publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2023-01-18 | Probing electron-electron interaction along with superconducting fluctuations in disordered TiN thin films | Here, we demonstrate an interplay between superconducting fluctuations and
electron-electron interaction (EEI) by low temperature magnetotransport
measurements for a set of 2D disordered TiN thin films. While cooling down the
sample, a characteristic temperature T* is obtained from the R(T) at which
superconducting fluctuations start to appear. The upturn in R(T) above T*
corresponds to weak localization (WL) and/or EEI. By the temperature and field
dependences of the observed resistance, we show that the upturn in R(T)
originates mainly from EEI with a negligible contribution from WL. Further, we
have used the modified Larkins electron-electron attraction strength
beta(T/Tc), containing a field induced pair breaking parameter, in the
Maki-Thompson (MT) superconducting fluctuation term. Here, the temperature
dependence of the beta(T/Tc) obtained from the magnetoresistance analysis shows
a diverging behavior close to Tc and it remains almost constant at higher
temperature within the limit of ln(T/Tc) < 1. Interestingly, the variation of
beta(T/Tc) on the reduced temperature (T/Tc) offers a common trend which has
been closely followed by all the concerned samples presented in this study.
Finally, the temperature dependence of inverse phase scattering time , as
obtained from the magnetoresistance analysis, clearly shows two different
regimes; the first one close to Tc follows the Ginzburg-Landau relaxation rate
, whereas, the second one at high temperature varies almost linearly with
temperature indicating the dominance of inelastic electron-electron scattering
for the dephasing mechanism. These two regimes are followed in a generic way by
all the samples in spite of being grown under different growth conditions. | 2301.07648v1 |
2023-02-08 | Bioabsorbable WE43 Mg alloy wires modified by continuous plasma electrolytic oxidation for implant applications. Part II: degradation and biological performance | The corrosion, mechanical degradation and biological performance of
cold-drawn WE43 Mg wires were analyzed as a function of thermo-mechanical
processing and the presence of a protective oxide layer created by continuous
plasma electrolytic oxidation (PEO). It was found that the corrosion properties
of the non-surface-treated wire could be optimized by means of thermal
treatment within certain limits, but the corrosion rate remained very high.
Hence, strength and ductility of these wires vanished after 24 h of immersion
in simulated body fluid at 37$^\circ$C and, as a result of that rather quick
degradation, direct tests did not show any MC3T3-E1 preosteoblast cell
attachment on the surface of the Mg wires. In contrast, surface modification of
the annealed WE43 Mg wires by a continuous PEO process led to the formation of
a homogeneous oxide layer of $\approx$ 8$\mu$m and significantly improved the
corrosion resistance and hence the biocompatibility of the WE43 Mg wires. It
was found that a dense layer of Ca/P was formed at the early stages of
degradation on top of the Mg(OH)2 layer and hindered the diffusion of the
Cl-ions which dissolve Mg(OH)2 and accelerate the corrosion of Mg alloys. As a
result, pitting corrosion was suppressed and the strength of the Mg wires was
above 100 MPa after 96 h of immersion in simulated body fluid at 37$^\circ$C.
Moreover, many cells were able to attach on the surface of the PEO
surface-modified wires during cell culture testing. These results demonstrate
the potential of thin Mg wires surface-modified by continuous PEO in terms of
mechanical, degradation and biological performance for bioabsorbable wire-based
devices. | 2302.13778v1 |
2023-02-28 | Quantifying interaction mechanism in infinite layer nickelate superconductors | The relationship between the long-range antiferromagnetic order in cuprates
and the high-temperature superconductivity in these compounds represents
unresolved, nearly four-decades long scientific problem. Because recently
discovered nickelate superconductors are crystallographical counterparts of
cuprates, many properties and difficulties into describing these compounds are
common to both families. Recently, Fowlie et al (2022 Nature Physics 18 1043)
aimed to detect the antiferromagnetic order in $R_{1-x}Sr_{x}NiO_{2}$ (R = Nd,
Pr, La, x ~ 0.2) films by using the muon spin rotation (muSR) technique. This
research group reported on the existence of short-range antiferromagnetic order
in all studied nickelates. Here, we aimed to reveal the existence of this
interaction in the same nickelate films by analyzing the temperature dependent
resistivity, $\rho(T)$, reported by the same research group. Global $\rho(T)$
data fits to the advanced Bloch-Gr\"uneisen model showed that each of
R1-xSrxNiO2 compounds can be characterized by a unique power-law exponent, p
(where p=2 for the electron-electron scattering, p=3 for the electron-magnon
scattering, and p=5 for the electron-phonon scattering), and global
characteristic temperature, $T_{\omega}$ (which has the meaning of the Debye
temperature at p=5). We found that p=2.0 in Nd- and Pr-based compounds, and
p=1.3 for La-based compound. The latter value does not have any interpretation
within established theoretical models. We also analyzed $\rho(T)$ data for
$Nd_{1-x}Sr_{x}NiO_{2}$ (0.125 < x < 0.325) reported by Lee et al (2022
arXiv2203.02580). Because our analysis showed that p-values in nickelates are
remarkably different from p=3, we call for the developent of a new theoretical
model to describe $\rho(T)$ in materials exhibiting a short-range
antiferromagnetic order. | 2302.14729v3 |
2023-03-11 | Non-Fermi-Liquid Behavior of Superconducting SnH$_4$ | We studied chemical interaction of Sn with H$_2$ by X-ray diffraction methods
at pressures of 180-210 GPa. A previously unknown tetrahydride SnH$_4$ with a
cubic structure (${fcc}$) exhibiting superconducting properties below ${T}$$_C$
= 72 K was obtained; the formation of a high molecular ${C2/m}$-SnH$_{14}$
superhydride and several lower hydrides, ${fcc}$ SnH$_2$ and
${C2}$-Sn$_{12}$H$_{18}$, was also detected. The temperature dependence of
critical current density ${J}$$_C$(T) in SnH$_4$ yields the superconducting gap
2$\Delta$(0) = 23 meV at 180 GPa. SnH$_4$ has unusual behavior in strong
magnetic fields: ${B,T}$-linear dependences of magnetoresistance and the upper
critical magnetic field ${B}$$_{C2}$(T) $\propto$ (${T}$$_C$ - ${T}$). The
latter contradicts the Wertheimer-Helfand-Hohenberg model developed for
conventional superconductors. Along with this, the temperature dependence of
electrical resistance of ${fcc}$ SnH$_4$ in non-superconducting state exhibits
a deviation from what is expected for phonon-mediated scattering described by
the Bloch-Gr\"uneisen model, and is beyond the framework of the Fermi liquid
theory. Such anomalies occur for many superhydrides, making them much closer to
cuprates than previously believed. | 2303.06339v2 |
2023-06-16 | Tailoring defects and nanocrystal transformation for optimal heating power in bimagnetic $Co_yFe_{1-y}O@Co_xFe_{3-x}O_4$ particles | The effects of cobalt incorporation in spherical heterostructured iron oxide
nanocrystals (NCs) of sub-critical size have been explored by colloidal
chemistry methods. Synchrotron X-ray total scattering methods suggest that
cobalt (Co) substitution in rock salt iron oxide NCs tends to remedy its vacant
iron sites, offering a higher degree of resistance to oxidative conversion.
Self-passivation still creates a spinel-like shell, but with higher volume
fraction of the rock salt Co-containing phase in the core. The higher divalent
metal stoichiometry in the rock salt phase, with increasing Co content, results
in a population of unoccupied tetrahedral metal sites in the spinel part,
likely through oxidative shell creation, involving an ordered defect-clustering
mechanism, directly correlated to the core stabilization. To shed light on the
effects of Co-substitution and atomic-scale defects (vacant sites), Monte Carlo
simulations suggest that designed NCs, with desirable, enhanced magnetic
properties (cf. exchange bias and coercivity), are developed with
magnetocrystalline anisotropy raised at relatively low content of Co ions in
the lattice. Growth of optimally performing candidates combines also a strongly
exchange-coupled system, secured through a high volumetric ratio rock salt
phase, interfaced by a not so defective spinel shell. In view of these
requirements, Specific Absorption Rate (SAR) calculations demonstrate that the
sufficiently protected from oxidation rock salt core and preserved over time
heterostructure, play a key role in magnetically-mediated heating efficacies,
for potential use of such NCs in magnetic hyperthermia applications. | 2306.09684v1 |
2023-11-19 | Discovery of Superconductivity and Electron-Phonon Drag in the Non-Centrosymmetric Weyl Semimetal LaRhGe$_3$ | We present an exploration of the effect of electron-phonon coupling and
broken inversion symmetry on the electronic and thermal properties of the
semimetal LaRhGe$_3$. Our transport measurements reveal evidence for
electron-hole compensation at low temperatures, resulting in a large
magnetoresistance of 3000% at 1.8 K and 14 T. The carrier concentration is on
the order of $10^{21}\rm{/cm}^3$ with high carrier mobilities of
$2000~\rm{cm}^2/\rm{Vs}$. When coupled to our theoretical demonstration of
symmetry-protected $\textit{almost movable}$ Weyl nodal lines, we conclude that
LaRhGe$_3$ supports a Weyl semimetallic state. We discover superconductivity in
this compound with a $T_{\text c}$ of 0.39(1) K and $B_{\rm{c}}(0)$ of 2.2(1)
mT, with evidence from specific heat and transverse-field muon spin relaxation.
We find an exponential dependence in the normal state electrical resistivity
below $\sim50$ K, while Seebeck coefficient and thermal conductivity
measurements each reveal a prominent peak at low temperatures, indicative of
strong electron-phonon interactions. To this end, we examine the
temperature-dependent Raman spectra of LaRhGe$_3$ and find that the lifetime of
the lowest energy $A_1$ phonon is dominated by phonon-electron scattering
instead of anharmonic decay. We conclude that LaRhGe$_3$ has strong
electron-phonon coupling in the normal state, while the superconductivity
emerges from weak electron-phonon coupling. These results open up the
investigation of electron-phonon interactions in the normal state of
superconducting non-centrosymmetric Weyl semimetals. | 2311.11402v2 |
2024-01-10 | Droplet morphology-based wettability tuning and design of fog harvesting mesh to minimize mesh-clogging | Fog harvesting relies on intercepting atmospheric or industrial fog by
placing a porous obstacle, e.g., a mesh and collecting the deposited water. In
the face of global water scarcity, such fog harvesting has emerged as a viable
alternative source of potable water. Typical fog harvesting meshes suffer from
poor collection efficiency due to aerodynamic bypassing of the oncoming fog
stream and poor collection of the deposited water from the mesh. One pestering
challenge in this context is the frequent clogging up of mesh pores by the
deposited fog water, which not only yields low drainage efficiency but also
generates high aerodynamic resistance to the oncoming fog stream, thereby
negatively impacting the fog collection efficiency. Minimizing the clogging is
possible by rendering the mesh fiber superhydrophobic, but that entails other
detrimental effects like premature dripping and flow-induced re-entrainment of
water droplets into the fog stream from the mesh fiber. Herein, we improvise on
the traditional interweaved metal mesh designs by defining critical parameters,
viz., mesh pitch, shade coefficient, and fiber wettability, and deduce their
optimal values from numerically and experimentally observed morphology of
collected fog-water droplets under various operating scenarios. We extend our
investigations over a varying range of mesh-wettability, including
superhydrophilic and hydrophobic fibers, and go on to find optimal shade
coefficients which would theoretically render clog-proof fog harvesting meshes.
The aerodynamic, deposition, and overall collection efficiencies are
characterized. Hydrophobic meshes with square pores, having fiber diameters
smaller than the capillary length scale of water, and an optimal shade
coefficient, are found to be the most effective design of such clog-proof
meshes. | 2401.05284v2 |
2024-02-18 | Impact of the La2NiO4+δ oxygen content on the synaptic properties of the TiN/La2NiO4+δ/Pt memristive devices | The rapid development of brain-inspired computing requires new artificial
components and architectures for its hardware implementation. In this regard,
memristive devices emerged as potential candidates for artificial synapses
because of their ability to emulate the plasticity of the biological synapses.
In this work, the synaptic behavior of the TiN/La2NiO4+{\delta}/Pt memristive
devices based on thermally annealed La2NiO4+{\delta} films is thoroughly
investigated. Using electron energy loss spectroscopy, we show that annealing
using reducing (Ar) or oxidizing (O2) atmospheres affects the interstitial
oxygen content ({\delta}) in the La2NiO4+{\delta} films. Electrical
characterization shows that both devices exhibit long-term
potentiation/depression and spike-timing-dependent plasticity, which makes them
suitable for neuromorphic applications. At the same time, the Ar annealed
TiN/La2NiO4+{\delta}/Pt device demonstrates non-volatile properties with low
energy consumption during the learning process. On the other hand, in the O2
annealed TiN/La2NiO4+{\delta}/Pt device the resistive switching behavior is
more volatile and requires more energy for synaptic learning. Finally, the
simulation tools show that spiking neural network architectures with
unsupervised learning rules based on the experimental data achieve high
inference accuracy in the digit recognition task, which proves the potential of
TiN/La2NiO4+{\delta}/Pt devices for artificial synapse applications. | 2402.11612v1 |
2024-03-12 | Electronic and dynamical properties of cobalt monogermanide CoGe phases under pressure | We present the pressure dependence of the electronic and dynamical properties
of six different CoGe phases: orthorhombic Cmmm, hexagonal P6/mmm and
P$\bar{6}$2m, monoclinic C2/m, cubic P2$_{1}$3, and orthorhombic Pnma. Using
first-principles DFT calculations and the direct force-constants method, we
study the dynamical stability of individual phases under external pressure. We
show that the orthorombic Cmmm and hexagonal P6/mmm structures are unstable
over a broad pressure range and most pronounced imaginary phonon soft mode in
both cases leads to a stable hexagonal P$\bar{6}$2m structure of the lowest
ground-state energy of all studied phases at ambient and low (below $\sim 3$
GPa) external pressure. Under these conditions, the cubic P2$_{1}$3 phase has
the highest energy, however, together with monoclinic C2/m and orthorombic Pnma
it is dynamically stable and all these three structures can potentially coexist
as meta-stable phases. Above $\sim 3$ GPa, the cubic P2$_{1}$3 phase becomes
the most energetically favorable. Fitting the Birch--Murnaghan equation of
state we derive bulk modulus for all mentioned phases, which indicate
relatively high resistance of CoGe to compression. Such conclusions are
confirmed by band structure calculations. Additionally, we show that electronic
bands of the hexagonal P$\bar{6}$2m phase reveal characteristic features of the
kagome-like structure, while in the cubic P2$_{1}$3 phase spectrum, one can
locate spin-1 and double Weyl fermions. In both cases, the external pressure
induces the Lifshitz transition, related to the modification of the Fermi
surface topology. | 2403.07580v1 |
1996-07-09 | Anomalous magnetic response of the valence-fluctuating compound YbInCu4 | The exact solution of the spin one-half Falicov-Kimball model, with random
hopping between the lattice sites, is used to explain the anomalous magnetic
response of Yb-based valence-fluctuating intermetallic compounds. The anomalous
behavior arises from an entropy-driven local-moment--nonmagnetic transition of
unhybridized Yb ions in these materials which can also be used to explain the
observed metamagnetism and resistivity anomalies. | 9607068v1 |
1996-09-27 | Magnetoresistance in La(1-x)SrxCoO3 for 0.05 - x - 0.25 | The dc resistivity, magnetoresistance and magnetic susceptibility of
La(1-x)SrxCoO3 compounds have been investigated in the temperature range of 4K
to 300K for magnetic fields up to 7 T. In the doping range studied (0.05 - x -
0.25) the electronic properties of the material exhibit a crossover from
semiconducting to metallic behavior. The magnetoresistance is highest in the
semiconducting state. A correlation was found between the energy gap determined
from the dc conductivity and the energy scale identified from neutron
scattering data. The results are interpreted in terms of a double exchange
model. | 9609274v1 |
1997-07-01 | e-h Coherence and Charging Effects in Ultrasmall Metallic Grains | We consider a model for electron tunneling between a pair of ultrasmall
metallic grains. Under appropriate circumstances, non-equilibrium final state
effects can strongly enhance tunneling and produce electron-hole coherence
between the grains. The model displays a quantum phase transition between a
Coulomb blockaded state to a coherent state exhibiting subohmic tunneling
conductance. The critical state of the junction exhibits a temperature
independent resistance of order $h/e^2$. Finally we discuss the possible
relevance to granular materials and quantum dots. In particular, similarities
between the quantum transition in our model and the metal-insulator transition
in granular wires observed by Herzog et al. are described in detail. | 9707014v1 |
1997-07-18 | Shearing the Vacuum - Quantum Friction | We consider two perfectly smooth featureless surfaces at T=0, defined only by
their respective dielectric functions, separated by a finite distance, and ask
the question whether they can experience any friction when sheared parallel to
their interface. We find large frictional effects comparable to everyday
frictional forces provided that the materials have resistivities of the order
of 1 m-Ohm and that the surfaces are in close proximity. The friction depends
solely on the reflection coefficients of the surfaces to electromagnetic waves
and its detailed behaviour with shear velocity and separation is dictated by
the dispersion of the reflectivity with frequency. | 9707190v2 |
1998-02-25 | Magnetization Controlled Superconductivity in a Film with Magnetic Dots | We consider a superconducting film with Magnetic Dots Array (MDA) placed on
it. Magnetic moments of these dots are supposed to be normal to the film and
strong enough to create vortices in the superconducting film. Magnetic
interaction between dots is negligible. Below the superconducting transition
temperature of the film in zero magnetic field the MDA with randomly magnetized
dots produces resistive state of the film. Paradoxically, in a finite magnetic
field the film with MDA is superconductive. | 9802276v1 |
1998-03-28 | Anomalous Hall Effect in Double Exchange Magnets | We investigate the possible origin of anomalous Hall effect in the CMR
(colossal magnetoresistance) materials - the doped rare earth manganites -
observed recently by Matl et al. It is demonstrated that the spin-orbit
interaction in the double exchange model couples magnetization to the Berry
phase associated with three dimensional spin textures and induces a non-zero
average topological flux which in turn generates an anomalous contribution to
transverse resistivity. The same effect, but involving the orbital Berry phase,
occurs in the model with orbital degeneracy and Coulomb repulsion. | 9803350v1 |
1998-07-13 | Magnetoresistance of Epitaxial Fe Wires with Varied Domain Wall Structure | The low temperature negative domain wall (DW) contribution to the resistivity
observed in expitaxial Fe microstructures has been investigated as a function
of film thickness. The DW spin structure changes from Bloch to Neel-like with
decreasing film thickness. Results suggest that an interplay between orbital
effects in the internal magnetic fields near DWs and thin film surface
scattering are at the origin of the observed negative wall contribution. | 9807183v1 |
1998-09-02 | Rolling friction of a hard cylinder on a viscous plane | The resistance against rolling of a rigid cylinder on a flat viscous surface
is investigated. We found that the rolling-friction coefficient reveals
strongly non-linear dependence on the cylinder's velocity. For low velocity the
rolling-friction coefficient rises with velocity due to increasing deformation
rate of the surface. For larger velocity, however, it decreases with velocity
according to decreasing contact area and deformation of the surface. | 9809053v1 |
1998-12-10 | Electric field and potential around localized scatterers in thin metal films studied by scanning tunneling potentiometry | Direct observation of electric potential and field variation near local
scatterers like grain boundaries, triple points and voids in thin platinum
films studied by scanning tunneling potentiometry is presented. The field is
highest at a void, followed by a triple point and a grain boundary. The local
field near a void can even be four orders of magnitude higher than the
macroscopic field. This indicates that the void is the most likely place for an
electromigration induced failure. The field build up near a scatterer strongly
depends on the grain connectivity which is quantified by the average grain
boundary reflection coefficient, estimated from the resistivity. | 9812167v1 |
1999-01-11 | Effect of disorder on the Kondo behavior of thin Cu(Mn) films | We have studied the influence of disorder on the Kondo effect in thin films
of Cu(Mn), i.e., Cu doped with a small amount of Mn. We find that the Kondo
contribution to the resistivity is suppressed when the elastic mean-free-path,
$\lambda$, is reduced. While this is qualitatively similar to results found
previously by our group in a different material, our new experiments reveal in
detail how this suppression depends on both film thickness and $\lambda$. These
results are compared with the theory of Martin, Wan, and Phillips. While there
is general qualitative agreement with this theory, there appear to be some
quantitative discrepancies. | 9901092v1 |
1999-03-10 | Large Thermopower in a Layered Oxide NaCo_2O_4 | A transition-metal oxide NaCo_2O_4 is a layered oxide in which CoO_2 and Na
alternately stack along the c axis. Recently we have found that this compound
shows unusually large thermopower with low resistivity, which is comparable to
those of Bi_2Te_3. The negative transverse magnetoresistance and the strongly
temperature-dependent Hall coefficient suggest that electron correlation
dominates the conduction mechanism in NaCo_2O_4. | 9903162v1 |
1999-07-05 | Chiral Glass Phase in Ceramic Superconductors | A three-dimensional lattice of the Josephson junctions with a finite
self-conductance is employed to model the ceramic superconductors. By Monte
Carlo simulations it is shown that the chiral glass phase is stable in three
dimensions even under the influence of screening. The nonlinear ac
susceptibility and the compensation effect are also studied. The compensation
effect is shown to be due to the existence of the chiral glass phase. In
agreement with experiments, this effect is demonstrated to be present in the
ceramic superconductors which show the paramagnetic Meissner effect. | 9907060v1 |
1999-09-01 | Polyethylene under tensile load: strain energy storage and breaking of linear and knotted alkanes probed by first-principles molecular dynamics calculations | The mechanical resistance of a polyethylene strand subject to tension and the
way its properties are affected by the presence of a knot is studied using
first-principles molecular dynamics calculations. The distribution of strain
energy for the knotted chains has a well-defined shape that is very different
from the one found in the linear case. The presence of a knot significantly
weakens the chain in which it is tied. Chain rupture invariably occurs just
outside the entrance to the knot, as is the case for a macroscopic rope. | 9909013v1 |
1999-11-09 | Heat capacity and transport studies of the ferromagnetic superconductor RuSr2GdCu2O8 | Resistivity, thermoelectric power and heat capacity are investigated in the
ferromagnetic superconductor RuSr2GdCu2O8 with and without Zn substitution. The
thermodynamic signatures of the ordering of the Ru moments and the paramagnetic
Gd moments as well as the onset of superconductivity are all clearly seen and
quantified. The materials are shown to exhibit bulk superconductivity which
coexists with spatially-uniform ferromagnetism. They appear to be typical
underdoped superconducting cuprates in which the pseudogap dominates
normal-state transport, thermodynamic and substitutional properties. However, a
field-induced increase in Tc could suggest some degree of triplet pairing. | 9911135v1 |
2000-02-14 | Scanned Probe Microscopy of Electronic Transport in Carbon Nanotubes | We use electrostatic force microscopy and scanned gate microscopy to probe
the conducting properties of carbon nanotubes at room temperature. Multi-walled
carbon nanotubes are shown to be diffusive conductors, while metallic
single-walled carbon nanotubes are ballistic conductors over micron lengths.
Semiconducting single-walled carbon nanotubes are shown to have a series of
large barriers to conduction along their length. These measurements are also
used to probe the contact resistance and locate breaks in carbon nanotube
circuits. | 0002209v1 |
2000-03-27 | Current and power spectrum in a magnetic tunnel device with an atomic size spacer | Current and its noise in a ferromagnetic double tunnel barrier device with a
small spacer particle were studied in the framework of the sequential tunneling
approach. Analytical formulae were derived for electron tunneling through the
spacer particle containing only a single energy level. It was shown that
Coulomb interactions of electrons with a different spin orientation lead to an
increase of the tunnel magnetoresistance. Interactions can also be responsible
for the negative differential resistance. A current noise study showed, which
relaxation processes can enhance or reduce fluctuations leading either to a
super-Poissonian or a sub-Poissonian shot noise. | 0003418v1 |
2000-05-25 | Magnetic-Field-Driven Superconductor-Insulator-Type Transition in Graphite | A magnetic-field-driven transition from metallic- to semiconducting-type
behavior in the basal-plane resistance takes place in highly oriented pyrolytic
graphite at a field $H_c \sim 1~$kOe applied along the hexagonal c-axis. The
analysis of the data reveals a striking similarity between this transition and
that measured in thin-film superconductors and Si MOSFET's. However, in
contrast to those materials, the transition in graphite is observable at almost
two orders of magnitude higher temperatures. | 0005439v1 |
2000-11-29 | Giant Magnetoresistance at the Interface of Iron Thin Films | Ag/Fe/Ag and Cr/Fe/Cr trilayers with a single $25 nm$ thick ferromagnetic
layer exhibit giant magnetoresistance (GMR) type behavior. The resistance
decreases for parallel and transversal magnetic field alignements with a
Langevin-type magnetic field dependence up to B=12 T. The phenomenon is
explained by a granular interface structure. Results on Fe/Ag multilayers are
also interpreted in terms of a granular interface magnetoresistance. | 0011491v1 |
2001-01-22 | Orbital Correlations in the Ferromagnetic Half-Metal $CrO_{2} | We deduce a model relevant for the description of the ferromagnetic
half-metal Chromium dioxide ($CrO_{2}$), widely used in magnetic recording
technology. The model describes the effect of dynamical, local orbital
correlations arising from local quantum chemistry of the material. A finite
temperature solution of the model in $d=\infty$ provides a natural explanation
of the optical response, photoemission, resistivity and the large Woods-Saxon
ratio observed in experiments. Our study confirms the important role of many
body dynamical correlation effects for a proper understanding of the metallic
phase of $CrO_{2}$. | 0101335v1 |
2001-03-06 | Coherent description of electrical and thermal impurity-and-phonon limited transport in simple metals | The electrical resistivity, thermoelectric power and electronic thermal
conductivity of simple (isotropic) metals are studied in a uniform way.
Starting from results of a variational solution of the Boltzmann equation, a
generalized Matthiessen rule is used in order to superpose the inelastic (or
not) electron-phonon and elastic electron-impurity scattering cross sections
("matrix elements"). The temperature dependence relative to these processes is
given through simple functions and physical parameters over the usually
investigated range of temperature for each transport coefficient. The coherence
of such results is emphasized. | 0103138v1 |
2001-03-08 | Localization corrections to the anomalous Hall effect in a ferromagnet | We calculate the localization corrections to the anomalous Hall conductivity
related to the contribution of spin-orbit scattering into the current vertex
(side-jump mechanism). We show that in contrast to the ordinary Hall effect,
there exists a nonvanishing localization correction to the anomalous Hall
resistivity. The correction to the anomalous Hall conductivity vanishes in the
case of side-jump mechanism, but is nonzero for the skew scattering. The total
correction to the nondiagonal conductivity related to both mechanisms, does not
compensate the correction to the diagonal conductivity. | 0103182v1 |
2001-03-23 | Premartensitic Transition in Ni2+xMn1-xGa Heusler Alloys | The temperature dependencies of the resistivity and magnetization of a series
of Ni2+XMn1-XGa (X = 0 - 0.09) alloys were investigated. Along with the
anomalies associated with ferromagnetic and martensitic transitions,
well-defined anomalies were observed at the temperature of premartensitic
transformation. The premartensitic phase existing in a temperature range 200 -
260 K in the stoichiometric Ni2MnGa is suppressed by the martensitic phase with
increasing Ni content and vanishes in Ni2.09Mn0.91Ga composition. | 0103483v1 |
2001-04-24 | Electrical current distribution across a metal-insulator-metal structure during bistable switching | Combining scanning electron microscopy (SEM) and electron-beam-induced
current (EBIC) imaging with transport measurements, it is shown that the
current flowing across a two-terminal oxide-based capacitor-like structure is
preferentially confined in areas localized at defects. As the thin-film device
switches between two different resistance states, the distribution and
intensity of the current paths, appearing as bright spots, change. This implies
that switching and memory effects are mainly determined by the conducting
properties along such paths. A model based on the storage and release of charge
carriers within the insulator seems adequate to explain the observed memory
effect. | 0104452v1 |
2001-04-24 | A simple one-dimensional model of heat conduction which obeys Fourier's law | We present the computer simulation results of a chain of hard point particles
with alternating masses interacting on its extremes with two thermal baths at
different temperatures. We found that the system obeys Fourier's law at the
thermodynamic limit. This result is against the actual belief that one
dimensional systems with momentum conservative dynamics and nonzero pressure
have infinite thermal conductivity. It seems that thermal resistivity occurs in
our system due to a cooperative behavior in which light particles tend to
absorb much more energy than the heavier ones. | 0104453v1 |
2001-06-29 | Landau diamagnetism revisited | The problem of diamagnetism, solved by Landau, continues to pose fascinating
issues which have relevance even today. These issues relate to inherent quantum
nature of the problem, the role of boundary and dissipation, the meaning of
thermodynamic limits, and above all, the quantum-classical crossover occasioned
by environment-induced decoherence. The Landau Diamagnetism provides a unique
paradigm for discussing these issues, the significance of which are
far-reaching. Our central result is a remarkable one as it connects the mean
orbital magnetic moment, a thermodynamic property, with the electrical
resistivity, which characterizes transport properties of materials. | 0106646v1 |
2001-07-12 | Theory of Angular Magnetoresistance in CPP spin valves | The resistance of CPP spin valve is a continuous function of the angle
$\theta $ between the magnetizations of both ferromagnets. We use the cicuit
theory for non-collinear magnetoelectronics to compute the angular
magnetoresistance of CPP spin valves taking the spin accumulation in the
ferromagnetic layers into account. | 0107250v1 |
2001-07-27 | Large magnetoresistance using hybrid spin filter devices | A magnetic "spin filter" tunnel barrier, sandwiched between a non-magnetic
metal and a magnetic metal, is used to create a new magnetoresistive tunnel
device, somewhat analogous to an optical polarizer-analyzer configuration. The
resistance of these trilayer structures depends on the relative magnetization
orientation of the spin filter and the ferromagnetic electrode. The spin
filtering in this configuration yields a previously unobserved
magnetoresistance effect, exceeding 100%. | 0107571v1 |
2001-08-17 | Negative Magneto-Resistance Beyond Weak Localization in Three-Dimensional Billiards: Effect of Arnold Diffusion | We investigate a semiclassical conductance for ballistic open
three-dimensional (3-d) billiards. For partially or completely broken-ergodic
3-d billiards such as SO(2) symmetric billiards, the dependence of the
conductance on the Fermi wavenumber is dramatically changed by the lead
orientation. Application of a symmetry-breaking weak magnetic field brings
about mixed phase-space structures of 3-d billiards which ensures a novel
Arnold diffusion that cannot be seen in 2-d billiards. In contrast to the 2-d
case, the anomalous increment of the conductance should inevitably include a
contribution arising from Arnold diffusion as well as a weak localization
correction. Discussions are devoted to the physical condition for observing
this phenomenon. | 0108276v1 |
2001-08-29 | Anomalous Co-site substitution effects on the physical properties of the thermoelectric oxide NaCo2O4 | We prepared polycrystalline samples of NaCo2-xMxO4 substituted for the Co
site by other 3d or 4d elements (M=Mn,Cu, Zn, Ru, Rh, and Pd). While some of
the elements (M=Mn,Ru and Rh) act as a strong scatterer to give rise to a rapid
increase in resistivity, the others (M=Cu, Zn and Pd) do not deteriorate the
electric conduction of the host. Most unusually, the Cu substitution
significantly enhances the thermopower, which increases the figure of merit by
several times at 100 K. | 0108485v1 |
2001-10-05 | Successive Phase Transitions in a Metal-Ordered Manganite Perovskite YBaMn2O6 | Structural, magnetic and electric properties of a metal-ordered perovskite
YBaMn2O6 have been studied by means of powder X-ray diffraction, DSC, magnetic
susceptibility, and electric resistivity. It is found that this material
undergoes a 1st order structural phase transition at Tc1=520 K, from a pseudo
orthorhombic (monoclinic) phase to a pseudo tetragonal (monoclinic) one.
Accompanied by this transition, the susceptibility exhibits a sharp drop, where
ferromagnetic exchange interaction becomes antiferromagnetic. Furthermore, two
more transitions, a metal-insulator transition at Tc2=480 K and an
antiferromagnetic ordering at Tc3=200 K, have been observed respectively. | 0110114v1 |
2002-04-29 | Nonlinear charging, and transport times in doped nanotubes junctions | The nonlinear capacitance in doped nanotube junctions is calculated self
consistently. It decreases as a function of the applied bias when the latter
becomes larger than the pseudogap of the nanotube. For this device, one can
deduce a relaxation time of about 0.1 femtosecond. Because of its negative
differential resistance (NDR), a switching time of less than a fs can also be
deduced. | 0204609v3 |
2002-06-24 | Boltzmann theory of engineered anisotropic magnetoresistance in (Ga,Mn)As | We report on a theoretical study of dc transport coefficients in (Ga,Mn)As
diluted magnetic semiconductor ferromagnets that accounts for quasiparticle
scattering from ionized Mn$^{2+}$ acceptors with a local moment $S=5/2$ and
from non-magnetic compensating defects. In metallic samples Boltzmann transport
theory with Golden rule scattering rates accounts for the principle trends of
the measured difference between resistances for magnetizations parallel and
perpendicular to the current. We predict that the sign and magnitude of the
anisotropic magnetoresistance can be changed by strain engineering or by
altering chemical composition. | 0206416v1 |
2002-07-16 | Carbon Nanotubes as Schottky Barrier Transistors | We show that carbon nanotube transistors operate as unconventional "Schottky
barrier transistors", in which transistor action occurs primarily by varying
the contact resistance rather than the channel conductance. Transistor
characteristics are calculated for both idealized and realistic geometries, and
scaling behavior is demonstrated. Our results explain a variety of experimental
observations, including the quite different effects of doping and adsorbed
gases. The electrode geometry is shown to be crucial for good device
performance. | 0207397v1 |
2002-09-13 | Some Thermal and Electrical Properties of Candelilla Wax | We report the values of some thermal and electrical properties of Candelilla
Wax (euphorbia cerifera). The open-cell photoacoustic technique and another
photothermic technique - based on the measure of the temperature decay of a
heated sample - were employed to obtain the thermal diffusivity ($\alpha_{s} =
0.026 \pm 0.00095 {cm}^{2}{/sec}$) as well as the thermal conductivity
($k=2.132 \pm 0.16 {W/mK}$) of this wax. The Kelvin null method was used to
measure the dark decay of the surface potential of the sample after a Corona
Discharge, obtaining a resistivity of $\rho_e=5.98 \pm 0.19 \times 10^{17}
{ohm-cm}$. | 0209328v1 |
2002-09-25 | Magnetic properties of Ni2.18Mn0.82Ga Heusler alloys with a coupled magnetostructural transition | Polycrystalline Ni2.18Mn0.82Ga Heusler alloys with a coupled
magnetostructural transition are studied by differential scanning calorimetry,
magnetic and resistivity measurements. Coupling of the magnetic and structural
subsystems results in unusual magnetic features of the alloy. These uncommon
magnetic properties of Ni2.18Mn0.82Ga are attributed to the first-order
structural transition from a tetragonal ferromagnetic to a cubic paramagnetic
phase. | 0209574v1 |
2002-10-04 | The Effects of the Misfit Structure on Thermoelectric Properties of Bi2-xPbxSr2Co2Oy Single Crystals | In-plane anisotropy of the resistivity and thermopower was measured for
single crystal Bi2-xPbxSr2Co2Oy. There is large in-plane anisotropy, which is
attributed to the anisotropic pseudogap formation due to the different crystal
symmetry between the square Bi2Sr2O4 layer and the triangular CuO2 layer. The
magnitude of the thermopower both along a- and b-axis direction increases with
Pb doping from x=0 to 0.4, where we observe discontinuous shrink of b-axis
length. We attribute this to the enhancement of the misfitness. Thus, we can
improve the thermoelectric properties by tuning the misfitness. | 0210087v1 |
2002-10-21 | Competing SDW Phases and Quantum Oscillations in (TMTSF)2ClO4 in Magnetic Field | We propose a new approach for studying spin density waves (SDW) in the
Bechgaard salt (TMTSF)2ClO4 where lattice is dimerized in transverse direction
due to anion ordering. The SDW response is calculated in the matrix formulation
that rigorously treats the hybridization of inter-band and intra-band SDW
correlations. Since the dimerization gap is large, of the order of transverse
bandwidth, we also develop an exact treatment of magnetic breakdown in the
external magnetic field. The obtained results agree with the experimental data
on the fast magneto-resistance oscillations. Experimentally found 260T rapid
oscillations and the characteristic Tc dependance on magnetic field of relaxed
material are fitted with our results for anion potential of the order of
interchain hopping. | 0210452v1 |
2002-10-28 | Fine "mist" vs large droplets in phase separated manganites | The properties of phase-separated systems, e.g. manganites, close to a I
order phase transition between charge-ordered insulator and ferromagnetic
metal, are usually described by the percolation picture. We argue that the
correlated occupation of metallic sites leads to the preferential formation of
larger metallic clusters, which explains the often observed inverse, or
``overshot'' hysteresis in manganites (when the resistivity with increasing
temperature is larger than with decreasing T). It also explains the recently
discovered thermal cycling effect in manganites. Thus in treating this and
similar systems in percolation picture, not only the total concentration of
metallic phase, but also the distribution of metallic clusters by shape and
size may significantly influence the properties of such systems. | 0210616v1 |
2002-11-12 | Infrared properties of W-doped charge-density-wave material K$_{0.3}$MoO$_3$ | The optical conductivity spectra of quasi-one dimensional compounds
K$_{0.3}$Mo$_{1-x}$W$_x$O$_3$ (x=0, 0.03 and 0.15) have been studied over broad
frequencies. While the dc resistivity measurements indicate no sign of CDW
transition in heavily W-doped blue bronze, the optical conductivity spectra
still show a single particle gap at around 0.2 eV for \textbf{E} parallel to
the chain direction. Such impurity effect challenges our understanding about
the occurrence of the optical gap with the CDW transition. | 0211225v1 |
2002-11-18 | Anomalous Hall Effect of Reentrant Spin Glass System Fe1-xAlx (x ~ 0.3) | The anomalous Hall coefficient Rs has been studied for the reentrant spin
glass system Fe0.7Al0.3 by measuring the magnetization M and the Hall
resistivity r_H. We have found that R_s exhibits anomalous temperature
dependence at the spin-glass transition temperature T_G, indicating that an
additional term appears along with the beginning of the spin glass phase. The
result is discussed in relation to the recent proposal of the chirality
mechanism of the Hall effect in the spin glass phase. | 0211368v1 |
2002-12-01 | The superconducting gap of \QTR{em}{in situ} $MgB_{2}$ thin films by microwave surface impedance measurements | Precision measurements of the microwave surface resistance $R_{s}$ of in situ
$MgB_{2}$ films directly reveal an exponential behavior of $R_{s}$ at low
temperature indicating a fully-gapped order parameter. The entire temperature
dependence of $R_{s}$ is well described by a Mattis-Bardeen formalism but with
a small gap ratio of $\Delta (0)/kT_{c}=0.72$, corresponding to $\Delta
(0)=1.9meV$. | 0212009v1 |
2002-12-09 | Conductance switching in a molecular device: the role of sidegroups and intermolecular interactio | We report first-principles studies of electronic transport in monolayers of
Tour wires functionalized with different side groups. An analysis of the
scattering states and transmission eigenchannels suggests that the
functionalization does not strongly affect the resonances responsible for
current flow through the monolayer. However, functionalization has a
significant effect on the interactions within the monolayer, so that monolayers
with NO$_2$ side groups exhibit local minima associated with twisted
conformations of the molecules. We use our results to interpret observations of
negative differential resistance and molecular memory in monolayers of NO$_2$
functionalized molecules in terms of a twisting of the central ring induced by
an applied bias potential. | 0212191v1 |
2003-04-24 | The spin-torque transistor | A magnetoelectronic thin-film transistor is proposed that can display
negative differential resistance and gain. The working principle is the
modulation of the soure-drain current in a spin valve by the magnetization of a
third electrode, which is rotated by the spin-torque created by a control
spin-valve. The device can operate at room temperature, but in order to be
useful, ferromagnetic materials with polarizations close to unity are required. | 0304550v1 |
2003-05-27 | Double Magnetic Transition in Pr0.5Sr0.5CoO3 | We report studies of polycrystalline samples of the metallic ferromagnet
Pr0.5Sr0.5CoO3 through measurements of the magnetization, a.c. magnetic
susceptibility, resistivity, and specific heat. We find an unusual anomaly
around TA = 120 K, much below the ferromagnetic transition (TC = 226 K). The
anomaly is manifested in field cooled magnetization as a downward step in low
fields (H less than or equal to 0.01 T) but is transformed into an upward step
for H greater than or equal to 0.05 T. The anomaly cannot be easily attributed
to antiferromagnetic ordering, but may correspond to a second ferromagnetic
transition or an alteration of the ferromagnetic state associated with orbital
ordering. | 0305621v1 |
2003-06-08 | Analysis Of Critical Power Loss In A Superconductor | A critical power dissipation resulting from an oscillating magnetic field, Hp
cos wt, can produce a magnetic breakdown field, H <Hc, the critical field of
the superconductor. The analysis shows, for example, why the breakdown field of
a superconducting microwave cavity can be well below Hc in some cases, and
indicates what the functional dependence of the cavity Q may be for values of
Hp near H . The effective resistivity of a single isolated oscillating fluxoid,
as well as that of a stationary normal region, is also derived for both type I
and type Il superconductors. | 0306202v1 |
2003-07-11 | Enhanced thermoelectric properties of NaxCoO2 whisker crystals | Single-crystalline whiskers of thermoelectric cobalt oxide, NaxCoO2, have
been grown by an unconventional method from potassium-containing compositions,
and their transport properties, and chemical compositions were determined. The
growth mechanism was analyzed and interpreted by means of thermogravimetric
analysis. At 300 K, electrical resistivity r and thermoelectric power S of the
whisker are 102 u ohm cm and 83 uV/K, respectively. The power-factor, S2/r,
thus is enhanced up to ~ 68 uW/K2 cm. | 0307277v1 |
2003-07-31 | Reflection of electrons from a domain wall in magnetic nanojunctions | Electronic transport through thin and laterally constrained domain walls in
ferromagnetic nanojunctions is analyzed theoretically. The description is
formulated in the basis of scattering states. The resistance of the domain wall
is calculated in the regime of strong electron reflection from the wall. It is
shown that the corresponding magnetoresistance can be large, which is in a
qualitative agreement with recent experimental observations. We also calculate
the spin current flowing through the wall and the spin polarization of electron
gas due to reflections from the domain wall. | 0307765v1 |
2003-08-16 | Frequency Dependence of Superconducting Cavity Q and Magnetic Breakdown Field | A theoretical explanation is given to account for the unexpected observation
that L- and S-band Nb superconducting cavities were found to have lower Q and
lower magnetic breakdown field than those of the higher X-band frequencies.
Both effects can be related to the trapping of magnetic flux in the cavity
walls. The frequency dependence arises from the frequency dependence of the
resistivity of oscillating fluxoids. Calculations based on this model are in
agreement with experimental observations. | 0308324v1 |
2003-08-22 | Relevance of Cooperative Lattice Effects and Correlated Disorder in Phase-Separation Theories for CMR Manganites | Previous theoretical investigations of colossal magnetoresistance (CMR)
materials explain this effect using a ``clustered'' state with preformed
ferromagnetic islands that rapidly align their moments with increasing external
magnetic fields. While qualitatively successful, explicit calculations indicate
drastically different typical resistivity values in two- and three-dimensional
lattices, contrary to experimental observations. This conceptual bottleneck in
the phase-separated CMR scenario is resolved here considering the cooperative
nature of the Mn-oxide lattice distortions. This induces power-law correlations
in the quenched random fields used in toy models with phase competition. When
these effects are incorporated, resistor-network calculations reveal very
similar results in two and three dimensions, solving the puzzle. | 0308456v1 |
2003-09-13 | Metal-insulator transition in Ca_{1-x}Li_xPd_3O_4 | Metal-insulator transition in Ca_{1-x}Li_xPd_3O_4 has been studied through
charge transport measurements. The resistivity, the Seebeck coefficient, and
the Hall coefficient are consistently explained in terms of a simple one-band
picture, where a hole with a moderately enhanced mass is itinerant
three-dimensionally. Contrary to the theoretical prediction [Phys. Rev. B62,
13426 (2000)], CaPd_3O_4 is unlikely to be an excitonic insulator, and holds a
finite carrier concentration down to 4.2 K. Thus the metal-insulator transition
in this system is basically driven by localization effects. | 0309335v1 |
2003-10-10 | Charge transport in l-DNA probed by conducting-AFM, and relationship with its structure | We studied the electrical conductivity of DNA samples as function of the
number of DNA molecules. We showed that the insulating gap (no current at low
voltage) increases from ~1-2 V for bundles and large ropes to ~4-7 V for few
DNA molecules. From the distance dependent variation of the current, a unique
hopping distance of ~3 nm is calculated (polaron-hopping model) independently
of the number of DNA in the sample. The highly resistive behavior of the single
DNA is correlated with its flattened conformation on the surface (reduced
thickness, ~0.5-1.5 nm, compared to its nominal value, ~2 nm). | 0310242v1 |
2003-12-18 | Spin momentum transfer in current perpendicular to the plane spin valves | We present experimental and numerical micromagnetic data on the effect of
spin momentum transfer in current perpendicular to the plane spin valves.
Starting from a configuration with orthogonal free and pinned layer
magnetizations, the free layer magnetization exhibits abrupt current induced
switching that is qualitatively consistent with the spin torque model. When
operating the spin valve as a field sensor, spin transfer can produce a change
in resistance that mimics an effective magnetic field and induce magnetic
instability that requires a larger bias field in order to stabilize the device. | 0312505v1 |
2004-03-24 | New Pyrochlore Oxide Superconductor RbOs2O6 | We report the discovery of a new pyrochlore oxide superconductor RbOs2O6. The
compound crystallizes in the same beta-pyrochlore structure as the recently
discovered superconductor KOs2O6, where Os atoms form a corner-sharing
tetrahedral network called the pyrochlore lattice with Rb or K atoms in the
cage. Resistivity, magnetic susceptibility and specific heat measurements on
polycrystalline samples evidence a bulk superconductivity with Tc = 6.3 K. | 0403601v2 |
2004-04-16 | Quenched growth of nanostructured lead thin films on insulating substrates | Lead island films were obtained via vacuum vapor deposition on glass and
ceramic substrates at 80 K. Electrical conductance was measured during vapor
condensation and further annealing of the film up to room temperature. The
resistance behavior during film formation and atomic force microscopy of
annealed films were used as information sources about their structure. A model
for the quenched growth, based on ballistic aggregation theory, was proposed.
The nanostructure, responsible for chemiresistive properties of thin lead films
and the mechanism of sensor response are discussed. | 0404393v2 |
2004-04-28 | Current-induced magnetization reversal in a (Ga,Mn)As-based magnetic tunnel junction | We report current-induced magnetization reversal in a ferromagnetic
semiconductor-based magnetic tunnel junction (Ga,Mn)As/AlAs/(Ga,Mn)As prepared
by molecular beam epitaxy on a p-GaAs(001) substrate. A change in
magneto-resistance that is asymmetric with respect to the current direction is
found with the excitation current of 10^6 A/cm^2. Contributions of both
unpolarized and spin-polarized components are examined, and we conclude that
the partial magnetization reversal occurs in the (Ga,Mn)As layer of smaller
magnetization with the spin-polarized tunneling current of 10^5 A/cm^2. | 0404663v1 |
2004-04-30 | Spin-dependent transport in molecular tunnel junctions | We present measurements of magnetic tunnel junctions made using a
self-assembled-monolayer molecular barrier. Ni/octanethiol/Ni samples were
fabricated in a nanopore geometry. The devices exhibit significant changes in
resistance as the angle between the magnetic moments in the two electrodes is
varied, demonstrating that low-energy electrons can traverse the molecular
barrier while maintaining spin coherence. An analysis of the voltage and
temperature dependence of the data suggests that the spin-coherent transport
signals can be degraded by localized states in the molecular barriers. | 0404740v1 |
2004-08-07 | Hystersis like behaviour in Thin Films with heating-cooling cycle | The expression of temperature distribution along a film thickness is derived
and distribution of temperature in the film as the substrate is heated is
shown. The variation of film resistance with different substrate temperature is
calculated and the existence of temperature gradient along the film thickness
with finite thermal conductivity leads to hysteresis like behaviour on
heating-cooling the film. | 0408163v1 |
2004-10-12 | Quasi-ballistic electron transport in double-wall carbon nanotubes | Room-temperature quasi-ballistic electron transport in double-wall carbon
nanotubes (DWNT) is demonstrated. Conductance dependence on the length was
measured by submerging DWNTs into liquid mercury. The conductance plots show
plateaus, indicating weak dependence of the electrode-tube-electrode electrical
resistance on the length of the connecting nanotube. We infer a mean free path
between 0.6 and 10 micron meters for around 80% of the DWNTs, which is in good
agreement with calculations based on the electron scattering by acoustic
phonons and by disorder. | 0410310v1 |
2004-11-07 | Sub 20 nm Short Channel Carbon Nanotube Transistors | Carbon nanotube field-effect transistors with sub 20 nm long channels and
on/off current ratios of > 1000000 are demonstrated. Individual single-walled
carbon nanotubes with diameters ranging from 0.7 nm to 1.1 nm grown from
structured catalytic islands using chemical vapor deposition at 700 degree
Celsius form the channels. Electron beam lithography and a combination of HSQ,
calix[6]arene and PMMA e-beam resists were used to structure the short channels
and source and drain regions. The nanotube transistors display on-currents in
excess of 15 microA for drain-source biases of only 0.4 Volt. | 0411177v1 |
2004-11-11 | Ferromagnetic-superconducting hybrid films and their possible applications: A direct study in a model combinatorial film | Model combinatorial films (CFs) which host a pure superconductor adjacent to
a ferromagneticsuperconducting hybrid film (HF) are manufactured for the study
of the influence of ferromagnetic nanoparticles (FNs) on the nucleation of
superconductivity. Careful resistance measurements were performed
simultaneously on two different sites of the CFs. Enhancement of
superconductivity and magnetic memory effects were observed only on the hybrid
site of the CFs but were absent on their purely superconducting part. Our
results give direct proof that the FNs modulate the superconducting order
parameter in an efficient and controlled way giving us the possibility of
miscellaneous practical applications. | 0411311v1 |
2004-12-20 | Carbon Nanotubes for Interconnect Applications | We briefly review the status of the application of carbon nanotubes (CNTs)
for future interconnects and present results concerning possible integration
schemes. Growth of single nanotubes at lithographically defined locations
(vias) has been achieved which is a prerequisite for the use of CNTs as future
interconnects. For the 20 nm node, a current density of 5 10^8 A/cm^2 and a
resistance of 7.8 kOhm could be achieved for a single multi-walled CNT vertical
interconnect. | 0412537v1 |
2005-01-12 | Nanoengineered Curie Temperature in Laterally-Patterned Ferromagnetic Semiconductor Heterostructures | We demonstrate the manipulation of the Curie temperature of buried layers of
the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the
effect of annealing. Patterning the GaAs-capped ferromagnetic layers into
nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As
layers and thus allows the removal of Mn interstitials using annealing. This
leads to an enhanced Curie temperature and reduced resistivity compared to
unpatterned samples. For a fixed annealing time, the enhancement of the Curie
temperature is larger for narrower nanowires. | 0501298v2 |
2005-01-29 | Spin accumulation and decay in magnetic Schottky barriers | The theory of charge and spin transport in forward-biased Schottky barriers
reveals characteristic and experimentally relevant features. The conductance
mismatch is found to enhance the current induced spin-imbalance in the
semiconductor. The GaAs|MnAs interface resistance is obtained from an analysis
of the magnetic field dependent Kerr rotation experiments by Stephens et al.
and compared with first-principles calculations for intrinsic interfaces. With
increasing current bias, the interface transparency grows towards the
theoretical values, reflecting increasingly efficient Schottky barrier
screening. | 0501726v1 |
2005-02-01 | Adsorption of Oxygen Molecules on Individual Carbon Single-walled Nanotubes | Our study of the adsorption of oxygen molecules on individual semiconductiong
single-walled carbon nanotubes at ambient conditions reveals that the
adsorption is physisorption, that the resistance without O2 increases by ~two
orders of magnitude as compared to that with O2, and that the sensitive
response is due to the pinning of the Fermi level near the top of the valence
band of the tube resulting from impurity states of O2 appearing above the
valence band. | 0502012v1 |
2005-03-07 | Physical properties, strontium ordering and structural modulation in layered hexagonal Sr0.35CoO2 | Layered Sr0.35CoO2 has been synthesized by means of an ion exchange reaction
from Na0.7CoO2. Resistivity measurements show that this material can be either
metallic or semiconducting depending on the annealing conditions. Magnetic
susceptibility, following the Curie-Weiss law, increases with lowering
temperature and shows a small anomalous kink at around 30 K.
Transmission-electron-microscopy observations reveal the presence of two
superstructures arising respectively from the intercalated Sr-ordering (a
compositional modulation) with q1 = a* / 3 + b* / 3 and a periodic structural
distortion (a transverse structural modulation) with q2 = a* / 2. | 0503136v1 |
2005-04-12 | Polaron Transport in the Paramagnetic Phase of Electron-Doped Manganites | The electrical resistivity, Hall coefficient, and thermopower as functions of
temperature are reported for lightly electron-doped Ca(1-x)La(x)MnO(3)(0 <= x
<= 0.10). Unlike the case of hole-doped ferromagnetic manganites, the magnitude
and temperature dependence of the Hall mobility for these compounds is found to
be inconsistent with small-polaron theory. The transport data are better
described by the Feynman polaron theory and imply intermediate coupling (alpha
\~ 5.4) with a band effective mass, m*~4.3 m_0, and a polaron mass, m_p ~ 10
m_0. | 0504303v1 |
2005-04-26 | Spin filtering through ferromagnetic BiMnO3 tunnel barriers | We report on experiments of spin filtering through ultra-thin single-crystal
layers of the insulating and ferromagnetic oxide BiMnO3 (BMO). The spin
polarization of the electrons tunneling from a gold electrode through BMO is
analyzed with a counter-electrode of the half-metallic oxide La2/3Sr1/3MnO3
(LSMO). At 3 K we find a 50% change of the tunnel resistances according to
whether the magnetizations of BMO and LSMO are parallel or opposite. This
effect corresponds to a spin filtering effciency of up to 22%. Our results thus
show the potential of complex ferromagnetic insulating oxides for spin
filtering and injection. | 0504667v1 |
2005-05-16 | Electronic mean free path in as-produced and purified single-wall carbon nanotubes | The effect of purification on room temperature electronic transport
properties of single-wall carbon nanotubes (SWNT) was studied by submerging
samples into liquid mercury. The conductance plots of purified SWNTs showed
plateaus, indicating weak dependence of the electrical resistance on the length
of the tube connecting the electrodes, providing evidence of quasi-ballistic
conduction in SWNTs. The electronic mean free path of the purified SWNTs
reached a few microns, which is longer than that of the as-produced SWNTs, and
which is consistent with the calculation based on the scattering by acoustic
phonons. | 0505377v1 |
2005-06-03 | Magnetic and Transport Properties of Fe-Ag granular multilayers | Results of magnetization, magnetotransport and Mossbauer spectroscopy
measurements of sequentially evaporated Fe-Ag granular composites are
presented. The strong magnetic scattering of the conduction electrons is
reflected in the sublinear temperature dependence of the resistance and in the
large negative magnetoresistance. The simultaneous analysis of the magnetic
properties and the transport behavior suggests a bimodal grain size
distribution. A detailed quantitative description of the unusual features
observed in the transport properties is given. | 0506072v2 |
2005-07-06 | A single molecule switch based on two Pd nanocrystals linked by a conjugated dithiol | Tunneling spectroscopy measurements have been carried out on a single
molecule device formed by two Pd nanocrystals (dia, $\sim$5 nm) electronically
coupled by a conducting molecule, dimercaptodiphenylacetylene. The I-V data,
obtained by positioning the tip over a nanocrystal electrode, exhibit negative
differential resistance (NDR) on a background M-I-M characteristics. The NDR
feature occurs at $\sim$0.67 V at 300 K and shifts to a higher bias of 1.93 V
at 90 K. When the tip is held in the middle region of the device, a coulomb
blockade region is observed ($\pm\sim$0.3 V). | 0507147v1 |
2005-07-15 | Spin transference and magnetoresistance amplification in a transistor | A current problem in semiconductor spin-based electronics is the difficulty
of experimentally expressing the effect of spin-polarized current in electrical
circuit measurements. We present a theoretical solution with the principle of
transference of the spin diffusion effects in the semiconductor channel of a
system with three magnetic terminals. A notable result of technological
consequences is the room temperature amplification of the magneto-resistive
effect, integrable with electronics circuits, demonstrated by computation of
current dependence on magnetization configuration in such a system with
currently achievable parameters. | 0507378v2 |
2005-09-27 | Electron-Hole Asymmetry in GdBaCo_{2}O_{5+x}: Evidence for Spin Blockade of Electron Transport in a Correlated Electron System | In RBaCo_{2}O_{5+x} compounds (R is rare earth) variability of the oxygen
content allows precise doping of CoO_2 planes with both types of charge
carriers. We study transport properties of doped GdBaCo_{2}O_{5+x} single
crystals and find a remarkable asymmetry in the behavior of holes and electrons
doped into a parent insulator GdBaCo_{2}O_{5.5}. Doping dependences of
resistivity, Hall response, and thermoelectric power reveal that the doped
holes greatly improve the conductivity, while the electron-doped samples always
remain poorly conducting. This doping asymmetry provides strong evidence for a
spin blockade of the electron transport in RBaCo_{2}O_{5+x}. | 0509673v1 |
2005-10-13 | The electrical current effect in phase separated La5/8-yPryCa3/8MnO3: Charge order melting vs. Joule heating | We have studied the effect of electric field on transport properties of the
prototypical phase separated manganite La5/8-yPryCa3/8MnO3 with y=0.34. Our
results show that the suggested image in which the charge ordered state is
melted by the appliance of an electric current and/or voltage has to be
revised. We were able to explain the observed resistivity drop in terms of an
artifact related to Joule heating and the particular hysteresis that the system
under study display, common to many other phase separated manganites. | 0510366v1 |
2005-12-16 | A possible minimum toy model with negative differential capacitance for self-sustained current oscillation | We generalize a simple model for superlattices to include the effect of
differential capacitance. It is shown that the model always has a stable
steady-state solution (SSS) if all differential capacitances are positive. On
the other hand, when negative differential capacitance is included, the model
can have no stable SSS and be in a self-sustained current oscillation behavior.
Therefore, we find a possible minimum toy model with both negative differential
resistance and negative differential capacitance which can include the
phenomena of both self-sustained current oscillation and $I-V$ oscillation of
stable SSSs. | 0512370v2 |
2006-01-13 | Gamma radiation exposure of MCT diode arrays | Investigations of electrical properties of long-wavelength infrared (LWIR)
mercury cadmium telluride (MCT) arrays exposed to gamma-radiation have been
performed. Resistance-area product characteristics of LWIR n{+}-p photodiodes
have been investigated using microprobe technique at T=78 K before and after an
exposure to various doses of gamma-radiation. The current transport mechanisms
for those structures are described within the framework of the balance equation
model taking into account the occupation of the trap states in the band gap. | 0601276v1 |
2006-01-13 | Influence of Roughness and Disorder on Tunneling Magnetoresistance | A systematic, quantitative study of the effect of interface roughness and
disorder on the magnetoresistance of FeCo$|$vacuum$|$FeCo magnetic tunnel
junctions is presented based upon parameter-free electronic structure
calculations. Surface roughness is found to have a very strong effect on the
spin-polarized transport while that of disorder in the leads (leads consisting
of a substitutional alloy) is weaker but still sufficient to suppress the huge
tunneling magneto-resistance (TMR) predicted for ideal systems. | 0601291v2 |
2006-02-09 | Strong Pinning Enhancement in MgB2 Using Very Small Dy2O3 Additions | 0.5 to 5.0 wt.% Dy2O3 was in-situ reacted with Mg + B to form pinned MgB2.
While Tc remained largely unchanged, Jc was strongly enhanced. The best sample
(only 0.5 wt.% Dy2O3) had a Jc of 6.5 x 10^5 A/cm^2 at 6K, 1T and 3.5 x 10^5
A/cm^2 at 20K, 1T, around a factor of 4 higher compared to the pure sample, and
equivalent to hot-pressed or nano-Si added MgB2 at below 1T. Even distributions
of nano-scale precipitates of DyB4 and MgO were observed within the grains. The
room temperature resistivity decreased with Dy2O3 indicative of improved grain
connectivity. | 0602234v1 |
2006-02-27 | Origin of the large thermoelectric power in oxygen-variable RBaCo_{2}O_{5+x} (R=Gd, Nd) | Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single
crystals have been studied upon continuous doping of CoO_2 planes with either
electrons or holes. The thermoelectric response and the resistivity behavior
reveal a hopping character of the transport in both compounds, providing the
basis for understanding the recently found remarkable divergence of the Seebeck
coefficient at x=0.5. The doping dependence of the thermoelectric power evinces
that the configurational entropy of charge carriers, enhanced by their spin and
orbital degeneracy, plays a key role in the origin of the large thermoelectric
response in these correlated oxides. | 0602618v1 |
2006-03-27 | Modeling transient absorption and thermal conductivity in a simple nanofluid | Molecular dynamics simulations are used to simulate the thermal properties of
a model fluid containing nanoparticles (nanofluid). By modelling transient
absorption experiments, we show that they provide a reliable determination of
interfacial resistance between the particle and the fluid. The flexibility of
molecular simulation allows us to consider separately the effect of
confinement, particle mass and Brownian motion on the thermal transfer between
fluid and particle. Finally, we show that in the absence of collective effects,
the heat conductivity of the nanofluid is well described by the classical
Maxwell Garnet equation model. | 0603704v1 |
2006-05-04 | Optical conductivity of charge carriers interacting with a two-level systems reservoir | Using the functional-integral method we investigate the effective dynamics of
a charged particle coupled to a set of two-level systems as a function of
temperature and external electric field. The optical conductivity and the
direct current (dc) resistivity induced by the reservoir are computed. Three
different regimes are found depending on the two-level system spectral
function, which may lead to a non-Drude optical conductivity in a certain range
of parameters. Our results contrast to the behavior found when considering the
usual bath of harmonic oscillators which we are able to recover in the limit of
very low temperatures. | 0605105v1 |
2006-05-24 | Controlling charge injection in organic field-effect transistors using self-assembled monolayers | We have studied charge injection across the metal/organic semiconductor
interface in bottom-contact poly(3-hexylthiophene) (P3HT) field-effect
transistors, with Au source and drain electrodes modified by self-assembled
monolayers (SAMs) prior to active polymer deposition. By using the SAM to
engineer the effective Au work function, we markedly affect the charge
injection process. We systematically examine the contact resistivity and
intrinsic channel mobility, and show that chemically increasing the injecting
electrode work function significantly improves hole injection relative to
untreated Au electrodes. | 0605605v1 |
2006-08-10 | Gate-controlled nuclear magnetic resonance in an AlGaAs/GaAs quantum Hall device | We study the resistively detected nuclear magnetic resonance (NMR) in an
AlGaAs/GaAs quantum Hall device with a side gate. The strength of the hyperfine
interaction between electron and nuclear spins is modulated by tuning a
position of the two-dimensional electron systems with respect to the polarized
nuclear spins using the side-gate voltages. The NMR frequency is systematically
controlled by the gate-tuned technique in a semiconductor device. | 0608237v1 |
2006-08-27 | Magnetic Switching of Phase-Slip Dissipation in NbSe2 Nanobelts | The stability of the superconducting dissipationless and resistive states in
single-crystalline NbSe2 nanobelts is characterized by transport measurements
in an external magnetic field (H). Current-driven electrical measurements show
voltage steps, indicating the nucleation of phase-slip structures. Well below
the critical temperature, the position of the voltage steps exhibits a sharp,
periodic dependence as a function of H. This phenomenon is discussed in the
context of two possible mechanisms: the interference of the order parameter and
the periodic rearrangement of the vortex lattice within the nanobelt. | 0608586v1 |
2006-08-28 | Inverse Spin Hall Effect by Spin Injection | Motivated by a recent experiment[Nature {\bf 442}, 176 (2006)], we present a
quantitative microscopic theory to investigate the inverse spin-Hall effect
with spin injection into aluminum considering both intrinsic and extrinsic
spin-orbit couplings using the orthogonalized-plane-wave method. Our
theoretical results are in good agreement with the experimental data. It is
also clear that the magnitude of the anomalous Hall resistivity is mainly due
to contributions from extrinsic skew scattering, while its spatial variation is
determined by the intrinsic spin-orbit coupling. | 0608594v2 |
2006-08-31 | Atomic and electronic structure of ultra-thin Al/AlOx/Al interfaces | Interfaces between metals based on AlO$_{x}$ represent the most popular basis
for Josephson junctions or, more recently, also for junctions exhibiting
substantial tunneling magneto-resistance. We have performed a computational
study of possible local geometric structures of such interfaces at the
ab-initio DFT/GGA level of approximation to complement recent experimental data
on ultra-thin AlO$_{x}$-based interfaces. We present two competing structures
that we characterise with their electronic properties: fragmentation and
interface energies. | 0608718v1 |
2006-09-01 | Nonlinear screening of charge impurities in graphene | It is shown that a ``vacuum polarization'' induced by Coulomb potential in
graphene leads to a strong suppression of electric charges even for undoped
case (no charge carriers). A standard linear response theory is therefore not
applicable to describe the screening of charge impurities in graphene. In
particular, it overestimates essentially the contributions of charge impurities
into the resistivity of graphene. | 0609026v3 |
2006-09-14 | Strain induced pressure effect in pulsed laser deposited thin films of the strongly correlated oxide V2O3 | V2O3 thin films about 10 nm thick were grown on Al2O3 (0001) by pulsed laser
deposition. The XRD analysis is in agreement with R-3c space group. Some of
them exhibit the metal / insulator transition characteristic of V2O3 bulk
material and others samples exhibit a metallic behavior. For the latter, the
XPS analysis indicates an oxidation state of +III for vanadium. There is no
metal / insulator transition around 150 K in this sample and a strongly
correlated Fermi liquid rho = AT2 behavior of the resistivity at low
temperature is observed, with a value of A of 1.2 10-4 ohm cm, 3 times larger
than the bulk value at 25 kbar. | 0609342v1 |
2006-09-19 | Adaptive Programming of Unconventional Nano-Architectures | Novel assembly processes for nanocircuits could present compelling
alternatives to the detailed design and placement currently used for computers.
The resulting architectures however may not be programmable by standard means.
In this paper, nanocomputers with unconventional architectures are programmed
using adaptive methods. The internals of the device are treated as a "black
box" and programming is achieved by manipulating "control voltages". Learning
algorithms are used to set the controls. As examples, logic gates and simple
arithmetic circuits are implemented. Additionally, similar methods allow for
reconfiguration of the devices, and makes them resistant to certain kinds of
faults. | 0609489v1 |
2006-09-20 | Spin Injection and Nonlocal Spin Transport in Magnetic Nanostructures | We theoretically study the nonlocal spin transport in a device consisting of
a nonmagnetic metal (N) and ferromagnetic injector (F1) and detector (F2)
electrodes connected to N. We solve the spin-dependent transport equations in a
device with arbitrary interface resistance from a metallic-contact to tunneling
regime, and obtain the conditions for efficient spin injection, accumulation,
and transport in the device. In a device containing a superconductor (F1/S/F2),
the effect of superconductivity on the spin transport is investigated. The
spin-current induced spin Hall effect in nonmagnetic metals is also discussed. | 0609508v1 |
2006-09-21 | Resistive and rectifying effects of pulling gold atoms at thiol-gold nano-contacts | We investigate, by means of first-principles calculations, structural and
transport properties of junctions made of symmetric dithiolated molecules
placed between Au electrodes. As the electrodes are pulled apart, we find that
it becomes energetically favorable that Au atoms migrate to positions between
the electrode surface and thiol terminations, with junction structures
alternating between symmetric and asymmetric. As a result, the calculated
$\emph{IV}$ curves alternate between rectifying and non-rectifying behaviors as
the electrodes are pulled apart, which is consistent with recent experimental
results. | 0609558v1 |
2006-11-15 | Tunneling anisotropic magnetoresistance and spin-orbit coupling in Fe/GaAs/Au tunnel junctions | We report the observation of tunneling anisotropic magnetoresistance effect
(TAMR) in the epitaxial metal-semiconductor system Fe/GaAs/Au. The observed
two-fold anisotropy of the resistance can be switched by reversing the bias
voltage, suggesting that the effect originates from the interference of the
spin-orbit coupling at the interfaces. Corresponding model calculations
reproduce the experimental findings very well. | 0611406v1 |
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