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Lobanov, Y.V.; Tong, C.-Y.E.; Hedden, A.S.; Blundell, R.; Voronov, B.M.; Gol'tsman, G.N. |
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Direct measurement of the gain and noise bandwidths of HEB mixers |
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2011 |
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IEEE Trans. Appl. Supercond. |
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IEEE Trans. Appl. Supercond. |
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21 |
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3 |
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645-648 |
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waveguide NbN HEB mixers |
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The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement. |
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RPLAB @ gujma @ |
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720 |
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Seleznev, V. A.; Tarkhov, M. A.; Voronov, B. M.; Milostnaya, I. I.; Lyakhno, V. Yu; Garbuz, A. S.; Mikhailov, M. Yu; Zhigalina, O. M.; Gol'tsman, G. N. |
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Deposition and characterization of few-nanometers-thick superconducting Mo-Re films |
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2008 |
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Supercond. Sci. Technol. |
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Supercond. Sci. Technol. |
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21 |
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11 |
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115006 (1 to 6) |
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We report on the fabrication and investigation of few-nanometers-thick superconducting molybdenum-rhenium (Mo-Re) films intended for use in nanowire single-photon superconducting detectors (SSPDs). Mo-Re films were deposited on sapphire substrates by DC magnetron sputtering of an Mo(60)-Re(40) alloy target in an atmosphere of argon. The films 2-10 nm thick had critical temperatures (Tc) from 5.6 to 9.7 K. HRTEM (high-resolution transmission electron microscopy) analysis showed that the films had a homogeneous structure. XPS (x-ray photoelectron spectroscopy) analysis showed the Mo to Re atom ratio to be 0.575/0.425, oxygen concentration to be 10%, and concentration of other elements to be 1%. |
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RPLAB @ gujma @ |
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723 |
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Il'in, K. S.; Lindgren, M.; Currie, M. A.; Semenov, D.; Gol'tsman, G. N.; Sobolewski, Roman; Cherednichenko, S. I.; Gershenzon, E. M. |
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Picosecond hot-electron energy relaxation in NbN superconducting photodetectors |
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2000 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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76 |
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19 |
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2752-2754 |
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NbN HEB detectors, two-temperature model, IF bandwidth |
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We report time-resolved characterization of superconducting NbN hot-electron photodetectors using an electro-optic sampling method. Our samples were patterned into micron-size microbridges from 3.5-nm-thick NbN films deposited on sapphire substrates. The devices were illuminated with 100 fs optical pulses, and the photoresponse was measured in the ambient temperature range between 2.15 and 10.6 K (superconducting temperature transition TC). The experimental data agreed very well with the nonequilibrium hot-electron, two-temperature model. The quasiparticle thermalization time was ambient temperature independent and was measured to be 6.5 ps. The inelastic electron–phonon scattering time Ï„e–ph tended to decrease with the temperature increase, although its change remained within the experimental error, while the phonon escape time Ï„es decreased almost by a factor of two when the sample was put in direct contact with superfluid helium. Specifically, Ï„e–ph and Ï„es, fitted by the two-temperature model, were equal to 11.6 and 21 ps at 2.15 K, and 10(±2) and 38 ps at 10.5 K, respectively. The obtained value of Ï„e–ph shows that the maximum intermediate frequency bandwidth of NbN hot-electron phonon-cooled mixers operating at TC can reach 16(+4/–3) GHz if one eliminates the bolometric phonon-heating effect. |
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0003-6951 |
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856 |
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Yagoubov, P.; Kroug, M.; Merkel, H.; Kollberg, E.; Gol'tsman, G.; Svechnikov, S.; Gershenzon, E. |
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Noise temperature and local oscillator power requirement of NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies |
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1998 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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73 |
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19 |
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2814-2816 |
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NbN HEB mixers, noise temperature, local oscillator power |
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In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband <cd><2018>DSB<cd><2019> noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2Ï«2 um. The amount of local oscillator power absorbed in the bolometer is less than 100 nW. |
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911 |
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Bell, M.; Sergeev, A.; Mitin, V.; Bird, J.; Verevkin, A.; Gol'tsman, G. |
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One-dimensional resistive states in quasi-two-dimensional superconductors |
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2007 |
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arXiv:0709.0709v1 [cond-mat.supr-con] |
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1-11 |
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We investigate competition between one- and two-dimensional topological excitations – phase slips and vortices – in formation of resistive states in quasi-two-dimensional superconductors in a wide temperature range below the mean-field transition temperature T(C0). The widths w = 100 nm of our ultrathin NbN samples is substantially larger than the Ginzburg-Landau coherence length ξ = 4nm and the fluctuation resistivity above T(C0) has a two-dimensional character. However, our data shows that the resistivity below T(C0) is produced by one-dimensional excitations, – thermally activated phase slip strips (PSSs) overlapping the sample cross-section. We also determine the scaling phase diagram, which shows that even in wider samples the PSS contribution dominates over vortices in a substantial region of current/temperature variations. Measuring the resistivity within seven orders of magnitude, we find that the quantum phase slips can only be essential below this level. |
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RPLAB @ atomics90 @ |
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948 |
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