Ultrasonic investigation of electron-phonon interaction in excitonic insulator transition

2023 Fiscal Year Final Research Report

• Project/Area Number: 22K13999
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: Tokyo University of Science
• Principal Investigator: Kurihara Ryosuke 東京理科大学, 創域理工学部先端物理学科, 助教 (00795114)
• Project Period (FY): 2022-04-01 – 2024-03-31
• Keywords: 超音波 / 励起子絶縁体 / 構造相転移 / ソフトモード / 電子-格子相互作用 / d電子系

Outline of Final Research Achievements

In Ta2NiSe5, an excitonic-insulator (EI) transition has been discussed as the origin of the structural phase transition at 328 K. The EI transition is usually driven by electronic correlations and the band structures are reconstructed. On the other hand, the contribution of electron-phonon interactions has also been proposed in Ta2NiSe5. Thus, the estimation of such interaction can play a key role in understanding EI transition.
In this study, we investigated the elastic soft modes of the structural phase (SP) transitions in Ta2NiSe5 by ultrasonic measurements. As a result, an elastic soft mode in the transverse elastic constant C55 was observed. Due to the elastic softening, we estimated the electron-phonon interaction coefficient to be 2500 K.

Free Research Field

固体の超音波物理

Academic Significance and Societal Importance of the Research Achievements

構造相転移は，物質の性質を劇的に変化させる相転移の一種である．例えばBaTiO3では，構造相転移に伴う強誘電性の獲得が生じ，産業応用上重要な物質となっている．また鉄ヒ素超伝導体では，高い転移温度を示す全く新しい超伝導の発現機構に対し構造相転移の寄与が指摘されるなど，新奇な物性の発見に寄り添った相転移の1つといえる．
本研究では，構造相転移を誘起する新奇な電子系の相転移として励起子絶縁体に着目し，その発現機構の理解を目指した．本研究により，構造相転移を引き起こす電子-格子相互作用の寄与とその大きさを実験的に検証でき，また可能な励起子絶縁体転移の機構についてどの電子系が重要となるかを検証できた．