Fractionally charged kinks in one-third-filled band CDW systems with the step-potential model

The topological excitations (kinks) in a one-dimensional one-third-filled band charge density wave system (i.e. a pi electron system) and their electronic spectra are studied. The geometry is obtained by finding the self-consistency between bond lengths and pi electron densities in the middle of each bond. The pi electron density distributions are evaluated with the step potential model. It is shown that the ground state of the perfectly trimerized system has a long-short-long bond sequence as expected from the anti-integrable limit and in contrast to the Su-Schrieffer approach. Nevertheless the kinks obtained are fractionally charged. Type 1 kinks have the (spin, charge) relation (¹/₂, -e/3) and (0, +2e/3), type II kinks (¹/₂, +e/3) and (0, -2e/3).