The spin polarization and transport properties at the surface of a three-dimensional topological insulator

We investigate the spin polarization and transport properties at the surface of a three-dimensional topological insulator by taking into account δ doping. It is shown that the conductance oscillates with the Fermi energy, the position and the aptitude of the δ doping. Also the conductance depends sensitively on the direction of the magnetization of the two ferromagnets, which originates from the control of the spin flow due to spin-momentum locking. Compared with the parallel configuration, a half wave loss may appear when the electron waves propagate through the antiparallel configuration. These characters are very helpful for making new types of magnetoresistance devices due to the practical applications.