AC JOSEPHSON EFFECT IN YBA2CU3O7-DELTA BICRYSTAL GRAIN-BOUNDARY JUNCTIONS

The ac Josephson effect in YBa2Cu3O7-delta bicrystal grain boundary ju nctions was studied in the temperature range from 4K to 90K. Junctions with widths from 0.2 to 50 mum were made on SrTiO3 bicrystal substrat es by laser ablation and e-beam lithography. The linewidth of the Jose phson oscillations is derived from the shape of the dc voltage respons e to low-intensity, f = 70 GHz radiation at voltages V congruent-to (h /2e) f, assuming the RSJ model. The effect of the size on the Josephso n behavior of this type of high-T(c) junctions was studied. Close to T (c) the linewidth of the Josephson oscillations was shown to be determ ined by thermal fluctuations.