Midgap State in Nearly Commensurate Charge-Density Waves

Abstract

The mean-field Fröhlich Hamiltonian in one dimension is diagonalized numerically in a self-consistent manner for systems with a nearly ½-, $\frac{1}{3}$-, or ¼-filled band. Near the Fermi energy, midgap states are present inside the main gap, and the location of the midgap states is not right in the center of the main gap. Recent absorption experiments on orthorhombic Ta${\mathrm{S}}_3$ are analyzed in terms of the above results.