Non-contact spin pumping by microwave evanescent fields

The angular momentum of evanescent light fields has been studied in nano-optics and plasmonics, but not in the microwave regime. Here we predict non-contact pumping of electron spin currents in conductors by the evanescent stray fields of excited magnetic nanostructures. The coherent transfer of the photon to the electron spin is proportional to the g-factor, which is large in narrowgap semiconductors and surface states of topological insulators. Electron correlation may lead to chirality of the spin injection.