Scaling spontaneous fluctuations in high-Tc superconductor films☆

Abstract Spontaneous conductivity fluctuations in high- T c superconducting films on sapphire and SrTiO 3 substrates have been measured through the superconducting transition. It is found that the normalized spectrum for the sapphire film is two orders of magnitude larger than for the SrTiO 3 film, due to a stronger disorder. At sufficiently low temperatures, the normalized spectrum scales with the conductivity, which proves the existence of a percolation superconducting network.