Rashba-Zener mechanism for nanoscale skyrmions and topological metals

Abstract

We report a microscopic electronic mechanism for nanoscale skyrmion formation and topological metalicity. The mechanism, which relies on combining the classic double-exchange (DE) physics with the Rashba spin orbit coupling (SOC), not only provides an accurate understanding of existence of skyrmions but also explains key features in small angle neutron scattering (SANS) and Lorentz transmission electron microscopy (LTEM) data on thin films of a variety of magnetic metals. The skyrmion states are characterized as disordered topological metals via explicit calculations of Bott index and Hall conductivity. Local density of states (LDOS) display characteristic oscillations that are shown to be arising from a combination of confinement effect and gauge-field induced Landau level physics. The presence of oscillations in LDOS, without external magnetic flux, is a direct consequence of the Rashba-Zener (RZ) mechanism. The results are based on hybrid simulations on a model that explicitly retains itinerant electronic degrees of freedom. A simple physical picture is provided via an effective short-range spin model with coupling constants that depend on electronic kinetic energy. The mechanism reported here not only opens up a new approach to understand skyrmion formation in metals, but also provides a guiding principle for discovering exotic topological metal states.