Type-I and Type-II Saddle Points and a Topological Flat Band in a Bi-Pyrochlore Superconductor CsBi2
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| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866910127329640448 |
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| author | Morita, Yusei Li, Yongkai Wei, Yu-Hao Nakayama, Kosuke Wang, Zhiwei Li, Hua-Yu Kato, Takemi Souma, Seigo Tanaka, Kiyohisa Ozawa, Kenichi Yin, Jia-Xin Takahashi, Takashi Kuang, Min-Quan Yao, Yugui Sato, Takafumi |
| author_facet | Morita, Yusei Li, Yongkai Wei, Yu-Hao Nakayama, Kosuke Wang, Zhiwei Li, Hua-Yu Kato, Takemi Souma, Seigo Tanaka, Kiyohisa Ozawa, Kenichi Yin, Jia-Xin Takahashi, Takashi Kuang, Min-Quan Yao, Yugui Sato, Takafumi |
| contents | The divergence of the electron density of states (DOS) plays an important role in enhancing many-body interactions and inducing various quantum phases in low-dimensional systems. However, such unique electronic structures remain experimentally elusive in three-dimensional (3D) systems, particularly those with strong spin-orbit coupling (SOC). Using angle-resolved photoemission spectroscopy and first-principles calculations for a Laves-phase superconductor CsBi$_2$, which features a Bi-pyrochlore 3D network with strong SOC, we identify two characteristic electronic structures with a large DOS. One is a dispersionless topological flat band with p-orbital character, locally formed around the U-K line, which enhances DOS near the Fermi level. The other involves type-I and type-II saddle points connected by a flat band, which cooperatively produce an enhancement in the DOS. Our findings suggest a novel mechanism for achieving a DOS enhancement and lay a foundation for exploring exotic phenomena driven by the interplay of multiple singularities with a large DOS, nontrivial topology, and strong SOC in 3D pyrochlores. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_07805 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Type-I and Type-II Saddle Points and a Topological Flat Band in a Bi-Pyrochlore Superconductor CsBi2 Morita, Yusei Li, Yongkai Wei, Yu-Hao Nakayama, Kosuke Wang, Zhiwei Li, Hua-Yu Kato, Takemi Souma, Seigo Tanaka, Kiyohisa Ozawa, Kenichi Yin, Jia-Xin Takahashi, Takashi Kuang, Min-Quan Yao, Yugui Sato, Takafumi Mesoscale and Nanoscale Physics Strongly Correlated Electrons The divergence of the electron density of states (DOS) plays an important role in enhancing many-body interactions and inducing various quantum phases in low-dimensional systems. However, such unique electronic structures remain experimentally elusive in three-dimensional (3D) systems, particularly those with strong spin-orbit coupling (SOC). Using angle-resolved photoemission spectroscopy and first-principles calculations for a Laves-phase superconductor CsBi$_2$, which features a Bi-pyrochlore 3D network with strong SOC, we identify two characteristic electronic structures with a large DOS. One is a dispersionless topological flat band with p-orbital character, locally formed around the U-K line, which enhances DOS near the Fermi level. The other involves type-I and type-II saddle points connected by a flat band, which cooperatively produce an enhancement in the DOS. Our findings suggest a novel mechanism for achieving a DOS enhancement and lay a foundation for exploring exotic phenomena driven by the interplay of multiple singularities with a large DOS, nontrivial topology, and strong SOC in 3D pyrochlores. |
| title | Type-I and Type-II Saddle Points and a Topological Flat Band in a Bi-Pyrochlore Superconductor CsBi2 |
| topic | Mesoscale and Nanoscale Physics Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2604.07805 |