A g-SiC[formula omitted] monolayer and its analogs: A new class of tunable Dirac cone materials and novel quantum spin Hall insulators

Abstract

Two-dimensional (2D) Dirac cone materials have received wide attention for their advanced properties, such as nearly-zero effective masses and ultrahigh carrier mobility. However, the robust zero bandgap limited their applications in high-performance electronic devices. In this work, we proposed a series of new 2D Dirac cone materials, termed as g-AB6 monolayers (A = C, Si, and Ge; B = C, Si, Ge, and Sn). We found that the coexistence of sp2 and sp3 hybridization would heavily decrease the structural stability, hence the stable g-AB6 monolayers were only composed of sp2 or sp3 hybridized atoms. The electronic calculations revealed that all g-AB6 monolayers considered are 2D Dirac materials with linear energy dispersions near Fermi level, and they possess high Fermi velocities. Among them, the Fermi velocity of the g-SiC6 monolayer is up to 7.11 × 105m/s, which is the highest value among the known group IVA binary Dirac materials. Additionally, the Dirac cone of g-SiC6 monolayer could be modulated by applying moderate in-plane uniaxial or shear strains (<5%), which are much easier than that of graphene and silicene. Moreover, the g-SiC6, g-GeSi6, g-SiGe6, and g-GeSn6 monolayer have been identified with nontrivial Z2 topological invariant (Z2 = 1), and the g-GeSn6 monolayer was demonstrated as a room temperature topological insulator due to that spin–orbit coupling opens a large bandgap of 319 meV. Considering that the g-AB6 monolayers possess excellent dynamical, thermal, and mechanical stability, the g-AB6 monolayers are a promising candidate for realizing high-speed tunable electronic devices.