モット絶縁体の導電性に意外な阻害要因があることを発見(Researchers find unexpected roadblock to conductivity in Mott insulators)

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2024-05-01 ブラウン大学

ブラウン大学の科学者を含む国際チームは、特定のモット絶縁体が電子が加わっても導電性を持たない理由を初めて基本的に説明する新理論を開発しました。この材料は、電子が追加されると通常の理解と異なり、電子が自由に動くのを阻害する二重極子(バイポラロン)を形成します。これにより、材料は絶縁体のままです。この発見は、モット絶縁体の性質を理解し制御するための科学的な取り組みに新たな光を当て、無駄な試みを減らすことが期待されます。

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スピン軌道ヤーンテラー双極子 Spin-orbital Jahn-Teller bipolarons

Lorenzo Celiberti,Dario Fiore Mosca,Giuseppe Allodi,Leonid V. Pourovskii,Anna Tassetti,Paola Caterina Forino,Rong Cong,Erick Garcia,Phuong M. Tran,Roberto De Renzi,Patrick M. Woodward,Vesna F. Mitrović,Samuele Sanna & Cesare Franchini
Nature Communications  Published:18 March 2024
DOI:https://doi.org/10.1038/s41467-024-46621-0

モット絶縁体の導電性に意外な阻害要因があることを発見(Researchers find unexpected roadblock to conductivity in Mott insulators)

Abstract

Polarons and spin-orbit (SO) coupling are distinct quantum effects that play a critical role in charge transport and spin-orbitronics. Polarons originate from strong electron-phonon interaction and are ubiquitous in polarizable materials featuring electron localization, in particular 3d transition metal oxides (TMOs). On the other hand, the relativistic coupling between the spin and orbital angular momentum is notable in lattices with heavy atoms and develops in 5d TMOs, where electrons are spatially delocalized. Here we combine ab initio calculations and magnetic measurements to show that these two seemingly mutually exclusive interactions are entangled in the electron-doped SO-coupled Mott insulator Ba2Na1−xCaxOsO6 (0 < x < 1), unveiling the formation of spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller lattice activity, converts the Os 5d1 spin-orbital Jeff = 3/2 levels, characteristic of the parent compound Ba2NaOsO6 (BNOO), into a bipolaron 5d2 Jeff = 2 manifold, leading to the coexistence of different J-effective states in a single-phase material. The gradual increase of bipolarons with increasing doping creates robust in-gap states that prevents the transition to a metal phase even at ultrahigh doping, thus preserving the Mott gap across the entire doping range from d1 BNOO to d2 Ba2CaOsO6 (BCOO).

1700応用理学一般
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