ANOMALOUS 1/F2 LOW-FREQUENCY NOISE IN HIGH-TEMPERATURE SUPERCONDUCTORS

A theoretical analysis for the anomalous low frequency noise enhancement with frequency dependence 1/f2 which was recently measured in micropatterned YBaCuO thin films was carried out. A generalization of the random fluctuation model we developed earlier led to plausible activation energies and accounted simultaneously for the frequency, temperature, and magnetic field dependence of the noise spectral power. In this approach the defect density functional D(n) where n is the density of defects in a single plane was derived. In the flux flow regime, D(n) has the simple form D(n) = (delta/xi) (1/n1/2xi)delta-1 where xi is the superconducting coherence length in the Cu-O planes, and delta = U(o)/kT represents the pinning energy of a flux line normalized to its thermal energy. These results are clear indications that the enhancement of noise with 1/f2 frequency dependence is strongly related to the dynamics of motion of free vortices and the number fluctuation of bound vortices.