Revisiting the Surface Impedance and Effective Medium Models Applied to Near-Field Radiative Heat Transfer

The role of the optics of surface and interfaces in the near-field radiative heat transfer for finite-layered media and superlattices is reviewed. The definition of surface impedance is compared with effective medium approximations for the dielectric functions. It is shown that the presence of polar materials makes the use of effective medium models ineffective, in particular, when the topmost layer supports surface modes. Furthermore, the effect on the near-field heat transfer is quantified when approximate methods are used.