Band structure renormalization and weak pseudogap behavior in Na_0.33CoO₂: Fluctuation exchange study based on a single-band model

Based on a single-band Hubbard model and the fluctuation exchange approximation, the effective mass and the energy band renormalization in Na_0.33CoO₂ is elaborated. The renormalization is observed to exhibit certain kind of anisotropy, which agrees qualitatively with the angle-resolved photoemission spectroscopy measurements. Moreover, the spectral function and density of states in the normal state are calculated, with a weak pseudogap behavior being seen, which is explained as a result of the strong Coulomb correlations. Our results suggest that the large Fermi surface associated with the a_1g band plays likely a central role in the charge dynamics.