Emergence of self-organized multivortex states in flocks of active rollers

Significance Active materials maintained out of equilibrium due to external energy consumption promise access to tunable structures capable of swarming, shape shifting, and self-healing—properties known mostly throughout the biological world. Developing fundamental understanding and controls of these synthetic systems remains challenging. Active colloidal dispersion of rollers energized by an alternating magnetic field reveals complex emergent dynamics of self-organized vortex structures. Reminiscent of the collective behavior observed in living systems, the emergent vortices are well localized in space and unbound from the geometrical constraints. Our findings provide fundamental insight into the emergence of macroscopic behavior in active roller dispersions and suggest strategies for self-assembled dynamic materials and particulate manipulation at the microscale.