Poynting vector in negative-index metamaterials

Metamaterials are characterized by counterintuitive phenomena, which have been debated since their first practical realization. Due to their anomalous backward power flow, it has been recently discussed whether even the classic definition of the Poynting vector, defining the power flux per unit surface, should be modified when dealing with metamaterials with exotic properties. Here, we settle this issue and fully clarify the physics of negative refraction, showing that the Poynting vector and other power relations in artificial materials may be unambiguously defined consistently with classic formulas for homogeneous media.