Classical and Josephson detection of terahertz radiation using YBa2Cu3O7-x [100]-tilt bicrystal junctions

Abstract

Detection of terahertz radiation using YBa2Cu3O7-x [100]-tilt bicrystal junctions with high IcRn- product up to 6 mV has been studied. Two types of the responses ΔV (V) have been observed. At low frequencies up to some frequency fl, the responses ΔV (V) were proportional to the second derivative of the V(I)-curve. At high frequencies f > fl, the responses ΔV (V) demonstrate odd-symmetric resonances at V = hf/2e. For low-resistance junctions, Josephson frequency-selective detection was found up to the frequency of 5.3 THz, which is above the frequency of the strongest optical mode (f0 = 4.6 THz) in YBa2Cu3O7-x. The frequency fl was found to increase with the resistance Rn and the IcRn-product of the junction. For high-resistance junctions with Rn = 23 Ω, classical detection was observed up to 0.4 THz range. The difference in detection mechanisms is attributed to a continuous type of spectra of Josephson oscillations at low voltages and to a discrete type of Josephson spectra at high voltages. Computer simulation of a Josephson detector has been carried out, considering intensive thermal fluctuations and a frequency-dependent impedance of the Josephson junction. It is shown that a classical detector, based on the [100]-tilt Josephson junctions with Rn = 100 Ohm at T = 40 K, might reach the values of noise equivalent power NEP < 2· 10−14 W/Hz½ at the frequencies up to 1.8 THz.