Regensburg 2000 – wissenschaftliches Programm
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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 nm(ε) and of localized nL||(x,ε) in-plane states and of nL⊥(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 jbn(T) which converts in the superconducting state to the Josephson tunnel current jcJ(T) and to the leakage tunnel current jbl(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 jbn, jcJ and jbl on temperature, voltage, doping and misorientation angle Θ are worked out. Consequences of the localized states nL(x,ε) as ’intrinsic defects’ causing noise, electric interface losses, leakage current jbl-enhancements and jcJ-reductions are discussed, especially in their consequences on electric RE and magnetic RresH rf residual surface resistances. Ways out of the ’surface chemistry dead lock’ with its tunnel anomalies and residual losses are analyzed to enhance jc and to reduce those anomalies.