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10 Sep 2012

Volume 101, Issue 11, Articles (11xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 113302 (2012); http://dx.doi.org/10.1063/1.4749791 (4 pages)

Chang-Hoon Shim, Shuzo Hirata, Juro Oshima, Tomohiko Edura, Reiji Hattori, and Chihaya Adachi
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Sub-micron normal-metal/insulator/superconductor tunnel junction thermometer and cooler using Nb

M. R. Nevala, S. Chaudhuri, J. Halkosaari, J. T. Karvonen, and I. J. Maasilta

Appl. Phys. Lett. 101, 112601 (2012); http://dx.doi.org/10.1063/1.4751355 (4 pages) | Cited 1 time

Online Publication Date: 10 September 2012

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We have fabricated Cu/AlOx-Al/Nb normal-metal/insulator/superconductor tunnel junction devices with a high value of the superconducting gap (up to ∼ 1 mV), using electron-beam lithography and angle evaporation techniques in the sub-micron scale. The subgap conductance of these junctions shows the expected strong temperature dependence, rendering them suitable for thermometry all the way from 100 mK to 6 K. In addition, some direct electronic cooling of the normal metal was also seen at bias values near the gap edge. The device performance was strongly influenced by the details of the Al layer geometry, with lateral spilling of the aluminium giving rise to strong extra subgap features, and the thickness of Al layer affecting the proximised superconducting gap value of the superconducting Al/Nb bilayer.
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85.25.Am Superconducting device characterization, design, and modeling
07.20.Dt Thermometers

Proposal of terahertz patch antenna fed by intrinsic Josephson junctions

Hidehiro Asai, Masashi Tachiki, and Kazuo Kadowaki

Appl. Phys. Lett. 101, 112602 (2012); http://dx.doi.org/10.1063/1.4751846 (4 pages) | Cited 2 times

Online Publication Date: 11 September 2012

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We propose a THz patch antenna, in which THz ac current is fed by intrinsic Josephson junctions (IJJs). The radiation power of the antenna for three different feed positions is calculated using the finite-difference time-domain method. We predict that the antenna will radiate sub-milliwatt terahertz waves with high radiation efficiency of over 20%. The maximum radiation power will depend on the position of the feed. We also show that the radiation characteristics of the antenna are described well by the equivalent inductance-capacitance-resistance circuit model.
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84.40.Ba Antennas: theory, components and accessories
85.25.Cp Josephson devices
02.70.Bf Finite-difference methods

Superconducting detector dynamics studied by quantum pump-probe spectroscopy

Reinier W. Heeres and Valery Zwiller

Appl. Phys. Lett. 101, 112603 (2012); http://dx.doi.org/10.1063/1.4750139 (4 pages) | Cited 1 time

Online Publication Date: 11 September 2012

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We explore the dynamics of superconducting single-photon detectors (SSPDs) on the picosecond time-scale using a correlated photon-pair source based on spontaneous parametric downconversion (SPDC), corresponding to a pump-probe experiment at the single-photon level. We show that the detector can operate in a regime where the two-photon detection probability is orders of magnitude larger than the single-photon detection probability. The characteristic relaxation time-scale of the out-of-equilibrium hot-spot is found to be ∼ 15 ps. Our measurement technique is an effective tool to study fast two-photon processes, without requiring a power-dependence measurements to determine the number of photons involved.
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85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Evaluation of vortex pinning across low angle grain boundary in YBa2Cu3O7 film

Tomoya Horide and Kaname Matsumoto

Appl. Phys. Lett. 101, 112604 (2012); http://dx.doi.org/10.1063/1.4752462 (4 pages)

Online Publication Date: 13 September 2012

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Vortex pinning potential across a 5° tilt low angle grain boundary (GB) was evaluated by measuring angular dependences of critical current density in a bicrystal YBa2Cu3O7 film under the variable Lorentz force configuration. Trapping angles of the GB depend on directions in the GB plane (70°–80° and 15°–45° for the c-axis direction and the ab plane one, respectively), due to anisotropic pinning of GB dislocations. Pinning potential across a GB is as large as that of heavy ion irradiated columnar defects, indicating that density and distribution of GBs should be controlled to improve vortex pinning in coated conductors.
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74.25.Wx Vortex pinning (includes mechanisms and flux creep)
61.72.Mm Grain and twin boundaries
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.80.Jh Ion radiation effects
74.78.-w Superconducting films and low-dimensional structures
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