A self-kneading chiral crystal*

Two-dimensional crystals with simple longitudinal interactions are known to melt through an interplay between configurational entropy and topological defect unbinding. We ask a deceptively simple question: what is the effect of adding transverse interactions on this phase and its transitions? To realize this more general class of matter, we build an active chiral crystal composed of spinning magnetic colloids, revealing a lively self-organized steady-state of crystalline whorls that blurs the line between solid and liquid. By combining experimental measurements with fully-resolved hydrodynamic and minimal model simulations, we find that this phase spontaneously arises from the interplay of odd stresses and conventional elasticity, which conspire to produce self-propelled topological defects. As a result, two-dimensional chiral crystals self-knead into an active dynamical phase which preserves order at small scales while powering macroscopic transport at system-spanning scales.