Numerical study of the dynamics of some long range spin glass models

We present results of a Monte Carlo study of the equilibrium dynamics of the one dimensional long-range Ising spin glass model. By tuning a parameter $\sigma$, this model interpolates between the mean field Sherrington-Kirkpatrick model and a proxy of the finite dimensional Edward-Anderson model. Activated scaling fits for the behavior of the relaxation time $\tau$ as a function of the number of spins $N$ (Namely $\ln(\tau)\propto N^{\psi}$) give values of $\psi$ that are not stable against inclusion of subleading corrections. Critical scaling ($\tau\propto N^{\rho}$) gives more stable fits, at least in the non mean field region. We also present results on the scaling of the time decay of the critical remanent magnetization of the Sherrington-Kirkpatrick model, a case where the simulation can be done with quite large systems and that shows the difficulties in obtaining precise values for dynamical exponents in spin glass models

Rare events analysis of temperature chaos in the Sherrington-Kirkpatrick model

We investigate the question of temperature chaos in the Sherrington-Kirkpatrick spin glass model, applying to existing Monte Carlo data a recently proposed rare events based data analysis method. Thanks to this new method, temperature chaos is now observable for this model, even with the limited size systems that can be currently simulated

Numerical estimate of finite size corrections to the free energy of the SK model using Guerra--Toninelli interpolation

I use an interpolating formula introduced by Guerra and Toninelli to investigate numerically the finite size corrections to the free energy of the Sherrington--Kirkpatrick model. The results are compatible with a $(1/12 N) \ln(N/N_0)$ behavior at $T_c$, as predicted by Parisi, Ritort and Slanina, and a $1/N^{2/3}$ behavior below $T_c$

What makes slow samples slow in the Sherrington-Kirkpatrick model

Using results of a Monte Carlo simulation of the Sherrington-Kirkpatrick model, we try to characterize the slow disorder samples, namely we analyze visually the correlation between the relaxation time for a given disorder sample $J$ with several observables of the system for the same disorder sample. For temperatures below $T_c$ but not too low, fast samples (small relaxation times) are clearly correlated with a small value of the largest eigenvalue of the coupling matrix, a large value of the site averaged local field probability distribution at the origin, or a small value of the squared overlap $$. Within our limited data, the correlation remains as the system size increases but becomes less clear as the temperature is decreased (the correlation with$$ is more robust) . There is a strong correlation between the values of the relaxation time for two distinct values of the temperature, but this correlation decreases as the system size is increased. This may indicate the onset of temperature chaos

A Determination of Interface Free Energies

We determine the interface free energy $F_{o.d.}$ between disordered and ordered phases in the q=10 and q=20 2-d Potts models using the results of multicanonical Monte Carlo simulations on $L^2$ lattices, and suitable finite volume estimators. Our results, when extrapolated to the infinite volume limit, agree to high precision with recent analytical calculations. At the transition point $\beta_t$ the probability distribution function of the energy exhibits two maxima. Their locations have $1/L^2$ corrections, in contradiction with claims of $1/L$ behavior made in the literature. Our data show a flat region inbetween the two maxima which characterizes two domain configurations.Comment: Submited to Nuclear Physics B (FS) Latex file, 24 pages, 11 PostScript figures. Saclay preprint SPhT-93/6

On the Tail of the Overlap Probability Distribution in the Sherrington--Kirkpatrick Model

We investigate the large deviation behavior of the overlap probability density in the Sherrington--Kirkpatrick model from several analytical perspectives. First we analyze the spin glass phase using the coupled replica scheme. Here generically $\frac1N \log P_N(q)$ $\approx$ $- {\cal A}$ $((|q|-q_{EA})^3$, and we compute the first correction to the expansion of \A in powers of $T_c-T$. We study also the $q=1$ case, where $P(q)$ is know exactly. Finally we study the paramagnetic phase, where exact results valid for all $q$'s are obtained. The overall agreement between the various points of view is very satisfactory. Data from large scale numerical simulations show that the predicted behavior can be detected already on moderate lattice sizes.Comment: 18 pages including ps figure

Instantons and Surface Tension at a First-Order Transition

We study the dynamics of the first order phase transition in the two dimensional 15-state Potts model, both at and off equilibrium. We find that phase changes take place through nucleation in both cases, and finite volume effects are described well through an instanton computation. Thus a dynamical measurement of the surface tension is possible. We find that the order-disorder surface tension is compatible with perfect wetting. An accurate treatment of fluctuations about the instanton solution is seen to be of great importance.Comment: HLRZ 65/93 [plain TeX, 10 pages including 3 ps figures.