Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics

TL;DR

This paper demonstrates the creation and analysis of various stable and metastable solitonic structures, including skyrmions and torons, in frustrated chiral nematic liquid crystals using optical and thermal techniques, revealing their stability and diversity.

Contribution

It introduces new methods to generate and classify complex solitonic structures in confined chiral nematics, expanding understanding of their stability and configurations.

Findings

Successful generation of baby-skyrmions with double twist cylinders.

Observation of complex textures with large skyrmion numbers.

Theoretical insights into stability based on free energy considerations.

Abstract

We explore spatially localized solitonic configurations of a director field, generated using optical realignment and laser-induced heating, in frustrated chiral nematic liquid crystals confined between substrates with perpendicular surface anchoring. We demonstrate that, in addition to recently studied torons and Hopf-fibration solitonic structures (hopfions), one can generate a host of other axially symmetric stable and metastable director field configurations where local twist is matched to the surface boundary conditions through introduction of point defects and loops of singular and nonsingular disclinations. The experimentally demonstrated structures include the so-called "baby-skyrmions" in the form of double twist cylinders oriented perpendicular to the confining substrates where their double twist field configuration is matched to the perpendicular boundary conditions by loops of twist disclinations. We also generate complex textures with arbitrarily large skyrmion numbers. A simple back-of-the-envelope theoretical analysis based on free energy considerations and the nonpolar nature of chiral nematics provides insights into the long-term stability and diversity of these inter-related solitonic field configurations, including different types of torons, cholestric-finger loops, two-dimensional skyrmions, and more complex structures comprised of torons, hopfions, and various disclination loops that are experimentally observed in a confinement-frustrated chiral nematic system.