Traveling and resting crystals in active systems

TL;DR

This paper introduces a unified microscopic field theory for active systems that predicts various crystalline states, including a novel transition from resting to traveling crystals driven by self-propulsion, with implications for designing new active materials.

Contribution

It unifies the phase-field-crystal model with the Toner-Tu theory to predict and characterize diverse active crystalline states, including a traveling crystal transition.

Findings

Prediction of a transition from resting to traveling crystals with increasing self-propulsion

Identification of various active crystalline states

Theoretical predictions verifiable in experiments and simulations

Abstract

A microscopic field theory for crystallization in active systems is proposed which unifies the phase-field-crystal model of freezing with the Toner-Tu theory for self-propelled particles. A wealth of different active crystalline states are predicted and characterized. In particular, for increasing strength of self-propulsion, a transition from a resting crystal to a traveling crystalline state is found where the particles migrate collectively while keeping their crystalline order. Our predictions, which are verifiable in experiments and in particle-resolved computer simulations, provide a starting point for the design of new active materials.