Occurrence of connected clusters in motility-induced phase-separated states of persistent active particles at zero temperature

TL;DR

This study investigates how jamming and cluster formation occur in active particles at zero temperature, revealing the conditions under which dense clusters form, remain stable, or become unstable due to activity, in a simplified two-dimensional model.

Contribution

It provides new insights into the relationship between jamming, phase separation, and activity in active particle systems at zero temperature with infinite persistence.

Findings

Jammed clusters occur at intermediate active-to-repulsive force ratios.

At lower activity, the dense phase has few overlaps and ends below jamming onset.

High activity leads to unstable small dense patches.

Abstract

To study the interplay of jamming, cluster formation, and motility-induced phase separation in the zero temperature limit in two dimensions, we consider a simple model system consisting of a bidisperse mixture of disks that are only subject to a repulsion force in case of overlaps and an active force. The orientation of the disks is chosen randomly in the beginning and does not change anytime during the simulation thus corresponding to an infinite persistence length. Simulations with our model system reveal that jammed clusters of particles occur in the dense phase of a phase-separated state in case of intermediate values of the ratio of active to repulsive force. However, for smaller activities there are only a few overlaps between the particles in the dense phase and the coexistence region ends at a packing fraction below the onset of jamming. Finally, for large activities small clusters corresponding to small patches of the dense phase are found that are unstable due to the activity. Our findings on how jamming and phase separation are related are relevant to many active particle systems whose zero temperature and long persistence limits correspond to our model system.