标题： 观察来自不同光谱电荷的非线性拓扑角态 显示英文标题

标题： Observation of nonlinear topological corner states originating from different spectral charges

摘要： 高阶拓扑绝缘体（HOTIs）是一种独特的拓扑材料，其支持的边缘态的维度至少比基础结构的维度低两个。 HOTIs在具有不同对称性的晶格上被观察到，但仅在截断HOTI产生与单元格相同离散旋转对称阶数的有限结构的几何形状中，从而确定了绝缘体边缘的几何形状。 在这里，我们实验上展示了基于凯库勒图案晶格的新类型二维（2D）HOTI，其离散旋转对称阶数不同于构成蜂窝晶格的单元格的对称阶数，混合边界有助于产生所有三种可能的角点，这些角点支持有效0D角态，特别是与光谱电荷5/6相关的角态。 我们还表明，线性角态在材料的聚焦非线性存在下会引发丰富的稳定混合非线性角态家族，从它们分叉出来。 这种新型的非线性角态在用飞秒激光写入技术刻写的透明非线性介质中的混合HOTI中被观察到。 我们的结果完善了HOTIs的类别，并为观察具有新内部结构和对称性的拓扑态开辟了道路。 显示英文摘要

摘要： Higher-order topological insulators (HOTIs) are unique topological materials supporting edge states with the dimensionality at least by two lower than the dimensionality of the underlying structure. HOTIs were observed on lattices with different symmetries, but only in geometries, where truncation of HOTI produces a finite structure with the same order of discrete rotational symmetry as that of the unit cell, thereby setting the geometry of insulator edge. Here we experimentally demonstrate a new type of two-dimensional (2D) HOTI based on the Kekule-patterned lattice, whose order of discrete rotational symmetry differs from that of the unit cells of the constituent honeycomb lattice, with hybrid boundaries that help to produce all three possible corners that support effectively 0D corner states of topological origin, especially the one associated with spectral charge 5/6. We also show that linear corner states give rise to rich families of stable hybrid nonlinear corner states bifurcating from them in the presence of focusing nonlinearity of the material. Such new types of nonlinear corner states are observed in hybrid HOTI inscribed in transparent nonlinear dielectric using fs-laser writing technique. Our results complete the class of HOTIs and open the way to observation of topological states with new internal structure and symmetry.