Spin polarization of tunneling current in barriers with spin–orbit coupling

Abstract

We present a general method for evaluating the maximum transmitted spin polarizationand optimal spin axis for an arbitrary spin–orbit coupling (SOC) barrier system, in whichthe spins lie in the azimuthal plane and finite spin polarization is achieved by wavevectorfiltering of electrons. Besides momentum filtering, another prerequisite for finite spinpolarization is asymmetric occupation or transmission probabilities of the eigenstates of theSOC Hamiltonian. This is achieved most efficiently by resonant tunneling through multipleSOC barriers. We apply our analysis to common SOC mechanisms in semiconductors: purebulk Dresselhaus SOC, heterostructures with mixed Dresselhaus and Rashba SOC andstrain-induced SOC. In particular, we find that the interplay between Dresselhaus andRashba SOC effects can yield several advantageous features for spin filter and spininjector functions, such as increased robustness to wavevector spread of electrons.