1. Bardeen, J., Cooper, L. N., and Schrieffer, J. R. (1957). Physical Review 108, 1175.
2. Bogoliubov, N. N. (1958). Sov. Phys.-JETF 41.
3. Bogoliubov, N. N. (1960). Physics 26, SI.
4. Cronström, C. and Noga, M. (2001). Czech. J. Phys. 51, 175.
5. Fetter, A. L. and Walecka, J. D. (1971). Quantum Theory of Many-Particle Systems, McGraw-Hill Inc. New York, p. 396.