Ultrafast generation of nanostructures with tunable topological properties by single laser pulse illumination

Abstract

Skyrmions, which have originally been introduced to explain how baryons could topologically emerge from a continuous meson field, have found many exciting applications in condensed-matter physics, where they describe topological states of matter in a wide range of systems. In magnetic materials they emerge as excitations corresponding to a spin arrangement in which the spins point in all the directions wrapping a sphere. Skyrmions have indeed been observed in chiral magnets, where they form regular lattices and are stabilized under an external magnetic field thanks to the presence of the Dzyaloshinskii-Moriya interaction (DMI). More recently, a new mechanism of Skyrmion materialization has been proposed, in which the frustration introduced in a thin ferromagnetic film by the magnetic dipole-dipole interaction leads to the stabilization of Skyrmions larger than those stabilized by DMI, consisting of magnetic domains at the center of which the magnetization points out of the film plane in the opposite direction with respect to the magnetization of the surrounding material. We report about the real-space observation by means of near-field optical Faraday microscopy of such stable Skyrmions in a thin TbFeCo film. The Skyrmions are generated after local excitation of the magnetic system by means of an intense laser pulse and do not need an external magnetic field for stabilization. The unique combination of ultrashort laser-induced magnetic excitation with subdiffraction near-field optical microscopy allows us not only to produce and observe Skyrmions as individual entities, but to also create and characterize bound Skyrmion-antiSkyrmion pairs, forming a topologically neutral entity.