Nonmagnetic resonant tunneling spin devices

We report device concepts for creating spin polarized current sources without external magnetic fields, using nonmagnetic semiconductor resonant tunneling structures. These devices contain asymmetric quantum wells where quantized states are spin-split by the Rashba effect, and achieve spin filtering by exploiting the phenomenon that the spin of a resonantly transmitted electron aligns with that of the quasibound state traversed. Achieving significant spin filtering using this approach is difficult because of the intrinsic properties of the spin-split quantum well states: the k||-dependent spin splitting is typically small and vanishes at the zone center; states with opposite k|| within a given spin-split subband have opposite spins so that there is no net spin when averaged over the subband. We have developed effective strategies for overcoming these challenges, and proposed a number of new concepts for designing heterostructure based spin devices.