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Zhang X, Lita AE, Smirnov K, Liu HL, Zhu D, Verma VB, et al. Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields. Phys Rev B. 2020;101(6):060508 (1 to 6).
Abstract: We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 to 1000μm and film thicknesses d∼4−6 and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T∗(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest either the presence of a highly conducting region that is dominating the electric transport, or a change in the vortex dynamics in narrow enough bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.
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Gol'tsman GN, Korneev A, Rubtsova I, Milostnaya I, Chulkova G, Minaeva O, et al. Ultrafast superconducting single-photon detectors for near-infrared-wavelength quantum communications. Phys Stat Sol (C). 2005;2(5):1480–8.
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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Antipov SV, Svechnikov SI, Smirnov KV, Vakhtomin YB, Finkel MI, Goltsman GN, et al. Noise temperature of quasioptical NbN hot electron bolometer mixers at 900 GHz. Physics of Vibrations. 2001;9(4):242–5.
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Kaurova NS, Finkel MI, Maslennikov SN, Vahtomin YB, Antipov SV, Smirnov KV, et al. Submillimeter mixer based on YBa2Cu3O7-x thin film. In: Proc. 1-st conf. Fundamental problems of high temperature superconductivity. Moscow-Zvenigorod; 2004. 291.
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Cherednichenko S, Kroug M, Merkel H, Kollberg E, Loudkov D, Smirnov K, et al. Local oscillator power requirement and saturation effects in NbN HEB mixers. In: Jet Propulsion Laboratory CIit.u.t.e of T, editor. Proc. 12th Int. Symp. Space Terahertz Technol. San Diego, CA, USA; 2001. p. 273–85.
Abstract: The local oscillator power required for NbN hot-electron bolometric mixers (P LO ) was investigated with respect to mixer size, critical temperature and ambient temperature. P LO can be decreased by a factor of 10 as the mixer size decreases from 4×0.4 µm 2 to 0.6×0.13 µm 2 . For the smallest volume mixer the optimal local oscillator power was found to be 15 nW. We found that for such mixer no signal compression was observed up to an input signal of 2 nW which corresponds to an equivalent input load of 20,000 K. For a constant mixer volume, reduction of T c can decrease optimal local oscillator power at least by a factor of 2 without a deterioration of the receiver noise temperature. Bath temperature was found to have minor effect on the receiver characteristics.
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Verevkin A, Xu Y, Zheng X, Williams C, Sobolewski R, Okunev O, et al. Superconducting NbN-based ultrafast hot-electron single-photon detector for infrared range. In: Proc. 12th Int. Symp. Space Terahertz Technol.; 2001. p. 462–8.
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Gol'tsman G, Semenov A, Smirnov K, Voronov B. Background limited quantum superconducting detector for submillimeter wavelengths. In: Proc. 12th Int. Symp. Space Terahertz Technol.; 2001. p. 469–75.
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Vahtomin YB, Finkel MI, Antipov SV, Voronov BM, Smirnov KV, Kaurova NS, et al. Gain bandwidth of phonon-cooled HEB mixer made of NbN thin film with MgO buffer layer on Si. In: Harvard university, editor. Proc. 13th Int. Symp. Space Terahertz Technol. Cambridge, MA, USA; 2002. p. 259–70.
Abstract: We present recently obtained values for gain bandwidth of NbN HEB mixers for different substrates and film thicknesses and for MgO buffer layer on Si at LO frequency of 0.85-1 THz. The maximal bandwidth, 5.2 GHz, was achieved for the device on MgO buffer layer on Si with a 2 nm thick NbN film. Functional devices based on NbN films of such thickness were fabricated for the first time due to an improvement of superconducting properties of NbN film deposited on MgO buffer layer on Si substrate.
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Meledin D, Tong CY-E, Blundell R, Kaurova N, Smirnov K, Voronov B, et al. The sensitivity and IF bandwidth of waveguide NbN hot electron bolometer mixers on MgO buffer layers over crystalline quartz. In: Harvard university, editor. Proc. 13th Int. Symp. Space Terahertz Technol. Cambridge, MA, USA; 2002. p. 65–72.
Abstract: We have developed and characterized waveguide phonon-cooled NbN Hot Electron Bolometer (FMB) mixers fabricated from a 3-4 nm thick NbN film deposited on a 200nm thick MgO buffer layer over crystalline quartz. Double side band receiver noise temperatures of 900-1050 K at 1.035 THz, and 1300-1400 K at 1.26 THz have been measured at an intermediate frequency of 1.5 GHz. The intermediate frequency bandwidth, measured at 0.8 THz LO frequency, is 3.2 GHz at the optimal bias point for low noise receiver operation.
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Semenov A, Hübers H-W, Richter H, Birk M, Krocka M, Mair U, et al. Performance of terahertz heterodyne receiver with a superconducting hot-electron mixer. In: Proc. 13th Int. Symp. Space Terahertz Technol.; 2002. p. 229–34.
Abstract: During the past decade major advances have been made regarding low noise mixers for terahertz heterodyne receivers. State of the art hot-electron-bolometer (HEB) mixers have noise temperatures close to the quantum limit and require less than a microwatt power from the local oscillator (L0). The technology is now at a point where the performance of a practical receiver employing such mixer, rather than the figures of merit of the mixer itself, is of major concern. We have incorporated a phonon-cooled NbN HEB mixer in a 2.5 THz heterodyne receiver and investigated its performance. This yields important information for future development of heterodyne receivers such as GREAT (German receiver for astronomy at THz frequencies aboard SOFIA) [1] and TELIS (Terahertz limb sounder), a balloon borne heterodyne receiver for atmospheric research [2]. Both are currently under development at DLR.
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