600 GHZ RESONANT MODE IN A PARALLEL ARRAY OF JOSEPHSON TUNNEL-JUNCTIONS CONNECTED BY SUPERCONDUCTING MICROSTRIP LINES

The high frequency properties of the one-dimensional transmission line consisting of a parallel array of resistively shunted Josephson tunne l junctions have been studied in the limit of relatively low damping w here this nonlinear system exhibits new and interesting phenomena. Her e we report on experimental and numerical investigations of a resonant step observed at a voltage corresponding to 600 GHz in the dc current -voltage characteristic of a parallel array of 20 identical small NbAl 2O3Nb Josephson junctions interconnected by short sections of supercon ducting microstrip line. The junctions are mutually phase locked due t o collective interaction with the line sections excited close to the h alf wavelength resonance. The phase locking range can be adjusted by m eans of an external dc magnetic field and the step size varies periodi cally with the magnetic field. The largest step corresponds to a super conducting phase difference of pi between neighboring junctions.