Plasmons are density waves of electrons, created when light hits the surface of a metal. Because these density waves are generated at optical frequencies, they can encode a lot of information. Plasmonics – called "light on a wire," - is thought to embody the strongest points of both optical and electronic data transfer. It would allow the transmission of data at optical frequencies along the surface of a tiny metal wire, despite the fact that the data travels in the electronic form rather than in a photonic form. The strength of plasmonic waves is that they can be easily converted to and from light waves. Main problems: losses and localization of light.
A metamaterial is a material which gains its properties from its structure rather than from properties of materials. In most cases in optics it is a nanostructured metal-dielectric composite. A metamaterial may exhibit some unusual properties, e.g. a negative refractive index, never occurred in nature. In optics metamaterials can help to produce a superlens and hyperlens with resolution beyond the diffraction limit revealing data with nanometer-scale features. Metamaterials are the key players in the new direction of transformation optics (e.g. in cloaking). Main problems: losses, anisotropy and bandwidth.
Plasmons waves exist in metamaterials and actually determine their properties, therefore both directions are intensively interwoven.