PHASE-DIAGRAMS OF THE ELECTRONIC-STATE OF THE ONE-DIMENSIONAL D-P MODEL

We investigate the one-dimensional (1D) d-p model, simulating a Cu-O linear chain with strong Coulomb repulsion, by using the numerical diagonalization method. Using the Luttinger liquid theory, we obtained phase diagrams of the ground state on Ud-Upd plane, where Ud and Upd represent on-site interaction at d sites and the nearest-neighbor interaction between p and d sites, respectively. In the weak-coupling region, they agree with the g-ology; a superconducting phase [SC(I)] is restricted to attractive interaction Upd<0. On the other hand, in the strong-coupling region, we found a superconducting phase [SC(II)] for repulsive interaction Upd> Ud and an insulating state with a charge gap for Ud>Udc and Upd>Updc with critical values Udc and Updc at half-filling. Away from half-filling, another superconducting phase [SC(III)] appears for Ud Upd>0; which has been found for Ud→ in the previous paper [Physica C 205, 170 (1993)]. An analysis of the spin gap suggests that the SC(I) and SC(II) include the Luther-Emery region (with spin gap) in part, while the SC(III) belongs to the Tomonaga-Luttinger region (without spin gap) in whole. © 1995 The American Physical Society.