Orientational hysteresis in swarms of active particles in external field

TL;DR

This study demonstrates that active particle swarms exhibit dynamic hysteresis similar to magnetic materials, with properties influenced by system parameters, and provides insights into controlling swarm behavior through external fields.

Contribution

The paper reveals the presence of dynamic hysteresis in active particle swarms and analyzes its properties, extending concepts from condensed matter physics to active matter systems.

Findings

Swarm order parameter shows hysteresis loops under oscillating external fields.

Hysteresis loop area scales with amplitude and frequency, influenced by system parameters.

Scaling exponents vary with parameters but can be predicted by a generic model.

Abstract

Structure and ordering in swarms of active particles have much in common with condensed matter systems like magnets or liquid crystals. A number of important characteristics of such materials can be obtained via dynamic tests such as hysteresis. In this work, we show that dynamic hysteresis can be observed also in swarms of active particles and possesses similar properties to the counterparts in magnetic materials. To study the swarm dynamics, we use computer simulations of the active Brownian particle model with dissipative interactions. The swarm is confined to a narrow linear channel and the one-dimensional polar order parameter is measured. In an oscillating external field, the order parameter demonstrates dynamic hysteresis with the shape of the loop and its area varying with the amplitude and frequency of the applied field, swarm density and the noise intensity. We measure the scaling exponents for the hysteresis loop area, which can be associated with the controllability of the swarm. Although the exponents are non-universal and depend on the system's parameters, their limiting values can be predicted using a generic model of dynamic hysteresis. We also discuss similarities and differences between the swarm ordering dynamics and two-dimensional magnets.