Fast Crystallization driven by active dopants*

Colloids have been instrumental in statistical mechanics to model the phase behavior of atomic liquids and solids. They notably played an important role in understanding the mechanisms at stake in crystallization, allowing for example to track individual particles, dislocations or grain boundaries, a daunting task for atomic systems. The theoretical framework of dissipative systems is open, and using active colloids -which continuously consume energy- allows us to probe dynamics out of traditional scope of equilibrium physics. We experimentally study the dynamics of a dense monolayer of passive colloids, relaxing after being quenched in a polycrystalline state with domains of mismatching orientations. A small fraction of active intruders navigates within the crystal. We study the evolution of the polycrystalline pattern, ensuing from the interplay between the self-propulsion of active particle highly constrained by lattice and the rearrangement of passive colloids induced by this internal activity. The intruders are shown to speed up grain growth leading to an ordered phase, with a reorganization dynamic dependent upon the number of intruder and their activity.