Alignment Destabilizes Crystal Orders in Active Systems

TL;DR

This study investigates how different alignment interactions affect the order and phases of two-dimensional active crystals, revealing that alignment destabilizes translational order and leads to various ordered phases.

Contribution

It provides a combined numerical and analytical analysis of active crystals with different alignment interactions, highlighting how alignment destabilizes translational order and induces distinct phases.

Findings

Vicsek-like alignment results in short-range translational order and quasi-long range bond-orientational order.

Elasticity-based alignment maintains quasi-long range translational order parallel to motion.

Results are generalized to higher dimensions.

Abstract

We combine numerical and analytical methods to study two dimensional active crystals formed by permanently linked swimmers and with two distinct alignment interactions. The system admits a stationary phase with quasi long range translational order, as well as a moving phase with quasi-long range velocity order. The translational order in the moving phase is significantly influenced by alignment interaction. For Vicsek-like alignment, the translational order is short-ranged, whereas the bond-orientational order is quasi-long ranged, implying a moving hexatic phase. For elasticity-based alignment, the translational order is quasi-long ranged parallel to the motion and short-ranged in perpendicular direction, whereas the bond orientational order is long-ranged. We also generalize these results to higher dimensions.