64 Physics 1973 FERENCES AND FOOTNOTES 1. Anderson, P. W, Concepts in Solids, W.A., Benjamin, Inc, New York, 1963 2. Anderson, P. W. Phys. Rev. 112, 1900(1958). 3. Cooper, L N, Les Prix Nobel en 1972, Nobel Foundation 1973, p. 64 4. Gor kov, L. P. J. Exptl. Theoret. Phys. (USSR)36, 1918(1959); translation: Soviet Phys. JETP 9, 1364(1959 ). 5. Meissner, H. Phys, Rev. 117, 672(1960) 6. Smith, P. H, Shapiro, S, Miles, J. L. and Nicol, J. Phys. Rev. Letters 6, 686 7. Giaever, I, Phys. Rev. Letters 5, 464(1960). 8. Giaever, I, Les Prix Nobel en 1973, Nobel Foundation 1974, p 9. Pippard, 4. B, Proceedings of the Vllth International Conference on Low Tem perature Physics, ed. Graham, G. M. and Hollis Hallett, A. C, North-Holland, Amsterdam 1961, p. 320 10. Gor, s result may be extended to finite temperatures by the following argument The density operator of a system in equilibrium has the form Z-1 exp B(H-uN where must contain a small symmetrybreaking term in order te semble in which has a definite value. Since this operator commutes with H- HN all quantities are time-independent if the Hamiltonian of the system is taken to be H-uH. Transition to a situation where the time dependence is given by the true Hamiltonian H can be accomplished by means of a gauge transformation, and con- sideration of the effect of this transformation on the electron operators gives im- mediately Gor,kovs result 1. Cohen, M. H, Falicov, L. M. and Phillips, C. Phys. Rev. Letters 8, 316(1962). 12. Nicol, J, Shapiro, S and Smith, P. H, Phys. Rev. Letters 5, 461(1960) 13. Giaever, I, Phys. Rev. Letters 5, 464( 1960). 14. Josephson, B. D, Phys. Letters 1, 251(1962) 15. Anderson, P. w. and Rowell, M, Phys. Rev. Letters 10, 230(1963) 16. Rowell, M, Phys. Rev. Letters 11, 200(1963) 17. Jaklevic, R. C, Lambe, J, Silver, A. H. and Mercereau, J. E, Phys. Rev. Letters 12,159(1964 18. Zimmerman, J. E, and Silver, A. H, Phys. Rev. 141, 367(1966) 19. Shapiro, S. Phys. Rev. Letters 11, 80(1963) 0. Langenberg, D. N, Parker, W. H. and Taylor, B. N, Phys. Rev. 150, 186( 1966). 21. Parker, W. H, Taylor, B. N. and Langenberg, D. N, Phys. Rev. Letters 18, 287 (1967) 22. Taylor, B. N, Parker, W. H. and Langenberg, D. N, The Fundamental Constants and quantum Electrodynamics, Academic Press, New York and London, 1969 23. Giaever, I, Phys. Rev. Letters 14, 904(1965) 24. Yanson, I. K, Svistunov, V. M. and Dmitrenko, I. M, J. Exptl. Theoret. Pl USSR) 21, 650(1965): translation: Soviet Phys. JETP 48, 976(1965) 5. Clarke, . Phil. Mag. 13, 115(1966).164 Physics 1973 R EFERENCES AND FOOTNOTES 1. Anderson, P. W., Concepts in Solids, W. A., Benjamin, Inc., New York, 1963. 2. Anderson, P. W. Phys. Rev. 112, 1900 (1958). 3. Cooper, L. N., Les Prix Nobel en 1972, Nobel Foundation 1973, p. 64. 4. Gor’kov, L. P., J. Exptl. Theoret. Phys. (USSR) 36, 1918 (1959); translation: Soviet Phys. JETP 9, 1364 (1959). 5. Meissner, H. Phys, Rev. 117, 672 (1960). 6. Smith, P. H., Shapiro, S., Miles, J. L. and Nicol, J. Phys. Rev. Letters 6, 686 (1961). 7. Giaever, I., Phys. Rev. Letters 5, 464 (1960). 8. Giaever, I., Les Prix Nobel en 1973, Nobel Foundation 1974, p. 9. Pippard, 4. B., Proceedings of the VIIth International Conference on Low Tem￾perature Physics, ed. Graham, G. M. and Hollis Hallett, A. C., North-Holland, Amsterdam 1961, p. 320. 10. Gor’kov’s result may be extended to finite temperatures by the following argument. The density operator of a system in equilibrium has the form Z-1 exp{pP(i--pN)} where must contain a small symmetrybreaking term in order to set up an en￾semble in which F has a definite value. Since this operator commutes with H-µN, all quantities are time-independent if the Hamiltonian of the system is taken to be H-µH. Transition to a situation where the time dependence is given by the true Hamiltonian H can be accomplished by means of a gauge transformation, and con￾sideration of the effect of this transformation on the electron operators gives im￾mediately Gor’kovs result ~oc ,=xp(-2 i p t/h). 11. Cohen, M. H., Falicov, L. M. and Phillips, J. C., Phys. Rev. Letters 8, 316 ( 1962). 12. Nicol, J., Shapiro, S. and Smith, P. H., Phys. Rev. Letters 5, 461 (1960). 13. Giaever, I., Phys. Rev. Letters 5, 464 ( 1960). 14. Josephson, B. D., Phys. Letters 1, 251 (1962). 15. Anderson, P. W. and Rowell, J. M., Phys. Rev. Letters 10, 230 (1963). 16. Rowell, J. M., Phys. Rev. Letters 11, 200 (1963). 17. Jaklevic, R. C., Lambe, J., Silver, A. H. and Mercereau, J. E., Phys. Rev. Letters 12, 159 (1964). 18. Zimmerman, J. E., and Silver, A. H., Phys. Rev. 141, 367 (1966). 19. Shapiro, S. Phys. Rev. Letters 11, 80 (1963). 20. Langenberg, D. N., Parker, W. H. and Taylor, B. N., Phys. Rev. 150, 186 ( 1966). 21. Parker, W. H., Taylor, B. N. and Langenberg, D. N., Phys. Rev. Letters 18, 287 (1967). 22. Taylor, B. N., Parker, W. H. and Langenberg, D. N., The Fundamental Constants and Quantum Electrodynamics, Academic Press, New York and London, 1969. 23. Giaever, I., Phys. Rev. Letters 14, 904 (1965). 24. Yanson, I. K., Svistunov, V. M. and Dmitrenko, I. M., J. Exptl. Theoret. Phys. (USSR) 21, 650 (1965); translation: Soviet Phys. JETP 48, 976 (1965). 25. Clarke, J., Phil. Mag. 13, 115 (1966)