T-fluctuations and dynamics of the resistive transition in thin superconducting films

Abstract

We investigate the temporal and spatial scales of resistance fluctuations (R-fluctuations) at the superconducting resistive transition in thin epitaxial TiN films, accessed through voltage fluctuations measurements in current-biased samples. The measured Lorentzian spectrum of the R-fluctuations identifies their correlation time, which is shown to coincide with the thermal relaxation time determined by a combination of the electron-phonon relaxation and the diffusion in reservoirs. Our data is quantitatively consistent with the model of spontaneous temperature fluctuations, the Tfluctuations, with a variance given by the textbook thermodynamic expression. We discuss the experimental indication that the T -fluctuations contribute to the broadening of the transition, in spite of vanishing in the limit of infinite sample volume. Our observations highlight important caveats in the accepted physical picture of the resistive transition.