History effect in inhomogeneous superconductors

A model was proposed to account for a different kind of history effect in the transport measurement of a sample with inhomogeneous flux pinning coupled with flux creep. The inhomogeneity of flux pinning was described in terms of alternating weak pinning (lower j_c) and strong pinning regions (higher j_c). The flux creep was characterized by logarithmic barrier. Based on this model, we numerically observed the same clockwise V-I loops as reported in references. Moreover, we predicted behaviors of the V-I loop at different sweeping rates of applied current dI/dt and magnetic fields B_a, etc. Electric transport measurement was performed in Ag-sheathed Bi_2-xPb_xSr₂Ca₂Cu₃O_y tapes immersed in liquid nitrogen with and without magnetic fields. A V-I loop at certain dI/dt and B_a was observed. It is found that the area of the loop is more sensitive to dI/dt than to B_a, which agrees well with our numerical results.