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拓扑材料可谓近年来凝聚态物理和材料研究中十足的热点。这一方面由于该类材料物理丰富，其载流子属性独特，如Dirac、Weyl 和Majorana费米子等，可以在凝聚态体系中实现高能物理中的粒子行为。另一方面由于其在量子计算以及超导体方面具有潜在应用前景。相比三维体系，二维拓扑材料因其潜在的器件小型化应用及性质易调控等优势更加引人关注。然而，潜在的二维拓扑材料数量庞大，开展高通量理论计算筛选，为实验合成提供指导十分必要。
来自美国国家标准局的研究人员开展了复杂的第一原理高通量计算筛选了二维拓扑材料，包含了磁性/非磁性的金属和绝缘体材料。他们提出一个简单的描述符—“自旋轨道溢出”来筛选拓扑材料。该溢出因子可以看成是占据反转能带的电子数目。由于该物理量能够反映自旋轨道耦合对于能带结构的影响程度，因此可以体现材料的拓扑行为。通过计算该溢出因子，他们快速筛选了JARVIS-DFT数据库中上千种二维材料。为了验证该因子的有效性，他们针对筛选出的材料基于wannier插值开展了拓扑性能计算，如Z2、Chern数、反常量子Hall电导等。通过筛选过程获得上百种拓扑材料，包括量子Hall绝缘体、量子反常Hall绝缘体和半金属。值得注意的是，当针对候选材料采用更高级的能带计算方法验证时，很多材料变得不再“拓扑”，这表明采用高级的电子结构计算方法对于准确指认拓扑材料十分重要。尽管如此，该工作提出的溢出因子作为初级筛选描述符用于寻找拓扑材料，减小实验和理论搜索空间，仍然是十分有效的。该文近期发表于npj Computational Materials 6: 49 (2020)，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。
Computational search for magnetic and non-magnetic 2D topological materials using unified spin–orbit spillage screening
Kamal Choudhary, Kevin F. Garrity, Jie Jiang, Ruth Pachter & Francesca Tavazza
Two-dimensional topological materials (2D TMs) have a variety of properties that make them attractive for applications including spintronics and quantum computation. However, there are only a few such experimentally known materials. To help discover new 2D TMs, we develop a unified and computationally inexpensive approach to identify magnetic and non-magnetic 2D TMs, including gapped and semi-metallic topological classifications, in a high-throughput way using density functional theory-based spin–orbit spillage, Wannier-interpolation, and related techniques. We first compute the spin–orbit spillage for the ~1000 2D materials in the JARVIS-DFT dataset, resulting in 122 materials with high-spillage values. Then, we use Wannier-interpolation to carry-out Z2, Chern-number, anomalous Hall conductivity, Curie temperature, and edge state calculations to further support the predictions. We identify various topologically non-trivial classes such as quantum spin-Hall insulators, quantum anomalous-Hall insulators, and semimetals. For a few predicted materials, we run G0W0+SOC and DFT+U calculations. We find that as we introduce many-body effects, only a few materials retain non-trivial band-topology, suggesting the importance of high-level density functional theory (DFT) methods in predicting 2D topological materials. However, as an initial step, the automated spillage screening and Wannier-approach provide useful predictions for finding new topological materials and to narrow down candidates for experimental synthesis and characterization.
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