Negative refraction in hyperbolic hetero-bicrystals.
Aaron J SternbachSamuel L MooreAndrey A RikhterShuai ZhangRan JingYinming ShaoB S Y KimSuheng XuS LiuJames H EdgarAngel RubioCory R DeanJames C HoneMichael M FoglerDmitri N BasovPublished in: Science (New York, N.Y.) (2023)
We visualized negative refraction of phonon polaritons, which occurs at the interface between two natural crystals. The polaritons-hybrids of infrared photons and lattice vibrations-form collimated rays that display negative refraction when passing through a planar interface between the two hyperbolic van der Waals materials: molybdenum oxide (MoO 3 ) and isotopically pure hexagonal boron nitride (h 11 BN). At a special frequency ω 0 , these rays can circulate along closed diamond-shaped trajectories. We have shown that polariton eigenmodes display regions of both positive and negative dispersion interrupted by multiple gaps that result from polaritonic-level repulsion and strong coupling.