Observation of vortex-glass fluctuations on YBCO ceramics at ultralow fields near Tc

Abstract

Using the thermal scanning susceptometry, completed with the thermal pulse 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 (superconducting domains promoted by the granular and defect structure of the material), the medium coherence length (ξ VG ~ 2 mm), medium correlation time (τ ~ 51.2 s), a dynamic ( z ~ 5.7) and a static ( v ~ 1.1) scaling exponents have been determined. Because the determined exponents of the instability are very similar to those predicted theoretically and verified experimentally for vortex-glass structures, we suggest that the observed fluctuations are produced by vortex-glass-like domains.