When the refractive index of a material approaches zero, peculiar physical properties arise. This research direction is one of the most fundamental branches of metamaterials and may have important impact on future electromagnetic materials. Our previous design established the foundation of double-zero materials (also called epsilon-mu-near-zero materials) with both near-zero permittivity and permeability, and a consequent cone-like dispersion (Read more). This work is regarded as one of the early milestones of dielectric metamaterials. We also revealed some novel properties of zero-refractive-index materials such as arbitrary flux control (Read more), the percolation of light and anti-doping effect (Read more), and the doping effect for coherent perfect absorption (Read more). We have recently realized 3D double-zero materials for acoustic (Read more) and electromagnetic (Read more) waves.