Magnetic instability in YBa2Cu3O7-delta films

Using a magneto-optic technique we have investigated the magnetic flux prop agation into and out of superconducting thin YBa2Cu3O7-delta films. After f ield cooling below T-c, the external magnetic field B-ext perpendicular to the film is changed which gives rise to shielding currents in the sample. T he current distribution is disturbed momentarily by heating with a focused laser pulse near the sample edge. This triggers a magnetic instability, in which a magnetic flux avalanche starts to propagate. (C) 2000 Elsevier Scie nce B.V. All rights reserved.