1. V. Shikin, T. Demel, and D. Heitman, Phys. Rev. B 46, 3971 (1992).
2. A. Govorov and A. Chaplik, Poverkhnost, No. 12, 5 (1987).
3. M. D’yakonov and A. Furman, Zh. Éksp. Teor. Fiz. 92, 1012 (1987) [Sov. Phys. JETP 65, 574 (1987)].
4. I. Dolgopolov and S. Dorozhkin, Poverkhnost, No. 2, 5 (1985).
5. N. Zhitenev, Pis’ma Zh. Éksp. Teor. Fiz. 55, 722 (1992) [JETP Lett. 55, 756 (1992)].