A fractional corner anomaly reveals higher-order topology
A fractional corner anomaly reveals higher-order topology
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DOI：
10.1126/science.aba7604
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发表时间：
2020-06-05
期刊：
影响因子：
56.9
通讯作者：
Bahl, Gaurav
中科院分区：
文献类型：
--
作者：
Peterson, Christopher W.;Li, Tianhe;Bahl, Gaurav
边界局域拓扑模式的光谱测量通常用于识别拓扑绝缘体。对于高阶绝缘体，这些模式出现在较高余维的边界处，例如二维材料的拐角处。不幸的是，这种光谱方法只有在拓扑模式的能量位于体带隙内时才是可行的，这对于许多拓扑晶体绝缘体是不需要的。这些绝缘体的关键拓扑特征是填充的大块手产生的部分电荷密度，但迄今为止还无法测量这种电荷分布。实验测量了旋转对称二维超材料中的边界局域分数电荷密度，发现了四分之一和三分之一的分数电荷密度。然后，我们引入了一个拓扑指标，允许明确识别高阶拓扑结构，即使没有间隙状态，我们证明了相关的高阶体积边界对应。
Spectral measurements of boundary-localized topological modes are commonly used to identify topological insulators. For high-order insulators, these modes appear at boundaries of higher codimension, such as the corners of a two-dimensional material. Unfortunately, this spectroscopic approach is only viable if the energies of the topological modes lie within the bulk bandgap, which is not required for many topological crystalline insulators. The key topological feature in these insulators is instead fractional charge density arising from filled bulk hands, but measurements of such charge distributions have not been accessible to date. We experimentally measure boundary-localized fractional charge density in rotationally symmetric two-dimensional metamaterials and find one-fourth and one-third fractionalization. We then introduce a topological indicator that allows for the unambiguous identification of higher-order topology, even without in-gap states, and we demonstrate the associated higher-order hulk-boundary correspondence.