1. V. F. Kovalenko and E. L. Nagaev, Sov. Phys. Usp. 29, 297 (1986).
2. V. G. Veselago, N. V. Vorob’eva, and R. A. Doroshenko, JETP Lett. 45, 512 (1987).
3. R. A. Doroshenko, M. S. Setchenkov, I. V. Vladimirov, and V. A. Timofeeva, Sov. Phys. Solid State 34, 202 (1992).
4. V. F. Kovalenko and S. N. Lyakhimets, Sov. Phys. Solid State 26, 1817 (1984).
5. I. V. Vladimirov, R. A. Doroshenko, S. V. Seregin, and R. S. Fakhretdinova, Phys. Solid State 40, 638 (1998).