Crystallization in a dense suspension of self-propelled particles

TL;DR

This study demonstrates that dense suspensions of self-propelled colloidal particles can crystallize at high densities, with the transition influenced by activity and exhibiting unique structural heterogeneities.

Contribution

It reveals how activity shifts the crystallization density and introduces structural heterogeneities in non-equilibrium suspensions.

Findings

Crystallization occurs at high densities in active colloids.

The freezing density depends on the criterion used.

Structural heterogeneities emerge during the transition.

Abstract

Using Brownian dynamics computer simulations we show that a two-dimensional suspension of self-propelled ("active") colloidal particles crystallizes at sufficiently high densities. Compared to the equilibrium freezing of passive particles the freezing density is both significantly shifted and depends on the structural or dynamical criterion employed. In non-equilibrium the transition is accompanied by pronounced structural heterogeneities. This leads to a transition region between liquid and solid in which the suspension is globally ordered but unordered liquid-like "bubbles" still persist.