Kompanets Victor O, Feng Suge, Zhang Yiqi, Kartashov Yaroslav V, Li Yongdong, Zhuravitskii Sergei A, Skryabin Nikolay N, Kireev Alexander V, Dyakonov Ivan V, Kalinkin Alexander A, Shang Ce, Kulik Sergei P, Chekalin Sergey V, Zadkov Victor N
Institute of Spectroscopy, Russian Academy of Sciences, Moscow, Troitsk, 108840, Russia.
Key Laboratory for Physical Electronics and Devices, Ministry of Education, School of Electronic Science and Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
Adv Mater. 2025 Jul;37(30):e2500556. doi: 10.1002/adma.202500556. Epub 2025 May 19.
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 are 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, a new type of 2D HOTI based on the Kekulé-patterned lattice is experimentally demonstrated, 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. It is also shown 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. The results complete the class of HOTIs and open the way to observation of topological states with new internal structure and symmetry.
高阶拓扑绝缘体（HOTIs）是一类独特的拓扑材料，其边缘态的维度比基础结构的维度至少低两个维度。在具有不同对称性的晶格上观察到了HOTIs，但仅在特定几何结构中，HOTI的截断会产生具有与晶胞相同阶数的离散旋转对称性的有限结构，从而确定了绝缘体边缘的几何形状。在此，通过实验展示了一种基于凯库勒图案晶格的新型二维HOTI，其离散旋转对称性的阶数与组成蜂窝晶格的晶胞不同，具有混合边界，有助于产生所有三种可能的角，这些角有效地支持拓扑起源的0D角态，特别是与光谱电荷5/6相关的角态。研究还表明，在材料存在聚焦非线性的情况下，线性角态会产生丰富的稳定混合非线性角态族，这些非线性角态从线性角态分叉而来。利用飞秒激光写入技术在透明非线性电介质中写入的混合HOTI中观察到了这种新型非线性角态。这些结果完善了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。
