Bound hole states and ferrons in high-T-c superconductors

Bound hole states induced by excess oxygen in CuO2 planes of La2CuO4+delta are studied in the framework of the extended Hubbard model with the use of the spin wave approximation and the Lanczos algorithm. It is shown that the bound states are subdivided into two groups connected with two sublattices of an antiferromagnetically ordered crystal. Perturbations introduced by t he excess oxygen in these sublattices are different. We interpret the bands at 0.13 and 0.5 eV observed in the impurity reflectivity spectrum of La2Cu O4+delta as connected with transitions from the lowest bound hole levels in these two groups to the hole band. These one-hole states are characterized by the z projection of the total spin \S-z\ = 1/2. It is shown that for pa rameters of p-type cuprates, the excess O2- ion with compensated spin does not lead to the formation of ferrons, ferromagnetically ordered regions aro und holes on the antiferromagnetic background. On the other hand, the spin- carrying defect O-, which is formed in Cu-O chains of the other cuprate per ovskite YBa2Cu3O6+x, may stabilize ferrons.