Homogenization of plasmonic nanocluster metamaterials

Metamaterials and plasmonics based on micro- and nanostructured metallic-dielectric composites are bringing an important revolution to the microwave and optics fields due to their potential for enabling the realization of novel physical properties unattainable from natural materials, such as isotropic negative refraction, slow light, near-field enhancement, as well as EM focusing and energy transfer beyond the diffraction limit. Such artificial composite structures owe their peculiar properties both to the constituent materials which comprise their elementary building blocks and to their specific spatial arrangement. The use of homogenization methods can provide a convenient characterization of EM-wave-matter interaction by describing metamaterials as bulk homogeneous materials with effective parameters that take into account their inherent qualities and complex nature. While the concept of homogenization theory is easily applied to the long-wavelength limit, e.g. the microwave regime where true sub-wavelength structures can be fabricated, the optical regime challenges the underlying hypothesis of a true subwavelength unit cell. Indeed, for artificial materials the size of the lattice constant is typically only moderately smaller than the wavelength of light. As a consequence, metamaterials can be characterized by nonnegligible spatial dispersion effects.