Bringing Together Two Paradigms of Nonequilibrium: Fragile versus Robust Aging in Driven Glassy Systems

There are two key paradigms for nonequilibrium dynamics: on the one hand, aging toward an equilibrium state that cannot be reached on reasonable timescales; on the other, external driving that can lead to nonequilibrium steady states. We explore how these two mechanisms interact by studying the behavior of trap models, which are paradigmatic descriptions of slow glassy dynamics, when driven by trajectory bias toward high or low activity. To diagnose whether the driven systems continue to age, we establish a framework for mapping the biased dynamics to a Markovian time evolution with time-dependent transition rates. We find that the original aging dynamics reacts in two qualitatively distinct ways to the driving: it can be destroyed by the driving of any nonzero strength (“fragile” aging), whereby the dynamics either reaches an active steady state or effectively freezes, or it can persist within a finite range of driving strengths around the undriven case (“robust” aging). This classification into fragile and robust aging could form the basis for distinguishing different universality classes of aging dynamics.