Doping dependence of the plasmon dispersion in 2H-TaSe2

Inelastic electron scattering is applied to investigate the impact of potassium intercalation on the charge-carrier plasmon energy and dispersion in the charge- density wave (CDW) bearing compound 2H-TaSe2. We observe an unususal doping dependence of the plasmon dispersion, which even changes sign on alkali addition. In contrast to the continous energy shift of the plasmon position on doping at lowest momentum transfer, its dispersion changes in a rather discontinuous manner. We argue that the observed dynamics can be explained only in a picture, where complex phenomena are taken into account, including the suppression of the CDW on doping as well as the interplay of the CDW and the plasma resonance.