Excitons in soliton and bipolaron lattice states of doped Peierls systems

TL;DR

This paper investigates exciton effects in doped Peierls systems' soliton and bipolaron lattice states using an electron-lattice model, revealing how electron-hole attraction influences excitation energies and oscillator strengths.

Contribution

It introduces a combined Hartree-Fock and single-CI approach to analyze excitonic effects in doped Peierls systems, highlighting the impact of electron correlations on optical properties.

Findings

Exciton binding reduces excitation energies when correlations are included.

Lower excited states have increased oscillator strengths in single-CI calculations.

Oscillator strengths of the lowest-energy exciton increase linearly with electron concentration.

Abstract

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.