Valence-skip mechanism of superconductivity in doped Dirac electron system

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03540
• 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: Okayama University
• Principal Investigator: Kobayashi Kaya 岡山大学, 異分野基礎科学研究所, 准教授 (60424090)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: バレンススキップ超伝導 / 超伝導 / ディラック物質

Outline of Final Research Achievements

We study cubic superconductor Ag1-xSn1+xSe2 for its possible Dirac electrons in superconductivity and for its uniqueness being a valence skipping superconductor candidate. The synthesis of single crystals and polycrystalline crystals of wide variety are performed and confirmed that superconducting transition temperatures, Tcs, vary depending on the ratio between Ag and Sn. Due to the discontinuous valence state changes of Sn, 2+ and 4+, charge dispropornation in spatial forms is expected. It is also expected to have two distinct Sn-Se distances, however, the observed electronic states in nuclear magnetic resonance (NMR) show only one state, while distinct two states observed in X-ray photoemission spectroscopy (XPS). The contradicting results suggests the valence skipping behavior in the superconductivity depend on the timescale and the two valence states overlap and distributed uniformly.

Free Research Field

超伝導物性

Academic Significance and Societal Importance of the Research Achievements

今回得られた結果は強相関系で実現するバレンススキップ超伝導に関して初めて実験的にバレンススキップを確認することが出来たなど、バレンススキップ超伝導に関して得られた重要な結果である。また、これまで考えられてきたような、空間的に局在した電子が動き出す描像ではなく、電子は一見金属的に見えるもののスナップショット的な測定を行うことによって分裂した状態の重ね合わせとみることもできるなど、超伝導発現に関して新しい局面をもたらすものであると考えられる。