Spin valley and giant quantum spin Hall gap of hydrofluorinated bismuth nanosheet

Abstract

Spin-valley and electronic band topological properties have been extensively explored in quantum material science, yet their coexistence has rarely been realized in stoichiometric two-dimensional (2D) materials. We theoretically predict the quantum spin Hall effect (QSHE) in the hydrofluorinated bismuth (Bi2HF) nanosheet where the hydrogen (H) and fluorine (F) atoms are functionalized on opposite sides of bismuth (Bi) atomic monolayer. Such Bi2HF nanosheet is found to be a 2D topological insulator with a giant band gap of 0.97 eV which might host room temperature QSHE. The atomistic structure of Bi2HF nanosheet is noncentrosymmetric and the spontaneous polarization arises from the hydrofluorinated morphology. The phonon spectrum and ab initio molecular dynamic (AIMD) calculations reveal that the proposed Bi2HF nanosheet is dynamically and thermally stable. The inversion symmetry breaking together with spin-orbit coupling (SOC) leads to the coupling between spin and valley in Bi2HF nanosheet. The emerging valley-dependent properties and the interplay between intrinsic dipole and SOC are investigated using first-principles calculations combined with an effective Hamiltonian model. The topological invariant of the Bi2HF nanosheet is confirmed by using Wilson loop method and the calculated helical metallic edge states are shown to host QSHE. The Bi2HF nanosheet is therefore a promising platform to realize room temperature QSHE and valley spintronics.

Spin and Charge Transport of Multiorbital Quantum Spin Hall Insulators

“…The first principles calculations reported in Refs. [24][25][26] show that the low-energy electronic properties of planar bismuthene (and of other elements of the VA-group), grown on a SiC substrate, or functionalized with halogen atoms, are reasonably well described by an effective tight-binding model Hamiltonian including only two orbitals (p x and p y ) per atom. Thus, to explore the transport properties of these novel 2D material we consider the model Hamiltonian H = H 0 + H I + H R , where…”

Structural and electronic properties of realistic two-dimensional amorphous topological insulators

“…In armchair nanoribbons, these states at K/K ′ -points mix and the spin-projection is no longer aligned with the z-axis [86]. These features are also observed for IV-V half-functionalized QSH phases [37] and Bi 2 HF [87]. Figure 9 shows the conductance of the amorphous topological insulator nanoribbons for parallel (δH ∥ = B ∥ σ y ) and perpendicular (δH ⊥ = B ⊥ σ z ) field directions using the 324 nm device setup of figure 6(d).…”

“…In the bulk, the valence band at the K/K ′ -points shows Zeeman-type splitting for s z and a Rashba-type spin-texture in in-plane directions. This effect is caused by strong SOC and polarization due to the functionalization [87]. Moreover, in the bulk, the states at the K and K ′ points have opposite spinpolarizations.…”

Topological electronic structure and Rashba effect in Bi thin layers: theoretical predictions and experiments

“…Bismuth thin films are candidates of choice. This has initiated a large amount of theoretical studies concentrating on the (1 1 1) face [10,[104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122][123]. Reports are on other crystallographic faces are rare.…”