Effective Hamiltonian and electronic states in oxide superconductors

The electronic states near the Fermi level in insulator-metal transition region of p-type oxide superconductors are studied in an effective Hamiltonian obtained from the p-d mixing model. The effective spin-spin interaction induces a tail structure at the top of the occupied p-band and a new narrow band develops with hole doping at the Fermi level, splitting from the main p-band. The obtained effective Hamiltonian seems to describe the change of electronic states even in insulator-metal transition region.