Quantum spin Hall insulators and topological Rashba-splitting edge states in two-dimensional CX3 (X = Sb, Bi)

Abstract

Two-dimensional topological materials attracted intense interest in condensed matter physics due to their topologically protected edge states and potential applications in electronic devices. Here, based on first-principles calculations, we found that a two-dimensional CX₃ (X = Sb, Bi) monolayer is a quantum spin Hall insulator with a large band gap. With the strong spin–orbit coupling effect, CX₃ exhibits noticeable bulk band gaps up to 470 meV, sufficiently large for realizing the quantum spin Hall effect at room temperature. The topological characteristic is confirmed by the Z₂ invariant since the system preserves time-reversal symmetry. Particularly, the CSb₃ monolayer displays unique topologically entangled Rashba-splitting edge states, resembling nearly free-electron quadratic dispersion. Such topologically entangled Rashba-like edge states derive from the spin–orbit coupling effect and inversion symmetry breaking on the edges. Moreover, we demonstrate that the topological properties are perfectly preserved in the CX₃ monolayer even with a h-BN substrate. The nontrivial quantum spin Hall state in the CX₃ monolayer will provide possibilities for studying a novel phenomenon of edge states and potential applications in low-dissipation electronic devices.