Rate exchange rather than relaxation controls structural recovery

We observe structural recovery after an electric field step by probing the dielectric loss profile near its maximum, which displays a field-induced shift towards lower frequencies. These dynamics display time aging-time superposition (TaTS) for the majority of relaxation modes, thus implying homogeneous recovery dynamics. Although assumed by generally accepted models, the same modes can not be responsible for structural relaxation and for structural recovery, as the former is heterogeneous and the latter is homogeneous regarding the nature of the dynamics. This conflict is resolved by proposing that structural recovery is governed by rate exchange, a process that refers to the homogeneous fluctuations of rate constants in equilibrium and restores ergodicity more slowly than the relaxation observed as a simple correlation decay. This recognition has wide-ranging consequences on how aging and nonlinear dynamics such as scanning calorimetry should be modeled.