Surface modes in a ferroelectric film

We discuss polarisation surface modes in the paraelectric phase of a cubic ferroelectric film by means of a phenomenological Landau theory. The film i s extended to infinity in the two(x, y) lateral directions and is in contac t with two semi-infinite isotropic dielectric media. Surface polarisation e nergy is taken into account in the expression of boundary conditions for po larisation modes which are treated in the electrostatic approximation. Ther e are two types of propagative normal modes : surface modes with an exponen tial dependence of the amplitude on distance across the film and so called guided wave modes. We have determined the frequencies and the eignvectors o f the modes.