Spin diffusion and magnetoresistance in ferromagnet/topological-insulator junctions

We study spin and charge diffusion in metallic-ferromagnet/topological-insulator junctions. The diffusive theory is constructed for the coupled transport of the spin-dependent electron densities in the ferromagnet and the charge density in the topological insulator. The diffusion equations for the coupled transport are derived perturbatively with respect to the strength of the interlayer tunneling. We analytically calculate spin accumulation in the ferromagnet and junction magnetoresistance associated with a current bias along the interface. It is found that due to the helical spin texture of the surface Dirac fermion, the spin accumulation and the junction magnetoresistance depend on the angle between the magnetization and the current-induced spin polarization on the surface of the topological insulator.

Figure 1

(a) Schematic picture of the model. (b) Dispersions of the TI and FM. The horizontal line denotes the Fermi level.