Kardakova, A., Shishkin, A., Semenov, A., Goltsman, G. N., Ryabchun, S., Klapwijk, T. M., et al. (2016). Relaxation of the resistive superconducting state in boron-doped diamond films. Phys. Rev. B, 93(6), 064506.
Abstract: We report a study of the relaxation time of the restoration of the resistive superconducting state in single crystalline boron-doped diamond using amplitude-modulated absorption of (sub-)THz radiation (AMAR). The films grown on an insulating diamond substrate have a low carrier density of about 2.5×1021cm−3 and a critical temperature of about 2K. By changing the modulation frequency we find a high-frequency rolloff which we associate with the characteristic time of energy relaxation between the electron and the phonon systems or the relaxation time for nonequilibrium superconductivity. Our main result is that the electron-phonon scattering time varies clearly as T−2, over the accessible temperature range of 1.7 to 2.2 K. In addition, we find, upon approaching the critical temperature Tc, evidence for an increasing relaxation time on both sides of Tc.
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Sidorova, M. V., Kozorezov, A. G., Semenov, A. V., Korneeva, Y. P., Mikhailov, M. Y., Devizenko, A. Y., et al. (2018). Nonbolometric bottleneck in electron-phonon relaxation in ultrathin WSi films. Phys. Rev. B, 97(18), 184512 (1 to 13).
Abstract: We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique, we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide. We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in τe−ph∼140–190 ps at TC=3.4K, supporting the results of earlier measurements by independent techniques.
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Sidorova, M., Semenov, A., Hübers, H. - W., Kuzmin, A., Doerner, S., Ilin, K., et al. (2018). Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux. Phys. Rev. B, 98(13), 134504 (1 to 14).
Abstract: We studied the effects of the external magnetic field and photon flux on timing jitter in photon detection by straight superconducting NbN nanowires. At two wavelengths 800 and 1560 nm, statistical distribution in the appearance times of photon counts exhibits Gaussian shape at small times and an exponential tail at large times. The characteristic exponential time is larger for photons with smaller energy and increases with external magnetic field while variations in the Gaussian part of the distribution are less pronounced. Increasing photon flux drives the nanowire from the discrete quantum detection regime to the uniform bolometric regime that averages out fluctuations of the total number of nonequilibrium electrons created by the photon and drastically reduces jitter. The difference between standard deviations of Gaussian parts of distributions for these two regimes provides the measure for the strength of electron-number fluctuations; it increases with the photon energy. We show that the two-dimensional hot-spot detection model explains qualitatively the effect of magnetic field.
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Gershenzon, E. M., Gol’tsman, G. N., Gousev, Y. P., Elant’ev, A. I., & Semenov, A. D. (1991). Electromagnetic radiation mixer based on electron heating in resistive state of superconductive Nb and YBaCuO films. IEEE Trans. Magn., 27(2), 1317–1320.
Abstract: A theory of an electron-heating mixer which makes it possible to calculate all the characteristics of the device is developed. It is shown that positive conversion gain is possible for such a mixer in the millimeter to near-infrared wavelength range. The dynamic range and the optimum heterodyne power can be selected from a very wide interval by varying the mixing element volume. Measurements made for Nb within the frequency range of 120-750 GHz confirm the theory. The conversion loss obtained at T=1.6 K and normalized to the element reaches 0.3 dB in the intermediate frequency band of 40 MHz; the possible noise temperature is 50 K. The estimation of noise temperature and output band for YBaCuO at T=77 yields 200 K and more than 10 GHz, respectively.
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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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