Helical Flow States in Active Nematics

We show that confining extensile nematics in 3D channels leads to the emergence of two self-organized flow states with nonzero helicity. The first is a pair of braided anti-parallel streams - this double helix occurs when the activity is moderate, anchoring negligible and reduced temperature high. The second consists of axially aligned counter-rotating vortices - this grinder train arises between spontaneous axial streaming and the vortex lattice. These two unanticipated helical flow states illustrate the potential of active fluids to break symmetries and form complex but organized spatio-temporal structures in 3D fluidic devices.