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Ambegaokar-Baratoff relations for Josephson critical current in heterojunctions with multigap superconductors

多ギャップ超伝導体を用いたヘテロジョセフソン接合におけるAmbegaokar-Baratoff関係式

太田 幸宏; 中井 宣之; 中村 博樹  ; 町田 昌彦  ; 猪谷 大介*; 大橋 洋士*; 小山 富男*; 松本 秀樹*

Ota, Yukihiro; Nakai, Noriyuki; Nakamura, Hiroki; Machida, Masahiko; Inotani, Daisuke*; Ohashi, Yoji*; Koyama, Tomio*; Matsumoto, Hideki*

多重トンネル径路を有するSISジョセフソン接合に適用できるようAmbegaokar-Baratoff関係式を拡張した。この結果を鉄系超伝導体(5バンド超伝導体)と通常のBCS超伝導体(1バンド超伝導体)からなるヘテロジョセフソン接合に適用することで、$$I_{rm c}R_{rm n}$$が理論的な上限値に評価される。われわれは、こうした上限値が鉄系超伝導体のペア対称性を同定するうえで有用であることを明らかにした。すなわち、測定された$$I_{rm c}R_{rm n}$$がこの上限値より小さければ、鉄系超伝導体は$$pm s$$対称性と結論づけることができる。

An extension of the Ambegaokar-Baratoff relation to a superconductor-insulator-superconductor (SIS) Josephson junction with multiple tunneling channels is derived. Applying the resultant relation to a SIS Josephson junction formed by an iron-based (five-band) and a single-band Bardeen-Cooper-Schrieffer (BCS) type superconductors, a theoretical bound of the Josephson critical current ($$I_{rm c}$$) multiplied by the resistance of the junction ($$R_{rm n}$$) is given. We reveal that such a bound is useful for identifying the pairing symmetry of iron-pnictide superconductors. One finds that if a measured value of $$I_{rm c}R_{rm n}$$ is smaller than the bound then the symmetry is $$pm s$$-wave, and otherwise $$s$$-wave without any sign changes. In addition, we stress that temperature dependence of $$I_{rm c}R_{rm n}$$ is sensitive to the difference of the gap functions from the BCS type gap formula in the above heterojunction.

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パーセンタイル:74.77

分野:Materials Science, Multidisciplinary

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