近日，瑞士保罗·谢勒研究所的Y. Soh及其研究团队取得一项新进展。经过不懈努力，他们发现金属铁磁体中的反常电子。相关研究成果已于2024年3月6日在国际权威学术期刊《自然》上发表。

该研究团队描述了揭示铁磁性金属Fe₃Sn₂非费米液体行为的光谱。研究人员在布里渊区中心发现了三个C₃对称的电子口袋，其中两个是密度泛函理论所期望的。第三个也是定义最清晰的能带出现在低温和结合能较低的情况下，这是通过其他两个能带中一个的分数化而产生的，最有可能的原因是由于预测恰好位于费米能级之上的平带增强了电子-电子相互作用。这一发现引发了新的议题，即关于平带的多体物理特性如何因其源自晶格几何还是强定域原子轨道而有所区别。

据悉，普通金属在定义明确的“费米”表面上含有电子液体，其中电子的行为就好像它们不相互作用一样。在没有跃迁到全新相(如绝缘体或超导体)的情况下，电子之间的相互作用会引起散射，这种散射是束缚能偏离费米能级的二次方。一个长期存在的难题是，某些材料并不符合“费米液体”的描述。一个共同的特征是电子之间相对于它们的动能有很强的相互作用。达到这种状态的一个途径是用特殊的晶格来降低电子的动能。扭曲双层石墨烯就是一个例子，在2×2超晶格上去除所有角点的三六边形平铺晶格(三角形“笼目”)也可以容纳狭窄的电子带，从而增强相互作用效应。

附：英文原文

Title: Anomalous electrons in a metallic kagome ferromagnet

Author: Ekahana, Sandy Adhitia, Soh, Y., Tamai, Anna, Goslbez-Martnez, Daniel, Yao, Mengyu, Hunter, Andrew, Fan, Wenhui, Wang, Yihao, Li, Junbo, Kleibert, Armin, Vaz, C. A. F., Ma, Junzhang, Lee, Hyungjun, Xiong, Yimin, Yazyev, Oleg V., Baumberger, Felix, Shi, Ming, Aeppli, G.

Issue&Volume: 2024-03-06

Abstract: Ordinary metals contain electron liquids within well-defined ‘Fermi’ surfaces at which the electrons behave as if they were non-interacting. In the absence of transitions to entirely new phases such as insulators or superconductors, interactions between electrons induce scattering that is quadratic in the deviation of the binding energy from the Fermi level. A long-standing puzzle is that certain materials do not fit this ‘Fermi liquid’ description. A common feature is strong interactions between electrons relative to their kinetic energies. One route to this regime is special lattices to reduce the electron kinetic energies. Twisted bilayer graphene is an example, and trihexagonal tiling lattices (triangular ‘kagome’), with all corner sites removed on a 2×2 superlattice, can also host narrow electron bands for which interaction effects would be enhanced. Here we describe spectroscopy revealing non-Fermi-liquid behaviour for the ferromagnetic kagome metal Fe₃Sn₂ We discover three C₃-symmetric electron pockets at the Brillouin zone centre, two of which are expected from density functional theory. The third and most sharply defined band emerges at low temperatures and binding energies by means of fractionalization of one of the other two, most likely on the account of enhanced electron–electron interactions owing to a flat band predicted to lie just above the Fermi level. Our discovery opens the topic of how such many-body physics involving flat bands could differ depending on whether they arise from lattice geometry or from strongly localized atomic orbitals.

DOI: 10.1038/s41586-024-07085-w

Source: https://www.nature.com/articles/s41586-024-07085-w