SIMULATION OF ELECTRICAL NOISE SPECTRUM IN BULK POLYCRYSTALLINE YBCO SUPERCONDUCTORS IN A MAGNETIC-FIELD

A study of the electrical noise spectrum in YBCO high-ir, polycrystall ine superconductors in a magnetic field, under different conditions of current density and temperature, is reported. In the range of very sm all values of the frequencies and for temperatures that are different from those corresponding to the noise peak, the frequency dependence o f the resistance noise is no longer 1/f, but it becomes 1/f(3/2). This effect is more evident when the magnetic field is increased. Starting from a two-parameter stochastic model reproducing the assembly of the individual noise sources, the change in the shape of the noise power spectrum is explained as due to the large difference between the mean lifetimes of the occupied and unoccupied states of the flux pinning ce nters. (C) 1998 Elsevier Science B.V.