Nonlinear dynamics in a superconductor glass

The authors present an investigation of the dynamical properties of a high-T/sub c/ granular superconductor (a sintered pellet of YBCO) carried out in the temperature range characteristic of the critical transition undergone by the disordered network of Josephson junctions connecting the superconductor grains. An AC susceptibility probe was used to study the influence that the variations of the intensity and the frequency of the AC probing field, as well as that of a superimposed DC field, have on the shape of the susceptibility curves. A Fourier analysis of the susceptibility signals has revealed the pronounced nonlinear character of the intergranular dynamics which is remarkably similar to that of spin glasses.>