CORRELATIONS AND INSULATING STATE IN LA2CUO4

For high-Tc superconductors La2-xSrxCuO4, most authors now agree on the importance of the intra-atomic Coulomb repulsion U on the copper sites. Thus starting with a band made from the dx2-y2 state of copper and p state of oxygen, we include this repulsion for both copper and oxygen atomic states. We describe the Gutzwiller approximation appropriate to this two-site Hubbard Hamiltonian. We show that for large values of U the intra-atomic Coulomb repulsion and (being the difference in energy between the copper d state and oxygen p state), we get a Hubbard-type splitting of the antibonding band which leads to an insulating state for the undoped compounds even for the nonmagnetic state (T>TN). © 1990 The American Physical Society.