Unusual flux jumps above 12K in non-homogeneous MgB ₂ thin films

Flux jumps are well known and widespread in superconducting thin films. Low temperature superconductors in particular show flux jumping below a certain threshold temperature. MgB ₂ thin films exhibit large flux jumps, so-called flux avalanches, at temperatures below about 10K. Above this temperature, the vortex state in MgB ₂ should be stable. Magneto-optical investigations of non-homogeneous MgB ₂ films show that large flux jumps can also occur in the temperature range considered as stable. However, their behavior is different from the jumps below 10K. This means in particular that the critical state is most probably not destroyed during the propagation of these jumps.