Liquid-Hexatic-Solid phases in active and passive Brownian particles determined by stochastic birth and death events

TL;DR

This study explores how stochastic birth and death processes influence the phase behavior of active and passive Brownian particles, revealing phase transitions and re-entrant phenomena driven by particle number fluctuations.

Contribution

It introduces a model incorporating stochastic birth and death in active/passive particles, uncovering novel phase behaviors and transitions not observed in traditional fixed-particle systems.

Findings

Identification of liquid, hexatic, and solid phases depending on parameters.

Observation of motility-induced phase separation in active particles.

Re-entrant transition to hexatic phase with increasing birth rate.

Abstract

We study the effects of stochastic birth and death processes on the structural phases of systems of active and passive Brownian particles subject to volume exclusion. The total number of particles in the system is a fluctuating quantity, determined by the birth and death parameters, and on the activity of the particles. As the birth and death parameters are varied we find liquid, hexatic and solid phases. For passive particles these phases are found to be spatially homogeneous. For active particles motility-induced phase separation (co-existing hexatic and liquid phases) occurs for large activity and sufficiently small birth rates. We also observe a re-entrant transition to the hexatic phase when the birth rate is increased. This results from a balance of an increasing number of particles filling the system, and a larger number of defects resulting from the birth and death dynamics.