Wang Kai, Zhang Yun, Zhao Wei, Li Ping, Ding Jian-Wen, Xie Guo-Feng, Guo Zhi-Xin
Department of Physics and Institute for Nanophysics and Rare-earth Luminescence, Xiangtan University, Xiangtan 411105, China.
Phys Chem Chem Phys. 2019 May 8;21(18):9310-9316. doi: 10.1039/c9cp01153f.
Realizing topological Dirac states in two-dimensional (2D) magnetic materials is particularly important to spintronics. Here, we propose that such states can be obtained in a transition-metal (Hf) monolayer grown on a 2D substrate with hexagonal hollow geometry (graphyne). We find that the significant orbital hybridizations between Hf and C atoms can induce sizable magnetism and bring three Dirac cones at/around each high-symmetry K(K') point in the Brillouin zone. One Dirac cone is formed by pure spin-up electrons from the dz2 orbital of Hf, and the remaining two are formed by crossover between spin-up electrons from the dz2 orbital and spin-down electrons from the hybridization of the dxy/x2-y2 orbitals of Hf atoms and the pz orbital of C atoms. We also find that the spin-orbit coupling effect can open sizable band gaps for the Dirac cones. The Berry curvature calculations further show the nontrivial topological nature of the system with a negative Chern number C = -3, which is mainly attributed to the Dirac states. Molecular dynamics simulations confirm the system's thermodynamic stability approaching room temperature. The results provide a new avenue for realizing the high-temperature quantum anomalous Hall effect based on 2D transition-metals.
在二维（2D）磁性材料中实现拓扑狄拉克态对自旋电子学尤为重要。在此，我们提出可以在具有六边形空心几何结构（石墨炔）的二维衬底上生长的过渡金属（铪）单层中获得此类状态。我们发现铪原子与碳原子之间显著的轨道杂化可诱导可观的磁性，并在布里渊区的每个高对称K（K'）点处/附近产生三个狄拉克锥。一个狄拉克锥由铪原子dz2轨道的纯自旋向上电子形成，其余两个由铪原子dz2轨道的自旋向上电子与铪原子dxy/x2 - y2轨道和碳原子pz轨道杂化产生的自旋向下电子之间的交叉形成。我们还发现自旋 - 轨道耦合效应可为狄拉克锥打开可观的带隙。贝里曲率计算进一步表明该系统具有非平凡的拓扑性质，其陈数C = - 3为负，这主要归因于狄拉克态。分子动力学模拟证实了该系统接近室温时的热力学稳定性。这些结果为基于二维过渡金属实现高温量子反常霍尔效应提供了一条新途径。
