Spectral study of the pseudogap in unitary Fermi gases

TL;DR

This paper provides a detailed spectral analysis of the pseudogap in unitary Fermi gases, supporting the pairing origin of the pseudogap through comparison with experimental data and advanced theoretical modeling.

Contribution

It introduces an iterative, self-consistent approach to calculate the spectral function, improving upon previous approximations in pairing fluctuation theory.

Findings

Quantitative agreement with experimental spectra.

Microscopic explanation of the pseudogap phenomenon.

Strengthened support for pairing fluctuation theory.

Abstract

The existence of a pseudogap in unitary Fermi gases has recently been established and measured experimentally [Li et al., Nature 626, 288 (2024)]. This lends strong support for the pairing origin as the mechanism of the pseudogap in Fermi superfluids. Here we present a spectral study of unitary Fermi gases, and show how the data can be understood quantitatively, when compared with theoretically calculated momentum-resolved rf or microwave spectra, and the pseudogap extracted from the spectra. We use an iterative treatment of the fermion self energy and hence the spectral function, beyond previous pseudogap approximation, based on a pairing fluctuation theory that incorporates both particle-particle and particle-hole T matrices, with self-consistent self energy feedback. Our results not only provide a microscopic explanation of the experimental data but also strengthen the support for both the pairing-induced pseudogap physics and the pairing fluctuation theory of Fermi superfluidity.