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

Nature Physics volume 13, pages 1215–1220 (2017)Cite this article

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Abstract

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.

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Figure 1: Real-space structures of a thin cell of a chiral liquid crystal.
Figure 2: Real-space observations of the half-skyrmion lattice structures and calculated real-space images.
Figure 3: Flickering of a hexagonal lattice of half-skyrmions.
Figure 4: Isolated half-skyrmions.

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Acknowledgements

A.N. and U.O. acknowledge partial support from NAS of Ukraine (grant 1.4B/186) and Ukrainian–Slovenian bilateral project (grants M/13-2013 and M/100-2014). J.F. thanks Slovenian Research Agency (ARRS research programme P1-0099 and project J1-2335) and the Centre of Excellence NAMASTE for generous financial support for his stay in University of Ljubljana, during which the important part of his work was carried out. J.F. is also supported by JSPS Grant-in-Aid (KAKENHI) for Scientific Research (Grant Numbers 25400437 and JP17H02947), the Cooperative Research Program of ‘Network Joint Research Centre for Materials and Devices,’ and the Supercomputer Center, the Institute for Solid State Physics, the University of Tokyo. I.M. and S.Ž. acknowledge support of the Slovenian Research Agency (ARRS) programme P1-0099 and grants J1-6723 and J1-7300. J.F. benefited greatly from valuable discussions with H. Kikuchi, Y. Okumura, H. Higuchi, H. Yoshida, H. Orihara, T. Ohzono and J. Kishine, and technical advice on numerical calculations by T. Miura.

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Author notes

  1. Andriy Nych and Jun-ichi Fukuda: These authors contributed equally to this work.

Authors and Affiliations

  1. Department of Molecular Photoelectronics, Institute of Physics, Nauky prospect, 46, Kyiv, 03680, Ukraine

    Andriy Nych & Uliana Ognysta

  2. Condensed Matter Department, Jožef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia

    Andriy Nych, Uliana Ognysta, Slobodan Žumer & Igor Muševič

  3. Department of Physics, Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan

    Jun-ichi Fukuda

  4. National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba 305-8568, Japan

    Jun-ichi Fukuda

  5. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia

    Jun-ichi Fukuda, Slobodan Žumer & Igor Muševič

Authors
  1. Andriy Nych
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Contributions

A.N. and U.O. designed and performed the experiments. J.F. developed a framework for the calculation of microscope images, and carried out the numerical calculations. I.M. initiated the experimental work and supervised the experiments. S.Ž. supervised the theoretical work. J.F. wrote the manuscript with the input from all the other authors. All the authors discussed and analysed the results and contributed to the manuscript.

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Correspondence to Andriy Nych or Jun-ichi Fukuda.

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Nych, A., Fukuda, Ji., Ognysta, U. et al. Spontaneous formation and dynamics of half-skyrmions in a chiral liquid-crystal film. Nature Phys 13, 1215–1220 (2017). https://doi.org/10.1038/nphys4245

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