Instabilities, defects, and defect ordering in an overdamped active nematic

TL;DR

This paper develops a universal continuum theory for dense overdamped active nematic liquid crystals, revealing instabilities, defect proliferation, and three distinct steady states, with implications for experimental and theoretical studies.

Contribution

It introduces a phenomenological, microscopic-independent model for active nematics, capturing defect dynamics and steady states in dense regimes.

Findings

Identifies a bend instability leading to defect proliferation.

Discovers three steady states: defect-ordered nematic, undulating nematic, turbulent nematic.

Characterizes phases and links theory to experiments.

Abstract

We consider a phenomenological continuum theory for an extensile, overdamped active nematic liquid crystal, applicable in the dense regime. Constructed from general principles, the theory is universal, with parameters independent of any particular microscopic realization. We show that it exhibits a bend instability similar to that seen in active suspensions, that leads to the proliferation of defects. We find three distinct nonequilibrium steady states: a defect-ordered nematic in which $+\frac{1}{2}$ disclinations develop polar ordering, an undulating nematic state with no defects, and a turbulent defective nematic. We characterize the phenomenology of these phases and identify the relationship of this theoretical description to experimental realizations and other theoretical models of active nematics.