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Beck, M., Leiderer, P., Kabanov, V. V., Gol'tsman, G., Helm, M., & Demsar, J. (2012). Energy-gap dynamics of a superconductor NbN studied by time-resolved terahertz spectroscopy. In INIS (Vol. 45, pp. 1–3).
Abstract: Using time-resolved terahertz (THz) spectroscopy we performed direct studies of the photoinduced suppression and recovery of the SC gap in a conventional SC NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the important microscopic constants: the Cooper pair-breaking rate via phonon absorption and the bare quasiparticle recombination rate. From the latter we were able to extract the dimensionless electron-phonon coupling constant, λ=1.1±0.1, in excellent agreement with theoretical estimates. The technique also allowed us to determine the absorbed energy required to suppress SC, which in NbN equals the thermodynamic condensation energy (in cuprates the two differ by an order of magnitude). Finally, we present the first studies of dynamics following resonant excitation with intense narrow band THz pulses tuned to above and below the superconducting gap. These suggest an additional process, particularly pronounced near Tc, that could be attributed to amplification of SC via effective quasiparticle cooling.
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Voronov, B. M., Gershenzon, E. M., Gol'tsman, G. N., Gubkina, T. O., & Semash, V. D. (1994). Superconductive properties of ultrathin NbN films on different substrates. Sverkhprovodimost': Fizika, Khimiya, Tekhnika, 7(6), 1097–1102.
Abstract: A study was made on dependence of surface resistance, critical temperature and width of superconducting transition on application temperature and thickness of NbN films, which varied within the range of 3-10 nm. Plates of sapphire, fused and monocrystalline quartz, MgO, as well as Si and silicon oxide were used as substrates. NbN films with 160 μθ·cm specific resistance and 16.5 K (Tc) critical temperature were obtained on sapphire substrates. Intensive growth of ΔTc was noted for films, applied on fused quartz, with increase of precipitation temperature. This is explained by occurrence of high tensile stresses in NbN films, caused by sufficient difference of thermal coefficients of expansion of NbN and quartz.
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Gousev, Y. P., Semenov, A. D., Gol'tsman, G. N., Sergeev, A. V., & Gershenzon, E. M. (1994). Electron-phonon interaction in disordered NbN films. Phys. B Condens. Mat., 194-196, 1355–1356.
Abstract: Electron-phonon interaction time has been investigated in disordered films of NbN. A temperatures below 5.5 K tau_eph ~ T -1"6 which is attributed to the renormalisation of phonon spectrum in thin films.
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Budyanskij, M. Y., Sejdman, L. A., Voronov, B. M., & Gubkina, T. O. (1992). Increase of reproducibility in production of superconducting thin films of niobium nitride. Sverkhprovodimost': Fizika, Khimiya, Tekhnika, 5(10), 1950–1954.
Abstract: Technique to control the composition of gas medium in the reactive magnetron discharge and the composition of the deposited films of niobium nitride using electrical parameters of discharge only, in particular, by δU = Up – Uar value at contant stabilized discharge current is described. Technique to select optimal condition for deposition of niobium nitride films when the films have composition meeting chemical formula, is suggested. Thin films of niobium nitride with up to 7 nm thickness and with rather high temperature of transition into superconducting state Tk > 10 K) and with low width of transition (δ < 0.6 K), are obtained. It is determined, that substrate material and dielectric sublayer do not affect. Tk value, while difference in coefficients of thermal expansion of substrate and of film affects δTk value.
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Корнеев, А. А., Окунев, О. В., Чулкова, Г. М., Смирнов, К. В., Милостная, И. И., Минаева, О. В., et al. (2015). Спонтанные и фотоиндуцированные резистивные состояния в узких сверхпроводящих NbN полосках. МПГУ.
Abstract: Монография посвящена актуальной проблеме современной фотоники: разработке высокочувствительных и быстродействующих сверхпроводниковых однофотонных детекторов на основе тонкой пленки NbN. В работе исследуются неравновесные процессы, протекающие в тонкой сверхпроводящей пленке после поглощения инфракрасного фотона и приводящие к возникновению резистивного состояния. На этих процессах основан механизм фотоотклика исследуемого в работе однофотонного детектора. В частности, исследуются зависимости квантовой эффективности и скорости темнового счета от геометрических параметров детектора: толщины пленки, ширины полоски, а также от величины транспортного тока детектора. Монография предназначена для студентов старших курсов, аспирантов и начинающих исследователей, работающих в области сверхпроводниковой наноэлектроники и радиофизики.
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