Analytical Expressions for the Electromagnetic Dyadic Green's Function in Graphene and Thin Layers

An analytical general analysis of the electromagnetic dyadic Green's function for 2-D sheet (or a very thin film) is presented, with an emphasis on the case of graphene. A modified steepest descent treatment of the fields from a point dipole given in the form of Sommerfeld integrals is performed. We sequentially derive the expressions for both out-of-plane and in-plane fields of both polarizations. It is shown that the analytical approximation provided is very precise in a wide range of distances from a point source down to a deep subwavelength region (1/100 of wavelength). We separate the contribution from the pole, the branch point, and discuss their interference. The asymptotic expressions for the fields are composed of the plasmon, Norton wave, and the components corresponding to free space.