4,791 research outputs found
Frequency dependent third cumulant of current in diffusive conductors
We calculate the frequency dispersion of the third cumulant of current in
diffusive-metal contacts. The cumulant exhibits a dispersion at the inverse
time of diffusion across the contact, which is typically much smaller than the
inverse time. This dispersion is much more pronounced in the case of
strong electron-electron scattering than in the case of purely elastic
scattering because of a different symmetry of the relevant second-order
correlation functions.Comment: 8 pages, 4 figure
Current fluctuations near to the 2D superconductor-insulator quantum critical point
Systems near to quantum critical points show universal scaling in their
response functions. We consider whether this scaling is reflected in their
fluctuations; namely in current-noise. Naive scaling predicts low-temperature
Johnson noise crossing over to noise power at strong
electric fields. We study this crossover in the metallic state at the 2d z=1
superconductor/insulator quantum critical point. Using a Boltzmann-Langevin
approach within a 1/N-expansion, we show that the current noise obeys a scaling
form with . We recover
Johnson noise in thermal equilibrium and at strong
electric fields. The suppression from free carrier shot noise is due to strong
correlations at the critical point. We discuss its interpretation in terms of a
diverging carrier charge or as out-of-equilibrium Johnson
noise with effective temperature .Comment: 5 page
On chaotic behavior of gravitating stellar shells
Motion of two gravitating spherical stellar shells around a massive central
body is considered. Each shell consists of point particles with the same
specific angular momenta and energies. In the case when one can neglect the
influence of gravitation of one ("light") shell onto another ("heavy") shell
("restricted problem") the structure of the phase space is described. The
scaling laws for the measure of the domain of chaotic motion and for the
minimal energy of the light shell sufficient for its escape to infinity are
obtained.Comment: e.g.: 12 pages, 8 figures, CHAOS 2005 Marc
Current in narrow channels of anisotropic superconductors
We argue that in channels cut out of anisotropic single crystal
superconductors and narrow on the scale of London penetration depth, the
persistent current must cause the transverse phase difference provided the
current does not point in any of the principal crystal directions. The
difference is proportional to the current value and depends on the anisotropy
parameter, on the current direction relative to the crystal, and on the
transverse channel dimension. An experimental set up to measure the transverse
phase is proposed.Comment: 3 pages, 1 figur
Statistics of speckle patterns
We develop a general method for calculating statistical properties of the
speckle pattern of coherent waves propagating in disordered media. In some
aspects this method is similar to the Boltzmann-Langevin approach for the
calculation of classical fluctuations. We apply the method to the case where
the incident wave experiences many small angle scattering events during
propagation, but the total angle change remains small. In many aspects our
results for this case are different from results previously known in the
literature. The correlation function of the wave intensity at two points
separated by a distance , has a long range character. It decays as a power
of and changes sign. We also consider sensitivities of the speckles to
changes of external parameters, such as the wave frequency and the incidence
angle.Comment: 4 pages, 2 figure
Nature of 45 degree vortex lattice reorientation in tetragonal superconductors
The transformation of the vortex lattice in a tetragonal superconductor which
consists of its 45 degree reorientation relative to the crystal axes is studied
using the nonlocal London model. It is shown that the reorientation occurs as
two successive second order (continuous) phase transitions. The transition
magnetic fields are calculated for a range of parameters relevant for
borocarbide superconductors in which the reorientation has been observed
Dissipation and coherent effects in narrow superconducting channels
We apply the time dependent Ginzburg-Landau equations (TDGL) to study small
ac currents of frequency in superconducting channels narrow on the
scale of London penetration depth. We show that TDGL have -dependent and
spatially uniform solutions that describe the order parameter with an
oscillating part of the double frequency coexisting with an ac electric field.
We evaluate the Ohmic losses (related neither to the flux flow nor to the phase
slips) and show that the resistivity reduction on cooling through the critical
temperature should behave as . If the channel is cut
out of an anisotropic material in a direction other than the principal axes,
the transverse phase difference and the Josephson voltage between the channel
sides are generated.Comment: 5 pages, 1 figures, Accepted for publication in Phys. Rev.
Thermal Fluctuations of the Electric Field in the Presence of Carrier Drift
We consider a semiconductor in a non-equilibrium steady state, with a dc
current. On top of the stationary carrier motion there are fluctuations. It is
shown that the stationary motion of the carriers (i.e., their drift) can have a
profound effect on the electromagnetic field fluctuations in the bulk of the
sample as well as outside it, close to the surface (evanescent waves in the
near field). The effect is particularly pronounced near the plasma frequency.
This is because drift leads to a significant modification of the dispersion
relation for the bulk and surface plasmons.Comment: Comments are welcom
Keldysh Ginzburg-Landau action of fluctuating superconductors
We derive Ginzburg-Landau action by systematically integrating out electronic
degrees of freedom in the framework of the Keldysh nonlinear sigma-model of
disordered superconductors. The resulting Ginzburg-Landau functional contains a
nonlocal -dependent contribution to the diffusion constant, which
leads, for example, to Maki-Thompson corrections. It also exhibits an anomalous
Gor'kov-Eliashberg coupling between and the scalar potential, as well
as a peculiar nonlocal nonlinear term. The action is gauge invariant and
satisfies the fluctuation dissipation theorem. It may be employed e.g. for
calculation of higher moments of the current fluctuations.Comment: 16 pages, 2 figure
Non-linear bigravity and cosmic acceleration
We explore the cosmological solutions of classes of non-linear bigravity
theories. These theories are defined by effective four-dimensional Lagrangians
describing the coupled dynamics of two metric tensors, and containing, in the
linearized limit, both a massless graviton and an ultralight one. We focus on
two paradigmatic cases: the case where the coupling between the two metrics is
given by a Pauli-Fierz-type mass potential, and the case where this coupling
derives from five-dimensional brane constructions. We find that cosmological
evolutions in bigravity theories can be described in terms of the dynamics of
two ``relativistic particles'', moving in a curved Lorenzian space, and
connected by some type of nonlinear ``spring''. Classes of bigravity
cosmological evolutions exhibit a ``locking'' mechanism under which the two
metrics ultimately stabilize in a bi-de-Sitter configuration, with relative
(constant) expansion rates. In the absence of matter, we find that a generic
feature of bigravity cosmologies is to exhibit a period of cosmic acceleration.
This leads us to propose bigravity as a source of a new type of dark energy
(``tensor quintessence''), exhibiting specific anisotropic features. Bigravity
could also have been the source of primordial inflation.Comment: 55 pages, 4 figures, references and comments added, final version
published in Phys. Rev.
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