Dynamic conductance of a ferromagnetic domain wall

Based on the nonequilibrium Green's function (NEGF) approach, we present a theoretical investigation of dynamic conductance G(ω) for general ac frequency ω of a ferromagnetic domain wall (DW). We stress that our theory satisfies the current conservation and gauge invariant conditions. In the case of a DW with well-resolved discrete energy states, the applied ac signal allows for inelastic tunnel events which are related to the photon emission and absorption. By tuning the ac frequency, we find that the photon assisted tunneling (PAT) smears off the main resonance gradually, and gives rise to photon sideband resonances when a photon energy ℏω matches the difference between the Fermi level of leads and some discrete state of DW.