We have investigated both DC and AC Josephson effects of the YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin film step-edge junctions; single step-edge junction on LaAlO/sub 3/ substrate with the step angle about 50-60/spl deg/ and biepitaxial double step-edge junction made on MgO substrate with a CeO/sub 2/ seed layer. The Josephson self-radiation was directly detected using the total power radiometer receiver systems with receiving frequencies of K band (21-23 GHz) and millimeter-wave (46-48 GHz and 71-73 GHz) range, respectively. For single step-edge junctions, the Josephson self-radiation peaks exhibited at the voltages corresponding to the basic Josephson voltage-frequency relation. The maximum first-harmonic self-radiation power at receiving frequency f/sub REC/=72 GHz and Josephson linewidth were P(I)=2.0/spl times/10/sup -3/W and /spl Delta/f=3.62 GHz at 4.2 K, respectively. For microwave irradiation, the harmonic Shapiro steps and additional half integer steps with their quasi-periodic variation satisfying the Josephson equation V=(n/m)(hf/2e) were clearly observed. For double step-edge junctions, we also observed the steps corresponding to the two junction boundaries on the two steep steps. These behaviors described with different current-phase relations corresponding to the crystal orientation relationship between the two junction boundaries.>
Potential for single-photon mm-wave detection by antenna-coupled Pb–graphene–Pb Josephson junctions (JJ) is evaluated. We consider the high-speed “video” (non-thermal) detection based on Shapiro steps induced by antenna-sourced AC currents across the JJ. Electrodynamic simulation informs the bowtie antenna design and estimates the AC current through JJ. Standard JJ models are used to estimate the corresponding AC voltage and the downward shift of the maximum zero-voltage DC current Ic, where a sharp transition occurs in the DC voltage–current curve. Calculated voltage responsivity for current biasing near Ic is compared with Johnson noise to estimate a lower limit for noise equivalent photon flux. Estimated responsivity is 0.9 MV/W M V / W at 300 GHz GHz , and the lower bound on the noise equivalent power is 0.11 fW/ Hz Hz giving a 2 photons per microsecond. Graphical abstract