2,405 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 $V \sim T^\psi$, with $\psi$ the thermal rounding exponent. We show that the
computed value of the thermal rounding exponent, $\psi = 0.15$, 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

### Luttinger liquid theory of purple bronze $Li_{0.9}Mo_6O_{17}$ in the charge regime

Molybdenum purple bronze Li$_{0.9}$Mo$_{6}$O$_{17}$ 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 $2k_F$ instabilities strongly suppress each other, the $4k_F$
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

### Hall effect in strongly correlated low dimensional systems

We investigate the Hall effect in a quasi one-dimensional system made of
weakly coupled Luttinger Liquids at half filling. Using a memory function
approach, we compute the Hall coefficient as a function of temperature and
frequency in the presence of umklapp scattering. We find a power-law correction
to the free-fermion value (band value), with an exponent depending on the
Luttinger parameter $K_{\rho}$. At high enough temperature or frequency the
Hall coefficient approaches the band value.Comment: 7 pages, 3 figure

### 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
Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O_{7-\d} (YBCO) by Hetel et al. [Nat. Phys.
3, 700 (2007)] we can extract the value of the vortex-core energy $\mu$, and
show that $\mu$ scales linearly with $T_c$ at low doping.Comment: 4pages, 3 figures. References added, final versio

### Spin rotational symmetry breaking by orbital current patterns in two-leg ladders.

We investigate the physical consequences of orbital current patterns (OCP) in
doped two-leg Cu-O Hubbard ladders. The internal symmetry of the pattern, in
the case of the ladder structure, differs slightly from that suggested so far
for cuprates. We focus on this OCP and look for measurable signatures of its
existence. We compute the magnetic field produced by the OCP at each lattice
site, and estimate its value in view of a possible experimental detection.
Using a renormalization group (RG) analysis, we determine the changes that are
caused by the SU(2) spin-rotational symmetry breaking which occurs when the OCP
is present in the ground state phase diagram. The most signifcant one is an
in-plane SDW gap opening in an otherwise critical phase, at intermediate
dopings. We estimate the value of this gap, give an analytic expression for the
correlation functions and examine some of the magnetic properties of this new
phase which can be revealed in measurements. We compute the conductance in the
presence of a single impurity, using an RG analysis. A discussion of the
various sources of SU(2) symmetry breaking underscores the specificity of the
OCP induced effects.Comment: 12 pages, 3 figures, submitted to PR

### Thermal rounding of the depinning transition

We study thermal effects at the depinning transition by numerical simulations
of driven one-dimensional elastic interfaces in a disordered medium. We find
that the velocity of the interface, evaluated at the critical depinning force,
can be correctly described with the power law $v\sim T^\psi$, where $\psi$ is
the thermal exponent. Using the sample-dependent value of the critical force,
we precisely evaluate the value of $\psi$ directly from the temperature
dependence of the velocity, obtaining the value $\psi = 0.15 \pm 0.01$. By
measuring the structure factor of the interface we show that both the
thermally-rounded and the T=0 depinning, display the same large-scale geometry,
described by an identical divergence of a characteristic length with the
velocity $\xi \propto v^{-\nu/\beta}$, where $\nu$ and $\beta$ are respectively
the T=0 correlation and depinning exponents. We discuss the comparison of our
results with previous estimates of the thermal exponent and the direct
consequences for recent experiments on magnetic domain wall motion in
ferromagnetic thin films.Comment: 6 pages, 3 figure

### 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

### Deconfinement and cold atoms in optical lattices

Despite the fact that by now one dimensional and three dimensional systems of
interacting particles are reasonably well understood, very little is known on
how to go from the one dimensional physics to the three dimensional one. This
is in particular true in a quasi-one dimensional geometry where the hopping of
particles between one dimensional chains or tubes can lead to a dimensional
crossover between a Luttinger liquid and more conventional high dimensional
states. Such a situation is relevant to many physical systems. Recently cold
atoms in optical traps have provided a unique and controllable system in which
to investigate this physics. We thus analyze a system made of coupled one
dimensional tubes of interacting fermions. We explore the observable
consequences, such as the phase diagram for isolated tubes, and the possibility
to realize unusual superfluid phases in coupled tubes systems.Comment: Proceedings of the conference on "Quantum Many Body Theories 13", to
be published by World Scientifi

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