Prediction of a room-temperature eight-coordinate two-dimensional topological insulator: penta-RuS4 monolayer

• Published in: NPJ 2D materials and applications 2017-09, Vol.1 (1), Article 29
• Main Authors: Yuan, Shijun, Zhou, Qionghua, Wu, Qisheng, Zhang, Yun, Chen, Qian, Hou, Jing-Min, Wang, Jinlan
• Format: Article
• Language: English
• Subjects: 639/301/1034/1038; 639/301/357/1018; 639/925/357/995; Chemistry and Materials Science; Computer simulation; Cones; Crystal structure; Density functional theory; Dimensional stability; Electronic structure; Energy bands; Energy gap; Fermi level; First principles; Materials Science; Monolayers; Nanotechnology; Prisms; Room temperature; Spin-orbit interactions; Surfaces and Interfaces; Thin Films; Tiling; Topological insulators; Topology
• ISSN: 2397-7132; 2397-7132
• DOI: 10.1038/s41699-017-0032-4

We predict a stable eight-coordinate two-dimensional RuS 4 monolayer, with a trilayer S–Ru–S and pentagonal rings tiling configuration by first-principles calculations. This monolayer exhibits unique anisotropic quadratic energy dispersion with two Dirac points emerging at the high-symmetric Γ point. When the spin-orbit coupling is included, a large nontrivial energy gap (70 meV) appears near the Fermi level. The topological nature of RuS 4 monolayer is also confirmed by the nontrivial Z 2 invariant and gapless edge states. A four-band tight-binding model is further proposed, which reveals that the topological states arise from the indirect interaction of the Ru- d xz and d yz orbitals. Computational materials: Topological insulator of 2D penta-RuS 4 First-principles calculations predict a stable, atomically thin RuS 4 crystal with eight-coordinate pentagonal structure. A team led by Jinlan Wang at Southeast University used ab-initio simulations based on density functional theory to design a RuS 4 crystal consisting of a Ru layer sandwiched between two S layers, with eight-coordinate Ru atoms sitting at the center of square prisms of S atoms. Penta-RuS 4 monolayers are energetically and dynamically stable, and exhibit anisotropic quadratic energy bands with two Dirac cones merging near the Fermi level. When the spin-orbit coupling effect is included in the band structure calculations owing to the fact that Ru is a heavy atom, a nontrivial topology emerges in the electronic structure, resulting in a bandgap opening of 70 meV. RuS 4 enriches the family of atomically thin topological insulators with a new eight-coordinate compound.