Electronic structure of TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}}
- Center for Space Microelectronics Technology, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109-8099 (United States)
- Science and Technology Center for Superconductivity, Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208-3112 (United States)
- Sandia National Laboratories, Albuquerque, New Mexico 87185-1421 (United States)
The core levels of TlBa{sub 2}CaCu{sub 2}O{sub 7{minus}{delta}} (Tl-1212) epitaxial films have been measured with x-ray photoelectron spectroscopy (XPS). The valence electronic structure has been determined using the full-potential linear muffin-tin-orbital band-structure method and measured with XPS. The calculations show that a van Hove singularity (VHS) lies above the Fermi level (E{sub F}) for the stoichiometric compound ({delta}=0), while for 50{percent} oxygen vacancies in the Tl-O layer ({delta}=0.5) E{sub F} is in close proximity to the VHS. Samples annealed in nitrogen (to reduce the hole overdoping by the removal of oxygen) exhibit higher core-level binding energies and a higher T{sub c}, consistent with a shift of E{sub F} closer to the VHS. Comparisons are made to the core levels and valence bands of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Tl-2212) and HgBa{sub 2}CaCu{sub 2}O{sub 6+{delta}} (Hg-1212). The similarity of the Cu 2p{sub 3/2} spectra for Tl-1212 and Tl-2212 indicates that the number of Tl-O layers has little effect on the Cu-O bonding. However, the Tl-1212 and Hg-1212 Cu 2p{sub 3/2} signals exhibit differences which suggest that the replacement of Tl{sup 3+} with Hg{sup 2+} results in a decrease in the O 2p{r_arrow}Cu 3d charge-transfer energy and differences in the probabilities of planar vs apical oxygen charge transfer and/or Zhang-Rice singlet-state formation. Differences between the Tl-1212 and the Tl-2212 and Hg-1212 measured valence bands are consistent with the calculated Cu 3d and (Tl,Hg) 6s/5d partial densities of states. {copyright} {ital 1997} {ital The American Physical Society}
- Research Organization:
- Sandia National Laboratories (SNL), Albuquerque, NM, and Livermore, CA (United States)
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 509054
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 55, Issue 21; Other Information: PBD: Jun 1997
- Country of Publication:
- United States
- Language:
- English
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