Pair correlations in the attractive Hubbard model

TL;DR

This paper investigates pair correlations in the attractive Hubbard model using ultracold fermions in a 2D optical lattice, revealing how pairing length scales vary with interaction and density, especially above the superfluid transition.

Contribution

It introduces a method combining fluctuation-dissipation theorem and equation of state to extract pair correlations and characterize pairing length scales in the model.

Findings

Pair correlations extend over a few lattice sites at low filling and weak interactions.

Pairing length scales depend on interaction strength and density.

Significant pair correlations are observed above the superfluid transition temperature.

Abstract

The mechanism of fermionic pairing is the key to understanding various phenomena such as high-temperature superconductivity and the pseudogap phase in cuprate materials. We study the pair correlations in the attractive Hubbard model using ultracold fermions in a two-dimensional optical lattice. By combining the fluctuation-dissipation theorem and the compressibility equation of state, we extract the interacting pair correlation functions and deduce a characteristic length scale of pairs as a function of interaction and density filling. At sufficiently low filling and weak on-site interaction, we observe that the pair correlations extend over a few lattice sites even at temperatures above the superfluid transition temperature.