Particle and pair spectra for strongly correlated Fermi gases: A real-frequency solver

TL;DR

This paper develops a real-frequency Keldysh approach to compute spectral functions of fermions and pairs in strongly correlated Fermi gases near the superfluid transition, capturing their mutual interactions and decay processes.

Contribution

It introduces a self-consistent Luttinger-Ward framework in real frequency for analyzing coupled fermion and pair spectra in the BCS-BEC crossover.

Findings

Computed spectral functions for fermions and pairs near the superfluid transition.

Captured damping and decay processes through self-consistent equations.

Provided insights into contact correlations and dynamical responses.

Abstract

The strongly attractive Fermi gas in the BCS-BEC crossover is efficiently described in terms of coupled fermions and fermion pairs, or molecules. We compute the spectral functions of both fermions and pairs in the normal state near the superfluid transition using a Keldysh formulation in real frequency. The mutual influence between fermions and pairs is captured by solving the self-consistent Luttinger-Ward equations: these include both the damping of fermions by scattering off dressed pairs, as well as the decay of pair states by dissociation into two dressed fermions. The pair spectra encode contact correlations between fermions and form the basis for computing dynamical response functions and transport properties.