Resistance oscillations and magnetic fingerprints in superconducting Au_0.7In_0.3 cylinders

Magnetoresistance of hollow Au_0.7In_0.3 cylinders of submicron diameter was measured in the superconducting transition regime. Depending on the amount of disorder present in the samples, resistance oscillations were either absent or found only below a certain temperature in the transition regime. For those samples where the resistance oscillations were completely suppressed, reproducible sample-specific magnetoresistance fluctuations (magnetic fingerprints) were observed, also in the low-temperature part of the transition regime. The amplitude of the conductance fluctuation exceeded that of the universal conductance fluctuation in normal metals by several orders of magnitude. The fluctuation disappeared as superconductivity in the samples was suppressed by increasing either temperature or magnetic field. Thermal cycling to temperatures much higher than the superconducting critical temperature resulted in irreversible changes in the fingerprint pattern. In addition, a negative magnetoresistance was found just above the transition temperature in some samples. The physical origin of these observations is discussed in the context of mesoscopic effects in disordered superconductors.