DOPING DEPENDENCE OF THE ELECTRONIC-STRUCTURE AND MAGNETIC ORDER IN HIGH-T(C) SUPERCONDUCTORS

The local densities of states of an extended Hubbard model describing the CuO2 planes of superconducting cuprates are calculated by means of an approximate treatment that divides the lattice into CuO2 clusters. The exact diagonalization of the Hamiltonian on these trimers is util ized to solve the lattice problem, where the hopping between different trimers is treated as a perturbation. The hole concentrations on both orbitals and the amplitude of the staggered magnetization are obtaine d as a function of the total number of holes. The overall shape of the band structure is in good agreement with exact diagonalization on lar ger clusters. The stoichiometric compound is found to be metallic in t he paramagnetic phase, but becomes a charge-transfer insulator in the antiferromagnetic phase. Electron and hole doping introduce a new band at the bottom or at the top of the charge-transfer gap, respectively. Magnetic order is destroyed when the antiferromagnetic phase becomes unstable against the paramagnetic phase.