Magnetic-field-induced damage in a superconducting YBa2Cu3O7−x film

During investigations of the magnetic flux dynamics in thin superconducting YBa₂Cu₃O_7?x films we have observed the spontaneous formation of a damage in the film, apparently induced by the applied magnetic field of 0.1 T. The damage developed within less than 40 ms (the time resolution of the experiment) and showed up in the magnetiooptically recorded image of the flux above the sample as a path for massive flux penetration. A subsequent analysis revealed a 1 μm wide gap in the YBa₂Cu₃O_7?x film which had developed over a major portion of the 1 · 1 cm² sample. It is suggested that the film locally melted as a result of an instability of the superconductor in the critical state.