Collective excitations of a model intercalate with inequivalent conducting layers
Review articleOpen access

AbstractWe describe an idealized stage-1 acceptor intercalate by means of a modified Visscher-Falicov model with alternating electron and hole layers. The electronic wave functions are strictly localized within each layer, where, in turn, they are taken to be plane-wave-like. Both intra- and interlayer Coulomb interactions are included. We calculate the dielectric response within the random-phase approximation, as a function of momentum, frequency, and effective-mass ratio me/mh > 1. The spectral function exhibits a fairly sharp, low-frequency “electron” plasmon resonance inside the “hole” pair continuum, as well as a higher frequency “hole” plasmon. The latter is only slightly modified by the electrons. The electron plasmon frequency, however, turns to zero as q tends to zero, and also gets sharper with increasing effective mass ratio and increasing wavelength. Because of its acoustic behaviour, it will not be observable optically, except possibly through hybridization with the longitudinal phonons. At larger momenta, electron loss spectroscopy appears more hopeful. Unlike the “hole” plasmon, the acoustic resonance will be sharper and more intense when the wavevector of the external field has a component perpendicular to the layer planes.

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