The role of aspect ratio and activity on how active nematic defects distribute on toroidal surfaces

Abstract

Active topological defects are one of the most exciting non-equilibrium systems of recent times. In our experiments, we confine an active nematic populated by positive and negative topological defects to a toroidal surface, and explore how the local geometry, parameterised by the Gaussian curvature, influences the distribution of defects. We find curvature-induced defect unbinding, for relatively thick tori and low activities. In contrast, for high activity and thin tori, which serve to locally approach the cylindrical limit, the relevance of the defect-curvature coupling is lost. Overall, our results illustrate how curvature and activity can both be used to affect how defects distribute on surfaces with varying curvature.