Berlin 2005 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

TT: Tiefe Temperaturen

TT 1: Superconductivity - Fabrication, Technical Optimization and Characterization

TT 1.5: Vortrag

Freitag, 4. März 2005, 11:15–11:30, TU H104

Density of critical current of Nb and NbN thin film bridges — •Konstantin Ilin¹, Michael Siegel¹, Alexei Semenov², Heinz-Wilhelm Hübers², and Andreas Engel³ — ¹Institut für Mikro- und Nanoelektronische Systeme, Universität Karlsruhe, Karlsruhe, Germany — ²DLR Institut für Planetenforschung, Berlin, Germany — ³Physics-Institute of the University of Zürich, Zürich, Switzerland

We present results of a systematic study of the critical current in superconducting Nb and NbN thin film bridges. The bridges with a width from 50 nm to 10µm were patterned from thin superconducting films by means of electron-beam lithography and ion milling. For both materials the nominal critical current density extrapolated to zero temperature varied with the bridge width and thickness. We attribute these variations to a fabrication-enhanced reduction of the effective, superconducting cross-section of the bridges with respect to their geometric cross-section and to an uneven distribution of the super-current over the superconducting core of the bridge. In very thin bridges, i.e. 5 nm and 8 nm for NbN and Nb, respectively, the nominal current density increased drastically when the bridge width became smaller than 500 nm. We associate the enhancement of the critical current in those bridges with the crossover from depinning of magnetic vortices to either their nucleation or breaking of Cooper pairs.