SUPERCONDUCTIVITY IN THE 2D ATTRACTIVE HUBBARD MODEL WITHIN A FUNCTIONAL FIELD-THEORETICAL RG

Abstract

We apply the functional field-theoretical renormalization group methodology up to two-loop order to the 2D attractive Hubbard model for weak bare interaction. Since the momentum-resolved quasiparticle weight ZΛ(p) is always close to unity in the RG flow, higher-order quantum fluctuations do not affect crucially the low-energy dynamics in this case. As a result, we observe a s-wave singlet superconducting quasi-long-range order phase as a function of doping in good agreement with other numerical methods. To assess the role played by the fluctuations we compare the critical temperature Tc in which the quasi-long-range superconducting order phase takes place within our approach with mean-field theory and quantum Monte Carlo results.