1. S. A. Danilkin, V. V. Zakurkin, S. I. Morozov, and V. V. Sumin, Fiz. Tverd. Tela (Leningrad) 22, 3327 (1980) [Sov. Phys. Solid State 22, 1948 (1980)].
2. S. I. Morozov, V. V. Sumin, A. V. Belushkin, and I. Natkanets, Fiz. Tverd. Tela (Leningrad) 29, 1653 (1987) [Sov. Phys. Solid State 29, 951 (1987)].
3. S. I. Morozov and V. V. Sumin, Fiz. Tverd. Tela (Leningrad) 33, 3107 (1991) [Sov. Phys. Solid State 33, 1756 (1991)].
4. S. I. Morozov and V. V. Kazarnikov, Fiz. Tverd. Tela (St. Petersburg) 35, 3145 (1993) [Phys. Solid State 35, 1549 (1993)].
5. S. I. Morozov, S. A. Danilkin, and V. T. Ém, Zh. Éksp. Teor. Fiz. 109, 2130 (1996) [JETP 82, 1148 (1996)].