In most cases, higher-order topological insulating phases are observed in crystalline materials and photonic/phononic crystals with high crystalline symmetries. Few exceptions include amorphous and quasi-crystalline matters, which have recently been demonstrated to exhibit such topological phases as well. This report reveals analytically and numerically that the photonic crystals with asymmetric sublattices can also exhibit second-order topological insulating phases. The appearance of band inversion for the change of unit cell parameters, the quantized 2D polarizations and topological corner charges, and the generation of corner states explicitly reveal the existence of such second-order photonic topological insulating phases. Quite interestingly, for arbitrarily shaped asymmetric unit cells, second-order topological corner states are also observed, provided that the intercell coupling dominates over the intracell one.

中文翻译：

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低对称性方格中的二阶光子拓扑角态

在大多数情况下，在晶体材料和具有高晶体对称性的光子/声子晶体中观察到高阶拓扑绝缘相。很少有例外包括无定形和准结晶物质，最近已证明它们也表现出这种拓扑相。该报告从分析和数值上揭示了具有不对称亚晶格的光子晶体也可以表现出二阶拓扑绝缘相。因晶胞参数变化而出现的能带反转、二维极化和拓扑角电荷以及角状态的产生明确揭示了这种二阶光子拓扑绝缘相的存在。非常有趣的是，对于任意形状的非对称晶胞，