Energy Dependence of the Photogalvanic Effect in a Bi₂Se₃ Nanoflake Device

Bi₂Se₃ is a prototypical topological insulator exhibiting gapped bulk states with topologically protected conducting surface states. Here we study the linear photogalvanic effect (LPGE) in a Bi₂Se₃ nanoflake device as a function of energy from 0.3 to 1.8 eV. At 800 nm (1.5 eV) with the laser polarized parallel to the current, we measure a positive or negative response when the laser excitation is close to one of the contacts. Fixing the laser at the peak response, we measuring the energy dependence of the LPGE as we scan from 0.3 eV to 1.8 eV. Peaks are seen at 0.35 eV, and other higher lying optical transitions. We modulate the 800 nm excitation laser between left and right circularly polarized light observing, when current flows, positive and negative peaks at the edge of the nanosheet in line scans, consistent with a spin-Hall effect.