1. A. J. Leggett, Rev. Mod. Phys., 1999, 71(2): S318
2. A. J. Leggett, Rev. Mod. Phys., 2001, 73(2): 307
3. É. B. Sonin, Sov. Phys. Usp., 1982, 25: 409
4. P. Nozières and D. Pines, The Theory of Quantum Liquids: Superfluid Bose Liquids, Redwood City: Addison-Wesley, 1990
5. L. Pitaevskii and S. Stringari, Bose-Einstein Condensation, Oxford: Clarendon, 2003