Plasmon–phonon coupling in graphene–hyperbolic bilayer heterostructures

Yin Ge, Yuan Jun, Jiang Wei, Zhu Jianfei, Ma Yungui^†,

Relative permittivity spectra of AlN (a) and ZnO (b). The c-axis of the crystals for AlN and ZnO is assumed to be in plane and out of plane, respectively. The dielectric functions of these two materials are described by Eq. (10). The hyperbolic regions are highlighted by the orange and green colors, respectively.