bilayer graphene. | 1206.3410v1 |
2015-07-23 | Electronic, magnetic and transport properties of Fe intercalated 2H-TaS$_2$ studied by means of the KKR-CPA method | The electronic, magnetic and transport properties of Fe intercalated
2H-TaS$_2$ have been investigated by means of the Korringa-Kohn-Rostoker (KKR)
method. The non-stoichiometry and disorder in the system has been accounted for
using the Coherent Potential Approximation (CPA) alloy theory. A pronounced
influence of disorder on the spin magnetic moment has been found for the
ferro-magnetically ordered material. The same applies for the spin-orbit
induced orbital magnetic moment and magneto-crystalline anisotropy energy. The
temperature-dependence of the resistivity of disordered 2H-Fe$_{0.28}$TaS$_2$
investigated on the basis of the Kubo-St\v{r}eda formalism in combination with
the alloy analogy model has been found in very satisfying agreement with
experimental data. This also holds for the temperature dependent anomalous Hall
resistivity $ \rho_{\rm xy}(T) $. The role of thermally induced lattice
vibrations and spin fluctuations for the transport properties is discussed in
detail. | 1507.06544v1 |
2018-07-18 | Thermoelectric stack sample cooling modification of a commercial atomic force microscopy | Enabling temperature dependent experiments in Atomic Force Microscopy is of
great interest to study materials and surface properties at the nanoscale. By
studying Curie temperature of multiferroic materials, temperature based phase
transition on crystalline structures or resistive switching phenomena are only
a few examples of applications. We present an equipment capable of cooling
samples using a thermoelectric cooling stage down to -61.4 C in a 15x15 mm
sample plate. The equipment uses a four-unit thermoelectric stack to achieve
maximum temperature range, with low electrical and mechanical noise. The
equipment is installed into a Keysight 5500LS Atomic Force Microscopy
maintaining its compatibility with all Electrical and Mechanical modes of
operation. We study the contribution of the liquid cooling pump vibration into
the cantilever static deflection noise and the temperature dependence of the
cantilever deflection. A La0.7Sr0.3MnO3-y thin film sample is used to
demonstrate the performance of the equipment and its usability by analysing the
resistive switching phenomena associated with this oxide perovskite. | 1807.06876v1 |
2019-01-21 | Ferromagnetic Kondo lattice behavior in Ce11Pd4In9 | We report on the low-temperature physical properties of a novel compound
Ce$_{11}$Pd$_4$In$_9$ that crystallizes with the orthorhombic
Nd$_{11}$Pd$_4$In$_9$-type crystal structure (space group $Cmmm$). The compound
exhibits ferromagnetic ordering at $T_{\rm {C}}$ = 18.6 K and an order-order
transition at $T_{\rm {t}}$ $\sim$~1.6 K, as inferred from the low-temperature
magnetic susceptibility, heat capacity and electrical resistivity data. In the
paramagnetic region, the electrical transport in Ce$_{11}$Pd$_4$In$_9$ is
dominated by Kondo effect. Below $T_{\rm {C}}$, a distinct contribution due to
ferromagnetic spin waves dominates the electrical resistivity data, while at
the lowest temperatures, the electrical transport and thermodynamic properties
are governed by strong electron-electron correlations. The features observed
conjointly hint at strongly correlated ground state in Ce$_{11}$Pd$_4$In$_9$ . | 1901.06888v1 |
2019-11-14 | Absence of evidence of spin transport through amorphous Y$_3$Fe$_5$O$_{12}$ | Long-distance transport of spin information in insulators without long-range
magnetic order has been recently reported. Here, we perform a complete
characterization of amorphous Y$_3$Fe$_5$O$_{12}$ (a-YIG) films grown on top of
SiO$_2$. We confirm a clear amorphous structure and paramagnetic behavior of
our a-YIG films, with semiconducting behavior resistivity that strongly decays
with increasing temperature. The non-local transport measurements show a signal
which is not compatible with spin transport and can be attributed to the drop
of the a-YIG resistivity caused by Joule heating. Our results emphasize that
exploring spin transport in amorphous materials requires careful procedures in
order to exclude the charge contribution from the spin transport signals. | 1911.06061v2 |
2019-11-15 | Design and Performance of Hafnium Optical and Near-IR Kinetic Inductance Detectors | We report on the design and performance of Microwave Kinetic Inductance
Detectors (MKIDs) sensitive to single photons in the optical to near-infrared
range using hafnium as the sensor material. Our test device had a
superconducting transition temperature of 395 mK and a room temperature normal
state resistivity of 97 $\mu \Omega$ cm with an RRR = 1.6. Resonators on the
device displayed internal quality factors of around 200,000. Similar to the
analysis of MKIDs made from other highly resistive superconductors, we find
that modeling the temperature response of the detector requires an extra
broadening parameter in the superconducting density of states. Finally, we show
that this material and design is compatible with a full-array fabrication
process which resulted in pixels with decay times of about 40 $\mu$s and
resolving powers of ~9 at 800 nm. | 1911.06434v1 |
2020-01-08 | Effect of memory electrical switching in metal/vanadium oxide/silicon structures with VO2 films obtained by the sol-gel method | Electrical switching and rectifying properties of the metal-VO2-Si
structures, on both p-type and n-type silicon, with vanadium dioxide films
obtained by an acetylacetonate sol-gel method, are studied. The switching
effect is shown to be due to the semiconductor-to-metal phase transition (SMPT)
in vanadium dioxide. The shift of the switching threshold voltage, accompanied
by the memory effect, in forward bias of the p-Si-VO2 anisotype heterojunction
is observed. To explain this effect, a model is proposed which suggests the
existence of an additional series resistance associated with a channel at the
VO2/Si interface, where a SiOx layer forms during the VO2 deposition process.
This resistance is responsible for both threshold switching characteristics,
and the memory effect, and the oxygen ion electromigration process is shown to
underlie this effect. Potential applications of the observed phenomena,
combining the effects of ReRAM and SMPT, in oxide electronics are discussed. | 2001.03055v1 |
2020-05-24 | Schottky barriers, emission regimes and contact resistances in 2H-1T' MoS$_2$ lateral metal-semiconductor junctions from first-principles | We have studied the finite bias transport properties of a 2H-1T' MoS$_2$
lateral metal-semiconductor (M-S) junction by non-equilibrium Green's functions
calculations, aimed at contacting the 2D channel in a field effect transistor.
Our results indicate that (a) despite the fundamentally different
electrostatics of line and planar dipoles, the Schottky barrier heights respond
similarly to changes in doping and applied bias in 2D and 3D M-S junctions, (b)
2H-1T' MoS$_2$ lateral junctions are free from Fermi level pinning, (c)
armchair interfaces have superior contacting properties vs.\ zigzag interfaces,
(d) 1T' contacts to $p$ channels will present a reduced contact resistance by a
factor of 4-10 with respect to $n$ channels and (e) contacts to intermediately
doped $n$ ($p$) channels operate in the field (thermionic) emission regime. We
also provide an improved procedure to experimentally determine the emission
regime in 2D material junctions. | 2005.11717v1 |
2020-06-12 | Blocking of conducting channels widens window for ferroelectric resistive switching in interface-engineered Hf0.5Zr0.5O2 tunnel devices | Films of Hf0.5Z0.5O2 (HZO) contain a network of grain boundaries. In (111)
HZO epitaxial films on (001) SrTiO3, for instance, twinned orthorhombic (o-HZO)
ferroelectric crystallites coexist with grain boundaries between o-HZO and a
residual paraelectric monoclinic (m-HZO) phase. These grain boundaries
contribute to the resistive switching response in addition to the genuine
ferroelectric polarization switching and have detrimental effects on device
performance. Here, it is shown that, by using suitable nanometric capping
layers deposited on HZO film, a radical improvement of the operation window of
the tunnel device can be achieved. Crystalline SrTiO3 and amorphous AlOx are
explored as capping layers. It is observed that these layers conformally coat
the HZO surface and allow to increase the yield and homogeneity of functioning
ferroelectric junctions while strengthening endurance. Data show that the
capping layers block ionic-like transport channels across grain boundaries. It
is suggested that they act as oxygen suppliers to the oxygen-getters grain
boundaries in HZO. In this scenario it could be envisaged that these and other
oxides could also be explored and tested for fully compatible CMOS
technologies. | 2006.07048v1 |
2020-07-09 | Fe3Se4: A Possible Ferrimagnetic Half-Metal? | Half-metallic ferromagnets show 100% spin-polarization at the Fermi level and
are ideal candidates for spintronic applications. Despite the extensive
research in the field, very few materials have been discovered so far. Here we
present results of electronic band structure calculations based on density
functional theory and extensive physical-property measurements for Fe3Se4
revealing signatures of half-metallicity. The spin-polarized electronic band
structure calculations predict half-metallic ferrimagnetism for Fe3Se4. The
electrical resistivity follows exponentially suppressed electron-magnon
scattering mechanism in the low-temperature regime and show a magnetoresistance
effect that changes the sign from negative to positive with decreasing
temperature around 100 K. Other intriguing observations include the anomalous
behavior of Hall resistance below 100 K and an anomalous Hall coefficient that
roughly follows the \r{ho}2 behavior. | 2007.04736v1 |
2020-07-29 | Quasiparticle and Nonquasiparticle Transport in Doped Quantum Paraelectrics | Charge transport in doped quantum paralectrics (QPs) presents a number of
puzzles, including a pronounced $T^2$ regime in the resistivity. We analyze
charge transport in a QP within a model of electrons coupled to a soft
transverse optical (TO) mode via a two-phonon mechanism. For $T$ above the
soft-mode frequency but below some characteristic scale ($E_0$), the
resistivity scales with the occupation number of phonons squared, i.e., as
$T^2$. The $T^2$ scattering rate does not depend on the carrier number density
and is not affected by a crossover between degenerate and non-degenerate
regimes, in agreement with the experiment. Temperatures higher than $E_0$
correspond to a non-quasiparticle regime, which we analyze by mapping the Dyson
equation onto a problem of supersymmetric quantum mechanics. The combination of
scattering by two TO phonons and by a longitudinal optical mode explains the
data quite well. | 2007.14947v2 |
2020-08-06 | Magnetic, transport, and thermal properties of $δ$-phase UZr$_2$ | Alloys of hexagonal $\delta$-phase UZr$_2$ have been synthesized and studied
by means of heat capacity, magnetic susceptibility, magnetization, electrical
resistivity, magnetoresistance, thermoelectric power, thermal conductivity
measurements, for the first time, at temperatures from 1.8 to 300 K and in
magnetic fields up to 8 T. The weak temperature dependence of the magnetic
susceptibility and the small value of both Seebeck (0.75 $\mu$V/K at room
temperature) and of the Sommerfeld coefficient (13.5 mJ mol$^{-1}$ K$^{-2}$)
point to 5$f$-electrons in this material having a delocalized nature. The
electrical resistivity and magnetoresistance indicate the presence of
significant electronic disorder in $\delta$-UZr$_2$, consistent with the
disorder in its crystal structure. Density functional theory calculations have
been performed and compared to experimental results. | 2008.02746v1 |
2020-12-29 | Magnetotransport signatures of chiral magnetic anomaly in the half-Heusler phase ScPtBi | Study of magnetotransport properties of ScPtBi revealed simultaneously: a
negative contribution to the longitudinal magnetoresistance, the planar Hall
effect, and distinct angular narrowing of the longitudinal magnetoresistance {
three hallmarks of chiral magnetic anomaly (pumping of axial charge between
Weyl nodes), a distinct property of topological semimetals. Electronic
structure calculations show that structural defects, such as antisites and
vacancies, bring substantial density of states at the Fermi level of ScPtBi,
indicating that it is a semimetal, not a zero-gap semiconductor, as predicted
earlier. This is in accord with electrical resistivity in ScPtBi, showing no
characteristics of semiconductor. Moreover, below 0.7K we observed an onset of
a superconducting transition, with the resistivity disappearing completely
below 0.23 K. | 2012.14819v2 |
2021-05-28 | Projected mushroom-type phase-change memory | Phase-change memory devices have found applications in in-memory computing
where the physical attributes of these devices are exploited to compute in
place without the need to shuttle data between memory and processing units.
However, non-idealities such as temporal variations in the electrical
resistance have a detrimental impact on the achievable computational precision.
To address this, a promising approach is projecting the phase configuration of
phase change material onto some stable element within the device. Here we
investigate the projection mechanism in a prominent phase-change memory device
architecture, namely mushroom-type phase-change memory. Using nanoscale
projected Ge2Sb2Te5 devices we study the key attributes of state-dependent
resistance, drift coefficients, and phase configurations, and using them reveal
how these devices fundamentally work. | 2105.13693v2 |
2021-08-04 | Current-induced breakdown of the quantum anomalous Hall effect | The quantum anomalous Hall effect (QAHE) realizes dissipationless
longitudinal resistivity and quantized Hall resistance without the need of an
external magnetic field. However, when reducing the device dimensions or
increasing the current density, an abrupt breakdown of the dissipationless
state occurs with a relatively small critical current, limiting the
applications of the QAHE. We investigate the mechanism of this breakdown by
studying multi-terminal devices and identified that the electric field created
between opposing chiral edge states lies at the origin. We propose that
electric-field-driven percolation of two-dimensional charge puddles in the
gapped surface states of compensated topological-insulator films is the most
likely cause of the breakdown. | 2108.02081v1 |
2021-10-08 | Universal Non-Volatile Resistive Switching Behavior in 2D Metal Dichalcogenides Featuring Unique Conductive-Point Random Access Memory Effect | Two-dimensional materials have been discovered to exhibit non-volatile
resistive switching (NVRS) phenomenon. In our work, we reported the universal
NVRS behavior in a dozen metal dichalcogenides, featuring low switching
voltage, large on/off ratio, fast switching speed and forming free
characteristics. A unique conductive-point random access memory (CPRAM) effect
is used to explain the switching mechanisms, supported by experimental results
from current-sweep measurements. | 2110.03863v1 |
2021-10-27 | Bound on resistivity in flat-band materials due to the quantum metric | The quantum metric is a central quantity of band theory but has so far not
been related to many response coefficients due to its nonclassical origin.
However, within a newly developed Kubo formalism for fast relaxation, the
decomposition of the dc electrical conductivity into both classical (intraband)
and quantum (interband) contributions recently revealed that the interband part
is proportional to the quantum metric. Here, we show that interband effects due
to the quantum metric can be significantly enhanced and even dominate the
conductivity for semimetals at charge neutrality and for systems with highly
quenched bandwidth. This is true in particular for topological flat-band
materials of nonzero Chern number, where for intermediate relaxation rates an
upper bound exists for the resistivity due to the common geometrical origin of
quantum metric and Berry curvature. We suggest to search for these effects in
highly tunable rhombohedral trilayer graphene flakes. | 2110.14658v3 |
2021-11-22 | First-principles-based screening method for resistivity scaling of anisotropic metals | The resistivity scaling of metals is a crucial limiting factor for further
downscaling of interconnects in nanoelectronic devices that affects signal
delay, heat production, and energy consumption. Here, we generalize a commonly
considered figure of merit for selecting promising candidate metals with highly
anisotropic Fermi surfaces in terms of their electronic transport properties at
the nanoscale. For this, we introduce a finite-temperature transport tensor,
based on band structures obtained from first principles. This transport tensor
allows for a straightforward comparison between highly anisotropic metals in
nanostructures with different lattice orientations and arbitrary transport
directions. By evaluating the temperature dependence of the tensor components,
we also assess the validity of a Fermi surface-based evaluation of the
transport properties at zero temperature, rather than considering standard
operating temperature conditions. | 2111.11121v2 |
2021-12-17 | Nanoscale laser flash measurements of diffuson transport in amorphous Ge and Si | The thermal properties of amorphous materials have attracted significant
attention due to their technological importance in electronic devices.
Additionally, the disorder-induced breakdown of the phonon gas model makes
vibrational transport in amorphous materials a topic of fundamental interest.
In the past few decades, theoretical concepts such as propagons, diffusons, and
locons have emerged to describe different types of vibrational modes in
disordered solids. But experiments can struggle to accurately determine which
types of vibrational states carry the majority of the heat. In the present
study, we use nanoscale laser flash measurements (front/back time-domain
thermoreflectance) to investigate thermal transport mechanisms in amorphous Ge
and amorphous Si thin-films. We observe a nearly linear relationship between
the amorphous film's thermal resistance and the film's thickness. The slope of
the film's thermal resistance vs. thickness corresponds to a
thickness-independent thermal conductivity of 0.4 and 0.6 W/(m-K) for a-Ge and
a-Si, respectively. This result reveals that the majority of heat currents in
amorphous Si and Ge thin films prepared via RF sputtering at room temperature
are carried by diffusons and/or propagons with mean free paths less than a few
nanometers. | 2112.09289v2 |
2022-01-06 | Insights to negative differential resistance in \texorpdfstring{MoS\textsubscript{2}}{MoS2} Esaki diodes: a first-principles perspective | \ce{MoS_2} is a two dimensional material with a band gap depending on the
number of layers and tunable by an external electric field. The experimentally
observed intralayer band-to-band tunneling and interlayer band-to-band
tunneling in this material present an opportunity for new electronic
applications in tunnel field effect transistors. However, such a widely
accepted concept has never been supported up by theoretical investigations
based on first principles. In this work, using density functional theory, in
conjunction with non-equilibrilibrium Green's function techniques and our
electric field gating method, enabled by a large-scale computational approach,
we study the relation between band alignment and transmission in planar and
side-stack \ce{MoS_2} $p$-$i$-$n$ junction configurations. We demonstrate the
presence of negative differential resistance for both in-plane and interlayer
current, a staple characteristic of tunnel diode junctions, and analyze the
physical origin of such an effect. Electrostatic potentials, the van der Waals
barrier, and complex band analysis are also examined for a thorough
understanding of Esaki Diodes. | 2201.02178v1 |
2022-05-21 | Increased Phase Coherence Length in a Porous Topological Insulator | The surface area of Bi2Te3 thin films was increased by introducing nanoscale
porosity. Temperature dependent resistivity and magnetotransport measurements
were conducted both on as-grown and porous samples (23 and 70 nm). The
longitudinal resistivity of the porous samples became more metallic, indicating
the increased surface area resulted in transport that was more surface-like.
Weak antilocalization (WAL) was present in all samples, and remarkably the
phase coherence length doubled in the porous samples. This increase is likely
due to the large Fermi velocity of the Dirac surface states. Our results show
that the introduction of nanoporosity does not destroy the topological surface
states but rather enhances them, making these nanostructured materials
promising for low energy electronics, spintronics and thermoelectrics. | 2205.10589v1 |
2022-07-11 | Spin-Orbit Proximity Effect in Bi/Co Multilayer: The Role of Interface Scattering | The Spin-Orbit Proximity Effect is the raise of Spin-Orbit Coupling at a
layer near to the interface with a strong spin-orbit material. It has been seen
in several system such as graphene and ferromagnetic layers. The control of the
Spin-Orbit Coupling can be a pathway to discover novel and exotic phases in
superconductor and semimetallic systems. Here, we study the magnetoelectrical
transport, i.e., magnetoresistance and anomalous Hall effect, in Cobalt/Bismuth
multilayers looking for traces of spin-orbit proximity effect and evaluate the
origin of such effect. Our results point for an increase of Spontaneous
Magnetic Anisotropy of Resistivity and Anomalous Hall Resistivity at very low
thicknesses of Cobalt. The analysis of the Anomalous Hall Resisitivity indicate
that the Bismuth layers change the scattering mechanism of Hall effect to the
extrinsic skew-scattering type, indicating that the spin-orbit proximity effect
could be related to the elastic scattering of cobalt free carriers by bismuth
sites at the interface. | 2207.04937v1 |
2022-08-22 | Unified intermediate coupling description of the pseudogap and the strange metal phases of cuprates | A one band Hubbard model with intermediate coupling is shown to describe the
two most important unusual features of a normal state: linear resistivity
strange metal and the pseudogap. Both the spectroscopic and transport
properties of the cuprates are considered on the same footing by employing a
relatively simple postgaussian approximation valid for the intermediate
couplings $U/t=1.5-4$ in relevant temperatures $T>100{\rm K}.$ In the doping
range $\ p=0.1-0.3$, the value of $U$ is smaller than that in the parent
material. For a smaller doping, especially in the Mott insulator phase, the
coupling is large compared to the effective tight binding scale and a different
method is required. This scenario provides an alternative to the paradigm that
the coupling should be strong, say $U/t>6$, in order to describe the strange
metal. We argue that to obtain phenomenologically acceptable underdoped normal
state characteristics like $T^{\ast }$, pseudogap values, and spectral weight
distribution, a large value of $U$ is detrimental. Surprisingly the resistivity
in the above temperature range is linear $\rho =\rho_{0}+\alpha \frac{m^{\ast
}}{e^{2}n\hbar }T$ with the "Planckian" coefficient $\alpha $ of order one. | 2208.10093v1 |
2022-09-05 | Charge-Density Wave Driven Giant Thermionic-Current Switching in 1T-TaS$_{2}$/2H-TaSe$_{2}$/2H-MoS$_{2}$ Heterostructure | 1T-TaS$_2$ exhibits several resistivity phases due to the modulation of
charge density wave (CDW). The fact that such phase transition can be driven
electrically has attracted a lot of attention in the recent past towards
\emph{active-metal} based electronics. However, the bias-driven resistivity
switching is not very large ($<$ 5 fold), and an enhancement in the same will
highly impact such phase transition devices. One aspect that is often
overlooked is that such phase transition is also accompanied by a significant
change in the local temperature due to the low thermal conductivity of
1T-TaS$_2$. In this work, we exploit such electrically driven phase transition
induced temperature change to promote carriers over a thermionic barrier in a
1T-TaS$_{2}$/2H-TaSe$_{2}$/2H-MoS$_{2}$ T-Junction, achieving a $964$-fold
abrupt switching in the current through the MoS$_2$ channel. The device is
highly reconfigurable and exhibits an abrupt reduction in current as well when
the biasing configuration changes. The results are promising for several
electronic applications, including neuromorphic chips, switching, nonlinear
devices, and industrial electronics such as current and temperature sensing. | 2209.02024v1 |
2022-11-18 | Pressure-induced superconductivity in PdTeI with quasi-one-dimensional PdTe chains | The quasi-one-dimensional material PdTeI exhibits unusual electronic
transport properties at ambient pressure. Here, we systematically investigate
both the structural and electronic responses of PdTeI to external pressure,
through a combination of electrical transport, synchrotron x-ray diffraction
(XRD), and Raman spectroscopy measurements. The charge density wave (CDW) order
in PdTeI is fragile and the transition temperature TCDW decreases rapidly with
the application of external pressure. The resistivity hump is indiscernible
when the pressure is increased to 1 GPa. Upon further compression, zero
resistance is established above 20 GPa, suggesting the occurrence of
superconductivity. Combined XRD and Raman data evidence that the emergence of
superconductivity is accompanied by a pressure-induced amorphization of PdTeI. | 2211.10294v1 |
2023-02-21 | Electron transport and scattering mechanisms in ferromagnetic monolayer Fe$_3$GeTe$_2$ | We study intrinsic charge-carrier scattering mechanisms and determine their
contribution to the transport properties of the two-dimensional ferromagnet
Fe$_3$GeTe$_2$. We use state-of-the-art first-principles calculations combined
with the model approaches to elucidate the role of the electron-phonon and
electron-magnon interactions in the electronic transport. Our findings show
that the charge carrier scattering in Fe$_3$GeTe$_2$ is dominated by the
electron-phonon interaction, while the role of magnetic excitations is
marginal. At the same time, the magnetic ordering is shown to effect
essentially on the electron-phonon coupling and its temperature dependence.
This leads to a sublinear temperature dependence of the electrical resistivity
near the Curie temperature, which is in line with experimental observations.
The room temperature resistivity is estimated to be $\sim$35 $\mu \Omega
\cdot$cm which may be considered as an intrinsic limit for monolayer
Fe$_3$GeTe$_2$. | 2302.10974v1 |
2023-03-20 | Thermal decomposition of the Kitaev material $α$-RuCl$_3$ and its influence on low-temperature behavior | We explore the effect of heat treatment in argon atmosphere under various
temperatures up to $500^\circ$C on single crystals of $\alpha$-RuCl$_3$ by
study of the mass loss, microprobe energy dispersive x-ray spectroscopy, powder
x-ray diffraction, electrical resistance as well as low-temperature magnetic
susceptibility and specific heat. Clear signatures of dechlorination and
oxidation of Ru appear for annealing temperatures beyond $300^\circ$C. Analysis
of the specific heat below 2~K reveals a RuO$_2$ mass fraction of order $1\%$
for pristine $\alpha$-RuCl$_3$ which increases up to $20\%$ after thermal
annealing, fully consistent with mass-loss analysis. The small RuO$_2$
inclusions drastically reduce the global electrical resistance and may thus
significantly affect low-temperature thermal transport and Hall effect. | 2303.11308v1 |
2023-09-08 | Re-entrance of resistivity due to the interplay of superconductivity and magnetism in $\ce{Eu_{0.73}Ca_{0.27}(Fe_{0.87}Co_{0.13})2As2}$ | By simultaneous Co and Ca-doping we were able to obtain an
$\ce{EuFe2As2}$-based compound with superconductivity appearing above the
antiferromagnetic order of $\ce{Eu^{2+}}$ magnetic moments. However, as soon as
the antiferromagnetic order appears a re-entrance behavior is observed
\textemdash{} instead of zero resistivity and diamagnetic signal down to the
temperature of \unit[2]{K}. By investigating magnetization, ac susceptibility
and electrical transport properties of
$\ce{Eu_{0.73}Ca_{0.27}(Fe_{0.87}Co_{0.13})2As2}$ and comparing them to
previously studied M\"ossbauer effect and neutron scattering measurements of
this and similar compounds an explanation of such behavior is proposed. | 2309.04308v2 |
2023-10-02 | Crystallographic-dependent bilinear magnetoelectric resistance in a thin WTe$_2$ layer | The recently reported Bilinear Magnetoeletric Resistance (BMR) in novel
materials with rich spin textures, such as bismuth selenide (Bi$_2$Se$_3$) and
tungsten ditelluride (WTe$_2$), opens new possibilities for probing the spin
textures via magneto-transport measurements. By its nature, the BMR effect is
directly linked to the crystal symmetry of the materials and its spin texture.
Therefore, understanding the crystallographic dependency of the effect is
crucial. Here we report the observation of crystallographic-dependent BMR in
thin WTe$_2$ layers and explore how it is linked to its spin textures. The
linear response measured in first harmonic signals and the BMR measured in
second harmonic signals are both studied under a wide range of magnitudes and
directions of magnetic field, applied current and at different temperatures. We
discover a three-fold symmetry contribution of the BMR when current is applied
along the a-axis of the WTe$_2$ thin layer at 10 K, which is absent for when
current is applied along the b-axis. | 2310.01058v1 |
2023-11-23 | Helicoidal Transformation Method for Finite Element Models of Twisted Superconductors | This paper deals with the modelling of superconducting and resistive wires
with a helicoidal symmetry, subjected to an external field and a transport
current. Helicoidal structures are three-dimensional, and therefore yield
computationally intensive simulations in a Cartesian coordinate system. We show
in this paper that by working instead with a helicoidal system of coordinates,
the problem to solve can be made two-dimensional, drastically reducing the
computational cost. We first introduce the state-of-the-art approach and apply
it on the h-phi-formulation with helicoidally symmetric boundary conditions
(e.g., axial external magnetic field, with or without transport current), with
an emphasis on the function space discretization. Then, we extend the approach
to general boundary conditions (e.g., transverse external magnetic field) and
present numerical results with linear materials. In particular, we discuss the
frequency-dependent losses in composite wires made of superconducting filaments
embedded in a resistive matrix. Finally, we provide outlook to the application
of the generalized model with nonlinear materials. | 2311.13919v2 |
2024-03-28 | Single-Crystal Growth and Characterization of Cuprate Superconductor (Hg,Re)Ba$_2$Ca$_2$Cu$_3$O$_{8+δ}$ | We grew (Hg,Re)Ba$_2$Ca$_2$Cu$_3$O$_{8+\delta}$ ((Hg,Re)1223) single crystals
with good reproducibility via the single-step flux method using monoxides as
raw materials. A double-sealing method using a thick-walled quartz tube and a
stainless-steel container was adopted for explosion protection. The maximum
crystal size was approximately 1 mm x 1 mm in the ab plane and 0.04 mm in
thickness. The crystal was square-shaped, reflecting the tetragonal crystal
structure of (Hg,Re)1223. Magnetic susceptibility measurements indicated a
critical temperature of 130 K. The in-plane resistivity exhibited a linear
temperature dependence, indicating that the sample was close to optimal doping
level. The out-of-plane resistivity was also measured, and the anisotropy
parameter was 250-650 at 300 K. | 2403.19182v1 |
2024-05-01 | Tunable viscous layers in Corbino geometry using density junctions | In sufficiently clean materials where electron-electron interactions are
strong compared to momentum-relaxing scattering processes, electron transport
resembles the flow of a viscous fluid. We study hydrodynamic electron transport
across density interfaces (n-n junctions) in a 2DEG in the Corbino geometry.
From numerical simulations in COMSOL using realistic parameters, we show that
we can produce tunable viscous layers at the density interface by varying the
density ratio of charge carriers. We quantitatively explain this observation
with simple analytic expressions together with boundary conditions at the
interface. We also show signatures of these viscous layers in the
magnetoresistance. Breaking down viscous and ohmic contributions, we find that
when outer radial region of the Corbino has higher charge density compared to
the inner region, the viscous layers at the interface serve to suppress the
magneto-resistance produced by momentum-relaxing scattering. Conversely, the
magneto-resistance is enhanced when the inner region has higher density than
the outer. Our results add to the repertoire of techniques for engineering
viscous electron flows, which hold a promise for applications in future
electronic devices. | 2405.00381v1 |
2003-06-06 | Collective transport and optical absorption near the stripe criticality | Within the stripe quantum critical point scenario for high $T_c$
superconductors, we point out the possible direct contribution of charge
collective fluctuations to the optical absorption and to the d.c. resistivity. | 0306176v1 |
2010-08-09 | Planes, Chains, and Orbits: Quantum Oscillations and High Magnetic Field Heat Capacity in Underdoped YBCO | The underlying physics of the magnetic-field-induced resistive state in high
temperature cuprate superconductors remains a mystery. One interpretation is
that the application of magnetic field destroys the d-wave superconducting gap
to uncover a Fermi surface that behaves like a conventional (i.e.Fermi Liquid)
metal (1). Another view is that an applied magnetic field destroys long range
superconducting phase coherence, but the superconducting gap amplitude survives
(2, 3). By measuring the specific heat of ultra-clean YBa2Cu3O6.56 (YBCO 6.56),
we obtain a measure of the quasi-particle density of states from the
superconducting state well into the magnetic-field-induced resistive state. We
have found that at very high magnetic fields the specific heat exhibits both
the conventional temperature dependence and quantum oscillations expected for a
Fermi Liquid. On the other hand, the magnetic field dependence of the
quasi-particle density of states follows a \sqrt{H} behavior that persists
right through the zero-resistance transition, evidencing the fully developed
d-wave superconducting gap over the entire magnetic field range measured. The
coexistence of these two phenomena pose a rigorous thermodynamic constraint on
theories of high-magnetic-field resistive state in the cuprates. | 1008.1568v1 |
2011-02-09 | Heavy Long-lived Mossbauer State of Niobium | A heavy niobium state showing 1/3 residual resistance is discovered below the
superconducting transition temperature. This niobium sample contains
high-density long-lived Mossbauer excitation. | 1102.1766v2 |
2015-12-21 | Kondo effect in CeX$_{c}$ (X$_{c}$=S, Se, Te) studied by electrical resistivity under high pressure | We have measured the electrical resistivity of cerium monochalcogenices, CeS,
CeSe, and CeTe, under high pressures up to 8 GPa. Pressure dependences of the
antiferromagnetic ordering temperature $T_{N}$, crystal field splitting, and
the $\ln T$ anomaly of the Kondo effect have been studied to cover the whole
region from the magnetic ordering regime at low pressure to the Fermi liquid
regime at high pressure. $T_{N}$ initially increases with increasing pressure,
and starts to decrease at high pressure as expected from the Doniach's diagram.
Simultaneously, the $\ln T$ behavior in the resistivity is enhanced, indicating
the enhancement of the Kondo effect by pressure. It is also characteristic in
CeX$_{c}$ that the crystal field splitting rapidly decreases at a common rate
of $-12.2$ K/GPa. This leads to the increase in the degeneracy of the $f$ state
and further enhancement of the Kondo effect. It is shown that the pressure
dependent degeneracy of the $f$ state is a key factor to understand the
pressure dependence of $T_{N}$, Kondo effect, magnetoresistance, and the peak
structure in the temperature dependence of resistivity. | 1512.06530v1 |
2019-10-01 | High transparency Bi2Se3 topological insulator nanoribbon Josephson junctions with low resistive noise properties | Bi$_2$Se$_3$ nanoribbons, grown by catalyst-free Physical Vapour Deposition,
have been used to fabricate high quality Josephson junctions with Al
superconducting electrodes. The conductance spectra (dI/dV) of the junctions
show clear dip-peak structures characteristic of multiple Andreev reflections.
The temperature dependence of the dip-peak features reveals a highly
transparent Al/Bi$_2$Se$_3$ topological insulator nanoribbon interface and
Josephson junction barrier. This is supported by the high values of the
Bi$_2$Se$_3$ induced gap and of I$_c$R$_n$ (I$_c$ critical current, R$_n$
normal resistance of the junction) product both of the order of 160 $\mu$eV, a
value close to the Al gap. The devices present an extremely low relative
resistance noise below 1$\times$10$^{-12}$ $\mu$m$^2$/Hz comparable to the best
Al tunnel junctions, which indicates a high stability in the transmission
coefficients of transport channels. The ideal Al/Bi$_2$Se$_3$ interface
properties, perfect transparency for Cooper pair transport in conjunction with
low resistive noise make these junctions a suitable platform for further
studies of the induced topological superconductivity and Majorana bound states
physics. | 1910.00280v2 |
2017-04-28 | Electric Field Effect in Multilayer Cr2Ge2Te6: a Ferromagnetic Two-Dimensional Material | The emergence of two-dimensional (2D) materials has attracted a great deal of
attention due to their fascinating physical properties and potential
applications for future nanoelectronic devices. Since the first isolation of
graphene, a Dirac material, a large family of new functional 2D materials have
been discovered and characterized, including insulating 2D boron nitride,
semiconducting 2D transition metal dichalcogenides and black phosphorus, and
superconducting 2D bismuth strontium calcium copper oxide, molybdenum
disulphide and niobium selenide, etc. Here, we report the identification of
ferromagnetic thin flakes of Cr2Ge2Te6 (CGT) with thickness down to a few
nanometers, which provides a very important piece to the van der Waals
structures consisting of various 2D materials. We further demonstrate the giant
modulation of the channel resistance of 2D CGT devices via electric field
effect. Our results illustrate the gate voltage tunability of 2D CGT and the
potential of CGT, a ferromagnetic 2D material, as a new functional quantum
material for applications in future nanoelectronics and spintronics. | 1704.08862v1 |
2023-09-26 | The p-Laplace "Signature" for Quasilinear Inverse Problems with Large Boundary Data | This paper is inspired by an imaging problem encountered in the framework of
Electrical Resistance Tomography involving two different materials, one or both
of which are nonlinear. Tomography with nonlinear materials is in the early
stages of developments, although breakthroughs are expected in the
not-too-distant future.
We consider nonlinear constitutive relationships which, at a given point in
the space, present a behaviour for large arguments that is described by
monomials of order p and q.
The original contribution this work makes is that the nonlinear problem can
be approximated by a weighted p-Laplace problem. From the perspective of
tomography, this is a significant result because it highlights the central role
played by the $p-$Laplacian in inverse problems with nonlinear materials.
Moreover, when p=2, this provides a powerful bridge to bring all the imaging
methods and algorithms developed for linear materials into the arena of
problems with nonlinear materials.
The main result of this work is that for "large" Dirichlet data in the
presence of two materials of different order (i) one material can be replaced
by either a perfect electric conductor or a perfect electric insulator and (ii)
the other material can be replaced by a material giving rise to a weighted
p-Laplace problem. | 2309.15206v1 |
2024-04-23 | An Accessible Instrument for Measuring Soft Material Mechanical Properties | Soft material research has seen significant growth in recent years, with
emerging applications in robotics, electronics, and healthcare diagnostics
where understanding material mechanical response is crucial for precision
design. Traditional methods for measuring nonlinear mechanical properties of
soft materials require specially sized samples that are extracted from their
natural environment to be mounted on the testing instrument. This has been
shown to compromise data accuracy and precision in various soft and biological
materials. To overcome this, the Volume Controlled Cavity Expansion (VCCE)
method was developed. This technique tests soft materials by controlling the
formation rate of a liquid cavity inside the materials at the tip of an
injection needle, and simultaneously measuring the resisting pressure which
describes the material response. Despite VCCE's early successes, expansion of
its application beyond academia has been hindered by cost, size, and expertise.
In response to this, the first portable, bench-top instrument utilizing VCCE is
presented here. This device, built with affordable, readily available
components and open-source software, streamlines VCCE experimentation without
sacrificing performance or precision. It is especially suitable for
space-limited settings and designed for use by non-experts, promoting
widespread adoption. The instrument's efficacy was demonstrated through testing
Polydimethylsiloxane (PDMS) samples of varying stiffness. This study not only
validates instrument performance, but also sets the stage for further
advancements and broader applications in soft material testing. All data, along
with acquisition, control, and post-processing scripts, are made available on
GitHub. | 2404.15036v1 |
2018-04-04 | High-Performance Flexible Magnetic Tunnel Junctions for Smart Miniaturized Instruments | Flexible electronics is an emerging field in many applications ranging from
in vivo biomedical devices to wearable smart systems. The capability of
conforming to curved surfaces opens the door to add electronic components to
miniaturized instruments, where size and weight are critical parameters. Given
their prevalence on the sensors market, flexible magnetic sensors play a major
role in this progress. For many high-performance applications, magnetic tunnel
junctions (MTJs) have become the first choice, due to their high sensitivity,
low power consumption etc. MTJs are also promising candidates for non-volatile
next-generation data storage media and, hence, could become central components
of wearable electronic devices. In this work, a generic low-cost regenerative
batch fabrication process is utilized to transform rigid MTJs on a 500 {\mu}m
silicon wafer substrate into 5 {\mu}m thin, mechanically flexible silicon
devices, and ensuring optimal utilization of the whole substrate. This method
maintains the outstanding magnetic properties, which are only obtained by
deposition of the MTJ on smooth high-quality silicon wafers. The flexible MTJs
are highly reliable and resistive to mechanical stress. Bending of the MTJ
stacks with a diameter as small as 500 {\mu}m is possible without compromising
their performance and an endurance of over 1000 cycles without fatigue has been
demonstrated. The flexible MTJs were mounted onto the tip of a cardiac catheter
with 2 mm in diameter without compromising their performance. This enables the
detection of magnetic fields and the angle which they are applied at with a
high sensitivity of 4.93 %/Oe and a low power consumption of 0.15 {\mu}W, while
adding only 8 {\mu}g and 15 {\mu}m to the weight and diameter of the catheter,
respectively. | 1804.01298v1 |
2017-01-30 | High quality factor manganese-doped aluminum lumped-element kinetic inductance detectors sensitive to frequencies below 100 GHz | Aluminum lumped-element kinetic inductance detectors (LEKIDs) sensitive to
millimeter-wave photons have been shown to exhibit high quality factors, making
them highly sensitive and multiplexable. The superconducting gap of aluminum
limits aluminum LEKIDs to photon frequencies above 100 GHz. Manganese-doped
aluminum (Al-Mn) has a tunable critical temperature and could therefore be an
attractive material for LEKIDs sensitive to frequencies below 100 GHz if the
internal quality factor remains sufficiently high when manganese is added to
the film. To investigate, we measured some of the key properties of Al-Mn
LEKIDs. A prototype eight-element LEKID array was fabricated using a 40 nm
thick film of Al-Mn deposited on a 500 {\mu}m thick high-resistivity,
float-zone silicon substrate. The manganese content was 900 ppm, the measured
$T_c = 694\pm1$ mK, and the resonance frequencies were near 150 MHz. Using
measurements of the forward scattering parameter $S_{21}$ at various bath
temperatures between 65 and 250 mK, we determined that the Al-Mn LEKIDs we
fabricated have internal quality factors greater than $2 \times 10^5$, which is
high enough for millimeter-wave astrophysical observations. In the dark
conditions under which these devices were measured, the fractional frequency
noise spectrum shows a shallow slope that depends on bath temperature and probe
tone amplitude, which could be two-level system noise. The anticipated white
photon noise should dominate this level of low-frequency noise when the
detectors are illuminated with millimeter-waves in future measurements. The
LEKIDs responded to light pulses from a 1550 nm light-emitting diode, and we
used these light pulses to determine that the quasiparticle lifetime is 60
{\mu}s. | 1701.08461v2 |
1997-08-21 | Charge Dynamics from Copper Oxide Materials | The charge dynamics of the copper oxide materials in the underdoped and
optimal doped regimes is studied within the framework of the fermion-spin
theory. The conductivity spectrum shows the non-Drude behavior at low energies
and unusual midinfrared peak, and the resistivity exhibits a linear behavior in
the temperature, which are consistent with experiments and numerical
simulations. | 9708165v2 |
2000-07-06 | Scaling of Crack Surfaces and Implications on Fracture Mechanics | The scaling laws describing the roughness development of crack surfaces are
incorporated into the Griffith criterion. We show that, in the case of a
Family-Vicsek scaling, the energy balance leads to a purely elastic brittle
behavior. On the contrary, it appears that an anomalous scaling reflects a
R-curve behavior associated to a size effect of the critical resistance to
crack growth in agreement with the fracture process of heterogeneous brittle
materials exhibiting a microcracking damage. | 0007100v1 |
2001-01-17 | Negative Magnetoresistance Produced by Hall Fluctuations in a Ferromagnetic Domain Structure | We present a model for a negative magnetoresistance (MR) that would develop
in a material with many ferromagnetic domains even if the individual domains
have no magnetoresistance and even if there is no boundary resistance. The
negative MR is due to a classical current-distortion effect arising from
spatial variations in the Hall conductivity, combined with a change in domain
structure due to an applied magnetic field. The negative MR can exceed 1000% if
the product of the carrier relaxation time and the internal magnetic field due
to spontaneous magnetization is sufficiently large. | 0101268v2 |
2001-03-06 | Rheology of a confined granular material | We study the rheology of a granular material slowly driven in a confined
geometry. The motion is characterized by a steady sliding with a resistance
force increasing with the driving velocity and the surrounding relative
humidity. For lower driving velocities a transition to stick-slip motion
occurs, exhibiting a blocking enhancement whith decreasing velocity. We propose
a model to explain this behavior pointing out the leading role of friction
properties between the grains and the container's boundary. | 0103143v1 |
2001-11-07 | Crumpling a Thin Sheet | Crumpled sheets have a surprisingly large resistance to further compression.
We have studied the crumpling of thin sheets of Mylar under different loading
conditions. When placed under a fixed compressive force, the size of a crumpled
material decreases logarithmically in time for periods up to three weeks. We
also find hysteretic behavior when measuring the compression as a function of
applied force. By using a pre-treating protocol, we control this hysteresis and
find reproducible scaling behavior for the size of the crumpled material as a
function of the applied force. | 0111095v1 |
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