Title: Activity-induced heterogeneity in a granular system approaching the glassy regime

Author (Table Talk): Chetan Yadav, UMass Amherst

Abstract:

We experimentally explore the approach to the glassy regime, when polar activity is introduced in a fraction of the particles in the system. In our experiments, a bi-disperse mixture of discs of size ratio 1:1.4 confined to a horizontal plane is fluidized by vertical vibrations. Discs can be designed to exhibit either isotropic motion in the plane, passive or a preferred polar mobility, Active. We compare dynamics in 50:50 mixtures of large active and small passive grains to 50:50 mixtures of large passive and small passive grains. At equal area fractions, the active system shows faster dynamics. The question we explore is whether activity merely speeds up the dynamics or if active and passive systems, chosen to have the same relaxation time, exhibit qualitatively different dynamics. When compared at the same relaxation time, we show stronger heterogeneity in the active mixture by analyzing the MSD-informed four-point correlation function. The active system shows stronger spatio-temporal velocity correlations, and longer-lived mobile chains.