Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT 84112, USA.
Nanoscale. 2019 Apr 11;11(15):7256-7262. doi: 10.1039/c9nr00906j.
A symmetry-protected 2D Dirac semimetal has attracted intense interest for its intriguing material properties. Here, we report a 2D nonsymmorphic Dirac semimetal state in a chemically modified group-VA 2D puckered structure. Based on first-principles calculations, we demonstrate the existence of 2D Dirac fermions in a one-side modified phosphorene structure in two different types: one with a Dirac nodal line (DNL) structure for light elements with negligible spin-orbit coupling (SOC) and the other having an hourglass band protected by a nonsymmorphic symmetry for heavy elements with strong SOC. In the absence of SOC, the DNL exhibits an anisotropic behavior and unique electronic properties, such as constant density of states. The Dirac node is protected from gap opening by the nonsymmorphic space group symmetry. In the presence of SOC, the DNL states split and form an hourglass-shaped dispersion due to the broken inversion symmetry and the Rashba SOC interaction. Moreover, around certain high symmetry points in the Brillouin zone, the spin orientation is enforced to be along a specific direction. We construct an effective tight-binding model to characterize the 2D nonsymmorphic Dirac states. Our result provides a promising material platform for exploring the intriguing properties of essential nodal-line and nodal-point fermions in 2D systems.
一种具有对称保护的二维狄拉克半金属因其有趣的材料特性而引起了极大的兴趣。在这里，我们报告了一种在化学改性的 VA 族二维褶皱结构中存在的非对称狄拉克半金属态。基于第一性原理计算，我们在两种不同类型的一侧改性磷烯结构中证明了二维狄拉克费米子的存在：一种是具有狄拉克节线（DNL）结构的轻元素，具有可忽略的自旋轨道耦合（SOC），另一种是具有非对称空间群对称性保护的沙漏能带的重元素，具有强 SOC。在没有 SOC 的情况下，DNL 表现出各向异性行为和独特的电子特性，例如恒定的态密度。非对称空间群对称性保护狄拉克节点免受带隙打开的影响。在存在 SOC 的情况下，由于反转对称性和 Rashba SOC 相互作用的破坏，DNL 态分裂并形成沙漏形色散。此外，在布里渊区的某些高对称点周围，自旋方向被强制沿特定方向。我们构建了一个有效的紧束缚模型来描述二维非对称狄拉克态。我们的结果为探索二维系统中基本节线和节点费米子的奇异性质提供了一个有前途的材料平台。
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