Finite-range effects in dilute Fermi gases at unitarity

TL;DR

This paper introduces a theoretical method to incorporate finite-range effects in dilute Fermi gases at unitarity, enabling the study of density-dependent properties beyond contact-interaction approximations.

Contribution

It develops a novel approach based on the low-energy T-matrix to account for finite-range effects, extending the validity of mean-field theories to higher densities.

Findings

Finite-range effects become significant at higher densities.

Density effects are relevant for ultracold gases with densities ten times higher than current experiments.

The method allows for more accurate modeling of ultracold Fermi gases at unitarity.

Abstract

We develop a theoretical method going beyond the contact-interaction approximation frequently used in mean-field theories of many-fermion systems, based on the low-energy T-matrix of the pair potential to rigorously define the effective radius of the interaction. One of the main consequences of our approach is the possibility to investigate finite-density effects, which are outside the range of validity of approximations based on delta-like potentials. We apply our method to the calculation of density dependent properties of an ultracold gas of 6Li atoms at unitarity, whose two-body interaction potential is calculated using ab initio quantum chemistry methods. We find that density effects will be significant in ultracold gases with densities one order of magnitude higher than those attained in current experiments.