Microscopic theory of light-induced ultrafast skyrmion excitation in transition metal films

Magnetic skyrmions are topological excitations of great promise for compact and efficient memory storage. However, to interface skyrmionics with electronic devices requires efficient and reliable ways of creating and destroying such excitations. In this work, we unravel the microscopic mechanism behind ultrafast skyrmion generation by femtosecond laser pulses in transition metal thin films. We employ a theoretical approach based on a two-band electronic model, and show that by exciting the itinerant electronic subsystem with a femtosecond laser ultrafast skyrmion nucleation can occur on a 100 fs timescale. By combining numerical simulations with an analytical treatment of the strong s–d exchange limit, we identify the coupling between electronic currents and the localized d-orbital spins, mediated via Rashba spin–orbit interactions among the itinerant electrons, as the microscopic and central mechanism leading to ultrafast skyrmion generation. Our results show that an explicit treatment of itinerant electron dynamics is crucial to understand optical skyrmion generation.