Spontaneous Cholesteric Phase in Ferroelectric Nematic Liquid Crystals: Preference for Integer Number of Pitches

TL;DR

This paper investigates how the cholesteric pitch in ferroelectric nematic liquid crystals is influenced by cell thickness and screening length, revealing conditions under which the pitch locks to an integer multiple of the cell thickness.

Contribution

It demonstrates that finite cell thickness and electrostatic screening length determine whether the cholesteric pitch is quantized or varies continuously.

Findings

Pitch locks to an integer number of cell thicknesses when screening length is large.

Multiple free energy minima exist for certain screening lengths.

Pitch behavior depends critically on electrostatic screening conditions.

Abstract

In a ferroelectric nematic liquid crystal, the electrostatic interaction can induce a spontaneous cholesteric helix, even if the material is not chiral. If the liquid-crystal cell is infinitely thick, then the predicted pitch depends continuously on material parameters. Here, we consider how the prediction must be modified in a cell of finite thickness. If the Debye screening length is large enough, we find that the free energy has multiple minima. In these minima, the cholesteric pitch is locked to the cell thickness, so that the cell contains an integer number of pitches. However, if the screening length is smaller, then the cholesteric pitch can vary continuously.