Plasmons in an Ultrathin Film of Weakly-Coupled Layered Materials

Electronic collective modes of an ultrathin film of transition metal dicalcogenides are investigated based on models in which the interlayer transfer integrals are neglected. First we study the two-dimensional plasmons in the film consisting of the different materials from layer to layer. Then, taking into account the intralayer polarization effect in the c direction, we show that the bulk-plasmon-like modes can appear in the quasi-two-dimensional systems. Analytical expression of the dispersion relation is given in the long wave limit while numerical calculations are performed for the whole range of wavelength in the random phase approximation.