Dynamical correlations in multiorbital Hubbard models: Fluctuation-exchange approximations

TL;DR

This paper compares the Fluctuation Exchange approximation with Quantum Monte-Carlo results for a two-band Hubbard model, revealing that the T-matrix approximation with full renormalization yields good agreement, especially in the multiorbital case.

Contribution

It demonstrates that the electron-electron T-matrix approximation with full renormalization accurately captures multiorbital Hubbard model correlations, extending previous single-band findings.

Findings

Good agreement with Quantum Monte-Carlo in multiband case

Non-self-consistent scheme clearly shows strong coupling crossover

FLEX behavior analyzed for higher orbital degeneracy

Abstract

We study the two band degenerate Hubbard model using the Fluctuation Exchange approximation (FLEX) method and compare the results with Quantum Monte-Carlo calculations. Both the self-consistent and the non-self-consistent versions of the FLEX scheme are investigated. We find that, contrary to 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 behavior of the FLEX for higher orbital degeneracy.