Charge order and superconductivity in low-dimensional organic conductors

We study the coexistent state of the spin density wave (SDW) and the charge density wave (CDW) in a one-dimensional extended Hubbard model. We find that the coexistent state of SDW and CDW is stabilized in various electron-filling cases when band parameters are for organic conductors. The ground state energies have cusp-like minima at n/4m-fillings, where n and m are integers. The maxima of the critical temperatures of the coexistent state at n/4m-fillings will be observed in X-ray scattering measurements. We discuss the suitable filling for superconductivity of which strong fluctuation in antiferromagnetic ordering may be the origin.