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Author Kitaygorsky, Jennifer; Komissarov, I.; Jukna, A.; Minaeva, O.; Kaurova, N.; Divochiy, A.; Korneev, A.; Tarkhov, M.; Voronov, B.; Milostnaya, I.; Gol'tsman, G.; Sobolewski, R. url  openurl
  Title Fluctuations in two-dimensional superconducting NbN nanobridges and nanostructures meanders Type Abstract
  Year 2007 Publication Proc. APS March Meeting Abbreviated Journal Proc. APS March Meeting  
  Volume 52 Issue 1 Pages L9.00013  
  Keywords  
  Abstract (up) We have observed fluctuations, manifested as sub-nanosecond to nanosecond transient, millivolt-amplitude voltage pulses, generated in two-dimensional NbN nanobridges, as well as in extended superconducting meander nanostructures, designed for single photon counting. Both nanobridges and nano-stripe meanders were biased at currents close to the critical current and measured in a range of temperatures from 1.5 to 8 K. During the tests, the devices were blocked from all incoming radiation by a metallic enclosure and shielded from any external magnetic fields. We attribute the observed spontaneous voltage pulses to the Kosterlitz-Thouless-type fluctuations, where the high enough applied bias current reduces the binding energy of vortex-antivortex pairs and, subsequently, thermal fluctuations break them apart causing the order parameter to momentarily reduce to zero, which in turn causes a transient voltage pulse. The duration of the voltage pulses depended on the device geometry (with the high-kinetic inductance meander structures having longer, nanosecond, pulses) while their rate was directly related to the biasing current as well as temperature.  
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  Call Number Serial 1027  
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Author Ejrnaes, M.; Cristiano, R.; Quaranta, O.; Pagano, S.; Gaggero, A.; Mattioli, F.; Leoni, R.; Voronov, B.; Gol’tsman, G. url  doi
openurl 
  Title A cascade switching superconducting single photon detector Type Journal Article
  Year 2007 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 91 Issue 26 Pages 262509 (1 to 3)  
  Keywords SSPD, SNSPD, parallel-wire  
  Abstract (up) We have realized superconducting single photon detectors with reduced inductance and increased signal pulse amplitude. The detectors are based on a parallel connection of ultrathin NbN nanowires with a common bias inductance. When properly biased, an absorbed photon induces a cascade switch of all the parallel wires generating a signal pulse amplitude of 2mV. The parallel wire configuration lowers the detector inductance and reduces the response time well below 1ns.

This work was performed in the framework of the EU project “SINPHONIA” NMP4-CT-2005-016433.
 
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  Series Volume Series Issue Edition  
  ISSN 0003-6951 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1418  
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Author Khosropanah, P.; Gao, J. R.; Laauwen, W. M.; Hajenius, M; Klapwijk, T. M. openurl 
  Title Low noise NbN hot electron bolometer mixer at 4.3 THz Type Journal Article
  Year 2007 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.  
  Volume 91 Issue Pages 221111 (1 to 3)  
  Keywords NbN HEB mixers, NbN, contacts cleaning  
  Abstract (up) We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times the quantum noise (hnu/2kB). Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.  
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  Notes Approved no  
  Call Number Serial 584  
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Author Gao, J. R.; Hajenius, M.; Yang, Z. Q.; Baselmans, J. J. A.; Khosropanah, P.; Barends, R.; Klapwijk, T. M. url  doi
openurl 
  Title Terahertz superconducting hot electron bolometer heterodyne receivers Type Journal Article
  Year 2007 Publication IEEE Trans. Appl. Supercond. Abbreviated Journal  
  Volume 17 Issue 2 Pages 252-258  
  Keywords HEB, mixer, direct detection effect  
  Abstract (up) We highlight the progress on NbN hot electron bolometer (HEB) mixers achieved through fruitful collaboration between SRON Netherlands Institute for Space Research and Delft University of Technology, the Netherlands. This includes the best receiver noise temperatures of 700 K at 1.63 THz using a twin-slot antenna mixer and 1050 K at 2.84 THz using a spiral antenna coupled HEB mixer. The mixers are based on thin NbN films on Si and fabricated with a new contact-process and-structure. By reducing their areas HEB mixers have shown an LO power requirement as low as 30 nW. Those small HEB mixers have demonstrated equivalent sensitivity as those with large areas provided the direct detection effect due to broadband radiation is removed. To manifest that a HEB based heterodyne receiver can in practice be used at arbitrary frequencies above 2 THz, we demonstrate a 2.8 THz receiver using a THz quantum cascade laser (QCL) as local oscillator.  
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  ISSN 1051-8223 ISBN Medium  
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  Notes Approved no  
  Call Number RPLAB @ asmirn @ Serial 557  
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Author Bell, M.; Sergeev, A.; Mitin, V.; Bird, J.; Verevkin, A.; Gol'tsman, G. openurl 
  Title One-dimensional resistive states in quasi-two-dimensional superconductors Type Journal Article
  Year 2007 Publication arXiv:0709.0709v1 [cond-mat.supr-con] Abbreviated Journal  
  Volume Issue Pages 1-11  
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  Abstract (up) 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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  Notes Approved no  
  Call Number RPLAB @ atomics90 @ Serial 948  
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