具有近理想量子几何条件的菱面体石墨的鼓面表面态
Drumhead Surface States of Rhombohedral Graphite with Near Ideal Quantum Geometry Condition
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中文总结 AI 辅助
本研究通过第一性原理计算探究菱面体石墨的拓扑性质与鼓面表面态的理想量子几何条件，发现其体相的拓扑特性及表面态平带的凸曲率，且表面态内缘满足严格理想量子几何条件，为后续多体研究提供基础。
中文摘要 AI 辅助
量子度量（$G(k)$）与贝里曲率（$Ω(k)$）大小相等的理想量子几何（IQG）条件（即$|Ω|$/Tr$G$=1），已与少层菱面体石墨烯（RG）平带中分数陈绝缘体的实现相关联。近期，IQG条件也被提出可用于厚RG层平带的超导性研究。我们利用密度泛函理论和Wannier函数，研究了体相RG的对称性保护拓扑、半无限RG表面的鼓面表面态（DSS），以及厚RG薄片的IQG条件。我们发现，体相RG在存在自旋轨道耦合（SOC）时是弱拓扑绝缘体，而在无SOC时则等效为具有手性节线的手性半金属。我们还发现，半无限和厚RG薄片的DSS平带具有显著的凸曲率，其深度与近期的角分辨光电子能谱实验结果一致。计算得到的IQG也呈现凸形，中心K点处为最小值，约为$|Ω|$/Tr$G$$\neq$1。但DSS区域的内缘满足严格的IQG条件，即$|Ω|$/Tr$G$=1。这些基于第一性原理计算的半无限和厚RG薄片研究结果，为单粒子水平下的本征DSS提供了有用信息，可供未来纳入多体相互作用和强关联的研究参考。
英文摘要
The ideal quantum geometry (IQG) condition of equal magnitude between quantum metric ($G(k)$) and Berry curvature ($Ω(k)$) as in $|Ω|$/Tr$G$=1 has been associated with realizing fractional Chern insulators for the flat band in few layers of rhombohedral graphene (RG). More recently the IQG condition has also been proposed for superconductivity in the flat band for thick RG layers. Using density functional theory and Wannier functions, we study the symmetry-protected topology of bulk RG, drumhead surface state (DSS) of semi-infinite RG surface, and the IQG condition for thick RG slabs. We find that bulk RG is a weak topological insulator with spin-orbit coupling (SOC), besides being effectively a chiral semimetal with chiral nodal line without SOC. We also find that the DSS flat band of semi-infinite and thick RG slabs have a sizable convex curvature with depth agreeing with the recent angular resolved phono-emission spectroscopy experiment. The calculated IQG also shows a convex shape with the K point at the center having a minimum with approximately $|Ω|$/Tr$G$$\approx$1. But the inner rim of the DSS region shows the strict IQG condition of $|Ω|$/Tr$G$=1. These results on semi-infinite and thick RG slabs from first-principles calculations provide useful information for the pristine DSS at the single particle level for future studies to consider when many-body interactions and strong correlations will be included.
