A local approach to the magnetism of high-Tc superconductors

Local densities of states, hole number and magnetization 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 trimers. The exact diagonalization of the Hamiltonian of these trimers is utilized to solve the lattice problem, where the hopping between different clusters is treated as a perturbation. The overall shape of the band structure is in good agreement with exact diagonalization on larger clusters. The stoichiometric compound is found to be metallic in the paramagnetic phase, but becomes a charge transfer insulator in the anti-ferromagnetic phase. Magnetic order is destroyed when the antiferromagnetic phase becomes unstable against the paramagnetic phase. ((orig.))