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Author (down) Zolotov, P. I.; Semenov, A. V.; Divochiy, A. V.; Goltsman, G. N.; Romanov, N. R.; Klapwijk, T. M. url  doi
openurl 
  Title Dependence of photon detection efficiency on normal-state sheet resistance in marginally superconducting films of NbN Type Journal Article
  Year 2021 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal IEEE Trans. Appl. Supercond.  
  Volume 31 Issue 5 Pages 1-5  
  Keywords NbN SSPD, SNSPD  
  Abstract We present an extensive set of data on nanowire-type superconducting single-photon detectors based on niobium-nitride (NbN) to establish the empirical correlation between performance and the normal-state resistance per square. We focus, in particular, on the bias current, compared to the expected depairing current, needed to achieve a near-unity detection efficiency for photon detection. The data are discussed within the context of a model in which the photon energy triggers the movement of vortices i.e. superconducting dissipation, followed by thermal runaway. Since the model is based on the non-equilibrium theory for conventional superconductors deviations may occur, because the efficient regime is found when NbN acts as a marginal superconductor in which long-range phase coherence is frustrated.  
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  Series Volume Series Issue Edition  
  ISSN 1051-8223 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1222  
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Author (down) Zhang, W.; Khosropanah, P.; Gao, J. R.; Kollberg, E. L.; Yngvesson, K. S.; Bansal, T.; Barends, R.; Klapwijk, T. M. openurl 
  Title Quantum noise in a terahertz hot electron bolometer mixer Type Journal Article
  Year 2010 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.  
  Volume 96 Issue 11 Pages 111113-(1-3)  
  Keywords HEB mixer, quantum limit, quantum noise, vacuum box, THz, Terahertz  
  Abstract We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model for HEB mixers, we confirm the effect of QN. The QN is found to be responsible for about half of the receiver noise at the highest frequency in our measurements. The beta-factor (the quantum efficiency of the HEB) obtained experimentally agrees reasonably well with the calculated value.  
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  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 624  
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Author (down) Yang, Z. Q.; Hajenius, M.; Baselmans, J. J. A.; Gao, J.R.; Klapwijk, T. M.; Voronov, B.; Gol’tsman, G. url  openurl
  Title Improved sensitivity of NbN hot electron bolometer mixers by vacuum baking Type Conference Article
  Year 2005 Publication Proc. 16th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 16th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 222-225  
  Keywords NbN HEB mixer  
  Abstract We find that the sensitivity of heterodyne receivers based on superconducting hot-electron bolometer (HEB) in- creases by 25 − 30% after baking at 85 o C and in a high vacuum. The devices studied are twin-slot antenna coupled HEB mixers with a small NbN bridge of 1×0.15 μm 2 . The mixer noise temperature, gain, and resistance versus temperature curve of a HEB before and after baking are compared and analyzed. We show that baking reduces the intrinsic noise of the mixer by 37 % and makes the superconducting transition of the bridge and the contacts sharper. We argue that the reduction of the noise is due to the improvement of the transparency of the contact/film interface. The lowest receiver noise temperature of 700 K is measured at a local oscillator frequency of 1.63 THz and a bath temperature of 4.3 K.  
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  ISSN ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1471  
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Author (down) Yang, Y.; Fedorov, G.; Shafranjuk, S. E.; Klapwijk, T. M.; Cooper, B. K.; Lewis, R. M.; Lobb, C. J.; Barbara, P. url  doi
openurl 
  Title Electronic transport and possible superconductivity at Van Hove singularities in carbon nanotubes Type Journal Article
  Year 2015 Publication Nano Lett. Abbreviated Journal Nano Lett.  
  Volume 15 Issue 12 Pages 7859-7866  
  Keywords carbon nanotubes, CNT, tunable superconductivity, van Hove singularities  
  Abstract Van Hove singularities (VHSs) are a hallmark of reduced dimensionality, leading to a divergent density of states in one and two dimensions and predictions of new electronic properties when the Fermi energy is close to these divergences. In carbon nanotubes, VHSs mark the onset of new subbands. They are elusive in standard electronic transport characterization measurements because they do not typically appear as notable features and therefore their effect on the nanotube conductance is largely unexplored. Here we report conductance measurements of carbon nanotubes where VHSs are clearly revealed by interference patterns of the electronic wave functions, showing both a sharp increase of quantum capacitance, and a sharp reduction of energy level spacing, consistent with an upsurge of density of states. At VHSs, we also measure an anomalous increase of conductance below a temperature of about 30 K. We argue that this transport feature is consistent with the formation of Cooper pairs in the nanotube.  
  Address Department of Physics, Georgetown University , Washington, District of Columbia 20057, United States  
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  ISSN 1530-6984 ISBN Medium  
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  Notes PMID:26506109; Suuplementary info (attached to pdf) DOI: 10.1021/acs.nanolett.5b02564 Approved no  
  Call Number Serial 1782  
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Author (down) Vercruyssen, N.; Verhagen, T. G. A.; Flokstra, M. G.; Pekola, J. P.; Klapwijk, T. M. openurl 
  Title Evanescent states and nonequilibrium in driven superconducting nanowires Type Journal Article
  Year 2012 Publication Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 85 Issue Pages 224503(1-10)  
  Keywords Al HEB, Al superconducting nanowire, global state, bimodal state, quasiclassical kinetic equations, Usadel equation  
  Abstract We study the nonlinear response of current transport in a superconducting diffusive nanowire between normal reservoirs. We demonstrate theoretically and experimentally the existence of two different superconducting states appearing when the wire is driven out of equilibrium by an applied bias, called the global and bimodal superconducting states. The different states are identified by using two-probe measurements of the wire, and measurements of the local density of states with tunneling probes. The analysis is performed within the framework of the quasiclassical kinetic equations for diffusive superconductors.  
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  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 898  
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