Topological boundary states, emerged at the spatial boundary between topological non-trivial and trivial phases, are usually gapless, or commonly referred as metallic states. For example, the surface state of a topological insulator is a gapless Dirac state. These metallic topological boundary states are typically well described by non-interacting fermions. However, the behavior of topological boundary states with significant electron-electron interactions, which could turn the gapless boundary states into gapped ordered states, e.g., density wave states or superconducting states, is of great interest theoretically, but is still lacking evidence experimentally. Here, we report the observation of incommensurable charge density wave (CDW) formed on the topological boundary states driven by the electron-electron interactions on the (001) surface of CoSi. The wavevector of CDW varies as the temperature changes, which coincides with the evolution of topological surface Fermi arcs with temperature. The orientation of CDW phase is determined by the chirality of the Fermi arcs, which indicates direct association between CDW and Fermi arcs. Our finding will stimulate the search of more interactions-driven ordered states, such as superconductivity and magnetism, on the boundaries of topological materials.
@article{arxiv.2110.07815,
title = {Charge instability of topological Fermi arcs in chiral crystal CoSi},
author = {Zhicheng Rao and Quanxin Hu and Shangjie Tian3 and Shunye Gao and Zhenyu Yuan and Cenyao Tang and Wenhui Fan and Jierui Huang and Yaobo Huang and Li Wang and Lu Zhang and Fangsen Li and Huaixin Yang and Hongming Weng and Tian Qian and Jinpeng Xu and Kun Jiang and Hechang Lei and Yu-Jie Sun and Hong Ding},
journal= {arXiv preprint arXiv:2110.07815},
year = {2021}
}