Noise in high Tc superconductors

Very recently, significant progress has been achieved in the understanding of the excessive strength and behavior of the conductance noise in the conductor-superconductor transition region of high T_c superconductors. For the high temperature part of the conductor-superconductor transition region, the model incorporates number and mobility noises of charge carriers: while in the low temperature part of the transition, classical and novel percolation noise effects (including possible effects due to flux motion) determine the behavior of the measured noise. In present high-quality (in situ annealed) films, the novel percolation noise effect (“p-noise,” Phys. Rev. Lett., vol. 71, p. 2817, 1993) seems to be the most important. Some other important topics will also be briefly examined in this review: magnetic noise, noise in devices, and practical problems of measurements (e.g., comparison of the noise of different materials, temperature fluctuations)