Unusual diffusion of chiral active Brownian particles in deformable and displaceable media

Chiral active Brownian particles convert stored or environmental energy into self-propulsion and rotation, driving systems far from equilibrium. How chirality influences diffusion in crowded environments composed of deformable and displaceable obstacles remains poorly understood. Here we show, through combined experiments and theory, that chiral active Brownian particles confined in an annular channel with deformable and displaceable ring obstacles exhibit a pronounced nonmonotonic dependence of diffusivity on obstacle density. The diffusion coefficient initially increases and then decreases with obstacle area fraction, reaching enhancements of nearly two orders of magnitude. Experiments and theory indicate that this behavior originates from a competition between obstacle-induced motion collimation and suppression of migration velocity. The enhancement also varies nonmonotonically with particle orbital radius due to differences in intrinsic free-space diffusivity. These findings provide insight into nonequilibrium transport in dynamically reconfigurable environments and suggest strategies for controlling chiral active matter in complex media.