  The study of liquid crystals at equilibrium has led to fundamental insights
into the nature of ordered materials, as well as to practical applications such
as display technologies. Active nematics are a fundamentally different class of
liquid crystals, driven away from equilibrium by the autonomous motion of their
constituent rod-like particles. This internally generated activity powers the
continuous creation and annihilation of topological defects, which leads to
complex streaming flows whose chaotic dynamics appear to destroy long-range
order. Here, we study these dynamics in experimental and computational
realizations of active nematics. By tracking thousands of defects over
centimetre-scale distances in microtubule-based active nematics, we identify a
non-equilibrium phase characterized by system-spanning orientational order of
defects. This emergent order persists over hours despite defect lifetimes of
only seconds. Similar dynamical structures are observed in coarse-grained
simulations, suggesting that defect-ordered phases are a generic feature of
active nematics.
