From node-line semimetals to large-gap quantum spin Hall states in a family of pentagonal group-IVA chalcogenide
From node-line semimetals to large-gap quantum spin Hall states in a family of pentagonal group-IVA chalcogenide
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DOI：
10.1103/physrevb.97.125312
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发表时间：
2017-10
影响因子：
3.7
通讯作者：
Run-Wu Zhang;Cheng-Cheng Liu-Cheng;Da-Shuai Ma;Yugui Yao
中科院分区：
文献类型：
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作者：
Run-Wu Zhang;Cheng-Cheng Liu-Cheng;Da-Shuai Ma;Yugui Yao
近年来，二维拓扑绝缘体在理论和实验上都引起了广泛的研究兴趣。结合第一性原理计算和$k \cdot p$模型，我们发现在p-CS$_2$和p-SiS$_2$以及其他五角形的IVX $_2 $薄膜（即p-IVX$_2$）中均出现了NL相（IV= C、Si、Ge、Sn、Pb; X=S、Se、Te）。p-IVX$_2$中的NLS形成以$\Gamma$点为中心的符号费米环，并受到镜像反射对称性的保护。随着原子序数的下移，NL半金属被驱动到二维TI中，由于显著的SOC效应，NL半金属的体带隙可达0.715eV，并且体带隙在双轴和单轴应变下都是可调的.此外，我们还提出了将p-PbTe$_2$晶体夹在两个NaI片之间的量子阱，其中p-PbTe$_2$仍然保持其非平凡的拓扑结构，具有相当大的带隙（$\sim $0.5 eV）。这些发现为NL半金属和TI的未来设计和制造提供了一个新的2D材料家族。
Two-dimensional (2D) topological insulators (TIs) have attracted tremendous research interest from both theoretical and experimental fields in recent years. However, it is much less investigated in realizing node line (NL) semimetals in 2D materials.Combining first-principles calculations and $k \cdot p$ model, we find that NL phases emerge in p-CS$_2$ and p-SiS$_2$, as well as other pentagonal IVX$_2$ films, i.e. p-IVX$_2$ (IV= C, Si, Ge, Sn, Pb; X=S, Se, Te) in the absence of spin-orbital coupling (SOC). The NLs in p-IVX$_2$ form symbolic Fermi loops centered around the $\Gamma$ point and are protected by mirror reflection symmetry. As the atomic number is downward shifted, the NL semimetals are driven into 2D TIs with the large bulk gap up to 0.715 eV induced by the remarkable SOC effect.The nontrivial bulk gap can be tunable under external biaxial and uniaxial strain. Moreover, we also propose a quantum well by sandwiching p-PbTe$_2$ crystal between two NaI sheets, in which p-PbTe$_2$ still keeps its nontrivial topology with a sizable band gap ($\sim$ 0.5 eV). These findings provide a new 2D materials family for future design and fabrication of NL semimetals and TIs.