s$_\pm$ pairing near a Lifshitz transition

TL;DR

This paper investigates s$_\pm$ superconducting pairing near a Lifshitz transition in a bilayer Hubbard model, revealing a peak in transition temperature and sign-changing gap functions on incipient and electron bands, relevant to iron-based superconductors.

Contribution

It demonstrates s$_\pm$ pairing with a maximum transition temperature beyond the Lifshitz point in a bilayer Hubbard model, addressing questions from experimental observations.

Findings

s$_\pm$ pairing peaks beyond the Lifshitz point

Gap function has opposite signs on hole and electron bands

Transition temperature reaches a maximum near the Lifshitz transition

Abstract

Observation of robust superconductivity in some of the iron based superconductors in the vicinity of a Lifshitz point where a spin density wave instability is suppressed as the {hole} band drops below the Fermi energy raise questions for spin-fluctuation theories. Here we discuss spin-fluctuation pairing for a bilayer Hubbard model, which goes through such a Lifshitz transition. We find s$_\pm$ pairing with a transition temperature that peaks beyond the Lifshitz point and a gap function that has essentially the same magnitude but opposite sign on the incipient hole band as it does on the electron band that has a Fermi surface.