著者

Asai Hidehiro Tachiki Masashi Kadowaki Kazuo

出版者

Elsevier

雑誌

Physica. C, Superconductivity and its applications (ISSN:09214534)

巻号頁・発行日

vol.491, pp.35-39, 2013-08

被引用文献数

2 1

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In this study, we investigate numerically the terahertz radiation from the mesa-structured intrinsic Josephson junctions (IJJs). The Sine–Gordon equation for inside of the mesa, and the Maxwell equation for outside of the mesa, are solved simultaneously. We consider the influence of a hot spot in the mesa where jc locally decreases, and calculate the radiation power as a function of the voltage. We observe strong radiation when the ac Josephson frequency satisfies the cavity resonance condition. For this strong radiation from the IJJs mesa, we calculate the radiation patterns. The radiation patterns reflect the existence of two types of internal modes: a uniform background mode and a cavity resonance mode. Furthermore, the radiation patterns are strongly affected by the diffraction at substrate edges.

著者

Klemm Richard A. Delfanazari Kaveh Tsujimoto Manabu Kashiwagi Takanari Kitamura Takeo Yamamoto Takashi Sawamura Masashi Ishida Kazuya Hattori Toshiaki Kadowaki Kazuo

出版者

Elsevier

雑誌

Physica. C, Superconductivity and its applications (ISSN:09214534)

巻号頁・発行日

vol.491, pp.30-34, 2013-08

被引用文献数

19 3

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In order to understand the radiation observed from the intrinsic Josephson junctions in triangular Bi2Sr2CaCu2O8+δ mesas, we calculate the transverse magnetic (TM) electromagnetic modes for thin equilateral cavities. A new set of distinct but degenerate TM modes coexists with the known modes of Helszajn and James, but are expected to lead to distinct radiation angular distribution patterns. Although we have been unable to solve for the exact TM modes of a thin cavity of general acute isosceles triangular shape, we solved exactly the closely related problems of the TM cavity modes of two thin circumscribing “pie-shaped” wedges, which provide highly accurate approximations to very acute isosceles triangular cavities.

著者

Klemm Richard A Kadowaki Kazuo

出版者

IOP Publishing

雑誌

Journal of physics. Condensed matter (ISSN:09538984)

巻号頁・発行日

vol.22, no.37, pp.375701, 2010-08

被引用文献数

74 36

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The angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a dc voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions is calculated. The boundary conditions are obtained from Love's equivalence principles. During coherent emission, a spatially uniform ac Josephson current density in the stack acts as a surface electric current density antenna source, leading to a harmonic radiation frequency spectrum, as in experiment, but absent in all cavity models of cylindrical mesas. Spatial fluctuations of the ac Josephson current allow its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization for general radiation directions, which may be fully or partially coherent. The higher ac Josephson harmonics do not excite other cylindrical cavity modes. For rectangular mesas, the lowest energy modes are empirically not excited, but the non-uniform ac Josephson current can excite the harmonic sequence of modes with spatial variation across the rectangular widths, leading to combined radiation outputs both for the fundamental and the higher harmonics, which combinations also may be either fully or partially coherent. The superconducting substrate is modeled as a perfect magnetic conductor, greatly reducing the STAR emitter power and modifying its angular dependence, especially parallel to the substrate. Based upon this substrate model, existing Bi2Sr2CaCu2O8 + δ crystals atop perfect electric conductors could have STAR emitter power in excess of 5 mW, acceptable for many device applications.

著者

Leiner Johannes Saleem Sajid Fenton J. C. Yamamoto Takashi Kadowaki Kazuo Warburton P. A.

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.95, no.25, pp.252505, 2009-12

被引用文献数

2 2

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We have measured the response of an array of Bi2Sr2CaCu2O8+delta intrinsic Josephson junctions to irradiation at 3 GHz. By measuring the dependence of the switching current upon the radio-frequency current for five of the junctions in the array we show quantitatively that the junctions have identical impedances at 3 GHz, this impedance being given by the inverse of the slope of the current-voltage characteristics.

著者

Das Pradip Suzuki Yusuke Tachiki Masashi Kadowaki Kazuo

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.83, no.22, pp.220513, 2011-06

被引用文献数

44

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We report on the observation of bulk superconductivity from dc magnetization measurements in a cylindrical single crystal of CuxBi2Se3. The magnitude of the magnetization in the Meissner state is very small, and the magnetic-field dependence of the magnetization just above the lower critical field Hc1 is very different from those of usual type-II superconductors. We studied the character of the vortex state theoretically in a spin-triplet pairing superconductor and compared it with the experimental results. The results showed that the superconductivity observed in CuxBi2Se3 is consistent with the spin-triplet pairing superconductivity with odd parity. We also observed a rapid relaxation phenomenon of the superconducting diamagnetism.

著者

Asai Hidehiro Tachiki Masashi Kadowaki Kazuo

出版者

American Physical Society

雑誌

Physical review B (ISSN:10980121)

巻号頁・発行日

vol.85, no.6, pp.064521, 2012-02

被引用文献数

42 18

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In this study, we numerically investigate the terahertz radiation from mesa-structured intrinsic Josephson junctions (IJJs) using a three-dimensional calculation model. We assume an in-phase mode of the phase differences and calculate electromagnetic fields inside and outside of the IJJs simultaneously. We consider the appearance of a hot spot in the mesa where jc locally decreases and investigate the change of the radiation power with varying hot-spot positions. The radiation powers for three different hot-spot positions are calculated as functions of voltage. We observe strong radiation when the ac Josephson frequency satisfies the cavity resonance condition. Transverse-magnetic modes TMm,n whose indices m and n are even appear regardless of the positions of hot spots. Meanwhile, the TMm,n cavity modes whose m or n are odd appear only when the hot spots break the reflectional symmetry of the mesa structure. Moreover, we calculate the radiation patterns emitted by the IJJs at these cavity resonance conditions. The radiation patterns reflect the existence of two types of internal modes, that is, a uniform background mode and a cavity resonance mode.

著者

Asai Hidehiro Tachiki Masashi Kadowaki Kazuo

出版者

American Institute of Physics

雑誌

Applied physics letters (ISSN:00036951)

巻号頁・発行日

vol.101, no.11, pp.112602, 2012-09

被引用文献数

23

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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.