Dynamic facilitation explains ‘democratic’ particle motion of metabasin transitions

Abstract

Transitions between metabasins in supercooled liquids seem to occur through rapid collective particle rearrangements. These events have been called ‘democratic’ as they appear homogeneous over a significant number of particles. This could suggest that ‘democratic’ rearrangements are fundamentally distinct to those leading to dynamic heterogeneity. Here we show, however, that this apparent homogeneous particle motion can be explained solely in terms of dynamic facilitation, and is therefore intriniscally heterogeneous. We do so by studying metabasin transitions in facilitated spin models and constrained lattice gases. We find that metabasin transitions occur through a sequence of locally facilitated events taking place over a relatively short time frame. When observed on small enough spatial windows these events appear sudden and homogeneous. Our results indicate that metabasin transitions, while apparently homogeneous and ‘democratic’, are yet another manifestation of dynamical heterogeneity in glass formers.