  We investigate collective phenomena with rotationally driven spinners of
concave shape. Each spinner experiences a constant internal torque in either a
clockwise or counterclockwise direction. Although the spinners are modeled as
hard, otherwise non-interacting rigid bodies, we find that their active motion
induces an effective interaction that favors rotation in the same direction.
With increasing density and activity, phase separation occurs via spinodal
decomposition, as well as self-organization into rotating crystals. We observe
the emergence of cooperative, super-diffusive motion along interfaces, which
can transport inactive test particles. Our results demonstrate novel phase
behavior of actively rotated particles that is not possible with linear
propulsion or in non-driven, equilibrium systems of identical hard particles.
