Landau-Zener and Rabi oscillations in the spin-dependent conductance

Abstract

We describe the spin-dependent quantum conductance in a wire where a magnetic eld is spatially modulated. The change in direction and intensity of the magnetic eld acts as aperturbation that mixes spin projections. This is exempli ed by a ferromagnetic nanowire. Therethe local eld varies smoothly its direction generating a domain wall (DW) as described by thewell-known Cabrera-Falicov model. Here, we generalize this model to include also a strength mod-ulation. We identify two striking diabatic regimes that appear when such magnetic inhogeneityoccurs. 1) If the eld strength at the DW is weak enough, the local Zeeman energies result in anavoided crossing. Thus, the spin- ip probability follows the Landau-Zener formula. 2) For strong elds, the spin-dependent conductance shows oscillations as a function of the DW width. Weinterpret them in terms of Rabi oscillations. Time and length scales obtained from this simpli edview show an excellent agreement with the exact dynamical solution of the spin-dependent trans-port. These results remain valid for other situations involving modulated magnetic structures andthus they open new prospects for the use of quantum interferences in spin-based devices.