Helicity-Dependent Photovoltaic Effect in Bi₂Se₃ Under Normal Incident Light

Topological insulators (TIs) form a new class of materials with an insulating bulk and conducting surfaces ensured by topologically protected surface states (TPSS). The impact of the helicity of a normally incident laser beam on the photovoltaic effect in the TI Bi₂Se₃ is investigated. 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.