Gao Heng, Wu Wei, Hu Tao, Stroppa Alessandro, Wang Xinran, Wang Baigeng, Miao Feng, Ren Wei
Department of Physics, Materials Genome Institute, Shanghai Key Laboratory of High Temperature Superconductors, and International Centre for Quantum and Molecular Structures, Shanghai University, 200444, Shanghai, China.
Consiglio Nazionale delle Ricerche (CNR-SPIN), Via Vetoio, I-67100, L'Aquila, Italy.
Sci Rep. 2018 May 9;8(1):7436. doi: 10.1038/s41598-018-25478-6.
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 (BiHF) nanosheet where the hydrogen (H) and fluorine (F) atoms are functionalized on opposite sides of bismuth (Bi) atomic monolayer. Such BiHF 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 BiHF 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 BiHF 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 BiHF 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 BiHF nanosheet is confirmed by using Wilson loop method and the calculated helical metallic edge states are shown to host QSHE. The BiHF nanosheet is therefore a promising platform to realize room temperature QSHE and valley spintronics.
自旋谷和电子能带拓扑性质在量子材料科学中已得到广泛研究，然而它们的共存现象在化学计量比的二维（2D）材料中却鲜有实现。我们从理论上预测了氢氟化铋（BiHF）纳米片中的量子自旋霍尔效应（QSHE），其中氢（H）和氟（F）原子在铋（Bi）原子单层的相对两侧进行功能化修饰。研究发现，这种BiHF纳米片是一种二维拓扑绝缘体，具有0.97 eV的巨大带隙，可能支持室温下的量子自旋霍尔效应。BiHF纳米片的原子结构是非中心对称的，其自发极化源于氢氟化形态。声子谱和从头算分子动力学（AIMD）计算表明，所提出的BiHF纳米片在动力学和热学上是稳定的。反演对称性破缺与自旋轨道耦合（SOC）共同导致了BiHF纳米片中自旋与谷之间的耦合。利用第一性原理计算结合有效哈密顿量模型，研究了新兴的谷依赖性质以及本征偶极子与自旋轨道耦合之间的相互作用。通过威尔逊回路方法确定了BiHF纳米片的拓扑不变量，并表明计算得到的螺旋金属边缘态支持量子自旋霍尔效应。因此，BiHF纳米片是实现室温量子自旋霍尔效应和谷自旋电子学的一个有前景的平台。
