Manifestation of nonlinear anomalous Hall effect by controlling charge-ordered domains in organic conductors

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K18594
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 13:Condensed matter physics and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: Osada Toshihito 東京大学, 物性研究所, 教授 (00192526)
• Project Period (FY): 2021-07-09 – 2024-03-31
• Keywords: 非線形異常ホール効果 / 有機導体 / ディラック電子系 / 電荷秩序 / ドメイン / 非線形異常エッチングスハウゼン効果

Outline of Final Research Achievements

The weak charge ordering state of an organic conductor α-(BEDT-TTF)2I3 is a gapped tilted Dirac electron system breaking inversion symmetry, which is expected to exhibit the nonlinear anomalous Hall effect. However, its observation is expected to be difficult due to the cancellation between the two types of domains. Therefore, we have attempted to observe the nonlinear anomalous Hall effect by selective forming of one domain by the current field cooling method. (1) We were able to observe the nonlinear anomalous Hall effect even with normal cooling. This implies an imbalance in the domain ratio. (2) No significant effect on selective domain forming was observed by the current field cooling. (3) We discovered the nonlinear anomalous Ettingshausen effect, which is a thermoelectric analogue of the nonlinear anomalous Hall effect.

Free Research Field

物性物理学（低次元物質の量子輸送現象・トポロジカル量子物性）

Academic Significance and Societal Importance of the Research Achievements

トポロジカル伝導現象は基礎・応用の観点から現代物性物理学の重要なトピックスの１つである。一方、有機分子性結晶は単純な電子構造を持ち、物質設計や物性制御の舞台を提供してきた。本研究は、有機分子性結晶においてトポロジカル伝導を初めて発現させたという意義を持つ。電流磁場中冷却法の有効性は確認できなかったが、観測を困難にするドメイン問題も大きな障害にはならないことが明らかとなった。さらに対応するトポロジカル熱電効果である非線形異常Ettingshausen効果の発見を通じ、トポロジカル物性物理の発展にも貢献できた。