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In particle theory, the skyrmion (/ˈskɜːrmi.ɒn/) is a hypothetical particle related originally[1] to baryons. It was described by Tony Skyrme in 1962 and consists of a quantum superposition of baryons and resonance states.[2] It could be predicted from some nuclear matter properties.[3]

Skyrmions as topological objects are important in solid state physics, especially in the emerging technology of spintronics. A two-dimensional magnetic skyrmion, as a topological object, is formed, e.g., from a 3D effective-spin "hedgehog" (in the field of micromagnetics: out of a so-called "Bloch point" singularity of homotopy degree +1) by a stereographic projection, whereby the positive north-pole spin is mapped onto a far-off edge circle of a 2D-disk, while the negative south-pole spin is mapped onto the center of the disk.

Mathematical definition[edit]

In field theory, skyrmions are homotopically non-trivial classical solutions of a nonlinear sigma model with a non-trivial target manifold topology – hence, they are topological solitons. An example occurs in chiral models[4] of mesons, where the target manifold is a homogeneous space of the structure group

\left(\frac{SU(N)_L\times SU(N)_R}{SU(N)_\text{diag}}\right)

where SU(N)L and SU(N)R are the left and right parts of the SU(N) matrix, and SU(N)diag is the diagonal subgroup.

If spacetime has the topology S3×R, then classical configurations can be classified by an integral winding number[5] because the third homotopy group

\pi_3\left(\frac{SU(N)_L\times SU(N)_R}{SU(N)_\text{diag}}\cong SU(N)\right)

is equivalent to the ring of integers, with the congruence sign referring to homeomorphism.

A topological term can be added to the chiral Lagrangian, whose integral depends only upon the homotopy class; this results in superselection sectors in the quantised model. A skyrmion can be approximated by a soliton of the Sine-Gordon equation; after quantisation by the Bethe ansatz or otherwise, it turns into a fermion interacting according to the massive Thirring model.

Skyrmions have been reported, but not conclusively proven, to be in Bose-Einstein condensates,[6] superconductors,[7] thin magnetic films[8] and in chiral nematic liquid crystals.[9]

Magnetic materials/data storage[edit]

One particular form of skyrmions is found in magnetic materials that break the inversion symmetry and where the Dzyaloshinskii-Moriya interaction plays an important role. They form "domains" as small as a 1 nm (e.g. in Fe on Ir(111)).[10] The small size and low energy consumption of magnetic skyrmions make them a good candidate for future data storage solutions and other spintronics devices.[11][12][13] Researchers could read and write skyrmions using scanning tunneling microscopy.[14] The topological charge, representing the existence and non-existence of skyrmions, can represent the bit states "1" and "0". Room temperature skyrmions were reported.[15][16]

Skyrmions operate at magnetic fields that are several orders of magnitude weaker than conventional magnetic devices. In 2015 a practical way to create and access magnetic skyrmions under ambient room-temperature conditions was announced. The device used arrays of magnetized cobalt disks as artificial Bloch skyrmion lattices atop a thin film of cobalt and palladium. Asymmetric magnetic nanodots were patterned with controlled circularity on an underlayer with perpendicular magnetic anisotropy (PMA). Polarity is controlled by a tailored magnetic field sequence and demonstrated in magnetometry measurements. The vortex structure is imprinted into the underlayer's interfacial region via suppressing the PMA by a critical ion-irradiation step. The lattices are identified with polarized neutron reflectometry and confirmed by magnetoresistance measurements.[17][18]

External links[edit]


  1. ^ At later stages the model was also related to mesons.
  2. ^ Wong, Stephen (2002). "What exactly is a Skyrmion?". arXiv:hep-ph/0202250 [hep/ph]. 
  3. ^ M.R.Khoshbin-e-Khoshnazar,"Correlated Quasiskyrmions as Alpha Particles",Eur.Phys.J.A 14,207-209 (2002).
  4. ^ Chiral models stress the difference between "left-handedness" and "right-handedness".
  5. ^ The same classification applies to the mentioned effective-spin "hedgehog" singularity": spin upwards at the northpole, but downward at the southpole.
    See also Döring, W. (1968). "Point Singularities in Micromagnetism". Journal of Applied Physics 39 (2): 1006. Bibcode:1968JAP....39.1006D. doi:10.1063/1.1656144. 
  6. ^ Al Khawaja, Usama; Stoof, Henk (2001). "Skyrmions in a ferromagnetic Bose–Einstein condensate". Nature 411 (6840): 918–20. Bibcode:2001Natur.411..918A. doi:10.1038/35082010. PMID 11418849. 
  7. ^ Baskaran, G. (2011). "Possibility of Skyrmion Superconductivity in Doped Antiferromagnet K2Fe4Se5". arXiv:1108.3562 [cond-mat.supr-con]. 
  8. ^ Kiselev, N. S.; Bogdanov, A. N.; Schäfer, R.; Rößler, U. K. (2011). "Chiral skyrmions in thin magnetic films: New objects for magnetic storage technologies?". Journal of Physics D: Applied Physics 44 (39): 392001. arXiv:1102.2726. Bibcode:2011JPhD...44M2001K. doi:10.1088/0022-3727/44/39/392001. 
  9. ^ Fukuda, J.-I.; Žumer, S. (2011). "Quasi-two-dimensional Skyrmion lattices in a chiral nematic liquid crystal". Nature Communications 2: 246. Bibcode:2011NatCo...2E.246F. doi:10.1038/ncomms1250. PMID 21427717. 
  10. ^ Heinze, Stefan; Von Bergmann, Kirsten; Menzel, Matthias; Brede, Jens; Kubetzka, André; Wiesendanger, Roland; Bihlmayer, Gustav; Blügel, Stefan (2011). "Spontaneous atomic-scale magnetic skyrmion lattice in two dimensions". Nature Physics 7 (9): 713–718. Bibcode:2011NatPh...7..713H. doi:10.1038/NPHYS2045. Lay summary (Jul 31, 2011). 
  11. ^ A. Fert, V. Cros, and J. Sampaio (2013). "Skyrmions on the track". Nature Nanotechnology 8: 152–156. doi:10.1038/nnano.2013.29. 
  12. ^ Y. Zhou, E. Iacocca, A.A. Awad, R.K. Dumas, F.C. Zhang, H.B. Braun and J. Akerman (2015). "Dynamically stabilized magnetic skyrmions". Nature Communications 6: 8193. doi:10.1038/ncomms9193. 
  13. ^ X.C. Zhang, M. Ezawa, Y. Zhou (2014). "Magnetic skyrmion logic gates: conversion, duplication and merging of skyrmions". Scientific Reports 5: 9400. doi:10.1038/srep09400. 
  14. ^ Romming, N.; Hanneken, C.; Menzel, M.; Bickel, J. E.; Wolter, B.; Von Bergmann, K.; Kubetzka, A.; Wiesendanger, R. (2013). "Writing and Deleting Single Magnetic Skyrmions". Science 341 (6146): 636–9. Bibcode:2013Sci...341..636R. doi:10.1126/science.1240573. PMID 23929977. Lay (Aug 8, 2013). 
  15. ^ Jiang, Wanjun; Upadhyaya, Pramey; Zhang, Wei; Yu, Guoqiang; Jungfleisch, M. Benjamin; Fradin, Frank Y.; Pearson, John E.; Tserkovnyak, Yaroslav; Wang, Kang L. (2015-07-17). "Blowing magnetic skyrmion bubbles". Science 349 (6245): 283–286. doi:10.1126/science.aaa1442. ISSN 0036-8075. PMID 26067256. 
  16. ^ D.A. Gilbert, B.B. Maranville, A.L. Balk, B.J. Kirby, P. Fischer, D.T. Pierce, J. Unguris, J.A. Borchers, K. Liu (8 October 2015). "Realization of ground state artificial skyrmion lattices at room temperature". Nature Communications 6: 8462. doi:10.1038/ncomms9462. Lay summaryNIST. 
  17. ^ Gilbert, Dustin A.; Maranville, Brian B.; Balk, Andrew L.; Kirby, Brian J.; Fischer, Peter; Pierce, Daniel T.; Unguris, John; Borchers, Julie A.; Liu, Kai (2015-10-08). "Realization of ground-state artificial skyrmion lattices at room temperature". Nature Communications 6. doi:10.1038/ncomms9462. 
  18. ^ "A new way to create spintronic magnetic information storage | KurzweilAI". October 9, 2015. Retrieved 2015-10-14.