Probing the Influence of Dielectric Environment upon Volume-confined Hyperbolic phonon Polaritons

The unique ability of hyperbolic phonon polaritons (HPhPs) to confine long-wavelength light to nanoscale volumes in low-loss, naturally hyperbolic materials – such as hexagonal boron nitride (hBN) – has generated immense interest. We employ nano-scale imaging and spectroscopy techniques to elucidate the characteristics of HPhPs to elucidate polariton characteristics as a function of the complex refractive index of the substrate, including the impact of both the real and imaginary contributions. Although higher-order polariton modes exhibit wavelengths weakly sensitive to the environment, the principal mode strongly depends on the substrate dielectric constant. Furthermore, we demonstrate a reconfigurable hyperbolic metasurface comprised of a heterostructure of hBN in direct contact with the phase-change material (PCM) single-crystal vanadium dioxide (VO2). Metallic and dielectric domains in VO2 provide spatially localized changes in the local dielectric environment, enabling launching, reflection, and transmission of hyperbolic phonon polaritons (HPhPs) at the PCM domain boundaries, and tuning the wavelength of HPhPs propagating in hBN over these domains.