Detuning dependence of excitonic optical Stark effect in inorganic-organic layered semiconductor

Summary form only given. We report the excitonic optical Stark effect in the inorganic-organic layered semiconductor, (C/sub 6/H/sub 5/C/sub 2/H/sub 2/NH/sub 4/)/sub 2/PbI/sub 4/. PbI/sub 4/ layers, in which lowest excitons are confined, are sandwiched by organic layers. Since the dielectric constants in inorganic layers are much smaller than that in PbI/sub 4/ layers, Coulomb interaction in the PbI/sub 4/ layer is strengthened, which results in the enhancement of the exciton oscillator strength (0.5 per formula unit). Thus, this semiconductor is quite attractive for investigating strong photon-exciton coupling. The pump-and-probe experiment was performed with 130 fs resolution. The pump pulse duration was 200 fs. The sample was the spin-coated film and was cooled to 10 K. The absorption spectra is shown without and with pumping at 2.30 eV. It is clearly observed that the exciton absorption is shifted to blue with co-circular (/spl sigma/+/spl sigma/+) polarization, while it is shifted to red with counter-circular (/spl sigma/+/spl sigma/-) polarization. The optical Stark effect is important for all-optical switching. We note that, in this semiconductor, the effect is quite large (/spl ap/5 /spl times/ 10/sup -9/ meV cm/sup 2//W at 2.30 eV). This fact is explained as due to the large exciton oscillator strength. Utilizing this, we have recently demonstrated ultrafast (200 fs) switching based on the photonic crystal slab structure.