Nematic twist--bend phase in an external field

TL;DR

This paper investigates how external fields influence the stability of the nematic twist--bend phase, revealing that positive anisotropy unwinds the helix while negative anisotropy leads to new nematic phases.

Contribution

It provides a theoretical analysis of the effects of external fields on the nematic twist--bend phase using Landau--de Gennes theory, highlighting the role of material anisotropy.

Findings

Positive anisotropy unwinds the helix to a polar uniaxial nematic.

Negative anisotropy induces a sequence of new nematic phases.

External fields significantly alter the stability and structure of the twist--bend phase.

Abstract

Nematic twist--bend is the fifth nematic phase recognized in nature. This phase exhibits spiral orientational order, thus it is a chiral structure and it can be stabilized in systems composed of achiral molecules. The microscopic origin of this spontaneous chiral symmetry breaking is to a large extent unknown but phenomenologically it appears stabilized by assuming coupling between steric polar and orientational orderings. Understanding of how external fields affect the stability of this phase is of great intellectual interest and of relevance to potential applications. Within mesoscopic Landau--de Gennes theory we find that for compounds with positive anisotropy the helix unwinds to a polar uniaxial nematic, however negative material anisotropy gives rise to a rich sequence of new nematic phases obtained via mechanism of flattening the conical spiral.