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

TL;DR

This paper introduces the concept of two-dimensional node-line semimetals in a novel honeycomb-kagome lattice, proposing specific compounds like Hg3As2 as candidates, and discusses how buckling or spin-orbit coupling can alter their topological states.

Contribution

It proposes the new concept of 2D node-line semimetals in a mixed honeycomb-kagome lattice and identifies specific compounds as potential realizations.

Findings

Identification of Hg3As2 as a 2D node-line semimetal

Band inversion between cation s and anion pz orbitals

Possible transition to Dirac or topological crystalline insulator states

Abstract

Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetals, and 3D node-line semimetals. In particular, several compounds (e.g., certain three-dimensional graphene networks, Cu3PdN, Ca3P2) were discovered to be 3D node-line semimetals, in which the conduction and the valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional (2D) Dirac semimetal (e.g., in graphene), 2D topological semimetals are much less investigated. Here, we propose the new concept of a 2D node-line semimetal and suggest that this state could be realized in a new mixed lattice (we name it as HK lattice) composed by kagome and honeycomb lattices. We find that A3B2 (A is a group-IIB cation and B is a group-VA anion) compounds (such as Hg3As2) with the HK lattice are 2D node-line semimetals due to the band inversion between cation s orbital and anion pz orbital. In the presence of buckling or spin-orbit coupling, the 2D node-line semimetal state may turn into 2D Dirac semimetal state or 2D topological crystalline insulating state.