Study on Electron Pair Formation in Molecular Superconductors with Orbital Degrees of Freedom

2023 Fiscal Year Final Research Report

• Project/Area Number: 19K05405
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 32020:Functional solid state chemistry-related
• Research Institution: Ehime University
• Principal Investigator: Takashi Yamamoto 愛媛大学, 理工学研究科(理学系), 准教授 (20511017)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 軌道自由度 / 分子性固体 / 超伝導体 / 金属－絶縁体転移 / 反強磁性 / 近赤外分光法 / 振動分光法 / 四次元X線回折

Outline of Final Research Achievements

Molecular conductors and magnets are useful model compounds in solid state physics. In this study, we investigated whether superconductors and other compounds with close orbital levels are also useful as model compounds. We were able to determine the occupied (unoccupied) orbitals and their levels by spectroscopic methods for metal-dithiolene complex salts with close HOMO and LUMO levels. In the metal-insulator phase transition of three platinum complex salts, an orbital degree-of-freedom-based phase transition was found in which the orbital levels of half of the molecules are swapped. In the palladium complex salt, a superconductor under pressure, a ground state with a partial Valence Bond Order was found due to instability of the outermost orbital. The orbital instability was also detected by X-ray diffraction.

Free Research Field

物理化学　機能物質科学　物性物理学

Academic Significance and Societal Importance of the Research Achievements

本研究成果により、近接した準位の軌道による効果が物性に影響を及ぼすと考えられている系の電子状態を探る本格的な実験的研究が可能になる。例えば、単一成分の分子性超伝導体における電子対の探索や、分子性のディラック電子系において光速に近いキャリアの源を探る研究などに着手できるようになる。無機物のd軌道とは異なり、HOMOとLUMOという二準位のみから成る単純な電子系を用いることで、磁性と伝導性や光学特性を絡めた新奇現象を探索することが可能になる。