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Dresden 2003 – scientific programme

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TT: Tiefe Temperaturen

TT 8: Supraleitung: Dünne Schichten, Josephsonkontakte, SQUIDs

TT 8.9: Talk

Tuesday, March 25, 2003, 11:45–12:00, HSZ304

Microwave Properties of epitaxial Y1−xCaxBa2Cu3O7−δ films — •Ermile Gaganidze1, Roland Heidinger1, Juergen Halbritter1, Michael Lorenz2, and Holger Hochmuth21Forschungszentrum Karlsruhe, Institut fuer Materialforschung I, Postfach 3640, 76021 Karlsruhe, Germany — 2Universitaet Leipzig, Fakultaet fuer Physik und Geowissenschaften, Institut fuer Experimentelle Physik II, Linnestr. 5, 04103 Leipzig, Germany

Ca (≤ 22 at %) substituting Y in YBa2Cu3O7−δ (YBCO) is well known to enhance the in-plane conductivity σ (T>Tc) and density of states nm and to enhance the critical current density jcJ(T<Tc) of bycristal boundaries. However, up to now no data are available on microwave properties of epitaxial Ca-doped YBCO films.
Here first results are presented on large area PLD grown Y1−xCaxBa2Cu3O7−δ (Y1−xCaxBCO) films on 3-inch r-cut sapphire wafer with a CeO2 buffer layer. The microwave surface resistance Rs(T,Hrf) at 8.5 GHz of Ca substituted Y0.9Ca0.1BCO shows clear reductions with respect to that of YBCO for temperatures below about 50 K up to the fields of 20 mT. Systematic studies and analysis of Rs(T<Tc,Hrf) of 170 nm thin Y1−xCaxBCO films with x =0; 0.1; 0.15 and 0.2 are presented. The separation of Rs in intrinsic Rint and extrinsic rf residual losses Rres(T,Hrf) and their field dependencies reveals a reduced mean free path l(T) due to weak scattering at Ca in Rint(T), and an enforced strength jcJ of natural weak links explainable by an enhanced nm by additional hole doping by Ca.

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