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Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 8: Postersitzung I: Supraleitung

TT 8.34: Poster

Monday, March 8, 2004, 14:30–19:00, Poster A

Evidence for a percolation-driven transition to coherent surface superconductivity — •Lars von Sawilski, Sara Casalbuoni, and Jürgen Kötzler — Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany

Above the upper critical field Hc2 we have investigated the field dependences of the surface conductance, G′−iG″, and the critical current Jc of different treated Niobium cylinders: as grown, chemically and electrolytically polished. The low frequency limits of G′(H) and G″(H) and of Jc(H) display power-law singularities, defining a transition to coherent surface superconductivity at Hc3c>Hc2. The critical exponents as well as the dynamical scaling of G′−iG″ studied between 0.1 Hz and 1 MHz are consistent with predictions for a two-dimensional percolation transition. Relating Hc3c to the conventional onset field for surface superconductivity Hc3, we find Hc3c/Hc3=0.81. Surprisingly, this ratio turns out to be independent of significant variations of Hc3 due to differently treated surfaces. This points to a new universal relation between the nucleation and the onset of long-range coherent surface superconductivity.

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