Relaxation rate fluctuations in glass-forming liquids

Liquids near the glass transition exhibit dynamical heterogeneity, i.e. regions with faster and slower relaxation that evolve over time. We show that the local relaxation rate provides a direct description of this phenomenon, and that dynamical heterogeneity can be quantified in terms of two-point spatio-temporal correlation functions of the relaxation rate. We apply this approach to numerical simulation data from glass-forming liquid models, and use it to investigate the characteristic size and lifetime of the heterogeneous regions. In particular, we study a model of rotating molecules, and compare the heterogeneous dynamics for the translational and rotational degrees of freedom.