Strong evidence for vortex-glass-collective-pinning theory in YBa2Cu3O7 superconductors

Magnetization studies on a melt textured-growth sample of YBa2Cu3O7-δ have tested several theoretical models to see which of them best describes the relaxation of supercurrents in this high-Tc superconductor. By combining conventional flux-creep experiments with measurements of magnetization versus magnetic-field sweep rate, we are able to detect the decay of magnetization in both its intermediate and very early stages, thereby expanding the observational window up to 5-6 decades of time. Among four recent models tested, only vortex-glass-collective-pinning theory consistently describes both stages. The resulting values for the characteristic exponent μ strongly depend on temperature and magnetic field. Values for the effective hopping time for vortices, teff, are ∼0.1 s.