Chirality transitions in a system of active flat spinners

Abstract

We study in this work the two-dimensional dynamics of an experimental system of disk-shaped rotors, fluidized by turbulent upflow. Contrary to previous knowledge, our experiments show the same particle chiral geometry can produce flows with different chiralities. In particular, we unveil a conspicuous complex chiral flow which displays multiple persistent vortices with either sign, located randomly in the system. This peculiar phase mediates a continuous transition, which takes place as the kinetic energy input increases, from a flow with positive chirality (one vortex rotating in the same direction as particles spin) to a flow with negative chirality (one vortex in opposite sense to particle spin). We find that these surprising transitions are determined by the specific state of the statistical correlations between particle-spin and translational velocity. We discuss how these correlations are determined in turn by the combined action of a series of mechanisms (for instance, heat dissipation at the boundaries, particle activity, average kinetic energy...), several of which are unveiled here.