Symmetry Breaking of Self-Propelling Topological Defects in Thin-Film Active Chiral Nematics

Current interests in active matter are inspired by its relevance to living systems, which often-times consist of mirror symmetry breaking molecules and structures. As a paradigmatic active matter system, active nematic liquid crystals have shown interesting dynamical phenomena. For example, it is found that +1/2 defects can self-propel along their symmetry axis in a two-dimensional active nematic. In this work, we combine continuum theory and hydrodynamic simulation to consider the self-propulsion dynamics of active +1/2 disclinations in a thin-film chiral nematic. In a flat film, these active defects are found move slower if the chirality is higher. Importantly, we further predict that +1/2 disclinations can exhibit chiral locomotion in a curved film. When these +1/2 disclinations interact, the symmetry breaking dynamics can give rise to rich and novel collective self-propulsion patterns. We explain our findings by considering the coupling between the active stress and the symmetry-breaking structure of the system. Finally, we discuss the experimental setting that could verify our predictions. As such, our work reveals an emergent symmetry breaking mechanism in active matter.