npj: 2D碳基Dirac材料的设计—基于sp-sp2碳层状材料的原子模拟
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石墨烯是一种无质量的狄拉克费米子系统，在动量空间中具有狄拉克点。石墨烯因具有自旋轨道耦合（SOC），也首次被确定为量子自旋霍尔（QSH）绝缘体，它能在狄拉克点处打开带隙。这一发现给人以新的启发，即研究石墨烯QSH效应有可能实现其在量子计算和自旋电子学方面的应用。尽管人们已在HgTe量子阱中观察到了QSH效应，但由于石墨烯的SOC强度太小（~1μeV），无法在实验可实现的温度范围内诱导出拓扑绝缘体相。
来自韩国建国大学的Hoonkyung Lee领导的研究小组利用原子模拟进行了系统的结构搜索和几何优化，以探索和设计能够容纳量子自旋霍尔相的原子级层状碳材料（2D材料）。从二维sp2-sp2杂化网络开始，原子模拟提供了31个碳层，这些碳层都具有各种类型无质量的狄拉克锥，同时包括各向同性或各向异性的狄拉克锥，以及共存的具有不同各向异性的不对称狄拉克锥。此外，他们还发现了21个没有自旋轨道耦合的狄拉克费米子系统，其中的19个有可能成为量子自旋霍尔绝缘体，却具有相当大的自旋轨道耦合。这些结果表明利用第一性原理可以预测各种无质量狄拉克锥的碳基系统，同时也为揭示二维材料中实现狄拉克锥提供了可行路线。
该文近期发表于npj Computational Materials 4: 54 (2018)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。
Design of 2D massless Dirac fermion systems and quantum spin Hall insulators based on sp–sp2 carbon sheets
Minwoo Park, Youngkuk Kim & Hoonkyung Lee
Graphene is a massless Dirac fermion system, featuringDirac points in momentum space.It was also firstidentified as a quantum spin Hall (QSH) insulator when considering spin–orbitcoupling (SOC), which opens a band gap at the Dirac points. This discovery hasinitiated new research efforts to study the QSH effect, towards its applicationfor quantum computing and spintronics. Although the QSH effect has beenobserved in HgTe quantum wells, the SOC strength of graphene is too small (~1µeV)to induce the topological insulator phase in an experimentally achievabletemperature regime. Here, we perform a systematic atomistic simulation to designtwo-dimensional sp–sp2hybrid carbon sheets to discover new Diracsystems, hosting the QSH phase. 21 out of 31 newly discovered carbon sheets areidentified as Dirac fermion systems without SOC, distinct from graphene in thenumber, shape, and position of the Dirac cones occurring in the Brillouin zone.Moreover, we find 19 out of the 21 new Dirac fermion systems become QSHinsulators with a sizable SOC gap enhanced up to an order of meV, thus allowingfor the QSH effect at experimentally accessible temperatures. In addition,based on the 26 Dirac fermion systems, we make a connection between the numberof Dirac points without SOC and the resultant QSH phase in the presence of SOC.Our findings present new prospects for the design of topological materials withdesired properties.
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