Tunable annealing of defects in self-aligning active crystals

Abstract

Obtaining defect-free single-crystals is of crucial importance in soft matter and materials science, spanning both fundamental interests and practical applications. Active crystals, encompassing diverse dense systems from living organisms to artificial metamaterials, can offer a promising platform for autonomous structural reorganization. We demonstrate that increasing spatiotemporal orientational fluctuations around the mean polarized state can enhance crystallographic order in active crystals. Poly-to-single-crystal transformations in defect-rich, self-aligned active Brownian crystals with coupled translational-rotational dynamics are investigated. We show that long-lived persistence with slow alignment controls the defect-annealing capability. By disentangling activity magnitude from associated timescales, we reveal activity-assisted annealing. Tuning the persistence length enables overcoming thermal energy barriers. Simultaneously adjusting persistence and alignment timescales can tune relaxation from `fast' to `slow', yielding defect-rich and defect-free crystals, respectively. Furthermore, active crystals of point particles are found to exhibit similar defect annealing when flocking is delayed by tuning the timescale of the velocity relaxation towards the polarized state. These findings suggest that the mechanism may extend to a broader class of active crystals. Our results intersect statistical physics of living soft matter with the mechanics of defects and microstructures, proposing a nonequilibrium route towards reconfigurable materials.