トポロジカル磁性体の新たな設計指針を確立 ― ディラック電子を持つ正方格子物質でホモロガス系列を発見 ―

2026-07-02 東北大学

図1. 高温超伝導体などの開発を支えてきたホモロガス系列の設計法を、トポロジカル量子物質へ拡張。

＜関連情報＞

• https://www.tohoku.ac.jp/japanese/2026/07/press20260702-01-topo.html
• https://pubs.acs.org/doi/10.1021/jacs.6c03149

ディラック型フェリ磁性体 Ce 3 Au 4 Ge 2 Bi 4は、正方格子トポロジカル物質の同族系列の一員である Dirac-Like Ferrimagnet Ce3Au4Ge2Bi4 as a Member of a Homologous Series of Square-Net Topological Materials

Atsushi Yamashita,Ryota Mizuno,Masayuki Ochi,Tatsuhiro Kojima,Hiraku Saito,Taro Nakajima,Akiko Nakao,Motoi Kimata,Masaki Kondo,Masashi Tokunaga,Takanori Kida,Masayuki Hagiwara,Masaki Nishi,Hiroshi Murakawa,Noriaki Hanasaki,and Hideaki Sakai
Journal of the American Chemical Society  Published July 1, 2026
DOI:https://doi.org/10.1021/jacs.6c03149

Abstract

Square-net compounds with the HfCuSi₂-type framework have been a promising platform for realizing topological electronic states and their interplay with quantum many-body phenomena. In these materials, the transition-metal tetrahedral layer sandwiched between square-net layers plays a crucial role in determining the correlated physical properties, yet their structural variety has been limited to the single-layer type. Here, we report the discovery of Ce₃Au₄Ge₂Bi₄, a new square-net compound that represents the bilayer member of a homologous series bridging the HfCuSi₂-type CeAuBi₂ (112 phase) and ThCr₂Si₂-type CeAu₂Ge₂ (122 phase). The bilayer structure of Ce₃Au₄Ge₂Bi₄ is formed by combining two tetrahedral layers of the 112 phase through the insertion of a 122-like block, resulting in two mixed-anion antifluorite-type layers. Intriguingly, both the magnetic and electronic structures are substantially modified relative to the 112 phase. Single-crystal neutron diffraction reveals that the triple Ce layers coordinated by the tetrahedral bilayer exhibit a ferrimagnetic (up–down–up) order, which can be viewed as a combination of the antiferromagnetic orders in the 112 and 122 phases. First-principles calculations demonstrate that hybridization between Ce 5d-orbital in the spacer layer and Bi 6p-orbital in the square-net layer reshapes the band dispersion into a type-II Dirac-like band. Consistently, magnetotransport measurements show pronounced quantum oscillations with multiple frequencies and extremely light effective masses. These results establish Ce₃Au₄Ge₂Bi₄ as a prototype of a new homologous family of square-net-based topological magnets, where both magnetic order and Dirac-like band can be tuned by controlling the number of spacer layers. This tunable structural framework offers a strategy for the rational design of square-net materials with tailored functionalities.