An interpretation of the Klein paradox is given on the basis of the single-particle approximation of the Dirac theory. The Klein paradox for the Dirac electron and Klein tunneling for charge carriers in graphene are considered from a unified point of view. The close connection between the phenomenon of "retrograde motion" in relativistic quantum mechanics and the propagation of waves in "left-handed" media in electrodynamics is emphasized. This methodological material is used in teaching the quantum mechanics course at the Moscow Institute of Physics and Technology.
03.65.Xp Tunneling, traversal time, quantum Zeno dynamics
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
$^1$Moscow Institute of Physics and Technology, Department of Theoretical Physics
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