  Compared to isotropic liquids, orientational order of nematic liquid crystals
makes their rheological properties more involved, and thus requires fine
control of the flow parameters to govern the orientational patterns. In
microfluidic channels with perpendicular surface alignment, nematics
discontinuously transition from perpendicular structure at low flow rates to
flow-aligned structure at high flow rates. Here we show how precise tuning of
the driving pressure can be used to stabilize and manipulate a previously
unresearched topologically protected chiral intermediate state which arises
before the homeotropic to flow-aligned transition. We characterize the
mechanisms underlying the transition and construct a phenomenological model to
describe the critical behaviour and the phase diagram of the observed chiral
flow state, and evaluate the effect of a forced symmetry breaking by
introduction of a chiral dopant. Finally, we induce transitions on demand
through channel geometry, application of laser tweezers, and careful control of
the flow rate.
