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Beck, Matthias; Leiderer, Paul; Kabanov, Viktor V.; Gol'tsman, Gregory; Helm, Manfred; Demsar, Jure |
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Energy-gap dynamics of a superconductor NbN studied by time-resolved terahertz spectroscopy |
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2012 |
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45 |
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12 |
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1-3 |
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NbN energy gap |
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Using time-resolved terahertz (THz) spectroscopy we performed direct studies of the photoinduced suppression and recovery of the SC gap in a conventional SC 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 important microscopic constants: the Cooper pair-breaking rate via phonon absorption and the bare quasiparticle recombination rate. From the latter we were able to extract the dimensionless electron-phonon coupling constant, λ=1.1±0.1, in excellent agreement with theoretical estimates. The technique also allowed us to determine the absorbed energy required to suppress SC, which in NbN equals the thermodynamic condensation energy (in cuprates the two differ by an order of magnitude). Finally, we present the first studies of dynamics following resonant excitation with intense narrow band THz pulses tuned to above and below the superconducting gap. These suggest an additional process, particularly pronounced near Tc, that could be attributed to amplification of SC via effective quasiparticle cooling. |
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1383 |
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Bulaevskii, L. N.; Graf, Matthias J.; Kogan, V. G. |
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Vortex-assisted photon counts and their magnetic field dependence in single-photon superconducting detectors |
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2012 |
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Phys. Rev. B |
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Phys. Rev. B |
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85 |
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1 |
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9 |
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SSPD; SNSPD; single-vortex crossing; normal-state belt |
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We argue that photon counts in a superconducting nanowire single-photon detector (SNSPD) are caused by the transition from a current-biased metastable superconducting state to the normal state. Such a transition is triggered by vortices crossing the thin and narrow superconducting strip from one edge to another due to the Lorentz force. Detector counts in SNSPDs may be caused by three processes: (a) a single incident photon with sufficient energy to break enough Cooper pairs to create a normal-state belt across the entire width of the strip (direct photon count), (b) thermally induced single-vortex crossing in the absence of photons (dark count), which at high-bias currents releases the energy sufficient to trigger the transition to the normal state in a belt across the whole width of the strip, and (c) a single incident photon of insufficient energy to create a normal-state belt but initiating a subsequent single-vortex crossing, which provides the rest of the energy needed to create the normal-state belt (vortex-assisted single-photon count). We derive the current dependence of the rate of vortex-assisted photon counts. The resulting photon count rate has a plateau at high currents close to the critical current and drops as a power law with high exponent at lower currents. While the magnetic field perpendicular to the film plane does not affect the formation of hot spots by photons, it causes the rate of vortex crossings (with or without photons) to increase. We show that by applying a magnetic field one may characterize the energy barrier for vortex crossings and identify the origin of dark counts and vortex-assisted photon counts. |
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RPLAB @ gujma @ |
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733 |
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Semenov, A. V.; Devyatov, I. A.; Korneev, A. A.; Smirnov, K. V.; Goltsman, G. N.; Melnikov, A. P. |
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Derivation of expression for thermodynamic potential of “dirty” superconductor |
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2012 |
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Rus. J. Radio Electron. |
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Rus. J. Radio Electron. |
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4 |
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dirty superconductor, Usadel theory, thermodynamic potential |
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We derive a formula for thermodynamic potential of dirty superconductor which express it via isotropic quasiclassical Green functions of Usadel theory. Our result allows unify description of dynamic processes and fluctuations in superconducting nano-electronic devices. |
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Russian |
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7 pages |
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1824 |
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Minaeva, O.; Fraine, A.; Korneev, A.; Divochiy, A.; Goltsman, G.; Sergienko, A. |
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High resolution optical time-domain reflectometry using superconducting single-photon detectors |
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Conference Article |
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2012 |
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Frontiers in Opt. 2012/Laser Sci. XXVIII |
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Frontiers in Opt. 2012/Laser Sci. XXVIII |
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Fw3a.39 |
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SSPD, SNSPD, Photodetectors; Fiber characterization; Light beams; Optical time domain reflectometry; Photon counting; Single mode fibers; Single photon detectors; Superconductors |
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We discuss the advantages and limitations of single-photon optical time-domain reflectometry with superconducting single-photon detectors. The higher two-point resolution can be achieved due to superior timing performance of SSPDs in comparison with InGaAs APDs. |
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Optical Society of America |
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1237 |
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Julia Toussaint, Roman Grüner, Marco Schubert, Torsten May, Hans-Georg Meyer, Benjamin Dietzek, Jürgen Popp, Matthias Hofherr, Matthias Arndt, Dagmar Henrich, Konstantin Il'in, and Michael Siegel |
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Superconducting single-photon counting system for optical experiments requiring time-resolution in the picosecond range |
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2012 |
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AIP REVIEW OF SCIENTIFIC INSTRUMENTS |
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83 |
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SSPD, picosecond, time-resolution |
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We have developed a cryogenic measurement system for single-photon counting, which can be used
in optical experiments requiring high time resolution in the picosecond range. The system utilizes
niobium nitride superconducting nanowire single-photon detectors which are integrated in a timecorrelated
single-photon counting (TCSPC) setup. In this work, we describe details of the mechanical
design, the electrical setup, and the cryogenic optical components. The performance of the complete
system in TCSPC mode is tentatively benchmarked using 140 fs long laser pulses at a repetition
frequency of 75MHz. Due to the high temporal stability of these pulses, the measured time resolution
of 35 ps (FWHM) is limited by the timing jitter of the measurement system. The result was crosschecked
in a Coherent Anti-stokes Raman Scattering (CARS) setup, where scattered pulses from a
β-barium borate crystal have been detected with the same time resolution. |
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RPLAB @ seleznev @ |
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885 |
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D. Henrich, L. Rehm S. Dörner, M. Hofherr, K. Il'in, A. Semenov, and M. Siegel |
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Detection efficiency of a spiral-nanowire superconducting single-photon detector |
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2012 |
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Critical current, Nanoscale devices, Superconducting photodetectors. |
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We investigate the detection efficiency of a spiral layout of a Superconducting Nanowire Single-Photon Detector (SNSPD). The design is less susceptible to the critical current reduction in sharp turns of the nanowire than the conventional meander design. Detector samples with different nanowire width from 300 to 100 nm are patterned from a 4 nm thick NbN film deposited on sapphire substrates. The critical current IC at 4.2 K for spiral, meander, and simple bridge structures is measured and compared. On the 100 nm wide samples, the detection efficiency is measured in the wavelength range 400-1700 nm and the cut-off wavelength of the hot-spot plateau is determined. In the optical range, the spiral detector reaches a detection efficiency of 27.6%, which is ~1.5 times the value of the meander. In the infrared range the detection efficiency is more than doubled. |
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D. Henrich, L. Rehm S. Dörner, M. Hofherr, K. Il'in, A. Semenov, and M. Siegel |
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RPLAB @ seleznev @ |
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880 |
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Smirnov, A. V.; Baryshev, A. M.; de Bernardis, P.; Vdovin, V. F.; Gol'tsman, G. N.; Kardashev, N. S.; Kuz'min, L. S.; Koshelets, V. P.; Vystavkin, A. N.; Lobanov, Yu. V.; Ryabchun, S. A.; Finkel, M. I.; Khokhlov, D. R. |
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The current stage of development of the receiving complex of the millimetron space observatory |
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2012 |
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Radiophys. Quant. Electron. |
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Radiophys. Quant. Electron. |
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54 |
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8 |
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557-568 |
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Millimetron space observatory, HEB applications |
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We present an overview of the state of the onboard receiving complex of the Millimetron space observatory in the development phase of its preliminary design. The basic parameters of the onboard equipment planned to create and required for astrophysical observations are considered. A review of coherent and incoherent detectors, which are central to each receiver of the observatory, is given. Their characteristics and limiting parameters feasible at the present level of technology are reported. |
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1079 |
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Pentin, I. V.; Smirnov, A. V.; Ryabchun, S. A.; Ozhegov, R. V.; Gol’tsman, G. N.; Vaks, V. L.; Pripolzin, S. I.; Pavel’ev, D. G.; Koshurinov, Y. I.; Ivanov, A. S. |
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Semiconducting superlattice as a solid-state terahertz local oscillator for NbN hot-electron bolometer mixers |
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2012 |
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Tech. Phys. |
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Tech. Phys. |
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57 |
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7 |
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971-974 |
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semiconducting superlattice frequency multiplier, NbN HEB mixers |
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We present the results of our studies of the semiconducting superlattice (SSL) frequency multiplier and its application as part of the solid state local oscillator (LO) in the terahertz heterodyne receiver based on a NbN hot-electron bolometer (HEB) mixer. We show that the SSL output power level increases as the ambient temperature is lowered to 4.2 K, the standard HEB operation temperature. |
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1063-7842 |
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1378 |
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Zhang, W.; Miao, W.; Yao, Q. J.; Lin, Z. H.; Shi, S. C.; Gao, J. R.; Goltsman, G. N. |
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Spectral response and noise temperature of a 2.5 THz spiral antenna coupled NbN HEB mixer |
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2012 |
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Phys. Procedia |
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Phys. Procedia |
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36 |
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334-337 |
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NbN HEB mixer |
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We report on a 2.5 THz spiral antenna coupled NbN hot electron bolometer (HEB) mixers, fabricated with in-situ process. The receiver noise temperature with lowest value of 1180 K is in good agreement with calculated quantum efficiency factor as a function of bias voltage. In addition, the measured spectral response of the spiral antenna coupled NbN HEB mixer shows broad frequency coverage of 0.8-3 THz, and corrected response for optical losses, FTS, and coupling efficiency between antenna and bolometer falls with frequency due to diffraction-limited beam of lens/antenna combination. |
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1875-3892 |
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1381 |
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Sclafani, M.; Marksteiner, M.; Keir, F. M. L.; Divochiy, A.; Korneev, A.; Semenov, A.; Gol'tsman, G.; Arndt, M. |
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Sensitivity of a superconducting nanowire detector for single ions at low energy |
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2012 |
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Nanotechnol. |
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Nanotechnol. |
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23 |
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6 |
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065501 (1 to 5) |
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NbN SSPD, SNSPD, superconducting single ion detector, SSID, SNSID |
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We report on the characterization of a superconducting nanowire detector for ions at low kinetic energies. We measure the absolute single-particle detection efficiency eta and trace its increase with energy up to eta = 100%. We discuss the influence of noble gas adsorbates on the cryogenic surface and analyze their relevance for the detection of slow massive particles. We apply a recent model for the hot-spot formation to the incidence of atomic ions at energies between 0.2 and 1 keV. We suggest how the differences observed for photons and atoms or molecules can be related to the surface condition of the detector and we propose that the restoration of proper surface conditions may open a new avenue for SSPD-based optical spectroscopy on molecules and nanoparticles. |
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Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Vienna, Austria |
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PMID:22248823 |
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