Persistence-Driven Void Formation in Dense Active-Passive Mixtures

TL;DR

This paper shows that increasing persistence in active-passive mixtures causes a transition from uniform fluidization to localized void formation, reorganizing relaxation through stress buildup and confinement rather than simple melting.

Contribution

It reveals a novel nonequilibrium localization mechanism driven by persistence, distinct from traditional active fluidization, in dense active-passive mixtures.

Findings

Persistence induces a transition to localized void formation.

Active dopants accumulate stress and nucleate voids.

Rearrangements localize at void boundaries, resembling crowd dynamics.

Abstract

It is well established that dilute active dopants can melt an arrested amorphous solid by enhancing cage breaking and accelerating structural relaxation. Yet it remains unclear whether increasing persistence simply amplifies this effective melting or instead reorganizes the fluidization mechanism itself. Here we show that, in a minimal active-passive mixture, increasing persistence drives a crossover from homogeneous fluidization to a localized mechanical instability, demonstrating that sustained active forcing restructures relaxation in space rather than merely strengthening it. Persistent dopants accumulate stress and nucleate voids as their mechanically perturbed regions overlap. In this regime, rearrangements localize at void boundaries, and active and passive particles exhibit comparable mobility, producing dynamics reminiscent of crowd mosh pits. Persistence therefore reorganizes fluidization through stress accumulation and confinement, revealing a distinct nonequilibrium localization mechanism in disordered solids.