Momentum-selective metal-insulator transition in the two-dimensional Hubbard model: An 8-site dynamical cluster approximation study

The dynamical cluster approximation with eight momentum cells reveals that the paramagnetic phase of the Hubbard model exhibits a pseudogap at intermediate coupling strengths and doping. We show that within this approximation the pseudogap arises because the metal-insulator transition is multistage and momentum-sector specific with Fermi- liquid metal and fully gapped insulator phases separated by an intermediate phase, in which some regions of the Brillouin zone are gapped while others sustain gapless quasiparticles. For reasonable second-neighbor hopping the pseudogap occurs for hole but not electron doping. The doping dependence of the gap is determined and results are presented for spectra. Comparison to dynamical mean-field studies on smaller clusters is made.