Effect of Strip Width on Low-Field Peak Effect of Critical Current Density in Bi2Sr2CaCu2O8+δ Superconducting Strips

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 Bi2Sr2CaCu2O8+delta (Bi-2212) whiskers with surface barriers by electrical transport measurements. J(c) shows a low-field peak effects; J(c) increases with the magnetic field ill 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-peak with w implies that the low-field peak effect observed in the Bi-2212 whiskers is associated with the effect of the finite w on dilute vortices.