  We study theoretically 2D HgTe/CdTe quantum well topological insulator (TI)
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 (EMF) in the conductor, which is proportional
to the photocurrent.
