Surface optical phonon coupled anisotropic plasmons of 2D semi-Dirac system

We investigated the surface optical (SO) phonon coupled plasmons in a 2D semi-Dirac system placed on a polar substrate with SO phonon modes in the presence of electron-phonon coupling within the random-phase approximation and self-consistent field theory. The 2D semi-Dirac spectrum is quadratic along one x direction and linear along the y direction, and its plasmon dispersion is strongly angle dependent. With considering only the lower SO phonon mode in SiO₂, the coupling between the semi-Dirac plasmon and the substrate SO phonon mode produces two hybrid anisotropic SO phonon coupled plasmons with an energy higher optical branch and an energy lower branch, respectively. Meanwhile, The anisotropic hybrid SO phonon coupled plasmon modes can be tuned by excitation direction, carrier density, band gap parameter, and layer distance. The obtained results indicate that semi-Dirac layer on a polar substrate can form a useful platform for tunable directional plasmonics in the terahertz and mid-infrared ranges.