Beck, M., Klammer, M., Lang, S., Leiderer, P., Kabanov, V. V., Gol’tsman, G. N., et al. (2011). Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy. arXiv:1102.5616v2 [cond-mat.supr-con].
Abstract: Using time-domain Terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor 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 bare quasiparticle recombination rate, the Cooper pair-breaking rate and the electron-phonon coupling constant, \lambda = 1.1 +/- 0.1, which is in excellent agreement with theoretical estimates.
|
Семенов, А. В., Девятов, И. А., Рябчун, С. А., Масленников, С. Н., Масленникова, А. С., Ларионов, П. А., et al. (2011). Поглощение терагерцового электромагнитного излучения в “грязной” сверхпроводниковой пленке при произвольном виде спектральных функций. Ж. Радиоэлектрон., 10, 7.
Abstract: A problem of absorption of high-frequency electromagnetic field in dirty superconductor is treated within Keldysh technic. Expression for the source term in the kinetic equation for quasiparticle distribution function is derived. The result is significant for deriving a consistent microscopic theory of superconducting detectors for terahertz frequency range, perspective detectors on kinetic inductance of current-biased superconducting strip and on Josephson inductance of tunnel.
В технике Келдыша рассмотрена задача о поглощении мощности высокочастотного электромагнитного поля в сверхпроводнике, удовлетворяющем условию грязного предела. Получено выражение для члена источника в кинетическом уравнении для функции распределения квазичастиц, справедливое при произвольном виде спектральных функций. Этот результат имеет значение для развития последовательной микроскопической теории сверхпроводниковых детекторов излучения терагерцового диапазона, в частности, перспективных детекторов на кинетической индуктивности смещённой током сверхпроводниковой полоски и джозефсоновской индуктивности туннельного контакта.
|
Tretyakov, I., Ryabchun, S., Finkel, M., Maslennikov, S., Maslennikova, A., Kaurova, N., et al. (2011). Ultrawide noise bandwidth of NbN hot-electron bolometer mixers with in situ gold contacts. IEEE Trans. Appl. Supercond., 21(3), 620–623.
Abstract: We report a noise bandwidth of 7 GHz in the new generation of NbN hot-electron bolometer (HEB) mixers that are being developed for the space observatory Millimetron. The HEB receiver driven by a 2.5-THz local oscillator offered a noise temperature of 600 K in a 50-MHz final detection bandwidth. As the filter center frequency was swept this value remained nearly constant up to the cutoff frequency of the cryogenic amplifier at 7 GHz. We believe that such a low value of the noise temperature is due to reduced radio frequency (RF) loss at the interface between the superconducting film and the gold contacts. We have also performed gain bandwidth measurements at the superconducting transition on HEB mixers with various lengths and found them to be in excellent agreement with the results of the analytical and numerical models developed for the HEB mixer with both diffusion and phonon cooling of hot electrons.
|
Lobanov, Y., Tong, E., Blundell, R., Hedden, A., Voronov, B., & Gol'tsman, G. (2011). Large-signal frequency response of an HEB mixer: from 300 MHz to terahertz. IEEE Trans. Appl. Supercond., 21(3), 628–631.
Abstract: We present a study of the large signal frequency response of an HEB mixer over a wide frequency range. In our experiments, we have subjected the HEB mixer to incident electromagnetic radiation from 0.3 GHz to 1 THz. The mixer element is an NbN film deposited on crystalline quartz. The mixer chip is mounted in a waveguide cavity, coupled to free space with a diagonal horn. At microwave frequencies, electromagnetic radiation is applied through the coaxial bias port of the mixer block. At higher frequencies the input signal passes via the diagonal horn feed. At each frequency, the incident power is varied and a family of I-V curves is recorded. From the curves we identify 3 distinct regimes of operation of the mixer separated by the phonon relaxation frequency and the superconducting energy gap frequency observed at about 3 GHz and 660 GHz respectively. In this paper, we will present observed curves and discuss the results of our experiment.
|
Ожегов, Р. В., Окунев, О. В., & Гольцман, Г. Н. (2009). Флуктуационная чувствительность сверхпроводящего болометрического смесителя на эффекте разогрева электронного газа. Радиотехника, (3), 120–124.
Abstract: Interest in research in the terahertz range is driven by a great number of various applications, where terahertz instruments may play a leading role. To name just a few, such applications include study of the cosmic microwave background radiation and the distribution of the dark matter, medicine, navigation, fire alarm, security systems and environmental monitoring. The paper discusses the possibility of using a receiver based on the hot-electron effect in superconducting films as an imaging system. We present the results of the noise equivalent temperature difference (NETD) measurements performed with a hot-electron bolometer mixer made from a thin superconducting film. The receiver with a noise temperature of ~ 3800 K at a local oscillator frequency of 300 GHz a bandwidth of 500 MHz and an integration time of 1 s has offered an NETD of 0.5 K. We have also developed a technique that enabled us to reduce the contribution of the mixer gain fluctuations to the overall system instability. As of this writing, the above value of the NETD is the lowest value offered for this type of receiver, which indicates the possibility to use such receivers in real-time imaging systems. The technique offered in the paper for achieving the limiting value of the NETD offers an alternative to the phase-locking scheme.
Представены результаты измерения флуктуационной чувствительности (NETD – noise equivalent temperature difference) болометрического смесителя на эффекте разогрева электронного газа в тонких сверхпроводящих пленках. Получено предельное значение NETD, равное 0,5 К, при шумовой температуре приемника 3800 К, ширине полосы преобразования 500 МГц, постоянной времени 1 с и частоте гетеродина 300 ГГц. Разработана методика достижения предельной флуктуационной чувствительности, позволяющая избежать влияния нестабильности коэффициента преобразования смесителя.
|
