Nodal Chain Semimetal in Geometric Frustrated Acoustic metamaterial

Geometrically frustrated systems and topological semimetals have both attracted much interest and been studied in various systems in recent years. Here we study the interplay between these two systems. We show that a Weyl point can be extended to a chain of degeneracy (a nodal chain) with nonzero charge of Berry flux through geometrical frustration. We propose to realize such a charged nodal chain in an acoustic metamaterial, based on both tight-binding and full-wave numerical simulations. Moreover, we observe a fan-like surface state spectrum, whose dispersion is controlled by the bulk band properties. Our work points to a new class of band degeneracy that carries non-zero Berry flux. The resulting topological metamaterial may be useful for controlling the flow of sound and light.