1. A. A. Kozlovskii and V. F. Khirnyi, Fiz. Tverd. Tela (St. Petersburg) 42(10), 1780 (2000) [Phys. Solid State 42, 1825 (2000)].
2. S. L. Ginzburg and N. E. Savitskaya, Zh. Éksp. Teor. Fiz. 117, 227 (2000) [JETP 90, 202 (2000)].
3. M. A. Zelikman, Fiz. Tverd. Tela (St. Petersburg) 42(10), 1768 (2000) [Phys. Solid State 42, 1813 (2000)].
4. C. Jeffries, Q. Lam, Y. Kim, et al., Phys. Rev. B 37, 9840 (1988).
5. A. I. Golovashkin, N. D. Kuz’michev, I. S. Levchenko, et al., Fiz. Tverd. Tela (Leningrad) 31(4), 233 (1989) [Sov. Phys. Solid State 31, 1409 (1989)].