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Singular Band Behavior of the Extended Emery Model for the Superconducting Cuprates

Mean field slave boson approximation is performed on the extended Emery model for the CuO$_2$ conducting plane. The model is parameterized by Cu-O charge transfer energy $\Delta_{; ; ; ; pd}; ; ; ; $, copper-oxygen overlap $t_0$, oxygen-oxygen overlap $t'$ and Coulomb interaction $U$ on the copper site taken as infinite. Special emphasis is placed on the role of $t'$ in the renormalization trends of the effective band parameters $\Delta_{; ; ; ; pf}; ; ; ; $ and $t$, replacing $\Delta_{; ; ; ; pd}; ; ; ; $ and $t_0$, at small doping $\delta$. It is shown that small, negative $t'$ expands the range of stability of the metallic phase, changing, in the second order of the perturbation theory, the nature of the metal-insulator transition point. In the nonperturbative limit, $t'$ modifies strongly the renormalization of $\Delta_{; ; ; ; pf}; ; ; ; $, making it saturate at the value of $4|t'|$. Finite doping suppresses the insulating state approximately symmetrically with respect to its sign. The regime $\Delta_{; ; ; ; pf}; ; ; ; \approx 4|t'|$ fits very well the ARPES spectra of Y123, Bi2212 and LSCO and also explains, in the latter case, the evolution of the FS with doping accompanied by the spectral weight- transfer from the oxygen to the resonant band.

high-temperature superconductivity; slave-boson renormalization; effective band-structure; strongly correlated systems

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