Three-dimensional skyrmions in Bose-Einstein condensates
Skyrmions are topological excitations first considered in the field theories in particle physics in the 1960s. Recently, two-dimensional skyrmions have gained interest in systems such as crystalline liquids, magnetic materials, and superfluids. Here, we experimentally observe three-dimensional skyrmions in an atomic spin-1 Bose-Einstein condensate . Skyrmionic spin texture gives rise to fascinating synthetic electromagnetic phenomena, including knotted magnetic field lines.
Furthermore, we conduct a numerical study on exotic 3D skyrmions hosted by the cyclic and biaxial nematic phases of a spin-2 Bose-Einstein condensate . These skyrmions exhibit exceptionally high mapping degrees resulting from the versatile symmetries of the corresponding order parameters.
 W. Lee, A. H. Gheorghe, K. Tiurev, T. Ollikainen, M. Möttönen, and D. S. Hall, Science Advances 4, eaao3820 (2018).
 K. Tiurev, T. Ollikainen, P. Kuopanportti, M. Nakahara, D. S. Hall, and M. Möttönen, New Journal of Physics 20, 055011 (2018).