Study of pressure-temperature phase diagram of superconductivity competing with electronic nematic and magnetic ordered phases in iron-based superconductor

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03516
• 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: Shimane University
• Principal Investigator: Miyoshi Kiyotaka 島根大学, 学術研究院理工学系, 教授 (10294365)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 鉄系超伝導 / 高圧 / 圧力相図 / ダイヤモンドアンビルセル

Outline of Final Research Achievements

Superconductivity in FeSe has been investigated under high pressure through the measurements of DC magnetization by using a diamond anvil cell. We have successfully observed that the disappearance of the superconductivity originating from the appearance of the non-superconducting ortho II phase above 7 GPa (5 GPa), when Ar (glycerin) is used as the pressure transmitting media. In contrast, it has been found that the superconductivity survives under pressure even above 7 GPa, when the thickness (t) of a platelet single crystal specimen is reduced. The survival of the superconductivity above 7 GPa is consistent with a previous observation under hydrostatic pressure by using a cubic anvil apparatus, suggesting that the hydrostaticity of the pressure is improved by reducing t. It is also inferred that the appearance of the ortho II phase is due to the uniaxial stress along the [001] direction.

Free Research Field

低温物性

Academic Significance and Societal Importance of the Research Achievements

本研究では、ダイヤモンドアンビルセル（DAC）を用いてFeSe単結晶を加圧し、OrthoⅡ相の出現を起源とする超伝導の消失を観測し、逆に薄い単結晶試料を用いれば静水圧性が改善され消失しないことを示した。FeSeとその関連系の圧力相図は研究対象として大変魅力的であるが、おそらくはこの超伝導消失の問題があるため、これまでに5 GPa以上の高圧域における圧力下物性の研究はほとんどなされてこなかった。本研究で発見されたFeSeの高圧下超伝導の観測を可能にする測定条件は、このような状況を打開するために極めて重要な知見であると言える。今後のFeSe関連系の圧力相図の解明が急加速することを期待している。