Surface contribution to the optical properties of nonlocal systems

Abstract
A simple formalism is developed for the calculation of the optical properties of a nonlocal system, treating the continuous change of its response functions near the surface as a perturbation. The surface impedance is obtained in terms of the surface impedance of the unperturbed system and of the surface conductivity. The results are very general since no assumption about the unperturbed system is made, and it is shown that they include those of previous theories.