Spectral Functions and rf Response of Ultracold Fermionic Atoms

TL;DR

This paper calculates the spectral functions and rf response of ultracold fermionic atoms near a Feshbach resonance, showing good agreement with experimental data and providing insights into the excitation spectrum and pair size.

Contribution

It offers a detailed theoretical analysis of spectral functions and rf response, aligning with experimental observations and connecting pair size to effective field theory corrections.

Findings

Spectral functions are peaked at energies modeled by a modified BCS dispersion.

The excitation spectrum at unitarity matches recent rf spectra near the critical temperature.

The pair size from spectral width agrees with that from superfluid effective field theory.

Abstract

We present a calculation of the spectral functions and the associated rf response of ultracold fermionic atoms near a Feshbach resonance. The single particle spectra are peaked at energies that can be modeled by a modified BCS dispersion. However, even at very low temperatures their width is comparable to their energy, except for a small region around the dispersion minimum. The structure of the excitation spectrum of the unitary gas at infinite scattering length agrees with recent momentum-resolved rf spectra near the critical temperature. A detailed comparison is made with momentum integrated, locally resolved rf spectra of the unitary gas at arbitrary temperatures and shows very good agreement between theory and experiment. The pair size defined from the width of these spectra is found to coincide with that obtained from the leading gradient corrections to the effective field theory of the superfluid.