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Miao, W., Zhang, W., Zhong, J. Q., Shi, S. C., Delorme, Y., Lefevre, R., et al. (2014). Non-uniform absorption of terahertz radiation on superconducting hot electron bolometer microbridges. <ef><bf><bc>Appl. Phys. Lett., 104, 052605(1–4).
Abstract: We interpret the experimental observation of a frequency-dependence of superconducting hot electron bolometer (HEB) mixers by taking into account the non-uniform absorption of the terahertz radiation on the superconducting HEB microbridge. The radiation absorption is assumed to be proportional to the local surface resistance of the HEB microbridge, which is computed using the Mattis-Bardeen theory. With this assumption the dc and mixing characteristics of a superconducting niobium-nitride (NbN) HEB device have been modeled at frequencies below and above the equilibrium gap frequency of the NbN film.
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Murphy, A., Semenov, A., Korneev, A., Korneeva, Y., Gol’tsman, G., & Bezryadin, A. (2014). Dark counts initiated by macroscopic quantum tunneling in NbN superconducting photon detectors. arXiv:1410.7689v2 [cond-mat.supr-con]. Retrieved June 6, 2024, from https://arxiv.org/abs/1410.7689v2
Abstract: We perform measurements of the switching current distributions of three w = 120 nm wide, 4 nm thick NbN superconducting strips which are used for single-photon detectors. These strips are much wider than the diameter the vortex cores, so they are classified as quasi-two-dimensional (quasi-2D). We discover evidence of macroscopic quantum tunneling by observing the saturation of the standard deviation of the switching distributions at temperatures around 2 K. We analyze our results using the Kurkijarvi-Garg model and find that the escape temperature also saturates at low temperatures, confirming that at sufficiently low temperatures, macroscopic quantum tunneling is possible in quasi-2D strips and can contribute to dark counts observed in single photon detectors.
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Lusche, R., Semenov, A., Korneeva, Y., Trifonov, A., Korneev, A., Gol'tsman, G., et al. (2014). Effect of magnetic field on the photon detection in thin superconducting meander structures. Phys. Rev. B, 89(10), 104513 (1 to 7).
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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Gol’tsman, G. N. (2014). Overview of recent results for superconducting NbN terahertz and optical detectors and mixers.
Abstract: We present our recent achievements in the development of sensitive and ultrafast thin-film superconducting sensors: hot-electron bolometers (HEB), HEB-mixers for terahertz range and infrared single-photon counters. These sensors have already demonstrated a performance that makes them devices-of-choice for many terahertz and optical applications.
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Lusche, R., Semenov, A., Ilin, K., Siegel, M., Korneeva, Y., Trifonov, A., et al. (2014). Effect of the wire width on the intrinsic detection efficiency of superconducting-nanowire single-photon detectors. J. Appl. Phys., 116(4), 043906 (1 to 9).
Abstract: A thorough spectral study of the intrinsic single-photon detection efficiency in superconducting TaN and NbN nanowires with different widths has been performed. The experiment shows that the cut-off of the intrinsic detection efficiency at near-infrared wavelengths is most likely controlled by the local suppression of the barrier for vortex nucleation around the absorption site. Beyond the cut-off quasi-particle diffusion in combination with spontaneous, thermally activated vortex crossing explains the detection process. For both materials, the reciprocal cut-off wavelength scales linearly with the wire width where the scaling factor agrees with the hot-spot detection model.
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