title: New Family of Quantum Spin Hall Insulators in Two-dimensional Transition-Metal Halide with Large Nontrivial Band Gaps.
abstract: Topological insulators (TIs) are promising for achieving dissipationless transport devices due to the robust gapless states inside the insulating bulk gap. However, currently realized two-dimensional (2D) TIs, quantum spin Hall (QSH) insulators, suffer from ultrahigh vacuum and extremely low temperature. Thus, seeking for desirable QSH insulators with high feasibility of experimental preparation and large nontrivial gap is of great importance for wide applications in spintronics. On the basis of the first-principles calculations, we predict a novel family of 2D QSH insulators in transition-metal halide MX (M = Zr, Hf; X = Cl, Br, and I) monolayers, especially, which is the first case based on transition-metal halide-based QSH insulators. MX family has the large nontrivial gaps of 0.12-0.4 eV, comparable with bismuth (111) bilayer (0.2 eV), stanene (0.3 eV), and larger than ZrTe5 (0.1 eV) monolayers and graphene-based sandwiched heterstructures (30-70 meV). Their corresponding 3D bulk materials are weak topological insulators from stacking QSH layers, and some of bulk compounds have already been synthesized in experiment. The mechanism for 2D QSH effect in this system originates from a novel d-d band inversion, significantly different from conventional band inversion between s-p, p-p, or d-p orbitals. The realization of pure layered MX monolayers may be prepared by exfoliation from their 3D bulk phases, thus holding great promise for nanoscale device applications and stimulating further efforts on transition metal-based QSH materials.
authors.affiliation: Bremen Center for Computational Materials Science, University of Bremen , Am Falturm 1, 28359 Bremen, Germany.
authors.forename: Liujiang
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Integrated Materials Design Centre, School of Chemical Engineering, University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Liangzhi
authors.initials: L
authors.lastname: Kou
authors.affiliation: Max Planck Institute for Chemical Physics of Solids , Noethnitzer Strasse 40, 01187 Dresden, Germany.
authors.forename: Yan
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Max Planck Institute for Chemical Physics of Solids , Noethnitzer Strasse 40, 01187 Dresden, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Felser
authors.affiliation: Bremen Center for Computational Materials Science, University of Bremen , Am Falturm 1, 28359 Bremen, Germany.
authors.forename: Feiming
authors.initials: F
authors.lastname: Hu
authors.affiliation: Department of Physics and Materials Science and Center for Functional Photonics, City University of Hong Kong , Kowloon Tong, Hong Kong SAR.
authors.forename: Guangcun
authors.initials: G
authors.lastname: Shan
authors.affiliation: Integrated Materials Design Centre, School of Chemical Engineering, University of New South Wales , Sydney, New South Wales 2052, Australia.
authors.forename: Sean C
authors.initials: SC
authors.lastname: Smith
authors.affiliation: Max Planck Institute for Chemical Physics of Solids , Noethnitzer Strasse 40, 01187 Dresden, Germany.|Max Planck Institute for the Physics of Complex Systems , Noethnitzer Strasse 38, 01187 Dresden, Germany.
authors.forename: Binghai
authors.initials: B
authors.lastname: Yan
authors.affiliation: Bremen Center for Computational Materials Science, University of Bremen , Am Falturm 1, 28359 Bremen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Frauenheim
keywords: Quantum spin Hall insulator; band inversion; first-principles calculations; gapless edge states; two-dimensional transition-metal halide