1,249 research outputs found

### Comment on "Ising Spin Glasses in a Magnetic Field"

In ref. cond-mat/9811419 Houdayer and Martin analyze the T=0 3d EA spin glass
with a magnetic field $B$. By using a new, powerful method, they determine an
effective critical field $B_c$ as a function of the lattice size $L$. They use
their results to deduce that the model is behaving like in the droplet approach
and not like the mean-field theory. We show here, by using some unpublished
data, that this very interesting method and numerical results are completely
compatible with the behavior implied by the Replica Symmetry Breaking theory.Comment: One page comment about ref. cond-mat/9811419, including two eps
figure

### 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

### Reply to Comment on "Ising Spin Glasses in a Magnetic Field"

The problem of the survival of a spin glass phase in the presence of a field
has been a challenging one for a long time. To date, all attempts using
equilibrium Monte Carlo methods have been unconclusive. In their comment to our
paper, Marinari, Parisi and Zuliani use out-of-equilibrium measurements to test
for an Almeida-Thouless line. In our view such a dynamic approach is not based
on very solid foundations in finite dimensional systems and so cannot be as
compelling as equilibrium approaches. Nevertheless, the results of those
authors suggests that there is a critical field near B=0.4 at zero temperature.
In view of this quite small value (compared to the mean field value), we have
reanalyzed our data. We find that if finite size scaling is to distinguish
between that small field and a zero field, we would need to go to lattice sizes
of about 20x20x20.Comment: reply to comment cond-mat/9812401 on ref. cond-mat/981141

### 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
$T\ne 0$ physics of the system.Comment: 14 pages and 4 ps 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 $V=10^4$: 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

### Spin glasses without time-reversal symmetry and the absence of a genuine structural glass transition

We study the three-spin model and the Ising spin glass in a field using
Migdal-Kadanoff approximation. The flows of the couplings and fields indicate
no phase transition, but they show even for the three-spin model a slow
crossover to the asymptotic high-temperature behaviour for strong values of the
couplings. We also evaluated a quantity that is a measure of the degree of
non-self-averaging, and we found that it can become large for certain ranges of
the parameters and the system sizes. For the spin glass in a field the maximum
of non-self-averaging follows for given system size a line that resembles the
de Almeida-Thouless line. We conclude that non-self-averaging found in
Monte-Carlo simulations cannot be taken as evidence for the existence of a
low-temperature phase with replica-symmetry breaking. Models similar to the
three-spin model have been extensively discussed in order to provide a
description of structural glasses. Their theory at mean-field level resembles
the mode-coupling theory of real glasses. At that level the one-step replica
symmetry approach breaking predicts two transitions, the first transition being
dynamical and the second thermodynamical. Our results suggest that in real
finite dimensional glasses there will be no genuine transitions at all, but
that some features of mean-field theory could still provide some useful
insights.Comment: 11 pages, 11 figure

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