Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures

Surface phonon polaritons (SPhPs) – the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons – offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. However, once a particular material is chosen, the SPhP characteristics are fixed by the spectral positions of the optic phonon frequencies. Here, we provide a demonstration of how the frequency of these optic phonons can be altered by employing different atomic-scale superlattices (SLs) of polar semiconductors, i.e., AlN and GaN. Using second harmonic generation (SHG) spectroscopy, we show that the optic phonon frequencies of the SLs exhibit a strong dependence on the layer thicknesses of the constituent materials. Furthermore, new vibrational modes emerge that are confined to the layers while others are centered at the AlN/GaN interfaces. As the IR dielectric function is governed by the optic phonon behavior in polar materials, controlling the optic phonon...