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Ota, Yukihiro; Machida, Masahiko; Koyama, Tomio*
Journal of Physics; Conference Series, 248, p.012090_1 - 012090_8, 2010/11
Since the discovery of iron-based superconductors, Josephson junctions including such new materials have been intensively studied in order to explore their pairing symmetry and application potential. One of interesting features of this type of materials is the presence of multiple (more than two) bands on Fermi surface and their contributions to superconductivity. As a result, iron-based superconductor junctions are possible to have multiple tunneling channels between the superconducting electrodes. In this paper, we show a theory of Josephson junctions with multigap superconductors. We discuss how the relative fluctuations between multiple gaps and the pairing symmetry modify the Shapiro steps.
Machida, Masahiko; Ota, Yukihiro; Sasa, Narimasa; Koyama, Tomio*; Matsumoto, Hideki*
Journal of Physics; Conference Series, 248, p.012037_1 - 012037_8, 2010/11
Times Cited Count：9 Percentile：90.88(Nanoscience & Nanotechnology)no abstracts in English
Koyama, Tomio*; Ota, Yukihiro; Machida, Masahiko
Journal of Physics; Conference Series, 248, p.012036_1 - 012036_6, 2010/11
Times Cited Count：2 Percentile：61.94(Nanoscience & Nanotechnology)We develop a theory for the Josephson effects in 2-gap intrinsic Josephson junctions stacks (IJJs). The coupled dynamical equations for the phase differences are derived from the low-energy effective Lagrangian. The equations describe the longitudinal Josephson plasma and the Josephson-Leggett (JL) mode propagating in the direction perpendicular to the junctions. Numerical results for the 
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characteristics are presented. The - characteristics shows multiple-branch structures similar to that in Bi-2212 IJJ's. When the Josephson frequency is approached to the JL mode frequency in non-uniform voltage branches, the JL mode is resonantly exited. At the resonant voltage a step-like structure appears in the - curves in low-voltage branches.
