Two dimensional topological insulators with tunable band gaps: HgTe and HgSe monolayers

TL;DR

This paper predicts and analyzes new 2D topological insulators based on HgTe and HgSe monolayers with tunable band gaps, achieved through strain and spin-orbit coupling, promising for room-temperature applications.

Contribution

It introduces a new class of 2D topological insulators with tunable band gaps using ab initio calculations, highlighting strain and SOC effects on their topological phases.

Findings

Monolayer HgTe transitions to a topological phase under tensile strain.

The topological band gap can be tuned from 0 to 0.20 eV.

Large band gaps make these materials suitable for room-temperature devices.

Abstract

Employing ab initio electronic calculations, we propose a new type of two-dimensional (2D) topological insulator (TI), monolayer (ML) low buckled (LB) mercury telluride (HgTe) and mercury selenide (HgSe), with tunable band gaps. Monolayer LB HgTe undergoes a transition to a topological nontrivial phase under the appropriate in-plane tensile strain ({\epsilon} > 2.6%) due to the combination effects of strain and spin orbital coupling (SOC). Under the 2.6%< {\epsilon} <4.2% tensile strain, the band inversion and topological nontrivial gap are induced by the SOC. For {\epsilon} >4.2%, the band inversion is already realized by strain but the topological gap is induced by SOC. The band gap of monolayer LB HgTe TI phase can be tuned over a wide range from 0 eV to 0.20 eV as the tensile strain increases from 2.6% to 7.4%. Similarly, the topological phase transition of monolayer LB HgSe is induced by strain and SOC as the strain {\epsilon} >3.1%. The topological band gap can be 0.05 eV as the strain increases to about 4.6%. The large band gap of 2D LB HgTe and HgSe monolayers make this type of material suitable for practical applications at room-temperature.