Role of out-of-plane copper orbitals in thallium cuprate

Abstract

To understand the role of out-of-plane copper orbitals, polarization dependent measurements of Cu ${\mathit{L}}_{3}$-absorption edge on well characterized Tl(2212) thin films have been performed. The density of unoccupied states having 3${\mathit{d}}_{{\mathit{z}}^{2}\mathrm{\ensuremath{-}}{\mathit{r}}^{2}}$ character is found to depend on the amount of doping suggesting that out-of-plane copper orbitals essentially play a role of hole reservoir. The energy shift in the positions of white lines of E\ensuremath{\parallel}(a,b) and E\ensuremath{\parallel}c spectra is also found to be doping dependent. The probable reason for the observed shift is discussed. \textcopyright{} 1996 The American Physical Society.