Fulde-Ferrell-Larkin-Ovchinnikov pairing as leading instability on the square lattice

TL;DR

This paper demonstrates, through unbiased Monte Carlo simulations, that spin-imbalanced fermions on a square lattice favor FFLO pairing as the leading instability, providing precise predictions on its stability and temperature range.

Contribution

It offers the first quantitative, well-controlled predictions of FFLO instability regions on the square lattice beyond mean-field approximations.

Findings

FFLO state is the dominant pairing instability in certain parameter regimes.

The FFLO phase can exist at temperatures up to half of the unpolarized superfluid transition.

Unbiased simulations confirm the location and stability of FFLO phases.

Abstract

We study attractively interacting spin-1/2 fermions on the square lattice subject to a spin population imbalance. Using unbiased diagrammatic Monte Carlo simulations we find an extended region in the parameter space where the Fermi liquid is unstable towards formation of Cooper pairs with non-zero center-of-mass momentum, known as the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. In contrast to earlier mean-field and quasi-classical studies we provide quantitative and well-controlled predictions on the existence and location of the relevant Fermi-liquid instabilities. The highest temperature where the FFLO instability can be observed is about half of the superfluid transition temperature in the unpolarized system.