Jia Yi-Zhen, Ji Wei-Xiao, Zhang Chang-Wen, Li Ping, Wang Pei-Ji
School of Physics and Technology, University of Jinan Jinan Shandong 250022 People's Republic of China
RSC Adv. 2018 Aug 6;8(49):27995-28001. doi: 10.1039/c8ra05458d. eCollection 2018 Aug 2.
Two-dimensional (2D) Bi-based films have attracted intensive attention recently. However, materials with spatial asymmetry are rarely reported, impeding their practical application. In the present work, based on density functional theory (DFT) calculations, we propose a new type of 2D asymmetric NaXBi (X = Sn and Pb) monolayer, which can realize the coexistence of a topological phase and the Rashba effect. The dynamical and thermal stability are confirmed by the phonon spectra and DFT molecular dynamic simulations. Analysis of the band structures reveals that NaPbBi is an intrinsic 2D topological insulator with a gap as large as 0.35 eV, far beyond room temperature. The non-trivial topology, caused by p - p band inversion, is confirmed by the topological index and helical edge states. Remarkably, unlike Bi(111) or BiX (X = H, F, Cl) monolayers, the inversion-symmetry breaking in NaPbBi gives rise to a sizable Rashba splitting energy of 64 meV, which is tunable under external strains (-1 to 7%). Also, an effective tight-binding (TB) model is constructed to understand the origin of the non-trivial topology of NaPbBi. Our work opens a new avenue to designing a feasible 2D asymmetric material platform for application in spintronics.
二维（2D）铋基薄膜近来备受关注。然而，具有空间不对称性的材料鲜有报道，这阻碍了它们的实际应用。在本工作中，基于密度泛函理论（DFT）计算，我们提出了一种新型的二维不对称NaXBi（X = Sn和Pb）单层，它能够实现拓扑相和Rashba效应的共存。通过声子谱和DFT分子动力学模拟证实了其动力学和热稳定性。对能带结构的分析表明，NaPbBi是一种本征二维拓扑绝缘体，其能隙高达0.35 eV，远高于室温。由p - p能带反转引起的非平凡拓扑结构，通过拓扑指数和螺旋边缘态得到证实。值得注意的是，与Bi(111)或BiX（X = H、F、Cl）单层不同，NaPbBi中的反演对称性破缺产生了高达64 meV的可观Rashba分裂能，该能量在外部应变（-1%至7%）下是可调的。此外，构建了一个有效的紧束缚（TB）模型来理解NaPbBi非平凡拓扑结构的起源。我们的工作为设计用于自旋电子学的可行二维不对称材料平台开辟了一条新途径。
