Passivity-Driven Order-Disorder Transitions in Self-Aligning Active Matter

TL;DR

This study investigates how passive particles influence order-disorder transitions in dense mixtures of active self-aligning disks, revealing a control parameter that leads to complex self-organizing behaviors.

Contribution

It introduces a mean-field model capturing the transition dichotomy and highlights the passive fraction as a key control parameter in active matter systems.

Findings

Passive fraction controls the nature of the order-disorder transition.

Isotropic mobility leads to multiple metastable states, while anisotropic mobility results in a single attractor.

Transitions can be continuous or discontinuous depending on mobility anisotropy.

Abstract

We study dense mixtures of passive and active self-aligning disks with isotropic or anisotropic mobility. We find that the passive fraction controls an order-disorder transition that is continuous in the isotropic case and discontinuous in the anisotropic one. A mean-field equation derived from the microscopic heading dynamics captures this dichotomy. Near the transition, both ordered regimes can exhibit multiple metastable oscillating or rotating states, depending on the spatial arrangement of passive particles and lattice defects, but with different transient dynamics: Systems with isotropic mobility visit multiple long-lived attractors during each simulation while systems with anisotropic mobility are trapped by a single attractor. Our results reveal the passive fraction as a physically relevant control parameter in active systems, leading to rich self-organizing dynamics.