Double excitation of surface modes at uniaxial-metal-isotropic films

We study the double excitation of surface modes at a metallic film that separates a uniaxial medium from an isotropic dielectric. We find that, for certain constitutive parameters of the structure, two normal modes can be associated to the film. It is found that the distance in the complex plane between the propagation constants of these modes can be considerably reduced by tuning conveniently film parameters, although the propagation constants are "reluctant" to coincide. We also show that a plane wave incident on the film from the crystal side can excite both modes simultaneously, without corrugating the surface or adding another layer. We obtain values of the film width for which the resonances appear at similar angles of incidence and show that these excitations are accompanied by an important increase of the power absorbed by the film and an enhancement of the fields at the two interfaces.