MONTE-CARLO STUDIES OF ISING SPIN-GLASS SYSTEMS - INVESTIGATIONS OF THE OVERLAP LENGTH IN SPIN-GLASSES

In order to determine if the effects of an overlap length are visible in an Ising Edwards-Anderson spin-glass model, we have performed Monte Carlo simulations that mimic experimental procedures. The spin system was quenched from a random initial condition to a temperature T-1, equilibrated in zero held for a time t(w1), whereupon the system was subjected to a perturbation in field Delta H, temperature Delta T, or bond Delta J with a duration t(w2). After the perturbation the original held, the temperature or bonds were restored. 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 magnetization due to positive or negative field, and the spin autocorrelation function q(t) were studied as functions of time. For small perturbations, Delta H < Delta H-0, Delta T < Delta T-0, or Delta J < Delta J(0), respectively, the system is undisturbed. For larger perturbations, the correlations built up during t(w1) are gradually destroyed. Similar results are found in all three types of simulations and the qualitative features are in agreement with experimental results. These features are found for both two-dimensional and three-dimensional spin-glass systems. The results can be interpreted in the domain models for spin glasses. Delta H-0 is found to be strongly dependent on the duration t(w2) of the perturbation. If t(w1) is constant and t(w2) increases, Delta H-0 decreases. If t(w1) is set equal to t(w2) and t(w1) = t(w2) is increased, Delta H-0 decreases, in agreement with the expected behavior. Delta H-0 was found to increase with increasing temperature T, which is in agreement with experimental results, but contrary to the theoretical expectations.