Superposition of decaying flux distributions: A memory effect from flux creep

A model is presented that considers the magnetic relaxation from thermally activated flux creep in a superconductor, after the application of two consecutive field steps separated by a waiting time ${\mathrm{t}}_{\mathrm{w}}$. The time evolution of the resulting superposition of flux distributions is expected to show a characteristic inflection point at a time ${\mathrm{t}}_{\mathrm{i}}^{\prime }$. The behavior is reminiscent of, but fundamentally different from, the memory effect of the superconducting-glass model. Measurements on ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ single crystals show the predicted temperature and field dependence of ${\mathrm{t}}_{\mathrm{i}}^{\prime }$.