Site-Specific X-Ray Absorption Spectroscopy of Y1−xCaxBa2Cu3O7−y: Overdoping and Role of Apical Oxygen for High Temperature Superconductivity
M. Merz, N. Nücker, P. Schweiss, S. Schuppler, C. T. Chen, V. Chakarian, J. Freeland, Y. U. Idzerda, M. Kläser, G. Müller-Vogt, Th. Wolf
DOI 10.1103/PhysRevLett.80.5192 · Physical Review Letters
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Abstract
Using polarization-dependent O1s and Cu2p near-edge x-ray absorption spectroscopy on detwinned Y1−xCaxBa2Cu3O7−y single crystals, the unoccupied electronic structure of the CuO2 planes and CuO3 chains has been studied. Unlike the conventional picture where superconductivity is related predominantly to the number of planar holes, we find clear evidence for a prominent role of the apical sites. For both under- and overdoped samples the hole states in the planes and chains are identified and hole counts for the relevant orbitals near the Fermi level are derived. Oxygen–deficient as well as oxygen–rich samples show that the holes introduced by replacing Y3+ with Ca2+ appear solely in the planes.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Y0.97Ca0.03Ba2Cu3O6.0 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 4.2 | Pressure not reported | unknown |
| Y0.88Ca0.12Ba2Cu3O6.0 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 4.2 | Pressure not reported | unknown |
| Y0.77Ca0.23Ba2Cu3O6.0 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 4.2 | Pressure not reported | unknown |
| YBa2Cu3O6.5 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 55 | Pressure not reported | unknown |
| YBa2Cu3O6.91 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 92 | Pressure not reported | unknown |
| Y0.9Ca0.1Ba2Cu3O6.91 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 78 | Pressure not reported | unknown |
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