Linear-response study of plasmon excitation in metallic thin films: Layer-dependent hybridization and dispersion

We present a theoretical study of collective plasmon excitation in metal thin films using the jellium model. The excitation spectra are calculated in the linear response theory and the time-dependent local density approximation. The evolution from surface plasmons at large thickness to the hybridized thin film plasmons at smaller thickness is obtained as functions of atomic layers and electron momenta. The energies of the hybridized plasmons follow qualitatively the classical electrodynamical model at large to intermediate thickness. For ultrathin films with a few atomic layers, these plasmon resonances evolve into intraband and interband transitions at small momenta. The latter results from the quantized electron states normal to the films.