1. See e.g. D.L. Greenaway, G. Harbeke: Optical Properties and Bandstructure of Semiconductors (Pergamon, Oxford, 1968)
2. H. Raether: Excitations of Plasmons and Interband Transitions Springer Tracts in Modern Physics, Vol. 28 (Springer, Berlin, Heidelberg 1980)
3. D.S. Chemla, D.A. Miller: J. Opt. Soc. Am B2, 1155 (1985)
4. H. Haug, S. Schmitt-Rink: J. Opt. Soc. Am B2, 1135 (1985)
5. W.R. Su, J.R. Schrieffer, A.J. Heeger: Phys. Rev B22, 2099 (1980)