Emergence and electrochemical control of Josephson effects in microfabricated single crystals of iron chalcogenide superconductors

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03547
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: Aoyama Gakuin University
• Principal Investigator: Kitano Haruhisa 青山学院大学, 理工学部, 教授 (00313164)
• Co-Investigator(Kenkyū-buntansha): 孫 悦 青山学院大学, 理工学部, 助教 (30824180)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 鉄カルコゲナイド / 対破壊電流密度 / ジョセフソン効果 / スピン軌道相互作用 / 電気化学

Outline of Final Research Achievements

Iron chalcogenide superconductors have minimal superconducting units and show various quantum-mechanical phenomena. We investigate the emergence and control of Josephson effects, intrinsic to this system, by using the microfabrication and electrochemical methods applied to high-quality single crystals.
We succeed in measuring the depairing current density, which determines the critical velocity of the superconducting Cooper pairs, by reducing the cross sectional area of narrow bridge devices and preventing the generation of flux quantum. Furthermore, we observe the dynamical enhancement of non-equilibrium Josephson current in the current-biased short bridge devices with the lateral area less than 1 squared micrometer. This suggests a possibility of the electrochemical adjustment of Josephson junction properties.

Free Research Field

物性物理、特に超伝導の基礎と応用

Academic Significance and Societal Importance of the Research Achievements

従来のジョセフソン効果の研究と応用は、銅酸化物系の固有ジョセフソン効果を除き、超伝導薄膜から作製される素子に限定されてきたが、本研究成果は、高品質単結晶への微細加工と電気化学処理により、ジョセフソン素子が作製できる可能性を示した。また、超伝導輸送電流の理論的限界値を与える対破壊電流密度も、ごく一部の薄膜試料に対する測定に限定されてきたが、本研究成果は高品質な単結晶試料に対して評価できることを実証した。今後、時間反転や空間反転などの対称性が破れた新奇超伝導状態における超伝導電子対の臨界速度を検証するための道が切り拓かれた。