Dichotomy of flat bands in the van der Waals ferromagnet Fe$_5$GeTe$_2$
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2025
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| author | Wu, Han Huang, Jianwei Hu, Chaowei Chen, Lei Hao, Yiqing Shi, Yue Malinowski, Paul Guo, Yucheng Jang, Bo Gyu Zhu, Jian-Xin May, Andrew F. Wang, Siqi Chen, Xiang Xie, Yaofeng Gao, Bin Zhang, Yichen Yue, Ziqin Ren, Zheng Hashimoto, Makoto Lu, Donghui Fedorov, Alexei Mo, Sung-Kwan Kono, Junichiro He, Yu Birgeneau, Robert J. Dai, Pengcheng Xu, Xiaodong Cao, Huibo Si, Qimiao Chu, Jiun-Haw Yi, Ming |
| author_facet | Wu, Han Huang, Jianwei Hu, Chaowei Chen, Lei Hao, Yiqing Shi, Yue Malinowski, Paul Guo, Yucheng Jang, Bo Gyu Zhu, Jian-Xin May, Andrew F. Wang, Siqi Chen, Xiang Xie, Yaofeng Gao, Bin Zhang, Yichen Yue, Ziqin Ren, Zheng Hashimoto, Makoto Lu, Donghui Fedorov, Alexei Mo, Sung-Kwan Kono, Junichiro He, Yu Birgeneau, Robert J. Dai, Pengcheng Xu, Xiaodong Cao, Huibo Si, Qimiao Chu, Jiun-Haw Yi, Ming |
| contents | Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantum destructive interference can quench the electronic kinetic energy. Although both have a narrow bandwidth, the two types of flat bands should exhibit very distinct spectral properties arising from their distinctive origins. So far, the two types of flat bands have only been realized in very different material settings and chemical environments, preventing a direct comparison. Here, we report the observation of the two types of flat bands within the same material system--an above-room-temperature van der Waals ferromagnet, Fe$_{5-x}$GeTe$_2$, distinguishable by a switchable iron site order. The contrasting nature of the flat bands is also identified by the remarkably distinctive temperature-evolution of the spectral features, indicating that one arises from electron correlations in the Fe(1) site-disordered phase, while the other geometrical frustration in the Fe(1) site-ordered phase. Our results therefore provide a direct juxtaposition of the distinct formation mechanism of flat bands in quantum materials, and an avenue for understanding the distinctive roles flat bands play in the presence of magnetism, topology, and lattice geometrical frustration, utilizing sublattice ordering as a key control parameter. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_03029 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Dichotomy of flat bands in the van der Waals ferromagnet Fe$_5$GeTe$_2$ Wu, Han Huang, Jianwei Hu, Chaowei Chen, Lei Hao, Yiqing Shi, Yue Malinowski, Paul Guo, Yucheng Jang, Bo Gyu Zhu, Jian-Xin May, Andrew F. Wang, Siqi Chen, Xiang Xie, Yaofeng Gao, Bin Zhang, Yichen Yue, Ziqin Ren, Zheng Hashimoto, Makoto Lu, Donghui Fedorov, Alexei Mo, Sung-Kwan Kono, Junichiro He, Yu Birgeneau, Robert J. Dai, Pengcheng Xu, Xiaodong Cao, Huibo Si, Qimiao Chu, Jiun-Haw Yi, Ming Strongly Correlated Electrons Quantum materials with bands of narrow bandwidth near the Fermi level represent a promising platform for exploring a diverse range of fascinating physical phenomena, as the high density of states within the small energy window often enables the emergence of many-body physics. On one hand, flat bands can arise from strong Coulomb interactions that localize atomic orbitals. On the other hand, quantum destructive interference can quench the electronic kinetic energy. Although both have a narrow bandwidth, the two types of flat bands should exhibit very distinct spectral properties arising from their distinctive origins. So far, the two types of flat bands have only been realized in very different material settings and chemical environments, preventing a direct comparison. Here, we report the observation of the two types of flat bands within the same material system--an above-room-temperature van der Waals ferromagnet, Fe$_{5-x}$GeTe$_2$, distinguishable by a switchable iron site order. The contrasting nature of the flat bands is also identified by the remarkably distinctive temperature-evolution of the spectral features, indicating that one arises from electron correlations in the Fe(1) site-disordered phase, while the other geometrical frustration in the Fe(1) site-ordered phase. Our results therefore provide a direct juxtaposition of the distinct formation mechanism of flat bands in quantum materials, and an avenue for understanding the distinctive roles flat bands play in the presence of magnetism, topology, and lattice geometrical frustration, utilizing sublattice ordering as a key control parameter. |
| title | Dichotomy of flat bands in the van der Waals ferromagnet Fe$_5$GeTe$_2$ |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2508.03029 |