14,157 research outputs found
Dielectric response of Anderson and pseudogapped insulators
Using a combination of analytic and numerical methods, we study the
polarizability of a (non-interacting) Anderson insulator in one, two, and three
dimensions and demonstrate that, in a wide range of parameters, it scales
proportionally to the square of the localization length, contrary to earlier
claims based on the effective-medium approximation. We further analyze the
effect of electron-electron interactions on the dielectric constant in
quasi-1D, quasi-2D and 3D materials with large localization length, including
both Coulomb repulsion and phonon-mediated attraction. The phonon-mediated
attraction (in the pseudogapped state on the insulating side of the
Superconductor-Insulator Transition) produces a correction to the dielectric
constant, which may be detected from a linear response of a dielectric constant
to an external magnetic field.Comment: 9 page
Impact of incomplete ionization of dopants on the electrical properties of compensated p-type silicon
This paper investigates the importance of incomplete ionization of dopants in compensated p-type Si and its impact on the majority-carrier density and mobility and thus on the resistivity. Both theoretical calculations and temperature-dependent Hall-effect measurements demonstrate that the carrier density is more strongly affected by incomplete ionization in compensated Si than in uncompensated Si with the same net doping. The previously suggested existence of a compensation-specific scattering mechanism to explain the reduction of mobility in compensated Si is shown not to be consistent with the T-dependence of the measuredcarrier mobility. The experiment also shows that, in the vicinity of 300 K, the resistivity of compensated Si has a much weaker dependence on temperature than that of uncompensated silicon
Anderson transition in systems with chiral symmetry
Anderson localization is a universal quantum feature caused by destructive
interference. On the other hand chiral symmetry is a key ingredient in
different problems of theoretical physics: from nonperturbative QCD to highly
doped semiconductors. We investigate the interplay of these two phenomena in
the context of a three-dimensional disordered system. We show that chiral
symmetry induces an Anderson transition (AT) in the region close to the band
center. Typical properties at the AT such as multifractality and critical
statistics are quantitatively affected by this additional symmetry. The origin
of the AT has been traced back to the power-law decay of the eigenstates; this
feature may also be relevant in systems without chiral symmetry.Comment: RevTex4, 4 two-column pages, 3 .eps figures, updated references,
final version as published in Phys. Rev.
Combining benchmarking and chain-linking for short-term regional forecasting
In this paper we propose a methodology to estimate and forecast the GDP of the different regions of a country, providing quarterly profiles paper offers a new instrument for short degree of synchronicity among regional business cycles. Technically, we combine time series models with benchma quarterly indicators and to estimate quarterly regional GDPs ensuring their temporal and transversal consistency with the National Accounts data. The methodology addresses the issue of non-additivity taking into account linked volume indexes used by the National Accounts and provides an efficient combination of structural as well as short-term information. The methodology is illustrated by an application to the quarterly GDP estimates and forecasts at the regional level (i.e., with a minimum compilation delay with respect to the national quarterly GDP)Forecasting, Spanish economy, Regional analysis, Benchmarking, Chain-linking
Vibrational Instabilities in Resonant Electron Transport through Single-Molecule Junctions
We analyze various limits of vibrationally coupled resonant electron
transport in single-molecule junctions. Based on a master equation approach, we
discuss analytic and numerical results for junctions under a high bias voltage
or weak electronic-vibrational coupling. It is shown that in these limits the
vibrational excitation of the molecular bridge increases indefinitely, i.e. the
junction exhibits a vibrational instability. Moreover, our analysis provides
analytic results for the vibrational distribution function and reveals that
these vibrational instabilities are related to electron-hole pair creation
processes.Comment: 19 pages, 3 figure
Quantum Interference and Decoherence in Single-Molecule Junctions: How Vibrations Induce Electrical Current
Quantum interference effects and decoherence mechanisms in single-molecule
junctions are analyzed employing a nonequilibrium Green's function approach.
Electrons tunneling through quasi-degenerate states of a nanoscale molecular
junction exhibit interference effects. We show that electronic-vibrational
coupling, inherent to any molecular junction, strongly quenches such
interference effects. As a result, the electrical current can be significantly
larger than without electronic-vibrational coupling. The analysis reveals that
the quenching of quantum interference is particularly pronounced if the
junction is vibrationally highly excited, e.g. due to current-induced
nonequilibrium effects in the resonant transport regime.Comment: 11 pages, 4 figure
Transport through superconductor/magnetic dot/superconductor structures
The coupling of two s-wave superconductors through a small magnetic dot is
discussed. Assuming that the dot charging energy is small compared to the
superconducting gap, , and that the moment of the dot is
classical, we develop a simple theory of transport through the dot. The
presence of the magnetic dot will position Andreev bound states within the
superconducting gap at energies tunable with the magnetic properties of the
dot. Studying the Josephson coupling it is shown that the constructed junction
can be tuned from a "0" to a ""-junction via a degenerate two-level state
either by changing the magnetic moment of the dot or by changing temperature.
Furthermore, it is shown that details of the magnetic dot can be extracted from
the sub-harmonic structure in the current-voltage characteristics of the
junction.Comment: 5 pages, 4 figures, paper presented at the conference SDP 2001 in
Tokyo on June 2
Breathers and kinks in a simulated crystal experiment
We develop a simple 1D model for the scattering of an incoming particle
hitting the surface of mica crystal, the transmission of energy through the
crystal by a localized mode, and the ejection of atom(s) at the incident or
distant face. This is the first attempt to model the experiment described in
Russell and Eilbeck in 2007 (EPL, v. 78, 10004). Although very basic, the model
shows many interesting features, for example a complicated energy dependent
transition between breather modes and a kink mode, and multiple ejections at
both incoming and distant surfaces. In addition, the effect of a heavier
surface layer is modelled, which can lead to internal reflections of breathers
or kinks at the crystal surface.Comment: 15 pages, 12 figures, based on a talk given at the conference
"Localized Excitations in Nonlinear Complex Systems (LENCOS)", Sevilla
(Spain) July 14-17, 200
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