The unusual phenomenon of negative refraction of light is central to the realization of interesting optical devices such as superlenses and other novel schemes for guiding and imaging light. However, achieving negative refraction for light-based quasiparticles called polaritons is challenging due to the much shorter wavelengths involved, which are typically squeezed by several orders of magnitude. Now, Xiao Lin and co-workers from China, the USA and Singapore predict that negative refraction should be possible for plasmon polaritons and phonon polaritons in graphene/boron nitride heterostructures. Using the finite-element simulation method, all-angle in-plane negative refraction was numerically predicted to occur at a frequency of 22.96 THz, where the confinement factor was 195. When the graphene or the boron nitride were replaced by a hybrid layer featuring both graphene and boron nitride, the frequency at which the effect occurs could be tuned as a function of the chemical potential of the graphene layer or the thickness of the boron nitride layer.
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Horiuchi, N. Negative refraction. Nature Photon 11, 454 (2017). https://doi.org/10.1038/nphoton.2017.130