Multi Weyl Points and the Sign Change of Their Topological Charges in Woodpile Photonic Crystals

TL;DR

This paper demonstrates the existence and tunability of Weyl points with different topological charges in simple, fabricable chiral woodpile photonic crystals, revealing their surface states and back-scattering immunity.

Contribution

It introduces a simple photonic crystal design hosting Weyl points with tunable topological charges and explains the physics behind charge sign change using a tight binding model.

Findings

Weyl points with charges 1 and 2 are found in chiral woodpile photonic crystals.

The topological charge sign can be tuned by adjusting material parameters.

Gapless surface states with back-scattering immunity are demonstrated.

Abstract

We show that Weyl points with topological charges 1 and 2 can be found in very simple chiral woodpile photonic crystals, which can be fabricated using current techniques down to the nano-scale. The sign of the topological charges can be tuned by changing the material parameters of the crystal, keeping the structure and the symmetry unchanged. The underlying physics can be understood using a tight binding model, which shows that the sign of the charge depends on the hopping range. Gapless surface states and their back-scattering immune properties are also demonstrated in these systems.