Dynamical correlations in multiorbital Hubbard models: fluctuation exchange approximations.

ABSTRACT

We study the two-band degenerate Hubbard model using the fluctuation exchange approximation (FLEX) and compare the results with quantum Monte Carlo (QMC) calculations. Both the self-consistent and the non-self-consistent versions of the FLEX scheme are investigated. We find that, unlike in the one-band case, in the multiband case, good agreement with the quantum Monte Carlo results is obtained within the electron-electron T-matrix approximation using the full renormalization of the one-particle propagators. The crossover to strong coupling and the formation of satellites is more clearly visible in the non-self-consistent scheme. Finally we discuss the behaviour of the FLEX for higher orbital degeneracy.