Topological crystalline insulators (TCIs) can exhibit unusual, quantized electric phenomena such as fractional electric polarization and boundary-localized fractional charge^1,2,3,4,5,6. This quantized fractional charge is the generic observable for identification of TCIs that lack clear spectral features^5,6,7, including ones with higher-order topology^8,9,10,11. It has been predicted that fractional charges can also manifest where crystallographic defects disrupt the lattice structure of TCIs, potentially providing a bulk probe of crystalline topology^10,12,13,14. However, this capability has not yet been confirmed in experiments, given that measurements of charge distributions in TCIs have not been accessible until recently¹¹. Here we experimentally demonstrate that disclination defects can robustly trap fractional charges in TCI metamaterials, and show that this trapped charge can indicate non-trivial, higher-order crystalline topology even in the absence of any spectral signatures. Furthermore, we uncover a connection between the trapped charge and the existence of topological bound states localized at these defects. We test the robustness of these topological features when the protective crystalline symmetry is broken, and find that a single robust bound state can be localized at each disclination alongside the fractional charge. Our results conclusively show that disclination defects in TCIs can strongly trap fractional charges as well as topological bound states, and demonstrate the primacy of fractional charge as a probe of crystalline topology.

拓扑晶体绝缘体 (TCI) 可以表现出不寻常的量子化电现象，例如分数电极化和边界局部分数电荷^1,2,3,4,5,6。这种量化的分数电荷是识别缺乏清晰光谱特征^5,6,7的 TCI 的通用可观察值，包括具有高阶拓扑的^{TCI 8,9,10,11}。据预测，分数电荷也可以在晶体缺陷破坏 TCI 的晶格结构的地方表现出来，从而可能提供晶体拓扑的体探针^10,12,13,14。然而，这种能力尚未在实验中得到证实，因为直到最近才可以测量 TCI 中的电荷分布¹¹. 在这里，我们通过实验证明向错缺陷可以有效地捕获 TCI 超材料中的分数电荷，并表明即使在没有任何光谱特征的情况下，这种捕获的电荷也可以指示非平凡的高阶晶体拓扑。此外，我们发现了捕获电荷与定位于这些缺陷的拓扑束缚态之间的联系。当保护性晶体对称性被破坏时，我们测试了这些拓扑特征的稳健性，并发现单个稳健的束缚态可以在分数电荷旁边的每个向错处定位。我们的结果最终表明，TCIs 中的向错缺陷可以强烈捕获分数电荷以及拓扑束缚态，并证明分数电荷作为晶体拓扑探针的首要地位。