Topological insulator states in a honeycomb lattice of s-triazines

Abstract

Two-dimensional (2D) graphitic carbon nitride materials have been drawing increasing attentions in energy conversion, environment protection and spintronic devices. Here, based on first-principles calculations, we demonstrate that the already-synthesized honeycomb lattice of s-triazines with a chemical formula of C₆N₆ (g-C₆N₆) has topologically nontrivial electronic states characterized by p_x,y-orbital band structures with a topological invariant of Z₂ = 1, and stronger spin-orbital coupling (SOC) than both graphene and silicene. The band gaps opened in the p_x,y-orbital bands due to SOC are 5.50 meV (K points) and 8.27 eV (Γ point), respectively, implying that the quantum spin Hall effect (QSHE) could be achieved in this 2D graphitic carbon nitride material at a temperature lower than 95 K. This offers a viable approach for searching for 2D Topological Insulators (TIs) in metal-free organic materials.