1. A. A. Abrikosov, L. P. Gor’kov, and I. E. Dzyaloshinskii, Quantum Field Theoretical Methods in Statistical Physics, Pergamon Press, Oxford, 1965 [Russian original, GIFML, Moscow 1962].
2. B. I. Halperin and T. M. Rice, Solid State Phys. 21, 115 (1968).
3. Yu. V. Kopaev, Tr. Fiz. Inst. Akad. Nauk SSSR 86, 3 (1975).
4. G. Gruner, Rev. Mod. Phys. 60, 1129 (1988).
5. G. Gruner, Rev. Mod. Phys. 66, 1 (1994).