Circling crystals in chiral active matter with self-alignment

Abstract: We study a crystal composed of active units governed by self-alignment and chirality. The first mechanism acts as an effective torque that aligns the particle orientation with its velocity, while the second drives individual particles along circular orbits. We find that even a weak degree of chirality, when coupled with self-alignment, induces collective motion of the entire crystal along circular trajectories in space. We refer to this phase as a circling crystal. When chirality outweigh self-alignment, the circular global motion is suppressed in favor of vortex-like regions of coordinated motion. This state is characterized by oscillating spatial velocity correlations, a power law decay of the energy spectrum, and oscillatory temporal correlations. Our findings can be tested experimentally in systems ranging from epithelial tissues to swarming robots, governed by chirality and self-alignment.