Angle-resolved photoemission microspectroscopy of oxygen-controlled ruthenium oxides

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K03842
• 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: Kurume Institute of Technology
• Principal Investigator: Ino Akihiro 久留米工業大学, 工学部, 教授 (60363040)
• Co-Investigator(Kenkyū-buntansha): 岩澤 英明 国立研究開発法人量子科学技術研究開発機構, 関西光科学研究所 放射光科学研究センター, 上席研究員 (90514068)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: モット絶縁体 / 遷移金属酸化物 / フェルミ面 / 光電子分光

Outline of Final Research Achievements

In order to elucidate the electronic structure responsible for the metal-insulator transition in layered ruthenium oxide Ca2RuO4, we have conducted research and development based on three main schemes: angle-resolved photoelectron "micro" spectroscopy, growth of high-quality single crystals, and metallization by controlling oxygen amount. Our direct observation has revealed that the introduction of a small amount of excess oxygen into the Mott insulator, Ca2RuO4, brings about a dramatic change in the energy distribution of the electronic state on the eV scale, and results in the emergence of two square-shaped sheets of Fermi surface. This indicates that the band-selective Mott transition occurs with introducing excess oxygen.

Free Research Field

物性物理学

Academic Significance and Societal Importance of the Research Achievements

層状ルテニウム酸化物Ca2RuO4は、電流・圧力・温度・元素置換などの外的刺激に敏感に反応するモット絶縁体ですが、絶縁相から金属相に至る電子状態の変化の経路が、外的刺激の種類によって異なり、多様な形態を示すことが判明しました。過剰酸素を導入したCa2RuO4+δのフェルミ面の直接観測から得られた知見は、強相関物質で見られる激しい物性現象のしくみの解明と制御方法の構築につながる有力な手がかりを提供します。