Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 15: Superconductivity: Poster Session
TT 15.45: Poster
Dienstag, 26. Februar 2008, 14:00–18:00, Poster B
Unexpected temperature-dependence of the critical current in NbN-microbridges — •Andreas Engel1, Holger Bartolf1, Luis Gomez1, Andreas Schilling1, Konstantin Il’in2, Michael Siegel2, Alexei Semenov3, and Heinz-Wilhelm Hübers3 — 1Physics Institute, University of Zürich, Winterthurerstr. 190, CH-8057 Zürich — 2Institute of Micro- and Nano-Electronic Systems, University of Karlsruhe, Hertzstr. 16, 76187 Karlsruhe — 3DLR e.V. Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin
Superconducting micro- and nanostructures made from NbN ultra-thin films are key elements of THz hot-electron bolometer mixers and single-photon detectors for the visible and near-infrared. Their detection mechanisms require operation with a biasing current close to but below the device’s critical current Ic at temperatures well below their critical temperature. We studied the temperature-dependence Ic(T) of up to 10 nm thick NbN bridges with widths between 100 nm and 10 µm. The temperature-dependence of the critical-current density jc of sub-micrometer wide bridges is well described by the de-pairing jc. They remain free of magnetic vortices due to a geometrically enhanced Bean-Livingston barrier. Micrometer-wide bridges show a cross-over from de-pairing to de-pinning jc with decreasing temperature. Moreover, at low temperatures, when Ic is determined by the de-pinning of magnetic vortices due to the self-field of the applied current or small external magnetic fields, Ic(T) may exhibit non-monotonic behavior, i.e. reduced Ic at lower temperature. We present experimental data of these unexpected features and discuss their possible reasons.