School of Physics and Technology, University of Jinan, Jinan, Shandong, 250022, People's Republic of China.
Sci Rep. 2017 Apr 3;7:45923. doi: 10.1038/srep45923.
The coexistence of nontrivial topology and giant Rashba splitting, however, has rare been observed in two-dimensional (2D) films, limiting severely its potential applications at room temperature. Here, we through first-principles calculations to propose a series of inversion-asymmetric group-IV films, ABZ (A ≠ B = Si, Ge, Sn, Pb; Z = F, Cl, Br), whose stability are confirmed by phonon spectrum calculations. The analyses of electronic structures reveal that they are intrinsic 2D TIs with a bulk gap as large as 0.74 eV, except for GeSiF, SnSiCl, GeSiCl and GeSiBr monolayers which can transform from normal to topological phases under appropriate tensile strain of 4, 4, 5, and 4%, respectively. The nontrivial topology is identified by Z topological invariant together with helical edge states, as well as the berry curvature of these systems. Another prominent intriguing feature is the giant Rashba spin splitting with a magnitude reaching 0.15 eV, the largest value reported in 2D films so far. The tunability of Rashba SOC and band topology can be realized through achievable compressive/tensile strains (-4 ~ 6%). Also, the BaTe semiconductor is an ideal substrate for growing ABZ films without destroying their nontrivial topology.
然而，非平庸拓扑和巨大的 Rashba 劈裂的共存在二维（2D）薄膜中很少被观察到，这严重限制了其在室温下的潜在应用。在这里，我们通过第一性原理计算提出了一系列非对称的 IV 族薄膜 ABZ（A ≠ B = Si、Ge、Sn、Pb；Z = F、Cl、Br），它们的稳定性通过声子谱计算得到了证实。电子结构分析表明，除了 GeSiF、SnSiCl、GeSiCl 和 GeSiBr 单层在适当的 4%、4%、5%和 4%拉伸应变下可以从正常相转变为拓扑相外，它们都是本征的 2D TI，具有高达 0.74 eV 的体隙。非平庸拓扑通过 Z 拓扑不变量以及这些体系的螺旋边缘态和 berry 曲率来识别。另一个引人注目的特征是巨大的 Rashba 自旋劈裂，大小达到 0.15 eV，这是迄今为止在 2D 薄膜中报道的最大值。Rashba SOC 和能带拓扑的可调谐性可以通过可实现的压缩/拉伸应变（-4 ～ 6%）来实现。此外，BaTe 半导体是生长 ABZ 薄膜的理想衬底，不会破坏其非平庸拓扑。
