Relation between the electronic structure and the superconductivity of cuprates as revealed by Cu 2<i>p</i>photoemission and theoretical investigations

Cu 2p core-level photoemission studies of ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$, ${\mathrm{BiPbSr}}_{2}$${\mathrm{Y}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$, and other cuprates show that the relative intensity of the satellite varies with the composition in a direction opposite to that of the hole concentration, ${\mathit{n}}_{\mathit{h}}$. The ${\mathit{I}}_{\mathit{S}}$/${\mathit{I}}_{\mathit{M}}$-${\mathit{n}}_{\mathit{h}}$ relations in the different cuprate series can be understood in terms of the \ensuremath{\Delta}/${\mathit{t}}_{\mathit{p}\mathit{d}}$ ratio, where \ensuremath{\Delta} is the charge-transfer excitation energy and ${\mathit{t}}_{\mathit{p}\mathit{d}}$ is the hybridization strength between the Cu 3d and O 2p orbitals. Interestingly, the ${\mathit{I}}_{\mathit{S}}$/${\mathit{I}}_{\mathit{M}}$ ratio increases with the \ensuremath{\Delta}/${\mathit{t}}_{\mathit{p}\mathit{d}}$ ratio in the cuprates. At a given value of ${\mathit{n}}_{\mathit{h}}$, e.g., around the value corresponding to maximum ${\mathit{T}}_{\mathit{c}}$, ${\mathit{I}}_{\mathit{S}}$/${\mathit{I}}_{\mathit{M}}$ increases in the same direction as ${\mathit{T}}_{\mathit{c}}$ among the different series of cuprates, suggesting thereby that ${\mathit{T}}_{\mathit{c}}$ itself may be determined by \ensuremath{\Delta}/${\mathit{t}}_{\mathit{p}\mathit{d}}$.