Multiple fluxoid transitions in mesoscopic superconducting rings

We report magnetic measurements of fluxoid transitions in mesoscopic, superconducting aluminum rings over nearly the whole superconducting temperature range. The transitions are induced by applying a flux to the ring so that the induced supercurrent approaches the critical current. Sufficiently close to $T_c$, the fluxoid number $n$ always changes by $\pm$ 1. Upon lowering the temperature, larger changes in $n$ occur. Below approximately 0.3 $T_c$, the final state after a transition is close to the ground state. The dynamics leading to this phenomenon are discussed in terms of the time dependent Ginzburg-Landau theory for gapless and gapped superconductors and a qualitative explanation based on the formation of a local hot spot.