Universality of active and passive phase separation in a lattice model

TL;DR

This study demonstrates that active and passive phase separation in a 2D lattice model share a universal critical behavior, with activity effectively enhancing interactions but preserving the universality class.

Contribution

The paper introduces a 2D lattice gas model exhibiting both MIPS and EPS, revealing a unified critical behavior across active and passive regimes.

Findings

MIPS and EPS critical points are connected via a nonequilibrium critical line.

Critical exponents are consistent with the 2D Ising universality class.

Activity enhances attractive interactions without altering critical properties.

Abstract

The motility-induced phase separation (MIPS) is the spontaneous aggregation of active particles, while equilibrium phase separation (EPS) is thermodynamically driven by attractive interactions between passive particles. Despite such difference in the microscopic mechanism, similarities between MIPS and EPS like free energy structure and critical phenomena have been discussed. Here we introduce and analyze a 2D lattice gas model that undergoes both MIPS and EPS by tuning activity and interaction parameters. Based on simulations and mean-field theory, we find that the MIPS and EPS critical points are connected through a line of nonequilibrium critical points. According to the size scaling of physical quantities and time evolution of the domain size, both the static and dynamical critical exponents seem consistent with the 2D spin-exchange Ising universality over the whole critical line. The results suggest that activity effectively enhances attractive interactions between particles and leaves intact the critical properties of phase separation.