Plasmon Modes of Axisymmetric Metallic Nanoparticles: A Group Theory Analysis

We report a thorough and rigorous analysis of the plasmon modes of axisymmetric metallic nanoparticles, based on group theory techniques and block diagonalization of the scattering T matrix. In particular, we discuss plasmonic excitations under plane-wave illumination of a silver nanorod and a nanodisk, and present a detailed comparative study of elongated silver nanoparticles of different shape, but with the same length and thickness. Our methodology allows for an unambiguous classification of the eigenmodes of nonspherical particles, according to the irreducible representations of the appropriate point symmetry group, and provides a consistent explanation of relevant extinction spectra elucidating aspects of the problem to a degree that goes beyond usual interpretation