Charge Fluctuations in One-Dimensional Quarter-Filled Spin Density Wave States with Dimerization

The charge fluctuation of the SDW (spin density wave) state has been examined for a system which consists of one-dimensional quarter-filled band with repulsive interactions of both on-site and nearest-neighbor site ( U and V ) and the dimerization energy ( t d ). The commensurability energy in the ground state is studied within the mean-field theory and the collective mode representing the charge fluctuation is calculated in terms of the random phase approximation. It is found that the gap of the excitation spectrum, ω g , induced by the commensurability energy vanishes at a critical value of V corresponding to the onset of the coexistence of 2 k F -SDW and 4 k F -CDW (charge density wave) where k F denotes the Fermi wave number. The spectral weight indicates the enhancement of the charge fluctuation in the presence of the energy V which competes with energies t d and U .