Sidorova, M., Semenov, A. D., Hübers, H. - W., Ilin, K., Siegel, M., Charaev, I., et al. (2020). Electron energy relaxation in disordered superconducting NbN films. Phys. Rev. B, 102(5), 054501 (1 to 15).
Abstract: We report on the inelastic-scattering rate of electrons on phonons and relaxation of electron energy studied by means of magnetoconductance, and photoresponse, respectively, in a series of strongly disordered superconducting NbN films. The studied films with thicknesses in the range from 3 to 33 nm are characterized by different Ioffe-Regel parameters but an almost constant product qTl (qT is the wave vector of thermal phonons and l is the elastic mean free path of electrons). In the temperature range 14–30 K, the electron-phonon scattering rates obey temperature dependencies close to the power law 1/τe−ph∼Tn with the exponents n≈3.2–3.8. We found that in this temperature range τe−ph and n of studied films vary weakly with the thickness and square resistance. At 10 K electron-phonon scattering times are in the range 11.9–17.5 ps. The data extracted from magnetoconductance measurements were used to describe the experimental photoresponse with the two-temperature model. For thick films, the photoresponse is reasonably well described without fitting parameters, however, for thinner films, the fit requires a smaller heat capacity of phonons. We attribute this finding to the reduced density of phonon states in thin films at low temperatures. We also show that the estimated Debye temperature in the studied NbN films is noticeably smaller than in bulk material.
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Gershenzon, E. M., Gershenzon, M. E., Goltsman, G. N., Lulkin, A., Semenov, A. D., & Sergeev, A. V. (1990). Electron-phonon interaction in ultrathin Nb films. Sov. Phys. JETP, 70(3), 505–511.
Abstract: A study was made of the heating of electrons in normal resistive states of superconducting thin Nb films. The directly determined relaxation time of the resistance of a sample and the rise of the electron temperature were used to find the electron-phonon interaction time rep,, The dependence of rep, on the mean free path of electrons re,, a 1-'demonstrated, in agreement with the theoretical predictions, that the contribution of the inelastic scattering of electrons by impurities to the energy relaxation process decreased at low temperatures and the observed temperature dependence rep, a T 2 was due to a modification of the phonon spectrum in thin fllms.
1. Much new information on the electron-phonon interaction time?;,, in thin films of normal metals and superconductors has been published recently. This information has been obtained mainly as a result of two types of measurement. One includes experiments on weak electron localization investigated by the method of quantum interference corrections to the conductivity of disordered conductors, which can be used to find the relaxation time T, of the phase of the electron wave function. In the absence of the scattering of electrons by paramagnetic impurities the relaxation time T, is associated with the most effective process of energy relaxation: T;= TL+ rep;, where T,, is the electronelectron relaxation time. At low temperatures, when the dependence T; a T is exhibited by thin disordered films, the dominant channel is that of the electron-electron relaxation and there is a lower limit to the temperature range in which rep, can be investigated.
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Sidorova, M., Semenov, A., Korneev, A., Chulkova, G., Korneeva, Y., Mikhailov, M., et al. (2018). Electron-phonon relaxation time in ultrathin tungsten silicon film. arXiv:1607.07321v1 [physics.ins-det].
Abstract: Using amplitude-modulated absorption of sub-THz radiation (AMAR) method, we studied electron-phonon relaxation in thin disordered films of tungsten silicide. We found a response time ~ 800 ps at critical temperature Tc = 3.4 K, which scales as minus 3 in the temperature range from 1.8 to 3.4 K. We discuss mechanisms, which can result in a strong phonon bottle-neck effect in a few nanometers thick film and yield a substantial difference between the measured time, characterizing response at modulation frequency, and the inelastic electron-phonon relaxation time. We estimate the electron-phonon relaxation time to be in the range ~ 100-200 ps at 3.4 K.
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Kardakova, A. I., Coumou, P. C. J. J., Finkel, M. I., Morozov, D. V., An, P. P., Goltsman, G. N., et al. (2015). Electron–phonon energy relaxation time in thin strongly disordered titanium nitride films. IEEE Trans. Appl. Supercond., 25(3), 1–4.
Abstract: We have measured the energy relaxation times from the electron bath to the phonon bath in strongly disordered TiN films grown by atomic layer deposition. The measured values of τ eph vary from 12 to 91 ns. Over a temperature range from 3.4 to 1.7 K, they follow T -3 temperature dependence, which are consistent with values of τ eph reported previously for sputtered TiN films. For the most disordered film, with an effective elastic mean free path of 0.35 nm, we find a faster relaxation and a stronger temperature dependence, which may be an additional indication of the influence of strong disorder on a superconductor.
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Florya, I. N., Korneeva, Y. P., Sidorova, M. V., Golikov, A. D., Gaiduchenko, I. A., Fedorov, G. E., et al. (2015). Energy relaxtation and hot spot formation in superconducting single photon detectors SSPDs. In EPJ Web of Conferences (Vol. 103, 10004 (1 to 2)).
Abstract: We have studied the mechanism of energy relaxation and resistive state formation after absorption of a single photon for different wavelengths and materials of single photon detectors. Our results are in good agreement with the hot spot model.
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Voevodin, E. I., Gershenzon, E. M., Goltsman, G. N., & Ptitsina, N. G. (1989). Energy-spectrum of shallow acceptors in Ge deformed strongly by a uniaxial pressure. Sov. Phys. and Technics of Semiconductors, 23(8), 843–846.
Abstract: Проведены исследования спектров фототермической ионизации мелких акцепторов (В, Аl) в Ge, предельно сжатом вдоль кристаллографической оси [100]. Из данных измерений с учетом теории построен энергетический спектр примесей. Показано, что энергии большого числа уровней четных и нечетных состояний хорошо соответствуют расчету, выполненному для примесей в анизотропном полупроводнике с параметром анизотропии γ=m∗⊥/m∗∥>1.
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Gershenzon, E., Goltsman, G., Elantev, A., & Kagane, M. (1978). Energy-spectrum of small donors and acceptors in germanium and effect of magnetic-field on it. In Izv. Akad. Nauk SSSR, Seriya Fizicheskaya (Vol. 42, pp. 1142–1148).
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Simonov, N. O., Korneeva, Y. P., Korneev, A. A., & Goltsman, G. N. (2020). Enhance of the superconducting properties of the NbN/Au bilayer bridges. In J. Phys.: Conf. Ser. (Vol. 1695, 012132 (1 to 4)).
Abstract: We experimentally demonstrate strong temperature dependence of the critical current of the superconducting 600-nm-wide and 5-μm-long bridge made of NbN/Au bilayer. The result is achieved due to the proximity effect realized between the highly disordered superconducting NbN layer and low resistive normal-metal Au layer.
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An, P., Kovalyuk, V., Golikov, A., Zubkova, E., Ferrari, S., Korneev, A., et al. (2018). Experimental optimisation of O-ring resonator Q-factor for on-chip spontaneous four wave mixing. In J. Phys.: Conf. Ser. (Vol. 1124, 051047).
Abstract: In this paper we experimentally studied the influence of geometrical parameters of the planar O-ring resonators on its Q-factor and losses. We systematically changed the gap between the bus waveguide and the ring, as well as the width of the ring. We found the highest Q = 5×105 for gap 2.0 μm and the ring width 2 μm. This work is important for further on-chip SFWM applications since the generation rate of the biphoton field strongly depends on the quality factor as Q3
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Neroev, V. V., Iomdina, E. N., Khandzhyan, A. T., Khodzhabekyan, N. V., Sengaeva, M. D., Ivanova, A. V., et al. (2021). Experimental study of the effect of corneal hydration and its biomechanical properties on the results of photorefractive keratectomy. Vestn. Oftalmol., 137(3), 68–75.
Abstract: Water content in the cornea may affect the outcome of its excimer laser ablation, especially in presbyopic patients with myopic refraction. This hypothesis can be tested by scanning the cornea in the terahertz (THz) range to determine its hydration level.
Purpose: To study the effect of hydration of the cornea determined by non-contact THz scanning and its biomechanical parameters on the results of photorefractive keratectomy (PRK) in an experiment.
Material and methods: PRK was performed using the Nidek EC-5000 QUEST excimer laser on 8 rabbit eyes. Corneal hydration was evaluated by determining the reflection coefficient (RC) in the THz electromagnetic radiation range before PRK, after 3-5 days, and after 1, 2, 3, and 4 months. Clinical examination included autorefractometry, assessment of corneal thickness and other anatomical and optical parameters of the anterior eye segment (Galilei G6, Ziemer Ophthalmic Systems AG 6.0.2, Switzerland), measurement of corneal hysteresis (CH) and corneal resistance factor (CRF) using the Ocular Response Analyzer (ORA; Reichert, USA), as well as tear production (Schirmer test).
Results: The initial water content in the cornea has a significant effect on the thickness of the removed layer, i.e. on the PRK effect, with correlation coefficient of Rs= -0.976 (p<0.01). The correlation between CH and the ablation depth is less pronounced (Rs=0.643), and CRF had no correlation with it (Rs= -0.089). Biomechanical indicators of the cornea depend on its hydration: changes in CH and CRF after excimer laser ablation qualitatively coincide with changes in RC, the correlation coefficient between RC and the initial value of CH is R= -0.619 (moderate negative correlation).
Conclusion: THz scanning is an effective non-contact technology for monitoring corneal hydration level. The mismatch of the hypoeffect of keratorefractive excimer laser intervention planned for patients with presbyopia with the actual outcome can be caused by individual decrease in the initial water content in the cornea.
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Polyakova, M. I., Florya, I. N., Semenov, A. V., Korneev, A. A., & Goltsman, G. N. (2019). Extracting hot-spot correlation length from SNSPD tomography data. In J. Phys.: Conf. Ser. (Vol. 1410, 012166 (1 to 4)).
Abstract: We present data of quantum detector tomography for the samples specifically optimized for this problem. Using this method, we take results of hot-spot correlation length of 17 ± 2 nm.
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Ryabchun, S. A., Tretyakov, I. V., Finkel, M. I., Maslennikov, S. N., Kaurova, N. S., Seleznev, V. A., et al. (2008). Fabrication and characterisation of NbN HEB mixers with in situ gold contacts. In Proc. 19th Int. Symp. Space Terahertz Technol. (pp. 62–67). Groningen, Netherlands.
Abstract: We present our recent results of the fabrication and testing of NbN hot-electron bolometer mixers with in situ gold contacts. An intermediate frequency bandwidth of about 6 GHz has been measured for the mixers made of a 3.5-nm NbN film on a plane Si substrate with in situ gold contacts, compared to 3.5 GHz for devices made of the same film with ex situ gold contacts. The increase in the intermediate frequency bandwidth is attributed to additional diffusion cooling through the improved contacts, which is further supported by the its dependence on the bridge length: intermediate frequency bandwidths of 3.5 GHz and 6 GHz have been measured for devices with lengths of 0.35 μm and 0.16 μm respectively at a local oscillator frequency of 300 GHz near the superconducting transition. At a local oscillator frequency of 2.5 THz the receiver has offered a DSB noise temperature of 950 K. When compared to the previous result of 1300 K obtained at the same local oscillator frequency for devices fabricated with an ex situ route, such a low value of the noise temperature may also be attributed to the improved gold contacts.
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Titova, N. A., Baeva, E. M., Kardakova, A. I., & Goltsman, G. N. (2020). Fabrication of NbN/SiNx:H/SiO2 membrane structures for study of heat conduction at low temperatures. In J. Phys.: Conf. Ser. (Vol. 1695, 012190).
Abstract: Here we report on the development of NbN/SiNx:H/SiO2-membrane structures for investigation of the thermal transport at low temperatures. Thin NbN films are known to be in the regime of a strong electron-phonon coupling, and one can assume that the phononic and electronic baths in the NbN are in local equilibrium. In such case, the cooling of the NbN-based devices strongly depends on acoustic matching to the substrate and substrate thermal characteristics. For the insulating membrane much thicker than the NbN film, our preliminary results demonstrate that the membrane serves as an additional channel for the thermal relaxation of the NbN sample. That implies a negligible role of thermal boundary resistance of the NbN-SiNx:H interface in comparison with the internal thermal resistance of the insulating membrane.
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Seliverstov, S., Maslennikov, S., Ryabchun, S., Finkel, M., Klapwijk, T. M., Kaurova, N., et al. (2015). Fast and sensitive terahertz direct detector based on superconducting antenna-coupled hot electron bolometer. IEEE Trans. Appl. Supercond., 25(3), 2300304.
Abstract: We characterize superconducting antenna-coupled hot-electron bolometers for direct detection of terahertz radiation operating at a temperature of 9.0 K. The estimated value of responsivity obtained from lumped-element theory is strongly different from the measured one. A numerical calculation of the detector responsivity is developed, using the Euler method, applied to the system of heat balance equations written in recurrent form. This distributed element model takes into account the effect of nonuniform heating of the detector along its length and provides results that are in better agreement with the experiment. At a signal frequency of 2.5 THz, the measured value of the optical detector noise equivalent power is 2.0 × 10-13 W · Hz-0.5. The value of the bolometer time constant is 35 ps. The corresponding energy resolution is about 3 aJ. This detector has a sensitivity similar to that of the state-of-the-art sub-millimeter detectors operating at accessible cryogenic temperatures, but with a response time several orders of magnitude shorter.
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Gershenzon, E. M., Gershenson, M. E., Goltsman, G. N., Karasik, B. S., Lyulkin, A. M., & Semenov, A. D. (1989). Fast-response superconducting electron bolometer. Pisma v Zhurnal Tekhnicheskoi Fiziki, 15(3), 88–92.
Abstract: The general design, operation, and performance characteristics of fast-response electronic bolometers using a thin superconducting Nb film on a leucosapphire substrate are briefly reviewed. The volt-watt sensitivity of the bolometrs is 2,000-200,000 V/W, the operating temperature is 1.6 K, and the time constant is 4-4.5 ns.
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