Exciton effects in soliton and bipolaron lattice states of doped electron-phonon Peierls systems

Abstract

Exciton effects on soliton and bipolaron lattice states are investigated using an electron-lattice Peierls model with long-range Coulomb interactions. The systems discussed are degenerate and non-degenerate conducting polymers. 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 exciton 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.