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

Lucio Mauro Carenza1, Giuseppe Negro2,*, Pasquale Digregorio1, Antonio Suma1, and Giuseppe Gonnella1

  • *Contact author: giuseppe.negro@ed.ac.uk
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Phys. Rev. Research 7, 043089 – Published 22 October, 2025

DOI: https://doi.org/10.1103/3t18-sq96

Abstract

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 Rs that remains constant over time. While activity enhances the resilience of clusters against shear-induced breakup, Rs decreases with growing shear rate γ̇, with an intermediate regime where Rs∝γ̇−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 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.

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Phys. Rev. Research 7, 043089– Published 22 October, 2025
  • Received 3 June 2025
  • Accepted 18 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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