A graphene-based technique for imaging thermomagnetic avalanches in superconducting thin films

We report on graphene-based technique for imaging thermomagnetic avalanches in superconducting thin films. The technique is useful for superconducting electronics inclosing superconducting spin-polarized devices working at the limit of critical current density, which could result in dendritic flux instabilities. The technique allows determining an extent to which superconducting films are vulnerable to the appearance of thermomagnetic avalanches threatening the functioning of device. This imaging technique is based on irreversible changes in the morphology of graphene layer that covers superconducting film at the influence of heat generated during the instability. These changes are investigated by optical imaging, atomic force microscopy and scanning electron microscopy. It is found that the technique can image strong thermomagnetic instabilities. Experiments that combined magneto-optical imaging (MOI) and the graphene cover showed that dendrites seen in MOI are not producing visible optical traces in the graphene cover, perhaps due to effective heat removal to the MOI indicator film. A tuning of graphene imaging technique and a search for alternative, more sensitive to heat, technique is necessary.