Translational and rotational dynamical heterogeneities in granular systems

TL;DR

This study uses X-ray tomography to analyze how particles in a 3D granular system exhibit coupled translational and rotational heterogeneities, revealing power-law cluster size distributions and early formation of clusters.

Contribution

It uncovers the coupling between translational and rotational dynamics and shows that clusters form at short times, contrasting glass-forming systems.

Findings

Power-law cluster size distribution independent of strain amplitude

Clusters form at times much shorter than the α-relaxation time

Strong coupling between translational and rotational degrees of freedom

Abstract

We use X-ray tomography to investigate the translational and rotational dynamical heterogeneities of a three dimensional hard ellipsoids granular packing driven by oscillatory shear. We find that particles which translate quickly form clusters with a size distribution given by a power-law with an exponent that is independent of the strain amplitude. Identical behavior is found for particles that are translating slowly, rotating quickly, or rotating slowly. The geometrical properties of these four different types of clusters are the same as those of random clusters. Different cluster types are considerably correlated/anticorrelated, indicating a significant coupling between translational and rotational degrees of freedom. Surprisingly these clusters are formed already at time scales that are much shorter than the $\alpha-$relaxation time, in stark contrast to the behavior found in glass-forming systems.