Frequency-selective incoherent detection of terahertz radiation by high-Tc Josephson junctions

Abstract

The detector response of YBa2Cu3O7−x Josephson grain-boundary junctions to monochromatic radiation with the frequency f in the range from 60 GHz to 4 THz has been studied. Frequency-selective odd-symmetric resonances in the responses ΔI(V) of these junctions to radiation with different frequencies f have been observed near the voltages V=hf/2e in almost a decade of spectral range for any operating temperature in the range from 30 to 85 K. The spectral range of the selective detection has scaled with the IcRn product of the Josephson junction, reaching the range of 0.16–3.1 THz for a IcRn product of 1.5 mV. A resolving power δf/f of around 10−3 has been demonstrated in the selective detection by Josephson junctions. The high-frequency falldown of the amplitude of the selective response has been found to be proportional to exp[−P/P0], where P=(hf/2e)2/Rn is the power dissipated in the junction at the resonance and P0 is a characteristic power level. The values of P0 for our junctions were around 20 μW at 34 K and 2 μW at 78 K.

Grain boundaries in high-Tcsuperconductors

“…Subsequently, (sub)millimeter-wave detection with artificial grain boundaries was attained, employing YBa 2 Cu 3 O 7Ϫ␦ step-edge junctions on MgO substrates (Fukumoto et al, 1993) and using series arrays of bicrys- tal and step-edge junctions (Huang et al, 1997). Utilizing YBa 2 Cu 3 O 7Ϫ␦ grain-boundary junctions on NdGaO 3 bicrystal substrates, Divin et al (1999Divin et al ( , 2000Divin et al ( , 2001 demonstrated Hilbert transform spectrometers operating from 60 GHz to 2.25 THz. In a similar configuration, shown in Fig.…”

Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K

“…The derived Hilbert spectrum is plotted and it shows a peak at 570 GHz. This frequency-selective response can be used for spectroscopic study [15,17,18]. The voltage response obtained near zero voltage is used for the imaging (video detection) described in this work.…”

“…These figures show that our step-edge Josephson junctions are suitable for detecting a very wide frequency range from microwave to THz waves. Studies [14,15] have shown that the maximum sensitivity of Josephson junctions occurs at a signal frequency f s ∼2f c . Detector 2 is tailored to give a maximum response at ∼600 GHz when cooled to 77 K, and ∼200 GHz when cooled to ∼81 K. On the contrary, detector 1 has a maximum frequency response of ∼600 GHz at ∼40 K and ∼200 GHz at ∼60 K. Temperatures below 77 K cannot be achieved via liquid nitrogen cooling.…”

“…Superconducting detectors are broadband in that they respond to RF frequencies from microwave to far-infrared. Broadband detection from GHz to ∼4 THz has been demonstrated using the HTS bicrystal Josephson junction detectors [14][15][16][17][18]. Josephson junctions, operating as video detectors, have a faster response than normal bolometers.…”

Quantization of the superconducting energy gap in an intense microwave field

“…As a result the superconducting gap assumes quantized values equal to multiples of the quarter of the photon energy. The quantization is a manifestation of nonequilibrium tuning (suppression or enhancement) of superconductivity by the microwave field.Superconducting Josephson junctions are used as sensitive detectors of microwave (MW) and terahertz signals [1][2][3][4][5][6][7][8]. Application of MW radiation leads to appearance of Shapiro and photon assisted tunneling (PAT) steps in the current-voltage (I-V ) characteristics of a junction at eV = ±nhf /2 and eV = ±2∆ ± nhf , respectively.…”