Electronic Phase Control and Development of Functionalities in Oxide Thin Films with Flat-band Structure

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K15168
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 29020:Thin film/surface and interfacial physical properties-related
• Research Institution: The University of Tokyo
• Principal Investigator: Fujita Takahiro 東京大学, 大学院工学系研究科(工学部), 助教 (60839687)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 酸化物薄膜 / 強相関電子系

Outline of Final Research Achievements

In this study, we have attempted to fabricate thin films of the pyrochlore-type oxide A2B2O7 (A = Sn, Pb; B = Nb, Ta), which is theoretically predicted to possess an unusual “quasi-flat” band structure, and to observe and control emergent quantum properties resulting from the unique band structure. Thin film samples fabricated by pulsed laser deposition exhibit good crystallinity and chemical composition while they are all electrically insulators. Optical measurements clarify that the optical band gaps increase in the order of Sn2Nb2O7, Sn2Ta2O7, Pb2Nb2O7, and Pb2Ta2O7. This trend can be explained by considering the energy levels of the atomic orbitals of the constituent elements in each compound. Focusing on the band structure reported in the previous first-principles calculations, we experimentally confirm that the difference in band gaps between direct and indirect transitions is a good indicator of the “flatness” of the quasi-flat band.

Free Research Field

酸化物薄膜

Academic Significance and Societal Importance of the Research Achievements

本研究成果は、「擬フラットバンド」を持つ酸化物における今後のバンドエンジニアリングと機能性開拓につながると期待される。また、昇華性元素を含む物質、特に未だに報告の限られているパイロクロア型酸化物の薄膜作製において重要な知見を与える。
加えて、本研究の過程において、同様に昇華性の高いBiやRu を含む物質の薄膜化や、当初予定していた薄膜試料への電界効果による物性制御に関する多くの知見を得ることができた。これらの知見を活かして、従来にない酸化物薄膜・ヘテロ界面試料における創発磁気輸送現象と、その制御に関する研究が進展中である。