Evolution of dynamical facilitation approaching the granular glass transition

TL;DR

This study examines how the relaxation dynamics and facilitation mechanisms in a dense granular monolayer evolve as the system approaches the granular glass transition, revealing a decline in facilitation's role.

Contribution

It provides experimental evidence that dynamical facilitation diminishes near the granular glass transition, highlighting changes in relaxation event organization with increasing density.

Findings

Cluster organization shifts from random to large avalanches with density

Dynamical facilitation becomes less conserved near the transition

Relaxation dynamics involve increasingly sparse and large events

Abstract

We investigate the relaxation dynamics of a dense monolayer of bidisperse beads by analyzing the experimental data previously obtained in a fluidized bed. We show that the dynamics is formed by elementary relaxation events called cage jumps. These aggregate on a very short time into clusters. Increasing the packing fraction makes the spatio-temporal organization of the clusters evolve from a rather scattered and random distribution towards a collection of sparse and large events, called avalanches. The avalanche process is a manifestation of dynamical facilitation. The study of its evolution with density reveals that dynamical facilitation becomes less conserved and play a lesser role for the structural relaxation approaching the granular glass transition.