Vortex Avalanches Induced by Single High-Frequency Pulses in MgB Films.

We report on avalanche-like flux features in the response of superconducting films of MgB, prepared by magnetron sputtering and an ex-situ annealing process, when a single high-frequency pulse is used as a perturbative source. The instability is observed as an abrupt jump in the output voltage signal of the SQUID magnetometer where the sample is measured as a function of temperature, magnetic field, and pulse width, at fixed nominal power and frequency values. The interaction between the high-frequency surface currents and the relaxing vortex system is suggested to explain the nucleation of avalanches. Local heating due to the pulse application is also considered as a contributing mechanism. [ABSTRACT FROM AUTHOR]