Atomistic mechanism of physical ageing in glassy materials

Using molecular simulations, we identify microscopic relaxation events of individual particles in ageing structural glasses, and determine the full distribution of relaxation times. We find that the memory of the waiting time t(omega) elapsed since the quench extends only up to the first relaxation event, while the distribution of all subsequent relaxation times (persistence times) follows a power law completely independent of history. Our results are in remarkable agreement with the well-known phenomenological trap model of ageing. A continuous-time random walk (CTRW) parametrized with the atomistic distributions captures the entire bulk diffusion behavior and explains the apparent scaling of the relaxation dynamics with t(omega) during ageing, as well as observed deviations from perfect scaling. Copyright (C) EPLA, 2009