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Tretyakov, Ivan; Ryabchun, Sergey; Finkel, Matvey; Maslennikova, Anna; Kaurova, Natalia; Lobastova, Anastasia; Voronov, Boris; Gol'tsman, Gregory |
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Low noise and wide bandwidth of NbN hot-electron bolometer mixers |
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2011 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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98 |
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033507 (1 to 3) |
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NbN HEB mixer |
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We report a record double sideband noise temperature of 600 K (5hν/kB) offered by a NbN hot-electron bolometer receiver at 2.5 THz. Allowing for standing wave effects, this value was found to be constant in the intermediate frequency range 1–7 GHz, which indicates that the mixer has an unprecedentedly large noise bandwidth in excess of 7 GHz. The insight into this is provided by gain bandwidth measurements performed at the superconducting transition. They show that the dependence of the bandwidth on the mixer length follows the model for an HEB mixer with diffusion and phonon cooling of the hot electrons. |
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RPLAB @ gujma @ |
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638 |
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Baek, Burm; Lita, Adriana E.; Verma, Varun; Nam, Sae Woo |
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Superconducting a-WxSi1–x nanowire single-photon detector with saturated internal quantum efficiency from visible to 1850 nm |
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Journal Article |
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2011 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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98 |
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25 |
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3 |
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SNSPD |
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We have developed a single-photon detector based on superconducting amorphous tungsten–silicon alloy (a-WxSi1–x) nanowire. Our device made from a uniform a-WxSi1–x nanowire covers a practical detection area (16 μm×16 μm) and shows high sensitivity featuring a plateau of the internal quantum efficiencies, i.e., efficiencies of generating an electrical pulse per absorbed photon, over a broad wavelength and bias range. This material system for superconducting nanowire detector technology could overcome the limitations of the prevalent nanowire devices based on NbN and lead to more practical, ideal single-photon detectors having high efficiency, low noise, and high count rates. |
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RPLAB @ gujma @ |
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665 |
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Marsili, Francesco; Najafi, Faraz; Herder, Charles; Berggren, Karl K. |
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Electrothermal simulation of superconducting nanowire avalanche photodetectors |
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2011 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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98 |
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9 |
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3 |
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SNAP |
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We developed an electrothermal model of NbN superconducting nanowire avalanche photodetectors (SNAPs) on sapphire substrates. SNAPs are single-photon detectors consisting of the parallel connection of N superconducting nanowires. We extrapolated the physical constants of the model from experimental data and we simulated the time evolution of the device resistance, temperature and current by solving two coupled electrical and thermal differential equations describing the nanowires. The predictions of the model were in good quantitative agreement with the experimental results. |
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658 |
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Bulaevskii, L. N.; Graf, M. J.; Batista, C. D.; Kogan, V. G. |
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Vortex-induced dissipation in narrow current-biased thin-film superconducting strips |
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2011 |
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Phys. Rev. B |
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Phys. Rev. B |
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83 |
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14 |
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9 |
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A vortex crossing a thin-film superconducting strip from one edge to the other, perpendicular to the bias current, is the dominant mechanism of dissipation for films of thickness d on the order of the coherence length ξ and of width w much narrower than the Pearl length Λâ‰<ab>wâ‰<ab>ξ. At high bias currents I*<I<Ic the heat released by the crossing of a single vortex suffices to create a belt-like normal-state region across the strip, resulting in a detectable voltage pulse. Here Ic is the critical current at which the energy barrier vanishes for a single vortex crossing. The belt forms along the vortex path and causes a transition of the entire strip into the normal state. We estimate I* to be roughly Ic/3. Furthermore, we argue that such “hot†vortex crossings are the origin of dark counts in photon detectors, which operate in the regime of metastable superconductivity at currents between I* and Ic. We estimate the rate of vortex crossings and compare it with recent experimental data for dark counts. For currents below I*, that is, in the stable superconducting but resistive regime, we estimate the amplitude and duration of voltage pulses induced by a single vortex crossing. |
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RPLAB @ gujma @ |
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688 |
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Расулова, Г.К.; Брунков, П.Н.; Пентин, И.В.; Ковалюк, В.В.; Горшков, К.Н.; Казаков, А.Ю.; Иванов, С.Ю.; Егоров, А.Ю.; Саксеев, Д.А.; Конников, С.Г. |
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Взаимная синхронизация двух связанных генераторов автоколебаний на основе сверхрешеток GaAs/AlGaAs |
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2011 |
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Журнал технической физики |
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ЖТФ |
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81 |
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6 |
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80-86 |
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Проведено исследование взаимодействия генераторов автоколебаний на основе 30-периодной слабосвязанной сверхрешетки GaAs/AlGaAs. Воздействие одного генератора автоколебаний на другой осуществлялось при заданном постоянном смещении в отсутствие в одном из них генерации автономных колебаний. Показано, что вынужденные колебания в захватывающем генераторе возникают из-за возбуждения колебаний в системе связанных осцилляторов, образующих границу электрополевого домена на частоте одной из высших гармоник вынуждающего колебания. |
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