  The influence of dendritic magnetic-flux penetration on the microwave
response of superconducting MgB2 films is investigated by a coplanar resonator
technique. The peculiar feature consists of jumps in the resonance curve,
induced by vortex avalanches freezing flux inside the resonator. Due to a
shaking effect, microwave currents maintain the vortex system close to a
nonequilibrium state, resulting in dendrite branching. Avalanche-size
distributions before and after flux-pinning tailoring by heavy-ion irradiation
are fully consistent with molecular dynamics simulations reported in
literature.
