npj：Fe3GeTe2 | 铁磁材料中的洪特金属

来源： npj计算材料学 

作为磁性二维范德华材料的典型代表，Fe₃GeTe₂是基础科学和应用研究的热点，它一方面显示出可调节到室温的高居里温度、大霍尔电流和重费米子行为等优秀性能。但是另一方面，它的电子行为和磁性仍没有明确，甚至不同报道存在着矛盾，比如准粒子质量的测试随实验条件可以差十几倍。因此本研究提出了一种新的理论机制来解释这种材料的电子行为与磁性。

来自韩国科学技术院物理所的Han教授团队引入考虑局域轨道效应的理论计算，获得了更准确的态密度，证明Fe₃GeTe₂是一种“洪特金属”。随后进一步发现贡献洪特金属性的Fe原子存在洪特耦合作用的格位依赖性。两种不同的Fe格位的电子散射率、准粒子有效质量与索末菲系数相差几倍甚至几十倍。因此Fe₃GeTe₂是一种“格位分化”的洪特金属。基于这种新的理论机制可以合理解释这种材料在重费米子行为和准粒子质量测试实验中的矛盾表现，比如不同实验条件所得的准粒子质量的差异可以归因于Fe格位的不同贡献比例，如果是准粒子有效质量较大的Fe格位（Fe-I）的贡献占优势，那么材料测得的准粒子质量就高。

该研究工作除了有利于理解Fe₃GeTe₂材料的电子关联性和解释互相矛盾的实验结果；而且也指出了精细的态密度计算和提高能带结构的准确性是正确理解电子关联作用的基础，从而有助于推动其他材料体系的研究。相关论文近期发布于npj Computational Materials 8: 245 (2022)。手机阅读原文，请点击本文底部左下角“阅读原文”，进入后亦可下载全文PDF文件。

Editorial Summary

As a representative magnetic two-dimensional van der Waals material, Fe₃GeTe₂ has attracted considerable attention from the point of view of both fundamental science and device applications. On the one hand, it displays many fascinating properties such as high Curie temperature up to room temperature, large anomalous Hall current and heavy fermion behavior. But on the other hand, its electronic and magnetic behaviors are still elusive, even with the reports seemingly contradictory to one another, for example, the measured quasiparticle masses exhibit an order of magnitude difference depending on experiment conditions. Therefore, this study proposes a new theoretical mechanism to explain the above electronic and magnetic properties of the material. 

Professor Han and his team from Department of Physics of KAIST in Republic of Korea have introduced calculations by considering local orbital effects to obtain more accurate density of states, which provides that Fe₃GeTe₂ is a "Hund metal". Furthermore, they found that Fe atoms, who mainly contributing to the Hund metallicity, show a site dependence of Hund coupling supported by the distinctive electron scattering rate, quasiparticle effective mass and Sommerfeld coefficient with difference of several or even dozens of times. And hence Fe₃GeTe₂is dubbed "site-differentiated" Hund metal. Based on the new point of view, the contradictory performance of this material in heavy fermion behavior and quasiparticle mass experiments can be reasonably explained, for example, the difference in quasiparticle masses obtained under different experimental probes can result from the variable contribution proportions of Fe sites, i.e. if the contribution of Fe site (Fe-I) with a large quasiparticle effective mass is dominant, then the quasiparticle mass measured will be higher. In addition to be useful to understand the electronic correlation of Fe₃GeTe₂ as well as the contradictory experimental results, the work also points out that the fine calculation of density of states and the improved accuracy of band structure are the basis for a correct understanding of electronic properties, which will promote studys of other materials. This article was recently published in npj Computational Materials 8: 245 (2022).

原文Abstract及其翻译

Fe₃GeTe₂: a site-differentiated Hund metal (Fe₃GeTe₂：一种格位分化的洪特金属)

Taek Jung Kim, Siheon Ryee & Myung Joon Han

AbstractMagnetism in two-dimensional (2D) van der Waals (vdW) materials has lately attracted considerable attention from the point of view of both fundamental science and device applications. Obviously, establishing a detailed and solid understanding of their magnetism is the key first step toward various applications. Although Fe₃GeTe₂ is a representative ferromagnetic (FM) metal in this family, many aspects of its magnetic and electronic behaviors still remain elusive. Here, we report our new finding that Fe₃GeTe₂ is a special type of correlated metal known as “Hund metal”. Furthermore, we demonstrate that Hund metallicity in this material is quite unique by exhibiting remarkable site dependence of Hund correlation strength, hereby dubbed “site-differentiated Hund metal”. Within this new picture, many of the previous experiments can be clearly understood, including the ones that were seemingly contradictory to one another.

摘要最近二维（2D）范德华（vdW）材料中的磁性在基础科学和器件应用领域都引起了相当大的关注。显然，有关其磁性的详细而扎实的理解是这种材料迈向各种应用的前提。尽管Fe₃GeTe₂是该家族中具有代表性的铁磁性（FM）金属，但其相当多的磁性和电子行为仍难以捉摸。在本文中，我们提供了一种新的见解，即Fe₃GeTe₂是一种特殊的、可归属于“洪特金属”的关联型金属材料，并且进一步指出这种材料的洪特金属性非常独特，体现为洪特关联强度具有明显的格位依赖性，从而可以将该材料称为“格位分化的洪特金属”。基于这种新的理论可以清楚解释已有的很多实验结果，其中也包括了那些看似相互矛盾的工作。

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