HALF-INTEGRAL CONSTANT VOLTAGE STEPS IN HIGH-TC GRAIN-BOUNDARY JUNCTIONS

A novel effect from microwave radiation near 9.3 GHz applied to high-T(c) YBa2Cu3O7-delta single grain boundary junctions was observed. In addition to the usual Shapiro steps resulting from the ac Josephson effect, constant voltage steps with voltages halfway between the voltages of the Shapiro steps were present. The widths of these ''half-integral'' steps were measured as a function of microwave power, and the influence of a magnetic field was investigated. From previous results on high-T(c) grain boundary junctions and a comparison of the results presented here with single- and multiple-junction effects in low-T(c) materials, we conclude that the half-integral steps are likely to be a result of grain boundaries being composed of multiple junctions in parallel.