Co-existence of charge order and spin Peierls lattice distortion in one-dimensional organic compounds

The ground state properties of the organic spin-Peierls compounds with one-dimensional quarter-filled band are investigated theoretically. In the strongly correlated regime, two insulating states compete to each other, which are the charge ordered state due to the inter-site Coulomb interaction, and the `dimer Mott' insulating state due to the combined effects of the electron-phonon and the on-site Coulomb interactions. In both of these states, the electron-phonon interaction further produces the lattice tetramization, which is interpreted as the spin-Peierls state