Excitons in soliton and bipolaron lattice states of doped Peierls systems

Exciton effects on soliton and bipolaron lattice states are investigated using an electron-lattice Peierls model with long-range Coulomb interactions. The Hartree-Fock (HF) approximation and the single-excitation configuration-interaction (single-CI) method are used to obtain optical absorption spectra. We discuss the following properties: (1) The attraction between the excited electron and the remaining hole makes the excitation energy smaller when the correlations are taken into account by the single-CI. The oscillator strengths of the lower excited states become relatively larger than in the HF calculations. (2) We look at variations of relative oscillator strengths of two or three kinds of excitons described by the single-CI. While the excess-electron concentration is small, the ratio of the oscillator strengths of the exciton with the lowest energy, which is calculated against the total electronic excitation oscillator strengths, increases almost linearly. The oscillator strengths accumulate at this exciton as the concentration increases.