Optical Absorption of Plasmonic Nanoparticles in Presence of a Local Interband Transition

The influences of a local interband transition on optical absorptions of plasmonic nanoparticles are investigated. It is found that the optical absorption associated with a local interband transition is remarkably enhanced because of the presence of a localized surface plasmon resonance. On the basis of the quasistatic theory, Mie calculations, and the classical models, the electromagnetic interaction of plasmon- and interband-dipole is studied. It is shown that two modes with different characters are generated because of the strong inherent interaction. As a consequence of this interaction, the two modes are repulsed, and an avoided crossing zone is constructed where the particle plasmon energy coincides with the energy of a local interband transition. The energies of the two modes are interchanged as the crossing zone traversed.