Plasmonic metamaterials.

Metamaterials, artificially structured composite materials with subwavelength unit cells, exhibit exotic properties not easily obtainable or unavailable in nature. Motivated by the promising applications of metamaterials at optical wavelengths in areas such as sub-diffraction-limited imaging and transformation optics, researchers have devoted considerable efforts to advancing the science and engineering of optical metamaterials. In the optical regime, plasmonic effects can play an important role when metals serve as one of the components in a metamaterial assembly. The objective of this dissertation is to understand the physics, unique properties and novel phenomena, arising from the interplay between metamaterials and plasmonics. In the dissertation, a new type of electromagnetic resonator whose unit cell is comprised of a pair of coupled ring resonators is investigated. It is found that the resonator possesses pronounced magnetic and electric plasmon responses. L-shaped resonators with four-fold rotational symmetry are also designed, in an attempt to suppress the bianisotropy exhibited by traditional split ring resonators. The nanoimprint lithography technique is used to fabricate magnetic metamaterials with advantages of high-throughput and low-cost. Furthermore, I present the demonstration of optical negative refraction in bulk metamaterials made of metallic nanowires, which are intrinsically low-loss and broad-band. To extend the metamaterial construction to a two-dimensional system, the propagation of surface plasmon polaritons on metallic thin films and structured metal surface is explored. In particular, it is shown that negative refraction of surface waves can be realized, by combining two regions supporting surface plasmon polaritons with group velocities opposite in signs. Finally, I perform a theoretical study of subwavelength plasmonic solitons in a nonlinear metamaterial: periodic structures consisting of nanoscale metallic and nonlinear dielectric slabs. Such solitons result from a balance between tunneling of surface plasmon modes and nonlinear self-trapping. The dynamics in such systems, arising from the threefold interplay among periodicity, nonlinearity, and surface plasmon polaritons, is substantially different from that in conventional nonlinear dielectric waveguide arrays. These findings may have novel applications in subwavelength imaging, waveguiding and transformation optics. It is expected that they will inspire both experimental and theoretical efforts in the emerging field of plasmonic metamaterials.