Two-Dimensional Transition Metal Dichalcogenides with a Hexagonal Lattice: Room Temperature Quantum Spin Hall Insulators

TL;DR

This paper predicts a new class of stable hexagonal 2D transition metal dichalcogenides that are room-temperature quantum spin Hall insulators with large band gaps, facilitating integration into nanoelectronic and spintronic devices.

Contribution

It introduces a new stable hexagonal lattice structure for 2D TMDCs that are topological insulators with large band gaps, expanding potential applications.

Findings

Identified stable 2D TMDCs with hexagonal lattice and large band gaps (41-198 meV).

WSe2 and WTe2 exhibit the largest band gaps among TMDC TIs, at 198 meV.

Hexagonal lattice enhances integration with other 2D materials.

Abstract

So far, several transition metal dichalcogenides (TMDCs) based two-dimensional (2D) topological insulators (TIs) have been discovered, all of them based on a tetragonal lattice. However, in 2D crystals, the hexagonal rather than the tetragonal symmetry is the most common motif. Here, based on first-principles calculations, we propose a new class of stable 2D TMDCs of composition MX2 (M=Mo, W, X=S, Se, Te) with a hexagonal lattice. They are all in the same stability range as other 2D TMDC allotropes that have been demonstrated experimentally, and they are identified to be practical 2D TIs with large band gaps ranging from 41 to 198 meV, making them suitable for applications at room-temperature. Besides, in contrast to tetragonal 2D TMDs, their hexagonal lattice will greatly facilitate the integration of theses novel TI states van-der-Waals crystals with other hexagonal or honeycomb materials, and thus provide a route for 2D-material-based devices for wider nanoelectronic and spintronic applications. The nontrivial band gaps of both WSe2 and WTe2 2D crystals are 198 meV, which are larger than that in any previously reported TMDC-based TIs. These large band gaps entirely stem from the strong spin-orbit coupling strength within the d orbitals of Mo/W atoms near the Fermi level. Our findings will significantly broaden the scientific and technological impact of both 2D TIs and TMDCs.