Anomalous voltage noise at the superconducting transition of tin films

We report voltage noise studies in the superconducting transition of thin Tin (Sn) films. Voltage noises are measured as a function of temperature and ac current. The noise spectral power S ^1/2 strongly depends on the temperature and current, with the peak temperature in S ^1/2 shifted down from that of dR/dT. Comparison with the dc noise measurement shows the S ^1/2 is much larger with ac current than dc. I-V characteristics and voltage noises are measured simultaneously to reveal the nature of the excess noises. The noise dependence on voltage strongly suggests the nature of vortex shot noise with a characteristic √V dependence for small V and reduction of S ^1/2 due to strong correlation of vortices at large V.