1. L. E. Gurevich and G. M. Nedlin, Soviet Phys.-JETP, 1961, 13, 568.
2. O. V. Konstantinov and V. I. Perel’, Soviet Phys.-JETP, 1961, 12, 142.
3. S. Fischer, Z. Phys., 1965, 184, 325.
4. K. Sugihara, J. Phys. Soc. Jpn., 1969, 27, 356.
5. H. Fukuyama, Solid State Commun., 1978, 26, 783.