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Author Swetz, D. S.; Bennett, D. A.; Irwin, K. D.; Schmidt, D. R.; Ullom, J. N. doi  openurl
  Title Current distribution and transition width in superconducting transition-edge sensors Type Journal Article
  Year 2012 Publication (up) Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 101 Issue Pages 242603  
  Keywords  
  Abstract Present models of the superconducting-to-normal transition in transition-edge sensors (TESs) do not describe the current distribution within a biased TES. This distribution is complicated by normal-metal features that are integral to TES design. We present a model with one free parameter that describes the evolution of the current distribution with bias. To probe the current distribution experimentally, we fabricated TES devices with different current return geometries. Devices where the current return geometry mirrors current flow within the device have sharper transitions, thus allowing for a direct test of the current-flow model.Measurements from these devices show that current meanders through a TES low in the resistivetransition but flows across the normal-metal features by 40% of the normal-state resistance. Comparison of transition sharpness between device designs reveals that self-induced magnetic fields play an important role in determining the width of the superconducting transition.  
  Address TES, current distribution  
  Corporate Author Thesis  
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  Notes Recommended by Klapwijk Approved no  
  Call Number Serial 930  
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Author Miao, W.; Zhang, W.; Zhong, J. Q.; Shi, S. C.; Delorme, Y.; Lefevre, R.; Feret, A; Vacelet, T url  doi
openurl 
  Title Non-uniform absorption of terahertz radiation on superconducting hot electron bolometer microbridges Type Journal Article
  Year 2014 Publication (up) Appl. Phys. Lett. Abbreviated Journal <ef><bf><bc>Appl. Phys. Lett.  
  Volume 104 Issue Pages 052605(1-4)  
  Keywords NbN HEB mixers, local oscillator power, RF nonuniform absorption  
  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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  Notes Approved no  
  Call Number Serial 935  
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Author Ferrari, S.; Kahl, O.; Kovalyuk, V.; Goltsman, G. N.; Korneev, A.; Pernice, W. H. P. url  doi
openurl 
  Title Waveguide-integrated single- and multi-photon detection at telecom wavelengths using superconducting nanowires Type Journal Article
  Year 2015 Publication (up) Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 106 Issue 15 Pages 151101 (1 to 5)  
  Keywords SSPD, SNSPD  
  Abstract We investigate single- and multi-photon detection regimes of superconducting nanowire detectors embedded in silicon nitride nanophotonic circuits. At near-infrared wavelengths, simultaneous detection of up to three photons is observed for 120 nm wide nanowires biased far from the critical current, while narrow nanowires below 100 nm provide efficient single photon detection. A theoretical model is proposed to determine the different detection regimes and to calculate the corresponding internal quantum efficiency. The predicted saturation of the internal quantum efficiency in the single photon regime agrees well with plateau behavior observed at high bias currents.

W. H. P. Pernice acknowledges support by the DFG Grant Nos. PE 1832/1-1 and PE 1832/1-2 and the Helmholtz society through Grant No. HIRG-0005. The Ph.D. education of O. Kahl is embedded in the Karlsruhe School of Optics and Photonics (KSOP). G. N. Goltsman acknowledges support by Russian Federation President Grant HШ-1918.2014.2 and Ministry of Education and Science of the Russian Federation Contract No.: RFMEFI58614X0007. A. Korneev acknowledges support by Statement Task No. 3.1846.2014/k. V. Kovalyuk acknowledges support by Statement Task No. 2327. We also acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) and the State of Baden-Württemberg through the DFG-Center for Functional Nanostructures (CFN) within subproject A6.4. We thank S. Kühn and S. Diewald for the help with device fabrication as well as B. Voronov and A. Shishkin for help with NbN thin film deposition and A. Semenov for helpful discussion about the detection mechanism of nanowire SSPD's.

The authors declare no competing financial interests.
 
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  ISSN 0003-6951 ISBN Medium  
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  Notes Approved no  
  Call Number Serial 1211  
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Author Kardakova, A.; Finkel, M.; Morozov, D.; Kovalyuk, V.; An, P.; Dunscombe, C.; Tarkhov, M.; Mauskopf, P.; Klapwijk, T.M.; Goltsman, G. doi  openurl
  Title The electron-phonon relaxation time in thin superconducting titanium nitride films Type Journal Article
  Year 2013 Publication (up) Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 103 Issue 25 Pages 252602 (1 to 4)  
  Keywords disordered TiN films, electron-phonon relaxation time  
  Abstract We report on the direct measurement of the electron-phonon relaxation time, τeph, in disordered TiN films. Measured values of τeph are from 5.5 ns to 88 ns in the 4.2 to 1.7 K temperature range and consistent with a T−3 temperature dependence. The electronic density of states at the Fermi level N0 is estimated from measured material parameters. The presented results confirm that thin TiN films are promising candidate-materials for ultrasensitive superconducting detectors.

The work was supported by the Ministry of Education and Science of the Russian Federation, Contract No. 14.B25.31.0007 and by the RFBR Grant No. 13-02-91159.
 
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  Notes Approved no  
  Call Number RPLAB @ kovalyuk @ Serial 941  
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Author Floet D. W.; Gao J. R.; Klapwijk T. M.; de Korte P. A. J. url  doi
openurl 
  Title Bias Dependence of the Thermal Time Constant in Nb Superconducting Diffusion-Cooled HEB Mixers Type Journal Article
  Year 2000 Publication (up) Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 77 Issue Pages 1719  
  Keywords  
  Abstract We present an experimental study of the intermediate frequency bandwidth of a Nb diffusion-cooled hot-electron bolometer mixer for different bias voltages. The measurements show that the bandwidth increases with increasing voltage. Analysis of the data reveals that this effect is mainly caused by a decrease of the intrinsic thermal time of the mixer and that the effect of electrothermal feedback through the intermediate frequency circuit is small. The results are understood using a qualitative model, which takes into account the different effective diffusion constants in the normal and superconducting domains.  
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  Notes Approved no  
  Call Number RPLAB @ atomics90 @ Serial 971  
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