Type-II Dirac photons at the metasurfaces

TL;DR

This paper reports the experimental realization of type-II Dirac points in metasurfaces, demonstrating their topological properties and gapless edge modes, advancing the field of topological photonics.

Contribution

The study introduces a practical metasurface design to realize and observe type-II Dirac points and their associated edge states in photonic systems.

Findings

Type-II Dirac points were experimentally realized in metasurfaces.

Gapless edge modes were observed at domain boundaries.

Metasurfaces serve as accessible platforms for topological photonics applications.

Abstract

Topological characteristics of energy bands, such as Dirac/Weyl nodes, have attracted substantial interest in condensed matter systems as well as in classical wave systems. Among these energy bands, the type-II Dirac point is a nodal degeneracy with tilted conical dispersion, leading to a peculiar crossing dispersion in the constant energy plane. Such nodal points have recently been found in electronic materials. The analogous topological feature in photonic systems remains a theoretical curiosity, with experimental realization expected to be challenging. Here, we experimentally realize the type-II Dirac point using a planar metasurface architecture, where the band degeneracy point is protected by the underlying mirror symmetry of the metasurface. Gapless edge modes are found and measured at the boundary between the different domains of the symmetry-broken metasurface. Our work shows that metasurfaces are simple and practical platforms for realizing electromagnetic type-II Dirac points, and their planar structure is a distinct advantage that facilitates applications in two-dimensional topological photonics.