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Bibliographic Details
Main Authors:	Liang, Bo, Liu, Yichen, Pang, Jie, Deng, Hanbin, Miao, Taimin, Zhu, Wenpei, Cai, Neng, Zhang, Tiantian, Liu, Jiayu, Jiang, Zhicheng, Liu, Zhanfeng, Zhu, Hongen, Li, Yuliang, Li, Tongrui, Xu, Mingkai, Chen, Hao, Ren, Xiaolin, Yin, Chaohui, Shu, Yingjie, Chen, Yiwen, Zhang, Yu-Tian, Liu, Zhengtai, Shen, Dawei, Ye, Mao, Zhang, Fengfeng, Zhang, Shenjin, Cui, Shengtao, Sun, Zhe, Miyamoto, Koji, Okuda, Taichi, Shimada, Kenya, Yang, Lihong, Yin, Jia-Xin, Zhao, Lin, Xu, Zuyan, Zhang, Haijun, Shi, Youguo, Zhou, X. J., Liu, Guodong
Format:	Preprint
Published:	2026
Subjects:	Materials Science
Online Access:	https://arxiv.org/abs/2601.18317
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Table of Contents:

Kagome materials are at the frontier of condensed matter physics. An ideal kagome lattice features only one geometrically frustrated flat band spanning the entire momentum space and a single Dirac cone at the Brillouin-zone corners. However, for the first time, here we observe unusual flat-band and Dirac physics in the newly discovered "322" kagome material Ni3In2S2 by combining high-resolution synchrotron- and laser-based angle-resolved photoemission spectroscopy with a micro-focused beam, scanning tunneling microscopy, and first-principles calculations. We resolve two distinct electronic flat-band states located in close proximity to the Fermi level: a robust Topological Surface Flat Band at ~40 meV below the Fermi level on the Sulfur-terminated surface, originating from weak topological insulator states, and a kagome lattice-derived flat band at ~100 meV binding energy with an ultranarrow bandwidth (~5 meV). Instead of the single Dirac cone, the Indium-terminated surface hosts a rare two-dimensional Dirac-node arc state, where the gapless Dirac nodes extend along an open one-dimensional line crossing the Brillouin-zone boundary, exhibiting sharp linear dispersion, exceptionally high Fermi velocity, and pronounced circular dichroism. These findings establish Ni3In2S2 as a unique topological kagome metal in which multiple flat-band states of different physical origin coexist with an unusual Dirac-node arc, opening an avenue for discovering flat-band--driven and topology-enabled quantum phenomena.

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