Role of Out-of-Plane Copper and Thallium Orbitals in Thallium Cuprate

F. Studer , C. Gasser , H. Murray , P. Srivastava , B. Sekhar , K. Garg , C. Chen

Simultaneous total and fluorescence yield XAS measurements on Cu L3-edge and, for the first time, total yield measurements at Tl L3-edge of well oriented Tl(2212) thin films are reported in this work. Also, Cu L3 and O K-edge measurements on overdoped Tl(2212) thin films using bulk sensitive fluorescence yield detection mode are reported showing that large out-of-plane hole densities do exist in the thallium cuprates at least for overdoped samples. Our results suggest that use of a bulk sensitive technique is necessary in order to get a reliable estimation of states having Cu 3dz2r2 character and thus a precise knowledge of sample stoichiometry. No direct correlation is found between Tc and out-of-plane covalent and doping hole densities such that theories based on the existence of large fraction of these out-of-plane unoccupied states are ruled out. To understand the role of out-of-plane copper orbitals, polarization dependent measurements of Cu L3-absorption edge on well characterised Tl(2212) thin films have been performed. The density of unoccupied states having 3dz2-r2 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//(a,b) and E//c spectra is also found to be doping dependent. The probable reason for the observed shift is discussed.

Domaines: Articles anciens

F. Studer, C. Gasser, H. Murray, P. Srivastava, B. Sekhar, et al.. Role of Out-of-Plane Copper and Thallium Orbitals in Thallium Cuprate. Journal de Physique IV Proceedings, 1997, 7 (C2), pp.C2-1085-C2-1087. ⟨10.1051/jp4:19972143⟩. ⟨jpa-00255205⟩