Non-Fermi liquid behavior in the 2D Hubbard model within COM(SCBA)

The two-dimensional Hubbard model is studied within the composite operator method (COM) with the electronic self-energy computed in the self-consistent Born approximation (SCBA). The COM describes interacting electrons in terms of the composite elementary excitations appearing in the system owing to the strong correlations; the residual interactions among these excitations are treated within the SCBA. The behavior of the momentum distribution function n(k) is analyzed for various values of filling. In contrast with the ordinary Fermi-liquid behavior found at high doping, non-Fermi-liquid features in n(k) are reported for low doping. These anomalous features are explained by looking at the strong antiferromagnetic correlations developing in the system in proximity of half-filling