Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, P. R. China.
University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, 100190, P. R. China.
Adv Mater. 2018 Apr;30(16):e1707055. doi: 10.1002/adma.201707055. Epub 2018 Mar 8.
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.
二维过渡金属硫属化物由于其新颖的性质和潜在的应用而引起了极大的关注。尽管二维过渡金属二硫化物由于其层状堆积的体相而易于制备，但二维过渡金属单硫化物却难以获得。最近，在 Cu(111)上制备了具有纳米尺度三角形孔的固有图案的单层原子层过渡金属单硫化物（CuSe）。第一性原理计算表明，具有孔的自由单层 CuSe 是不稳定的，而无孔的 CuSe 则具有由镜像反射对称保护的狄拉克节线费米子（DNLF）。这种非常罕见的 DNLF 态由位于自旋轨道耦合间隙内的拓扑非平凡边缘态证实。受无孔蜂窝状 CuSe 的有前途的性质的启发，通过分子束外延在 Cu(111)表面上制备了单层 CuSe，并通过高分辨率扫描隧道显微镜成功地进行了确认。角分辨光电子能谱与 CuSe/Cu(111)的计算能带结构的良好吻合表明，该样品是具有蜂窝状晶格的单层 CuSe。这些结果表明，蜂窝状单层过渡金属单硫化物可以成为研究二维 DNLF 的新平台。
