Controlled pairing symmetries in a Fermi-Hubbard ladder with band flattening

TL;DR

This paper investigates how band flattening in a Fermi-Hubbard ladder influences unconventional pairing and non-Fermi liquid behavior, revealing competing pairing channels driven by band geometry.

Contribution

It demonstrates that band flattening and ring exchange induce different $d$-wave pairing symmetries and non-Fermi liquid states in a minimal ladder model.

Findings

Flattening of the lower band produces non-Fermi liquid behavior.

Band geometry induces different $d$-wave pairing symmetries.

Competing pairing channels are identified in the model.

Abstract

Band flattening has been identified as key ingredient to correlation phenomena in Moir\'e materials and beyond. Here, we examine strongly repulsive fermions on a ladder -- a minimal platform for unconventional $d$-wave pairing -- and show that flattening of the lower band through an additional diagonal hopping term produces non-Fermi liquid behavior, evidenced by the violation of Luttinger's theorem, as well as axial $d$-wave pairing correlations. Alternatively, plaquette ring exchange can also generate pairing, albeit with a distinct diagonal $d$-wave pairing symmetry. Hence, our finding showcases a competition of different unconventional pairing channels, and demonstrates via a simple model how band geometry can induce fermionic pairing. This offers broadly relevant insights for correlated flat-band systems, ranging from ultracold atoms to strongly interacting electrons in solids.