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 S1/2 strongly depends on the temperature and current, with the peak temperature in S1/2 shifted down from that of dR/dT. Comparison with the dc noise measurement shows the S1/2 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 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sqrt{V}$\end{document} dependence for small V and reduction of S1/2 due to strong correlation of vortices at large V.