Hysteresis Effects and Flux Pinning in a Macroscopic Cylindrical Hole Drilled in Superconducting Bi-Sr-Ca-Cu-O

A. Kiliç ； H. Yetiş ； K. Kiliç ； A. Altinkok ； M. Olutaş ； H. Sözeri

《Chinese Journal of Physics》 50卷4期 (2012/08) Pp. 670-698

並列摘要

We report experimental results on the flux dynamics in a polycrystalline superconducting Bi1:7Pb0:3Sr2Ca2Cu3Ox (BSCCO) sample with a macroscopic cylindrical hole (CH) drilled through it. Current-voltage (I-V) curve measurements were carried out as a function of current sweep rates (dI/dt) of the transport current at zero magnetic field (H = 0) and under an external magnetic field (H≠0) at a temperature just below Tc on the BSCCO sample before and after drilling the CH, in order to investigate the effects of the CH on the transport properties. The hysteresis effects in the I-V curves of the sample without the CH disappear for all given dI/dt values in the presence of an external magnetic field, and the I-V curves exhibit a nearly linear behavior, which can be taken as an indication of flux flow effects. However, for the same magnetic field, temperature, and dI/dt values, the hysteresis effects in the I-V curves of the sample with the CH are still observed. This interesting observation suggests that the CH acts as an attractive macroscopic pinning center for flux lines and inhibits the flux motion. In the I-V curves of the sample with the CH, a downward curvature is observed in the low current region when Imax has a relatively high value, as the transport current is increased with high values of dI/dt. The hysteresis effects in the I-V curves are considered as a kind of superheated state of coherent motion of the flux lines which try to keep their integrity. In this procedure, at low values of Imax, the voltage response of the sample with a CH increases beginning from zero, which indicates the presence of an obstruction to the penetration of transport current due to both the surface effects and the CH. How the current sweep rate controls the degree of current-induced organization of the flux lines in the sample is also discussed.