Spin‐dependent current through a ferromagnetic resonant tunnelling quantum well

Abstract

AbstractWe study the nonequilibrium quantum transport through a ferromagnetic quantum well (FQW) coupled to two nonmagnetic leads. A formal expression for the spin‐polarized current is derived with the Keldysh nonequilibrium‐Green‐function technique. Then the retarded Green function for the FQW, which is needed in the general expression for the transmission coefficient T(E), is calculated by using Zubarev's double‐time‐Green‐function technique. The derived expression for T(E) includes, e.g., the shift and the life‐time broadening of the electronic states inside the FQW due to the tunnelling processes and the strong exchange interaction between the charge carrier spins and the localized spins of the magnetic electrons. Numerical results are presented for a simple FQW model structure consisting of a diluted III–V ferromagnetic semiconductor between the insulating barriers. A single resonant level inside the FQW is coupled to the nonmagnetic leads by tunnelling and to the ferromagnetic subsystem by the exchange interaction. Novel effects predicted by the model are discussed, such as the broadening of the resonant level due to the spin‐disorder scattering in a 2D‐hole gas and the large spontaneous spin‐splitting of the resonant level in a ferromagnetic phase transition. These effects are seen in the calculated T(E) and the spin current through the FQW, which show strong temperature and magnetic field dependences at temperatures close to the Curie temperature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)