Berlin 2005 – scientific programme
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TT: Tiefe Temperaturen
TT 23: Posters Superconductivity, Solids at Low Temperature
TT 23.19: Poster
Monday, March 7, 2005, 14:00–18:00, Poster TU D
Surface critical currents below and above Hc2(T) of Niobium — •Lars von Sawilski and Jürgen Kötzler — Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany
By using a conventional and a novel gradient [1] inductive method, the critical current at the surface of Nb-cylinders is measured below and above the upper critical field, respectively. Upon smoothing the surface of as-grown cylinders by chemical and electrical polishing from some 100 nm to 1 nm, not only the critical current below Hc2 is decreased by a factor of three but also the flux-jumps disappears, possibly due to a reduction of pinning at the surface. On the other hand, jc(H>Hc2) increased towards the value predicted for a multiply connected superconducting surface [2]. However, chemical impurities induced by polishing, may cause a strong degradation of jc, though the critical fields are enhanced.
[1] J. Kötzler et al., PRL 92, 067005 (2004)
[2] H. J. Fink and L. J. Barnes, PRL 15, 792 (1965)