Observation of nonlinear topological corner states originating from different spectral charges

Abstract

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.

21 pages, 6 figures

References in corpus (15)

• Topological Photonics
• Scheme to Achieve Silicon Topological Photonics
• Electric Multipole Moments, Topological Multipole Moment Pumping, and Chiral Hinge States in Crystalline Insulators
• $(d-2)$-dimensional edge states of rotation symmetry protected topological states
• Higher-order topological insulators and semimetals on the breathing Kagome and pyrochlore lattices
• Peculiar Width Dependence of the Electronic Property of Carbon Nanoribbons
• Visualization of higher-order topological insulating phases in two-dimensional dielectric photonic crystals
• Direct observation of corner states in second-order topological photonic crystal slabs
• Metallic Graphene Nanodisks
• Active topological photonics
• Low-threshold topological nanolasers based on second-order corner state
• Bimorphic Floquet Topological Insulators
• Tight-binding methods for general longitudinally driven photonic lattices -- edge states and solitons
• Observation of $\pi$ solitons in oscillating waveguide arrays
• Light bullets in Su-Schrieffer-Heeger photonic topological insulators