title: Anomalous expansion of the copper-apical-oxygen distance in superconducting cuprate bilayers.
abstract: We have introduced an improved x-ray phase-retrieval method with unprecedented speed of convergence and precision, and used it to determine with sub-Angstrom resolution the complete atomic structure of epitaxial La(2-x)Sr(x)CuO(4) ultrathin films. We focus on superconducting heterostructures built from constituent materials that are not superconducting in bulk samples. Single-phase metallic or superconducting films are also studied for comparison. The results show that this phase-retrieval diffraction method enables accurate measurement of structural modifications in near-surface layers, which may be critically important for elucidation of surface-sensitive experiments. Specifically we find that, while the copper-apical-oxygen distance remains approximately constant in single-phase films, it shows a dramatic increase from the metallic-insulating interface of the bilayer towards the surface by as much as 0.45 A. The apical-oxygen displacement is known to have a profound effect on the superconducting transition temperature.
authors.affiliation: Brookhaven National Laboratory, Upton, NY 11973, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Zhou
authors.forename: Yizhak
authors.initials: Y
authors.lastname: Yacoby
authors.forename: Vladimir Y
authors.initials: VY
authors.lastname: Butko
authors.forename: Gennady
authors.initials: G
authors.lastname: Logvenov
authors.forename: Ivan
authors.initials: I
authors.lastname: Bozovic
authors.forename: Ron
authors.initials: R
authors.lastname: Pindak
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