Pair Correlations in the Two-Dimensional Fermi Gas

TL;DR

This paper investigates the two-dimensional Fermi gas at finite temperature, using virial expansion to analyze spectral functions and contact, and suggests that observed pairing gaps are due to strong pair correlations rather than pseudogap phenomena.

Contribution

It provides a theoretical analysis of spectral functions and contact in the 2D Fermi gas, challenging previous assumptions about the pseudogap regime.

Findings

Spectral functions agree qualitatively with recent photoemission data.

Pair correlations are strong and occur at weaker interactions than previously thought.

The pairing gap is attributed to high-temperature pairing rather than pseudogap effects.

Abstract

We consider the two-dimensional Fermi gas at finite temperature with attractive short-range interactions. Using the virial expansion, which provides a controlled approach at high temperatures, we determine the spectral function and contact for the normal state. Our calculated spectra are in qualitative agreement with recent photoemission measurements [M. Feld et al., Nature 480, 75 (2011)], thus suggesting that the observed pairing gap is a feature of the high-temperature gas rather than being evidence of a pseudogap regime just above the superfluid transition temperature. We further argue that the strong pair correlations result from the fact that the crossover to bosonic dimers occurs at weaker interactions than previously assumed.