The Axial Oxygen Atom and Superconductivity in YBa2Cu3O7

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Science  10 Mar 1989:
Vol. 243, Issue 4896, pp. 1340-1343
DOI: 10.1126/science.243.4896.1340


Changes in the copper K-edge x-ray absorption spectrum of YBa2Cu3O7 across the critical temperature indicate that, accompanying the superconducting transition, the mean square relative displacement of some fraction of the Cu2-O4 bonds becomes smaller or more harmonic (or both), that there may be a slight increase in the associated Cul-O4 distance, and that electronic states involving these atom pairs become more atomic-like. If there is an association between the superconductivity and this lattice instability, then the bridging axial oxygen is of central importnce in determining the high tranition temperature of YBa2Cu3O7. Because this structural perturbation will affect the dynamic polrizability of the copper oxygen sublattice, it is consistent with an excitonic pairing mhanism in these materials.

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