The building blocks of dynamical heterogeneities in dense granular media

TL;DR

This study experimentally links short-term collective cage jumps to long-term dynamical heterogeneities in dense granular media under cyclic shear, highlighting the role of facilitation in relaxation processes.

Contribution

It reveals that dynamical heterogeneities arise from a two-timescale process involving clustered cage jumps and avalanches, providing new insights into granular relaxation dynamics.

Findings

Dynamical heterogeneities stem from short-time collective events.

Clusters of cage jumps aggregate into avalanches over larger timescales.

Facilitation influences relaxation but is not conserved as in some models.

Abstract

We investigate experimentally the connection between short time dynamics and long time dynamical heterogeneities within a dense granular media under cyclic shear. We show that dynamical heterogeneities result from a two timescales process. Short time but already collective events consisting in clustered cage jumps concentrate most of the non affine displacements. On larger timescales such clusters appear aggregated both temporally and spatially in avalanches which eventually build the large scales dynamical heterogeneities. Our results indicate that facilitation plays an important role in the relaxation process although it does not appear to be conserved as proposed in many models studied in the literature.