This paper presents spectroscopic investigations of the normal-state properties of ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ and ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathit{y}}$ single crystals. Ultraviolet photoemission and electron energy loss data are consistent with the filling in of the charge transfer gap upon doping due to spectral weight transfer mechanisms. The modifications occurring in the surface electronic properties after exposure to pure ${\mathrm{O}}_2$ and after the deposition of one monolayer of bismuth are studied and discussed.

• Received 21 March 1995

DOI:https://doi.org/10.1103/PhysRevB.52.3727