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Author Yagoubov, P.; Kroug, M.; Merkel, H.; Kollberg, E.; Hübers, H.-W.; Schubert, J.; Schwaab, G.; Gol'tsman, G.; Gershenzon, E. url  openurl
  Title NbN hot electron bolometric mixers at frequencies between 0.7 and 3.1 THz Type Conference Article
  Year 1999 Publication (down) Proc. 10th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 10th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 238-246  
  Keywords NbN HEB mixers  
  Abstract The performance of NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixers is investigated in the 0.7-3.1 THz frequency range. The devices are made from a 3.5-4 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The length of the bolometer microbridge is 0.1- 0.2 gm, the width is 1-2 gm. The best results of the DSB receiver noise temperature measured at 1.5 GHz intermediate frequency are: 800 K at 0.7 THz, 1100 K at 1.6 THz, 2000 K at 2.5 THz and 4200 K at 3.1 THz. The measurements were performed with a far infrared laser as the local oscillator (LO) source. The estimated LO power required is less than 500 nW at the receiver input. First results on the spiral antenna polarization measurements are reported.  
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  Notes Approved no  
  Call Number Serial 1575  
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Author Il'in, K. S.; Gol'tsman, G. N.; Voronov, B. M.; Sobolewski, Roman url  openurl
  Title Characterization of the electron energy relaxation process in NbN hot-electron devices Type Conference Article
  Year 1999 Publication (down) Proc. 10th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 10th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 390-397  
  Keywords HEB mixers, SSPD, SNSPD, NbN films, Nb films  
  Abstract We report on transient measurements of electron energy relaxation in NbN films with 300-fs time resolution. Using an electro-optic sampling technique, we have studied the photoresponse of 3.5-nm-thick NbN films deposited on sapphire substrates and exposed to 100-fs-wide optical pulses. Our experimental data analysis was based on the two-temperature model and has shown that in our films at the superconducting transition 10.5 K the inelastic electron-phonon scattering time was about (111}+-__.2) ps. This response time indicated that the maximum intermediate-frequency band of a NbN hot-electron phonon-cooled mixer should reach (16+41-3) GHz if one eliminates the bolometric phonon-heating effect. We have suggested several ways to increase the effectiveness of phonon cooling to achieve the above intrinsic value of the NbN mixer bandwidth.  
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  Notes Approved no  
  Call Number Serial 1576  
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Author Antipov, S. V.; Svechnikov, S. I.; Smirnov, K. V.; Vakhtomin, Y. B.; Finkel, M. I.; Goltsman, G. N.; Gershenzon, E. M. url  openurl
  Title Noise temperature of quasioptical NbN hot electron bolometer mixers at 900 GHz Type Journal Article
  Year 2001 Publication (down) Physics of Vibrations Abbreviated Journal Physics of Vibrations  
  Volume 9 Issue 4 Pages 242-245  
  Keywords NbN HEB mixers  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1069-1227 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1550  
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Author Svechnikov, S. I.; Antipov, S. V.; Vakhtomin, Y. B.; Goltsman, G. N.; Gershenzon, E. M.; Cherednichenko, S. I.; Kroug, M.; Kollberg, E. url  openurl
  Title Conversion and noise bandwidths of terahertz NbN hot-electron bolometer mixers Type Journal Article
  Year 2001 Publication (down) Physics of Vibrations Abbreviated Journal Physics of Vibrations  
  Volume 9 Issue 3 Pages 205-210  
  Keywords NbN HEB mixers  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1069-1227 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1551  
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Author Gol'tsman, G. N.; Korneev, A.; Rubtsova, I.; Milostnaya, I.; Chulkova, G.; Minaeva, O.; Smirnov, K.; Voronov, B.; Słysz, W.; Pearlman, A.; Verevkin, A.; Sobolewski, R. url  doi
openurl 
  Title Ultrafast superconducting single-photon detectors for near-infrared-wavelength quantum communications Type Journal Article
  Year 2005 Publication (down) Phys. Stat. Sol. (C) Abbreviated Journal Phys. Stat. Sol. (C)  
  Volume 2 Issue 5 Pages 1480-1488  
  Keywords NbN SSPD, SNSPD  
  Abstract We present our progress on the research and development of NbN superconducting single‐photon detectors (SSPD's) for ultrafast counting of near‐infrared photons for secure quantum communications. Our SSPD's operate in the quantum detection mode based on the photon‐induced hotspot formation and subsequent development of a transient resistive barrier across an ultrathin and submicron‐width superconducting stripe. The devices are fabricated from 4‐nm‐thick NbN films and kept in the 4.2‐ to 2‐K temperature range. The detector experimental quantum efficiency in the photon‐counting mode reaches above 40% for the visible light and up to 30% in the 1.3‐ to 1.55‐µm wavelength range with dark counts below 0.01 per second. The experimental real‐time counting rate is above 2 GHz and is limited by our readout electronics. The SSPD's timing jitter is below 18 ps, and the best‐measured value of the noise‐equivalent power (NEP) is 5 × 10–21 W/Hz1/2 at 1.3 µm. In terms of quantum efficiency, timing jitter, and maximum counting rate, our NbN SSPD's significantly outperform semiconductor avalanche photodiodes and photomultipliers in the 1.3‐ to 1.55‐µm range.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1610-1634 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1479  
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Author Beck, M.; Klammer, M.; Lang, S.; Leiderer, P.; Kabanov, V. V.; Gol'tsman, G. N.; Demsar, J. doi  openurl
  Title Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy Type Journal Article
  Year 2011 Publication (down) Phys. Rev. Lett. Abbreviated Journal Phys. Rev. Lett.  
  Volume 107 Issue 17 Pages 4  
  Keywords NbN thin film, energy gap dynamics  
  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, λ=1.1±0.1, which is in excellent agreement with theoretical estimates.  
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  Notes Approved no  
  Call Number RPLAB @ gujma @ Serial 641  
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Author Beck, M.; Rousseau, I.; Klammer, M.; Leiderer, P.; Mittendorff, M.; Winnerl, S.; Helm, M.; Gol'tsman, G.N.; Demsar, J. url  doi
openurl 
  Title Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses Type Journal Article
  Year 2013 Publication (down) Phys. Rev. Lett. Abbreviated Journal Phys. Rev. Lett.  
  Volume 110 Issue 26 Pages 267003 (1 to 5)  
  Keywords NbN thin films, energy gap  
  Abstract Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Delta/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2Delta/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.  
  Address Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457, Germany  
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  Series Volume Series Issue Edition  
  ISSN 0031-9007 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:23848912 Approved no  
  Call Number Serial 1370  
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Author Semenov, A. D.; Nebosis, R. S.; Gousev, Yu. P.; Heusinger, M. A.; Renk, K. F. openurl 
  Title Analysis of the nonequilibrium photoresponse of superconducting films to pulsed radiation by use of a two-temperature model Type Journal Article
  Year 1995 Publication (down) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 52 Issue 1 Pages 581-590  
  Keywords HEB, NbN phonon scecific heat, Cp  
  Abstract Photoresponse of a superconducting film in the resistive state to pulsed radiation has been studied in the framework of a model assuming that two different effective temperatures can be assigned to the quasiparticle and phonon nonequilibrium distributions. The coupled electron-phonon-substrate system is described by a system of time-dependent energy-balance differential equations for effective temperatures. An analytical solution of the system is given and calculated voltage transients are compared with experimental photoresponse signals taking into account the radiation pulse shape and the time resolution of the readout electronics. It is supposed that a resistive state (vortices, fluxons, network of intergrain junctions, hot spots, phase slip centers) provides an ultrafast connection between electron temperature changes and changes of the film resistance and thus plays a minor role in the temporal evolution of the response. In accordance with experimental observations a two-component response was revealed from simulations. The slower component corresponds to a bolometric mechanism while the fast component is connected with the relaxation of the electron temperature. Calculated photoresponse transients are presented for different ratios of the electron and phonon specific heat, radiation pulse durations and fluences, and frequency band passes of registration electronics. From the amplitude of the bolometric component we determine the radiation energy absorbed in a film. This enables us to reveal an intrinsic electron-phonon scattering time even if it is much shorter than the time resolution of readout electronics. We analyze experimental voltage transients for NbN, YBa2Cu3O7, and TlBa2Ca2Cu3O9 superconducting films and find the electron-phonon interaction times at the transition temperatures of 17, 2.5, and 1.8 ps, respectively. The values are in reasonable agreement with data of other experiments.  
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  Notes Approved no  
  Call Number Serial 903  
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Author Sidorova, M.; Semenov, Alexej D.; Hübers, H.-W.; Ilin, K.; Siegel, M.; Charaev, I.; Moshkova, M.; Kaurova, N.; Goltsman, G. N.; Zhang, X.; Schilling, A. url  doi
openurl 
  Title Electron energy relaxation in disordered superconducting NbN films Type Journal Article
  Year 2020 Publication (down) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 102 Issue 5 Pages 054501 (1 to 15)  
  Keywords NbN SSPD, SNSPD, HEB, bandwidth, relaxation time  
  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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  Series Volume Series Issue Edition  
  ISSN 2469-9950 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1266  
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Author Lusche, R.; Semenov, A.; Korneeva, Y.; Trifonov, A.; Korneev, A.; Gol'tsman, G.; Hübers, H.-W. url  doi
openurl 
  Title Effect of magnetic field on the photon detection in thin superconducting meander structures Type Journal Article
  Year 2014 Publication (down) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 89 Issue 10 Pages 104513 (1 to 7)  
  Keywords NbN SSPD, SNSPD  
  Abstract We have studied the influence of an externally applied magnetic field on the photon and dark count rates of meander-type niobium nitride superconducting nanowire single-photon detectors. Measurements have been performed at a temperature of 4.2 K, and magnetic fields up to 250 mT have been applied perpendicularly to the meander plane. While photon count rates are field independent at weak applied fields, they show a strong dependence at fields starting from approximately ±25 mT. This behavior, as well as the magnetic field dependence of the dark count rates, is in good agreement with the recent theoretical model of vortex-assisted photon detection and spontaneous vortex crossing in narrow superconducting lines. However, the local reduction of the superconducting free energy due to photon absorption, which is the fitting parameter in the model, increases much slower with the photon energy than the model predicts. Furthermore, changes in the free-energy during photon counts and dark counts depend differently on the current that flows through the meander. This indicates that photon counts and dark counts occur in different parts of the meander.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1098-0121 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1367  
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