Superconducting thin films can get unstable against magnetic flux jumping. At low temperatures, the probability of an unstable critical state increases since a high critical current density leads to large gradients in the flux density distribution. This phenomenon is often referred to as magnetic flux avalanches. The formation and propagation of these avalanches can be extensively described using a thermomagnetic model. The description of the avalanche process gets more complex when the superconducting film is not homogeneous. Quantitative magneto-optical imaging at tailored MgB${}_2$ films revealed that the stability of the current-carrying state is substantially reduced in inhomogeneous superconductors. This is closely related to flux focusing and increased electric fields.

• Received 3 August 2011

DOI:https://doi.org/10.1103/PhysRevB.84.094533