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Karasik, B. S., Gol'tsman, G. N., Voronov, B. M., Svechnikov, S. I., Gershenzon, E. M., Ekstrom, H., et al. (1995). Hot electron quasioptical NbN superconducting mixer. IEEE Trans. Appl. Supercond., 5(2), 2232–2235.
Abstract: Hot electron superconductor mixer devices made of thin NbN films on SiO/sub 2/-Si/sub 3/N/sub 4/-Si membrane have been fabricated for 300-350 GHz operation. The device consists of 5-10 parallel strips each 5 /spl mu/m long by 1 /spl mu/m wide which are coupled to a tapered slot-line antenna. The I-V characteristics and position of optimum bias point were studied in the temperature range 4.5-8 K. The performance of the mixer at higher temperatures is closer to that predicted by theory for uniform electron heating. The intermediate frequency bandwidth versus bias has also been investigated. At the operating temperature 4.2 K a bandwidth as wide as 0.8 GHz has been measured for a mixer made of 6 nm thick film. The bandwidth tends to increase with operating temperature. The performance of the NbN mixer is expected to be better for higher frequencies where the absorption of radiation should be more uniform.
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Sergeev, A., Semenov, A., Trifonov, V., Karasik, B., Gol'tsman, G., & Gershenzon, E. (1994). Heat transfer in YBaCuO thin film/sapphire substrate system. J. Supercond., 7(2), 341–344.
Abstract: The thermal boundary resistance at the YBaCuO thin film/Al2O3 substrate interface was investigated. The transparency for thermal phonons incident on the interface as well as for phonons moving from the substrate was determined. We have measured a transient voltage response of current-biased films to continuously modulated radiation. The observed knee in the modulation frequency dependence of the response reflects the crossover from the diffusion regime to the contact resistance regime of the heat transfer across the interface. The values of transparency were independently deduced both from the phonon escape time and from the time of phonon return to the film which were identified with peculiarities in the frequency dependence. The results are much more consistent with the acoustic mismatch theory than the diffuse mismatch model.
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Nebosis, R. S., Heusinger, M. A., Semenov, A. D., Lang, P. T., Schatz, W., Steinke, R., et al. (1993). Ultrafast photoresponse of an YBa2Cu3O7-δ film to far-infrared radiation pulses. Opt. Lett., 18(2), 96–97.
Abstract: We report the observation of an ultrafast photoresponse of a high-T(c), film to far-infrared radiation pulses. The response of a sample, consisting of a current-carrying structured YBa(2)Cu(3)O(7-delta) film cooled to liquid-nitrogen temperature, was studied by use of ultrashort laser pulses from an optically pumped far-infrared laser in the frequency range from 0.7 to 7 THz. We found that the response time was limited by the time resolution, 120 ps, of our electronic registration equipment.
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Gershenzon, E. M., Gol’tsman, G. N., Semenov, A. D., & Sergeev, A. V. (1991). Mechanism of picosecond response of granular YBaCuO films to electromagnetic radiation. IEEE Trans. Magn., 27(2), 1321–1324.
Abstract: Ultrafast mechanisms of radiation detection in granular YBaCuO films are studied in the wide wavelength range from millimeter waves to near infrared. With an increase in radiation frequency, the Josephson detection at the grain-boundary weak links is replaced by electron heating into the grains. This change occurs in the submillimeter wavelength range. The electron-phonon relaxation time tau /sub eph/ is determined from direct measurements, quasi-stationary electron heating measurements, and the frequency dependence of the current at which maximum voltage shift is observed. The temperature dependence of tau /sub eph/ at T<or=40 K was found to be tau /sub eph/ approximately T/sup -1/. The results show that detectors with a response time of a few picoseconds at nitrogen temperature are attainable.
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Gershenzon, E. M., Gol’tsman, G. N., Dzardanov, A. L., & Zorin, M. A. (1991). Ultrafast superconductive switch. IEEE Trans. Magn., 27(2), 2844–2846.
Abstract: The transition from superconductive to resistive state caused by infrared radiation and bias current pulses was investigated in order to minimize switching time tau and driving power W. Experimental results for Nb microstrips confirm the correctness of calculations based on the model of electron heating. For Nb switches, tau measured directly is 0.3-0.8 ns for radiation pulses and 1-3 ns for bias current pulses at T=4.2 K, while for YBaCuO switches at T=77 K it is expected to be several picoseconds. For an YBaCuO sample with the dimensions of 5*2*0.15 mu m/sup 2/, W was 10 mW, and it can be further reduced to the order of several microwatts by decreasing the volume of the sample.
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