Defect delocalization in confined 3D active nematics

Active nematics are an intriguing class of orientationally-ordered materials which spontaneously flow by means of continuous active stress generation. When confined, the emergent dynamics transition from chaotic flows to more coherent states with reduced defect density. In addition, when the confining surface has tangential alignment, the total topological charge of defects is dictated by the surface topology. The active dynamics of these topologically-induced defects have been explored in spherical confinement, however they remain less studied for other closed surfaces, where geometry can be harnessed to localize defects. Here, we numerically simulate 3D active nematics in cylindrical confinement. At low activities, defects are attracted to the cylinder edges where the nematic deformation is greatest. As activity is tuned, defects undergo a variety of dynamical transitions, including a critical activity at which defects escape the end caps and drive a delocalization transition. At this threshold, defect lines proliferate across the cylinder. We reveal how the localized and delocalized states differ in terms of their defect winding properties and contour length scaling. These results highlight how surface geometry can be utilized to control active topological dynamics.