Magnetic flux noise in superconducting rings and disks close to the superconducting transition

We report measurements of the magnetic flux noise in a series of superconducting rings and disks having a wide range of superconducting transition temperatures. In the absence of an applied magnetic field, the behavior of rings can be described in terms of a loop containing one or two superconducting weak links. We observe logarithmic flux creep in discrete flux quanta when a magnetic field is applied to such rings and then abruptly removed. For a Y-Ba-Cu-O ring and a complete disk, the behavior in the presence of an applied field is well described by a model in which the film displays a temperature-dependent resistivity. We offer an explanation for the observation that for a given superconductor and measurement geometry, the magnitude of the noise peak close to the superconducting transition T-c is similar for all specimens and we find that the magnitude of this peak is directly proportional to the transition temperature.