Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 34: Superconductivity - Vortex Dynamics, Vortex Phases, Pinning

TT 34.9: Vortrag

Freitag, 30. März 2007, 12:30–12:45, H19

Structurally induced anisotropic formation of vortex avalanches — •J. Albrecht¹, H.-U. Habermeier², A. Matveev³, D.V. Shantsev⁴, Y.M. Galperin⁴, and T.H. Johansen⁴ — ¹MPI für Metallforschung, Heisenbergstr. 3, D-70569 Stuttgart, Germany — ²MPI für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany — ³Chemistry Department, Lomonosov MSU, 119992 Moscow, Russia — ⁴Department of Physics, University of Oslo, Blindern, 0316 Oslo, Norway

Anisotropic penetration of magnetic flux in MgB2 films grown on vicinal sapphire substrates is investigated using magneto-optical imaging. Regular penetration above 10 K proceeds more easily along the substrate surface steps, anisotropy of the critical current being 6 %. At lower temperatures the penetration occurs via abrupt dendritic avalanches that preferentially propagate perpendicular to the surface steps. This inverse anisotropy in the penetration pattern becomes dramatic very close to 10 K where all flux avalanches propagate in the strongest-pinning direction. The observed behavior is fully explained using a thermomagnetic model of the dendritic instability.