67,757 research outputs found
Driven interfaces in random media at finite temperature : is there an anomalous zero-velocity phase at small external force ?
The motion of driven interfaces in random media at finite temperature and
small external force is usually described by a linear displacement at large times, where the velocity vanishes according to the
creep formula as for . In this paper,
we question this picture on the specific example of the directed polymer in a
two dimensional random medium. We have recently shown (C. Monthus and T. Garel,
arxiv:0802.2502) that its dynamics for F=0 can be analyzed in terms of a strong
disorder renormalization procedure, where the distribution of renormalized
barriers flows towards some "infinite disorder fixed point". In the present
paper, we obtain that for small , this "infinite disorder fixed point"
becomes a "strong disorder fixed point" with an exponential distribution of
renormalized barriers. The corresponding distribution of trapping times then
only decays as a power-law , where the exponent
vanishes as as . Our
conclusion is that in the small force region , the divergence of
the averaged trapping time induces strong
non-self-averaging effects that invalidate the usual creep formula obtained by
replacing all trapping times by the typical value. We find instead that the
motion is only sub-linearly in time , i.e. the
asymptotic velocity vanishes V=0. This analysis is confirmed by numerical
simulations of a directed polymer with a metric constraint driven in a traps
landscape. We moreover obtain that the roughness exponent, which is governed by
the equilibrium value up to some large scale, becomes equal to
at the largest scales.Comment: v3=final versio
Coherence Resonance in Chaotic Systems
We show that it is possible for chaotic systems to display the main features
of coherence resonance. In particular, we show that a Chua model, operating in
a chaotic regime and in the presence of noise, can exhibit oscillations whose
regularity is optimal for some intermediate value of the noise intensity. We
find that the power spectrum of the signal develops a peak at finite frequency
at intermediate values of the noise. These are all signatures of coherence
resonance. We also experimentally study a Chua circuit and corroborate the
above simulation results. Finally, we analyze a simple model composed of two
separate limit cycles which still exhibits coherence resonance, and show that
its behavior is qualitatively similar to that of the chaotic Chua systemComment: 4 pages (including 4 figures) LaTeX fil
Notes on Decoherence at Absolute Zero
The problem of electron decoherence at low temperature is analyzed from the
perspective of recent experiments on decoherence rate measurement and on
related localization phenomena in low-dimensional systems. Importance of
decoherence at zero temperature, perhaps induced by quantum fluctuations, is
put in a broader context.Comment: 7 pages in PRB format, 1 figur
Dynamical correlation functions of one-dimensional superconductors and Peierls and Mott insulators
I construct the spectral function of the Luther-Emery model which describes
one-dimensional fermions with one gapless and one gapped degree of freedom,
i.e. superconductors and Peierls and Mott insulators, by using symmetries,
relations to other models, and known limits. Depending on the relative
magnitudes of the charge and spin velocities, and on whether a charge or a spin
gap is present, I find spectral functions differing in the number of
singularities and presence or absence of anomalous dimensions of fermion
operators. I find, for a Peierls system, one singularity with anomalous
dimension and one finite maximum; for a superconductor two singularities with
anomalous dimensions; and for a Mott insulator one or two singularities without
anomalous dimension. In addition, there are strong shadow bands. I generalize
the construction to arbitrary dynamical multi-particle correlation functions.
The main aspects of this work are in agreement with numerical and Bethe Ansatz
calculations by others. I also discuss the application to photoemission
experiments on 1D Mott insulators and on the normal state of 1D Peierls
systems, and propose the Luther-Emery model as the generic description of 1D
charge density wave systems with important electronic correlations.Comment: Revtex, 27 pages, 5 figures, to be published in European Physical
Journal
Coherence scale of coupled Anderson impurities
For two coupled Anderson impurities, two energy scales are present to
characterize the evolution from local moment state of the impurities to either
of the inter-impurity singlet or the Kondo singlet ground states. The high
energy scale is found to deviate from the single-ion Kondo temperature and
rather scales as Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction when it
becomes dominant. We find that the scaling behavior and the associated physical
properties of this scale are consistent with those of a coherence scale defined
in heavy fermion systems.Comment: 10 pages, 7 figures, extended versio
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