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3 Aug 1998

Volume 73, Issue 5, pp. 557-700

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Terahertz NbN/AlN/NbN mixers with Al/SiO/NbN microstrip tuning circuits

Yoshinori Uzawa, Zhen Wang, and Akira Kawakami

Appl. Phys. Lett. 73, 680 (1998); http://dx.doi.org/10.1063/1.121946 (3 pages) | Cited 22 times

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We have developed a low-noise quasioptical NbN/AlN/NbN superconductor-insulator-superconductor (SIS) mixer that operates at terahertz frequencies. The mixer uses a MgO hyperhemispherical lens with an antireflection cap, a single-crystal NbN log-periodic antenna, and two-junction tuning circuits which employ Al/SiO/NbN microstriplines. The NbN/AlN/NbN junction size was about 0.9 μm in diameter, and the current density was about 45 kA/cm2. The frequency dependence of the receiver noise temperature was investigated by using an optically pumped far-infrared laser and a backward-wave oscillator as a local oscillator at several frequencies from 670 to 1082 GHz. The experimental results showed that the center frequency was around 800 GHz, and the receiver noise temperature measured by the standard Y-factor method was 457 K (DSB) at 783 GHz including a 9-μm-thick Mylar beam splitter loss and other optical losses at the physical bath temperature of 4.2 K. This is the first SIS mixer based on NbN with low-noise performance (12hν/kB) above the gap frequency of Nb. © 1998 American Institute of Physics.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
74.25.Sv Critical currents
74.40.-n Fluctuation phenomena

Properties of superconducting Nd1+xBa2−xCu3O7−δ thin films deposited by dc magnetron sputtering

M. Salluzzo, I. Maggio-Aprile, and Ø. Fischer

Appl. Phys. Lett. 73, 683 (1998); http://dx.doi.org/10.1063/1.121947 (3 pages) | Cited 20 times

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We report the superconducting properties of Nd1+xBa2−xCu3O7−δ thin films deposited by dc magnetron sputtering from stoichiometric Nd1Ba2Cu3O7−δ and off-stoichiometric Nd1.12Ba1.88Cu3O7−δ targets. Highly epitaxial c-axis oriented samples with thicknesses ranging from 5 to 100 nm were obtained on SrTiO3(100) substrates from both targets. A suppression of screw-dislocation mediated growth for off-stoichiometric films is observed by STM, resulting in smooth surfaces with roughness of 2–3 nm on a 1 μm2 area. The effects of the deposition conditions on the structural and superconducting properties are investigated and discussed in relation to the Nd–Ba substitution in the Nd1+xBa2−xCu3O7−δ system. © 1998 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.Nq Composition and phase identification
81.15.Cd Deposition by sputtering
61.66.Bi Elemental solids
61.66.Dk Alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)

Submillimeter-band high-power generation using multilayered Josephson junctions

A. V. Ustinov and S. Sakai

Appl. Phys. Lett. 73, 686 (1998); http://dx.doi.org/10.1063/1.121948 (3 pages) | Cited 33 times

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We report on numerical simulations of 10- and 19-layer stacked Josephson junctions. Simulations are performed using the experimentally feasible parameters for Nb/Al–AlOx/Nb junctions. With an appropriate choice of parameters such as magnetic field and coupling, the current–voltage curves of N-layer stacks systematically indicate in-phase locking among the inner N−2 junctions. The simulation results suggest that multilayer Josephson junctions are very promising as submillimeter-band high-power oscillators. © 1998 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
84.30.Ng Oscillators, pulse generators, and function generators
74.78.Fk Multilayers, superlattices, heterostructures
85.25.Am Superconducting device characterization, design, and modeling
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