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Author Baeva, E. M.; Titova, N. A.; Kardakova, A. I.; Piatrusha, S. U.; Khrapai, V. S. url  doi
openurl 
  Title Universal bottleneck for thermal relaxation in disordered metallic films Type Journal Article
  Year 2020 Publication JETP Lett. Abbreviated Journal Jetp Lett.  
  Volume (down) 111 Issue 2 Pages 104-108  
  Keywords NbN disordered metallic films, thermal relaxation  
  Abstract We study the heat relaxation in current biased metallic films in the regime of strong electron–phonon coupling. A thermal gradient in the direction normal to the film is predicted, with a spatial temperature profile determined by the temperature-dependent heat conduction. In the case of strong phonon scattering, the heat conduction occurs predominantly via the electronic system and the profile is parabolic. This regime leads to the linear dependence of the noise temperature as a function of bias voltage, in spite of the fact that all the dimensions of the film are large compared to the electron–phonon relaxation length. This is in stark contrast to the conventional scenario of relaxation limited by the electron–phonon scattering rate. A preliminary experimental study of a 200-nm-thick NbN film indicates the relevance of our model for materials used in superconducting nanowire single-photon detectors.  
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  ISSN 0021-3640 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1164  
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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 Phys. Rev. Lett. Abbreviated Journal Phys. Rev. Lett.  
  Volume (down) 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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  ISSN 0031-9007 ISBN Medium  
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  Notes PMID:23848912 Approved no  
  Call Number Serial 1370  
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Author Shcherbatenko, M.; Tretyakov, I.; Lobanov, Yu.; Maslennikov, S. N.; Kaurova, N.; Finkel, M.; Voronov, B.; Goltsman, G.; Klapwijk, T. M. doi  openurl
  Title Nonequilibrium interpretation of DC properties of NbN superconducting hot electron bolometers Type Journal Article
  Year 2016 Publication Appl. Phys. Lett. Abbreviated Journal  
  Volume (down) 109 Issue 13 Pages 132602  
  Keywords HEB mixer, contacts  
  Abstract We present a physically consistent interpretation of the dc electrical properties of niobiumnitride (NbN)-based superconducting hot-electron bolometer mixers, using concepts of nonequilibrium superconductivity. Through this, we clarify what physical information can be extracted from the resistive transition and the dc current-voltage characteristics, measured at suitably chosen temperatures, and relevant for device characterization and optimization. We point out that the intrinsic spatial variation of the electronic properties of disordered superconductors, such as NbN, leads to a variation from device to device.  
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  Call Number Serial 1107  
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Author Smirnov, K. V.; Divochiy, A. V.; Vakhtomin, Y. B.; Sidorova, M. V.; Karpova, U. V.; Morozov, P. V.; Seleznev, V. A.; Zotova, A. N.; Vodolazov, D. Y. url  doi
openurl 
  Title Rise time of voltage pulses in NbN superconducting single photon detectors Type Journal Article
  Year 2016 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume (down) 109 Issue 5 Pages 052601  
  Keywords SSPD, SNSPD  
  Abstract We have found experimentally that the rise time of voltage pulse in NbN superconducting single photon detectors increases nonlinearly with increasing the length of the detector L. The effect is connected with dependence of resistance of the detector Rn, which appears after photon absorption, on its kinetic inductance Lk and, hence, on the length of the detector. This conclusion is confirmed by our calculations in the framework of two temperature model.

D.Yu.V. acknowledges the support from the Russian Foundation for Basic Research (Project No. 15-42-02365). K.V.S. acknowledges the financial support from the Ministry of Education and Science of the Russian Federation (Contract No. 3.2655.2014/K).		  
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  ISSN 0003-6951 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1236  
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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 Phys. Rev. Lett. Abbreviated Journal Phys. Rev. Lett.  
  Volume (down) 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 Maingault, L.; Tarkhov, M.; Florya, I.; Semenov, A.; Espiau de Lamaëstre, R.; Cavalier, P.; Gol’tsman, G.; Poizat, J.-P.; Villégier, J.-C. url  doi
openurl 
  Title Spectral dependency of superconducting single photon detectors Type Journal Article
  Year 2010 Publication J. Appl. Phys. Abbreviated Journal J. Appl. Phys.  
  Volume (down) 107 Issue 11 Pages 116103 (1 to 3)  
  Keywords NbN SSPD, SNSPD  
  Abstract We investigate the effect of varying both incoming optical wavelength and width of NbN nanowires on the superconducting single photon detectors (SSPD) detection efficiency. The SSPD are current biased close to critical value and temperature fixed at 4.2 K, far from transition. The experimental results are found to verify with a good accuracy predictions based on the “hot spot model,” whose size scales with the absorbed photon energy. With larger optical power inducing multiphoton detection regime, the same scaling law remains valid, up to the three-photon regime. We demonstrate the validity of applying a limited number of measurements and using such a simple model to reasonably predict any SSPD behavior among a collection of nanowire device widths at different photon wavelengths. These results set the basis for designing efficient single photon detectors operating in the infrared (2–5 μm range).

This work was supported by European projects FP6 STREP “SINPHONIA” (Contract No. NMP4-CT-2005-16433) and IP “QAP” (Contract No. 15848).		  
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  ISSN 0021-8979 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1392  
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Author Ferrari, S.; Kahl, O.; Kovalyuk, V.; Goltsman, G. N.; Korneev, A.; Pernice, W. H. P. url  doi
openurl 
  Title Waveguide-integrated single- and multi-photon detection at telecom wavelengths using superconducting nanowires Type Journal Article
  Year 2015 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume (down) 106 Issue 15 Pages 151101 (1 to 5)  
  Keywords SSPD, SNSPD  
  Abstract We investigate single- and multi-photon detection regimes of superconducting nanowire detectors embedded in silicon nitride nanophotonic circuits. At near-infrared wavelengths, simultaneous detection of up to three photons is observed for 120 nm wide nanowires biased far from the critical current, while narrow nanowires below 100 nm provide efficient single photon detection. A theoretical model is proposed to determine the different detection regimes and to calculate the corresponding internal quantum efficiency. The predicted saturation of the internal quantum efficiency in the single photon regime agrees well with plateau behavior observed at high bias currents.

W. H. P. Pernice acknowledges support by the DFG Grant Nos. PE 1832/1-1 and PE 1832/1-2 and the Helmholtz society through Grant No. HIRG-0005. The Ph.D. education of O. Kahl is embedded in the Karlsruhe School of Optics and Photonics (KSOP). G. N. Goltsman acknowledges support by Russian Federation President Grant HШ-1918.2014.2 and Ministry of Education and Science of the Russian Federation Contract No.: RFMEFI58614X0007. A. Korneev acknowledges support by Statement Task No. 3.1846.2014/k. V. Kovalyuk acknowledges support by Statement Task No. 2327. We also acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) and the State of Baden-Württemberg through the DFG-Center for Functional Nanostructures (CFN) within subproject A6.4. We thank S. Kühn and S. Diewald for the help with device fabrication as well as B. Voronov and A. Shishkin for help with NbN thin film deposition and A. Semenov for helpful discussion about the detection mechanism of nanowire SSPD's.

The authors declare no competing financial interests.		  
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  ISSN 0003-6951 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1211  
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Author Kardakova, A.; Finkel, M.; Morozov, D.; Kovalyuk, V.; An, P.; Dunscombe, C.; Tarkhov, M.; Mauskopf, P.; Klapwijk, T.M.; Goltsman, G. doi  openurl
  Title The electron-phonon relaxation time in thin superconducting titanium nitride films Type Journal Article
  Year 2013 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume (down) 103 Issue 25 Pages 252602 (1 to 4)  
  Keywords disordered TiN films, electron-phonon relaxation time  
  Abstract We report on the direct measurement of the electron-phonon relaxation time, τeph, in disordered TiN films. Measured values of τeph are from 5.5 ns to 88 ns in the 4.2 to 1.7 K temperature range and consistent with a T−3 temperature dependence. The electronic density of states at the Fermi level N0 is estimated from measured material parameters. The presented results confirm that thin TiN films are promising candidate-materials for ultrasensitive superconducting detectors.

The work was supported by the Ministry of Education and Science of the Russian Federation, Contract No. 14.B25.31.0007 and by the RFBR Grant No. 13-02-91159.		  
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  Notes Approved no  
  Call Number RPLAB @ kovalyuk @ Serial 941  
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Author Fedorov, G.; Kardakova, A.; Gayduchenko, I.; Charayev, I.; Voronov, B.M.; Finkel, M.; Klapwijk, T.M.; Morozov, S.; Presniakov, M.; Bobrinetskiy, I.; Ibragimov, R.; Goltsman, G. url  doi
openurl 
  Title Photothermoelectric response in asymmetric carbon nanotube devices exposed to sub-terahertz radiation Type Journal Article
  Year 2013 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume (down) 103 Issue 18 Pages 181121 (1 to 5)  
  Keywords carbon nanotubes, CNT, THz radiation, SiO2 substrate  
  Abstract We report on the voltage response of carbon nanotube devices to sub-terahertz (THz) radiation. The devices contain carbon nanotubes (CNTs), which are over their length partially suspended and partially Van der Waals bonded to a SiO2 substrate, causing a difference in thermal contact. We observe a DC voltage upon exposure to 140 GHz radiation. Based on the observed gate voltage and power dependence, at different temperatures, we argue that the observed signal is both thermal and photovoltaic. The room temperature responsivity in the microwave to THz range exceeds that of CNT based devices reported before. Authors thank Professor P. Barbara for providing the catalyst for CNT growth and Dr. N. Chumakov and V. Rylkov for stimulating discussions. The work was supported by the RFBR (Grant No. 12-02-01291-a) and by the Ministry of Education and Science of the Russian Federation (Contract No. 14.B25.31.0007). G.F. acknowledges support of the RFBR grant 12-02-01005-a.  
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  ISSN 0003-6951 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1171  
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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 Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume (down) 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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  ISSN 2469-9950 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1266  
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