We analyze the interaction-induced renormalization of single-particle excitations in the two-dimensional Hubbard model at weak coupling using the Wick-ordered version of the functional renormalization group. The self-energy is computed for real frequencies by integrating a flow equation with renormalized two-particle interactions. In the vicinity of hot spots, that is, points where the Fermi surface intersects the umklapp surface, self-energy effects beyond the usual quasiparticle renormalizations and damping occur near instabilities of the normal, metallic phase. Strongly enhanced renormalized interactions between particles at different hot spots generate a pronounced low-energy peak in the imaginary part of the self-energy, leading to a pseudogaplike double-peak structure in the spectral function for single-particle excitations.

• Received 8 June 2004

DOI:https://doi.org/10.1103/PhysRevB.71.115116