Terahertz spectral analysis by ac Josephson effect in high-T/sub c/ bicrystal junctions

Wideband frequency metrology using high temperature superconducting Josephson junctions

“…On the other hand, compared with the published results operated at high temperatures [7], [8], here we have only one junction operating at only one temperature; yet from 76 GHz to 3.1 THz, which is around 50 : 1 frequency band, we have observed responses. This is mainly due to the fact that the junction has a suitable product, and is operated at low temperature.…”

“…When a weak monochromatic signal at frequency is applied to a junction, the -curve will shift from the dc one to . According to the RSJ model, at any voltage the current response is an odd-symmetric resonance around the voltage [7], [8]. For junctions with the same product, the maximum amplitude at is inversely proportional to the Josephson oscillation line-width , which is proportional to and the operation temperature , and frequency-independent at high frequency range.…”

“…The time constant of 300 ms has been selected to get a channel bandwidth of about 1 Hz. A personal computer is used to collect the experimental data and calculate the current response , as well as the spectrum using Hilbert-transform program [7], [8], which is a standard one in the MATLAB mathematical function library. All measurements are carried out in a radio-frequency (RF) shielding room, but no -metal or other magnetic shielding materials are used here.…”

“…In this connection, responses up to several THz were demonstrated using low-Tc Nb point contacts at 4 K [6], where the highest possible frequency was much higher than its gap frequency or characteristic frequency. In recent years, HTS Josephson junctions have been developed, and are shown to meet the requirements similar to those of Although the responses up to 4.25 THz have been obtained using HTS junctions with product of 1.5 mV and of 7 at 35 K [7], and product of 1.8 mV and of 2 at 20 K [8], some of the response problems still remain to be solved. In this paper we are going to show that the highest operating frequency and the maximum value of normalized response are proportional to the product of the junction.…”

Millimeter-Wave Sensitivity of YBCO Grain Boundary Josephson Junctions Coupled With Coplanar Waveguide-Fed Slot Dipole Antennas

“…Approaching the performance of sensitive detectors in this spectrum range, highJosephson junction are of interest because of their high sensitivity over the spectrum range and a benefit of the self mixing detection capable of spectrometry [2], [3]. We have demonstrated the response up to 4.25 THz using (YBCO) grain boundary Josephson junctions directly placed on the feed points of planar log-periodic antennas (LPDA).…”