Correlation studies on flux flow noise of polycrystalline niobium and vanadium foils

Using two movable contact pairs, cross-correlation functions of flux flow noise from polycrystalline niobium and vanadium foils have been measured. The results are compared with theoretical predictions derived from Clem's theory for the voltage associated with vortex motion across superconductors. Two cases are considered: (a) shot noise of randomly distributed flux entities moving with constant velocity and (b) noise due to locally generated random fluctuations of vortex velocity. There is strong evidence that the observed flux flow noise is produced by local flux flow fluctuations at pinning sites.Supported by Deutsche Forschungsgemeinschaft.