41,798 research outputs found
Understanding delocalization in the Continuous Random Dimer model
We propose an explanation of the bands of extended states appearing in random
one dimensional models with correlated disorder, focusing on the Continuous
Random Dimer model [A.\ S\'{a}nchez, E.\ Maci\'a, and F.\ Dom\'\i nguez-Adame,
Phys.\ Rev.\ B {\bf 49}, 147 (1994)]. We show exactly that the transmission
coefficient at the resonant energy is independent of the number of host sites
between two consecutive dimers. This allows us to understand why are there
bands of extended states for every realization of the model as well as the
dependence of the bandwidths on the concentration. We carry out a perturbative
calculation that sheds more light on the above results. In the conclusion we
discuss generalizations of our results to other models and possible
applications which arise from our new insight of this problem.Comment: REVTeX 3.0, 4 pages, 4 figures (hard copy on request from
[email protected]), Submitted to Phys Rev
Rayleigh scattering and atomic dynamics in dissipative optical lattices
We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [S. Guibal et al., Phys. Rev. Lett. 78, 4709 (1997); C. Jurczak et al., Phys. Rev. Lett. 77, 1727 (1996)], we study whether the Rayleigh resonance originates from the diffraction on a density grating and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance
Breathers in FPU systems, near and far from the phonon band
There exists a recent mathematical proof on the existence of small amplitude
breathers in FPU systems near the phonon band, which includes a prediction of
their amplitude and width. In this work we obtain numerically these breathers,
and calculate the range of validity of the predictions, which extends
relatively far from the phonon band. There exist also large amplitude breathers
with the same frequency, with the consequence that there is an energy gap for
breather creation in these systems.Comment: 3 pages, 2 figures, proceeding of the conference on Localization and
to and Energy Transfer in Nonlinear Systems, June 17-21, 2002, San Lorenzo de
El Escorial, Madrid, Spain. To be published by World Scientifi
Electron and Phonon Temperature Relaxation in Semiconductors Excited by Thermal Pulse
Electron and phonon transient temperatures are analyzed in the case of
nondegenerate semiconductors. An analytical solution is obtained for
rectangular laser pulse absorption. It is shown that thermal diffusion is the
main energy relaxation mechanism in the phonon subsystem. The mechanism depends
on the correlation between the sample length and the electron cooling length in
an electron subsystem. Energy relaxation occurs by means of the electron
thermal diffusion in thin samples (), and by means of the electron-phonon
energy interaction in thick samples (). Characteristic relaxation times are
obtained for all the cases, and analysis of these times is made. Electron and
phonon temperature distributions in short and long samples are qualitatively
and quantitatively analyzed for different correlations between the laser pulse
duration and characteristic times.Comment: 33 pages, 16 figure
Stochastic resonance in periodic potentials: realization in a dissipative optical lattice
We have observed the phenomenon of stochastic resonance on the Brillouin
propagation modes of a dissipative optical lattice. Such a mode has been
excited by applying a moving potential modulation with phase velocity equal to
the velocity of the mode. Its amplitude has been characterized by the
center-of-mass (CM) velocity of the atomic cloud. At Brillouin resonance, we
studied the CM-velocity as a function of the optical pumping rate at a given
depth of the potential wells. We have observed a resonant dependence of the CM
velocity on the optical pumping rate, corresponding to the noise strength. This
corresponds to the experimental observation of stochastic resonance in a
periodic potential in the low-damping regime
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