History-dependent relaxation and the energy scale of correlation in the electron glass

We present an experimental study of the energy relaxation in Anderson-insulating indium-oxide films excited far from equilibrium. In particular, we focus on the effects of history on the relaxation of the excess conductance ΔG. The natural relaxation law of ΔG is logarithmic: namely, ΔG∝ln(t). This may be observed over more than five decades following, for example, cool quenching the sample from high temperatures. On the other hand, when the system is excited from a state S_o in which it has not fully reached equilibrium to a state S_n, the ensuing relaxation law is logarithmic only over time t shorter than the time t_w it spent in S_o. For times t <˜t_w, ΔG(t) shows a systematic deviation from the logarithmic dependence. It was previously shown that when the energy imparted to the system in the excitation process is small, this leads to ΔG∝P(t/t_w) (simple aging). Here we test the conjecture that “simple aging” is related to a symmetry in the relaxation dynamics in S_o and S_n. This is done by using an experimental procedure that is more sensitive to deviations in the relaxation dynamics. It is shown that simple aging may still be obeyed [albeit with a modified P(t/t_w)] even when the symmetry of relaxation in S_o and S_n is perturbed by a certain degree. The implications of these findings to the question of aging and the energy scale associated with correlations are discussed.