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TT: Tiefe Temperaturen

TT 12: Fachsymposium: Korngrenzen in HTSL

TT 12.8: Vortrag

Dienstag, 28. März 2000, 17:15–17:30, H18

HTS Grain Boundaries and their Transport Properties in the Normal- and Superconducting state — •J. Halbritter — Institut für Materialforschung I, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany

The basic ingredients of HTS are the quasi-two dimensional metallic conduction in CuO-planes being separated by quasi-insulating blocking layers. The counteraction of in-plane overlap Γ^|| and out-of plane overlap Γ^⊥, of charging energies Δ U^|| and Δ U^⊥, and of densities of extended n_m(ε) and of localized n_L^||(x,ε) in-plane states and of n_L^⊥(x,ε) blocking layer states yield the tunnel transport across the plaques. The resonant tunnel model describes quantitatively the out of plane transport and the transport across external ab-surfaces and in-plane weak links in the normal state j_bn(T) which converts in the superconducting state to the Josephson tunnel current j_cJ(T) and to the leakage tunnel current j_bl(T). With an atomistic model on interface relaxation and chemistry, i.e. on non local stoichiometry with cluster bonds extending about 1 nm, the dependencies of j_bn, j_cJ and j_bl on temperature, voltage, doping and misorientation angle Θ are worked out. Consequences of the localized states n_L(x,ε) as ’intrinsic defects’ causing noise, electric interface losses, leakage current j_bl-enhancements and j_cJ-reductions are discussed, especially in their consequences on electric R^E and magnetic R_res^H rf residual surface resistances. Ways out of the ’surface chemistry dead lock’ with its tunnel anomalies and residual losses are analyzed to enhance j_c and to reduce those anomalies.