1. V. L. Ginzburg, Zh. Éksp. Teor. Fiz. 23, 236 (1952).
2. L. P. Gor’kov, Zh. Éksp. Teor. Fiz. 37, 1407 (1960) [Sov. Phys. JETP 10, 998 (1960)].
3. L. P. Gor’kov and T. K. Melik-Barkhudarov, Zh. Éksp. Teor. Fiz. 45, 1493 (1963) [Sov. Phys. JETP 18, 1035 (1963)].
4. E. Helfand and N. R. Werthamer, Phys. Rev. 147, 288 (1966).
5. N. R. Werthamer, in Superconductivity, edited by R. D. Parks (Marcel Dekker, N. Y., 1969), Vol. 1, p. 321.