Surface polaritons on uniaxial antiferromagnets

Abstract

We investigate the properties of surface polaritons on uniaxial antiferromagnets. In zero applied field we find that surface polaritons may exist in a band of frequencies forbidden to bulk polaritons and that propagation is reciprocal, i.e., if the mode has frequency $\ensuremath{\omega}$ and wave vector ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}}$, then $\ensuremath{\omega}(+{\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}})=\ensuremath{\omega}(\ensuremath{-}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}}_{\ensuremath{\parallel}})$. When a field is applied parallel to the surface, along the anisotropy axis, surface and bulk polaritons may exist in the same frequency range, and the dispersion relation of the surface polaritons is no longer reciprocal. We show that surface polaritons may be easily detected through a standard attenuated total reflection measurement. The case of an antiferromagnetic metal is also discussed, since the negative dielectric constant of the metal influences the dispersion relation in a qualitative manner.