Stiffness Measurements of thin and narrow superconducting rings

A central goal in the study of superconductors is to determine their coherence length, x. This is not trivial for thin films. We overcome this difficulty using a Stiffnessometer. In the present case we study a MoSi ring shaped film. Our old data analyses were based on a mean-field approximation in which the critical flux was determined by the ring’s outer radius only. A more recent theory by R. Rabaglia, A. Keren and A. Turner, based on stability to fluctuations, suggests that the inner radius is the decisive parameter but not the only one. By measuring rings of different dimensions, we show that the mean-field based theory is not correct. The new, stability approach, does a much better job explaining the data and provides a reliable value of x. Finally, a strange phenomenon of periodic flux jumps was observed in some rings