Superconductivity and transport properties of epitaxial YBa₂(Cu_1-xZn_x)₃O₇-thin films

The influence of Zn-doping on the superconducting properties of epitaxial c-axis oriented YBa₂(Cu_1-xZn_x)₃O₇-film was investigated. The authors find a depression of the superconducting T_c of -10.5 K/(at.% Zn). In the range of small doping concentrations x<or=0.005 the Zn-atoms act as effective pinning centers. This becomes evident by an enhancement of both the depinning field and the average activation energy for flux creep. The absolute values of the critical current density are not depressed for these concentrations. Measurements of the angular dependence of the critical transport current density j_c^ab( phi ) in the ab-plane on the angle of an applied magnetic field show for Zn-doped films more structures than for undoped films. For explanation of j_c^ab( phi ) a model based on intrinsic pinning in combination with the pinning effectivity of the Zn-impurities is discussed.