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 Tc is similar for all specimens and we find that the magnitude of this peak is directly proportional to the transition temperature.