Theory of FFLO state in the excitonic phase and novel superconductivity

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K05539
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Condensed matter physics II
• Research Institution: Niigata University
• Principal Investigator: Yoshiaki Ono 新潟大学, 自然科学系, 教授 (40221832)
• Co-Investigator(Kenkyū-buntansha): 佐野 和博 三重大学, 工学研究科, 教授 (40201537)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 励起子相 / FFLO状態 / 励起子揺らぎ / 超伝導 / 多バンドハバード模型 / 第一原理計算 / 乱雑位相近似 / 動的平均場理論

Outline of Final Research Achievements

Excitonic states in the semimetallic Ta2NiSe5 under high pressure have been investigated on the basis of the realistic quasi one-dimensional three-chain Hubbard model. It has been shown that the system shows three types of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) excitonic orders characterized by the condensation of excitons with finite center-of-mass momentum corresponding to the three types of nesting vectors of Fermi surfaces. It has also been found that, near the FFLO excitonic phase, the largely enhanced excitonic fluctuations mediate the Cooper pairs with finite center-of-mass momentum resulting in the FFLO superconductivity. In addition, we have studied the electron correlation effects by using the dynamical mean-field theory and have found that the excitonic state with a huge effective mass of the quasi-particles is realized in the strong correlation regime.

Free Research Field

数物系科学

Academic Significance and Societal Importance of the Research Achievements

Ta2NiSe5は伝導バンドと価電子バンドが2 : 1の異なる縮重度をもつことに着眼し、FFLO 励起子相が圧力下の半金属で必然的に生じる電子-正孔のインバランスにより導かれる機構とその特異物性を初めて解明するとともに、その励起子揺らぎを媒介とする超伝導も含めて励起子相の物理を統一的に理解したことが、本研究の学術的意義である。また、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。