Spontaneous rotation of an inclusion in a chiral active bath.

Abstract

Active matter systems are known to drive directed transport and rotation when coupled to passive inclusions. We study the dynamics of a geometrically symmetric inclusion, termed a torquer, in a bath of chiral active Brownian particles. Despite being geometrically symmetric and non-motile, the torquer exhibits persistent rotation due to spatially inhomogeneous torques arising from angularly biased collisions with active particles. This interaction-driven symmetry breaking does not rely on shape anisotropy or external forcing. Through simulations, we identify two distinct regimes of rotation: one dominated by density gradients at low chirality and another by increased impact frequency at high chirality. Our results demonstrate that persistent rotational dynamics can be realised in a symmetric inclusion, from anisotropic interaction with the active bath.