Optically Excited Longitudinal Plasmons in Potassium

Abstract

Oscillatory structure in the absorption of thin potassium films has been observed for energies just above the plasmon energy in a wavelength-modulated photoemission experiment. This structure is shown to be due to resonant excitation of longitudinal plasmons. Observation of up to ten resonances allows the evaluation of the dispersion relation, which shows a quadratic behavior in agreement with a theoretical formula based on the Boltzmann equation.