Arrested phase separation and chiral symmetry breaking in active dumbbells under shear

Through molecular dynamics simulations, we investigate the phase separation and aggregation dynamics of active dumbbell particles in two-dimensions subjected to shear. We find that the growth of the phase-separated region is arrested when shear is applied, with the average clusters size plateauing towards a value $R_s$ that remains constant over time. While activity enhances the resilience of clusters against shear-induced breakup, $R_s$ decreases with growing shear rate $\dot{\gamma }$, with an intermediate regime where $R_s\propto {\dot{\gamma }}^{-1}$. We find that clusters in the stationary state are progressively less polarized and increasingly elongated with increasing shear. At the same time, we find a breaking in chiral symmetry of both rotation direction and internal organization of clusters: typically, dumbbells point towards the cluster center with a small non-zero angle, such that the active torque opposes the shear torque, with cluster’s angular velocity well captured by a simplified analytical model. We argue this conformation makes clusters more stable against shear.