1. G. Leibfried and W. Ludwig, in Solid State Physics, Ed. by F. Seitz and D. Turnbull (Academic Press, New York, 1961).
2. N. W. Ashkroft and N. D. Mermin, Solid State Physics (Holt, Rinehart and Winston, Philadelphia, 1976), Vol. 2.
3. C. E. Bottani and G. Caglioti, Europhys. News 14 (12), 10 (1983).
4. N. N. Gorobey and A. S. Luk’yanenko, Phys. Solid State 56, 2259 (2014).
5. V. S. Postnikov, Solid State Physics and Chemistry (Metallurgiya, Moscow, 1978), p. 544 [in Russian].