13,987 research outputs found
Current-voltage characteristics of quasi-one-dimensional superconductors: An S-curve in the constant voltage regime
Applying a constant voltage to superconducting nanowires we find that its
IV-characteristic exhibits an unusual S-behavior. This behavior is the direct
consequence of the dynamics of the superconducting condensate and of the
existence of two different critical currents: j_{c2} at which the pure
superconducting state becomes unstable and j_{c1}<j_{c2} at which the phase
slip state is realized in the system.Comment: 4 pages, 5 figures, replaced with minor change
Electron propagation in crossed magnetic and electric fields
Laser-atom interaction can be an efficient mechanism for the production of
coherent electrons. We analyze the dynamics of monoenergetic electrons in the
presence of uniform, perpendicular magnetic and electric fields. The Green
function technique is used to derive analytic results for the field--induced
quantum mechanical drift motion of i) single electrons and ii) a dilute Fermi
gas of electrons. The method yields the drift current and, at the same time it
allows us to quantitatively establish the broadening of the (magnetic) Landau
levels due to the electric field: Level number k is split into k+1 sublevels
that render the th oscillator eigenstate in energy space. Adjacent Landau
levels will overlap if the electric field exceeds a critical strength. Our
observations are relevant for quantum Hall configurations whenever electric
field effects should be taken into account.Comment: 11 pages, 2 figures, submitte
Generalizing the DGLAP Evolution of Fragmentation Functions to the Smallest x Values
An approach which unifies the Double Logarithmic Approximation at small x and
the leading order DGLAP evolution of fragmentation functions at large x is
presented. This approach reproduces exactly the Modified Leading Logarithm
Approximation, but is more complete due to the degrees of freedom given to the
quark sector and the inclusion of the fixed order terms. We find that data from
the largest x values to the peak region can be better fitted than with other
approaches.Comment: 10 pages, 3 figure
Temporal response to harmonic driving in electroconvection
The temporal evolution of the spatially periodic electroconvection (EC)
patterns has been studied within the period of the driving ac voltage by
monitoring the light intensity diffracted from the pattern. Measurements have
been carried out on a variety of nematic systems, including those with negative
dielectric and positive conductivity anisotropy, exhibiting "standard EC"
(s-EC), those with both anisotropies negative exhibiting "non-standard EC"
(ns-EC), as well as those with the two anisotropies positive. Theoretical
predictions have been confirmed for stationary s-EC and ns-EC patterns.
Transitions with Hopf bifurcation have also been studied. While traveling had
no effect on the temporal evolution of dielectric s-EC, traveling conductive
s-EC and ns-EC patterns exhibited a substantially altered temporal behavior
with a dependence on the Hopf frequency. It has also been shown that in
nematics with both anisotropies positive, the pattern develops and decays
within an interval much shorter than the period, even at relatively large
driving frequencies.Comment: 19 pages, 5 figure
Anderson Localization of Polar Eigenmodes in Random Planar Composites
Anderson localization of classical waves in disordered media is a fundamental
physical phenomenon that has attracted attention in the past three decades.
More recently, localization of polar excitations in nanostructured
metal-dielectric films (also known as random planar composite) has been subject
of intense studies. Potential applications of planar composites include local
near-field microscopy and spectroscopy. A number of previous studies have
relied on the quasistatic approximation and a direct analogy with localization
of electrons in disordered solids. Here I consider the localization problem
without the quasistatic approximation. I show that localization of polar
excitations is characterized by algebraic rather than by exponential spatial
confinement. This result is also valid in two and three dimensions. I also show
that the previously used localization criterion based on the gyration radius of
eigenmodes is inconsistent with both exponential and algebraic localization. An
alternative criterion based on the dipole participation number is proposed.
Numerical demonstration of a localization-delocalization transition is given.
Finally, it is shown that, contrary to the previous belief, localized modes can
be effectively coupled to running waves.Comment: 22 pages, 7 figures. Paper was revised and a more precise definition
of the participation number given, data for figures recalculated accordingly.
Accepted to J. Phys.: Cond. Mat
Multifractality: generic property of eigenstates of 2D disordered metals.
The distribution function of local amplitudes of eigenstates of a
two-dimensional disordered metal is calculated. Although the distribution of
comparatively small amplitudes is governed by laws similar to those known from
the random matrix theory, its decay at larger amplitudes is non-universal and
much slower. This leads to the multifractal behavior of inverse participation
numbers at any disorder. From the formal point of view, the multifractality
originates from non-trivial saddle-point solutions of supersymmetric
-model used in calculations.Comment: 4 two-column pages, no figures, submitted to PRL
Effects of Scale-Free Disorder on the Anderson Metal-Insulator Transition
We investigate the three-dimensional Anderson model of localization via a
modified transfer-matrix method in the presence of scale-free diagonal disorder
characterized by a disorder correlation function decaying asymptotically
as . We study the dependence of the localization-length exponent
on the correlation-strength exponent . % For fixed disorder ,
there is a critical , such that for ,
and for , remains that of the
uncorrelated system in accordance with the extended Harris criterion. At the
band center, is independent of but equal to that of the
uncorrelated system. The physical mechanisms leading to this different behavior
are discussed.Comment: submitted to Phys. Rev. Let
Transverse quasilinear relaxation in inhomogeneous magnetic field
Transverse quasilinear relaxation of the cyclotron-Cherenkov instability in
the inhomogeneous magnetic field of pulsar magnetospheres is considered. We
find quasilinear states in which the kinetic cyclotron-Cherenkov instability of
a beam propagating through strongly magnetized pair plasma is saturated by the
force arising in the inhomogeneous field due to the conservation of the
adiabatic invariant. The resulting wave intensities generally have nonpower law
frequency dependence, but in a broad frequency range can be well approximated
by the power law with the spectral index -2. The emergent spectra and fluxes
are consistent with the one observed from pulsars.Comment: 14 Pages, 4 Figure
Localization of non-interacting electrons in thin layered disordered systems
Localization of electronic states in disordered thin layered systems with b
layers is studied within the Anderson model of localization using the
transfer-matrix method and finite-size scaling of the inverse of the smallest
Lyapunov exponent. The results support the one-parameter scaling hypothesis for
disorder strengths W studied and b=1,...,6. The obtained results for the
localization length are in good agreement with both the analytical results of
the self-consistent theory of localization and the numerical scaling studies of
the two-dimensional Anderson model. The localization length near the band
center grows exponentially with b for fixed W but no
localization-delocalization transition takes place.Comment: 6 pages, 5 figure
- âŠ