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Author 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 (up) 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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  Notes Approved no  
  Call Number Serial 898  
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Author Romijn, J.; Klapwijk, T. M.; Renne, M. J.; Mooij, J. E. doi  openurl
  Title Critical pair-breaking current in superconducting aluminum strips far below Tc Type Journal Article
  Year 1982 Publication (up) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 26 Issue 7 Pages 3648-3655  
  Keywords superconducting nanowire  
  Abstract Critical currents of narrow, thin aluminum strips have been measured as a function of temperature. For the smallest samples uniformity of the current density is obtained over a large temperature range. Hence the intrinsic limit on the currentcarrying capacity of the superconductor was measured outside the Ginzburg-Landau -regime. The experimental values are compared with recent theoretical predictions by Kupriyanov and Lukichev. An approximate method of solving their equations is given, the results of which agree with the exact solution to within 1%. Experimental data are in excellent agreement with theoretical predictions. The absolute values agree if one assumes a ρl value of 4×10–16 Ωm2 with vF=1.3×106 m/s. This value for ρl is the same as that found from measurements of the anomalous skin effect but differs from values extracted from size-effect-limited resistivity.  
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  ISSN ISBN Medium  
  Area Expedition Conference  
  Notes Recommended by Klapwijk Approved no  
  Call Number Serial 925  
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Author Heslinga, D. R.; Shafranjuk, S. E.; van Kempen, H.; Klapwijk, T. M. url  doi
openurl 
  Title Observation of double-gap-edge Andreev reflection at Si/Nb interfaces by point-contact spectroscopy Type Journal Article
  Year 1994 Publication (up) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 49 Issue 15 Pages 10484-10494  
  Keywords Nb, Si, Nb-Si, Nb/Si, Si/Nb, Andreev reflection, point-contact spectroscopy  
  Abstract Andreev reflection point-contact spectroscopy is performed on a bilayer consisting of 50-nm degenerately doped Si backed with Nb. Due to the short mean free path both injection into and transport across the Si layer are diffusive, in contrast to the ballistic conditions prevailing in clean metal layers. Nevertheless a large Andreev signal is observed in the point-contact characteristics, not reduced by elastic scattering in the Si layer or by interface scattering, but only limited by the transmission coefficient of the metal-semiconductor point contact. Two peaks in the Andreev reflection probability are visible, marking the values of the superconducting energy gap at the interface on the Nb and Si sides. This interpretation is supported by a method of solving the Bogolubov equations analytically using a simplified expression for the variation of the order parameter close to the interface. This observation enables a comparison with theoretical predictions of the gap discontinuity in the proximity effect. It is found that the widely used de Gennes model does not agree with the experimental data.  
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  Publisher American Physical Society Place of Publication Editor  
  Language Summary Language Original Title  
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  ISSN ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1005  
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Author Coumou, P. C. J. J.; Driessen, E. F. C.; Bueno, J.; Chapelier, C.; Klapwijk, T. M. url  doi
openurl 
  Title Electrodynamic response and local tunneling spectroscopy of strongly disordered superconducting TiN films Type Journal Article
  Year 2013 Publication (up) Phys. Rev. B Abbreviated Journal  
  Volume 88 Issue 18 Pages 180505 (1 to 5)  
  Keywords strongly disordered superconducting TiN films, microwave resonators  
  Abstract We have studied the electrodynamic response of strongly disordered superconducting TiN films using microwave resonators, where the disordered superconductor is the resonating element in a high-quality superconducting environment of NbTiN. We describe the response assuming an effective pair-breaking mechanism modifying the density of states and compare this to local tunneling spectra obtained using scanning tunneling spectroscopy. For the least disordered film (kFl=8.7, Rs=13Ω), we find good agreement, whereas for the most disordered film (kFl=0.82, Rs=4.3kΩ), there is a strong discrepancy, which signals the breakdown of a model based on uniform properties.  
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  Notes Approved no  
  Call Number Serial 1069  
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Author Kardakova, A.; Shishkin, A.; Semenov, A.; Goltsman, G. N.; Ryabchun, S.; Klapwijk, T. M.; Bousquet, J.; Eon, D.; Sacépé, B.; Klein, T.; Bustarret, E. url  doi
openurl 
  Title Relaxation of the resistive superconducting state in boron-doped diamond films Type Journal Article
  Year 2016 Publication (up) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 93 Issue 6 Pages 064506  
  Keywords boron-doped diamond films, resistive superconducting state, relaxation time  
  Abstract We report a study of the relaxation time of the restoration of the resistive superconducting state in single crystalline boron-doped diamond using amplitude-modulated absorption of (sub-)THz radiation (AMAR). The films grown on an insulating diamond substrate have a low carrier density of about 2.5×1021cm−3 and a critical temperature of about 2K. By changing the modulation frequency we find a high-frequency rolloff which we associate with the characteristic time of energy relaxation between the electron and the phonon systems or the relaxation time for nonequilibrium superconductivity. Our main result is that the electron-phonon scattering time varies clearly as T−2, over the accessible temperature range of 1.7 to 2.2 K. In addition, we find, upon approaching the critical temperature Tc, evidence for an increasing relaxation time on both sides of Tc.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 2469-9950 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1167  
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Author Peltonen, J. T.; Astafiev, O. V.; Korneeva, Y. P.; Voronov, B. M.; Korneev, A. A.; Charaev, I. M.; Semenov, A. V.; Golt'sman, G. N.; Ioffe, L. B.; Klapwijk, T. M.; Tsai, J. S. url  doi
openurl 
  Title Coherent flux tunneling through NbN nanowires Type Journal Article
  Year 2013 Publication (up) Phys. Rev. B Abbreviated Journal Phys. Rev. B  
  Volume 88 Issue 22 Pages 220506 (1 to 5)  
  Keywords NbN nanowires  
  Abstract We demonstrate evidence of coherent magnetic flux tunneling through superconducting nanowires patterned in a thin highly disordered NbN film. The phenomenon is revealed as a superposition of flux states in a fully metallic superconducting loop with the nanowire acting as an effective tunnel barrier for the magnetic flux, and reproducibly observed in different wires. The flux superposition achieved in the fully metallic NbN rings proves the universality of the phenomenon previously reported for InOx. We perform microwave spectroscopy and study the tunneling amplitude as a function of the wire width, compare the experimental results with theories, and estimate the parameters for existing theoretical models.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1098-0121 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1369  
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Author Hajenius, M.; Baselmans, J. J. A.; Gao, J. R.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol’tsman, G. url  openurl
  Title Improved NbN phonon cooled hot electron bolometer mixers Type Conference Article
  Year 2003 Publication (up) Proc. 14th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 14th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 413-423  
  Keywords NbN HEB mixers  
  Abstract NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized with negligible contact resistance to Au pads. By adding either a 5 nm Nb or a 10 nm NbTiN layer between the Au and NbN, to preserve superconductivity in the NbN under the Au contact pad, superior noise temperatures have been obtained. Using DC I,V curves and resistive transitions in combination with process parameters we analyze the nature of these improved devices and determine interface transparencies.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Tucson, USA Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
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  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 337  
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Author Baselmans, J. J. A.; Hajenius, M.; Gao, J. R.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol'tsman, G. url  openurl
  Title Noise performance of NbN hot electron bolometer mixers at 2.5 THz and its dependence on the contact resistance Type Conference Article
  Year 2003 Publication (up) Proc. 14th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 14th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 11-19  
  Keywords NbN HEB mixers  
  Abstract NbN hot electron bolometer mixers (HEBM) are at this moment the best heterodyne receivers for frequencies above 1 Thz. However, the fabrication procedure of these devices is such that the quality of the interface between the NbN superconducting film and the contact structure is not under good control. The result is a low transparency interface between the bolometer itself and the contact/antenna structure. In this paper we report a detailed experimental study on a novel idea to increase the transparency of this interface. This leads to a record sensitivity and more reproducible performance. We compare identical bolometers, coupled with a spiral antenna, with different NbN bolometer-contact pad interfaces. We find that cleaning the NbN interface alone results in an increase in the noise temperature. However, cleaning the NbN interface and adding a thin additional superconductor prior to the gold contact deposition improves the noise temperature of the HEBm with more than a factor of 2. A device with a contact pad on top of an in-situ cleaned NbN film consisting of 10 nm of NbTiN and 40 nm of gold has a DSB noise temperature of 1050 K at 2.5 THz.  
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  Notes Approved no  
  Call Number Serial 1497  
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Author Baselmans, J. J. A.; Hajenius, M.; Gao, J. R.; Baryshev, A.; Kooi, J.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol’tsman, G. url  openurl
  Title Hot electron bolometer mixers with improved interfaces: sensitivity, LO power and stability Type Conference Article
  Year 2004 Publication (up) Proc. 15th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 15th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 17-24  
  Keywords NbN HEB mixers  
  Abstract We study twin slot antenna coupled NbN hot electron bolometer mixers with an improved contact structure and a small volume, ranging from 1 µm × 0.1 µm to 2 × 0.3 µm. We obtain a DSB receiver noise temperature of 900 K at 1.6 THz and 940 K at 1.9 THz. To explore the practical usability of such small HEB mixers we evaluate the LO power requirement, the sensitivity and the stability. We find that the LO power requirement of the smallest mixers is reduced to about 240 nW at the Si lens of the mixer. This value is larger than expected from the isothermal technique and the known losses in the lens by a factor of 3-3.5. The stability of these receivers is characterized using a measurement of the Allan Variance. We find an Allan time of 0.5 sec. in an 80 MHz bandwidth. A small increase in stability can be reached by using a higher bias at the expense of a significant amount of sensitivity. The stability is sufficient for spectroscopic applications in a 1 MHz bandwidth at a 1 Hz chopping frequency.  
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  Notes Approved no  
  Call Number Serial 1491  
Permanent link to this record
 
 
Author Hajenius, M.; Baselmans, J. J. A.; Gao, J. R.; Klapwijk, T. M.; de Korte 2, P. A. J.; Voronov, B.; Gol’tsman, G. url  openurl
  Title Increased bandwidth of NbN phonon cooled hot electron bolometer mixers Type Conference Article
  Year 2004 Publication (up) Proc. 15th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 15th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 381-386  
  Keywords NbN HEB mixers, IF bandwidth  
  Abstract We study experimentally the IF gain bandwidth of NbN phonon-cooled hot-electron-bolometer (HEB) mixers for a set of devices with different contact structures but an identical NbN film. We observe that the IF bandwidth depends strongly on the exact contact structure and find an IF gain bandwidth of 6 GHz for a device with an additional superconducting layer (NbTiN) in between the active NbN film and the gold contact to the antenna. These results contradict the common opinion that the IF bandwidth is determined by the phonon-escape time between the NbN film and the substrate. Hence we calculate the IF gain bandwidth of a superconducting film using a two-temperature model. We find that the bandwidth increases strongly with operating temperature and is not limited by the phonon escape time. This is because of strong temperature dependence of the phonon specific heat in the NbN film.  
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  ISSN ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1494  
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