1. L. D. Landau, private communication to D. Shoenberg; see D. Shoenberg,Superconductivity (Cambridge University Press, 1938), p. 59.
2. I. L. Landau and Y. V. Sharvin,JETP Lett. 15, 59 (1972).
3. I. L. Landau and Y. V. Sharvin,JETP Lett. 10, 121 (1969).
4. I. L. Landau,Sov. Phys. JETP 49, 889 (1979).
5. D. Robin, L. Rinderer, and E. Posada,J. Low Temp. Phys. 46, 331 (1982).