反钙钛矿结构Cu $_3$ PdN的拓扑节线半金属态和Dirac半金属态
Topological Nodal Line Semimetal and Dirac Semimetal State in Antiperovskite Cu$_3$PdN
摘要：
基于第一性原理计算和有效模型分析，我们提出了立方反钙钛矿材料Cu $_3$ PdN在忽略自旋轨道耦合（SOC）时，由于时间反演和反转对称性的共存，可以保持三维拓扑节线半金属态.由于立方对称性，总共有三个节线圆。还导出了“鼓头”状表面平坦带。当包含SOC时，每个节线演化为一对受C $_4$晶体对称性保护的稳定的3D狄拉克点。这与迄今已知的狄拉克半金属，如Na $_3$ Bi和Cd $_3$ As $_2$，都只有一对狄拉克点有显著的区别。一旦C $_4$对称性被破缺，狄拉克点被带隙，系统成为具有（1;111）Z $_2$指数的强拓扑绝缘体。
英文摘要：
Based on first-principles calculation and effective model analysis, we propose that the cubic antiperovskite material Cu$_3$PdN can host a three-dimensional (3D) topological nodal line semimetal state when spin-orbit coupling (SOC) is ignored, which is protected by coexistence of time-reversal and inversion symmetry. There are three nodal line circles in total due to the cubic symmetry. "Drumhead"-like surface flat bands are also derived. When SOC is included, each nodal line evolves into a pair of stable 3D Dirac points as protected by C$_4$ crystal symmetry. This is remarkably distinguished from the Dirac semimetals known so far, such as Na$_3$Bi and Cd$_3$As$_2$, both having only one pair of Dirac points. Once C$_4$ symmetry is broken, the Dirac points are gapped and the system becomes a strong topological insulator with (1;111) Z$_2$ indices.
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