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Comment on "Boson-fermion model beyond the mean-field approximation"

R. Friedberg, H. C. Ren, O. Tchernyshyov

cond-mat.supr-conarXiv:cond-mat/9705089

Abstract

In a recent paper [A.S.Alexandrov, J.Phys.:Condens.Matter 8, 6923 (1996); cond-mat/9603111], it has been suggested that there is no Cooper pairing in boson-fermion models of superconductivity. We show that this conjecture is based on an inconsistent approximation that violates an exact identity. Quite generally, the divergence of the fermion t-matrix (the Thouless criterion) is accompanied by the condensation of a boson mode.

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