Negative refraction gives rise to the Klein paradox

Electromagnetic negative refraction in metamaterials has attracted increasingly great interest since its first experimental verification in 2001. It potentially leads to the applications superior to conventional devices including compact antennas for mobile stations, imaging beyond the diffraction limit, and high-resolution radars, not to mention the anomalous wave propagation in fundamental optics. Here, we report how metamaterials could be used to simulate the negative refraction of spin-zero particles interacting with a strong potential barrier, which gives rise to the Klein paradox-a counterintuitive relativistic process. We address the underlying physics of analogous wave propagation behaviors in those two entirely different domains of quantum and classical.