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 Bi2-xPbxSr2Ca2Cu3Oy 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.