Self-Organized Critical Coexistence Phase in Repulsive Active Particles

TL;DR

This paper investigates motility-induced phase separation in repulsive active particles, revealing a self-organized critical coexistence phase with algebraically distributed gas bubbles and anomalous coarsening dynamics, supported by a simplified bubble model.

Contribution

It demonstrates the existence of a self-organized critical coexistence phase in repulsive active particles and introduces a reduced bubble model to explain the phenomena.

Findings

Gas bubbles are algebraically distributed up to a large cutoff scale.

At large system size, the system becomes microphase-separated with finite bubble scale.

The coarsening dynamics differ between the dense phase and gas bubbles.

Abstract

We revisit motility-induced phase separation in two models of active particles interacting by pairwise repulsion. We show that the resulting dense phase contains gas bubbles distributed algebraically up to a typically large cutoff scale. At large enough system size and/or global density, all the gas may be contained inside the bubbles, at which point the system is microphase-separated with a finite cut-off bubble scale. We observe that the ordering is anomalous, with different dynamics for the coarsening of the dense phase and of the gas bubbles. This phenomenology is reproduced by a "reduced bubble model" that implements the basic idea of reverse Ostwald ripening put forward in Tjhung et al. [Phys. Rev. X 8, 031080 (2018)].