Cubic metamaterial crystal supporting broadband isotropic chiral phonons

Starting from the achiral body-centered-cubic Wigner-Seitz cell, a truncated octahedron, we design a chiral simple-cubic metamaterial crystal which exhibits chiral phonons for all phonon propagation directions in three-dimensional (3D) space over a broad frequency range as well as nearly isotropic acoustical activity. The resulting blueprint has simple-cubic crystal symmetry and is radically simpler than previous proposals based on 3D quasicrystalline or 3D triclinic truss lattices, making it amenable to state-of-the-art 3D additive manufacturing. To emphasize this aspect, we present electron micrographs of microstructured metamaterial samples fabricated by using 3D laser nanoprinting.