Novel transport phenomena induced by phonon dynamics associated with polar structural transition

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K14652
• 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: Osaka University
• Principal Investigator: Takahashi Hidefumi 大阪大学, 基礎工学研究科, 助教 (50748473)
• Project Period (FY): 2019-04-01 – 2021-03-31
• Keywords: 熱電効果 / 強相関電子 / 強誘電体 / 超伝導 / 極性金属 / 磁性

Outline of Final Research Achievements

Recently, we have found that the semimetallic MoTe2 with a polar-nonpolar structural phase transition shows a peculiar thermoelectric effect that cannot be explained by the conventional band picture, and improved the thermoelectric performance by suppressing the structural phase transition temperature. In order to clarify the correlation between the polar structural instability and the thermoelectric properties, we performed Raman spectroscopy and single-crystal structural analysis. As a result, we observed a softening of polar phonons and an unusual change in the temperature of atomic positions at low temperatures, where the thermoelectric performance increases, suggesting a correlation between the polar phonon instability and the thermoelectric effect. We also succeeded in the single crystal synthesis of materials with polar structural instability and controlled the structural phase transition.

Free Research Field

物性物理

Academic Significance and Societal Importance of the Research Achievements

本研究では、低温で高い効率を示す熱電材料の物質探索とその起源解明を目指した。半金属材料MoTe2に注目し、低温での高い熱電性能と構造相転移との関係を調べるため、ラマン分光や放射光を用いた実験を行った。その結果、低温での構造の不安定化に伴い熱電性能が増大することを明らかにし、熱電性能向上の理論モデルの提案を行った。今後、本研究の結果に基づいたさらに高い性能を持つ熱電材料の開拓につながることが期待される。