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Baeva, E. M., Sidorova, M. V., Korneev, A. A., Smirnov, K. V., Divochy, A. V., Morozov, P. V., et al. (2018). Thermal properties of NbN single-photon detectors. Phys. Rev. Applied, 10(6), 064063 (1 to 8).
Abstract: We investigate thermal properties of a NbN single-photon detector capable of unit internal detection efficiency. Using an independent calibration of the coupling losses, we determine the absolute optical power absorbed by the NbN film and, via resistive superconductor thermometry, the temperature dependence of the thermal resistance Z(T) of the NbN film. In principle, this approach permits simultaneous measurement of the electron-phonon and phonon-escape contributions to the energy relaxation, which in our case is ambiguous because of the similar temperature dependencies. We analyze Z(T) with a two-temperature model and impose an upper bound on the ratio of electron and phonon heat capacities in NbN, which is surprisingly close to a recent theoretical lower bound for the same quantity in similar devices.
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Zolotov, P. I., Divochiy, A. V., Vakhtomin, Y. B., Lubenchenko, A. V., Morozov, P. V., Shurkaeva, I. V., et al. (2018). Influence of sputtering parameters on the main characteristics of ultra-thin vanadium nitride films. In J. Phys.: Conf. Ser. (Vol. 1124, 051030).
Abstract: We researched the relation between deposition and ultra-thin VN films parameters. To conduct the experimental study we varied substrate temperature, Ar and N2 partial pressures and deposition rate. The study allowed us to obtain the films with close to the bulk values transition temperatures and implement such samples in order to fabricate superconducting single-photon detectors.
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Romanov, N. R., Zolotov, P. I., Vakhtomin, Y. B., Divochiy, A. V., & Smirnov, K. V. (2018). Electron diffusivity measurements of VN superconducting single-photon detectors. In J. Phys.: Conf. Ser. (Vol. 1124, 051032).
Abstract: The research of ultrathin vanadium nitride (VN) films as a promising candidate for superconducting single-photon detectors (SSPD) is presented. The electron diffusivity measurements are performed for such devices. Devices that were fabricated out from 9.9 nm films had diffusivity coefficient of 0.41 cm2/s and from 5.4 nm – 0.54 cm2/s. Obtained values are similar to other typical SSPD materials. The diffusivity that increases along with decreasing of the film thickness is expected to allow fabrication of the devices with improved characteristics. Fabricated VN SSPDs showed prominent single-photon response in the range 0.9-1.55 µm.
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Zolotov, P., Divochiy, A., Vakhtomin, Y., Moshkova, M., Morozov, P., Seleznev, V., et al. (2018). Photon-number-resolving SSPDs with system detection efficiency over 50% at telecom range. In Proc. AIP Conf. (Vol. 1936, 020019).
Abstract: We used technology of making high-efficiency superconducting single-photon detectors as a basis for improvement of photon-number-resolving devices. By adding optical cavity and using an improved NbN superconducting film, we enhanced previously reported system detection efficiency at telecom range for such detectors. Our results show that implementation of optical cavity helps to develop four-section device with quantum efficiency over 50% at 1.55 µm. Performed experimental studies of detecting multi-photon optical pulses showed irregularities over defining multi-photon through single-photon quantum efficiency.
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Smirnov, K., Divochiy, A., Vakhtomin, Y., Morozov, P., Zolotov, P., Antipov, A., et al. (2018). NbN single-photon detectors with saturated dependence of quantum efficiency. Supercond. Sci. Technol., 31(3), 035011 (1 to 8).
Abstract: The possibility of creating NbN superconducting single-photon detectors with saturated dependence of quantum efficiency (QE) versus normalized bias current was investigated. It was shown that the saturation increases for the detectors based on finer films with a lower value of Rs300/Rs20. The decreasing of Rs300/Rs20 was related to the increasing influence of quantum corrections to conductivity of superconductors and, in turn, to the decrease of the electron diffusion coefficient. The best samples have a constant value of system QE 94% at Ib/Ic ~ 0.8 and wavelength 1310 nm.
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Симонов, Н. О., Флоря, И. Н., Корнеева, Ю. П., Корнеев, А. А., & Гольцман, Г. Н. (2018). Однофотонный отклик в тонких сверхпроводящих MoNx пленках. In Сборн. науч. труд. VII международн. конф. по фотонике и информац. опт. (pp. 408–409).
Abstract: Продемонстрирован однофотонный отклик, при токе близком к критическому, в MoNx сверхпроводящих полосках шириной 70-104 нм. MoNx детекторы, имеющие коэффициент диффузии D≈0.32 см2/с и время электрон-фононного взаимодействия ηe-ph≈300 пс, достигают квантовой эффективности QE≈20% на длине волны λ=1550 нм. Возможность реализации однофотонного детектора в данном материале, подтверждает существующую теорию вихревого механизма возникновения фотоотклика в узких сверхпроводящих полосках.
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Золотов, Ф. И., Дивочий, А. В., Вахтомин, Ю. Б., Пентин, И. В., Морозов, П. В., Селезнев, В. А., et al. (2018). Применение тонких сверхпроводниковых пленок нитрида ванадия для изготовления счетчиков одиночных ИК-фотонов. In Сборн. науч. труд. VII международн. конф. по фотонике и информац. опт. (pp. 60–61).
Abstract: Получены первые результаты по применению сверхпроводниковых пленок нитрида ванадия (VN) для детекторов одиночных фотонов ИК-диапазона. Изучение сверхпроводниковых однофотонных детекторов (SSPD), изготовленных на основе ультратонких (~5 нм) пленок VN, показало возможность создания устройств с близкой к насыщению зависимостью квантовой эффективности от тока смещения детекторов в телекоммуникационном диапазоне длин волн. Также нами были исследованы кинетическая индуктивность изготовленных структур с различной длиной сверхпроводниковой полоски и времена релаксации электронов в тонких сверхпроводниковых пленках VN.
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Korneeva, Y. P., Vodolazov, D. Y., Semenov, A. V., Florya, I. N., Simonov, N., Baeva, E., et al. (2018). Optical single-photon detection in micrometer-scale NbN bridges. Phys. Rev. Applied, 9(6), 064037 (1 to 13).
Abstract: We demonstrate experimentally that single-photon detection can be achieved in micrometer-wide NbN bridges, with widths ranging from 0.53 to 5.15 μm and for photon wavelengths of 408 to 1550 nm. The microbridges are biased with a dc current close to the experimental critical current, which is estimated to be about 50% of the theoretically expected depairing current. These results offer an alternative to the standard superconducting single-photon detectors, based on nanometer-scale nanowires implemented in a long meandering structure. The results are consistent with improved theoretical modeling based on the theory of nonequilibrium superconductivity, including the vortex-assisted mechanism of initial dissipation.
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Korneev, A., Korneeva, Y., Florya, I., Semenov, A., & Goltsman, G. (2018). Photon switching statistics in multistrip superconducting single-photon detectors. IEEE Trans. Appl. Supercond., 28(7), 1–4.
Abstract: We study photon count statistics in superconducting single-photon detectors consisting of up to 70 narrow superconducting strips connected in parallel. Using interarrival time analysis, we demonstrate that our samples are operated in the “arm-trigger” regime and require up to seven subsequently absorbed photons to form a resistive state in the whole sample. We also performed numerical simulation of the light and dark count rates versus detector bias current, which are in good agreement with the experimental results.
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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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