Dendritic instability in YBa2Cu3O7-δ films triggered by transient magnetic fields

Superconducting films of YBa2Cu3O7-delta are shown to become thermomagnetically unstable when experiencing a time-varying perpendicular magnetic field. Using magneto-optical imaging and ramping the applied field at rates up to 3000 T/s, dendritic flux avalanches were observed in two different films, one grown by evaporation on sapphire and one by laser ablation on SrTiO3. The unstable behavior occurs over a wide temperature range limited by an upper threshold value of 40K for the film on sapphire, and 20K for the one on SrTiO3. At 7K for the same films, the threshold ramping rates are 1000 T/s and 3000 T/s, respectively. The avalanches are causing permanent damage by leaving a micron wide track where the superconductor melted during the thermomagnetic runaway. (C) 2014 AIP Publishing LLC.