Albrecht J, Matveev A T, Strempfer J, Habermeier H-U, Shantsev D V, Galperin Y M, Johansen T H
Max-Planck-Institut für Metallforschung, Heisenbergstrasse. 3, D-70569 Stuttgart, Germany.
Phys Rev Lett. 2007 Mar 16;98(11):117001. doi: 10.1103/PhysRevLett.98.117001. Epub 2007 Mar 12.
Anisotropic penetration of magnetic flux in MgB(2) 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, the 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.
