1. See, for example, Knight, W. D.: In: Proc. XIV Colloque Ampère, Ljubljana, 1966. Ed.: R. Blinc. Amsterdam: North-Holland Publishing Co. 1967, p. 311.
2. Delrieu, J. M., Winter, J. M.: Solid State Commun.4, 545 (1966).
3. Redfield, A. G.: Phys. Rev.162, 367 (1967).
4. Rossier, D., MacLaughlin, D. E.: Following article. Phys. kondens. Materie11, 66 (1970).
5. Hebel, L. C., Slichter, C. P.: Phys. Rev.113, 1504 (1959).