Comment on 'Effect of on-site Coulomb repulsion on superconductivity in the boson-fermion model' (T. Domanski, Phys. Rev. B v.66, 134512 (2002))

Abstract

The two-dimensional boson-fermion model of high-temperature superconductors, numerically studied by Domanski (Phys. Rev. B v.66, 134512 (2002)) is not a superconductor. The critical temperature of the model is zero for any symmetry of the order parameter. The opposite conclusion advocated by Domanski and some other authors stems from an erroneous mean-field approximation neglecting the boson self-energy. The approximation is qualitatively incorrect even in three dimensions. Taking into account the boson self-energy changes the phase transition in 3D BFM, which is not a mean-field second-order phase transition. There are real bosons in the model at and below Tc of 3D BFM, but not only fermions and their Cooper pairs.