  We have studied the circular photogalvanic effect (CPGE) in Cu/Bi bilayers.
When a circularly polarized light in the visible range is irradiated to the
bilayer from an oblique incidence, we find a photocurrent that depends on the
helicity of light. Such photocurrent appears in a direction perpendicular to
the light plane of incidence but is absent in the parallel configuration. The
helicity dependent photocurrent is significantly reduced for a Bi single layer
film and the effect is nearly absent for a Cu single layer film. Conventional
interpretation of the CPGE suggests the existence of spin-momentum locked
band(s) of a Rashba type in the Cu/Bi bilayer. In contrast to previous reports
on the CPGE studied in other systems, however, the light energy used here to
excite the carriers is much larger than the band gap of Bi. Moreover, the CPGE
of the Cu/Bi bilayer is larger when the energy of the light is larger: the
helicity dependent photocurrent excited with a blue light is nearly two times
larger than that of a red light. We therefore consider the CPGE of the Cu/Bi
bilayer may have a different origin compared to conventional systems.
