Strong evidence for vortex-glass–collective-pinning theory in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ superconductors

Magnetization studies on a melt textured-growth sample of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ have tested several theoretical models to see which of them best describes the relaxation of supercurrents in this high-${\mathit{T}}_{\mathit{c}}$ 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, ${\mathit{t}}_{\mathit{e}\mathit{f}\mathit{f}}$, are ∼0.1 s.