Kargarian Mehdi, Randeria Mohit, Lu Yuan-Ming
Department of Physics, The Ohio State University, Columbus, OH 43210.
Department of Physics, The Ohio State University, Columbus, OH 43210
Proc Natl Acad Sci U S A. 2016 Aug 2;113(31):8648-52. doi: 10.1073/pnas.1524787113. Epub 2016 Jul 19.
Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at [Formula: see text] where gapless states on the side surfaces are protected only near [Formula: see text] We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2 Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.
受近期探测狄拉克半金属（DSM）Na3Bi和Cd3As2反常表面态的实验启发，我们提出了标题中的问题。我们发现，与外尔半金属形成显著对比的是，DSM的无隙表面态通常不受拓扑保护，除非在表面布里渊区的时间反演不变平面上。我们首先在一个具有一对位于[公式：见原文]的狄拉克节点的最小四能带模型中证明这一发现，其中侧面的无隙态仅在[公式：见原文]附近受到保护。然后，我们使用针对Na3Bi和Cd3As2空间群的K理论分析，验证了我们关于DSM中不存在保护双费米弧的拓扑不变量的结论。一般来说，这些弧会变形为费米口袋，类似于拓扑绝缘体的表面态，并且随着化学势的变化，这个口袋可以合并到体狄拉克费米面的投影中。我们对DSM表面态的掺杂依赖性做出了精确预测，这些预测可以通过角分辨光电子能谱和量子振荡实验进行检验。
