Ideal type-II Weyl points in twisted one-dimensional dielectric photonic crystals

TL;DR

This paper demonstrates a method to realize ideal type-II Weyl points in a one-dimensional layered photonic crystal using anisotropic materials, enabling topological transitions and surface states without complex structural design.

Contribution

It introduces a novel approach to achieve ideal type-II Weyl points in 1D photonic crystals through anisotropic materials and twist angle tuning, simplifying topological photonic device design.

Findings

Topological transition from Dirac to Weyl points observed

Gapless surface states demonstrated at interfaces

Transformation to non-ideal Weyl points by symmetry breaking

Abstract

Weyl points are the degenerate points in three-dimensional momentum space with nontrivial topological phase, which are usually realized in classical system with structure and symmetry designs. Here we proposed a one-dimensional layer-stacked photonic crystal using anisotropic materials to realize ideal type-II Weyl points without structure designs. The topological transition from two Dirac points to four Weyl points can be clearly observed by tuning the twist angle between layers. Besides, on the interface between the photonic type-II Weyl material and air, gappless surface states have also been demonstrated in an incomplete bulk bandgap. By breaking parameter symmetry, these ideal type-II Weyl points at the same frequency would transform into the non-ideal ones, and exhibit topological surface states with single group velocity. Our work may provide a new idea for the realization of photonic Weyl points or other semimetal phases by utilizing naturally anisotropic materials.