Local fluctuations in the ageing of a simple structural glass

The presence of dynamical heterogeneities-that is, nanometre-scale regions of molecules rearranging cooperatively at very different rates compared with the bulk(1,2)-is increasingly being recognized as crucial to our understanding of the glass transition, from the non-exponential relaxation to the divergence of the relaxation times(3). Although recent experiments(4-11) and simulations(12-14) have observed their presence directly, a clear physical picture of their origin is still lacking. Here, we present the first detailed characterization of the statistics of local fluctuations in a simulation of the ageing of a continuous-space, quasi-realistic structural glass model. A possible physical mechanism(15-18) for the origin of dynamical heterogeneities in the non-equilibrium dynamics of glassy systems predicts universal scaling of the probability distributions of two-time local fluctuations. We find that to a first approximation this scaling is indeed satisfied by our results. We propose to test our results using confocal microscopy and atomic force microscopy experiments.