▎ 摘　　要

We use infrared spectroscopy to explore the hybridization of graphene plasmons and hexagonal boron nitride (hBN) phonons in their heterostructures with different compositions. We show that the degree of plasmon-phonon hybridization and the slowing of the light group velocity within the infrared transparency window due to the plasmon-phonon destructive interference are dominated by hBN phonon oscillating strength, which can be tuned by varying the hBN thickness in a layer-by-layer manner. However, the plasmon oscillating strength in metallic graphene governs the magnitude of infrared extinction, which exceeds 6% at around 7 mu m in a graphene/hBN/graphene heterostructure due to the strong plasmon dipole-dipole coupling. Our work demonstrates that the infrared optical responses of graphene-hBN heterostructures can be engineered by controlling the coupling strength of plasmon-phonon hybridization and the overall plasmon oscillating strength simultaneously, thus opening the avenue for the light manipulation and detection in the mid-infrared regime based on such layered heterostructures.