Investigation of the geometrical barrier in Bi-2212 using the magneto-optical technique

It has been found that the penetration of vortices into a weak pinning crys tal is governed by a geometrical barrier and they form a dome-shaped flux p rofile across the crystal. Using the powerful magneto-optical technique, we investigated this geometrical barrier in a high-purity Bi2Sr2CaCu2O8+x sin gle-crystal platelet Our results show that over the temperature range 20-70 K the dome-shaped profile is observed. Also, the influences of the edge sh ape and the roughness on the geometrical barrier are discussed.