MONTE-CARLO EVIDENCE FOR THE EXISTENCE OF AN OVERLAP LENGTH IN ISING SPIN-GLASS SYSTEMS

Monte Carlo simulations of an Ising spin glass model have been performed. The spin system was quenched from a random initial condition, equilibrated for a time t(wl), whereupon the system was subjected to a field perturbation for a time t(w2). After waiting for a time t(w3), a weak magnetic field h was applied. The susceptibility CHI(t) = (M+(t)-M-(t))/2h, where M+/-(t) is the magnetisation due to a positive/negative field h, was studied as function of time. The time dependence of the susceptibility shows behaviour similar to results of temperature cycling experiments. We show, for the first time, that the effects of an overlap length are seen also in field cyclings.