Ergodicity breaking of an inorganic glass aging near Tg probed by elasticity relaxation

We performed a series of aging experiments with an inorganic glass (As2Se3) at a temperature T2 near the glass transition point Tg by first relaxing it at T1. The relaxations of Young's modulus were monitored, which were (almost if not ideally) exponential with T1-dependent relaxation time tau, corroborating the Kovacs' paradox in an inorganic glass. Associated with the divergence of tau, the quasiequilibrated Young's modulus E infinity does not converge either. An elastic model of relaxation time and a Mori-Tanaka analysis of E infinity lead to a similar estimate of the persistent memory of the history, illuminating ergodicity breaking within the accessible experimental time, as described in the Gardner transition theory. Experiments with different T2 exhibit a critical temperature Tp similar to Tg, i.e., when T2 > Tp, both tau and E infinity converge. The results unveil a long-expected phenomenon that structural glass transition could be a zero-to-nonzero transition, manifested by a nonvanishing structural memory in aging when the temperature is below Tp in the glass transition range. This demonstrates the existence of the ergodicity breaking deep in the glass state and Tp could be the Gardner transition point of the structural glass.