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Two-dimensional skyrmion bags in liquid crystals and ferromagnets

Abstract

Reconfigurable, ordered matter offers great potential for future low-power computer memory by storing information in energetically stable configurations. Among these, skyrmions—which are topologically protected, robust excitations that have been demonstrated in chiral magnets1,2,3,4 and in liquid crystals5,6,7—are driving much excitement about potential spintronic applications8. These information-encoding structures topologically resemble field configurations in many other branches of physics and have a rich history9, although chiral condensed-matter systems so far have yielded realizations only of elementary full and fractional skyrmions. Here we describe stable, high-degree multi-skyrmion configurations where an arbitrary number of antiskyrmions are contained within a larger skyrmion. We call these structures skyrmion bags. We demonstrate them experimentally and numerically in liquid crystals and numerically in micromagnetic simulations either without or with magnetostatic effects. We find that skyrmion bags act like single skyrmions in pairwise interaction and under the influence of current in magnetic materials, and are thus an exciting proposition for topological magnetic storage and logic devices.

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Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding authors on reasonable request.

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Acknowledgements

D.F. and M.R.D. acknowledge the funding by the Leverhulme Trust Research Programme Grant RP2013-K-009, SPOCK: Scientific Properties Of Complex Knots. The authors also thank A. Bogdanov, M. Gradhand, A. Leonov, A. Saxena, P. M. Sutcliffe and W. Zakrzewski for comments. Research at CU-Boulder (P.J.A., J.-S.B.T. and I.I.S.) was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Award ER46921, contract DE-SC0010305.

Author information

C.K. originally discovered the skyrmion bag configurations. D.F. performed the theoretical analysis, with input from C.K. and M.R.D. P.J.A. and J.-S.B.T. performed the experiments with suggestions from I.I.S. and D.F. J.-S.B.T. performed the numerical analysis in LCs and C.K. in magnets. I.I.S. provided experimental techniques and materials and directed the LC component of the project. P.J.A., J.-S.B.T. and I.I.S. analysed the experimental data. All authors contributed to the preparation of the manuscript.

Correspondence to Mark R. Dennis or Ivan I. Smalyukh.

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The authors declare no competing interests.

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Journal peer review information: Nature Physics thanks Ingo Dierking and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figures 1–6, Supplementary Table 1 and Supplementary References 1–10.

Supplementary Video 1

A 6π-twist target skyrmion collapses to an elementary full skyrmion in liquid crystals.

Supplementary Video 2

A skyrmionium transforms smoothly into the uniform state.

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Further reading

Fig. 1: Solitonic structures of a fractional skyrmion, skyrmion and skyrmionium.
Fig. 2: LC skyrmion bag configurations and decay of target skyrmions.
Fig. 3: Skyrmion bag configurations in chiral ferromagnets.
Fig. 4: Current-induced motions and data encoding of skyrmion bags.