Gallium bismuth halide GaBi-X2 (X = I, Br, Cl) monolayers with distorted hexagonal framework: Novel room-temperature quantum spin Hall insulators

Abstract

Quantum Spin Hall (QSH) insulators with a large topologically nontrivial bulk gap are crucial for future applications of the QSH effect. Among these, group III-V monolayers and their halides with chair structure (regular hexagonal framework, RHF) were widely studied. Using first-principles calculations, we propose a new structure model for the functionalized group III-V monolayers, which consist of rectangular GaBi-X 2 (X=I, Br, Cl) monolayers with a distorted hexagonal framework (DHF).These structures have a much lower energy than the GaBi-X 2 monolayers with chair structure.Remarkably, the DHF GaBi-X 2 monolayers are all QSH insulators, which exhibit sizeable nontrivial band gaps ranging from 0.17 eV to 0.39 eV. Those band gaps can be widely tuned by applying different spin-orbit coupling (SOC) strengths, resulting in a distorted Dirac cone.

New nanoporous graphyne monolayer as nodal line semimetal: Double Dirac points with an ultrahigh Fermi velocity

“…The slope of the band close to the Dirac point P is indicated by S and a similar label can be applied to Q/P'/Q'.From the Dirac point with linear bands, we can calculate the Fermi velocity (v F ) by a linear fitting of the first-principles calculations date. Because the Dirac points are not at the high symmetry points, the double Dirac points can be regarded as two distorted Dirac points, which is similar to that in phagraphene 10 /distorted GaBi-X 2 monolayers (X = I, Br, Cl)60 /YN 2 . 61 In general, the distorted Dirac point has two different Fermi velocities along the high-symmetry line directions.…”

Carbon-rich carbon nitride monolayers with Dirac cones: Dumbbell C4N

“…First, the SOC effect is related to the element type: the heavier the element, the more pronounced the SOC effect becomes. Structures including heavy elements, such as Bi, can have a large SOC effect [55,56]. Second, the SOC effect is also related to the atomic orbitals forming the Dirac cone.…”

Single-layer metal halides MX2 (X = Cl, Br, I): stability and tunable magnetism from first principles and Monte Carlo simulations

“…33,34 Monolayer GaBiCl 2 , ZrBr and HfCl were identified as room-temperature quantum spin Hall insulators with large nontrivial band gaps. 35,36 FeCl 2 displays a half-metallic ferromagnetic ground state. 37,38 Recent experimental studies demonstrated that single crystals of CrI 3 can be cleaved very easily, possess a ferromagnetic order even in the monolayer form, and are stable in air/water, in the absence of CrI 2 contamination.…”