Effective action approach to the Leggett's mode in two-band superconductors S. G. Sharapov, V. P. Gusynin and H. Beck Eur. Phys. J. B, 30 1 (2002) 45-51 Published online: 19 November 2002 DOI: 10.1140/epjb/e2002-00356-9