Topological spin textures in the helimagnet FeGe

We report on the real-space observation of a type of spin texture, i.e., the Swiss-roll-like vortex, in cubic helimagnet ($B20$-type) FeGe in terms of the Lorentz electron microcopy. This structure is enabled by the weak spin anisotropy in FeGe and the two-dimensional confinement, as revealed by a theoretical analysis that takes into account the Berry phase [Proc. R. Soc. London, Ser. A 392, 45 (1984)] associated with the curved spin stripes, i.e., the change in the spiral direction.