Exclusive surface polaritons in graphene/hBN metamaterials

Surface plasmon–phonon polaritons are studied in a hexagonal boron nitride/graphene metamaterial (hBN/Gr MM). Two styles of surface polaritons are predicted, or ordinary surface polaritons (OSPs) and ghost surface polaritons (GSPs), which appear in different frequency ranges. These surface polaritons are some bi-hybridization surface waves, i.e., exciton- and polarization-hybridization surface polaritons. OSPs are similar in behavior to conventional surface polaritons. However, GSP's dispersion feature is beyond one's imagination, and their dispersion curves exhibit an interesting picture. In addition to having a positive group velocity, the GSPs can also have a negative group velocity or even the singularity of group velocity for continuously changing wavenumbers. Another main feature of GSPs is that their Poynting vector displays a series of interferent fringes in the MM due to the coherency of the two branch waves.