Berlin 2005 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 23: Posters Superconductivity, Solids at Low Temperature
TT 23.36: Poster
Montag, 7. März 2005, 14:00–18:00, Poster TU D
Josephson current through a Pb/Cu/Pb nanobridge — •Jonas Hanisch1, Alexander Cosceev1, Christoph Sürgers1, Hilbert v. Löhneysen1,2, and Gernot Goll1 — 1Physikalisches Institut, Universität Karlsruhe, D-76128 Karlsruhe, Germany — 2Forschungszentrum Karlsruhe, Institut für Festkörperphysik, D-76021 Karlsruhe, Germany
The superconducting state is a macroscopic quantum state characterized by a macroscopic wave function with amplitude and phase. The Josephson effect which occurs through a weak link between two superconductors is a direct consequence of the macroscopic phase carried by each superconductor. There exist several possibilities to manufacture a weak link. Here we report on a simple fabrication method and the characterization of planar Josephson contacts between two Pb electrodes weakly coupled through a Cu nanobridge on a sapphire substrate. In these superconductor (S)/normal metal (N)/superconductor junctions the Josephson coupling is mediated via the proximity effect at the S/N interfaces. For a long dirty junction (l≪ ξN, where l is the mean-free-path and ξN is the coherence length in N) the Josephson current Ic is proportional to L/ξN·exp(−L/ξN) which gives an upper limit for the length L of the normal-metal bridge in order to observe Josephson coupling. A Josephson current of up to 750 µA at 1.5 K was observed in junctions with L well below 1 µm which is only 1/8 of the theoretically expected value. The reduction might originate from oxide layers at the normal metal/superconductor interfaces. The temperature and magnetic-field dependence of the Josephson current was investigated as well.