2020 |
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Sidorova M, Semenov AD, Hübers H-W, Ilin K, Siegel M, Charaev I, et al. Electron energy relaxation in disordered superconducting NbN films. Phys Rev B. 2020;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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2018 |
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Sidorova M, Semenov A, Hübers H-W, Kuzmin A, Doerner S, Ilin K, et al. Timing jitter in photon detection by straight superconducting nanowires: Effect of magnetic field and photon flux. Phys Rev B. 2018;98(13):134504 (1 to 14).
Abstract: We studied the effects of the external magnetic field and photon flux on timing jitter in photon detection by straight superconducting NbN nanowires. At two wavelengths 800 and 1560 nm, statistical distribution in the appearance times of photon counts exhibits Gaussian shape at small times and an exponential tail at large times. The characteristic exponential time is larger for photons with smaller energy and increases with external magnetic field while variations in the Gaussian part of the distribution are less pronounced. Increasing photon flux drives the nanowire from the discrete quantum detection regime to the uniform bolometric regime that averages out fluctuations of the total number of nonequilibrium electrons created by the photon and drastically reduces jitter. The difference between standard deviations of Gaussian parts of distributions for these two regimes provides the measure for the strength of electron-number fluctuations; it increases with the photon energy. We show that the two-dimensional hot-spot detection model explains qualitatively the effect of magnetic field.
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2014 |
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Lusche R, Semenov A, Ilin K, Siegel M, Korneeva Y, Trifonov A, et al. Effect of the wire width on the intrinsic detection efficiency of superconducting-nanowire single-photon detectors. J Appl Phys. 2014;116(4):043906 (1 to 9).
Abstract: A thorough spectral study of the intrinsic single-photon detection efficiency in superconducting TaN and NbN nanowires with different widths has been performed. The experiment shows that the cut-off of the intrinsic detection efficiency at near-infrared wavelengths is most likely controlled by the local suppression of the barrier for vortex nucleation around the absorption site. Beyond the cut-off quasi-particle diffusion in combination with spontaneous, thermally activated vortex crossing explains the detection process. For both materials, the reciprocal cut-off wavelength scales linearly with the wire width where the scaling factor agrees with the hot-spot detection model.
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2013 |
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Lusche R, Semenov A, Il'in K, Korneeva Y, Trifonov A, Korneev A, et al. Effect of the wire width and magnetic field on the intrinsic detection efficiency of superconducting nanowire single-photon detectors. IEEE Trans Appl Supercond. 2013;23(3):2200205.
Abstract: We present thorough measurements of the intrinsic detection efficiency in the wavelength range from 350 to 2500 nm for meander-type TaN and NbN superconducting nanowire single-photon detectors with different widths of the nanowire. The width varied from 70 nm to 130 nm. The open-beam configuration allowed us to accurately normalize measured spectra and to extract the intrinsic detection efficiency. For detectors from both materials the intrinsic detection efficiency at short wavelengths amounts at 100% and gradually decreases at wavelengths larger than the specific cut-off wavelengths, which decreases with the width of the nanowire. Furthermore, we show that applying weak magnetic fields perpendicular to the meander plane decreases the smallest detectable photon flux.
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2012 |
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Henrich D, Dorner S, Hofherr M, Il'in K, Semenov A, Heintze E, et al. Broadening of hot-spot response spectrum of superconducting NbN nanowire single-photon detector with reduced nitrogen content. J Appl Phys. 2012;112.
Abstract: The spectral detection efficiency and the dark count rate of superconducting nanowire
single-photon detectors (SNSPD) have been studied systematically on detectors made from thin
NbN films with different chemical compositions. Reduction of the nitrogen content in the 4 nm
thick NbN films results in a decrease of the dark count rates more than two orders of magnitude
and in a red shift of the cut-off wavelength of the hot-spot SNSPD response. The observed
phenomena are explained by an improvement of uniformity of NbN films that has been confirmed
by a decrease of resistivity and an increase of the ratio of the measured critical current to the
depairing current. The latter factor is considered as the most crucial for both the cut-off
wavelength and the dark count rates of SNSPD. Based on our results we propose a set of criteria
for material properties to optimize SNSPD in the infrared spectral region. VC 2012 American
Institute of Physics. [http://dx.doi.org/10.1063/1.4757625]
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Inderbitzin K, Engel A, Schilling A, Il'in K, Siegel M. An ultra-fast superconducting Nb nanowire single-photon detector for soft x-rays. Appl Phys Lett. 2012;101.
Abstract: Although superconducting nanowire single-photon detectors (SNSPDs) are well studied regarding the
detection of infrared/optical photons and keV-molecules, no studies on continuous x-ray photon
counting by thick-film detectors have been reported so far. We fabricated a 100 nm thick niobium
x-ray SNSPD (an X-SNSPD) and studied its detection capability of photons with keV-energies in
continuous mode. The detector is capable to detect photons even at reduced bias currents of 0.4%,
which is in sharp contrast to optical thin-film SNSPDs. No dark counts were recorded in extended
measurement periods. Strikingly, the signal amplitude distribution depends significantly on the photon
energy spectrum.VC
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2007 |
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Semenov A, Haas P, Ilin K, Hubers H, Siegel M, Engel A, et al. Energy resolution and sensitivity of a superconducting quantum detector. Phys C: Supercond. 2007;460-462:1491–2.
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Semenov A, Richter H, Smirnov A, Günther B, Hübers H-W, Il’in K, et al. Development of HEB mixers for GREAT and for security screening [abstract]. In: Proc. 18th Int. Symp. Space Terahertz Technol.; 2007. 184.
Abstract: We report the study on the quasioptical coupling efficiency and the gain bandwidth of NbN hot-electron bolometer mixers developed for the 4.7 THz channel of the German receiver for Astronomy at THz-frequencies (GREAT) and for security screening at subterahertz frequencies. Radiation coupling efficiency and directive properties of integrated lens antennas with log-spiral, log-periodic and double-slot planar feeds coupled to a hot-electron bolometer were experimentally studied at frequencies from 1 THz to 6 THz and compared with simulations based on the method of moments and the physical-optics ray tracing. For all studied antennas the modeled spectral dependence of the coupling efficiency fits to the experimental data obtained with both Fourier transform spectroscopy and noise temperature measurements only if the complex impedance of the bolometer is explicitly taken into account. Our experimental data did not indicate any noticeable contribution of the quantum noise to the system noise temperature. The experimentally observed deviation of the beam pattern from the model prediction increases with frequency and is most likely due to a non- ideality of the presently used lenses. Study of the intermediate frequency mixer gain at local oscillator (LO) frequencies between 2.5 THz and 0.3 THz showed an increase of the gain bandwidth at low LO frequencies that was understood as the contribution of the direct interaction of magnetic vortices with the radiation field. We have found that the non- homogeneous hot-spot model more adequately describes variation of the intermediate frequency bandwidth with the applied local oscillator power than any of uniform mixer models. The state-of-the-day performance of the GREAT 4.7-THz channel and the 0.8-THz security scanner will be presented.
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2006 |
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Semenov AD, Il'in K, Siegel M, Smirnov A, Pavlov S, Richter H, et al. Evidence of non-bolometric mixing in the bandwidth of a hot-electron bolometer. Supercond Sci Technol. 2006;19(10):1051–6.
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2004 |
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Il'in K, Siegel M, Semenov A, Engel A, Hübers H-W, Hollmann E, et al. Thickness dependence of superconducting properties of ultrathin Nb and NbN films. In: AKF-Frühjahrstagung.; 2004.
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