Traveling fronts in active-passive particle mixtures

TL;DR

This study numerically investigates phase-separated mixtures of active and passive particles, revealing a novel steady-state with traveling interfaces driven by flux imbalance and spontaneous symmetry breaking.

Contribution

It introduces the discovery of traveling fronts in active-passive particle mixtures and explains their formation through interface instability and flux imbalance.

Findings

Traveling fronts observed in active-passive mixtures.

Interface velocity decreases linearly with active particle fraction.

Spontaneous symmetry breaking causes advancing and receding interfaces.

Abstract

The emergent dynamics in phase-separated mixtures of isometric active and passive Brownian particles is studied numerically in two dimensions. A novel steady-state of well-defined traveling fronts is observed, where the interface between the dense and the dilute phase propagates and the bulk of both phases is (nearly) at rest. Two kind of interfaces, advancing and receding, are formed by spontaneous symmetry breaking, induced by an instability of a planar interface due to the formation of localized vortices. The propagation arises due to flux imbalance at the interface, strongly resembling traveling fronts in reaction-diffusion systems. Above a threshold, the interface velocity decreases linearly with increasing fraction of active particles.