Formation and Evolution of Nonlinear Excitations in Low Dimensional Materials

We present femtosecond time-resolved optical measurements of the formation and evolution of excitons, polarons, and solitons in mixed-valence halide-bridged platinum chain materials in which the electronic excitations are confined to the one-dimensional geometry defined by the chain. Interpretation of the dynamics is aided by global analysis, a signal processing technique that extracts time-dependent spectral components, allowing the overlapping spectra associated with each type of electronic excitation to be identified and individually tracked. In the platinum chain materials, the nature of the photogenerated excitations can be controlled via the optical excitation energy, with excitation well above the optical gap energy resulting in the formation of charged polarons in addition to the self-trapped excitons that form following excitation near the band edge. For low-energy excitation, our results show the evolution of initially generated excitons into self-trapped excitons, followed by dissociation into soliton pairs. For high-energy excitation, we find that polarons are generated as primary photoexcitations, with branching between polaron and exciton formation.