Boundary Criticality of PT-Invariant Topology and Second-Order Nodal-Line Semimetals
Boundary Criticality of PT-Invariant Topology and Second-Order Nodal-Line Semimetals
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$mathcalPT$ 的边界临界性-不变拓扑和二阶节点线半金属
DOI：
10.1103/physrevlett.125.126403
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Y. X. Zhao
中科院分区：
文献类型：
--
作者：
K. Wang;J. X. Dai;L. B. Shao;S. A. Yang;Y. X. Zhao
对于传统的拓扑相位，边界无隙模式由体拓扑不变量决定。基于发展的解析方法来解决高阶边界模式，我们提出了不变的二维拓扑绝缘体和三维拓扑半金属，超越了这个体积边界对应框架。在体积拓扑不变量不变的情况下，它们的一阶边界经历了用二阶边界零模式分离不同相的转变。对于二维拓扑绝缘体，螺旋边缘模式出现在两个二阶拓扑绝缘体相位的过渡点，分别与对角和非对角角零模式。因此，对于3D拓扑半金属，临界性对应于狄拉克半金属相的表面螺旋费米弧。有趣的是，我们发现，3D系统一般属于一个新的二阶半金属线相，具有缺口的表面，但一对对角或非对角铰链费米弧。
For conventional topological phases, the boundary gapless modes are determined by bulk topological invariants. Based on developing an analytic method to solve higher-order boundary modes, we present-invariant 2D topological insulators and 3D topological semimetals that go beyond this bulk-boundary correspondence framework. With unchanged bulk topological invariants, their first-order boundaries undergo transitions separating different phases with second-order boundary zero modes. For the 2D topological insulator, the helical edge modes appear at the transition point for two second-order topological insulator phases with diagonal and off-diagonal corner zero modes, respectively. Accordingly, for the 3D topological semimetal, the criticality corresponds to surface helical Fermi arcs of a Dirac semimetal phase. Interestingly, we find that the 3D system generically belongs to a novel second-order nodal-line semimetal phase, possessing gapped surfaces but a pair of diagonal or off-diagonal hinge Fermi arcs.