341 research outputs found
Out-of-equilibrium dynamical fluctuations in glassy systems
In this paper we extend the earlier treatment of out-of-equilibrium
mesoscopic fluctuations in glassy systems in several significant ways. First,
via extensive simulations, we demonstrate that models of glassy behavior
without quenched disorder display scalings of the probability of local two-time
correlators that are qualitatively similar to that of models with short-ranged
quenched interactions. The key ingredient for such scaling properties is shown
to be the development of a critical-like dynamical correlation length, and not
other microscopic details. This robust data collapse may be described in terms
of a time-evolving Gumbel-like distribution. We develop a theory to describe
both the form and evolution of these distributions based on a effective
sigma-model approach.Comment: 20 pages, RevTex, 9 figure
Green's Function Approach to the Edge Spectral Density
It is shown that the conventional many-body techniques to calculate the
Green's functions can be applied to the wide, compressible edge of a quantum
Hall bar. The only ansatz we need is the existence of stable density modes that
yields a simple equation of motion of the density operators. We derive the
spectral density at a finite temperature and show how the tunneling
characteristics of a sharp edge can be deduced as a limiting case.Comment: Revised and Enlarged. Submitted to Phys. Rev.
Out-of-equilibrium relaxation of the Edwards-Wilkinson elastic line
We study the non-equilibrium relaxation of an elastic line described by the
Edwards-Wilkinson equation. Although this model is the simplest representation
of interface dynamics, we highlight that many (not though all) important
aspects of the non-equilibrium relaxation of elastic manifolds are already
present in such quadratic and clean systems. We analyze in detail the aging
behaviour of several two-times averaged and fluctuating observables taking into
account finite-size effects and the crossover to the stationary and equilibrium
regimes. We start by investigating the structure factor and extracting from its
decay a growing correlation length. We present the full two-times and size
dependence of the interface roughness and we generalize the Family-Vicsek
scaling form to non-equilibrium situations. We compute the incoherent cattering
function and we compare it to the one measured in other glassy systems. We
analyse the response functions, the violation of the fluctuation-dissipation
theorem in the aging regime, and its crossover to the equilibrium relation in
the stationary regime. Finally, we study the out-of-equilibrium fluctuations of
the previously studied two-times functions and we characterize the scaling
properties of their probability distribution functions. Our results allow us to
obtain new insights into other glassy problems such as the aging behavior in
colloidal glasses and vortex glasses.Comment: 33 pages, 16 fig
Magnetic Field Dependence of the Level Spacing of a Small Electron Droplet
The temperature dependence of conductance resonances is used to measure the
evolution with the magnetic field of the average level spacing
of a droplet containing electrons created by lateral confinement of a
two-dimensional electron gas in GaAs. becomes very small (eV) near two critical magnetic fields at which the symmetry of the
droplet changes and these decreases of are predicted by
Hartree-Fock (HF) for charge excitations. Between the two critical fields,
however, the largest measured eV is an order of
magnitude smaller than predicted by HF but comparable to the Zeeman splitting
at this field, which suggests that the spin degrees of freedom are important.
PACS: 73.20.Dx, 73.20.MfComment: 11 pages of text in RevTeX, 4 figures in Postscript (files in the
form of uuencoded compressed tar file
Fluctuations of two-time quantities and time-reparametrization invariance in spin-glasses
This article is a contribution to the understanding of fluctuations in the
out of equilibrium dynamics of glassy systems. By extending theoretical ideas
based on the assumption that time-reparametrization invariance develops
asymptotically we deduce the scaling properties of diverse high-order
correlation functions. We examine these predictions with numerical tests in a
standard glassy model, the 3d Edwards-Anderson spin-glass, and in a system
where time-reparametrization invariance is not expected to hold, the 2d
ferromagnetic Ising model, both at low temperatures. Our results enlighten a
qualitative difference between the fluctuation properties of the two models and
show that scaling properties conform to the time-reparametrization invariance
scenario in the former but not in the latter.Comment: 17 pages, 5 figure
Anomalous Quantum Diffusion at the Superfluid-Insulator Transition
We consider the problem of the superconductor-insulator transition in the
presence of disorder, assuming that the fermionic degrees of freedom can be
ignored so that the problem reduces to one of Cooper pair localization. Weak
disorder drives the critical behavior away from the pure critical point,
initially towards a diffusive fixed point. We consider the effects of Coulomb
interactions and quantum interference at this diffusive fixed point. Coulomb
interactions enhance the conductivity, in contrast to the situation for
fermions, essentially because the exchange interaction is opposite in sign. The
interaction-driven enhancement of the conductivity is larger than the
weak-localization suppression, so the system scales to a perfect conductor.
Thus, it is a consistent possibility for the critical resistivity at the
superconductor-insulator transition to be zero, but this value is only
approached logarithmically. We determine the values of the critical exponents
and comment on possible implications for the interpretation of
experiments
Non-equilibrium tunneling into general quantum Hall edge states
In this paper we formulate the theory of tunneling into general Abelian
fractional quantum Hall edge states. In contrast to the simple Laughlin states,
a number of charge transfer processes must be accounted for. Nonetheless, it is
possible to identify a unique value corresponding to dissipationless transport
as the asymptotic large- conductance through a tunneling junction, and find
fixed points (CFT boundary conditions) corresponding to this value. The
symmetries of a given edge tunneling problem determine the appropriate boundary
condition, and the boundary condition determines the strong-coupling operator
content and current noise.Comment: 6 pages, 3 figures; published versio
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