Strong correlation and strong coupling effects in the excitonic phase and its vicinity region based on the first-principles calculations and the quantum many-body calculations

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K03399
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 13010:Mathematical physics and fundamental theory of condensed matter physics-related
• Research Institution: Niigata University
• Principal Investigator: Yoshiaki Ono 新潟大学, 自然科学系, 教授 (40221832)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 励起子相 / 超伝導 / ２バンド・ハバード模型 / 動的平均場理論 / 励起子感受率 / 超伝導感受率

Outline of Final Research Achievements

The two-band Hubbard model, which is the basic model for high-Tc cuprate superconductors, is investigated using dynamical mean-field theory, which allows non-perturbative consideration of electron correlation effects. Based on the analytical expression of the superconductivity susceptibility derived from the Bethe-Salpeter equation, the superconducting transition temperature Tc is numerically calculated with high accuracy using the exact diagonalization method. As a result, a detailed superconducting phase diagram of this model is obtained for the first time. For the electron-hole two-band Hubbard model, which is the basic model of the excitonic phase, the excitonic susceptibility is calculated with good accuracy using the same calculation method, and the exciton transition temperature Tc is determined by its divergence. As a result, a detailed exciton phase diagram for this model as functions of Coulomb interaction and band splitting is obtained for the first time.

Free Research Field

数物系科学

Academic Significance and Societal Importance of the Research Achievements

オンサイトの斥力相互作用のみを含む２バンド・ハバード模型や電子－正孔２バンド・ハバード模型で、詳細な超伝導相図や励起子相図を得た初めての研究であり、強相関効果による超伝導や励起子相の発現機構解明という観点で意義がある。また、計算手法として、vertex関数の3振動数依存性により従来は計算が困難であった超伝導感受率を、高振動数領域におけるvertex関数の解析表式を併用することにより克服した点でも意義がある。さらに、得られた結果はTa2NiSe5の実験をよく説明している。このような励起子相の示す異常物性の解明は、今後の新たな材料やデバイス開発にも繋がると期待され、社会的意義があると考えられる。