Mechanism of memory and rejuvenation in aging spin glasses
In plain words
A spin glass cooled, held at one temperature and then cooled further appears to start aging anew (rejuvenation), yet it recovers its earlier state when reheated (memory). Which microscopic processes produce both effects at once is not settled.
Precise statement
In temperature-cycling protocols on spin-glass samples and in large simulations of the $3\mathrm{D}$ Edwards-Anderson model, identify the mechanism (growing correlation lengths, temperature chaos, hierarchical states) that yields both rejuvenation of the out-of-phase susceptibility $\chi''(\omega,t)$ after a step $\Delta T$ and memory of earlier aging plateaus. An answer is a theory that predicts $\chi''(\omega,t)$ quantitatively as a function of $\Delta T$ and waiting times.
What would settle it
A model that reproduces measured $\chi''(\omega, t)$ curves for several temperature-step protocols with no free parameters beyond equilibrium properties.
Status in the literature
Large-scale simulations by the Janus collaboration (2023) reproduced memory and rejuvenation and linked them to more than one growing length scale; a quantitative match to experiment is lacking.