Schematic of measurement system and photos of the sample. The blow-up shows an enlarged fragment of the array of high-temperature superconductor Josephson junctions.
Distribution of electric field intensity in the quasioptical resonator including a horn antenna and a plane mirror. The standing wave was formed at some resonant frequencies which could be adjusted by the distance of the horn antenna and the plane mirror. The inset shows the uniform electric field distribution on the cross section of the antinodes.
(a) Measurements of the junction array located on the MgO substrate. The curve of the third subarray without irradiation (curve a); the curve of the third subarray under irradiation at 76.10 GHz (curve b); the curve of the fourth subarray without irradiation (curve c); the curve of the fourth subarray under irradiation at 76.10 GHz (curve d). The normalized Shapiro steps of different subarrays were exhibited in the inset. (b) Distribution of electric field intensity on the MgO substrate shows the nonuniform irradiation power for different subarrays along the grain boundary. The position of each subarray is marked by its order number.
Distribution of electric field intensity on the 0.5-mm-thick substrate shows a resonance mode around 77 GHz.
Measurements of the junction array located on the 0.3 mm thick YSZ substrate with and without the attached thin substrate of LaAlO. With the attached substrate, curve a shows the characteristic of the total series array including eight subarrays without irradiation; curve b: the characteristic under irradiation at 77.10 GHz; curve c: the detected emission power while sweeping the bias current through the array. Without the attached substrate, there was only a maximum of five biased subarrays from which the Shapiro steps could be observed. The curves of these five subarrays without and with irradiation at 68.98 GHz are shown by curve d and curve e, respectively. The detected emission from the total array is showed by curve f.
The simulation model for irradiation: the junction array (black color) with half-wavelength antennas was located on the YSZ substrate (blue color). The additional thin substrate of LaAlO (orange color) was attached on the backside of the YSZ substrate. The junction was modeled by the lumped element in the CST microwave studio software, by means of which the induced voltage of each junction could be observed. (a) Three-dimensional view; (b) enlarged view.
Induced voltage spectra of 50 junctions inside the total array from 65 to 80 GHz without and with the attached substrate of LaAlO are shown separately in (a) and (b).
Significant measurement records of the Shapiro steps and self-emission of the Josephson junction arrays of 536 junctions located on the YSZ substrates with different thicknesses and attached thin substrates.
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