1. L. D. Landau, inCollected Works, Vol. 2 (Nauka, Moscow, 1969), p. 119; English transl.:Collected Papers of L. D. Landau (Pergamon Press, Oxford, 1965?70).
2. L. A. Bol'shov, A. M. Dykhne, A. P. Napartovitch, inProceedings of the XV Conference on Emission Electronics, Vol. 1 (Institute of Physics Press, Kiev, 1973), p. 6.
3. A. F. Andreev and A. Y. Parshin,ZhETF 75:1511 (1978).
4. V. I. Marchenko,Pis'ma ZheTF 35:459 (1982).
5. K. O. Keshishev, A. Y. Parshin, and A. V. Babkin,Pis'ma ZhETF 30:63 (1979).