Spontaneous rotation of polar active particles in a colloidal suspension*

Polar active particles constitute a wide class of active matter that is able to propel along a preferential direction, given by their polar axis. Recent experiments and simulations showed that they can spontaneously break their polar symmetry and transition from a persistent Brownian motion with enhanced rotational diffusion to circular trajectories. Here, we demonstrate a generic active mechanism that leads to their spontaneous chiralization through a symmetry-breaking instability. We find that the transition of an active particle from a polar to a chiral symmetry is characterized by the emergence of active rotation and of circular trajectories. The instability is driven by the advection of a solute that interacts differently with the two portions of the particle surface and it occurs through a supercritical pitchfork bifurcation.