Critical currents of small Bi2Sr2CaCu2O8+x intrinsic Josephson junction stacks in external magnetic fields

We present a study of the critical currents of small sized intrinsic Josephson junction stacks in external magnetic fields applied parallel to the CuO2 layers. The stacks consisting of 5-12 junctions were realized as mesa structures patterned on top of Bi2Sr2CaCu2O8+x single crystals. Lateral mesa dimensions ranged from 10x10 to 0.8x0.8 mu m(2). For the largest structures a complex magnetic field dependence of the critical currents was found. With decreasing mesa dimensions the critical currents systematically approached a Fraunhofer-type magnetic field dependence, Measurements agree well with the results of numerical calculations using coupled sine-Gordon equations.