Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 14: Wachstum und Transport in dünnen Filmen

TT 14.7: Talk

Wednesday, March 29, 2000, 16:15–16:30, H19

Surface resistances R(T ≤ 0.9 T_c, H_rf, f) of YBCO by weak links and indications for point defects — •Alexander Dierlamm, Ermile Gaganidze, and Juergen Halbritter — Forschungszentrum Karlsruhe, IMF 1, Postfach 3640, D-76021 Karlsruhe, Germany

YBa₂Cu₃O_7−x contains nets of weak or strong links, point defects and other extrinsic and intrinsic reasons for rf residual losses. HTS-in-plane weak links show very much reduced j_cJ(T) ≃ j_cJ(0)(1−T/T_c)-values compared to theory and a large leakage current j_bl of the order of j_cJ ∝ 1/R_bl due to a high density of intermediate states in disordered HTS junction material. The finite residual losses R_res(T,H_rf,f) are due to the finite normal conducting leakage current of weak links with R_bl(T ≤ 0.9 T_c) ≃ const. in distances a_J. Quantitative agreement experiment - model in T and frequency dependence is obtained by measured values of a_J(≃ 0.2−20 µ m), of R_bn(≃ 1000 −1 nΩcm²) and of j_cJ(≃ 10² − 10⁷ A/cm²) with j_cJR_bl² ≃ 5× 10⁻¹² AΩ² cm². The observed scaling R_res(H_rf) ∝ 1/j_cJ^3/2(H_rf) indicates Josephson fluxon penetration in long weak links. The effect of point defect on T, H_rf and f dependence is discussed.