An elementary model of nonexponential decay. II. Applications to measurements in superconductors and in a spin glass

Abstract

For part I see ibid, vol.6, p.2893 (1994). The 'elementary decay model' (EDM), which allows an interpretation of most nonexponential decay functions, is applied to representative published decay curves measured in superconductors and in a metallic spin glass. Features attributed previously to different regimes connected by crossover regions can be interpreted by monotonically changing parameters. For high-Tc superconductors I-V curves are also analysed with the adequately transformed EDM. In addition, the excess conductivity in the paraconductive region above Tc is well modelled by an Arrhenius excitation, which also extends below Tc in multilayers of YBCO. Measurements previously interpreted by Ueff varies as J- mu can also be interpreted by the EDM, which is close to Ueff varies as -ln J evaluated by Blatter et al. (1990). The rapid drop in resistivity close to a transition into a vortex-glass state measured in the pV range by Gammel et al. (1991) in YBCO could also be fitted by the EDM. Further, the 'ageing' or 'memory' effect in a metallic spin glass is well interpreted by the EDM. In particular, the 'memory' effect is shown to be a consequence of plotting nonexponential decay data against the logarithm of a retarded time and is therefore not a unique indication for a spin glass.