1,038 research outputs found
Dynamics below the depinning threshold
We study the steady-state low-temperature dynamics of an elastic line in a
disordered medium below the depinning threshold. Analogously to the equilibrium
dynamics, in the limit T->0, the steady state is dominated by a single
configuration which is occupied with probability one. We develop an exact
algorithm to target this dominant configuration and to analyze its geometrical
properties as a function of the driving force. The roughness exponent of the
line at large scales is identical to the one at depinning. No length scale
diverges in the steady state regime as the depinning threshold is approached
from below. We do find, a divergent length, but it is associated only with the
transient relaxation between metastable states.Comment: 4 pages, 3 figure
Universal Statistics of the Critical Depinning Force of Elastic Systems in Random Media
We study the rescaled probability distribution of the critical depinning
force of an elastic system in a random medium. We put in evidence the
underlying connection between the critical properties of the depinning
transition and the extreme value statistics of correlated variables. The
distribution is Gaussian for all periodic systems, while in the case of random
manifolds there exists a family of universal functions ranging from the
Gaussian to the Gumbel distribution. Both of these scenarios are a priori
experimentally accessible in finite, macroscopic, disordered elastic systems.Comment: 4 pages, 4 figure
Domain scaling and marginality breaking in the random field Ising model
A scaling description is obtained for the --dimensional random field Ising
model from domains in a bar geometry. Wall roughening removes the marginality
of the case, giving the correlation length in , and for power law behaviour with
, . Here, (lattice, continuum) is one of four rough wall exponents provided by the
theory. The analysis is substantiated by three different numerical techniques
(transfer matrix, Monte Carlo, ground state algorithm). These provide for
strips up to width basic ingredients of the theory, namely free energy,
domain size, and roughening data and exponents.Comment: ReVTeX v3.0, 19 pages plus 19 figures uuencoded in a separate file.
These are self-unpacking via a shell scrip
Nonperturbative Functional Renormalization Group for Random Field Models. III: Superfield formalism and ground-state dominance
We reformulate the nonperturbative functional renormalization group for the
random field Ising model in a superfield formalism, extending the
supersymmetric description of the critical behavior of the system first
proposed by Parisi and Sourlas [Phys. Rev. Lett. 43, 744 (1979)]. We show that
the two crucial ingredients for this extension are the introduction of a
weighting factor, which accounts for ground-state dominance when multiple
metastable states are present, and of multiple copies of the original system,
which allows one to access the full functional dependence of the cumulants of
the renormalized disorder and to describe rare events. We then derive exact
renormalization group equations for the flow of the renormalized cumulants
associated with the effective average action.Comment: 28 page
Steric repulsion and van der Waals attraction between flux lines in disordered high Tc superconductors
We show that in anisotropic or layered superconductors impurities induce a
van der Waals attraction between flux lines. This attraction together with the
disorder induced repulsion may change the low B - low T phase diagram
significantly from that of the pure thermal case considered recently by Blatter
and Geshkenbein [Phys. Rev. Lett. 77, 4958 (1996)].Comment: Latex, 4 pages, 1 figure (Phys. Rev. Lett. 79, 139 (1997)
Dislocations in the ground state of the solid-on-solid model on a disordered substrate
We investigate the effects of topological defects (dislocations) to the
ground state of the solid-on-solid (SOS) model on a simple cubic disordered
substrate utilizing the min-cost-flow algorithm from combinatorial
optimization. The dislocations are found to destabilize and destroy the elastic
phase, particularly when the defects are placed only in partially optimized
positions. For multi defect pairs their density decreases exponentially with
the vortex core energy. Their mean distance has a maximum depending on the
vortex core energy and system size, which gives a fractal dimension of . The maximal mean distances correspond to special vortex core
energies for which the scaling behavior of the density of dislocations change
from a pure exponential decay to a stretched one. Furthermore, an extra
introduced vortex pair is screened due to the disorder-induced defects and its
energy is linear in the vortex core energy.Comment: 6 pages RevTeX, eps figures include
On Integrable Doebner-Goldin Equations
We suggest a method for integrating sub-families of a family of nonlinear
{\sc Schr\"odinger} equations proposed by {\sc H.-D.~Doebner} and {\sc
G.A.~Goldin} in the 1+1 dimensional case which have exceptional {\sc Lie}
symmetries. Since the method of integration involves non-local transformations
of dependent and independent variables, general solutions obtained include
implicitly determined functions. By properly specifying one of the arbitrary
functions contained in these solutions, we obtain broad classes of explicit
square integrable solutions. The physical significance and some analytical
properties of the solutions obtained are briefly discussed.Comment: 23 pages, revtex, 1 figure, uses epsfig.sty and amssymb.st
Phase transitions in a disordered system in and out of equilibrium
The equilibrium and non--equilibrium disorder induced phase transitions are
compared in the random-field Ising model (RFIM). We identify in the
demagnetized state (DS) the correct non-equilibrium hysteretic counterpart of
the T=0 ground state (GS), and present evidence of universality. Numerical
simulations in d=3 indicate that exponents and scaling functions coincide,
while the location of the critical point differs, as corroborated by exact
results for the Bethe lattice. These results are of relevance for optimization,
and for the generic question of universality in the presence of disorder.Comment: Accepted for publication in Phys. Rev. Let
Interlayer tunneling in double-layer quantum Hall pseudo-ferromagnets
We show that the interlayer tunneling I--V in double-layer quantum Hall
states displays a rich behavior which depends on the relative magnitude of
sample size, voltage length scale, current screening, disorder and thermal
lengths. For weak tunneling, we predict a negative differential conductance of
a power-law shape crossing over to a sharp zero-bias peak. An in-plane magnetic
field splits this zero-bias peak, leading instead to a ``derivative'' feature
at , which gives a direct measure of
the dispersion of the Goldstone mode corresponding to the spontaneous symmetry
breaking of the double-layer Hall state.Comment: 4 pgs. RevTex, submitted to Phys. Rev. Let
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