Wideband Detection Of Electromagnetic Signals By High-T-C Josephson Junctions With Comparable Josephson And Thermal Energies

Detection mechanisms in Josephson junctions with energies E-j comparable to thermal energies kT have been studied. The responses Delta V of YBa2Cu3O7-x bicrystal junctions to monochromatic radiation with frequencies f ranging from 94GHz to 3.1THz can be described in terms of classical rectification on a static nonlinear V-I curve at low frequencies and frequency modulation of the ac Josephson current at high frequencies, with an interplay between these mechanisms at intermediate frequencies. An electrical noise-equivalent power of (9 +/- 3) x10(-15)W/Hz(1/2), a responsivity of (3.4 +/- 0.5) x 10(5)V/W, and a dynamic power range of 5x10(4) have been demonstrated for the square-law classical detection of 94GHz radiation with the junctions at 50K. The effect of background radiation on the V-I curves of YBa2Cu3O7-x bicrystal junctions was found to have an optical noise-equivalent temperature of <= 30mK/Hz(1/2). The main contribution to the effect comes from the interplay between the classical and Josephson detection mechanisms. The spectral and power dependencies of the responses Delta V of Josephson junctions have been numerically simulated within the resistively shunted junction model at various values of kT/E-j, and the results are in acceptable agreement with the experimental data.