Quantifying Rejuvenation and Memory in Spin Glasses

Memory is among the most striking features of far-from-equilibrium systems. Whether a universal mechanism is responsible for memory is unknown, but spin glasses stand out. Memory effects are particularly strong in these systems because of the large attainable coherence lengths. More importantly, spin glass dynamics are now understood in great detail. In this context, rejuvenation is the observation that when the system is aged at a temperature T₁ for a time t_w1 and then cooled to a sufficiently lower T₂ the spin glass reverts apparently to the same state it would have achieved had it been cooled directly to T₂. We regard rejuvenation as a consequence of temperature chaos in spin glasses. However, when the spin glass is then warmed back to temperature T₁ it appears to have returned to its aged state, hence memory. We have developed a quantitative formulation for memory in rejuvenated glasses utilizing the measured coherence length, ξ_Zeeman related to the Zeeman effect; and the calculated coherence length, ξ_micro^native, the size of the glassy domains. In combination, they account quantitatively for memory from experment and simulations. We have confirmed that rejuvenation and temperature chaos are strongly related effects. Our results are based on first principles without the need for extraneous parameters. Our approach is easily extended to the many other glassy systems that exhibit these phenomena.