A second-order topological insulator (SOTI) in d spatial dimensions features topologically protected gapless states at its (d−2)-dimensional boundary at the intersection of two crystal faces, but is gapped otherwise. As a novel topological state, it has been attracting great interest, but it remains a challenge to identify a realistic SOTI material in two dimensions (2D). Here, based on combined first-principles calculations and theoretical analysis, we reveal the already experimentally synthesized 2D material graphdiyne as the first realistic example of a 2D SOTI, with topologically protected 0D corner states. The role of crystalline symmetry, the robustness against symmetry-breaking, and the possible experimental characterization are discussed. Our results uncover a hidden topological character of graphdiyne and promote it as a concrete material platform for exploring the intriguing physics of higher-order topological phases.
@article{arxiv.1904.09985,
title = {Two-dimensional second-order topological insulator in graphdiyne},
author = {Xian-Lei Sheng and Cong Chen and Huiying Liu and Ziyu Chen and Zhi-Ming Yu and Y. X. Zhao and Shengyuan A. Yang},
journal= {arXiv preprint arXiv:1904.09985},
year = {2020}
}