Abstract

It is well known that photons carrying momentum ħk exert a positive pressure on an object in vacuum. However, whether photons push or pull an object immersed inside a dielectric medium is not so straightforward due to the century-old debate associated with the definition of photon momentum inside dielectrics [1–2]. This question becomes even more puzzling with the advent of metamaterials, which can have negative refractive indices and hence the momentum and energy flux can be in opposite directions, which seemingly indicates a photon tension in such a kind of material.

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