Fig. 1: Spin-selective transition rules and separation of the OSE and BSS in lead halide perovskites.

a Schematic illustration of the crystal structure of CsPbI₃ perovskite phase. b Conduction band (CB) and valence band (VB) edge states coupled to circularly-polarized photons. c Interaction energy diagram of the optical Stark shift driven by a nonresonant σ⁺ photon, which occurs at the VB | − 1/2〉 and CB | + 1/2〉 states. The shift can be detected only with σ⁺σ⁺ pump-probe configuration. d Interaction energy diagram for the Bloch–Siegert shift driven by a nonresonant σ⁺ photon, which occurs at the VB | + 1/2〉 and CB | −1/2〉 states and can be detected only with σ⁺σ⁻ pump-probe configuration.