Fluxoid state transitions in mesoscopic superconducting rings: Effect of geometrical symmetry

Transitions between fluxoid states in asymmetric mesoscopic superconducting rings are investigated experimentally. We detected the fluxoid state transitions by the voltage change across current-biased small tunnel junctions attached to the ring. We found that the temperature above which the hysteresis and voltage jump in the transition disappear is lower in less symmetric rings, which is qualitatively consistent with the theoretical prediction that the one-dimensional vortex state is stabilized in asymmetric rings