Two-time correlations for probing the aging dynamics of glassy colloids.

We present results for the aging dynamics of a dense 2D colloidal system obtained with molecular dynamics simulations. To this end, systems are quenched to densities far above the glass transition with relaxation time scales that used to be prohibitive for such a comprehensive study. We performed extensive simulations to gather detailed statistics about rare rearrangement events. With a simple criterion for identifying irreversible events based on Voronoi tessellations, we find that the rate of those events decelerates hyperbolically. We track the probability density function for particle displacements, the van-Hove function, with sufficient statistics as to reveal its two-time dependence that is indicative of aging. Those displacements, measured from a waiting time tw after the quench up to times t, exhibit a data collapse as a function of t/tw. These findings can be explained comprehensively as manifestations of record dynamics, i.e., a relaxation dynamic driven by record-breaking fluctuations. We show that an on-lattice model of a colloid that was built on record dynamics indeed reproduces the experimental results in great detail.