Series YBCO grain boundary Josephson junctions as a terahertz harmonic mixer

Josephson devices have demonstrated the capability to work as harmonic mixers at terahertz frequencies. Low temperature devices, in particular Nb-Nb point contacts have proven particularly successful. However, practical applications of these devices have been limited by the need of utilizing liquid helium. To overcome this limitation we have investigated the use of high-T-c devices. In this paper, we report mixings up to the 154th harmonic at zero-bias in a series of YBa2Cu3O7-delta (YBCO) grain boundary Josephson junctions. We have integrated a meander series of three bicrystal YBCO Josephson junctions with a log-periodic antenna. When properly operated, this configuration allows to reach a harmonic number much higher than what possible with a single junction. This shows that the mixing performance benefits from the synchronous operation which also results in an improvement of dynamic range. We believe that the integration of a higher number of phase-locked junctions may further improve the mixer's performance. Future studies should investigate the effect of higher number of junctions on the mixer performances, as well as the effect of the meander length.