Effective single component description of steady state structures of passive particles in an active bath

TL;DR

This paper models passive particles in an active bath, revealing how effective interactions lead to various structural orders, confirmed by simulations, enhancing understanding of non-equilibrium collective behaviors.

Contribution

It introduces a simplified single-component description of passive particles' structures in an active bath based on effective interactions, validated by microscopic simulations.

Findings

Four distinct structural orders identified: disorder, disordered cluster, ordered cluster, poly-crystalline.

Effective interactions switch between attractive and repulsive depending on parameters.

Structural transitions are driven by changes in the effective interaction nature.

Abstract

We model a binary mixture of passive and active Brownian particles in two dimensions using the effective interaction between passive particles in the active bath. The activity of active particles and the size ratio of two types of particles are two control parameters in the system. The effective interaction is calculated from the average force on two particles generated by the active particles. The effective interaction can be attractive or repulsive, depending on the system parameters. The passive particles form four distinct structural orders for different system parameters viz; disorder (D), disordered cluster (DC), ordered cluster (OC), and poly-crystalline order (P C). The change in structure is dictated by the change in nature of the effective interaction. We further confirm the four structures using full microscopic simulation of active and passive mixture. Our study is useful to understand the different collective behaviour in non-equilibrium systems.