A Quantum Spin Hall Round Disk as a Spin Rotator and Filter

We study theoretically the spin transport of a Quantum Spin Hall round disk. When an electron traverses the disk in virtue of the edge states, its spin’s in-plane component can be rotated by a magnetic flux through the disk. The spin rotation occurs due to the interference of two helical edge states with opposite spins, which is regarded as the Aharonov-Bohm effect in the spin space and a manifestation of the Berry phase. Besides, the disk has a spin filter effect on the tunneling current when we apply an appropriate magnetic field and gate voltage on it. The spin polarization ratio can reach 100% when the couplings between the disk and leads are weak.