Active particle dynamics beyond the jamming density

TL;DR

This study explores how active particles can remain dynamic beyond the jamming density by analyzing phase transitions influenced by density, self-propulsion, and noise, revealing an optimal noise level for unjamming.

Contribution

It introduces a phase diagram for active particles with Vicsek alignment, identifying four phases and the conditions for unjamming beyond typical density limits.

Findings

Four distinct phases identified based on diffusion and order.

Existence of an optimal noise level for minimal unjamming force.

Active particles can remain dynamic at high densities.

Abstract

Many biological systems form colonies at high density. Passive granular systems will be jammed at such densities, yet for the survival of biological systems it is crucial that they are dynamic. We construct a phase diagram for a system of active particles interacting via Vicsek alignment, and vary the density, self-propulsion force, and orientational noise. We find that the system exhibits four different phases, characterized by transitions in the effective diffusion constant and in the orientational order parameter. Our simulations show that there exists an optimal noise such that particles require a minimal force to unjam, allowing for rearrangements.