Local Singlet State in Effective Hamiltonian for a CuO₂ Layer: Case of a Single Cu Spin and a Hole

Abstract

Based on the effective Hamiltonian for a CuO₂ layer of high T_c oxides, we have examined the case of a single Cu spin and a single hole in a Bloch band, whose structure is determined not only by direct transfer integrals between oxygens but also by the indirect one via Cu sites. It is found that the singlet state is strongly stabilized because of the particular feature of the band structure and that the triplet state is also possible below the hole band.