  As a result of nonequilibrium forces, purely repulsive self-propelled
particles undergo macrophase separation between a dense and a dilute phase. We
present a thorough study of the ordering kinetics of such motility-induced
phase separation (MIPS) in active Brownian particles in two dimensions, and we
show that it is generically accompanied by microphase separation. The growth of
the dense phase follows a law akin to the one of liquid-gas phase separation.
However, it is made of a mosaic of hexatic microdomains whose size does not
coarsen indefinitely, leaving behind a network of extended topological defects
from which microscopic dilute bubbles arise. The characteristic length of these
finite-size structures increases with activity, independently of the choice of
initial conditions.
