Transport properties of Ca doped superconducting epitaxial YBCO films

Jürgen Halbritter1, Ermile Gaganidze1, Holger Hochmuth2 und Michael Lorenz2
1FZK, IMF I, Postfach 3640, 76021 Karlsruhe, Germany
2Universität Leipzig, Fakultät für Physik und Geowissenschaften, Linnéstr. 5, D-04103 Leipzig, Germany

O doping enhancing the CuO plane density of states nm is well known to improve normal conducting and superconducting dc, ac and rf transport properties of YBCO by orders of magnitude. By Ca doping Y1-xCaxBa2Cu3O7-d enhancing nm similarely transport improvements by factors below 2 to 10 have been found for bicrystal junctions and single crystals, only. To study the effect of Ca doping on epitaxial PLD films on CeO2/Al2O3 we performed systematic transport studies for nominal x = 0.1, 0.15 and 0.2. The resulting superconducting rf properties, and therewith the mean values of the weak link critical current density jcJ, degraded with Ca content confirming trends found by dc measurements of PLD films on STO and on LAO and by rf measurements of doped films on Al2O3 and on LAO. The normal conducting weak link resistance Rbn decreased with x in line with nm enhancements but jcJRbn decreased also. Reasons for the jcJ and jcJRbn degradations and for the differences between Ca doped YBCO bicrystal junction and natural junctions in epitaxial films will be given.