Steering Magnetic Skyrmions with Currents: A Nonequilibrium Green's Functions Approach

Abstract

Magnetic skyrmions, topologically protected vortex‐like configurations in spin textures, are of wide conceptual and practical appeal, notably in relation to the making of so‐called race‐track memory devices. Skyrmions can be created, steered, and destroyed with magnetic fields and/or (spin) currents. Here the authors focus on the latter mechanism, analyzed via a microscopic treatment of the skyrmion–current interaction. The system considered is an isolated skyrmion in a square‐lattice cluster, interacting with electron spins in a current‐carrying quantum wire. For the theoretical description, a quantum formulation of spin‐dependent currents via nonequilibrium Green's functions (NEGF) within the generalized Kadanoff–Baym ansatz (GKBA) is employed. This is combined with a treatment of skyrmions based on classical localized spins, with the skyrmion motion described via Ehrenfest dynamics. With the mixed quantum–classical scheme, the authors assess how time‐dependent currents can affect the skyrmion dynamics, and how this in turn depends on electron–electron and spin–orbit interactions in the wire. This study shows the usefulness of a quantum–classical treatment of skyrmion steering via currents, as a way for example to validate/extract an effective, classical‐only, description of skyrmion dynamics from a microscopic quantum modeling of the skyrmion–current interaction.