Jin Yuanjun, Wang Rui, Xu Hu
Department of Physics & Institute for Quantum Science and Engineering , Southern University of Science and Technology , Shenzhen 518055 , People's Republic of China.
Institute for Structure and Function & Department of Physics , Chongqing University , Chongqing 400044 , People's Republic of China.
Nano Lett. 2018 Dec 12;18(12):7755-7760. doi: 10.1021/acs.nanolett.8b03492. Epub 2018 Nov 21.
The topological quantum states in two-dimensional (2D) materials are fascinating subjects of research, which usually highlight electron-related systems. In this work, we present a recipe that leads to Dirac phonon states with a quantized valley Berry phase in 2D hexagonal lattices by first-principles calculations. We show that candidates possessing the 3-fold rotational symmetry at the corners of the hexagonal Brillouin zone host valley Dirac phonons, which are guaranteed to remain intact with respect to perturbations. We identify that such special topological features populated by Dirac phonons can be realized in various 2D materials. In particular, the monolayer CrI, an attractive 2D magnetic semiconductor with exotic applications in spintronics, is an ideal platform to investigate nontrivial phonons in experiments. We further confirm that the phonon Berry phase is quantized to ± π at two inequivalent valleys. The phonon edge states terminated at the projection of phonon Dirac cones are clearly visible. This work demonstrates that 2D hexagonal lattices with attractive valley Dirac phonons will extend the knowledge of valley physics, providing wide applications of topological phonons.
二维（2D）材料中的拓扑量子态是引人入胜的研究课题，通常聚焦于与电子相关的系统。在这项工作中，我们通过第一性原理计算提出了一种方法，可在二维六角晶格中产生具有量子化谷贝里相位的狄拉克声子态。我们表明，在六角布里渊区角点具有三重旋转对称性的候选材料拥有谷狄拉克声子，并且这些声子在受到微扰时能确保保持完整。我们确定，由狄拉克声子构成的这种特殊拓扑特征可在各种二维材料中实现。特别是，单层CrI，一种在自旋电子学中具有奇特应用的引人关注的二维磁性半导体，是在实验中研究非平凡声子的理想平台。我们进一步证实，在两个不等价谷处，声子贝里相位被量子化为±π。终止于声子狄拉克锥投影处的声子边缘态清晰可见。这项工作表明，具有引人关注的谷狄拉克声子的二维六角晶格将拓展谷物理的知识，为拓扑声子提供广泛应用。
