Active Microrheology in Active Matter Systems: Mobility, Intermittency and Avalanches

TL;DR

This study investigates how a driven particle moves through active matter, revealing non-monotonic mobility, activity-induced crystallization, and avalanche-like jumps, with implications for understanding active jamming and dynamic heterogeneity.

Contribution

It provides new insights into the mobility and velocity fluctuations of particles in active matter, identifying distinct phases and dynamic regimes including crystallization and jamming.

Findings

Non-monotonic mobility behavior correlated with structural changes.

Activity-induced uniform crystallization at moderate activity levels.

Avalanche-like jumps with power-law size distributions in active jamming.

Abstract

We examine the mobility and velocity fluctuations of a driven particle moving through an active matter bath of self-mobile disks for varied density or area coverage and varied activity. We show that the driven particle mobility can exhibit non-monotonic behavior that is correlated with distinct changes in the spatial-temporal structures that arise in the active media. We demonstrate that the probe particle velocity distributions exhibit specific features in the different dynamic regimes, and identify an activity-induced uniform crystallization that occurs for moderate activity levels and that is distinct from the previously observed higher activity cluster phase. The velocity distribution in the cluster phase has telegraph noise characteristics produced when the probe particle moves alternately through high mobility areas that are in the gas state and low mobility areas that are in the dense phase. For higher densities and large activities, the system enters what we characterize as an active jamming regime. Here the probe particle moves in intermittent jumps or avalanches which how power-law distributed sizes that are similar to the avalanche distributions observed for non-active disk systems near the jamming transition.