From Motility-Induced Phase-Separation to Glassiness in Dense Active Matter

TL;DR

This paper investigates the complex phase behavior of dense active matter, revealing a crossover from glassy dynamics to motility-induced phase separation driven by activity levels, with implications for understanding biological and synthetic active systems.

Contribution

It introduces a comprehensive phase diagram for active glasses, highlighting the distinct mechanisms of fluidization at different activity regimes, including a novel nonequilibrium glass transition.

Findings

Disordered active materials exhibit both MIPS and glassiness.

Glass transition mechanisms differ from equilibrium systems.

A crossover from effective temperature-controlled to activity-driven dynamics.

Abstract

Dense active systems are widespread in nature, examples range from bacterial colonies to biological tissues. Dense clusters of active particles can be obtained by increasing the packing fraction of the system or taking advantage of a peculiar phenomenon named motility-induced phase separation (MIPS). In this work, we explore the phase diagram of a two-dimensional model of active glass and show that disordered active materials develop a rich collective behaviour encompassing both MIPS and glassiness. We find that, although the glassy state is almost indistinguishable from that of equilibrium glasses, the mechanisms leading to its fluidization do not have any equilibrium counterpart. Our results can be rationalized in terms of a crossover between a low-activity regime, where glassy dynamics is controlled by an effective temperature, and a high-activity regime, which drives the system towards MIPS.