2D transition metal chalcogenides have attracted tremendous attention due to their novel properties and potential applications. Although 2D transition metal dichalcogenides are easily fabricated due to their layer‐stacked bulk phase, 2D transition metal monochalcogenides are difficult to obtain. Recently, a single atomic layer transition metal monochalcogenide (CuSe) with an intrinsic pattern of nanoscale triangular holes is fabricated on Cu(111). The first‐principles calculations show that free‐standing monolayer CuSe with holes is not stable, while hole‐free CuSe is endowed with the Dirac nodal line fermion (DNLF), protected by mirror reflection symmetry. This very rare DNLF state is evidenced by topologically nontrivial edge states situated inside the spin–orbit coupling gaps. Motivated by the promising properties of hole‐free honeycomb CuSe, monolayer CuSe is fabricated on Cu(111) surfaces by molecular beam epitaxy and confirmed success with high resolution scanning tunneling microscopy. The good agreement of angle resolved photoemission spectra with the calculated band structures of CuSe/Cu(111) demonstrates that the sample is monolayer CuSe with a honeycomb lattice. These results suggest that the honeycomb monolayer transition metal monochalcogenide can be a new platform to study 2D DNLFs.

中文翻译：

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狄拉克节点线费米子蜂窝状单层CuSe的外延生长

二维过渡金属硫族化物因其新颖的性能和潜在的应用而备受关注。尽管由于二维过渡金属二卤化物的层堆叠体相而易于制造，但很难获得二维过渡金属单硫属化物。最近，在Cu（111）上制作了具有纳米级三角形孔固有图案的单原子层过渡金属单硫属元素化物（CuSe）。第一性原理计算表明，带有孔的独立单层CuSe不稳定，而无孔CuSe则被狄拉克节点线费米子（DNLF）赋予，并受到镜面反射对称性的保护。这种非常罕见的DNLF状态由位于自旋-轨道耦合间隙内的拓扑非平凡边缘状态证明。受到无孔蜂窝状CuSe的有前途的特性的激励，通过分子束外延在Cu（111）表面上制备单层CuSe，并通过高分辨率扫描隧道显微镜证实了成功。角度分辨的光发射光谱与计算得出的CuSe / Cu（111）的能带结构吻合良好，表明样品是具有蜂窝晶格的单层CuSe。这些结果表明，蜂窝单层过渡金属单硫属元素化物可以成为研究二维DNLF的新平台。