School of Physics and State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China.
Nanoscale. 2017 Jun 29;9(25):8740-8746. doi: 10.1039/c7nr00411g.
As a new type of quantum matter, Dirac node line (DNL) semimetals are currently attracting widespread interest in condensed matter physics and materials science. The DNL, featured by a closed line consisting of linear band crossings in the momentum space, was mostly predicted in three-dimensional materials. Here, we propose a tight-binding (TB) model of p + p or p + s orbitals defined on the two-dimensional (2D) Lieb lattice for the 2D version of DNL semimetals. The DNL states in these models are caused by the inversion of the bands with different symmetries and thus robust against spin-orbit interaction. By means of first-principles calculations, we demonstrate two candidate materials: BeC and BeH monolayers, which have Fermi circles centred at Γ(0,0) and K(1/2,1/2) points, respectively. Their Fermi velocities are higher than that in graphene. The non-zero Z topological invariant accompanied by the edge states is revealed in these materials. This work opens an avenue for the design of 2D DNL semimetals.
作为一种新型的量子物质，狄拉克节线（DNL）半导体目前在凝聚态物理和材料科学领域引起了广泛的关注。DNL 的特征是在动量空间中由线性能带交叉组成的封闭线，主要在三维材料中被预测到。在这里，我们提出了一个由 p + p 或 p + s 轨道定义的紧束缚（TB）模型，用于二维（2D） Lieb 晶格的 DNL 半导体的 2D 版本。这些模型中的 DNL 态是由不同对称性的能带反转引起的，因此对自旋轨道相互作用具有鲁棒性。通过第一性原理计算，我们证明了两种候选材料：BeC 和 BeH 单层，它们分别在 Γ(0,0)和 K(1/2,1/2)点有中心在原点的费米圆。它们的费米速度高于石墨烯。在这些材料中揭示了具有非零 Z 拓扑不变量和边缘态的存在。这项工作为设计二维 DNL 半导体开辟了一条途径。
