Active cholesterics: odder than odd elasticity

TL;DR

This paper reveals that chirality in active liquid crystals introduces a unique 'odder' elasticity, fundamentally altering their dynamics and enabling controllable vortex structures, unlike their equilibrium counterparts.

Contribution

It demonstrates how chirality modifies active liquid crystal dynamics through odder elasticity, distinguishing active cholesterics from smectic-A phases and enabling new controllable vortex configurations.

Findings

Active cholesterics exhibit fundamentally different hydrodynamics from smectic-A liquid crystals.

Chiral layered states are generically unstable but can be stabilized in certain experimental setups.

Vortex arrays with anti-ferromagnetic vorticity can be engineered and controlled by external strain.

Abstract

In equilibrium liquid crystals, chirality leads to a variety of spectacular three-dimensional structures, but chiral and achiral phases with the same broken continuous symmetries have identical long-time, large-scale dynamics. In this paper, we demonstrate that chirality qualitatively modifies the dynamics of layered liquid crystals in active systems in both two and three dimensions due to an active "odder" elasticity. In three dimensions, we demonstrate that the hydrodynamics of active cholesterics differs fundamentally from smectic-A liquid crystals, unlike their equilibrium counterpart. This distinction can be used to engineer a columnar array of vortices, with anti-ferromagnetic vorticity alignment, that can be switched on and off by external strain. A two-dimensional chiral layered state -- an array of lines on an incompressible, free-standing film of chiral active fluid with a preferred normal direction -- is generically unstable. However, this instability can be tuned in easily realisable experimental settings, when the film is either on a substrate or in an ambient fluid.