Resistive noise and heat effects in the granular oxide superconductor BaPb0.75Bi0.25O3

Abstract

For weak applied magnetic fields the frequency spectrum of the voltage fluctuations was measured for Josephson ceramic samples of BaPb0.75Bi0.25O3 with Tc approximately=10 K. The measurements were carried out in the resistive state. It is shown that the spectral density Sv(f) in the frequency region 20 Hz<f<500 Hz is described by a function f- alpha , where alpha approximately=1 for small H and alpha approximately=2-2.5 for H>or approximately=10 Oe. For currents I>or approximately=0.8 mA through the sample, oscillations with a fundamental frequency f1<or=100 Hz and two harmonics f2 and f3 were observed. For larger currents these oscillations die out and instead several new oscillations appear. Flicker noise with alpha approximately=1 is due to the existence of the superconducting glass state. The transition to a alpha >or approximately=2 and the emergence of the oscillations apparently occur owing to heating effects.