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 $j_c).\mathrm{}$ 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 ${\mathrm{Bi}}_{2-x}{\mathrm{Pb}}_x{\mathrm{Sr}}_2{\mathrm{Ca}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ 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.