Anthony Lollo

Phase slips result in many interesting properties of superconducting materials, such as the finite resistance of thin superconducting nanowires, the decay of current in superconducting rings, and the flux periodicity of the critical temperature, Tc, in hollow superconducting cylinders or rings. Though the first experiments were performed in 1961, the goal of observing coherent macroscopic quantum tunneling in uniform superconductors has sparked recent interest in the field.

 

We present measurements of the supercurrent in arrays of uniform isolated mesoscopic aluminum rings as a function of applied magnetic field, measured through cantilever torque magnetometry. These measurements are taken over the full range of applied magnetic fields for which the rings are superconducting and for 400 mK < T < 1300 mK. We fit the supercurrent data to Ginzburg-Landau (GL) theory for a 1-dimensional superconducting ring with the inclusion of finite width. This detailed analysis extends the range of both temperature and applied magnetic fields over which prior measurements were quantitatively analyzed. Further, we show that phase slips occur deterministically as the free energy barrier separating two metastable states vanishes. We also present measurements of the distribution of applied magnetic fields at which a phase slip occurs for two individual isolated superconducting rings each of different radius. We find that as temperature is increased the mean and standard deviation decrease, while the skewness is always close to −1.