Fig. 2. Spin-selective OSE.

(A) Optical selection rule for the lowest singlet exciton in PEPI. Both the electron and the hole have a total angular momentum quantum number $\mathit{J}=\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ and a magnetic quantum number ${\mathit{m}}_{\mathit{J}}=\pm \raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$. (B) Schematic of the spin-selective OSE mechanism in PEPI, showing only the m_J in ket notation. The red (blue) arrow illustrates the interaction between the σ⁺ (σ⁻) photon that forms the Floquet quasi-states (green line). The hybridization of the equilibrium states (red or blue lines) with the Floquet quasi-states results in the shift in energy levels. The dashed (solid) lines represent the energy levels before (after) the repulsion. Repulsion only occurs between the equilibrium states and the Floquet states with the same m_J. (C) Co-circularly and counter-circularly polarized pump and probe TA spectra at various Δt. (D) The corresponding kinetics at the negative ΔA peak (2.37 eV). mOD, milli-optical density.