Spontaneous formation and dynamics of half-skyrmions in a chiral liquid-crystal film

• Published in: Nature physics 2017-12, Vol.13 (12), p.1215-1220
• Main Authors: Nych, Andriy, Fukuda, Jun-ichi, Ognysta, Uliana, Žumer, Slobodan, Muševič, Igor
• Format: Article
• Language: English
• Subjects: 639/301/923/919; 639/766/119; Atomic; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Crystal defects; Film thickness; Hexagonal lattice; Hypothetical particles; Lattice parameters; Liquid crystals; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Optics; Particle theory; Physics; Theoretical; Thin films
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys4245

Skyrmions are coreless vortex-like excitations emerging in diverse condensed-matter systems, and real-time observation of their dynamics is still challenging. Here we report the first direct optical observation of the spontaneous formation of half-skyrmions. In a thin film of a chiral liquid crystal, depending on experimental conditions including film thickness, they form a hexagonal lattice whose lattice constant is a few hundred nanometres, or appear as isolated entities with topological defects compensating their charge. These half-skyrmions exhibit intriguing dynamical behaviour driven by thermal fluctuations. Numerical calculations of real-space images successfully corroborate the experimental observations despite the challenge because of the characteristic scale of the structures close to the optical resolution limit. A thin film of a chiral liquid crystal thus offers an intriguing platform that facilitates a direct investigation of the dynamics of topological excitations such as half-skyrmions and their manipulation with optical techniques. Spontaneous formation of a half-skyrmion lattice is observed in a thin-film chiral liquid crystal. The dynamics are shown to be thermally driven — presenting a platform to study the thermal fluctuations of topological defects.