Momentum-dependent dielectric function of polyacetylene

Abstract

The momentum-dependent dielectric function of trans-polyacetylene was computed from electron-energy-loss spectra for momenta $q$ between 0.1 and 0.7 ${\mathrm{\AA }}^{-1\mathrm{}}$. The spectrum of direct interband transitions broadens and shifts to higher energy with increasing $q$. The observed linear plasmon dispersion is well correlated with interband excitation spectra calculated in a simple tight-binding band-structure model. The fundamental absorption threshold is dominated by excitonic effects leading to a weakly dispersive absorption edge.