X-ray photoelectron investigation of the valence-band electronic structure of superconducting Y-Ba-Cu oxide
M. H. Frommer
DOI 10.1103/PhysRevB.38.2444 · Physical Review B
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Abstract
The valence-band electronic structure of single-phase YBa2Cu3O7−δ orthorhombic (superconducting) and tetragonal (nonsuperconducting) materials was studied at room temperature using x-ray photoelectron spectroscopy. The valence-band (VB) data have very clearly resolved spectral features and appear to yield more information than the core-level spectra which are hybrid states of combined Cu 2p, Cu 3d, and O 2p states. The difference in the density of states (DOS) is striking in that the orthorhombic material has a significant peak at an energy corresponding to bare Cu 3d8 holes (Cu3+ sites), whereas the tetragonal material has a very much smaller contribution at that energy. In the main part of the VB there is a shift of the maximum in the DOS away from EF for the orthorhombic material with respect to the tetragonal. The DOS near EF is lower for the former material compared to the latter. When this region is resolved into component peaks the results correspond to Cu 3d9L and Cu 3d10L2 holes, where L is the ligand or O hole(s), which arise from the hybridization of Cu 3d and O 2p states. These are, therefore, not bare d holes but represent holes screened by O-to-Cu charge transfer. The data are in very good agreement with a configuration-interaction calculation for a CuO610− cluster by Fujimori et al., both in shape and energies. The increased participation of oxygen in the VB of orthorhombic material is observed.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YBa2Cu3O7-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 89 | Pressure not reported | onset |
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