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.
