Role of Geometry on the Color of Flux Noise in dc SQUIDs

摘要

We examine the behavior of low frequency flux noise measured in ten Nb-NbOx-PbIn dc SQUIDs in the temperature range 1 K to 20 mK. As previously reported, the flux noise power spectrum Sphi(f) typically scales with frequency as A/f(exp alpha). Remarkably, the excess noise power A at 1 Hz increases as the temperature is decreased below about 0.7 K, saturating to a value around (10 mu phi (subo))2/hz below about 0.2 K. Here we report on the dependence of both the magnitude A and the slope alpha on the size and linewidth of the SQUID loops. In particular, at the lowest temperatures we find that alpha declines to values as low as 0.5 in the smallest devices, while alpha is in the range 0.9 1 for the largest devices.