Theoretical study on the orbital and magnetic fluctuations on multi-orbital strongly-correlated electron systems

2020 Fiscal Year Final Research Report

• Project/Area Number: 17K14338
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Condensed matter physics II
• Research Institution: Nagoya University
• Principal Investigator: Yamakawa Youichi 名古屋大学, 理学研究科, 講師 (60750312)
• Project Period (FY): 2017-04-01 – 2021-03-31
• Keywords: 高温超伝導 / 強相関電子系 / 軌道秩序 / 磁気秩序 / 鉄系超伝導体 / 銅酸化物

Outline of Final Research Achievements

In this study, we investigated the electronic states in Fe-based and cuprate superconductors based on the higher-order many-body effect described by vertex corrections. As a result, we found that the orbital fluctuations are developed in electron-doped FeSe thanks to the interference between spin fluctuations. The high-temperature superconductivity appears due to the orbital fluctuations. Also, the pressure-induced magnetic transition in FeSe is well explained based on this study. We also showed that the resonance-like structure obtained by neutron scattering measurement is consistent with the s++ wave superconductivity due to orbital-fluctuations. In addition, we proposed the bond and spin-current orders as the origins of recently discovered charge-density wave and the pseud-gap nature in cuprate superconductors.

Free Research Field

数物系科学

Academic Significance and Societal Importance of the Research Achievements

鉄系超伝導体をはじめとした多軌道強相関電子系では、電子の軌道・電荷・スピン自由度に起因して、様々な興味深い性質が現れる。本研究で明らかにしたバーテックス補正に起因した軌道揺らぎの発達とフルギャップs波超伝導発現の機構は、電子ドープFeSeの高温超伝導、ひいては鉄系全般の超伝導発現機構解明に貢献する結果である。また、銅酸化物高温超伝導体で新たに発見された電荷密度波、および擬ギャップ現象の起源として、バーテックス補正に起因したボンド・スピン流秩序という新機構を提唱した。鉄系および銅酸化物系超伝導体では、共にスピン・軌道・電荷の結合という共通の物理があり、強相関電子系において広く実現が期待される。