FLEX$+$DMFT Analysis for Superconductivity in Systems with Coexisting Wide and Narrow Bands

Abstract

In this chapter, we study superconductivity and electron correlation effects in the bilayer Hubbard model with coexisting wide and incipient narrow bands originating from multiple sites within the unit cell. We have applied the FLEX$+$DMFT method, which we have extended to multi-band systems in the present thesis, to study electron correlation effects and spin-fluctuation-mediated superconductivity. We found that the method can capture the so-called pseudogap behavior, a hallmark of strong electron correlation, which is hardly seen in the FLEX result. Based on the analysis of the Eliashberg equation, we found that a pairing mechanism exploiting an incipient band discussed in the previous studies is still valid even with the local vertex corrections coming from the DMFT part of the self-energy.