Quantum spin Hall states in the lateral heteromonolayers of WTe2-MoTe2

TL;DR

This study uses density functional theory to explore the topological phases and electronic properties of lateral heteromonolayers of WTe2 and MoTe2, revealing quantum spin Hall states and interface effects relevant for electronic applications.

Contribution

It provides the first detailed theoretical analysis of topological states in WTe2-MoTe2 heteromonolayers, highlighting the role of strain and interface orientation in their electronic properties.

Findings

Identification of topologically nontrivial and trivial phases in monolayers.

Discovery of helical quantum spin Hall states at heterointerfaces.

Effect of lattice mismatch strain on band gap widening.

Abstract

We used density functional theory to investigate the lateral heteromonolayers of WTe2 and MoTe2. We confirmed that topologically nontrivial and trivial phases are energetically favored for the WTe2 and MoTe2 monolayers, taken out of bulk Td-WTe2 and 2H-MoTe2, respectively. We considered heteromonolayers consisting of these stable building blocks. In the Td-WTe2 and 2H-MoTe2 heteromonolayers with the interfaces oriented perpendicular to the dimer chains of W atoms in Td-WTe2 (y direction), two pairs of helical (quantum spin Hall [QSH]) states, one at each interface, connect the valence and conduction bands. The strain induced by the large lattice mismatch of the two materials in the y direction widens the band gap of the QSH insulator of the Td-WTe2 monolayer and is essential for electronic applications. Furthermore, one-dimensional channels embedded in the layer can help avoid chemical degradation from the edges and facilitate the densification of conducting channels. For the heteromonolayer with interfaces in the x direction, the difference in atomic structure between the two interfaces due to low symmetry creates an energy difference between two helical states and a potential gradient in the wide band gap 2H-MoTe2 region, resulting in various interface localized bands.