Fig. 1.

Circular photogalvanic effect. Shown is a schematic illustration of the effect and the experimental setup. (A) Rashba-type spin splittings cause a shift of the bands along the k direction and lift their spin degeneracy. Excitation with left- (${\sigma }^{-}$) and right-handed (${\sigma }^{+}$) circularly polarized light creates photocarriers on opposite branches of the band structure. Since the associated group velocities d$E$/d$k$ differ in sign, a transverse spin current is induced. (B) In the experiment, a (${\mathrm{C}\mathrm{H}}_3{\mathrm{N}\mathrm{H}}_3$)${\mathrm{P}\mathrm{b}\mathrm{I}}_3$ single crystal with gold contacts (channel width: 1 mm) is illuminated at nonnormal incidence by light of tunable photon energy close to the band gap.