1. Review articles on this subject are Marton, L., L. B. Leder, and H. Mendlowitz: Advances in Electronics and Electron Physics, New York, 1955, where earlier literature is collected
2. Review articles on this subject are Klemperer, O., and J. P. G. Shepherd: Advances in Physics 12, 355 (1963)
3. Theoretical work is resumed in the book Pines, D.: Elementary Excitations in Solids (New York 1963)
4. For example: Raimes, St.: The wave mechanics of electrons in metals (Amsterdam 1961)
5. Ferrell, R. A.: Phys. Rev. 107, 450 (1957)