publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2012-04-16 | Complementary Resistive Switching in Tantalum Oxide-Based Resistive Memory Devices | Complementary resistive switches (CRS) are considered as a potential solution
for the sneak path problem in large-scale integration of passive crossbar
resistive memory arrays. A typical CRS is composed of two bipolar memory cells
that are connected anti-serially. Here we report a tantalum-oxide based
resistive memory that achieves the complementary switching functionality within
a single memory cell. The complementary switching effect is accompanied by
switching polarity reversal in different voltage bias regimes. These effects
were explained by the redistribution of oxygen vacancies inside the
tantalum-oxide layers. The effects of symmetry breaking on bipolar switching
and complementary switching were also discussed. | 1204.3515v2 |
2014-03-16 | InGaN/GaN Tunnel Junctions For Hole Injection in GaN Light Emitting Diodes | InGaN/GaN tunnel junction contacts were grown on top of an InGaN/GaN blue
(450 nm) light emitting diode wafer using plasma assisted molecular beam
epitaxy. The tunnel junction contacts enable low spreading resistance n-GaN top
contact layer thereby requiring less top metal contact coverage on the surface.
A voltage drop of 5.3 V at 100 mA, forward resistance of 2 x 10-2 ohm cm2 and a
higher light output power are measured in tunnel junction LED. A low resistance
of 5 x 10-4 ohm cm2 was measured in a MBE grown tunnel junction on GaN PN
junction device, indicating that the tunnel junction LED device resistance is
limited by the regrowth interface and not by the intrinsic tunneling
resistance. | 1403.3932v1 |
2014-12-01 | Resistivity minimum in strongly phase separated manganite thin films: impact of intrinsic and extrinsic perturbations | The origin of the resistivity minimum observed in strongly phase separated
manganites has been investigated in single crystalline thin films of LPCMO
(x~0.42, y~0.40). The antiferromagnetic/charge ordered insulator
(AFM/COI)-ferromagnetic metal (FMM) phase transition, coupled with the colossal
hysteresis between the field cool cooled and field cooled warming magnetization
demonstrates strongly phase separated nature, which gives rise to
non-equilibrium magnetic liquid state that freezes into a magnetic glass. The
thermal cycling and magnetic field dependence of the resistivity unambiguously
shows that the pronounced resistivity minimum observed during warming is a
consequence non-equilibrium states resulting from the magnetic frustration
created by the delicate coexistence of the FMM and AFM/COI phases. The
non-equilibrium states and hence the resistivity minimum is extremely sensitive
to the relative fraction of the coexisting phases and can be tuned by intrinsic
and extrinsic perturbations like the defect density, thermal cycling and
magnetic field. | 1412.0418v1 |
2015-01-05 | Reversed anisotropy of the in-plane resistivity in the antiferromagnetic phase of iron tellurides | We systematically investigated the anisotropic in-plane resistivity of the
iron telluride including three kinds of impurity atoms: excess Fe, Se
substituted for Te, and Cu substituted for Fe. Sizable resistivity anisotropy
was found in the magneto-structurally ordered phase whereas the sign is
opposite ($\rho_a$ $>$ $\rho_b$, where the $b$-axis parameter is shorter than
the $a$-axis one) to that observed in the transition-metal doped iron arsenides
($\rho_a$ $<$ $\rho_b$). On the other hand, our results demonstrate that the
magnitude of the resistivity anisotropy in the iron tellurides is correlated
with the amount of impurities, implying that the resistivity anisotropy
originates from an exotic impurity effect like that in the iron arsenides. This
suggests that the anisotropic carrier scattering by impurities is a universal
phenomenon in the magneto-structurally ordered phase of the iron-based
materials. | 1501.00774v1 |
2015-05-21 | Resistance minimum and electrical conduction mechanism in polycrystalline CoFeB thin films | The temperature dependent resistance $R$($T$) of polycrystalline
ferromagnetic CoFeB thin films of varying thickness are analyzed considering
various electrical scattering processes. We observe a resistance minimum in
$R$($T$) curves below $\simeq$ 29 K, which can be explained as an effect of
intergranular Coulomb interaction in a granular system. The structural and
Coulomb interaction related scattering processes contribute more as the film
thickness decreases implying the role of disorder and granularity. Although the
magnetic contribution to the resistance is the weakest compared to these two,
it is the only thickness independent process. On the contrary, the negative
coefficient of resistance can be explained by electron interaction effect in
disordered amorphous films. | 1505.05711v2 |
2015-10-29 | Magneto-transport behaviour of Bi2Se3-xTex: Role of disorder | Magnetoresistance and Hall resistance measurements have been carried out in
fastcooled single crystals of Bi2Se3-xTex (x: 0 to 2) in 4 to 300 K temperature
range, under magnetic fields up to 15 T. The variation of resistivity with
temperature that points to a metallic behaviour in Bi2Se3, shows an upturn at
low temperatures in the Te doped samples. Magnetoresistance measurements in
Bi2Se3 show clear signatures of Shubnikov de Hass oscillations that gets
suppressed in the Te doped samples. In the Bi2SeTe2 sample, the
magneto-resistance shows a cusp like positive magneto-resistance at low
magnetic fields and low temperatures, a feature associated with weak
antilocalisation (WAL), that crosses over to negative magneto-resistance at
higher fields. The qualitatively different magnetotransport behaviour seen in
Bi2SeTe2 as compared to Bi2Se3 is rationalised in terms of the disorder,
through an estimate of the carrier density, carrier mobility and an analysis in
terms of the Ioffe Regel criterion with support from Hall Effect measurements. | 1510.08561v1 |
2015-12-10 | Mini array of quantum Hall devices based on epitaxial graphene | Series connection of four quantum Hall effect (QHE) devices based on
epitaxial graphene films was studied for realization of a quantum resistance
standard with an up-scaled value. The tested devices showed quantum Hall
plateaux RH,2 at filling factor i = 2 starting from relatively low magnetic
field (between 4 T and 5 T) when temperature was 1.5 K. Precision measurements
of quantized Hall resistance of four QHE devices connected by triple series
connections and external bonding wires were done at B = 7 T and T = 1.5 K using
a commercial precision resistance bridge with 50 microA current through the QHE
device. The results showed that the deviation of the quantized Hall resistance
of the series connection of four graphene-based QHE devices from the expected
value of 4*RH,2 = 2h/e^2 was smaller than the relative standard uncertainty of
the measurement (< 1*10^-7) limited by the used resistance bridge. | 1512.03163v2 |
2016-01-04 | Making Consistent Contacts to Graphene: Effect of Architecture and Growth Induced Defects | The effect of contact architecture, graphene defect density and
metal-semiconductor work function difference on resistivity of metal-graphene
contacts have been investigated. An architecture with metal on the bottom of
graphene is found to yield resistivities that are lower, by a factor of 4, and
most consistent as compared to metal on top of graphene. Growth defects in
graphene film were found to further reduce resistivity by a factor of 2. Using
a combination of method and metal used, the contact resistivity of graphene has
been decreased by a factor of 10 to 1200 +- 250 Ohm-um using Palladium as the
contact metal. While the improved consistency is due to the metal being able to
contact uncontaminanted graphene in the metal on the bottom architecture, lower
contact resistivities observed on defective graphene with the same metal is
attributed to the increased number of modes of quantum transport in the
channel. | 1601.00429v1 |
2016-06-13 | Effect of interstitial impurities on the field dependent microwave surface resistance of niobium | Previous work has demonstrated that the radio frequency surface resistance of
niobium resonators is dramatically reduced when nitrogen impurities are
dissolved as interstitial in the material. The origin of this effect is
attributed to the lowering of the Mattis and Bardeen surface resistance
contribution with increasing accelerating field. Meanwhile, an enhancement of
the sensitivity to trapped magnetic field is typically observed for such
cavities. In this paper we conduct the first systematic study on these
different components contributing to the total surface resistance as a function
of different levels of dissolved nitrogen, in comparison with standard surface
treatments for niobium resonators. Adding these results together we are able to
show for the first time which is the optimum surface treatment that maximizes
the Q-factor of superconducting niobium resonators as a function of expected
trapped magnetic field in the cavity walls. These results also provide new
insights on the physics behind the change in the field dependence of the Mattis
and Bardeen surface resistance, and of the trapped magnetic vortex induced
losses in superconducting niobium resonators. | 1606.04174v1 |
2016-10-18 | Dichotomy between in-plane magnetic susceptibility and resistivity anisotropies in extremely strained $BaFe_{2}As_{2}$ | The in-plane resistivity and uniform magnetic susceptibility anisotropies of
$BaFe_{2}As_{2}$ are obtained with a new method, in which a large
symmetry-breaking uniaxial strain is applied using a substrate with a very
anisotropic thermal expansion. The resistivity anisotropy and its corresponding
elastoresistivity exhibit very similar diverging behavior as those obtained
from piezo-stack experiments. This suggests that the resistivity anisotropy is
more a direct measure of magnetism than of nematicity, since the nematic
transition is no longer well-defined under a large strain. In strong contrast
to the large resistivity anisotropy above $T_{N}$, the anisotropy of the
in-plane magnetic susceptibility develops largely below $T_{N}$. Using an
itinerant model, we show that the observed anisotropy ($\chi_{b}>\chi_{a}$) is
determined by spin-orbit coupling and the orientation of the magnetic moments
in the antiferromagnetic phase, and that the anisotropy is dominated by
intra-orbital ($yz,yz$) contributions of the Umklapp susceptibility. | 1610.05575v2 |
2016-12-15 | Reaction-Drift Model for Switching Transients in Pr$_{0.7}$Ca$_{0.3}$MnO$_3$ Based Resistive RAM | Earlier, the DC hole-current modeling of PCMO RRAM by drift-diffusion (DD)
including self-heating (SH) in TCAD (but without ionic transport) was able to
explain the experimentally observed SCLC characteristics, prior to resistive
switching. Further, transient analysis using DD+SH model was able to reproduce
the experimentally observed fast current increase at ~100ns timescale followed
by saturation increases, prior to resistive switching. However, resistive
switching requires the inclusion of ionic transport. We propose a
Reaction-Drift (RD) model of oxide ions, which is combined with the DD+SH
model. Experimentally, SET operations consist of 3 stages and RESET operations
consists of 4 stages. The DD+SH+RD model is able to reproduce the entire
transient behavior over 10$^{-8}$-1s range in timescale for both SET and RESET
operations for a range of bias, temperature. Remarkably, a universal RESET
behaviour of $log(I)\propto m*log(t)$, where $m\approx -1/10$, is reproduced.
The quantitatively different voltage time dilemma for SET and RESET is also
replicated for a range of ambient temperature. This demonstrates a
comprehensive model for resistance switching in PCMO based RRAM. | 1612.05293v2 |
2018-06-20 | Domain wall resistance in CoFeB-based heterostructures with interface Dzyaloshinskii-Moriya interaction | We have studied the domain wall resistance in W/Ta/CoFeB/MgO
heterostructures. The Ta layer thickness is varied to control the type of
domain walls via changes in the interfacial Dzyaloshinskii Moriya interaction.
We find a nearly constant domain wall resistance against the Ta layer
thickness. Adding contributions from the anisotropic magnetoresistance, spin
Hall magnetoresistance and anomalous Hall effect describe well the domain wall
resistance of the thick Ta layer films. However, a discrepancy remains for the
thin Ta layer films wherein chiral N\'eel-like domain walls are found. These
results show the difficulty of studying the domain wall type from resistance
measurements. | 1806.07750v1 |
2019-02-12 | Designing multi-level resistance states for multi-bit storage using half doped manganites | Designing nonvolatile multi-level resistive devices is the necessity of time
to go beyond traditional one-bit storage systems, thus enhancing the storage
density. Here, we explore the electronic phase competition scenario to design
multi-level resistance states using a half doped CE-type charge ordered
insulating bulk manganite, $Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3$ (SCSMO). By
introducing electronic phase coexistence in a controllable manner in SCSMO, we
show that the system can be stabilized into several metastable states, against
thermal cycling, up to 62 K. As a result the magnetization (and the
resistivity) remains unaltered during the thermal cycling. Monte Carlo
calculations using two-band double exchange model, including super-exchange,
electron-phonon coupling, and quenched disorder, show that the system freezes
into a phase coexistence metastable state during the thermal cycling due to the
chemical disorder in SCSMO. Using the obtained insights we outline a pathway by
utilizing four reversible metastable resistance states to design a prototype
multi-bit memory device. | 1902.04377v1 |
2019-03-02 | On the origin of the anomalous peak in the resistivity of TiSe$_2$ | Resistivity measurements of TiSe$_2$ typically show only a weak change in
gradient at the charge density wave transition at $T_{CDW}\approx$ 200~K, but
more prominently feature a broad peak at a lower $T_{peak}\sim$ 165~K, which
has remained poorly understood despite decades of research on the material.
Here we present quantitative simulations of the resistivity using a simplified
parametrization of the normal state band structure, based on recent
photoemission data. Our simulations reproduce the overall profile of the
resistivity of TiSe$_2$, including its prominent peak, without implementing the
CDW at all. We find that the peak in resistivity corresponds to a crossover
between a low temperature regime with electron-like carriers only, to a regime
around room temperature where thermally activated and highly mobile hole-like
carriers dominate the conductivity. Even when implementing substantial
modifications to model the CDW below the transition temperature, we find that
these thermal population effects still dominate the transport properties of
TiSe$_2$. | 1903.00756v1 |
2012-06-13 | Modelling of Current Percolation Channels in Emerging Resistive Switching Elements | Metallic oxides encased within Metal-Insulator-Metal (MIM) structures can
demonstrate both unipolar and bipolar switching mechanisms, rendering them the
capability to exhibit a multitude of resistive states and ultimately function
as memory elements. Identifying the vital physical mechanisms behind resistive
switching can enable these devices to be utilized more efficiently, reliably
and in the long-term. In this paper, we present a new approach for analysing
resistive switching by modelling the active core of two terminal devices as 2D
and 3D grid circuit breaker networks. This model is employed to demonstrate
that substantial resistive switching can only be supported by the formation of
continuous current percolation channels, while multi-state capacity is ascribed
to the establishment and annihilation of multiple channels. | 1206.2746v1 |
2019-06-07 | Extended Nyquist formula for a resistance subject to a heat flow | The Nyquist formula quantifies the thermal noise driven fluctuations of
voltage across a resistance in equilibrium. We deal here with the case of a
resistance driven out of equilibrium by putting it in contact with two
thermostats at different temperatures. We reach a non-equilibrium steady state
where a heat flux is flowing through the resistance. Our measurements
demonstrate anyway that a simple extension of the Nyquist formula to the non
uniform temperature field describes with an excellent precision the thermal
noise. For a metallic ohmic material, the fluctuations are actually equivalent
to those of a resistance in equilibrium with a single thermostat at the mean
temperature between the hot and cold sources. | 1906.02974v2 |
2020-06-22 | Optimal design of a bilayer for the highest thermal resistance: A lesson learned from the shells of snails from hydrothermal extreme environment | Inspired by the unique design of the shells of snails inhabiting the deep-sea
hydrothermal environment, here we theoretically study the temperature response
of a bilayer to an external thermal impulse. A semi-analytical solution to the
temperature field in the bilayer is obtained, allowing us to assess the peak
temperature that occurs on the inner wall as a quantitative indicator of the
thermal resistance of the bilayer. The structural determining factors of the
thermal resistance of a bilayer are then investigated by examining the effects
of the stacking sequence and volume fractions of the constitutive layers on the
peak temperature on the inner wall. Our results indicate that the stacking
sequence of the two layers in a bilayer, as well as their volume fractions,
play important roles in determining the thermal resistance. For two layers with
given materials, there exists an optimal stacking sequence and thickness ratio
giving rise to the best thermal resistance. The results of our work not only
account for the unique laminated design of the snail shells from hydrothermal
environments but also provide practical guidelines for the design of multilayer
thermal barriers in engineering. | 2006.11987v1 |
2020-11-01 | Reduction of interfacial thermal resistance of overlapped graphene by bonding carbon chains | Exploring the mechanism of interfacial thermal transport and reducing the
interfacial thermal resistance is of great importance for thermal management
and modulation. Herein, the interfacial thermal resistance between overlapped
graphene nanoribbons is largely reduced by adding bonded carbon chains by
performing molecular dynamics simulations. And the analytical model
(cross-interface model, CIM) is utilized to analyze and explain the
two-dimensional thermal transport mechanism at cross-interface. An order of
magnitude reduction in interfacial thermal resistance is found as the graphene
nanoribbons are bonded by just one carbon chain. Interestingly, the decreasing
rate of interfacial thermal resistance slows down gradually with the increasing
of the number of carbon chains, which can be explained by the proposed
theoretical relationship based on CIM. Moreover, by the comparison of CIM and
traditional simplified model, the accuracy of CIM is verified and demonstrated
in overlapped graphene nanoribbons. This work provides a new way to improve the
interfacial thermal transport and reveal the essential mechanism for
low-dimensional materials applied in thermal management. | 2011.00494v1 |
2021-04-15 | Origins of anisotropic transport in electrically-switchable antiferromagnet $\mathrm{Fe_1/3NbS_2}$ | Recent experiments on the antiferromagnetic intercalated transition metal
dichalcogenide $\mathrm{Fe_{1/3}NbS_2}$ have demonstrated reversible
resistivity switching by application of orthogonal current pulses below its
magnetic ordering temperature, making $\mathrm{Fe_{1/3}NbS_2}$ promising for
spintronics applications. Here, we perform density functional theory
calculations with Hubbard U corrections of the magnetic order, electronic
structure, and transport properties of crystalline $\mathrm{Fe_{1/3}NbS_2}$,
clarifying the origin of the different resistance states. The two
experimentally proposed antiferromagnetic ground states, corresponding to
in-plane stripe and zigzag ordering, are computed to be nearly degenerate.
In-plane cross sections of the calculated Fermi surfaces are anisotropic for
both magnetic orderings, with the degree of anisotropy sensitive to the Hubbard
U value. The in-plane resistance, computed within the Kubo linear response
formalism using a constant relaxation time approximation, is also anisotropic,
supporting a hypothesis that the current-induced resistance changes are due to
a repopulating of AFM domains. Our calculations indicate that the transport
anisotropy of $\mathrm{Fe_{1/3}NbS_2}$ in the zigzag phase is reduced relative
to stripe, consistent with the relative magnitudes of resistivity changes in
experiment. Finally, our calculations reveal the likely directionality of the
current-domain response, specifically, which domains are energetically
stabilized for a given current direction. | 2104.07591v1 |
2021-08-01 | First-principles study on the electrical resistivity in zirconium dichalcogenides with multi-valley bands: mode-resolved analysis of electron-phonon scattering | Based on the first-principles calculations, we study the electron-phonon
scattering effect on the resistivity in the zirconium dichalcogenides,
$\text{Zr}_{}\text{S}_{2}$ and $\text{Zr}_{}\text{Se}_{2}$, whose electronic
band structures possess multiple valleys at conduction band minimum. The
computed resistivity exhibits non-linear temperature dependence, especially for
$\text{Zr}_{}\text{S}_{2}$, which is also experimentally observed on some TMDCs
such as $\text{Ti}_{}\text{S}_{2}$ and $\text{Zr}_{}\text{Se}_{2}$. By
performing the decomposition of the contributions of scattering processes, we
find that the intra-valley scattering by acoustic phonons mainly contributes to
the resistivity around 50 K. Moreover, the contribution of the intra-valley
scattering by optical phonons becomes dominant even above 80 K, which is a
sufficiently low temperature compared with their frequencies. By contrast, the
effect of the inter-valley scattering is found to be not significant. Our study
identifies the characteristic scattering channels in the resistivity of the
zirconium dichalcogenides, which provides critical knowledge to microscopically
understand electron transport in systems with multi-valley band structure. | 2108.00474v1 |
2024-02-15 | What can we learn from nonequilibrium response of a strange metal? | We critically address the recent experiment [Science 382, 907 (2023)] on
nonequilibrium transport and noise in a strange metal YbRh2Si2 patterned into
the nanowire shape. In the long device, resistivity, differential resistance
and current noise data seem to be consistent allowing us to extract
electron-phonon coupling and the temperature dependence of electron-phonon
scattering length. The obtained values can be reconciled with the experimental
data for the short device only assuming the significant contact resistance. We
discuss its possible origin as due to the current redistribution between
YbRh2Si2 and its gold covering, and reveal that this redistribution contact
resistance should be proportional to the YbRh2Si2 resistivity. We also discuss
some subtleties of the noise measurements. Overall, neglecting electron-phonon
energy relaxation even in the shortest devices is arguable so that the observed
shot noise suppression can hardly be attributed to the failure of quasiparticle
concept. | 2402.09946v1 |
2023-07-27 | Reduced stress propagation leads to increased mechanical failure resistance in auxetic materials | Materials with negative Poisson ratio have the counter-intuitive property of
expanding laterally when they are stretched longitudinally. They are
accordingly termed auxetic, from the Greek auxesis meaning to increase.
Experimental studies have demonstrated auxetic materials to have superior
material properties, compared with conventional ones. These include synclastic
curvature, increased acoustic absorption, increased resilience to material
fatigue, and increased resistance to mechanical failure. Until now, the latter
observations have remained poorly understood theoretically. With this
motivation, the contributions of this work are twofold. First, we elucidate
analytically the way in which stress propagates spatially across a material
following a localised plastic failure event, finding a significantly reduced
stress propagation in auxetic materials compared with conventional ones. In
this way, a plastic failure event occurring in one part of a material has a
reduced tendency to trigger knock-on plastic events in neighbouring regions.
Second, via the numerical simulation of a lattice elastoplastic model, we
demonstrate a key consequence of this reduced stress propagation to be an
increased resistance to mechanical failure. This is seen not only via an
increase in the externally measured yield strain, but also via a decreased
tendency for plastic damage to percolate internally across a sample in
catastrophic system-spanning clusters. | 2307.14914v2 |
2014-11-28 | Signature of high Tc around 25K in higher quality heavily boron-doped diamond | Diamond has outstanding physical properties: the hardest known material, a
wide band gap, the highest thermal conductivity, and a very high Debye
temperature. In 2004, Ekimov et al. discovered that heavily boron-doped
(B-doped) diamond becomes a superconductor around 4 K. Our group successfully
controlled the boron concentration and synthesized homoepitaxially grown
superconducting diamond films by a CVD method. By CVD method, we found that
superconductivity appears when the boron concentration (nB) exceeds a
metal-insulator transition concentration of 3.0x10^20 cm^-3 and its Tczero
increases up to 7.4 K with increasing nB. We additionally elucidated that the
holes formed at the valence band are responsible for the metallic states
leading to superconductivity. The calculations predicted that the hole doping
into the valence band induces strong attractive interaction and a rapid
increase in Tc with increasing boron concentration. According to the
calculations, if substitutional doped boron could be arranged periodically or
the degree of disorder is reduced, a Tc of approximately 100 K could be
achieved via minimal percent doping. In this work, we have successfully
observed zero resistivity above 10 K and an onset of resistivity reduction at
25.2 K in heavily B-doped diamond film. However, the effective carrier
concentration is similar to that of superconducting diamond with a lower Tc. We
found that the carrier has a longer mean free path and lifetime than previously
reported, indicating that this highest Tc diamond has better crystallinity
compared to that of other superconducting diamond films. In addition, the
susceptibility shows a small transition above 20 K in the high quality diamond,
suggesting a signature of superconductivity above 20 K. These results strongly
suggest that heavier carrier doped defect-free crystalline diamond could give
rise to high Tc diamond. | 1411.7752v1 |
2019-08-21 | Fatigue-resistant high-performance elastocaloric materials via additive manufacturing | Elastocaloric cooling, which exploits the latent heat released and absorbed
as stress-induced phase transformations are reversibly cycled in shape memory
alloys, has recently emerged as a frontrunner in non-vapor-compression cooling
technologies. The intrinsically high thermodynamic efficiency of elastocaloric
materials is limited only by work hysteresis. Here, we report on creating
high-performance low-hysteresis elastocaloric cooling materials via additive
manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established
knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are
found to be beneficial to elastocaloric performances when they are combined
with the binary Ti-Ni compound in nanocomposite configurations. The resulting
microstructure gives rise to quasi-linear stress-strain behaviors with
extremely small hysteresis, leading to enhancement in the materials efficiency
by a factor of five. Furthermore, despite being composed of more than 50%
intermetallic phases, the reversible, repeatable elastocaloric performance of
this material is shown to be stable over one million cycles. This result opens
the door for direct implementation of additive manufacturing to elastocaloric
cooling systems where versatile design strategy enables both topology
optimization of heat exchangers as well as unique microstructural control of
metallic refrigerants. | 1908.07900v1 |
2019-07-31 | Quantum oscillations in diamond field effect transistors with a h-BN gate dielectric | Diamond has attracted attention as a next-generation semiconductor because of
its various exceptional properties such as a wide bandgap and high breakdown
electric field. Diamond field effect transistors, for example, have been
extensively investigated for high-power and high-frequency electronic
applications. The quality of their charge transport (i.e., mobility), however,
has been limited due to charged impurities near the diamond surface. Here, we
fabricate diamond field effect transistors by using a monocrystalline hexagonal
boron nitride as a gate dielectric. The resulting high mobility of charge
carriers allows us to observe quantum oscillations in both the longitudinal and
Hall resistivities. The oscillations provide important information on the
fundamental properties of the charge carriers, such as effective mass,
lifetime, and dimensionality. Our results indicate the presence of a
high-quality two-dimensional hole gas at the diamond surface and thus pave the
way for studies of quantum transport in diamond and the development of low-loss
and high-speed devices. | 1907.13500v2 |
2021-12-08 | High-Mg Calcite Nanoparticles Within a Low-Mg Calcite Matrix via Spinodal Decomposition: A Widespread Phenomenon in Biomineralization | During the process of biomineralization, organisms utilize various
biostrategies to enhance the mechanical durability of their skeletons. In this
work, we establish that the presence of high-Mg nanoparticles embedded within
lower Mg calcite matrices is a widespread strategy utilized by various
organisms from different kingdoms and phyla to improve the mechanical
properties of their high Mg calcite skeletons. We show that such phase
separation and the formation of high-Mg nanoparticles are achieved through
spinodal decomposition of an amorphous Mg calcite precursor. Such decomposition
is independent of the biological characteristics of the studied organisms
belonging to different phyla and even kingdoms, but rather originates from
their similar chemical composition and a specific Mg content within their
skeletons, which generally ranges from 14 to 48 mol percent of Mg. We show
evidence of high Mg calcite nanoparticles in the cases of 6 biologically
different organisms all demonstrating more than 14 mol percent Mg calcite, and
consider it likely that this phenomenon is immeasurably more prevalent in
nature. We also establish the absence of these high Mg nanoparticles in
organisms whose Mg content is lower than 14 mol percent, providing further
evidence that whether or not spinodal decomposition of an amorphous Mg calcite
precursor takes place is determined by the amount of Mg it contains. The
valuable knowledge gained from this biostrategy significantly impacts the
understanding of how biominerals, though comprised of intrinsically brittle
materials, can effectively resist fracture. | 2112.04141v1 |
2022-08-11 | Superconductivity above 80 K in polyhydrides of hafnium | Studies on polyhydrides are attracting growing attentions recently due to
their potential high temperature superconductivity (SC). We here report the
discovery of SC in hafnium polyhydrides at high pressures. The hafnium
superhydrides are synthesized at high pressure and high temperature conditions
using diamond anvil cell in combination with in-situ high pressure laser
heating technique. The SC was investigated by in-situ high pressure resistance
measurements in applied magnetic fields. A superconducting transition with
onset Tc ~83 K was observed at 243 GPa. The upper critical field Hc2(0) was
estimated to be 24 Tesla by GL theory and the consequent superconducting
coherent length to be ~37 angstrom. Our results suggest that the
superconducting phase is from C2/m-HfH14. This is the first 5d transition metal
polyhydride superconductor with Tc above the liquid nitrogen temperature. | 2208.05816v2 |
2001-05-16 | Superconducting properties of well-shaped MgB2 single crystal | We report measurements of the transport and the magnetic properties of
high-quality, sub-millimeter-sized MgB2 single crystals with clear
hexagonal-plate shapes. The low-field magnetization and the magnetic hysteresis
curves show the vortex pinning of these crystals to be very weak. The Debye
temperature of $\Theta_{D}\sim 1100$ K, obtained from the zero-field resistance
curve, suggests that the normal-state transport properties are dominated by
electron-phonon interactions. The resistivity ratio between 40 K and 300 K was
about 5, and the upper critical field anisotropy ratio was 3 $\pm$ 0.2 at
temperatures around 32 K. | 0105330v7 |
2003-09-24 | Quantum Effects in Thermal Conductivity of Solid Krypton - Methane Solutions | The dynamic interaction of a quantum rotor with its crystalline environment
has been studied by measurement of the thermal conductivity of solid
Kr1_c(CH4)_c solutions at c = 0.05-0.75 in the temperature region from 2 up to
40K. The thermal resistance of the solutions was mainly determined by the
resonance scattering of phonons by CH4 molecules with the nuclear spin I=1 (the
nuclear spin of T-species). The influence of the nuclear spin conversion on the
temperature dependence of the thermal conductivity k(T) was found: a clearly
defined minimum on k(T), its temperature position depending on the CH4
concentration. It was shown that the anisotropy molecular field not increase
monotonously with the CH4 concentration. A compensation effect in the mutual
orientation arrangement of the neighboring rotors is observed at c > 0.5. The
temperature dependence of Kr1_c(CH4)_c is described within the Debye model of
thermal conductivity taking into account the lower limit of the phonon mean
free path. The anomalous temperature dependence of the thermal resistance shows
the evolution of the phonon-rotation coupling at varying temperature. It
increases strongly when the character of CH4 rotation changes from the quantum
at low temperatures to classical at high temperatures. Also, a jump of thermal
conductivity (a sharp increase in k(T) within a narrow temperature range) was
observed, whose position varies from 9.7 K to 8.4 K when the CH4 concentration
changes from 0.25 to 0.45. | 0309542v1 |
2005-05-19 | Strongly correlated properties of the thermoelectric cobalt oxide Ca3Co4O9 | We have performed both in-plane resistivity, Hall effect and specific heat
measurements on the thermoelectric cobalt oxide Ca$_{3}$Co$_{4}$O$_{9}$. Four
distinct transport regimes are found as a function of temperature,
corresponding to a low temperature insulating one up to $T_{min}\approx $63 K,
a strongly correlated Fermi liquid up to $T^*\approx $140 K, with
$\rho=\rho_0+AT^2$ and $A\approx 3.63$ $10^{-2} \mu \Omega cm/K^{2}$, followed
by an incoherent metal with $k_Fl\leq 1$ and a high temperature insulator above
T$^{**}\approx $510 K . Specific heat Sommerfeld coefficient $\gamma = 93$
mJ/(mol.K$^{2}$) confirms a rather large value of the electronic effective mass
and fulfils the Kadowaki-Woods ratio $A/\gamma^2 \approx 0.45$ 10$^{-5}$ $\mu
\Omega cm.K^2/(mJ^2mol^{-2})$. Resistivity measurements under pressure reveal a
decrease of the Fermi liquid transport coefficient A with an increase of $T^*$
as a function of pressure while the product $A(T^*)^2/a$ remains constant and
of order $h/e^2$. Both thermodynamic and transport properties suggest a strong
renormalization of the quasiparticles coherence scale of order $T^*$ that seems
to govern also thermopower. | 0505464v1 |
2005-10-03 | New Misfit-Layered Cobalt Oxide (CaOH)1.14CoO2 | We found a new cobalt oxide (CaOH)1.14CoO2 by utilizing the high-pressure
technique. X-ray and electron diffraction studies revealed that the compound
has layer structure which consists of CdI2-type CoO2 layers and rock-salt-type
double CaOH atomic layers. The two subcells have incommensurate periodicity
along the a-axis, resulting in modulated crystal structure due to the
inter-subcell interaction. The structural modulation affects carrier conduction
through the potential randomness. We found that the two-dimensional (2-D)
variable-range hopping (VRH) regime with hole conduction is dominant at low
temperature for this compound, and that the conduction mechanism undergoes
crossover from the 2-D VRH regime to thermal activation-energy type one with
increasing temperature. Based on the experimental results of resistivity,
thermoelectric power, magnetic susceptibility and specific heat measurements,
we suggested a possible electronic-band structure model to explain these
results. The cobalt t2g-derivative band crosses Fermi energy level near the
band edge, yielding small finite density of localized states at the Fermi level
in the band. The observed resistivity, Seebeck coefficient, large Pauli
paramagnetic component in the magnetic susceptibility and comparatively small
Sommerfeld constant in the specific heat are principally attributed to the
holes in the t2g-derivative band. We estimated the Wilson ratio to be about
2.8, suggesting the strong electron correlation realized in this compound. | 0510031v1 |
2007-09-12 | The Hot-Spot Phenomenon and its Countermeasures in Bipolar Power Transistors by Analytical Electro-Thermal Simulation | This communication deals with a theoretical study of the hot spot onset (HSO)
in cellular bipolar power transistors. This well-known phenomenon consists of a
current crowding within few cells occurring for high power conditions, which
significantly decreases the forward safe operating area (FSOA) of the device.
The study was performed on a virtual sample by means of a fast, fully
analytical electro-thermal simulator operating in the steady state regime and
under the condition of imposed input base current. The purpose was to study the
dependence of the phenomenon on several thermal and geometrical factors and to
test suitable countermeasures able to impinge this phenomenon at higher biases
or to completely eliminate it. The power threshold of HSO and its localization
within the silicon die were observed as a function of the electrical bias
conditions as for instance the collector voltage, the equivalent thermal
resistance of the assembling structure underlying the silicon die, the value of
the ballasting resistances purposely added in the emitter metal
interconnections and the thickness of the copper heat spreader placed on the
die top just to the aim of making more uniform the temperature of the silicon
surface. | 0709.1831v1 |
2007-09-14 | An inhomogeneous Josephson phase in thin-film and High-Tc superconductors | In many cases inhomogeneities are known to exist near the metal (or
superconductor)-insulator transition, as follows from well-known domain-wall
arguments. If the conducting regions are large enough (i.e. when the T=0
superconducting gap is much larger than the single-electron level spacing), and
if they have superconducting correlations, it becomes energetically favorable
for the system to go into a Josephson-coupled zero-resistance state before
(i.e. at higher resistance than) becoming a "real" metal. We show that this is
plausible by a simple comparison of the relevant coupling constants. For small
grains in the above sense, the electronic grain structure is washed out by
delocalization and thus becomes irrelevant. When the proposed "Josephson state"
is quenched by a magnetic field, an insulating, rather then a metallic, state
should appear. This has been shown to be consistent with the existing data on
oxide materials as well as ultra-thin films. We discuss the Uemura correlations
versus the Homes law, and derive the former for the large-grain Josephson array
(inhomogenous superconductor) model. The small-grain case behaves like a dirty
homogenous metal. It should obey the Homes law provided that the system is in
the dirty supeconductivity limit. A speculation why that is typically the case
for d-wave superconductors is presented. | 0709.2321v1 |
2009-03-18 | Two-dimensional electrochemical model for mixed conductors: a study of ceria | A two-dimensional small bias model has been developed for a patterned metal
current collector $|$ mixed oxygen ion and electronic conductor (MIEC) $|$
patterned metal current collector electrochemical cell in a symmetric gas
environment. Specifically, we compute the electrochemical potential
distributions of oxygen vacancies and electrons in the bulk and near the
surface for $\text{Pt} | \text{Sm}_{0.15}\text{Ce}_{0.85}\text{O}_{1.925} |
\text{Pt}$ symmetric cell in a $\text{H}_2-\text{H}_2\text{O}-\text{Ar}$
(reducing) atmosphere from 500 to $650^o C$. Using a two-dimensional
finite-element model, we show that two types of electronic current exist within
the cell: an in-plane drift-diffusion current that flows between the gas $|$
ceria chemical reaction site and the metal current collector, and a cross-plane
current that flows between the two metal electrodes on the opposite side of the
cell. By fitting the surface reaction constant $\tilde k_f^0$ to experimental
electrode resistance values while fixing material properties such as bulk ionic
and electronic equilibrium defect concentrations and mobilities, we are able to
separate the electrode polarization into the surface reaction component and the
in-plane electron drift-diffusion component. We show that for mixed conductors
with a low electronic conductivity (a function of oxygen partial pressure) or a
high surface reaction rate constant, the in-plane electron drift-diffusion
resistance can become rate-limiting in the electrode reaction. | 0903.3250v1 |
2009-11-11 | The pseudogap behavior in the stoichiometric FeSe superconductor (Tc~9.4 K) | This paper reports the synthesis and superconducting behaviors of the
tetragonal iron-chalcogenide superconductor FeSe. The electrical resistivity
and magnetic moment measurements confirmed its superconductivity with a
$T_c^{zero}$ and $T_c^{mag}$ at 9.4 K under ambient pressure. EPMA indicated
the sample to have a stoichiometric Fe:Se ratio of 1:1 ($\pm$0.02). The Seebeck
coefficient which was 12.3 $\mu$V/K at room temperature, changed to a negative
value near 200 K, indicating it to be a two carriers material. Above $T_c$, the
$\rho(T)$ curve revealed an 'S' shape. Hence $d\rho(T)/dT$, and
$d^2\rho(T)/dT^2$ showed pseudogap-like behavior at $T^*$=110 K according to
the resistivity curvature mapping (RCM) method for high $T_c$ cuprates.
Moreover, the magnetoresistance $\rho_H(T)/\rho_{H=0}$ under a magnetic field
and the Seebeck coefficient $S(T)$ revealed revealed pseudogap-like behavior
near $T^*$. Interestingly, at the same temperature, 30 K, the sign of $S(T)$
and all signs of $d^2\rho(T)/dT^2$ changed from negative to positive above
$T_c$. | 0911.2045v2 |
2010-07-22 | Anisotropic fluctuations and quasiparticle excitations in FeSe_0.5Te_0.5 | We present data for the temperature dependence of the magnetic penetration
depth lambda(T), heat capacity C(T), resistivity R(T) and magnetic torque ?tau
for highly homogeneous single crystal samples of Fe1:0Se0:44(4)Te0:56(4).
lambda(T) was measured down to 200mK in zero field. We find lambda(T) follows a
power law lambda~T^n with n = 2.2 +/- 0.1. This is similar to some 122
iron-arsenides and likely results from a sign-changing pairing state combined
with strong scattering. Magnetic fields of up to B =55T or 14T were used for
the ? tau(B) and C(T)/R(T) measurements respectively. The specific heat,
resistivity and torque measurements were used to map out the (H,T) phase
diagram in this material. All three measurements were conducted on exactly the
same single crystal sample so that the different information revealed by these
probes is clearly distinguished. Heat capacity data strongly resemble those
found for the high Tc cuprates, where strong fluctuation effects wipe-out the
phase transition at Hc2. Unusually, here we find the fluctuation effects appear
to be strongly anisotropic. | 1007.3914v2 |
2010-11-09 | Frustrated Metastable Behavior of Magnetic and Transport Properties in Charge Ordered La1-xCaxMnO3+d Manganites | We have studied the effect of metastable, irreversibility induced by repeated
thermal cycles on the electric transport and magnetization of polycrystalline
samples of La1-xCaxMnO3 (0.48\leq x \leq 0.55) close to charge ordering. With
time and thermal cycling (T<300 K) there is an irreversible transformation of
the low-temperature phase from a partially ferromagnetic and metallic to one
that is less ferromagnetic and highly resistive for the composition close to
charge ordering (x=050 and 0.52). Irrespective of the actual ground state of
the compound, the effect of thermal cycling is towards an increase of the
amount of the insulating phase. We have observed the magnetic relaxation in the
metastable state and also the revival of the metastable state (in a relaxed
sample) due to high temperature thermal treatment. We observed changes in the
resistivity and magnetization as the revived metastable state is cycled. The
time changes in the magnetization are logarithmic in general and activation
energies are consistent with those expected for electron transfer between Mn
ions. Changes induced by thermal cycling can be inhibited by applying magnetic
field. These results suggest that oxygen non-stoichiometry results in
mechanical strains in this two-phase system, leading to the development of
frustrated metastable states which relax towards the more stable charge-ordered
and antiferromagnetic microdomains. Our results also suggest that the growth
and coexistence of phases gives rise to microstructural tracks and strain
accommodation, producing the observed irreversibility. | 1011.2179v1 |
2011-05-17 | The metallic transport of (TMTSF)_2X organic conductors close to the superconducting phase | Comparing resistivity data of quasi-one dimensional superconductors
(TMTSF)_2PF_6 and (TMTSF)_2ClO_4 along the least conducting c*-axis and along
the high conductivity a -axis as a function of temperature and pressure, a low
temperature regime is observed in which a unique scattering time governs
transport along both directions of these anisotropic conductors. However, the
pressure dependence of the anisotropy implies a large pressure dependence of
the interlayer coupling. This is in agreement with the results of
first-principles DFT calculations implying methyl group hyperconjugation in the
TMTSF molecule. In this low temperature regime, both materials exhibit for rc a
temperature dependence aT + bT^2. Taking into account the strong pressure
dependence of the anisotropy, the T-linear rc is found to correlate with the
suppression of the superconducting Tc, in close analogy with ra data. This work
is revealing the domain of existence of the 3D coherent regime in the generic
(TMTSF)_2X phase diagram and provides further support for the correlation
between T-linear resistivity and superconductivity in non-conventional
superconductors. | 1105.3323v2 |
2011-11-29 | Towards the Realization of Higher Connectivity in MgB2 Conductors: In-situ or Sintered Ex-situ? | The two most common types of MgB2 conductor fabrication technique - in-situ
and ex-situ - show increasing conflicts concerning the connectivity, an
effective current-carrying cross-sectional area. An in-situ reaction yields a
strong intergrain coupling with a low packing factor, while an ex-situ process
using pre-reacted MgB2 yields tightly packed grains, however, their coupling is
much weaker. We studied the normal-state resistivity and microstructure of
ex-situ MgB2 bulks synthesized with varied heating conditions under ambient
pressure. The samples heated at moderately high temperatures of ~900{\deg}C for
a long period showed an increased packing factor, a larger intergrain contact
area and a significantly decreased resistivity, all of which indicate the
solid-state self-sintering of MgB2. Consequently the connectivity of the
sintered ex-situ samples exceeded the typical connectivity range 5-15% of the
in-situ samples. Our results show self-sintering develops the superior
connectivity potential of ex-situ MgB2, though its intergrain coupling is not
yet fulfilled, to provide a strong possibility of twice or even much higher
connectivity in optimally sintered ex-situ MgB2 than in in-situ MgB2. | 1111.6767v2 |
2012-07-25 | Metallic state in La-doped YBa$_2$Cu$_3$O$_y$ thin films with $n$-type charge carriers | We report hole and electron doping in La-doped YBa$_2$Cu$_3$O$_y$(YBCO) thin
films synthesized by pulsed laser deposition technique and subsequent
\emph{in-situ} postannealing in oxygen ambient and vaccum. The $n$-type samples
show a metallic behavior below the Mott limit and a high carrier density of
$\sim2.8$ $\times$ 10$^{21}$ cm$^{-3}$ at room temperature (\emph{T}) at the
optimally reduced condition. The in-plane resistivity ($\rho$$_{ab}$) of the
$n$-type samples exhibits a quadratic \emph{T} dependence in the
moderate-\emph{T} range and shows an anomaly at a relatively higher \emph{T}
probably related to pseudogap formation analogous to underdoped
Nd$_{2-x}$Ce$_x$CuO$_4$ (NCCO). Furthermore, $\rho$$_{ab}$(T), \emph{T}$_c$ and
\emph{T} with minimum resistivity (\emph{T}$_{min}$) were investigated in both
$p$- and $n$-side. The present results reveal the $n$-$p$ asymmetry (symmetry)
within the metallic-state region in an underdoped cuprate and suggest the
potential toward ambipolar superconductivity in a single YBCO system. | 1207.5914v1 |
2012-11-28 | Photoconductivity effects in mixed-phase BSCCO whiskers | We report on combined photoconductivity and annealing experiments in
whisker-like crystals of the Bi-Sr-Ca-Cu-O (BSCCO) high-Tc superconductor. Both
single-phase Bi2Sr2CaCu2O8+\delta (Bi-2212) samples and crystals of the mixed
phases Bi2Sr2Ca2Cu3O10+x (Bi-2223)/Bi-2212 have been subjected to annealing
treatments at 90{\deg}C in air in a few hours steps, up to a maximum total
annealing time of 47 h. At every step, samples have been characterized by means
of electrical resistance vs temperature (R vs T) and resistance vs time at
fixed temperature (R vs t) measurements, both in the dark and under
illumination with a UV-VIS halogen arc lamp. A careful comparison of the
results from the two techniques has shown that, while for single-phase samples
no effect is recorded, for mixed-phase samples an enhancement in the
conductivity that increases with increasing the annealing time is induced by
the light at the nominal temperature T = 100 K, i.e. at an intermediate
temperature between the critical temperatures of the two phases. A simple
pseudo-1D model based on the Kudinov's scheme [Kudinov et al., Phys. Rev. B 47,
9017-28, (1993)] has been developed to account for the observed effects, which
is based on the existence of Bi-2223 filaments embedded in the Bi-2212 matrix
and on the presence of electronically active defects at their interfaces. This
model reproduces fairly well the photoconductive experimental results and shows
that the length of the Bi-2223 filaments decreases and the number of defects
increases with increasing the annealing time. | 1211.6594v1 |
2013-01-03 | Studies of YBa2Cu3O6+x degradation and surface conductivity properties by Scanning Spreading Resistance Microscopy | Local surface conductivity properties and surface degradation of c-axis
oriented YBa2Cu3O6+x (YBCO) thin films were studied by Scanning Spreading
Resistance Microscopy (SSRM). For the surface degradation studies, the YBCO
surface was cleaned by ion beam etching and the SSRM surface conductivity map
has been subsequently repeatedly measured over several hours in air and pure
nitrogen. Average surface conductivity of the scanned area was gradually
decreasing over time in both cases, faster in air. This was explained by oxygen
out-diffusion in both cases and chemical reactions with water vapor in air. The
obtained surface conductivity images also revealed its high inhomogenity on
micrometer and nanometer scale with numerous regions of highly enhanced
conductivity compared to the surroundings. Furthermore, it has been shown that
the size of these conductive regions considerably depends on the applied
voltage. We propose that such inhomogeneous surface conductivity is most likely
caused by varying thickness of degraded YBCO surface layer as well as varying
oxygen concentration (x parameter) within this layer, what was confirmed by
scanning Auger electron microscopy (SAM). In our opinion the presented findings
might be important for analysis of current-voltage and differential
characteristics measured on classical planar junctions on YBCO as well as other
perovskites. | 1301.0397v1 |
2013-02-21 | Electronic transport on carbon nanotube networks: a multiscale computational approach | Carbon nanotube networks are one of the candidate materials to function as
malleable, transparent, conducting films, with the technologically promising
application of being used as flexible electronic displays. Nanotubes disorderly
distributed in a film offers many possible paths for charge carriers to travel
across the entire system, but the theoretical description of how this charge
transport occurs is rather challenging for involving a combination of intrinsic
nanotube properties with network morphology aspects. Here we attempt to
describe the transport properties of such films in two different length scales.
Firstly, from a purely macroscopic point of view we carry out a geometrical
analysis that shows how the network connectivity depends on the nanotube
concentration and on their respective aspect ratio. Once this is done, we are
able to calculate the resistivity of a heavily disordered networked film.
Comparison with experiment offers us a way to infer about the junction
resistance between neighbouring nanotubes. Furthermore, in order to guide the
frantic search for high-conductivity films of nanotube networks, we turn to the
microscopic scale where we have developed a computationally efficient way for
calculating the ballistic transport across these networks. While the ballistic
transport is probably not capable of describing the observed transport
properties of these films, it is undoubtedly useful in establishing an upper
value for their conductivity. This can serve as a guideline in how much room
there is for improving the conductivity of such networks. | 1302.5379v1 |
2013-12-05 | Giant topological Hall effect in strained Fe$_{0.7}$Co$_{0.3}$Si epilayers | The coupling of electron spin to real-space magnetic textures leads to a
variety of interesting magnetotransport effects. The skyrmionic spin textures
often found in chiral B20-lattice magnets give rise, via real-space Berry
phases, to the topological Hall effect, but it is typically rather small. Here,
B20-ordered Fe$_{0.7}$Co$_{0.3}$Si epilayers display a giant topological Hall
effect due to the combination of three favourable properties: they have a high
spin-polarisation, a large ordinary Hall coefficient, and dense chiral spin
textures. The topological Hall resistivity is as large as 820 n$\Omega$cm at
helium temperatures. Moreover, we observed a drop in the longitudinal
resistivity of 100 n$\Omega$cm at low temperatures in the same field range,
suggesting that it is also of topological origin. That such strong effects can
be found in material grown in thin film form on commercial silicon wafer bodes
well for skyrmion-based spintronics. | 1312.1722v1 |
2013-12-23 | Signatures of electronic phase separation in the Hall effect of anisotropically strained La0.67Ca0.33MnO3 films | Systematic transport measurements have been performed on a series of
La0.67Ca0.33MnO3 (LCMO) thin films with varying degrees of anisotropic strain.
The strain is induced via epitaxial growth on NdGaO3(001) substrates and varied
by controlling the thermal annealing time. An antiferromagnetic insulating
(AFI) state, possibly associated with charge ordering, emerges upon thermal
annealing. The Hall effect in these materials exhibits features that are
indicative of a percolative phase transition and correlate closely with the
emergence of the AFI state. In the paramagnetic phase, the Hall resistivity
takes on two slopes in all samples: a decreasing negative slope with increasing
temperature at low fields, which is attributed to the carrier hopping motion,
and an almost temperature independent positive slope at high fields due to
diffusive transport of holes. Significantly, the crossover fields of the Hall
resistivity slope at different temperatures correspond to the same
magnetization, which is interpreted as the critical point of a magnetic
field-driven percolative phase transition. At lower temperatures near the
zero-field metal-insulator transition, pronounced enhancement of the Hall
coefficient with the development of the AFI state is observed. The enhancement
peaks near the magnetic field-driven percolation; its magnitude correlates with
the strength of the AFI state and is suppressed with the melting of the AFI
state by an in-plane magnetic field. The observations resemble many features of
the enhancement of the Hall coefficient in granular metal films near the
composition-driven percolation. | 1312.6670v1 |
2014-04-16 | Origin of High Temperature Oxidation Resistance of Ti-Al-Ta-N Coatings | Alloying Ti-Al-N coatings with Ta has proven to enhance their hardness,
thermal stability, and oxidation resistance. However, especially for
arc-evaporated Ti-Al-Ta-N coatings only limited information on the detailed
influence of the elements on various properties is available. Therefore, we
have developed arc-evaporated Ti1-x-yAlxTayN coatings with various Al (x = 0.50
- 0.65) and Ta (y = 0.00 - 0.15) contents. While the thermal stability of our
coatings during annealing in inert He atmosphere increases with increasing Ta
content, best results are obtained for specific Ta-Al ratios during oxidation.
Single phase cubic Ti0.32Al0.60Ta0.08N yields a mass-gain of only ~5 % after 5
h at 950 {\deg}C in synthetic air, whereas Ti0.35Al0.65N is completely oxidized
after 15 min. This is in part based on the suppressed anatase and direct rutile
TiO2 formation at a defined Ta-Al content. Consequently, the anatase-to-rutile
transformation, generally observed for Ti1-xAlxN, is absent. This reduces the
generation of pores and cracks within the oxide scale and especially at the
nitride-oxide interface, leading to the formation of a protective rutile and
corundum based oxide scale. This is also reflected in the pronounced decrease
in activation energy for the protective scale formation from 232 kJ/mol for
Ti0.35Al0.65N down to 14.5 kJ/mol for Ti0.32Al0.60Ta0.08N. Based on our results
we can conclude that especially phase transformations within the oxide scale
need to be suppressed, as the connected volume changes lead to the formation of
cracks and pores. | 1404.4345v1 |
2014-12-02 | Effect of phase separation induced supercooling on magnetotransport properties of epitaxial La5/8-yPryCa3/8MnO3 (y~0.4) thin film | Thin films of La5/8-yPryCa3/8MnO3 (y~0.4) have been grown on single crystal
SrTiO3 (001) by RF sputtering. The structural and surface characterizations
confirm the epitaxial nature of these film. However, the difference between the
rocking curve of the (002) and (110) peaks and the presence of pits/holes in
the step-terrace type surface morphology suggests high density of defect in
these films. Pronounced hysteresis between the field cool cooled (FCC) and
field cooled warming (FCW) magnetization measurements suggest towards the
non-ergodic magnetic state. The origin of this nonergodicity could be traced to
the magnetic liquid like state arising from the delicacy of the coexisting
magnetic phases, viz., ferromagnetic and antiferromagnetic-charge ordered
(FM/AFM-CO). The large difference between the insulator metal transitions
during cooling and warming cycles (TIMC~64 K and TIMW~123 K) could be regarded
as a manifestation of the nonergodicity leading to supercooling of the magnetic
liquid while cooling. The nonergodicity and supercooling are weakened by the
AFM-FM phase transition induced by an external magnetic field. TIM and small
polaron activation energy corresponding the magnetic liquid state (cooling
cycle) vary nonlinearly with the applied magnetic field but become linear in
the crystalline solid state (warming cycle). The analysis of the low
temperature resistivity data shows that electron-phonon interaction is
drastically reduced by the applied magnetic field. The resistivity minimum in
the lower temperature region of the self-field warming curve has been explained
in terms of the Kondo like scattering in the magnetically inhomogeneous regime. | 1412.0862v1 |
2016-11-09 | Unusual non saturating Giant Magneto-resistance in single crystalline Bi2Te3 topological insulator | We report synthesis, structural details and electrical transport properties
of topological insulator Bi2Te3. The single crystalline specimens of Bi2Te3 are
obtained from high temperature (950C) melt and slow cooling (2C/hour). The
resultant crystals were shiny, one piece (few cm) and of bright silver color.
The Bi2Te3 crystal is found to be perfect with clear [00l] alignment. The
powder XRD pattern being carried out on crushed crystals showed that Bi2Te3
crystallized in R3m symmetry with a = b = 4.3866(2) A, c = 30.4978(13) A and
Gamma = 120degree. The Bi position is refined to (0, 0, 0.4038 (9)) at Wyckoff
position 6c and of Te are (0, 0, 0) at Wyckoff position 3a and at (0, 0,
0.2039(8)) at 6c. Ambient pressure and low temperature (down to 2K) electrical
transport measurements revealed metallic behavior. Magneto transport
measurements under magnetic field showed huge non saturating magneto resistance
(MR) reaching up to 250% at 2.5K and under 50KOe field. Summarily, the short
communication clearly demonstrates that Bi2Te3 topological insulator exhibit
non-saturating large positive MR at low temperature of say below 10K. The non
saturating MR is seen right up to room temperature albeit with much decreased
magnitude. Worth mentioning is the fact that these crystals are bulk in nature
and hence the anomalous MR is clearly an intrinsic property and not due to the
size effect as reported for nano-wires or thin films of the same. | 1611.02859v2 |
2016-11-28 | Grand Design Spiral Arms in A Young Forming Circumstellar Disk | We study formation and long-term evolution of a circumstellar disk in a
collapsing molecular cloud core using a resistive magnetohydrodynamic
simulation. While the formed circumstellar disk is initially small, it grows as
accretion continues and its radius becomes as large as 200 AUs toward the end
of the Class-I phase. A pair of grand-design spiral arms form due to
gravitational instability in the disk, and they transfer angular momentum in
the highly resistive disk. Although the spiral arms disappear in a few
rotations as expected in a classical theory, new spiral arms form recurrently
as the disk soon becomes unstable again by gas accretion. Such recurrent spiral
arms persist throughout the Class-0 and I phase. We then perform synthetic
observations and compare our model with a recent high-resolution observation of
a young stellar object Elias 2-27, whose circumstellar disk has grand design
spiral arms. We find good agreement between our theoretical model and the
observation. Our model suggests that the grand design spiral arms around Elias
2-27 are consistent with material arms formed by gravitational instability. If
such spiral arms commonly exist in young circumstellar disks, it implies that
young circumstellar disks are considerably massive and gravitational
instability is the key process of angular momentum transport. | 1611.09361v2 |
2017-09-27 | Pressure induced spin crossover in disordered α-LiFeO2 | Structural, magnetic and electrical-transport properties of {\alpha}-LiFeO2,
crystallizing in the rock salt structure with random distribution of Li and Fe
ions, have been studied by synchrotron X-ray diffraction, 57Fe M\"ossbauer
spectroscopy and electrical resistance measurements at pressures up to 100 GPa
using diamond anvil cells. It was found that the crystal structure is stable at
least to 82 GPa, though a significant change in compressibility has been
observed above 50 GPa. The changes in the structural properties are found to be
on a par with a sluggish Fe3+ high- to low-spin (HS-LS) transition (S=5/2 to
S=1/2) starting at 50 GPa and not completed even at ~100 GPa. The HS-LS
transition is accompanied by an appreciable resistance decrease remaining a
semiconductor up to 115 GPa and is not expected to be metallic even at about
200 GPa. The observed feature of the pressure-induced HS-LS transition is not
an ordinary behavior of ferric oxides at high pressures. The effect of Fe3+
nearest and next nearest neighbors on the features of the spin crossover is
discussed. | 1709.09680v1 |
2018-03-24 | Ion implantation in nanodiamonds: size effect and energy dependence | Nanoparticles are ubiquitous in nature and are increasingly important for
technology. They are subject to bombardment by ionizing radiation in a diverse
range of environments. In particular, nanodiamonds represent a variety of
nanoparticles of significant fundamental and applied interest. Here we present
a combined experimental and computational study of the behaviour of
nanodiamonds under irradiation by xenon ions. Unexpectedly, we observed a
pronounced size effect on the radiation resistance of the nanodiamonds:
particles larger than 8 nm behave similarly to macroscopic diamond (i.e.
characterized by high radiation resistance) whereas smaller particles can be
completely destroyed by a single impact from an ion in a defined energy range.
This latter observation is explained by extreme heating of the nanodiamonds by
the penetrating ion. The obtained results are not limited to nanodiamonds,
making them of interest for several fields, putting constraints on processes
for the controlled modification of nanodiamonds, on the survival of dust in
astrophysical environments, and on the behaviour of actinides released from
nuclear waste into the environment. | 1803.09081v1 |
2020-09-14 | Memristive control of mutual SHNO synchronization for neuromorphic computing | Synchronization of large spin Hall nano-oscillators (SHNO) arrays is an
appealing approach toward ultra-fast non-conventional computing based on
nanoscale coupled oscillator networks. However, for large arrays, interfacing
to the network, tuning its individual oscillators, their coupling, and
providing built-in memory units for training purposes, remain substantial
challenges. Here, we address all these challenges using memristive gating of
W/CoFeB/MgO/AlOx based SHNOs. In its high resistance state (HRS), the memristor
modulates the perpendicular magnetic anisotropy (PMA) at the CoFeB/MgO
interface purely by the applied electric field. In its low resistance state
(LRS), and depending on the voltage polarity, the memristor adds/subtracts
current to/from the SHNO drive. The operation in both the HRS and LRS affects
the SHNO auto-oscillation mode and frequency, which can be tuned up to 28
MHz/V. This tuning allows us to reversibly turn on/off mutual synchronization
in chains of four SHNOs. We also demonstrate two individually controlled
memristors to tailor both the coupling strength and the frequency of the
synchronized state. Memristor gating is therefore an efficient approach to
input, tune, and store the state of the SHNO array for any non-conventional
computing paradigm, all in one platform. | 2009.06594v1 |
2022-02-09 | Electron-Electron Interaction and Weak Antilocalization Effect in a Transition Metal Dichalcogenide Superconductor | In disordered transition-metal dichalcogenide (TMD) superconductor, both the
strong spin-orbit coupling (SOC) and disorder show remarkable effects on
superconductivity. However, the features of SOC and disorder were rarely
detected directly. Here we report the quantum transport behaviors arising from
the interplay of SOC and disorder in the TMD superconductor 1T-NbSeTe. Before
entering the superconducting state, the single crystal at low temperature shows
a resistivity upturn, which is T1/2 dependent and insensitive to the applied
magnetic fields. The magnetoresistance (MR) at low temperatures shows a H1/2
dependence at high magnetic fields. The characteristics are in good agreement
with the electron-electron interaction (EEI) in a disordered conductor. In
addition, the upturn changes and MR at low magnetic fields suggest the
contribution of weak antilocalization (WAL) effect arising from the strong SOC
in the material. Moreover, the quantitative analyses of the transport features
in different samples imply anomalous disorder-enhanced superconductivity that
needs to be further understood. The results reveal the disorder enhanced EEI
and the strong SOC induced WAL effect in 1T-NbSeTe, which illustrate the
resistivity minimum in the widely studied doped superconductors. The work also
provides insights into the disorder effect on the superconductivity. | 2202.04338v1 |
2016-03-21 | Measurement of Characteristic Impedance of Silicon Fiber Sheet based readout strips panel for RPC detector in INO | The India based Neutrino Observatory (INO) is a mega science project of
India, which is going to use near about 30, 000 Resistive Plate Chambers (RPC)
as active detector elements for the study of atmospheric neutrino oscillations.
Each RPC detector will consist of two orthogonally placed readout strips panel
for picking the signals generated in the gas chamber. The area of RPC detector
in INO-ICAL (Iron Calorimeter) experiment will be 2m x 2m, therefore the
dimension of readout strips panel will also be of 2m x 2m. To get undistorted
signals pass through the readout strips panel to frontend electronics, their
Characteristic Impedance should be matched with each other. For the matching of
Characteristic Impedance we have used the principle of termination. In the
present paper we will describe the need and search of new dielectric material
for the fabrication of flame resistant, waterproof and flexible readout pickup
strips panel. We will also describe the measurement of Characteristic Impedance
of plastic honeycomb based readout strips panel and Silicon Fiber sheet based
readout strips panel in a comparative way, and its variation under loading and
with time. | 1603.06334v1 |
2017-04-18 | Extruded Mg based hybrid composite alloys studied by longitudinal impression creep | The creep behaviour of a creep-resistant AE42 magnesium alloy reinforced with
Saffil short fibres and SiC particulates in various combinations has been
examined in the longitudinal direction, i.e., the plane containing random fibre
orientation was parallel to the loading direction, in the temperature range of
175-300 C at the stress levels ranging from 60 to 140 MPa using impression
creep test technique. At 175 C, normal creep behaviour, i.e., strain rate
decreasing with strain and then reaching a steady state, is observed at all the
stresses employed. At 240 C, normal creep behaviour is observed up to 80 MPa
and reverse creep behaviour, i.e., strain rate increasing with strain, then
reaching a steady state and again decreasing, is observed above that stress. At
300 C, reverse creep behaviour is observed at all the stresses employed. This
pattern remains the same for all the composites. The reverse creep behaviour is
found to be associated with the fibre breakage. The stress exponent is found to
be very high for all the composites. However, after taking the threshold stress
into account, the stress exponent varies from 3.9 to 7.0, which suggests
viscous glide and dislocation climb being the dominant creep mechanisms. The
apparent activation energy Qc was not calculated due to insufficient data at
any stress level either for normal or reverse creep behaviour. The creep
resistance of the hybrid composites is found to be comparable to that of the
composite reinforced with 20% Saffil short fibres at all the temperatures and
stress levels investigated. | 1704.06563v2 |
2018-08-12 | High-pressure polymorphism of BaFe2Se3 | BaFe2Se3 is a potential superconductor material exhibiting transition at 11 K
and ambient pressure. Here we extended the structural and performed electrical
resistivity measurements on this compound up to 51 GPa and 20 GPa,
respectively, in order to distinguish if the superconductivity in this sample
is intrinsic to the BaFe2Se3 phase or if it is originating from minor FeSe
impurities that show a similar superconductive transition temperature. The
electrical resistance measurements as a function of pressure show that at 5 GPa
the superconducting transition is observed at around 10 K, similar to the one
previously observed for this sample at ambient pressure. This indicates that
the superconductivity in this sample is intrinsic to the BaFe2Se3 phase and not
to FeSe with Tc > 20 K at these pressures. Further increase in pressure
suppressed the superconductive signal and the sample remained in an insulating
state up to the maximum achieved pressure of 20 GPa. Single-crystal and powder
X-ray diffraction measurements revealed two structural transformations in
BaFe2Se3: a second order transition above 3.5 GPa from Pnma (CsAg2I3-type
structure) to Cmcm (CsCu2Cl3-type structure) and a first order transformation
at 16.6 GPa. Here, {\gamma}-BaFe2Se3 transforms into {\delta}-BaFe2Se3 (Cmcm,
CsCu2Cl3-type average structure) via a first order phase transition mechanism.
This transitions is characterized by a significant shortening of the b lattice
parameter of {\gamma}-BaFe2Se3 (17%) and accompanied by an anisotropic
expansion in the orthogonal ac plane at the transition point. | 1808.03952v1 |
2019-03-14 | Electric Switching of the Charge-Density-Wave and Normal Metallic Phases in Tantalum Disulfide Thin-Film Devices | We report on switching among three charge-density-wave phases - commensurate,
nearly commensurate, incommensurate - and the high-temperature normal metallic
phase in thin-film 1T-TaS2 devices induced by application of an in-plane
electric field. The electric switching among all phases has been achieved over
a wide temperature range, from 77 K to 400 K. The low-frequency electronic
noise spectroscopy has been used as an effective tool for monitoring the
transitions, particularly the switching from the incommensurate
charge-density-wave phase to the normal metal phase. The noise spectral density
exhibits sharp increases at the phase transition points, which correspond to
the step-like changes in resistivity. Assignment of the phases is consistent
with low-field resistivity measurements over the temperature range from 77 K to
600 K. Analysis of the experimental data and calculations of heat dissipation
suggest that Joule heating plays a dominant role in the electric-field induced
transitions in the tested 1T-TaS2 devices on Si/SiO2 substrates. The
possibility of electrical switching among four different phases of 1T-TaS2 is a
promising step toward nanoscale device applications. The results also
demonstrate the potential of noise spectroscopy for investigating and
identifying phase transitions in materials. | 1903.06050v1 |
2015-06-26 | Negative Differential Resistance in Boron Nitride Graphene Heterostructures: Physical Mechanisms and Size Scaling Analysis | Hexagonal boron nitride (hBN) is drawing increasing attention as an insulator
and substrate material to develop next generation graphene-based electronic
devices. In this paper, we investigate the quantum transport in
heterostructures consisting of a few atomic layers thick hBN film sandwiched
between graphene nanoribbon electrodes. We show a gate-controllable vertical
transistor exhibiting strong negative differential resistance (NDR) effect with
multiple resonant peaks, which stay pronounced for various device dimensions.
We find two distinct mechanisms that are responsible for NDR, depending on the
gate and applied biases, in the same device. The origin of first mechanism is a
Fabry-P\'e like interference and that of the second mechanism is an in-plane
wave vector matching when the Dirac points of the electrodes align. The hBN
layers can induce an asymmetry in the current-voltage characteristics which can
be further modulated by an applied bias. We find that the electron-phonon
scattering introduces the decoherence and therefore suppresses first mechanism
whereas second mechanism remains relatively unaffected. We also show that the
NDR features are tunable by varying device dimensions. The NDR feature with
multiple resonant peaks, combined with the ultrafast tunneling speed provides
prospect for the graphene-hBN-graphene heterostructure in the high-performance
electronics. | 1506.08207v1 |
2015-07-02 | Massive $2$-form field and holographic ferromagnetic phase transition | In this paper, we investigate in some detail the holographic ferromagnetic
phase transition in an AdS${_4}$ black brane background by introducing a
massive 2-form field coupled to the Maxwell field strength in the bulk. In the
two probe limits, one is to neglect the back reaction of the 2-form field to
the background geometry and to the Maxwell field, and the other to neglect the
back reaction of both the Maxwell field and the 2-form field, we find that the
spontaneous magnetization and the ferromagnetic phase transition always happen
when the temperature gets low enough with similar critical behavior. We
calculate the DC resistivity in a semi-analytical method in the second probe
limit and find it behaves as the colossal magnetic resistance effect in some
materials. In the case with the first probe limit, we obtain the off-shell free
energy of the holographic model near the critical temperature and compare with
the Ising-like model. We also study the back reaction effect and find that the
phase transition is always second order. In addition, we find an analytical
Reissner-Norstr\"om-like black brane solution in the Einstein-Maxwell-2-form
field theory with a negative cosmological constant. | 1507.00546v2 |
2018-12-31 | Growth, Characterization and High Field Magneto-Conductivity of Co0.1Bi2Se3 Topological Insulator | We report the crystal growth as well as transport properties of Co added
Bi2Se3 single crystals. The values of the lattice parameters a and b for Co
added sample were observed to increase as compared to the pure Bi2Se3. The
Raman spectroscopy displayed higher Raman shift of corresponding vibrational
modes for Co0.1Bi2Se3, and the resistivity curves with and without applied
magnetic field shows a metallic behaviour. Both the crystals were subjected to
magneto-resistance (MR) measurements under applied fields of 14Tesla. The value
of MR is found to decrease from about 380 (5K, 14 Tesla) for Bi2Se3 to 200
degree for Co0.1Bi2Se3. To elaborate the transport properties of pure and Co
added Bi2Se3 crystals, the magneto-conductivity is fitted to the HLN (Hikami
Larkin Nagaoka) equation and it is found that the charge conduction is mainly
dominated by surface driven WAL (weak anti-localization) with negligible bulk
WL (weak localization) contribution in both crystals alike. The MH curves of
Co0.1Bi2Se3 crystal at different temperatures displayed a combination of both
ferromagnetic and diamagnetic behaviour. On the other hand, the Electron
Paramagnetic Resonance (EPR) revealed that pure Bi2Se3 is diamagnetic whereas,
Co orders ferro-magnetically with resonating field around 3422Oe at room
temperature. | 1812.11713v1 |
2019-11-28 | Low-friction, wear-resistant, and electrically homogeneous multilayer graphene grown by chemical vapor deposition on molybdenum | Chemical vapour deposition (CVD) is a promising method for producing
large-scale graphene (Gr). Nevertheless, microscopic inhomogeneity of Gr grown
on traditional metal substrates such as copper or nickel results in a spatial
variation of Gr properties due to long wrinkles formed when the metal substrate
shrinks during the cooling part of the production cycle. Recently, molybdenum
(Mo) has emerged as an alternative substrate for CVD growth of Gr, mainly due
to a better matching of the thermal expansion coefficient of the substrate and
Gr. We investigate the quality of multilayer Gr grown on Mo and the relation
between Gr morphology and nanoscale mechanical and electrical properties, and
spatial homogeneity of these parameters. With atomic force microscopy (AFM)
based scratching, Kelvin probe force microscopy, and conductive AFM, we measure
friction and wear, surface potential, and local conductivity, respectively. We
find that Gr grown on Mo is free of large wrinkles that are common with growth
on other metals, although it contains a dense network of small wrinkles. We
demonstrate that as a result of this unique and favorable morphology, the Gr
studied here has low friction, high wear resistance, and excellent homogeneity
of electrical surface potential and conductivity. | 1911.12653v1 |
2021-02-23 | Strain-tuning of nematicity and superconductivity in single crystals of FeSe | Strain is a powerful experimental tool to explore new electronic states and
understand unconventional superconductivity. Here, we investigate the effect of
uniaxial strain on the nematic and superconducting phase of single crystal FeSe
using magnetotransport measurements. We find that the resistivity response to
the strain is strongly temperature dependent and it correlates with the sign
change in the Hall coefficient being driven by scattering, coupling with the
lattice and multiband phenomena. Band structure calculations suggest that under
strain the electron pockets develop a large in-plane anisotropy as compared
with the hole pocket. Magnetotransport studies at low temperatures indicate
that the mobility of the dominant carriers increases with tensile strain. Close
to the critical temperature, all resistivity curves at constant strain cross in
a single point, indicating a universal critical exponent linked to a
strain-induced phase transition. Our results indicate that the superconducting
state is enhanced under compressive strain and suppressed under tensile strain,
in agreement with the trends observed in FeSe thin films and overdoped
pnictides, whereas the nematic phase seems to be affected in the opposite way
by the uniaxial strain. By comparing the enhanced superconductivity under
strain of different systems, our results suggest that strain on its own cannot
account for the enhanced high $T_c$ superconductivity of FeSe systems. | 2102.11984v1 |
2021-02-24 | Calibration of manganin pressure gauge for diamond-anvil cells | Pressure calibration for most diamond-anvil cell (DAC) experiments is mainly
based on the ruby scale, which is key to implement this powerful tool for
high-pressure study. However, the ruby scale can often hardly be used for
programmably-controlled DAC devices, especially the piezoelectric-driving
cells, where a continuous pressure calibration is required. In this work, we
present an effective pressure gauge for DACs made of manganin metal, based on
the four-probe resistivity measurements. Pressure dependence of its resistivity
is well established and shows excellent linear relations in the 0 - 30 GPa
pressure range with a slope of 23.4 (9) GPa for the first-cycle compression, in
contrast to that of multiple-cycle compression and decompression having a
nearly identical slope of 33.7 (4) GPa likely due to the strain effect. In
addition, such-established manganin scale can be used for continuously
monitoring the cell pressure of piezoelectric-driving DACs, and the reliability
of this method is also verified by the fixed-point method with a Bi pressure
standard. Realization of continuous pressure calibration for
programmably-controlled DACs would offer many opportunities for study of
dynamics, kinetics, and critical behaviors of pressure-induced phase
transitions. | 2102.12125v1 |
2021-03-19 | A Robust nitridation technique for fabrication of disordered superconducting TiN thin films featuring phase slip events | Disorder induced phase slip (PS) events appearing in the current voltage
characteristics (IVCs) are reported for two-dimensional TiN thin films produced
by a robust substrate mediated nitridation technique. Here, high temperature
annealing of Ti/Si3N4 based metal/substrate assembly is the key to produce
majority phase TiN accompanied by TiSi2 and elemental Si as minority phases.
The method itself introduces different level of disorder intrinsically by
tuning the amount of the non-superconducting minority phases that are
controlled by annealing temperature (Ta) and the film thickness. The
superconducting critical temperature (Tc) strongly depends on Ta and the
maximum Tc obtained from the demonstrated technique is about 4.8 K for the
thickness range of about 12 nm and above. Besides, the dynamics of IVCs get
modulated by the appearance of intermediated resistive steps for decreased Ta
and the steps get more prominent for reduced thickness. Further, the deviation
in the temperature dependent critical current (Ic) from the Ginzburg-Landau
theoretical limit varies strongly with the thickness. Finally, the Tc,
intermediate resistive steps in the IVCs and the depairing current are observed
to alter in a similar fashion with Ta and the thickness indicating the
robustness of the synthesis process to fabricate disordered nitride-based
superconductor. | 2103.10751v2 |
2021-07-22 | Temperature dependence of on-state inter-terminal capacitances (Cgd and Cgs) of SiC MOSFETs and frequency limitations of their measurements | Inter-terminal capacitances (ITCs) have major influence on the dynamic
performance of power SiC MOSFETs. Knowledge of the exact values for the ITCs is
required in order to perform accurate and predictive compact model simulations
of their dynamic performance. Since commercial SiC MOSFETs are capable of
operating in a wide range of temperatures, it is important to know the values
of ITCs in the whole temperature range of operation. Direct measurements of the
ITCs with standard equipment is possible only at low current levels (i.e. in
the off-state (Vgs < Vth) for Vds > 0 V), however their values in the on-state
(Vgs>Vth) also influence the MOSFETs switching performance. In this work, ITCs
of a planar SiC MOSFET in the on-state are studied by the means of a calibrated
TCAD model, revealing substantial temperature dependence in the range of
300-450 K. In the first approximation, this temperature dependence of the ITCs
can be explained by a weaker temperature dependence of the MOSFET channel
resistance in comparison to its JFET and epitaxial layer resistances. In
addition, it is shown that at high frequencies stray inductances of the
TO-247-3 package result in a change of the extracted values of the on-state
ITCs. This effect is already notable at 1 MHz. | 2107.10408v1 |
2021-07-24 | Anomalous Nernst thermopower and giant magnetostriction in microwave synthesized La0.5Sr0.5CoO3 | Ferromagnetic metallic oxides have potential applications in spincaloric
devices which utilize the spin property of charge carriers for interconversion
of heat and electricity through the spin Seebeck or the anomalous Nernst effect
or both. In this work, we synthesized polycrystalline La0.5S0.5CoO3 by
microwave irradiation method and studied its transverse thermoelectric voltage
(Nernst thermopower) and change in the linear dimension of the sample (Joule
magnetostriction) in response to external magnetic fields. In addition,
magnetization, temperature dependences of electrical resistivity, and
longitudinal Seebeck coefficient (Sxx) in absence of an external magnetic field
were also measured. The sample is ferromagnetic with a Curie temperature of TC
= 247 K and shows a metal-like resistivity above and below TC with a negative
sign of Sxx suggesting charge transport due to electrons. Magnetic field
dependence of the Nernst thermopower (Sxy) at a fixed temperature shows a rapid
increase at low fields and a tendency to saturate at high fields as like the
magnetization. Anomalous contribution to Sxy was extracted from total Sxy
measured and it exhibits a maximum value of ~ 0.21 microV/K at 180 K for H = 50
kOe, which is comparable to the value found in a single crystal for a lower Sr
content. The Joule magnetostriction is positive, i.e., the length of the sample
expands along the direction of the magnetic field and it does not saturate even
at 50 kOe. The magnetostriction increases with decreasing temperature below TC
and reaches a maximum value of 500 ppm at T = 40 K and below. Coexistence of
the anomalous Nernst thermopower and giant magnetostriction in a single
compound has potential applications for thermal energy harvesting and
low-temperature actuators, respectively. | 2107.11535v1 |
2022-01-15 | Fabrication and micro-Raman spectroscopy of arrays of copper phthalocyanine molecular-magnet microdisks | Phthalocyanines as organic semiconductors and molecular magnets provide
plenty of industrial or high-tech applications from dyes and pigments up to gas
sensors, molecular electronics, spintronics and quantum computing. Copper
phthalocyanine (CuPc) belongs among the most used phthalocyanines, typically in
the form of powder or films but self-grown nanowires are also known. Here we
describe an opposite, i.e., top-down approach based on fabrication of ordered
arrays of CuPc microstructures (microdisks) using electron beam lithography and
other steps. Among critical points of this approach belongs a choice of a
proper resist and a solvent. Fabricated CuPc microdisks have a diameter of 5
${\mu}$m and heights from 7 up to 70 nm. Micro-Raman spectroscopy of the films
and microdisks reveals a crystalline ${\beta}$ phase associated with a
paramagnetic form. Additional measurements with an increasing laser power show
a significant shift (${\Delta}{\omega}$ ~ 7.1 cm$^{-1}$ ) and broadening of a
peak at 1532 rel$\cdot$cm$^{-1}$ corresponding to the phonon B1g mode. The
observed smooth changes exclude a phase transition and confirm the thermally
stable polymorph. Our versatile fabrication technique using the common
lithographic resist brings new possibilities for the fabrication of various
micro/nanostructures such as micromagnets, heterostructures or organic
electronic devices. | 2201.08235v1 |
2022-07-06 | Mechanism of the Resistivity Switching Induced by the Joule Heating in Crystalline NbO$_2$ | Recently the memristive electrical transport properties in NbO$_2$ have
attracted much attention for their promising application to the neuromorphic
computation. At the center of debates is whether the metal-to-insulator
transition (MIT) originates from the structural distortion (Peierls) or the
electron correlation (Mott). With inputs from experiments and first principles
calculations, we develop a thermodynamical model rooted in the scenario of the
MIT driven by a $2^{nd}$ order Peierls instability. We find that the
temperature dependence of the electrical conductivity can be accurately fit by
the band gap varying with temperature due to the gradual weakening of the Nb-Nb
dimers. The resistivity switching can consequently be understood by dimer-free
metallic domains induced by local Joule heating. In solving the heat equation,
we find that the steady state can not be reached if the applied voltage exceeds
a threshold, resulting in the chaotic behavior observed in the high voltage and
current states. With the Ginzburg-Landau theory and the Joule heating equation,
the evolution of the metallic domains under bias voltage can be simulated and
directly verified by experiments. | 2207.02682v2 |
2022-12-13 | Deep multilevel wet etching of fused silica glass microstructures in BOE solution | Fused silica glass is a material of choice for micromechanical, microfluidic,
and optical devices due to its ultimate chemical resistance, optical,
electrical, and mechanical performance. Wet etching in hydrofluoric solutions
especially a buffered oxide etching (BOE) solution is still the key method for
fabricating fused silica glass-based microdevices. It is well known that
protective mask integrity during deep fused silica wet etching is a big
challenge due to chemical stability of fused glass and extremely aggressive BOE
properties. Here, we propose a multilevel fused silica glass microstructures
fabrication route based on deep wet etching through a stepped mask with just a
one grayscale photolithography step. First, we provide a deep comprehensive
analysis of a fused quartz dissolution mechanism in BOE solution and calculate
the main fluoride fractions like $HF^-_2$, $F^-$, $(HF)_2$ components in a BOE
solution as a function of pH and $NH_4F:HF$ ratio at room temperature. Then, we
experimentally investigate the influence of BOE concentration ($NH_4F:HF$ from
1:1 to 14:1) on the mask resistance, etch rate and profile isotropy during
fused silica 60 minutes etching through a metal/photoresist mask. Finally, we
demonstrate a high-quality multilevel over-200 um isotropic wet etching process
with the rate up to 3 um/min, which could be of a great interest for advanced
fused silica microdevices with flexure suspensions, inertial masses,
microchannels, and through-wafer holes. | 2212.06699v1 |
2023-03-02 | Evolution of complex magnetic phases and metal-insulator transition through Nb substitution in La$_{0.5}$Sr$_{0.5}$Co$_{1-x}$Nb$_x$O$_3$ | We report the evolution of structural, magnetic, transport, and electronic
properties of bulk polycrystalline La$_{0.5}$Sr$_{0.5}$Co$_{1-x}$Nb$_x$O$_3$
($x =$ 0.025--0.25) samples. The Rietveld refinement of the x-ray diffraction
patterns with R$\bar3$c space group reveals that the lattice parameters and
rhombohedral distortion monotonously increase with the Nb$^{5+}$(4$d^0$)
substitution ($x$). The magnetic susceptibility exhibits a decrease in the
magnetic ordering temperature and net magnetization with $x$, which manifests
that the Nb substitution dilutes the ferromagnetic (FM) double exchange
interaction and enhances the antiferromagnetic (AFM) super-exchange
interaction. Interestingly, for the $x>$ 0.1 samples the FM order is completely
suppressed and the emergence of a glassy state is clearly evident. Moreover,
the decrease in the coercivity (H$\rm_{C}$) and remanence (M$\rm_{r}$) with $x$
in the magnetic isotherms measured at 5~K further confirms the dominance of AFM
interactions and reduction of FM volume fraction for the $x>$ 0.1 samples. More
interestingly, we observe resistivity minima for the $x=$ 0.025 and 0.05
samples, which are analyzed using the quantum corrections in the conductivity,
and found that the weak localization effect dominates over the renormalized
electron-electron interactions in the 3D limit. Further, a semiconducting
resistivity behavior is obtained for $x>$ 0.05, which follows the Arrhenius law
at high temperatures ($\sim$160--320~K), and the 3D-variable range hopping
prevails in the low-temperature region ($<$160~K). The core-level photoemission
spectra confirm the valence state of constituent elements and the absence of
Co$^{2+}$ is discernible. | 2303.01108v1 |
2023-10-18 | Electrically-driven amplification of terahertz acoustic waves in graphene | In graphene devices, the electronic drift velocity can easily exceed the
speed of sound in the material at moderate current biases. Under this
condition, the electronic system can efficiently amplify acoustic phonons,
leading to the exponential growth of sound waves in the direction of the
carrier flow. Here, we demonstrate that such phonon amplification can
significantly modify the electrical properties of graphene devices. We observe
a super-linear growth of the resistivity in the direction of the carrier flow
when the drift velocity exceeds the speed of sound, causing up to a 7 times
increase over 8 micrometers. The resistance growth is observable for carrier
densities away from the Dirac point and is enhanced at cryogenic temperatures.
These observations are explained by a theoretical model for the
electrical-amplification of acoustic phonons, which reach frequencies up to 2.2
terahertz with the nanoscale wavelength set by gate-tunable ~kF transitions
across the Fermi surface. These findings offer a route to high-frequency
on-chip sound generation and detection, which can be used to modulate and probe
electronic physics in van der Waals heterostructures in the terahertz frequency
range. | 2310.12225v1 |
2024-04-24 | Structural investigation of the quasi-one-dimensional topological insulator Bi$_4$I$_4$ | The bismuth-halide Bi$_4$I$_4$ undergoes a structural transition around
$T_P\sim 300$K, which separates a high-temperature $\beta$ phase ($T>T_P$) from
a low-temperature $\alpha$ phase ($T<T_P$). $\alpha$ and $\beta$ phases are
suggested to host electronic band structures with distinct topological
classifications. Rapid quenching was reported to stabilize a metastable
$\beta$-Bi$_4$I$_4$ at $T<T_P$, making possible a comparative study of the
physical properties of the two phases in the same low-temperature range. In
this work, we present a structural investigation of the Bi$_4$I$_4$ before and
after quenching together with electrical resistivity measurements. We found
that rapid cooling does not consistently lead to a metastable
$\beta$-Bi$_4$I$_4$, and a quick transition to $\alpha$-Bi$_4$I$_4$ is
observed. As a result, the comparison of putative signatures of different
topologies attributed to a specific structural phase should be carefully
considered. The observed phase instability is accompanied by an increase in
iodine vacancies and by a change in the temperature dependence of electrical
resistivity, pointing to native defects as a possible origin of our finding.
Density functional theory (DFT) calculations support the scenario that iodine
vacancies, together with bismuth antisites and interstitials, are among the
defects that are more likely to occur in Bi$_4$I$_4$ during the growth. | 2404.16194v1 |
1998-12-22 | Theory of Colossal Magnetoresistance in Doped Manganites | The exchange interaction of polaronic carriers with localized spins leads to
a ferromagnetic/paramagnetic transition in doped charge-transfer insulators
with strong electron-phonon coupling. The relative strength of the exchange and
electron-phonon interactions determines whether the transition is first or
second order. A giant drop in the number of current carriers during the
transition, which is a consequence of local bound pair (bipolaron) formation in
the paramagnetic phase, is extremely sensitive to an external magnetic field.
Below the critical temperature of the transition, $T_c$, the binding of the
polarons into immobile pairs competes with the ferromagnetic exchange between
polarons and the localized spins on Mn ions, which tends to align the polaron
moments and, therefore, breaks up those pairs. The number of carriers abruptly
increases below $T_c$ leading to a sudden drop in resistivity. We show that the
carrier density collapse describes the colossal magnetoresistance of doped
manganites close to the transition.
Below $T_c$, transport occurs by polaronic tunneling, whereas at high
temperatures the transport is by hopping processes. The transition is
accompanied by a spike in the specific heat, as experimentally observed. The
gap feature in tunneling spectroscopy is related to the bipolaron binding
energy, which depends on the ion mass. This dependence explains the giant
isotope effect of the magnetization and resistivity upon substitution of
$^{16}$O by $^{18}$O. It is shown also that the localization of polaronic
carriers by disorder {\em cannot} explain the observed huge sensitivity of the
transport properties to the magnetic field in doped manganites. | 9812355v1 |
1999-02-22 | Hall-effect in LuNi_2B_2C and YNi_2B_2C borocarbides: a comparative study | The Hall effect in LuNi_2B_2C and YNi_2B_2C borocarbides has been
investigated in normal and superconducting mixed states. The Hall resistivity
rho_{xy} for both compounds is negative in the normal as well as in the mixed
state and has no sign reversal below T_c typical for high-T_c superconductors.
In the mixed state the behavior of both systems is quite similar. The scaling
relation rho_{xy}\sim\rho_{xx}^\beta (\rho_{xx} is the longitudinal
resistivity) was found with \beta=2.0 and 2.1 for annealed Lu- and Y-based
compounds, respectively. The scaling exponent \beta decreases with increasing
degree of disorder and can be varied by annealing. This is attributed to a
variation of the strength of flux pinning. In the normal state weakly
temperature dependent Hall coefficients were observed for both compounds. A
distinct nonlinearity in the \rho_{xy} dependence on field H was found for
LuNi_2B_2C in the normal state below 40K, accompanied by a large
magnetoresistance (MR) reaching +90% for H=160kOe at T=20K. At the same time
for YNi_2B_2C only linear \rho_{xy}(H) dependences were observed in the normal
state with an approximately three times lower MR value. This difference in the
normal state behavior of the very similar Lu- and Y-based borocarbides seems to
be connected with the difference in the topology of the Fermi surface of these
compounds. | 9902299v1 |
2000-07-21 | Effect of γ-irradiation on superconductivity in polycrystalline YBa_{2}Cu_{3}O_{7-δ} | A bulk polycrystalline sample of YBa_{2}Cu_{3}O_{7-\delta} (\delta \approx
0.1) has been irradiated by \gamma-rays with ^{60}Co source. Non-monotonic
behavior of T_c (defined as the temperature at which normal resistance is
halved) with increasing irradiation dose \Phi (up to about 220 MR) is observed:
T_c decreases at low doses (\Phi \leq 50 MR) from initial value (\approx 93 K)
by about 2 K and then rises, forming minimum. At highest doses (\Phi \geq 120
MR) T_c goes down again. The temperature width, \delta T_c, of resistive
transition increases rather sharp with dose below 75 MR and somewhat drops at
higher dose. We believe that this effect is revealed for the first time at
\gamma-irradiation of high-T_c superconductor. The cross section for the
displacement of lattice atoms in YBCO by \gamma-rays due to the Compton process
were calculated, and possible dpa values were estimated. The results obtained
are discussed taking into account that the sample is granular superconductor
and, hence, the observed variations of superconducting properties should be
connected primarily with the influence of \gamma-rays on intergrain Josephson
coupling. | 0007345v1 |
2004-08-13 | The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy | The effect of the variation of oxygen content on structural, magnetic and
transport properties in the electron-doped manganites La0.9Te0.1MnOy has been
investigated. All samples show a rhombohedral structure with the space group .
The Curie temperature decreases and the paramagnetic-ferromagnetic (PM-FM)
transition becomes broader with the reduction of oxygen content. The
resistivity of the annealed samples increases slightly with a small reduction
of oxygen content. Further reduction in the oxygen content, the resistivity
maximum increases by six orders of magnitude compared with that of the
as-prepared sample, and the r(T) curves of samples with y = 2.86 and y = 2.83
display the semiconducting behavior () in both high-temperature PM phase and
low-temperature FM phase, which is considered to be related to the appearance
of superexchange ferromagnetism (SFM) and the localization of carriers. The
results are discussed in terms of the combined effects of the increase in the
Mn2+/(Mn2++Mn3+) ratio, the partial destruction of double exchange (DE)
interaction, and the localization of carriers due to the introduction of oxygen
vacancies in the Mn-O-Mn network. | 0408302v1 |
2007-09-14 | Crystallography, magnetic susceptibility, heat capacity, and electrical resistivity of heavy fermion LiV$_2$O$_4$ single crystals grown using a self-flux technique | Magnetically pure spinel compound ${\rm LiV_2O_4}$ is a rare $d$-electron
heavy fermion. Measurements on single crystals are needed to clarify the
mechanism for the heavy fermion behavior in the pure material. In addition, it
is known that small concentrations ($< 1$ mol%) of magnetic defects in the
structure strongly affect the properties, and measurements on single crystals
containing magnetic defects would help to understand the latter behaviors.
Herein, we report flux growth of ${\rm LiV_2O_4}$ and preliminary measurements
to help resolve these questions. The magnetic susceptibility of some as-grown
crystals show a Curie-like upturn at low temperatures, showing the presence of
magnetic defects within the spinel structure. The magnetic defects could be
removed in some of the crystals by annealing them at 700 $^\circ$C\@. A very
high specific heat coefficient $\gamma$ = 450 mJ/(mol K${^2}$\@) was obtained
at a temperature of 1.8 K for a crystal containing a magnetic defect
concentration $n$${\rm_{defect}}$ = 0.5 mol%. A crystal with $n$${\rm
_{defect}}$ = 0.01 mol% showed a residual resistivity ratio of 50. | 0709.2387v3 |
2009-08-26 | On the strong impact of doping in the triangular antiferromagnet CuCrO2 | Electronic band structure calculations using the augmented spherical wave
method have been performed for CuCrO2. For this antiferromagnetic (T_N = 24 K)
semiconductor crystallizing in the delafossite structure, it is found that the
valence band maximum is mainly due to the t_2g orbitals of Cr^3+ and that spin
polarization is predicted with 3 mu_B per Cr^3+. The structural
characterizations of CuCr1-xMgxO2 reveal a very limited range of Mg^2+
substitution for Cr^3+ in this series. As soon as x = 0.02, a maximum of 1% Cr
ions substituted by Mg site is measured in the sample. This result is also
consistent with the detection of Mg spinel impurities from X-ray diffraction
for x = 0.01. This explains the saturation of the Mg^2+ effect upon the
electrical resistivity and thermoelectric power observed for x > 0.01. Such a
very weak solubility limit could also be responsible for the discrepancies
found in the literature. Furthermore, the measurements made under magnetic
field (magnetic susceptibility, electrical resistivity and Seebeck coefficient)
support that the Cr^4+ "holes", created by the Mg^2+ substitution, in the
matrix of high spin Cr^3+ (S = 3/2) are responsible for the transport
properties of these compounds. | 0908.3828v1 |
2009-12-02 | Magnetotransport of La0.70ca0.3-xsrxmno3 (Ag): A Potential Room Temperature Bolometer and Magnetic Sensor | Here we report the optimized magneto-transport properties of polycrystalline
La0.70Ca0.3-xSrxMnO3 and their composites with Ag. The optimization was carried
out by varying the Sr and Ag contents simultaneously to achieve large
temperature coefficient of resistance (TCR) as well as low field
magneto-resistance (MR) at room temperature. Sharpest paramagnetic
(PM)-ferromagnetic (FM) and insulator-metal (IM) transition is observed in the
vicinity of the room temperature (TC=300 K=TIM) for the composition
La0.70Ca0.20Sr00.10MnO3:Ag0.20. Partial substitution of larger Sr2+ ions at the
Ca2+ ions sites controls the magnitude of the FM and IM transition
temperatures, while the Ag induces the desired sharpness in these transitions.
For the optimized composition, maximum TCR and MR are tuned to room temperature
(300 K) with the former being as high as 9% and the later being 20 and 30
percent at 5 and 10 kOe magnetic fields respectively. Such sharp single peak
(TCR= 9 percent) at room temperature can be used for the bolometric and
infrared detector applications. The achievement of large TCR and low field MR
at T~300K in polycrystalline samples is encouraging and we believe that further
improvements can be achieved in thin films, which, by virtue of their low
conduction noise, are more suitable for device applications. | 0912.0347v2 |
2012-08-16 | Gate tunable quantum transport in double layer graphene | We analyze the effect of screening provided by the additional graphene layer
in double layer graphene heterostructures (DLGs) on transport characteristics
of DLG devices in the metallic regime. The effect of gate-tunable charge
density in the additional layer is two-fold: it provides screening of the
long-range potential of charged defects in the system, and screens out Coulomb
interactions between charge carriers. We find that the efficiency of defect
charge screening is strongly dependent on the concentration and location of
defects within the DLG. In particular, only a moderate suppression of
electron-hole puddles around the Dirac point induced by the high concentration
of remote impurities in the silicon oxide substrate could be achieved. A
stronger effect is found on the elastic relaxation rate due to charged defects
resulting in mobility strongly dependent on the electron denisty in the
additional layer of DLG. We find that the quantum interference correction to
the resistivity of graphene is also strongly affected by screening in DLG. In
particular, the dephasing rate is strongly suppressed by the additional
screening that supresses the amplitude of electron-electron interaction and
reduces the diffusion time that electrons spend in proximity of each other. The
latter effect combined with screening of elastic relaxation rates results in a
peculiar gate tunable weak-localization magnetoresistance and quantum
correction to resistivity. We propose suitable experiments to test our theory
and discuss the possible relevance of our results to exisiting data. | 1208.3470v2 |
2012-10-20 | Tunable spin reorientation transition and magnetocaloric effect in Sm0.7-xLaxSr0.3MnO3 series | We report electrical resistivity, magnetic and magnetocaloric properties in
Sm0.7-xLaxSr0.3MnO3 series for x= 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, and
0.7. All the compounds show second order paramagnetic to ferromagnetic
transition at T = Tc which is tunable anywhere between 83 K and 373 K with a
proper choice of the doping level (x). The insulating ferromagnet x= 0
transforms to ferromagnetic metal below Tc for x= 0.1 and the insulator-metal
transition temperature shifts up with increasing x. The magnetization (M)
exhibits an interesting behavior as a function of temperature and doping level.
The field-cooled M(T) of all but x= 0.7 compound show a cusp at a temperature
T* much below Tc. While the Tc increases monotonically with increasing x, T*
increases gradually, attains a maximum value (T*= 137 K) for x= 0.6 and
decreases rapidly thereafter. It is suggested that the decrease of M(T) below
T* is due to ferrimagnetic interaction between Sm(4f) and Mn(3d) sublattices
that promotes spin-reorientation transition of the Mn-sublattice. The observed
anomalous feature in M(T) does not have impact on the dc resistivity. Magnetic
entropy change (delta Sm) was estimated from magnetization isotherms. The sign
of delta Sm is found to change from negative above T* to positive below T*
indicating the coexistence of normal and inverse magnetocaloric effects. delta
Sm is nearly composition independent (-delta Sm is about 1.5 J/Kg K for delta H
= 1 Tesla) and refrigeration capacity lies between 50 and 80 J/kg K for x =
0.1-0.6. The tunability of Curie temperature with a nearly constant delta Sm
value along with high refrigeration capacity makes this series of compounds
interesting for magnetic refrigeration over a wide temperature range. | 1210.5595v1 |
2012-11-27 | Anisotropic Impurity-States, Quasiparticle Scattering and Nematic Transport in Underdoped Ca(Fe1-xCox)2As2 | Iron-based high temperature superconductivity develops when the `parent'
antiferromagnetic/orthorhombic phase is suppressed, typically by introduction
of dopant atoms. But their impact on atomic-scale electronic structure, while
in theory quite complex, is unknown experimentally. What is known is that a
strong transport anisotropy with its resistivity maximum along the crystal
b-axis, develops with increasing concentration of dopant atoms; this
`nematicity' vanishes when the `parent' phase disappears near the maximum
superconducting Tc. The interplay between the electronic structure surrounding
each dopant atom, quasiparticle scattering therefrom, and the transport
nematicity has therefore become a pivotal focus of research into these
materials. Here, by directly visualizing the atomic-scale electronic structure,
we show that substituting Co for Fe atoms in underdoped Ca(Fe1-xCox)2As2
generates a dense population of identical anisotropic impurity states. Each is
~8 Fe-Fe unit cells in length, and all are distributed randomly but aligned
with the antiferromagnetic a-axis. By imaging their surrounding interference
patterns, we further demonstrate that these impurity states scatter
quasiparticles in a highly anisotropic manner, with the maximum scattering rate
concentrated along the b-axis. These data provide direct support for the recent
proposals that it is primarily anisotropic scattering by dopant-induced
impurity states that generates the transport nematicity; they also yield simple
explanations for the enhancement of the nematicity proportional to the dopant
density and for the occurrence of the highest resistivity along the b-axis. | 1211.6454v1 |
2013-05-16 | Different routes to pressure-induced volume collapse transitions in gadolinium and terbium metals | The sudden decrease in molar volume exhibited by most lanthanides under high
pressure is often attributed to changes in the degree of localization of their
4f-electrons. We give evidence, based on electrical resistivity measurements of
dilute Y(Gd) and Y(Tb) alloys to 120 GPa, that the volume collapse transitions
in Gd and Tb metals have different origins, despite their being neighbors in
the periodic table. Remarkably, the change under pressure in the magnetic state
of isolated Pr or Tb impurity ions in the nonmagnetic Y host appears to closely
mirror corresponding changes in pure Pr or Tb metals. The collapse in Tb
appears to be driven by an enhanced negative exchange interaction between 4f
and conduction electrons under pressure (Kondo resonance) which, in the case of
Y(Tb), dramatically alters the superconducting properties of the Y host, much
like previously found for Y(Pr). In Gd our resistivity measurements suggest
that a Kondo resonance is not the main driver for its volume collapse. X-ray
absorption and emission spectroscopies clearly show that 4f local moments
remain largely intact across both volume collapse transitions ruling out 4f
band formation (delocalization) and valence transition models as possible
drivers. The results highlight the richness of behavior behind the volume
collapse transition in lanthanides and demonstrate the stability of the 4f
level against band formation to extreme pressure. | 1305.3852v4 |
2014-04-09 | Quantum transport evidence for a three-dimensional Dirac semimetal phase in Cd3As2 | The material termed three-dimensional (3D) Dirac semimetal has attracted
great interests recently, since it is an electronic analogue to two-dimensional
graphene. Starting from this novel phase, various topologically distinct phases
may be obtained, such as topological insulator, Weyl semimetal, quantum spin
Hall insulator, and topological superconductor. Soon after the theoretical
predictions, the angle-resolve photoemission spectroscopy and scanning
tunnelling microscopy experiments gave evidences for 3D Dirac points in Na3Bi
and Cd3As2. Here we report quantum transport properties of Cd3As2 single
crystal in magnetic field. A sizable linear quantum magnetoresistance is
observed at high temperature. With decreasing temperature, the Shubnikov-de
Haas oscillations appear in both longitudinal resistance Rxx and transverse
Hall resistance Rxy. From the strong oscillatory component \Delta Rxx, the
linear dependence of Landau index n on 1/B gives an n-axis intercept 0.58. Our
quantum transport result clearly reveals a nontrivial \pi\ Berry's phase, thus
provides strong bulk evidence for a 3D Dirac semimetal phase in Cd3As2. This
may open new perspectives for its use in electronic devices. | 1404.2557v3 |
2014-04-15 | Formation of a topological non-Fermi liquid in MnSi | Fermi liquid theory provides a remarkably powerful framework for the
description of the conduction electrons in metals and their ordering phenomena,
such as superconductivity, ferromagnetism, and spin- and charge-density-wave
order. A different class of ordering phenomena of great interest concerns spin
configurations that are topologically protected, that is, their topology can be
destroyed only by forcing the average magnetization locally to zero. Examples
of such configurations are hedgehogs (points at which all spins are either
pointing inwards or outwards) or vortices. A central question concerns the
nature of the metallic state in the presence of such topologically distinct
spin textures. Here we report a high-pressure study of the metallic state at
the border of the skyrmion lattice in MnSi, which represents a new form of
magnetic order composed of topologically non-trivial vortices. When long-range
magnetic order is suppressed under pressure, the key characteristic of the
skyrmion lattice - that is, the topological Hall signal due to the emergent
magnetic flux associated with their topological winding - is unaffected in sign
or magnitude and becomes an important characteristic of the metallic state. The
regime of the topological Hall signal in temperature, pressure and magnetic
field coincides thereby with the exceptionally extended regime of a pronounced
non-Fermi-liquid resistivity. The observation of this topological Hall signal
in the regime of the NFL resistivity suggests empirically that spin
correlations with non-trivial topological character may drive a breakdown of
Fermi liquid theory in pure metals. | 1404.4050v1 |
2014-09-12 | Observation of topological surface state quantum Hall effect in an intrinsic three-dimensional topological insulator | A three-dimensional (3D) topological insulator (TI) is a quantum state of
matter with a gapped insulating bulk yet a conducting surface hosting
topologically-protected gapless surface states. One of the most distinct
electronic transport signatures predicted for such topological surface states
(TSS) is a well-defined half-integer quantum Hall effect (QHE) in a magnetic
field, where the surface Hall conductivities become quantized in units of
(1/2)e2/h (e being the electron charge, h the Planck constant) concomitant with
vanishing resistance. Here, we observe well-developed QHE arising from TSS in
an intrinsic TI of BiSbTeSe2. Our samples exhibit surface dominated conduction
even close to room temperature, while the bulk conduction is negligible. At low
temperatures and high magnetic fields perpendicular to the top and bottom
surfaces, we observe well-developed integer quantized Hall plateaus, where the
two parallel surfaces each contributing a half integer e2/h quantized Hall (QH)
conductance, accompanied by vanishing longitudinal resistance. When the bottom
surface is gated to match the top surface in carrier density, only odd integer
QH plateaus are observed, representing a half-integer QHE of two degenerate
Dirac gases. This system provides an excellent platform to pursue a plethora of
exotic physics and novel device applications predicted for TIs, ranging from
magnetic monopoles and Majorana particles to dissipationless electronics and
fault-tolerant quantum computers. | 1409.3778v2 |
2014-12-23 | Magnetic and structural transitions in La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals | La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals have been grown out of an
NaAs flux in an alumina crucible and characterized by measuring magnetic
susceptibility, electrical resistivity, specific heat, as well as single
crystal x-ray and neutron diffraction. La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single
crystals show a structural phase transition from a high temperature tetragonal
phase to a low-temperature orthorhombic phase at T$_s$\,=\,125\,K. This
structural transition is accompanied by an anomaly in the temperature
dependence of electrical resistivity, anisotropic magnetic susceptibility, and
specific heat. Concomitant with the structural phase transition, the Fe moments
order along the \emph{a} direction with an ordered moment of
0.7(1)\,$\mu_{\textup{B}}$ at \emph{T}\,=\,5 K. The low temperature stripe
antiferromagnetic structure is the same as that in other
\emph{A}Fe$_{2}$As$_{2}$ (\emph{A}\,=\,Ca, Sr, Ba) compounds.
La$_{0.5-x}$Na$_{0.5+x}$Fe$_2$As$_2$ provides a new material platform for the
study of iron-based superconductors where the electron-hole asymmetry could be
studied by simply varying La/Na ratio. | 1412.7447v1 |
2015-01-08 | Structure and bonding in amorphous iron carbide thin films | We investigate the amorphous structure, chemical bonding, and electrical
properties of magnetron sputtered Fe1-xCx (0.21<x<0.72) thin films. X-ray,
electron diffraction and transmission electron microscopy show that the Fe1-xCx
films are amorphous nanocomposites, consisting of a two-phase domain structure
with Fe-rich carbidic FeCy, and a carbon-rich matrix. Pair distribution
function analysis indicates a close-range order similar to those of crystalline
Fe3C carbides in all films with additional graphene-like structures at high
carbon content (71.8 at% C). From X-ray photoelectron spectroscopy
measurements, we find that the amorphous carbidic phase has a composition of
15-25 at% carbon that slightly increases with total carbon content. X-ray
absorption spectra exhibit increasing number of unoccupied 3d states and
decreasing number of C 2p states as a function of carbon content. These changes
signify a systematic redistribution in orbital occupation due to
charge-transfer effects at the domain-size dependent carbide/matrix interfaces.
Four-point probe resistivity of the Fe1-xCx films increases exponentially with
carbon content from 200 mu-Ohm-cm (x=0.21) to 1200 mu-Ohm-cm (x=0.72), and is
found to depend on the total carbon content rather than the composition of the
carbide. Our findings open new possibilities for modifying the resistivity of
amorphous thin film coatings based on transition metal carbides by control of
amorphous domain structures. | 1501.01839v1 |
2015-09-09 | Controlling the Electrical Properties of Undoped and Ta-doped TiO2 Polycrystalline Films via Ultra-Fast Annealing Treatments | We present a study on the crystallization process of undoped and Ta doped
TiO2 amorphous thin films. In particular, the effect of ultra-fast annealing
treatments in environments characterized by different oxygen concentrations is
investigated via in-situ resistance measurements. The accurate examination of
the key parameters involved in this process allows us to reduce the time needed
to obtain highly conducting and transparent polycrystalline thin films
(resistivity about $6 \times 10^{-4}$ {\Omega}cm, mean transmittance in the
visible range about $81\%$) to just 5 minutes (with respect to the 180 minutes
required for a standard vacuum annealing treatment) in nitrogen atmosphere (20
ppm oxygen concentration) at ambient pressure. Experimental evidence of
superficial oxygen incorporation in the thin films and its detrimental role for
the conductivity are obtained by employing different concentrations of
traceable 18O isotopes during ultra-fast annealing treatments. The results are
discussed in view of the possible implementation of the ultra-fast annealing
process for TiO2-based transparent conducting oxides as well as electron
selective layers in solar cell devices; taking advantage of the high control of
the ultra-fast crystallization processes which has been achieved, these two
functional layers are shown to be obtainable from the crystallization of a
single homogeneous thin film. | 1509.02744v1 |
2016-10-14 | rHARM: Accretion and Ejection in Resistive GR-MHD | Turbulent magnetic diffusivity plays an important role for accretion disks
and the launching of disk winds. We have implemented magnetic diffusivity,
respective resistivity in the general relativistic MHD code HARM. This paper
describes the theoretical background of our implementation, its numerical
realization, our numerical tests and preliminary applications. The test
simulations of the new code rHARM are compared with an analytic solution of the
diffusion equation and a classical shock tube problem. We have further
investigated the evolution of the magneto-rotational instability (MRI) in tori
around black holes for a range of magnetic diffusivities. We find indication
for a critical magnetic diffusivity (for our setup) beyond which no MRI
develops in the linear regime and for which accretion of torus material to the
black hole is delayed. Preliminary simulations of magnetically diffusive thin
accretion disks around Schwarzschild black holes that are threaded by a
large-scale poloidal magnetic field show the launching of disk winds with mass
fluxes of about 50% of the accretion rate. The disk magnetic diffusivity allows
for efficient disk accretion that replenishes the mass reservoir of the inner
disk area and thus allows for long-term simulations of wind launching for more
than 5000 time units. | 1610.04445v1 |
2016-10-26 | Doping of Ga in antiferromagnetic semiconductor alpha-Cr2O3oxide and its effects on modified magnetic and electronic properties | The samples of Ga doped Cr2O3 oxide have been prepared using chemical
co-precipitation route. X-ray diffraction pattern and Raman spectra have
confirmed rhombohedral crystal structure with space group R3-C. Magnetic
measurement has indicated the dilution of antiferromagnetic (AFM) spin order in
Ga doped alpha-Cr2O3 system oxide, where the AFM transition temperature of bulk
alpha-Cr2O3 oxide at about 320 K has been suppressed and ferrimagnetic behavior
is observed from the analysis of the temperature dependence of magnetization
data below 350 K. Apart from Ga doping effect, the spin freezing (50 K-70 K)
and superparamagnetic behavior of the surface spins at lower temperatures,
typically below 50 K, have been exhibited due to nano-sized grains of the
samples. All the samples showed non-linear current-voltage (I-V)
characteristics. However, I-V characteristics of the Ga doped samples are
remarkably different from alpha-Cr2O3 sample. The I-V curves of Ga doped
samples have exhibited many unique electronic properties, e.g., bi-stable (low
resistance- LR and high resistance-HR) electronic states and negative
differential resistance (NDR). Optical absorption spectra revealed three
electronic transitions in the samples associated with band gap energy at about
2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively. | 1610.08426v1 |
2018-02-21 | Multi-Terminal Memtransistors from Polycrystalline Monolayer MoS2 | In the last decade, a 2-terminal passive circuit element called a memristor
has been developed for non-volatile resistive random access memory and has more
recently shown promise for neuromorphic computing. Compared to flash memory,
memristors have higher endurance, multi-bit data storage, and faster read/write
times. However, although 2-terminal memristors have demonstrated basic neural
functions, synapses in the human brain outnumber neurons by more than a factor
of 1000, which implies that multiterminal memristors are needed to perform
complex functions such as heterosynaptic plasticity. Previous attempts to move
beyond 2-terminal memristors include the 3-terminal Widrow-Hoff memistor and
field-effect transistors with nanoionic gates or floating gates, albeit without
memristive switching in the transistor. Here, we report the scalable
experimental realization of a multi-terminal hybrid memristor and transistor
(i.e., memtransistor) using polycrystalline monolayer MoS2. Two-dimensional
(2D) MoS2 memtransistors show gate tunability in individual states by 4 orders
of magnitude in addition to large switching ratios with high cycling endurance
and long-term retention of states. In addition to conventional neural learning
behavior of long-term potentiation/depression, 6-terminal MoS2 memtransistors
possess gate-tunable heterosynaptic functionality that is not achievable using
2-terminal memristors. For example, the conductance between a pair of two
floating electrodes (pre-synaptic and post-synaptic neurons) is varied by 10X
by applying voltage pulses to modulatory terminals. In situ scanning probe
microscopy, cryogenic charge transport measurements, and device modeling reveal
that bias-induced MoS2 defect motion drives resistive switching by dynamically
varying Schottky barrier heights. | 1802.07783v1 |
2019-02-20 | Effect of the temperature and magnetic field induced martensitic transformation in bulk Fe$_{45}$Mn$_{26}$Ga$_{29}$ alloy on its electronic structure and physical properties | Effect of the temperature and magnetic field induced martensitic
transformation (MT) on the electronic structure and some physical properties of
bulk Fe$_{45.2}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy has been investigated.
{According to the experimental results of DSC, magnetic and transport
measurements direct and reverse martensitic transformation without external
magnetic field takes place within 194 $\leq T \leq$ 328 K temperature range
with a hysteresis up to $\Delta T \approx$ 100 K defined as $\Delta T$ =
$A_{f,s}$ - $M_{s,f}$, where $A_{f,s}$ and $M_{s,f}$ are the critical
temperatures of direct and reverse martensitic transformation. External
magnetic field of $\mu_{0}H$ = 5 T causes a high-temperature shift of MT
temperatures.} MT from parent austenite L2$_{1}$ phase to martensitic
tetragonally distorted L2$_{1}$ one (i. e. to L1$_{0}$) causes significant
changes in the electronic structure of alloy, a drastic increase in alloy
magnetization, a decrease in the alloy resistivity, and a reversal of the sign
of the temperature coefficient of resistivity from negative to positive. At the
same time experimentally determined optical properties of
Fe$_{45.6}$Mn$_{25.9}$Ga$_{28.9}$ Heusler alloy in austenitic and martensitic
states look visually rather similar being noticeable different in microscopic
nature as can be concluded from first-principle calculations. Experimentally
observed changes in the physical properties of the alloy are discussed in terms
of the electronic structures of an austenite and martensite phases. | 1902.07462v1 |
2020-02-04 | Single-defect Memristor in MoS$_2$ Atomic-layer | Non-volatile resistive switching, also known as memristor effect in two
terminal devices, has emerged as one of the most important components in the
ongoing development of high-density information storage, brain-inspired
computing, and reconfigurable systems. Recently, the unexpected discovery of
memristor effect in atomic monolayers of transitional metal dichalcogenide
sandwich structures has added a new dimension of interest owing to the
prospects of size scaling and the associated benefits. However, the origin of
the switching mechanism in atomic sheets remains uncertain. Here, using
monolayer MoS$_2$ as a model system, atomistic imaging and spectroscopy reveal
that metal substitution into sulfur vacancy results in a non-volatile change in
resistance. The experimental observations are corroborated by computational
studies of defect structures and electronic states. These remarkable findings
provide an atomistic understanding on the non-volatile switching mechanism and
open a new direction in precision defect engineering, down to a single defect,
for achieving optimum performance metrics including memory density, switching
energy, speed, and reliability using atomic nanomaterials. | 2002.01574v1 |
2020-04-07 | Temperature dependence of transport mechanisms in organic multiferroic tunnel junctions | Organic multiferroic tunnel junctions (OMFTJs) with multi-resistance states
have been proposed and drawn intensive interests due to their potential
applications, for examples of memristor and spintronics based synapse devices.
The ferroelectric control of spin-polarization at ferromagnet
(FM)/ferroelectric organic (FE-Org) interface by electrically switching the
ferroelectric polarization of the FE-Org has been recently realized. However,
there is still a lack of understanding of the transport properties in OMFTJs,
especially the interplay between the ferroelectric domain structure in the
organic barrier and the spin-polarized electron tunneling through the barrier.
Here, we report on a systematic study of the temperature dependent transport
behavior in La0.6Sr0.4MnO3/PVDF/Co OMFTJs. It is found that the thermal
fluctuation of the ferroelectric domains plays an important role on the
transport properties. When T>120K, the opposite temperature dependence of
resistance for in up and down ferroelectric polarization states results in a
rapid diminishing of tunneling electroresistance (TER). These results
contribute to the understanding of the transport properties for designing high
performance OMFTJs for memristor and spintronics applications. | 2004.03284v1 |
2020-09-16 | High Field Magneto-Transport of Mixed Topological Insulators Bi2Se3-xTex (x = 0, 1, 2 & 3) | The article comprises structural, microstructural, and physical properties
analysis of Bi2Se3-xTex (x= 0, 1, 2 and 3) mixed topological insulator (MTI)
single crystals. All the crystals were grown through a well-optimized
solid-state reaction route via the self-flux method. These MTI are well
characterized through XRD (X-ray Diffraction), SEM (Scanning Electron
Microscopy), EDAX (Energy Dispersive spectroscopy), and thereby, the physical
properties are analyzed through the RT (Resistance vs temperature) down to 10K
as well as the magneto-resistance (MR) measurements (at 5K) in a magnetic field
of up to 10 Tesla. The MR drastically varies from x=0 to x=3 in MTI, from a
huge 400 percent, it goes down to 20 percent and 5 percent and eventually back
to 315 percent. This fascinated behaviour of MR is explained in this article
through HLN (Hikami-Larkin-Nagaoka) equation and an additional term. This
article not only proposed the mesmerizing behavior of MR in MTI but also
explains the reason through competing WAL (Weak Anti-Localization) and WL (Weak
Localization) conduction processes. | 2009.07757v1 |
2016-03-05 | Development and characterization of single gap glass RPC | India-based Neutrino Observatory (INO) facility is going to have a 50 kton
magnetized Iron CALorimeter (ICAL) detector for precision measurements of
neutrino oscillations using atmospheric neutrinos. The proposed ICAL detector
will be a stack of magnetized iron plates (acting as target material)
interleaved with glass Resistive Plate Chambers (RPCs) as the active detector
elements. An RPC is a gaseous detector made up of two parallel electrode plates
having high bulk resistivity like that of float glass and bakelite. For the
ICAL detector, glass is preferred over bakelite as it does not need any kind of
surface treatment to achieve better surface uniformity and also the cost of
associated electronics is reduced. Under the detector R&D efforts for the
proposed glass RPC detector, a few glass RPCs of 1m X 1m dimension are
fabricated procuring glass of ~ 2 mm thickness from one of the Indian glass
manufacturers (Asahi). In the present paper, we report the characterization of
RPC based on leakage current study, muon detection efficiency and noise rate
studies with varying gas compositions. | 1603.01719v5 |
2017-08-08 | High Surface Conductivity of Fermi Arc Electrons in Weyl semimetals | Weyl semimetals (WSMs), a new type of topological condensed matter, are
currently attracting great interest due to their unusual electronic states and
intriguing transport properties such as chiral anomaly induced negative
magnetoresistance, a semi--quantized anomalous Hall effect and the debated
chiral magnetic effect. These systems are close cousins of topological
insulators (TIs) which are known for their disorder tolerant surface states.
Similarly, WSMs exhibit unique topologically protected Fermi arcs surface
states. Here we analyze electron--phonon scattering, a primary source of
resistivity in metals at finite temperatures, as a function of the shape of the
Fermi arc where we find that the impact on surface transport is significantly
dependent on the arc curvature and disappears in the limit of a straight arc.
Next, we discuss the effect of strong surface disorder on the resistivity by
numerically simulating a tight binding model with the presence of quenched
surface vacancies using the Coherent Potential Approximation (CPA) and
Kubo--Greenwood formalism. We find that the limit of a straight arc geometry is
remarkably disorder tolerant, producing surface conductivity that is a factor
of 50 larger of a comparable set up with surface states of TI. Finally, a
simulation of the effects of surface vacancies on TaAs is presented,
illustrating the disorder tolerance of the topological surface states in a
recently discovered WSM material. | 1708.02415v1 |
2019-08-21 | Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi | We report a combined theoretical and experimental investigation of
half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi.
Room temperature XRD analysis reveals that the alloy crystallizes in L21
disorder instead of pristine Y-type structure due to 50% swap disorder between
the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal
a net magnetization of 4 $\mu_B$ with Curie temperature of ~780 K. Resistivity
measurement reveals the presence of localization effect below 35 K while above
100 K, a linear dependence is observed. Resistivity behavior indicates the
absence of single magnon scattering, which indirectly supports the
half-metallic nature. The majority spin band near the Fermi level clearly
indicates the overlap of flat eg bands with sharply varying conduction bands
that are responsible for the localization. In-depth analysis of the projected
atomic d-orbital character of band structure reveals unusual bonding, giving
rise to the flat eg bands purely arising out of Ru ions. Co-Ru swap disorder
calculations indicate the robustness of half-metallic nature, even when the
structure changes from Y-type to L21-type, with no major change in the net
magnetization of the system. Thus, robust half-metallic nature, stable
structure, and high Curie temperature make this alloy quite a promising
candidate to be used as a source of highly spin-polarized currents in
spintronic applications. | 1908.07804v1 |
2012-03-10 | How local is the Phantom Force? | The phantom force is an apparently repulsive force, which can dominate the
atomic contrast of an AFM image when a tunneling current is present. We
described this effect with a simple resistive model, in which the tunneling
current causes a voltage drop at the sample area underneath the probe tip.
Because tunneling is a highly local process, the areal current density is quite
high, which leads to an appreciable local voltage drop that in turn changes the
electrostatic attraction between tip and sample. However, Si(111)-7\times7 has
a metallic surface-state and it might be proposed that electrons should instead
propagate along the surface-state, as through a thin metal film on a
semiconducting surface, before propagating into the bulk. In this article, we
investigate the role of the metallic surface-state on the phantom force. First,
we show that the phantom force can be observed on H/Si(100), a surface without
a metallic surface-state. Furthermore, we investigate the influence of the
surface-state on our phantom force observations of Si(111)-7\times7 by
analyzing the influence of the macroscopic tip radius R on the strength of the
phantom force, where a noticeable effect would be expected if the local voltage
drop would reach extensions comparable to the tip radius. We conclude that a
metallic surface-state does not suppress the phantom force, but that the local
resistance Rs has a strong effect on the magnitude of the phantom force. | 1203.2258v1 |
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