The chirality dependent spin filter design in the graphene-like junction

We investigate the chirality-dependent spin transport in a graphene-like topological insulator (TI) TI/n junction, where a perpendicular magnetic field or an off-resonant circularly/polarized light field is applied to the normal (n) region. It is found that the coupling between the helical edge states of the TI and chiral edge states from the magnetic/light field results in a perfect spin filtering effect and only one spin species can tunnel through the junction interface. The origin is ascribed to the chirality-conservation requirement, since the two spin species have the opposite chiralities in the TI region and in the n region both of them have the same chiralities. For a TI/n superlattice structure, the spin filtering effect is enhanced and even survives in a fairly strong disorder environment.