TY - JOUR

T1 - Liquid Crystalline Half-Skyrmions and Their Optical Properties

AU - Fukuda, Jun ichi

AU - Nych, Andriy

AU - Ognysta, Uliana

AU - Žumer, Slobodan

AU - Muševič, Igor

N1 - Funding Information:
The authors thank Prof. Oleg D. Lavrentovich for valuable comments on the manuscript. This work was supported by JSPS KAKENHI (Grant numbers JP25400437, JP17H02947, and JP21H01049), the Cooperative Research Program of “Network Joint Research Center for Materials and Devices,” Slovenian Research Agency (ARRS research program P1‐0099, grants J1‐6723 and J1‐7300, and project J1‐2335), the Center of Excellence NAMASTE, NAS of Ukraine (grant 1.4B/186). Part of the numerical calculations was carried out at the Supercomputer Center, the Institute for Solid State Physics, the University of Tokyo.
Publisher Copyright:
© 2022 Wiley-VCH GmbH

PY - 2022

Y1 - 2022

N2 - Liquid crystals have intrigued physicists as a platform that facilitates direct visualization of topological concepts. Here, the theoretical and experimental studies demonstrating that a thin film of a chiral liquid crystal forms topological entities known as half-Skyrmions, swirl-like orientational order that spans the hemisphere of the order parameter space (Formula presented.), are reviewed. They appear in the form of a hexagonal lattice or in an isolated manner, accompanied by topological line defects to satisfy topological constraints. Under an optical microscope, half-Skyrmions appear as dark spots, and their hexagonal lattice yields a Kossel diagram comprising a hexagonal arrangement of circular arcs. These experimental observations are corroborated by numerical calculations of the orientational order based on the Landau-de Gennes theory with an orientational order parameter of a second-rank tensor, and construction of its optical images and Kossel diagrams by directly solving Maxwell equations for light wave. A thin film of a chiral liquid crystal thus provides an interesting system for the investigation of topological concepts, and spontaneous formation of a half-Skyrmion lattice whose periodicity is of the order of the wavelength of visible light has a potential for photonics applications as well as poses a challenging problem on optics.

AB - Liquid crystals have intrigued physicists as a platform that facilitates direct visualization of topological concepts. Here, the theoretical and experimental studies demonstrating that a thin film of a chiral liquid crystal forms topological entities known as half-Skyrmions, swirl-like orientational order that spans the hemisphere of the order parameter space (Formula presented.), are reviewed. They appear in the form of a hexagonal lattice or in an isolated manner, accompanied by topological line defects to satisfy topological constraints. Under an optical microscope, half-Skyrmions appear as dark spots, and their hexagonal lattice yields a Kossel diagram comprising a hexagonal arrangement of circular arcs. These experimental observations are corroborated by numerical calculations of the orientational order based on the Landau-de Gennes theory with an orientational order parameter of a second-rank tensor, and construction of its optical images and Kossel diagrams by directly solving Maxwell equations for light wave. A thin film of a chiral liquid crystal thus provides an interesting system for the investigation of topological concepts, and spontaneous formation of a half-Skyrmion lattice whose periodicity is of the order of the wavelength of visible light has a potential for photonics applications as well as poses a challenging problem on optics.

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U2 - 10.1002/andp.202100336

DO - 10.1002/andp.202100336

M3 - Review article

AN - SCOPUS:85122277382

JO - Annalen der Physik

JF - Annalen der Physik

SN - 0003-3804

ER -