2,990 research outputs found
Random-Manifold to Random-Periodic Depinning of an Elastic Interface
We study numerically the depinning transition of driven elastic interfaces in
a random-periodic medium with localized periodic-correlation peaks in the
direction of motion. The analysis of the moving interface geometry reveals the
existence of several characteristic lengths separating different length-scale
regimes of roughness. We determine the scaling behavior of these lengths as a
function of the velocity, temperature, driving force, and transverse
periodicity. A dynamical roughness diagram is thus obtained which contains, at
small length scales, the critical and fast-flow regimes typical of the
random-manifold (or domain wall) depinning, and at large length-scales, the
critical and fast-flow regimes typical of the random-periodic (or
charge-density wave) depinning. From the study of the equilibrium geometry we
are also able to infer the roughness diagram in the creep regime, extending the
depinning roughness diagram below threshold. Our results are relevant for
understanding the geometry at depinning of arrays of elastically coupled thin
manifolds in a disordered medium such as driven particle chains or vortex-line
planar arrays. They also allow to properly control the effect of transverse
periodic boundary conditions in large-scale simulations of driven disordered
interfaces.Comment: 19 pages, 10 figure
Thermal rounding exponent of the depinning transition of an elastic string in a random medium
We study numerically thermal effects at the depinning transition of an
elastic string driven in a two-dimensional uncorrelated disorder potential. The
velocity of the string exactly at the sample critical force is shown to behave
as , with the thermal rounding exponent. We show that the
computed value of the thermal rounding exponent, , is robust and
accounts for the different scaling properties of several observables both in
the steady-state and in the transient relaxation to the steady-state. In
particular, we show the compatibility of the thermal rounding exponent with the
scaling properties of the steady-state structure factor, the universal
short-time dynamics of the transient velocity at the sample critical force, and
the velocity scaling function describing the joint dependence of the
steady-state velocity on the external drive and temperature
Bragg- and Moving-glasses: a theory of disordered vortex lattices
We study periodic lattices, such as vortex lattices in type II
superconductors in a random pinning potential.
For the static case we review the prediction that the phase diagram of such
systems consists of a topologically ordered Bragg glass phase, with quasi long
range translational order, at low fields. This Bragg glass phase undergoes a
transition at higher fields into another glassy phase, with dislocations, or a
liquid. This proposition is compatible with a large number of experimental
results on BSCCO or Thalium compounds. Further experimental consequences of our
results and relevance to other systems will be discussed.
When such vortex systems are driven by an external force, we show that, due
to periodicity in the direction transverse to motion, the effects of static
disorder persist even at large velocity. In , at weak disorder, or large
velocity the lattice forms a topologically ordered glass state, the ``moving
Bragg glass'', an anisotropic version of the static Bragg glass. The lattice
flows through well-defined, elastically coupled, static channels. We determine
the roughness of the manifold of channels and the positional correlation
functions. The channel structure also provides a natural starting point to
study the influence of topological defects such as dislocations. In or at
strong disorder the channels can decouple along the direction of motion leading
to a ``smectic'' like flow. We also show that such a structure exhibits an
effective transverse critical pinning force due to barriers to transverse
motion, and discuss the experimental consequences of this effect.Comment: Proceedings of M2S-HTSC-V conference (Beijing, Feb 97) to be
published in Physica C; 4 pages, 3 figures, uses espcrc2.st
Some experimental tests of Tomonaga-Luttinger liquids
The Tomonaga-Luttinger-Liquid (TLL) has been the cornerstone of our
understanding of the properties of one dimensional systems. This universal set
of properties plays in one dimension, the same role than Fermi liquid plays for
the higher dimensional metals. I will give in these notes an overview of some
of the experimental tests that were made to probe such TLL physics. In
particular I will detail some of the recent experiments that were made in spin
systems and which provided remarkable quantitative tests of the TLL physics.Comment: Part of the special issue on "Luttinger liquids", Vieri Mastropietro
e
Luttinger liquid theory of purple bronze in the charge regime
Molybdenum purple bronze LiMoO is an exceptional
material known to exhibit one dimensional (1D) properties for energies down to
a few meV. This fact seems to be well established both in experiments and in
band structure theory. We use the unusual, very 1-dimensional band dispersion
obtained in \emph{ab-initio} DFT-LMTO band calculations as our starting point
to study the physics emerging below 300meV. A dispersion perpendicular to the
main dispersive direction is obtained and investigated in detail. Based on
this, we derive an effective low energy theory within the Tomonaga Luttinger
liquid (TLL) framework. We estimate the strength of the possible interactions
and from this deduce the values of the TLL parameters for charge modes. Finally
we investigate possible instabilities of TLL by deriving renormalization group
(RG) equations which allow us to predict the size of potential gaps in the
spectrum. While instabilities strongly suppress each other, the
instabilities cooperate, which paves the way for a possible CDW at the lowest
energies. The aim of this work is to understand the experimental findings, in
particular the ones which are certainly lying within the 1D regime. We discuss
the validity of our 1D approach and further perspectives for the lower energy
phases.Comment: We wish to acknowledge financial support of MaNEP, SectionI
Mode coupling induced dissipative and thermal effects at long times after a quantum quench
An interaction quench in a Luttinger liquid can drive it into an athermal
steady state. We analyze the effects on such an out of equilibrium state of a
mode coupling term due to a periodic potential. Employing a perturbative
renormalization group approach we show that even when the periodic potential is
an irrelevant perturbation in equilibrium, it has important consequences on the
athermal steady state as it generates a temperature as well as a dissipation
and hence a finite life-time for the bosonic modes.Comment: 4+ pages and 2 figure
Spectroscopy for cold atom gases in periodically phase-modulated optical lattices
The response of cold atom gases to small periodic phase modulation of an
optical lattice is discussed. For bosonic gases, the energy absorption rate is
given, within linear response theory, by imaginary part of the current
correlation function. For fermionic gases in a strong lattice potential, the
same correlation function can be probed via the production rate double
occupancy. The phase modulation gives thus direct access to the conductivity of
the system, as function of the modulation frequency. We give an example of
application in the case of one dimensional bosons at zero temperature and
discuss the link between the phase- and amplitude-modulation.Comment: 4 pages, 2 figures, final versio
Doping dependence of the vortex-core energy in bilayer films of cuprates
The energy needed to create a vortex core is the basic ingredient to address
the physics of thermal vortex fluctuations in underdoped cuprates. Here we
theoretically investigate its role on the occurrence of the
Beresinskii-Kosterlitz-Thouless transition in a bilayer film with
inhomogeneity. From the comparison with recent measurements of the penetration
depth in two-unit cell thin films of
YCaBaCuO_{7-\d} (YBCO) by Hetel et al. [Nat. Phys.
3, 700 (2007)] we can extract the value of the vortex-core energy , and
show that scales linearly with at low doping.Comment: 4pages, 3 figures. References added, final versio
Mott transition in one dimension
I review some of the results on the Mott transition in one dimensional
systems. In particular I discuss the phase diagram and critical properties of
both Mott transitions at fixed filling and upon doping, as well as the dc and
ac conductivity. Application of these results to organic conductors is
discussed.Comment: Proceedings of the SCES96 conference (August 96), 6 pages, 6 figures,
uses epsfi
- …