  We report the first observation of epsilon near zero (ENZ) phonon polaritons
in an ultrathin AlN film fully hybridized with surface phonon polaritons (SPhP)
supported by the adjacent SiC substrate. Employing a strong coupling model for
the analysis of the dispersion and electric field distribution in these
hybridized modes, we show that they share the most prominent features of the
two precursor modes. The novel ENZ-SPhP coupled polaritons with a highly
propagative character and deeply sub-wavelength light confinement can be
utilized as building blocks for future infrared and terahertz (THz)
nanophotonic integration and communication devices.
