The 2D Hubbard model and the pseudogap: a COM(SCBA) study

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 main idea of the COM is to describe interacting electrons in terms of the composite elementary excitations appearing in the system owing to strong correlations; the residual interactions among these excitations are treated within the SCBA. By analysing the spectral function A(k, omega) on varying the filling, we find, at high doping, the ordinary Fermi-liquid behaviour of a weakly interacting metal and, at low doping, the opening of a pseudogap, as reported for cuprates superconductors.