Flux-flow noise in magnetically coupled superconductors observation of a 1/f spectrum

Earlier measurements of flux-flow noise spectra are discussed, and it is pointed out that this method has severe limitations as a means for studying the detailed nature of flux motion. It is also argued that the commonly used picture of flux-bundle movement is unsatisfactory from a physical point of view and should be replaced by a model in which flux motion is more coordinated and more dependent on properties of the flux-line lattice. An experiment to test this idea is described, involving the measurement of noise spectra in pairs of magnetically coupled superconducting films. The noise power spectra obtained follow a 1/f law, thus differing from spectra measured in bulk materials and so preventing any general interpretation of the results. However, it is thought that the behaviour observed is more consistent with the proposed pattern of flux motion than with the earlier flux-bundle picture.