1. T. Fukuzawa, E. E. Mendez, and J. M. Hong, Phys. Rev. Lett. 64, 3066 (1990); J. A. Kash, M. Zachav, E. E. Mendez et al., ibid. 66, 2247 (1991).
2. U. Sivan, P. M. Solomon, and H. Strikman, Phys. Rev. Lett. 68, 1196 (1992).
3. L. V. Butov, A. Zrenner, G. Abstreiter et al., Phys. Rev. Lett. 73, 304 (1994).
4. M. Bayer, V. B. Timofeev, F. Faller et al., Phys. Rev. B 54, 8799 (1996).
5. Yu. E. Lozovik and Yu. E. Yudson, JETP Lett. 22, 274 (1975); Zh. Éksp. Teor. Fiz. 71, 738 (1976) [Sov. Phys. JETP 44, 389 (1976)]; Yu. E. Lozovik and V. I. Yudson, Solid State Commun. 19, 391 (1976); A. V. Klyuchnik and Yu. E. Lozovik, Zh. Éksp. Teor. Fiz. 76, 670 (1979) [Sov. Phys. JETP 49, 335 (1979)].