Low frequency noise in superconducting Sn films at the transition temperature

We have measured the noise power spectrum of tin films evaporated on glass substrates biased at the transition temperature. The spectrum is close to 1/f between 0.1 and 1000 Hz. The noise is found to be correlated over a correlation length (D/πf)^1/2, where D is the diffusivity of tin film. We have also studied samples in which a thin layer of aluminum was predeposited before tin evaporation. The aluminum layer appears to greatly reduce the thermal boundary resistance between tin and the substrate. The amplitude of noise for such samples is greatly reduced below 10 Hz, where it is almost independent of frequency. These results are in accord with the thermal diffusion theory proposed by Clarke and Voss. They should have important implications on future construction of superconducting bolometers.