Single-orientation Crystalline Domains of Active Brownian Particles Lead to Collective Motions

TL;DR

This paper demonstrates that active Brownian particles form structure-ordered domains that move collectively, with motion linked to single-orientation crystalline regions stabilized by boundary forces, revealing the structure-motion relationship.

Contribution

It uncovers the connection between crystalline domain orientation and collective motion in active Brownian particles without attractive interactions.

Findings

Motion regions coincide with single-orientation crystalline domains

Domains translate or rotate as whole units due to net active forces or torques

Boundary particles stabilize domains and collective motion

Abstract

Active Brownian particles, even without attractive and anisotropic inter-particle interactions, can form a high-density phase featuring structure-ordered domains as well as collective motion regions under thermal noise. However, the mechanism, particularly the relationship between the motion and structure, remains unclear. In this study, we show that the motion-correlation regions are spatially coincident with the single-orientation crystalline domains. Each domain translates or rotates as a whole due to the net active force or torque acting upon it, allowing relative motions between these crystalline domains. The particles at domain boundaries usually have the active forces pointing inward, which helps to stabilize these structure-ordered domains and their corresponding collective motion regions.