Coherent phase locking of high-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub y/ Josephson junctions

We measured I-V curves and noise characteristics of high-T/sub c/ YBa/sub 2/Cu/sub 3/O/sub y/ step-edge Josephson junctions and serial junction arrays under microwave irradiation. The junctions were fabricated on step-edge MgO[100] substrates with low step angles (/spl sim/30/spl deg/). The junction array shows the resistively shunted junction (RSJ) behavior for at least 50 junctions and reveals a coherent phase locking under microwave irradiation. The variation of I/sub c/ was 16% for a 150-junctions array distributed along the step-edge line of 1.5 mm in width. The voltage noise, S/sub v/, of the serial junction array scales as the number of junctions, N. The value of S/sub IR/, (S/sub IR/=|(/spl delta/I/sub c//I/sub c/)||(/spl delta/R/R)|), for a single and 50-junctions obtained from the fluctuation measurement is consistent with the result derived from I/sub c/R/sub n//spl prop/(J/sub c/)/sup q/, with q=0.5.