History effect in inhomogeneous superconductors

Abstract

A model was proposed to account for a new 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 region (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−x Pb x Sr 2 Ca 2 Cu 3 O y tapes immersed in liquid nitrogen with and without magnetic fields. 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 is in agreement well with our numerical results.

Superconductivity and short-range order in metallic glassesFexNi1−xZr2

“…These two processes then result in clockwise hysteresis loops. Similar phenomena have been observed previously in granular superconductors 31,32,33 and inhomogeneous superconductors 29,30,34 . This model explains why we witness an increase in the width of hysteresis loops with increasing B sweep rate: for slower sweep rate the vortices have more time to penetrate into the strong-pinning grains or to diffuse into the weak-pinning regions upon increasing and decreasing the magnetic field before the measurement is taken.…”

“…Therefore, after we apply a certain field, and by the time we take the measurement, the vortex distribution has reached a more homogeneous configuration for slower sweep speeds and results in smaller hysteresis loops. A similar observation was made by Liu et al 29 and Xu et al 30 from numerical simulations and experimental measurements of flux creep in a superconductor with inhomogeneous pinning properties. In these cases however, the size of hysteresis loops was observed to increase with increasing driving current and driving force sweep rate, but the result is equivalent: changing the sweep rate amounts to changing the observation time window.…”

“…In the literature, simulations of V-I characteristics in superconductors with inhomogeneous pinning potentials show clockwise hysteresis loops 29,30 . Such hysteresis loops result from dynamical effects and interplay between vortex trapping in the strong and weak pinning regions.…”

“…As such, the size (or width) of the hysteresis loops is seen to depend on the sweep rate of the external variable with respect to which the loop is observed; in Refs. 29 and 30 , this is the driving current and driving force. As is the case in our B field-induced hysteresis loops, the size of the loops increases in these Refs.…”

“…As is the case in our B field-induced hysteresis loops, the size of the loops increases in these Refs. 29,30 for faster driving force sweep speeds.…”