ABSTRACT
Plasmon is one of collective excitations described in the classical
regime. However, the constituent electrons follow, in principles, the
quantum mechanical regime. Therefore, the limit of the classical
description already attracted great interest at the early stage
of plasmon studies in 1980s. After the extensive development
of plasmonics and metamaterials in 2000s, it was an issue to
determinewhere the boundary should be properly set for plasmonic
resonators. In this chapter, we survey the classical limit that has been
clarified based on experimental results.
