Active particles with delayed attractions form quaking crystallites

Abstract

- Perception-reaction delays have experimentally been found to cause a spontaneous circling of microswimmers around a fxed target particle. Here we investigate a many-body version of such an experiment with Brownian-dynamics simulations of active particles in a plane. For short delays, they form a hexagonal crystallite around the target. The bifurcation to a chiral dynamical phase, seen for longer delays, maps onto that for a single active particle. Different angular velocities at different distances from the target induce shear stresses that grow with increasing delay. By exciting shear bands, they shake and intermittently break the rotating crystallite. For long delays, it detaches from the target to circle around it near the preferred single-particle orbit as a compact spinning satellite, trembling from what could be called tidal quakes.