Photogalvanic effect in the HgTe/CdTe topological insulator due to edge-bulk optical transitions

We study theoretically the 2D HgTe/CdTe quantum well topological insulator illuminated by circularly polarized light with frequencies higher than the difference between the equilibrium Fermi level and the bottom of the conduction band (THz range). We show that electron-hole asymmetry results in spin-dependent electric dipole transitions between edge and bulk states, and we predict an occurrence of a circular photocurrent. If the edge state is tunnel-coupled to a conductor, then the photocurrent can be detected by measuring an electromotive force in the conductor, which is proportional to the photocurrent.