Shape-anisotropy inverses the behavior of emergent vortices in active chiral fluids

Active colloidal fluids exhibit spontaneous emergence of large-scale correlated states demonstrating complex collecting dynamics and self-organization. Temporal activity modulations have been successfully utilized to orchestrate response of active fluids revealing a wealth of emergent self-assembled patterns such as multiple vortices and alternating lattices. In geometrically confined systems activity modulations trigger unexpected yet robust polar state reversals of a macroscopic vortex formed by colloidal rollers, enabling controlled cycling of a global chiral state of the system. Here, we reveal that an introduction of a slight degree of shape anisotropy into an ensemble of dielectric Quincke rollers turns it into a chiral active fluid comprised of rollers of arbitrary handedness. The chiral rollers dynamically self-assemble into multiple self-organized freestanding vortices with spontaneously selected sense of rotation. We demonstrate that upon reactivation of the system after a complete cessation of activity beyond all relevant timescales the vortices simultaneously restore their previous chiral states in striking contrast to the chiral state reversal demonstrated by spherical particles. The analysis of the local asymmetries imprinted by the hydrodynamic interactions in the particle positional order within the vortices reveals that the shape-anisotropy reverses the sign of the effective tangential force parameter in each vortex, resulting in the suppression of reversals and the restoration of chiral states of all vortices in the multi-vortical state in consecutive periods of activity. The results provide insights into the emergence of complex collective behavior in chiral colloidal fluids governed by a delicate interplay between the shape anisotropy, chiral motion, and temporal activity modulations.