Exploration for novel superconductivity in epitaxial thin films of iron chalcogenides

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K14651
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: The University of Tokyo
• Principal Investigator: Nabeshima Fuyuki 東京大学, 大学院総合文化研究科, 助教 (30782776)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: 鉄カルコゲナイド超伝導体 / 磁気輸送特性 / ミュオンスピン緩和 / 磁場侵入長 / 薄膜

Outline of Final Research Achievements

We found that carrier density and the superconducting transition temperature (Tc) have positive correlation from measurement of magneto-transport and magnetic penetration depth of thin films of FeSe1－xTexと FeSe1－ySy. Our results suggest that the different Tc behavior between Te- and S-substitution results from the fact that Te- and S-substitution affect Fermi surface, or carrier density, differently. This also suggests that the electronic nematicity and its fluctuations do not play the primary role on superconductivity in iron chalcogenides. Furthermore, we demonstrated for the first time that S substitution induce magnetic order in FeSe from muon spin relaxation measurements of thin films of FeSe1－ySy.

Free Research Field

超伝導

Academic Significance and Societal Importance of the Research Achievements

鉄カルコゲナイド超伝導体FeSeは超伝導転移温度Tcが低いものの，様々な方法でTcを大幅に上昇させることができ，さらなるTcの向上や実用化を目指し，超伝導メカニズム解明に向けて精力的に研究がなされている．FeSeは静水圧下でTcが4倍程度に増大するが，元素置換による格子の圧縮（化学圧力）ではTcの上昇は見られない．磁気的なゆらぎが超伝導の重要因子の一つだと考えられているが，本研究により，物理圧力と同様に化学圧力でも磁気秩序が誘起されることが明らかになった．今後この磁気秩序を詳しく調べることで物理圧力と化学圧力でのTcの違いを明らかにし，この物質のTc上昇のメカニズムを解明できる可能性がある．