1. I. L. Maksimov, Yu. N. Mastakov, and N. A. Tailanov, Fiz. Tverd. Tela (Leningrad) 28, 2323 (1986) [Sov. Phys. Solid State 28, 1300 (1986)].
2. C. P. Bean, Phys. Rev. Lett. 8, 250 (1962).
3. R. G. Mints and A. L. Rakhmanov, Instabilities in Semiconductors (Nauka, Moscow, 1984).
4. V. I. Karpman, Non-Linear Waves in Dispersive Media (Nauka, Moscow, 1973; Pergamon, Oxford, 1975).