Series YBCO grain boundary Josephson junctions as a terahertz harmonic mixer

Abstract

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 YBa 2 Cu 3 O 7−δ (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.

A broadband detector based on series YBCO grain boundary Josephson junctions

“…The fabrication of bicrystal junctions requires the use of a meander-type microstrip since, for the formation of a weak link, it is necessary for the superconducting film to cross the grain boundary. In the first case implemented in [ 3 ], the length of the meander is minimal ( Figure 3a ). To minimize this length, the two parts of the antenna are displaced vertically relative to each other.…”

“…High-temperature superconducting (HTSC) Josephson junctions (JJs) have great potential as promising materials for creating high-frequency devices, such as microwave generators [ 1 – 2 ], sensitive detectors or mixers [ 3 – 4 ], and voltage standards [ 5 – 7 ]. Recent impressive developments in this area make this possible [ 8 – 10 ].…”

“…One possible way to solve this problem is to replace a single JJ by a chain or an array of JJs combined with planar coupling structures. The task of developing and calculating such systems is quite complex and faced with obscures such as unresolved Shapiro steps [ 18 – 19 ] and parasitic resonances [ 3 ].…”

“…To effectively match JJs with open space and the incoming external signal, dipole antennas for each junction can be used [ 20 ], but the development of a broadband detector requires the use of spiral [ 4 ], log-periodic [ 3 ], or other types of broadband antennas. In this case JJs are integrated into the single receiving system.…”

Nonmonotonous temperature dependence of Shapiro steps in YBCO grain boundary junctions

“…Such abilities raise not only fundamental interest in HTSC JJs but also an active search for ways to practically use such JJs. In recent years, the limiting characteristics of detectors and mixers based on HTSC JJs [6][7][8][9][10][11] have been actively studied. Josephson junctions have also been used for various spectroscopic applications [12].…”