Magnetic instability in HTSC films

Abstract We have investigated the short time dynamics in the magnetic flux distribution of thin YBa 2 Cu 3 O 7-x films by means of time resolved magnetooptics. Local heating of the superconductor with a focussed laser pulse in a region with high shielding currents leads to an instability in the magnetic flux distribution. A pump probe technique allowed to visualize changes in the flux distribution on a nanosecond time scale. The instability develops in two steps giving rise to additional flux penetration and to a branching of the flux front into the superconductor.