Fractionally Charged States in Quarter-Filled Electron-Phonon Systems

Abstract

Various fractionally charged states in nearly quarter-filled one-dimensional electron-phonon systems are numerically investigated for Su-Schrieffer-Heeger's model. Three types of solitons are obtained depending on the excess electron number δ n = N e - N /2 and spin s with N and N e the total numbers of lattice sites and electrons; they may be called phase solitons, charged amplitude solitons and a neutral amplitude soliton for (δ n , s ) = (±1/2, 0), (±1/2, 1/2) and (0, 1/2), respectively. The states for the other δ n 's are found to consist of proper combinations of the above solitons well separated from one another. Electronic levels corresponding to localized states associated with the solitons exist not only within the gap between the conduction and valence bands but also below the valence band. Creation energies and widths of the solitons are calculated for various coupling constants.