J. Phys. IV France
Volume 06, Numéro C3, Avril 1996
Proceedings of the Second European Workshop on Low Temperature Electronics
Page(s) C3-259 - C3-264
Proceedings of the Second European Workshop on Low Temperature Electronics

J. Phys. IV France 06 (1996) C3-259-C3-264

DOI: 10.1051/jp4:1996339

Fractal Structure Near the Percolation Threshold for YBa2Cu3O7 Epitaxial Films

M. Baziljevich1, A.V. Bobyl2, H. Bratsberg1, R. Deltour3, M.E. Gaevski4, Yu.M. Galperin1, V. Gasumyants3, T.H. Johansen1, I.A. Khrebtov5, V.N. Leonov5, D.V. Shantsev2 and R.A. Suris4

1  University of Oslo, 0316 Oslo 3, Norway
2  St. Petersburg State Technical University, St. Petersburg 195251, Russia
3  Université Libre de Bruxelles, 1050 Brusseles, Belgium
4  A.I. Ioffe Physical-Technical Institute, St. Petersburg 194021, Russia
5  S.I. Vavilov State Optical Institute, St. Petersburg 199034, Russia

Inhomogeneity of the properties of YBa2Cu3O7 epitaxial c-oriented films has been investigated. Using a low - temperature SEM the lateral distribution of local critical temperature has been determined with spatial resolution of 2 µm. The technique provides a direct observation of the percolative character of the superconducting transition on a microbridge scale. It is shown for the first time that near the percolation threshold the current channel has a very rough, irregular configuration and the fractal dimensionality of the superconducting cluster is estimated as 1.55. The magnetic field imaging of samples is carried out and a quantitative correlation between Tc-map and the map of critical density of shielding currents is observed. The transition curves R(T) over a wide range of resistances and bias currents are described in terms of the network model. The model takes into account both the spatial distribution of Tc and the presence of random weak links with a wide distribution of their critical currents.

© EDP Sciences 1996