Unconventional superconductivity due to interband polarization

TL;DR

This paper demonstrates that in a multiband Hubbard model, interband polarization induces an effective attractive interaction leading to unconventional superconductivity, with potential relevance to twisted bilayer graphene.

Contribution

It reveals a novel mechanism for superconductivity from repulsive interactions via interband polarization effects, supported by analytical and numerical methods.

Findings

Interband processes induce effective attraction at small momentum transfers.

Correlated hopping terms are key to the pairing mechanism.

Similarities with twisted bilayer graphene suggest broader relevance.

Abstract

We analyze in detail the superconductivity that arises in an extended Hubbard model describing a multiband system with repulsive interactions. We show that virtual interband processes induce an effective attractive interaction for small momentum transfers, a situation not found in most models of superconductivity from repulsion. This attraction can be traced back, in real space, to the presence of correlated hopping terms induced by interband polarization. We reveal this physics with both strong-coupling expansion and many-body perturbation theory, supplemented by numerical calculations. Finally, we point out interesting similarities with the problem of interacting electrons in twisted bilayer graphene, suggesting the importance of interband contribution to superconductivity.