Intrinsic non-Dirac quantum spin Hall effect and hydrogenation modulated topological state in honeycomb-Kagome WI₃ monolayer

Abstract As one type of important topological quantum states, the quantum spin Hall (QSH) effect realized in two-dimensional (2D) materials still maintains sufficient attractiveness due to its promising spintronic applications. By using the first-principles calculations, we theoretically investigate the structural, electronic and topological properties of a newly 2D honeycomb-Kagome WI 3 monolayer (ML). The WI 3 ML possesses the excellent dynamical, thermal and mechanical stabilities, as has been confirmed by phonon spectra, molecular dynamics simulations and elastic constants calculations, respectively. It is found that the WI 3 ML behaves a type-II quadratic non-Dirac band dispersion around the Fermi level in the absence of spin–orbit coupling (SOC), while that may be adjusted to the type-I and/or type-III case based on the half-unilateral hydrogenation method. In the presence of SOC, the system may transform from the quadratic non-Dirac semimetal state into an intrinsic QSH state with nonzero topological invariant and Dirac-like edge states. The nontrivial topology of the system should originate from the strong SOC interaction of the degenerate W d x 2 –y 2 / d xy states at Γ point, and a nearly 0.10 eV nontrivial global band gap has been obtained under the 4% compressive strain. The half/fully-substitutional Mo doping, hydrogenation modulation as well as substrate effect on the electronic structures and topological states of the WI 3 ML have been explored. Intriguingly, the unilateral hydrogenated WI 3 ML present a topological semimetal phase with robust nontrivial edge stets against SOC and in-plane biaxial strain, while the fully hydrogenated one exhibits a Dirac-type QSH state around the high-symmetry K / K ′ points. Therefore, the honeycomb-Kagome WI 3 ML should be the potential candidate platform for future low-power nanoelectronic and spintronic applications.