Effective Hamiltonian of oxide superconductors and a narrow band near the Fermi level

The change of an electronic state near the insulator-metal transition is studied by an effective Hamiltonian obtained from the highly correlated p-d mixing model. The d-electron freedom is reduced to only its spin freedom. The model becomes a modified Kondo model in the sense that the spin interaction between the p and d electrons is momentum dependent, and its strength and dependence on momentum are correlated with the kinetic term of the p electron. The results show that a tail structure at the top of the occupied p band is induced and a new narrow band develops at the Fermi level, which is split from the main p band. The effects of a nonbonding band are also discussed.