A theory was derived for local vibrations near to point and line defects in a conducting medium. In crystals with light isotopes, there were transverse local vibrations in the optical frequency range. In crystals with heavy isotopes, there were longitudinal vibrations. The latter vibrations were caused by Coulomb interactions which involved defects, lattice ions and conduction electrons. The presence of the electron sub-system led to an exponential decrease in the amplitude of the vibrations over macroscopic distances. The distance was of the order of the wavelength of a transverse electromagnetic wave in the medium, or was of the order of the Debye length.

Local Optical Vibrations near Point and Line Defects in Semiconductors. F.G.Bass, V.L.Falko, S.I.Khankina: Fizika i Tekhnika Poluprovodnikov, 1995, 29[1], 114-24 (Semiconductors, 1995, 29[1], 60-5)