Casimir force on a thin slab: The influence of surrounding media and the role of surface polaritons

Abstract

We consider the Casimir force on a metallic slab with the thickness in the nanometer range, bounded by different dielectric media. In such systems the force is large $(\ensuremath{\sim}{10}^{6}\phantom{\rule{0.3em}{0ex}}\mathrm{N}∕{\mathrm{m}}^{2})$ and, depending on the selected configuration, it can be squeezing or relaxing. The mode analysis, performed numerically as well as analytically under the assumption of inert bounding media, indicates that the force on a thin metallic slab is, in many situations, predominantly due to the surface polariton (SP) modes of the system (an obvious exception is the configuration with the slab sandwiched between two highly reflecting plates). Thus, the sign and the magnitude of the Casimir force are typically determined by competing contributions from the two SP modes existing in the model adopted, and are controllable by properly designing the system parameters. The same conclusion holds for a more complex description of polar dielectric media, assuming that the characteristic frequencies of polar modes in dielectrics are much smaller than the characteristic plasma frequency of a metallic slab.