A statistical approach to rejuvenation and memory in spin glasses

Rejuvenation and memory in spin glasses are approached from a statistical perspective. The analysis is based on temperature chaos being a "rare-event-driven phenomenon." Three regions are identified with increasing magnitudes of negative temperature shifts -δT (δT > 0). The first region exhibits reversibile dynamics for δT sufficiently small. The second is the chaotic regime for larger δT where the dynamics re-start, termed "rejuvenation." Only a few spatial regions of size of the order of the spin glass correlaton length go chaotic. The large number of separated correlated regions for correlation lengths much less than the sample thickness or crystallie size (e.g. thin films or bulk samples) suggests that, as the temperature is lowered further, the probability that those regions that went chaotic in the rejuvenation regime would go chaotic again is statistically small. The growth of free energy barriers in these "rare" regions as the temperature is lowered further (δT increasing) "freezes" their dynamics. As the temperature is raised back to the rejuvenation regime, their dynamics are "revived" and return to those initially measured. This is the origin of "memory."