Two-Dimensional Node-Line Semimetals in a Honeycomb-Kagome Lattice

• Published in: Chinese physics letters Vol. 34; no. 5; pp. 106 - 110
• Main Author: 卢金炼 罗伟 李雪阳 杨晟祺 曹觉先 龚新高 向红军
• Format: Journal Article
• Language: English
• Published: 01.05.2017
• Subjects: 二维; 半金属; 奇偶校验; 晶格; 绝缘状态; 自旋轨道耦合; 节点; 蜂窝
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307X/34/5/057302

Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional （3D） Weyl semimetals, 3D Dirac semimetMs, and 3D node-line semimetals （NLSs）. In particular, several compounds （e.g., certain 3D graphene networks, Cu3PdN, Ca3P2 ） were discovered to be 3D NLSs, in which the conduction and valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional （2D） Dirac semimetal （e.g., graphene）, 2D topological semimetals are much less investigated. Here we propose a new concept of a 2D NLS and suggest that this state could be realized in a new mixed lattice （named as HK lattice） composed by Kagome and honeycomb lattices. It is found that A3B2 （A is a group-liB cation and B is a group-VA anion） compounds （such as Hg3As2） with the HK lattice are 2D NLSs due to the band inversion between the cation Hg-s orbital and the anion As-pz orbital with respect to the mirror symmetry. Since the band inversion occurs between two bands with the same parity, this peculiar 2D NLS could be used as transparent conductors. In the presence of buckling or spin-orbit coupling, the 2D NLS state may turn into a 2D Dirac semimetal state or a 2D topological crystalline insulating state. Since the band gap opening due to buckling or spin-orbit coupling is small, Hg3As3 with the HK lattice can still be regarded as a 2D NLS at room temperature. Our work suggests a new route to design topological materials without involving states with opposite parities.