1. M. I. Klinger and V. G. Karpov, Zh. Éksp. Teor. Fiz. 82, 1687 (1982) [Sov. Phys. JETP 55, 976 (1982)].
2. S. A. Dembovskii, A. S. Zyubin, and F. V. Grigor’ev, Fiz. Tekh. Poluprovodn. 32, 944 (1998) [Semiconductors 32, 843 (1998)].
3. K. Saeki, Phys. Rev. Lett. 80, 1224 (1998).
4. L. I. Manevich, A. V. Savin, V. V. Smirnov, and S. N. Volkov, Usp. Fiz. Nauk 164, 937 (1999).