Onset of a Pseudogap Regime in Ultracold Fermi Gases

TL;DR

This paper uses Quantum Monte Carlo simulations to identify the emergence of a pseudogap regime in ultracold Fermi gases near unitarity, revealing complex finite-temperature behavior involving preformed Cooper pairs.

Contribution

It provides ab initio evidence for the pseudogap regime in ultracold Fermi gases and maps its onset and evolution near the unitary point, aligning with experimental data.

Findings

Pseudogap regime appears at (k_{F}a)^{-1}≈ -0.05

The gap evolution matches recent spectroscopy data

Finite temperature phase involves preformed Cooper pairs

Abstract

We show, using an ab initio approach based on Quantum Monte Carlo technique, that the pseudogap regime emerges in ultracold Fermi gases close to the unitary point. We locate the onset of this regime at a value of the interaction strength corresponding to (k_{F}a)^{-1}\approx -0.05 (a - scattering length). We determine the evolution of the gap as a function of temperature and interaction strength in the Fermi gas around the unitary limit and show that our results exhibit a remarkable agreement with the recent wave-vector resolved radio frequency spectroscopy data. Our results indicate that a finite temperature structure of the Fermi gas around unitarity is more complicated and involves the presence of the phase with preformed Cooper pairs, which however do not contribute to the long range order.