Multiple Weyl points and the sign change of their topological charges in woodpile photonic crystals

Abstract

Weyl points in photonic systems have gained much attention for their novel properties, such as topologically protected robustness and gapless surface states. However, many Weyl photonic crystal structures designed previously are probably too complicated for nanofabrication. Here, the authors discover that Weyl points can be found in metallic chiral woodpile photonic crystals, which can be fabricated using current nanotechnology. Weyl points with topological charge not only 1 but also 2 can be found in these photonic crystals. When the constituent materials change from the air-in-metal to metal-in-air configuration, the sign of the topological charge will change, leading to a topological phase transition, and the bands change from topologically trivial to nontrivial. Gapless surface states exist in the latter case and robust transport properties have also been demonstrated numerically. When the metallic component is replaced by dielectric materials, such as silicon, the Weyl points still exist. These woodpile photonic crystals should become promising platforms for exploring Weyl point related physics at optical frequencies.