Geometrical Aspects of Aging and Rejuvenation in the Ising Spin Glass: A Numerical Study

We present a comprehensive study of non-equilibrium phenomena in the low temperature phase of the Edwards-Anderson Gaussian spin glass in 3 and 4 spatial dimensions. Many effects can be understood in terms of a time dependent coherence length, $\ell_T$, such that length scales smaller that $\ell_T$ are equilibrated, whereas larger length scales are essentially frozen. The time and temperature dependence of $\ell_T$ is found to be compatible with critical power-law dynamical scaling for small times/high temperatures, crossing over to an activated logarithmic growth for longer times/lower temperatures, in agreement with recent experimental results. The activated regime is governed by a `barrier exponent' psi which we estimate to be psi ~ 1.0 and psi ~ 2.3 in 3 and 4 dimensions, respectively. We observe for the first time the rejuvenation and memory effects in the four dimensional sample, which, we argue, is unrelated to `temperature chaos'. Our discussion in terms of length scales allows us to address several experimentally relevant issues, such as super-aging versus sub-aging effects, the role of a finite cooling rate, or the so-called Kovacs effect.