Characterization of 40 GHz and 762 GHz sources with superconducting Josephson cantilevers in a THz microscope

Josephson cantilevers, based on high temperature superconducting Josephson junctions, are versatile detectors for the measurement of frequency and power of microwave and terahertz radiation. A Josephson cantilever consists of at least one Josephson junction, which is equipped with an antenna structure for better coupling. The Josephson junctions, made from the high-temperature superconductor YBa2Cu3O7, are deployed on LaAIO3or MgO bicrystal substrates. Four feedlines are used to carry out four-terminal sensing. The THz microscope was developed, to allow three dimensional measurements [1]. In this measurement setup, the Josephson cantilever is mounted on a 15 × 15 × 15 mm3positioning system inside a vacuum chamber. The Josephson cantilever is cooled by a cryocooler that allows operating temperatures down to 30 K. A triangular current is injected into the junction and the current-voltage characteristic is recorded at each spatial point. The frequency and the power of the external radiation can be determined from the recorded data by evaluating the occurring Shapiro steps using Hilbert spectroscopy [2]. When the Josephson cantilever is irradiated with more than one frequency at a time, it behaves as a frequency mixer, due to its nonlinear current-voltage characteristic. In this work, we investigated the mixing of 40 GHz and 762 GHz signals with the THz microscope.