769 research outputs found
Comment on ``Triviality of the Ground State Structure in Ising Spin Glasses''
We show that the evidence of cond-mat/9906323 does not discriminate among
droplet model and mean field like behavior.Comment: 1 page comment with two .ps figures included. Rewritten version, one
error correcte
Off-Equilibrium Dynamics of a 4D Spin Glass with Asymmetric Couplings
We study the off-equilibrium dynamics of the Edwards-Anderson spin glass in
four dimensions under the influence of a non-hamiltonian perturbation. We find
that for small asymmetry the model behaves as the hamiltonian one, while for
large asymmetry the behaviour of the model can be well described by an
interrupted aging scenario. The autocorrelation function C(t_w+\tau,t_w) scales
as \tau/t_w^\beta, with \beta a function of the asymmetry. For very long
waiting times the previous regime crosses over to a time translational
invariant regime (TTI) with stretched exponential relaxation. The model does
not show signs of reaching a TTI regime for weak asymmetry, but in the aging
regime the exponent \beta is always different from one, showing a non trivial
aging scenario.Comment: Latex, 12 pages, 9 figure
Numerical Simulations of the 4D Edwards-Anderson Spin Glass with Binary Couplings
We present numerical results that allow a precise determination of the
transition point and of the critical exponents of the 4D Edwards-Anderson Spin
Glass with binary quenched random couplings. We show that the low T phase
undergoes Replica Symmetry Breaking. We obtain results on large lattices, up to
a volume : we use finite size scaling to show the relevance of our
results in the infinite volume limit.Comment: 18 pages + 17 figures, revised bibliography and minor typos. Added
Journal Re
Small Window Overlaps Are Effective Probes of Replica Symmetry Breaking in 3D Spin Glasses
We compute numerically small window overlaps in the three dimensional Edwards
Anderson spin glass. We show that they behave in the way implied by the Replica
Symmetry Breaking Ansatz, that they do not qualitatively differ from the full
volume overlap and do not tend to a trivial function when increasing the
lattice volume. On the contrary we show they are affected by small finite
volume effects, and are interesting tools for the study of the features of the
spin glass phase.Comment: 9 pages plus 5 figure
Low T Dynamical Properties of Spin Glasses Smoothly Extrapolate to T=0
We compare ground state properties of 3D Ising Spin Glasses with Gaussian
couplings with results from off-equilibrium numerical simulations at non zero
(but low) temperatures. We find that the non-zero temperature properties of the
system smoothly connect to the T=0 behavior, confirming the point of view that
results established at T=0 typically also give relevant information about the
physics of the system.Comment: 14 pages and 4 ps figure
On Heteropolymer Shape Dynamics
We investigate the time evolution of the heteropolymer model introduced by
Iori, Marinari and Parisi to describe some of the features of protein folding
mechanisms. We study how the (folded) shape of the chain evolves in time. We
find that for short times the mean square distance (squared) between chain
configurations evolves according to a power law, . We discuss
the influence of the quenched disorder (represented by the randomness of the
coupling constants in the Lennard-Jones potential) on value of the critical
exponent. We find that decreases from to when
the strength of the quenched disorder increases.Comment: 12 pages, very simple LaTeX file, 6 figures not included, sorry. SCCS
33
On the Phase Structure of the 3D Edwards Anderson Spin Glass
We characterize numerically the properties of the phase transition of the
three dimensional Ising spin glass with Gaussian couplings and of the low
temperature phase. We compute critical exponents on large lattices. We study in
detail the overlap probability distribution and the equilibrium overlap-overlap
correlation functions. We find a clear agreement with off-equilibrium results
from previous work. These results strongly support the existence of a
continuous spontaneous replica symmetry breaking in three dimensional spin
glasses.Comment: 30 pages and 17 figures. Final version to be published in PR
Equilibrium valleys in spin glasses at low temperature
We investigate the 3-dimensional Edwards-Anderson spin glass model at low
temperature on simple cubic lattices of sizes up to L=12. Our findings show a
strong continuity among T>0 physical features and those found previously at
T=0, leading to a scenario with emerging mean field like characteristics that
are enhanced in the large volume limit. For instance, the picture of space
filling sponges seems to survive in the large volume limit at T>0, while
entropic effects play a crucial role in determining the free-energy degeneracy
of our finite volume states. All of our analysis is applied to equilibrium
configurations obtained by a parallel tempering on 512 different disorder
realizations. First, we consider the spatial properties of the sites where
pairs of independent spin configurations differ and we introduce a modified
spin overlap distribution which exhibits a non-trivial limit for large L.
Second, after removing the Z_2 (+-1) symmetry, we cluster spin configurations
into valleys. On average these valleys have free-energy differences of O(1),
but a difference in the (extensive) internal energy that grows significantly
with L; there is thus a large interplay between energy and entropy
fluctuations. We also find that valleys typically differ by sponge-like space
filling clusters, just as found previously for low-energy system-size
excitations above the ground state.Comment: 10 pages, 8 figures, RevTeX format. Clarifications and additional
reference
4D Spin Glasses in Magnetic Field Have a Mean Field like Phase
By using numerical simulations we show that the 4D Edwards Anderson
spin glass in magnetic field undergoes a mean field like phase transition. We
use a dynamical approach: we simulate large lattices (of volume ) and work
out the behavior of the system in limit where both and go to infinity,
but where the limit is taken first. By showing that the dynamic
overlap converges to a value smaller than the static one we exhibit replica
symmetry breaking. The critical exponents are compatible with the ones obtained
by mean field computations.Comment: Physrev format, 5 ps figures include
On the Effects of Changing the Boundary Conditions on the Ground State of Ising Spin Glasses
We compute and analyze couples of ground states of 3D spin glass systems with
the same quenched noise but periodic and anti-periodic boundary conditions for
different lattice sizes. We discuss the possible different behaviors of the
system, we analyze the average link overlap, the probability distribution of
window overlaps (among ground states computed with different boundary
conditions) and the spatial overlap and link overlap correlation functions. We
establish that the picture based on Replica Symmetry Breaking correctly
describes the behavior of 3D Spin Glasses.Comment: 25 pages with 11 ps figures include
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