Effect of Strip Width on Low-Field Peak Effect of Critical Current Density in Bi_2Sr_2CaCu_2O_8+δ Superconducting Strips

摘要

We investigate the dependence of the critical current density J_c along the crystal a-axis on the magnetic field along the c-axis at high temperatures below the superconducting transition temperature in individual Bi_2Sr_2CaCu_2O_8+δ (Bi-2212) whiskers with surface barriers by electrical transport measure_ments. J_c shows a low-field peak effect; J. increases with the magnetic field in a low-field region and shows a peak at the threshold field H_peak below 100 Oe. A comparison of the low-field peak effects in whiskers of different widths shows that H_peak depends on the sample width (i.e., the lateral dimension); the lateral axis is perpendicular to the magnetic field and the direction of current flow. A decrease in the sample width w shifts H_peak toward a higher field. This systematic variation in H_pedk with ω implies that the low-field peak effect observed in the Bi-2212 whiskers is associated with the effect of the finite ω on dilute vortices.