Observation of surface mode arcs associated with nodal surfaces in electromagnetic metacrystals

Abstract

In this article, we designed, fabricated, and characterized an electromagnetic metacrystal that topologically carries nontrivial nodal surface degeneracies. Compared with nodal surfaces observed in an acoustic system, the topological charge of the nodal surface in our system is compensated by charge-2 Weyl points, and we designed our system considering the rules of symmetry. To demonstrate the existence of the nodal surfaces and their topological properties, we have experimentally observed surface state arcs derived from helicoid sheets of surface states connecting the nodal surface with a charge-2 Weyl point. The surface states support the robust unidirectional transport on the surface, and the nodal surface provides more degrees of freedom to engineer the dispersion of surface states. Our system offers a platform to explore this new class of gapless topological electromagnetic wave systems.