Intermittency, aging and record fluctuations

Aging in spin glasses is analyzed via the Probability Density Function (PDF) of the heat transfer between system and bath over a small time $\delta t$. The PDF contains a Gaussian part, describing reversible fluctuations, and an exponential tail caused by intermittent events. We find that the relative weight of these two parts depends, for fixed $\delta t$, on the ratio of the total sampling time to the age $t_w$. Fixing this ratio, the intensity of the intermittent events is proportional to $\delta t/t_w$ and independent of the temperature. The Gaussian part has a variance with the same temperature dependence as the variance of the equilibrium energy in a system with an exponential density of states. All these observations are explained assuming that, for any $t_w$, intermittent events are triggered by local energy fluctuations exceeding those previously occurred.