PHASE-LOCKING IN 2-JUNCTION SYSTEMS OF HIGH-TEMPERATURE SUPERCONDUCTOR NORMAL METAL-SUPERCONDUCTOR JUNCTIONS

Mutual phase locking between two high-temperature step-edge supercondu cting-normal metal-superconducting junctions has been investigated usi ng a two-junction circuit with a nonsuperconducting feedback path. The strength of the phase-locked state has been characterized as a functi on of locking frequency and temperature. Results are presented for a p lanar circuit as well as for a multilayer circuit incorporating a supe rconducting ground plane. The observed behavior was significantly enha nced for the circuit over a ground plane. Characterization of the phas e locked state at 4 K yielded locking strengths as large as \I-L\/(I) over bar(c)=9%, and maximum locking frequencies to 1.06 THz. The magni tude of the locking strength decreased rapidly with increasing tempera ture with complete loss of coherence occurring at temperatures greater than 35K.