Doping Dependence of the Chemical Potential in Bi2Sr2Ca1-xYxCu2O8+ Delta

A detailed study of the doping dependence of valence- and core-level spectra of Bi2Sr2Ca1-xYxCu2O8+delta leads to the conclusion that the chemical potential shifts in a manner consistent with that of a simple doped semiconductor. The spectroscopically observed filling in of the gap upon doping of the correlated insulator is therefore not due to midgap states pinning the Fermi level, but most likely due to spectral weight resulting from the incoherent part of the one-electron Green's function.