Livio Nicola Carenza — Koç University - Physics Department #
Do active liquid crystals exist after all? #
Quasi-long ranged order is the hallmark of two-dimensional liquid crystals. At equilibrium, this property implies that the correlation function of the local orientational order parameter decays with distance as a power law: i.e. C(r) ∼ |r|^{–η}, with η a temperature-dependent exponent. While in general non-universal, η = 1/4 universally at the Kosterlitz-Thouless transition, where orientational order is lost due to disclination unbinding. Does this definition of liquid crystal order in two dimensions also apply to active liquid crystals? And if not, are these more or less ordered than their passive counterpart?  Using a combination of analytical and computational techniques in this talk I will demonstrate that, in active liquid crystals the notion of quasi-long ranged order fundamentally differs from its equilibrium counterpart and is ultimately dictated by the interplay between translational and orientational dynamics. As a consequence, the exponent η is allowed to vary continuously in the range 0 < η ≤ 2, with the upper bound corresponding to the isotropic phase. I will support our theoretical predictions with a survey of recent experimental data, reflecting a wide variety of different realization of orientational order in two dimensions.