OBSERVATION OF VORTEX-GLASS FLUCTUATIONS ON YBCO CERAMICS AT ULTRALOWFIELDS NEAR T-C

Using the thermal scanning susceptometry, completed with the thermal p ulse method, a series of hills has been observed on the susceptibility (real component) curves of Y-based ceramic superconductors. Supposing that these are the manifestations of cooperative vortices (supercondu cting domains promoted by the granular and defect structure of the mat erial), the medium coherence length (xi(VG) similar to 2 mm), medium c orrelation time (tau similar to 51.2 s), a dynamic (z similar to 5.7) and a static (nu similar to 1.1) scaling exponents have been determine d. Because the determined exponents of the instability are very simila r to those predicted theoretically and verified experimentally for vor tex-glass structures, we suggest that the observed fluctuations are pr oduced by vortex-glass-like domains.