Thermodynamic Properties of Universal Fermi Gases

TL;DR

This paper presents a mean-field-like theory for the thermodynamic properties of universal Fermi gases, deriving self-consistent equations for the self-energy and validating results against experimental data.

Contribution

It introduces a self-consistent, momentum-dependent self-energy approach for both attractive and repulsive universal fermions, extending to population-imbalanced cases.

Findings

Good agreement with high-temperature experimental data

Analytical expression for momentum-dependent self-energy for attractive fermions

Iterative calculation of self-energy for repulsive fermions

Abstract

We develop a simple, mean-field-like theory for the normal phase of a unitary Fermi gas by deriving a self-consistent equation for its self-energy via a momentum-dependent coupling constant for both attractive and repulsive universal fermions. For attractive universal fermions in the lower branch of a Feshbach resonance, we use zero-temperature Monte Carlo results as a starting point for one-step iteration in order to derive an analytical expression for the momentum-dependent self-energy. For repulsive universal fermions in the upper branch of a Feshbach resonance, we iteratively calculate the momentum-dependent self-energy via our self-consistent equation. Lastly, for the case of population imbalance, we propose an ansatz for higher order virial expansion coefficents. Overall, we find that our theory is in good agreement with currently available, high temperature experimental data.