Universality in the current decay and flux creep of Y-Ba-Cu-O high-temperature superconductors

Recent data on flux creep in a variety of Y-Ba-Cu-O superconductors show a temperature-independent plateau in the magnetization decay Sieq-d lnM(t)/d ln(t), with values clustered in the range S=0.020 0.035. This apparent universality in S, which appears at odds with conventional flux-creep theories, can be explained naturally if one assumes the existence of a truly superconducting ordered phase at low temperatures that has a strongly nonlinear (exponential) I-V characteristic. © 1990 The American Physical Society.