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25 Jun 2012

Volume 100, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 100, 261104 (2012); http://dx.doi.org/10.1063/1.4711253 (4 pages)

Marcelo Davanço, Jun Rong Ong, Andrea Bahgat Shehata, Alberto Tosi, Imad Agha, Solomon Assefa, Fengnian Xia, William M. J. Green, Shayan Mookherjea, and Kartik Srinivasan
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Probing quasiparticle excitations in a hybrid single electron transistor

H. S. Knowles, V. F. Maisi, and J. P. Pekola

Appl. Phys. Lett. 100, 262601 (2012); http://dx.doi.org/10.1063/1.4730407 (4 pages)

Online Publication Date: 26 June 2012

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We investigate the behavior of quasiparticles in a hybrid electron turnstile with the aim of improving its performance as a metrological current source. The device is used to directly probe the density of quasiparticles and monitor their relaxation into normal metal traps. We compare different trap geometries and reach quasiparticle densities below 3 μm−3 for pumping frequencies of 20 MHz. Our data show that quasiparticles are excited both by the device operation itself and by the electromagnetic environment of the sample. Our observations can be modelled on a quantitative level with a sequential tunneling model and a simple diffusion equation.
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85.35.Gv Single electron devices

Superconductor-insulator transition controlled by annealing in Ga implanted Si

V. Heera, J. Fiedler, M. Voelskow, A. Mücklich, R. Skrotzki, T. Herrmannsdörfer, and W. Skorupa

Appl. Phys. Lett. 100, 262602 (2012); http://dx.doi.org/10.1063/1.4732081 (4 pages) | Cited 1 time

Online Publication Date: 27 June 2012

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Heavily Ga implanted Si nanolayers covered with a thin SiO2 layer exhibit a superconductor-insulator transition in dependence on annealing conditions. The transition characteristics resemble those of ultrathin quench-condensed metal films although the implanted layer differs clearly in composition, width, and nanostructure. This implies a general physical mechanism for the superconductor-insulator transition in thin, disordered layers which is supposed to be a quantum phase transition between dual states—the superconducting and the superinsulating one. There is a resistance criterion for the phase transition closely associated with a critical hole concentration.
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74.62.Yb Other effects
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
74.62.-c Transition temperature variations, phase diagrams

Spatially dependent sensitivity of superconducting meanders as single-photon detectors

G. R. Berdiyorov, M. V. Milošević, and F. M. Peeters

Appl. Phys. Lett. 100, 262603 (2012); http://dx.doi.org/10.1063/1.4731627 (4 pages) | Cited 2 times

Online Publication Date: 28 June 2012

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The photo-response of a thin current-carrying superconducting stripe with a 90° turn is studied within the time-dependent Ginzburg-Landau theory. We show that the photon acting near the inner corner (where the current density is maximal due to the current crowding [J. R. Clem and K. K. Berggren, Phys. Rev. B 84, 174510 (2011)]) triggers the nucleation of superconducting vortices at currents much smaller than the expected critical one, but does not bring the system to a higher resistive state and thus remains undetected. The transition to the resistive state occurs only when the photon hits the stripe away from the corner due to there uniform current distribution across the sample, and dissipation is due to the nucleation of a kinematic vortex-antivortex pair near the photon incidence. We propose strategies to account for this problem in the measurements.
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85.25.-j Superconducting devices

Monolithic high-temperature superconducting heterodyne Josephson frequency down-converter

J. Du, T. Zhang, J. C. Macfarlane, Y. J. Guo, and X. W. Sun

Appl. Phys. Lett. 100, 262604 (2012); http://dx.doi.org/10.1063/1.4731878 (4 pages) | Cited 1 time

Online Publication Date: 29 June 2012

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A monolithic microwave integrated circuit (MMIC) frequency down-converter based on a compact high-Tc superconducting (HTS) device is demonstrated. The on-chip integrated HTS down-converter consists of a 7–9 GHz bandpass filter for RF input, a lowpass filter for intermediate frequency output, and a self-pumped Josephson heterodyne mixer. All the above passive and active components are fabricated on a single 10 mm × 20 mm chip of YBa2Cu3O7−x film on MgO substrate. Characterization of this MMIC HTS down-converter in terms of frequency response, conversion gain, frequency-tuneability, bias dependence, dynamic range, linearity, and intrinsic noise are presented in this paper.
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85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
84.30.Vn Filters
84.40.Lj Microwave integrated electronics

Etch induced microwave losses in titanium nitride superconducting resonators

Martin Sandberg, Michael R. Vissers, Jeffrey S. Kline, Martin Weides, Jiansong Gao, David S. Wisbey, and David P. Pappas

Appl. Phys. Lett. 100, 262605 (2012); http://dx.doi.org/10.1063/1.4729623 (4 pages) | Cited 4 times

Online Publication Date: 29 June 2012

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We have investigated the correlation between the microwave loss and patterning method for coplanar waveguide titanium nitride resonators fabricated on silicon wafers. Three different methods were investigated: fluorine- and chlorine-based reactive ion etches and an argon-ion mill. At high microwave probe powers, the reactive etched resonators showed low internal loss, whereas the ion-milled samples showed dramatically higher loss. At single-photon powers, we found that the fluorine-etched resonators exhibited substantially lower loss than the chlorine-etched ones. We interpret the results by use of numerically calculated filling factors and find that the silicon surface exhibits a higher loss when chlorine-etched than when fluorine-etched. We also find from microscopy that re-deposition of silicon onto the photoresist and side walls is the probable cause for the high loss observed for the ion-milled resonators.
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85.25.Qc Superconducting surface acoustic wave devices and other superconducting devices
84.40.Az Waveguides, transmission lines, striplines
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