ROLE OF OUT-OF-PLANE COPPER ORBITALS IN THALLIUM CUPRATE

To understand the role of out-of-plane copper orbitals, polarization d ependent measurements of Cu L(3)-absorption edge on well characterized Tl(2212) thin films have been performed. The density of unoccupied st ates having 3d(z2-r2) character is found to depend on the amount of do ping suggesting that out-of-plane copper orbitals essentially play a r ole of hole reservoir. The energy shift in the positions of white line s of E parallel to(a,b) and E parallel to c spectra is also found to b e doping dependent. The probable reason for the observed shift is disc ussed.