  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 anamolous 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 behaviours in those two entirely different domains
of quantum and classical.
