Orientational order of motile defects in active nematics

TL;DR

This paper investigates the emergent orientational order of motile defects in active nematics, revealing a non-equilibrium phase with long-range defect alignment that persists despite rapid defect turnover, through experimental and computational analysis.

Contribution

It demonstrates the existence of a defect-ordered phase in active nematics, combining experimental tracking and simulations to reveal a generic non-equilibrium ordering phenomenon.

Findings

Defects form a system-spanning orientational order.

Order persists over hours despite short defect lifetimes.

Simulations replicate experimental defect ordering.

Abstract

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.