  Chiral active particles (or self-propelled circle swimmers) feature a rich
collective behavior, comprising rotating macro-clusters and micro-flock
patterns which consist of phase-synchronized rotating clusters with a
characteristic self-limited size. These patterns emerge from the competition of
alignment interactions and rotations suggesting that they might occur
generically in many chiral active matter systems. However, although excluded
volume interactions occur naturally among typical circle swimmers, it is not
yet clear if macro-clusters and micro-flock patterns survive their presence.
The present work shows that both types of pattern do survive but feature
strongly enhance fluctuations regarding the size and shape of the individual
clusters. Despite these fluctuations, we find that the average micro-flock size
still follows the same characteristic scaling law as in the absence of excluded
volume interactions, i.e. micro-flock sizes scale linearly with the
single-swimmer radius.
