论文标题
非一般退化点的出生配额
Birth Quota of Non-Generic Degeneracy Points
论文作者
论文摘要
Weyl点是依赖三维参数空间的汉密尔顿能量光谱中的通用和稳定的特征。在通用的扰动上,非一般隔离的二重变性点(例如多向点点)分裂为Weyl点,以去除微调或保护对称性。所得的Weyl点的数量至少为$ | Q | $,其中$ Q $是与非传播退化点相关的拓扑费用。在这里,我们表明,这种非一般退化点也具有出生配额,即,在任何扰动时可以从中可以诞生的最大数量的Weyl点。出生配额是与非生成退化点相关的局部多样性,这是从奇异理论中知道的地图细菌的不变性。这不仅适用于带有Hermitian Hamiltonian的三维参数空间,而且还适用于带有手性对称性汉密尔顿的二维参数空间。我们说明了二维晶体和三维晶体的带结构的功能。我们的工作在奇异理论和拓扑结构结构以及更广泛的参数依赖性量子系统之间建立了牢固而有力的联系。
Weyl points are generic and stable features in the energy spectrum of Hamiltonians that depend on a three-dimensional parameter space. Non-generic isolated two-fold degeneracy points, such as multi-Weyl points, split into Weyl points upon a generic perturbation that removes the fine-tuning or protecting symmetry. The number of the resulting Weyl points is at least $|Q|$, where $Q$ is the topological charge associated to the non-generic degeneracy point. Here, we show that such a non-generic degeneracy point also has a birth quota, i.e., a maximum number of Weyl points that can be born from it upon any perturbation. The birth quota is a local multiplicity associated to the non-generic degeneracy point, an invariant of map germs known from singularity theory. This holds not only for the case of a three-dimensional parameter space with a Hermitian Hamiltonian, but also for the case of a two-dimensional parameter space with a chiral-symmetric Hamiltonian. We illustrate the power of this result for band structures of two- and three-dimensional crystals. Our work establishes a strong and powerful connection between singularity theory and topological band structures, and more broadly, parameter-dependent quantum systems.