Transport Properties of YBa2Cu3O7 Josephson Junctions at THz Frequencies

For application in a THz scanning microscope we employ Josephson junctions from the high-temperature superconductor YBa2Cu3O7 on a so called Josephson cantilever to measure the local microwave power density in the half space above a device under test. The Josephson junctions are prepared by pulsed laser deposition and argon ion etching on symmetric LaAlO3 30∘-bicrystal substrates. To achieve high sensitivity at THz frequencies, a high IcRn product is required. Therefore, the Josephson junctions are operated on a cryo-cooler at low temperature of about 36 K under vacuum conditions. The high frequency characterization is accomplished in the near field of a Gaussian far infrared gas laser beam optically pumped by a CO2 laser. We use strong emission lines of formic acid at 762 GHz and 1.2 THz for the investigations and report on the electrical transport properties determined from the current-voltage characteristics of the Josephson junctions under influence of external magnetic field and far-infrared radiation.