Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest, Hungary.
Nat Commun. 2012 Jun 19;3:912. doi: 10.1038/ncomms1910.
The 'expanded fulleride' Cs(3)C(60) is an antiferromagnetic insulator in its normal state and becomes a molecular superconductor with T(c) as high as 38 K under pressure. There is mounting evidence that superconductivity is not of the conventional BCS type and electron-electron interactions are essential for its explanation. Here we present evidence for the dynamic Jahn-Teller effect as the source of the dramatic change in electronic structure occurring during the transition from the metallic to the localized state. We apply infrared spectroscopy, which can detect subtle changes in the shape of the C(60)3- ion due to the Jahn-Teller distortion. The temperature dependence of the spectra in the insulating phase can be explained by the gradual transformation from two temperature-dependent solid-state conformers to a single one, typical and unique for Jahn-Teller systems. These results unequivocally establish the relevance of the dynamic Jahn-Teller effect to overcoming Hund's rule and forming a low-spin state, leading to a magnetic Mott-Jahn-Teller insulator.
“扩展富勒烯”Cs(3)C(60) 在正常状态下是反铁磁绝缘体,在压力下变为 T(c)高达 38 K 的分子超导体。越来越多的证据表明,超导性不是传统的 BCS 类型,电子-电子相互作用对于其解释至关重要。在这里,我们提供了动态 Jahn-Teller 效应作为导致金属到局域态转变过程中电子结构剧烈变化的来源的证据。我们应用了红外光谱学,它可以检测到 C(60)3- 离子形状由于 Jahn-Teller 畸变而发生的微妙变化。在绝缘相中的光谱的温度依赖性可以通过从两个依赖于温度的固态构象体逐渐转变为一个典型的、独特的 Jahn-Teller 体系的单个构象体来解释。这些结果明确确立了动态 Jahn-Teller 效应与克服 Hund 规则和形成低自旋态、导致磁 Mott-Jahn-Teller 绝缘体的相关性。