Fulde-Ferrell-Larkin-Ovchinnikov superfluidity in one-dimensional optical lattices

TL;DR

This paper investigates the FFLO superfluid phase in one-dimensional optical lattices using the attractive Hubbard model, revealing quasi-long range order and coupling between spin and charge degrees of freedom across various interaction strengths.

Contribution

It provides a detailed numerical analysis of FFLO correlations and spin-charge coupling in 1D systems, highlighting implications for experimental observation and stabilization.

Findings

Pairing correlations show quasi-long range order with FFLO oscillations.

Spin and charge degrees of freedom are coupled even at small imbalances.

Coupling many 1D systems may stabilize long-range FFLO order.

Abstract

Spin-polarized attractive Fermi gases in one-dimensional (1D) optical lattices are expected to be remarkably good candidates for the observation of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We model these systems with an attractive Hubbard model with population imbalance. By means of the density-matrix renormalization-group method we compute the pairing correlations as well as the static spin and charge structure factors in the whole range from weak to strong coupling. We demonstrate that pairing correlations exhibit quasi-long range order and oscillations at the wave number expected from FFLO theory. However, we also show by numerically computing the mixed spin-charge static structure factor that charge and spin degrees of freedom appear to be coupled already for small imbalance. We discuss the consequences of this coupling for the observation of the FFLO phase, as well as for the stabilization of the quasi-long range order into long-range order by coupling many identical 1D systems, as in quasi-1D optical lattices.