Dynamical Heterogeneity close to the Jamming Transition in a Sheared Granular Material

TL;DR

This study experimentally investigates the dynamic heterogeneity in a dense granular material near the jamming transition under cyclic shear, revealing correlated grain relaxations and a measurable dynamical correlation length.

Contribution

It provides the first experimental measurement of multi-point correlation functions and dynamical heterogeneity in sheared granular materials near jamming.

Findings

Grain relaxations are strongly correlated and spatially heterogeneous.

Self-intermediate scattering function shows slower than exponential relaxation.

A dynamical correlation length is extracted from mobility patterns.

Abstract

The dynamics of a bi-dimensional dense granular packing under cyclic shear is experimentally investigated close to the jamming transition. Measurement of multi-point correlation functions are produced. The self-intermediate scattering function, displaying slower than exponential relaxation, suggests dynamic heterogeneity. Further analysis of four point correlation functions reveal that the grain relaxations are strongly correlated and spatially heterogeneous, especially at the time scale of the collective rearrangements. Finally, a dynamical correlation length is extracted from spatio-temporal pattern of mobility. Our experimental results open the way to a systematic study of dynamic correlation functions in granular materials.