  Topological insulators (TIs) form a new class of materials with insulating
bulk and surface conduction ensured by topologically protected surface states
(TPSS). We investigate the impact of the helicity of a normally incident laser
beam on the photovoltaic effect in the TI Bi2Se3. The observation of a helicity
dependent photovoltaic effect for normally incident light indicates the
presence of out-of-plane spin components for some TPSSs due to the hexagonal
warping. In addition, fluctuations in the electrostatic potential at the
surface locally break the rotational symmetry of the film allowing the helicity
dependent photovoltaic effect. Our result suggests that engineering local
electrostatic potentials in Bi2Se3 would allow the control of optically
generated spin currents, which may be useful for applications in
spin-optoelectronics.
