276 research outputs found
Intensity correlations and mesoscopic fluctuations of diffusing photons in cold atoms
We study the angular correlation function of speckle patterns that result
from multiple scattering of photons by cold atomic clouds. We show that this
correlation function becomes larger than the value given by Rayleigh law for
classical scatterers. These large intensity fluctuations constitute a new
mesoscopic interference effect specific to atom-photon interactions, that could
not be observed in other systems such as weakly disordered metals. We provide a
complete description of this behavior and expressions that allow for a
quantitative comparison with experiments.Comment: 4 pages, 2 figure
Vortex nucleation through edge states in finite Bose-Einstein condensates
We study the vortex nucleation in a finite Bose-Einstein condensate. Using a
set of non-local and chiral boundary conditions to solve the
Schrdinger equation of non-interacting bosons in a rotating trap, we
obtain a quantitative expression for the characteristic angular velocity for
vortex nucleation in a condensate which is found to be 35% of the transverse
harmonic trapping frequency.Comment: 24 pages, 8 figures. Both figures and the text have been revise
Energy levels and their correlations in quasicrystals
Quasicrystals can be considered, from the point of view of their electronic
properties, as being intermediate between metals and insulators. For example,
experiments show that quasicrystalline alloys such as AlCuFe or AlPdMn have
conductivities far smaller than those of the metals that these alloys are
composed from. Wave functions in a quasicrystal are typically intermediate in
character between the extended states of a crystal and the exponentially
localized states in the insulating phase, and this is also reflected in the
energy spectrum and the density of states. In the theoretical studies we
consider in this review, the quasicrystals are described by a pure hopping
tight binding model on simple tilings. We focus on spectral properties, which
we compare with those of other complex systems, in particular, the Anderson
model of a disordered metal.Comment: 15 pages including 19 figures. Review article, submitted to Phil. Ma
Localization of Matter Waves in 2D-Disordered Optical Potentials
We consider ultracold atoms in 2D-disordered optical potentials and calculate
microscopic quantities characterizing matter wave quantum transport in the
non-interacting regime. We derive the diffusion constant as function of all
relevant microscopic parameters and show that coherent multiple scattering
induces significant weak localization effects. In particular, we find that even
the strong localization regime is accessible with current experimental
techniques and calculate the corresponding localization length.Comment: 4 pages, 3 figures, figures changed, references update
Effect of Magnetic Impurities on Energy Exchange between Electrons
In order to probe quantitatively the effect of Kondo impurities on energy
exchange between electrons in metals, we have compared measurements on two
silver wires with dilute magnetic impurities (manganese) introduced in one of
them. The measurement of the temperature dependence of the electron phase
coherence time on the wires provides an independent determination of the
impurity concentration. Quantitative agreement on the energy exchange rate is
found with a theory by G\"{o}ppert et al. that accounts for Kondo scattering of
electrons on spin-1/2 impurities.Comment: 4 page
Investigating the early pottery Neolithic of northern Syria:New evidence from Tell Sabi Abyad
Persistent currents in Dirac fermion rings
The persistent current in strictly one-dimensional Dirac systems is investigated within two different models, defined in the continuum and on a lattice, respectively. The object of the study is the effect of a single magnetic or nonmagnetic impurity in the two systems. In the continuum Dirac model, an analytical expression for the persistent current flowing along a ring with a single delta-like magnetic impurity is obtained after regularization of the unbounded negative energy states. The predicted decay of the persistent current agrees with the lattice simulations. The results are generalized to finite temperatures. To realize a single Dirac massless fermion, the lattice model breaks the time-reversal symmetry, and in contrast with the continuum model, a pointlike nonmagnetic impurity can lead to a decay in the persistent current
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