Magnetic and superconducting instabilities of the Hubbard model at the Van Hove filling

We use a novel temperature-flow renormalization group technique to analyze magnetic and superconducting instabilities in the two-dimensional t - t' Hubbard model for particle densities close to the Van Hove filling as a function of the next-nearest-neighbor hopping t'. In the one-loop flow at the Van Hove filling, the characteristic temperature for the flow to strong coupling is suppressed drastically around t(c)' approximate to -0.33t, suggesting a quantum critical point between d-wave pairing at moderate t' > t(c)' and ferromagnetism for t' < t(c)'. Upon increasing the particle density in the latter regime, the leading instability occurs in the triplet pairing channel.