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 cluster size plateauing toward a value <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>R</a:mi> <a:mi>s</a:mi> </a:msub> </a:math> that remains constant over time. While activity enhances the resilience of clusters against shear-induced breakup, <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:msub> <b:mi>R</b:mi> <b:mi>s</b:mi> </b:msub> </b:math> decreases with growing shear rate <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mover accent="true"> <c:mi>γ</c:mi> <c:mo>̇</c:mo> </c:mover> </c:math> , with an intermediate regime where <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:msub> <e:mi>R</e:mi> <e:mi>s</e:mi> </e:msub> <e:mo>∝</e:mo> <e:msup> <e:mover accent="true"> <e:mi>γ</e:mi> <e:mo>̇</e:mo> </e:mover> <e:mrow> <e:mo>−</e:mo> <e:mn>1</e:mn> </e:mrow> </e:msup> </e:mrow> </e:math> . 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 toward the cluster center with a small nonzero angle, such that the active torque opposes the shear torque, with cluster's angular velocity well captured by a simplified analytical model. We argue that this conformation makes clusters more stable against shear.