Excess Voltage Noises in the Superconducting Transition in 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 applied current. The noise spectral power S$^{1/2}$ is peaked during the superconducting transition, with the peak temperature shifted downward 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 correlate the voltage noise with the vortex motion. The noise depends on the voltage with a characteristic $\sqrt V $ dependence for small V, suggesting shot noise nature for the excess noises.