Symmetry protected topological phases characterized by isolated exceptional points
Symmetry protected topological phases characterized by isolated exceptional points
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以孤立异常点为特征的对称保护拓扑相
DOI：
10.1103/physrevb.99.165148
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发表时间：
2019
影响因子：
3.7
通讯作者：
Song Z.
中科院分区：
文献类型：
--
作者：
Lin S.;Jin L.;Song Z.
在非厄米系统中，伴随本征态合并的例外点（EPs）具有许多奇异的特征。EP通常对系统参数敏感;在这里，我们报告了在二维非厄米双层正方形晶格的布里渊区（BZ）中对称保护的孤立EP。在对称性的保护下，孤立的EP只能在BZ中移动、合并和分裂。系统的布洛赫哈密顿量的本征态下的泡利矩阵的平均值定义了一个真实的平面向量场，其拓扑缺陷是孤立的EP与涡。缠绕数表征了非厄米特系统的涡旋，揭示了系统的拓扑性质。不同的拓扑相对应于不同的EP构型，除非伴随EP的合并或分裂发生拓扑相变，否则EP构型是不变的。
Exceptional points (EPs) associated with the coalescence of eigenstates in non-Hermitian systems have many exotic features. The EPs are generally sensitive to system parameters; here we report symmetry protected isolated EPs in the Brillouin zone (BZ) of a two-dimensional non-Hermitian bilayer square lattice. Protected by symmetry, the isolated EPs only move, merge, and split in the BZ. The average values of Pauli matrices under the eigenstate of the system's Bloch Hamiltonian define a real planar vector field, the topological defects of which are isolated EPs associated with vortices. The winding number characterizes the vortices and reveals the topological properties of the non-Hermitian system. Different topological phases correspond to different EP configurations, which are unchanged unless topological phase transition occurs accompanying the EPs merging or splitting.