High T_c superconductivity due to coexisting wide and narrow bands: A fluctuation exchange study on the Hubbard ladder as a test case

TL;DR

This study suggests that high-temperature superconductivity can occur when the Fermi level is near both wide and narrow bands, due to enhanced interband scattering, demonstrated through a Hubbard ladder model analysis.

Contribution

The paper introduces a mechanism for high T_c superconductivity involving coexisting wide and narrow bands, supported by fluctuation exchange calculations on a Hubbard ladder.

Findings

High T_c is possible with Fermi level near coexisting bands.

Interband pair scattering channels enhance superconductivity.

Predicted higher T_c with electron doping compared to hole doping.

Abstract

We propose that when the Fermi level lies within a wide band and also lies close to but not within a coexisting narrow band, high $T_c$ superconductivity may take place due to the large number of interband pair scattering channels and the small renormalization of the quasiparticles. We show using fluctuation exchange method that this mechanism works for the Hubbard model on a ladder lattice with diagonal hoppings. From this viewpoint, we give a possible explanation for the low $T_c$ for the actual hole doped ladder compound, and further predict a higher $T_c$ for the case of electron doping.