BOUND HOLE STATES AND FERRONS IN LA2CUO4+DELTA

Bound hole states induced by excess oxygen in La2CuO4+delta are studie d in the framework of the extended Hubbard model, using the spin-wave approximation and the Lanczos algorithm. We interpret the band at 0.5 eV in the impurity reflectivity spectrum as connected with the transit ion from the lowest bound hole level (S-z=1/2) to the unperturbed hole band. It is shown that in the realistic parameter range the excess O2 - ion does not lead to the formation of ferrons. [S0163-1829(98)03818- 1].