Dynamical Clustering Interrupts Motility Induced Phase Separation in Chiral Active Brownian Particles*

Motility-induced phase separation (MIPS) is one of the intriguing findings in active matter systems, which has been widely studied in linear self-propulsion models such as active Brownian particles (ABPs). However, such linear models fail to describe chiral swimming patterns observed both in biological and active colloidal systems. Therefore, the self-propulsion torque is introduced into the circle-ABPs (cABPs) model.

In this work, using computer simulations and dynamic mean-field theory, we demonstrate that sufficiently fast rotation of cABPs in two dimensions generates a dynamical clustering state resulted from the short wavelength instability, which interrupts the conventional MIPS. Multiple clusters arise from the combination of the standard MIPS cohesion, and the circulating current that causes cluster disintegration. The steady state current is allowed by the detailed balance broken at continuum level. Microscopically, the current with non-zero curl originates from the motility “relieved” by automatic rotation.

This mechanism sheds light on the understanding of dynamic clusters formation observed in a variety of active matter systems, and may help examine the generalization of effective thermodynamic concepts developed in the context of MIPS.