Orbital, charge and spin degrees of freedom in molecular solids

2019 Fiscal Year Final Research Report

• Project/Area Number: 15K05478
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Functional solid state chemistry
• Research Institution: Ehime University
• Principal Investigator: Yamamoto Takashi 愛媛大学, 理工学研究科(理学系), 准教授 (20511017)
• Project Period (FY): 2015-04-01 – 2020-03-31
• Keywords: 分子固体 / 軌道自由度 / 縮退軌道 / 電荷自由度 / 電荷再配列 / スピン自由度 / スピン液体 / 伝導性

Outline of Final Research Achievements

Orbital degeneracy in the two-dimensional molecular solids were examined. (1) Me4P[Pt(dmit)2]2 exhibited the phase transition around 200 K. HOMO and LUMO levels in 50 % of dimers were interchanged below 200 K. The same phenomena were observed in Me4N[Pt(dmit)2]2 and Me4Sb[Pt(dmit)2]2. This result indicates the orbital degeneracy was canceled below the phase transition temperature. (2) The magnetic transition and charge disproportionation were observed at the same transition temperature. (3) In contrast, the interchange of the HOMO and LUMO levels remained below the phase transition temperature of Cs[Pd(dmit)2]2. The vibrational spectroscopy revealed that the competition between several kinds of inter-dimer interactions was canceled below the phase transition temperature. This competition was also observed in EtMe3Sb[Pt(dmit)2]2 at the liquid helium temperature. This result suggests that charge and lattice fluctuation is the driving force of the geometrical frustration.

Free Research Field

機能物質化学

Academic Significance and Societal Importance of the Research Achievements

本研究により、無機物のような軌道自由度と、大きな格子揺らぎといった分子由来の特性を組み合わせた、新しい物性を開拓できる可能性が広がった。軌道の縮退は分子同士の距離に比例する尺度で評価できることを明らかにしたので、今後の研究の進展により、単一成分の分子結晶を始めとする様々な伝導体・超伝導体における伝導機構の解明が期待される。スピン液体として注目されてきた現象の作動原理を明らかにし、スピンだけでなく格子や電荷の自由度も重要であることを示した。