Strong correlation between local free volume and stringlike motions in a hard-disk glass former

Glass formers are ubiquitous, but their dynamics under deep supercooling are still under intensive debate. Free volume plays a central role in many theoretical descriptions, but earlier studies often reported only weak correlations between local free volume and particle mobility. We analyze free volume by measuring excess local unoccupied volume around jumping particles in a dense hard-disk system. While free volume in highly localized regions is found to be quite uncorrelated with dynamics at structural relaxation time scales, strong correlations are clearly observed between regions of several particle diameters wide and dynamics at much shorter times. Free volume is shown to be more abundant at tails than at heads during stringlike particle jumping motions.