Electronic structure of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Y}}_{\mathit{x}}$${\mathrm{Cu}}_2$${\mathrm{O}}_{8+\mathrm{\delta }}$: Cu 2p x-ray-photoelectron spectra and occupied and unoccupied low-energy states

In this paper we will present measurements, using various kinds of spectroscopy, on the hole-doped compound ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Y}}_{\mathit{x}}$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$, with x ranging from 0.0 to 1.0. Cu 2p x-ray photoelectron spectra are compared with cluster calculations using nonlocal screening effects. The consequences of hole doping and multiplet interaction are also studied. The photoemission and inverse-photoemission data indicate that the appearance of intensity at the Fermi level is a result of the shift of the chemical potential to the top of the valence band combined with a shift of spectral weight from high- to low-energy states.