Global structure of ground-state phase diagrams in the one-dimensional anisotropic extended Hubbard model

We discuss global structures of ground-state phase diagrams in a one-dimensional half-filled electron system with on-site and spin-dependent nearest-neighbor-site Coulomb interactions. We compare our numerical calculation data for phase boundary lines with their analytical expressions in three limiting regions of interaction parameters and find good agreement between them. In the intermediate-coupling region, however, we observe nontrivial structures of phase diagrams: For systems with weak easy-plain anisotropy, both the bond-located spin- and charge-density-wave phases are realized. The latter contacts with the ferromagnetic phase stabilized in the strong-coupling region. On the other hand, when anisotropy becomes large, the intermediate phase disappears and consequently a direct transition between the former and ferromagnetic phase is observed.