Superconductivity of epitaxially grown α-axis YBCO films on SrTiO3 substrate

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Abstract
The a-axis oriented YBa2Cu3Ox (YBCO) films were epitaxially grown on (100) SrTiO3 substrate by dc-100 MHz hybrid plasma sputtering. The films prepared at different temperatures with and without in situ annealing had different superconductivity, which was improved with the degradation of the crystallinity of the films. The Raman spectra for the films were very similar to each other and to that expected for YBa2Cu3O7, in spite of the different superconductivity. This indicates the importance of the symmetry of the Cu–O chains rather than the oxygen content for the superconductivity. In Rutherford backscattering measurements using a 3.05 MeV He2+ ion beam, an increase of dechanneling due to the barium atoms along the film depth was clearly observed only for the most improved superconducting film. This result suggests that the relief of the strain contained in the film is also important for improving the superconductivity in the case of a-axis oriented YBCO films.