Abstract
Two-dimensional (2D) topological insulators (TIs) with large band gaps are of great importance for the future applications of quantum spin Hall (QSH) effect. Employing ab initio electronic calculations we propose a novel type of 2D topological insulators, the monolayer (ML) low-buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gap. We demonstrate that LB HgTe (HgSe) monolayers undergo a trivial insulator to topological insulator transition under in-plane tensile strain of 2.6% (3.1%) due to the combination of the strain and the spin orbital coupling (SOC) effects. Furthermore, the band gaps can be tuned up to large values (0.2 eV for HgTe and 0.05 eV for HgSe) by tensile strain, which far exceed those of current experimentally realized 2D quantum spin Hall insulators. Our results suggest a new type of material suitable for practical applications of 2D TI at room-temperature.
Highlights
Two-dimensional (2D) topological insulators (TIs) with large band gaps are of great importance for the future applications of quantum spin Hall (QSH) effect
In contrast to 2D TIs from group-IV elements, the mercury chalcogenides are composed of heavy elements having large spin orbit coupling (SOC) which combined with the 2D quantum confinement can lead to significant changes in the electronic band structure and the frontier band ordering compared with their 3D parent material
Based on ab initio structure and phonon-mode calculations we predict that the 2D LB HgTe and HgSe monolayers are stable
Summary
Two-dimensional (2D) topological insulators (TIs) with large band gaps are of great importance for the future applications of quantum spin Hall (QSH) effect. We demonstrate that LB HgTe (HgSe) monolayers undergo a trivial insulator to topological insulator transition under in-plane tensile strain of 2.6% (3.1%) due to the combination of the strain and the spin orbital coupling (SOC) effects. The band gaps can be tuned up to large values (0.2 eV for HgTe and 0.05 eV for HgSe) by tensile strain, which far exceed those of current experimentally realized 2D quantum spin Hall insulators. In contrast to 2D TIs from group-IV elements, the mercury chalcogenides are composed of heavy elements having large spin orbit coupling (SOC) which combined with the 2D quantum confinement can lead to significant changes in the electronic band structure and the frontier band ordering compared with their 3D parent material. The LB structure allows the formation of two different topological edge states in the zigzag and armchair edges
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