High temperature superconducting Josephson junction terahertz harmonic mixer system

We show a Josephosn junction terahertz harmonic mixer system, in which the high temperature superconducting (HTS) Josephson junction is set up on a cold figure in the small pulse-tube cryocooler working at the bath temperature of 60 K. We improved the experiments by several methods, such as choosing MgO as the substrate, assembling a well-designed planar logarithm periodic antenna to the junction, and using the quasi-optical system with one silicon hyper-hemispherical lens and two off-axis parabolic mirrors on the optical path. During the measurements, the sample was illuminated by a 623 GHz microwave source, and the Shapiro steps in the IV curves of YBCO/MgO bi-crystal junction were observed. The ultimate harmonic order is 24.