The Finite Temperature Pairing Gap of a Unitary Fermi Gas by Quantum Monte Carlo Calculations

TL;DR

This study uses Quantum Monte Carlo to analyze the temperature-dependent spectral properties of a unitary Fermi gas, revealing a pseudogap phase above the superfluid transition temperature.

Contribution

It provides the first detailed spectral analysis of a unitary Fermi gas at finite temperature using advanced Monte Carlo and data reconstruction techniques.

Findings

Identification of a pseudogap phase up to T* ≈ 0.20εF

Accurate parametrization of quasiparticle spectrum with three temperature-dependent functions

Validation of an independent quasiparticle model below T_c

Abstract

We calculate the one-body temperature Green's (Matsubara) function of the unitary Fermi gas via Quantum Monte Carlo, and extract the spectral weight function $A(p,\omega)$ using the methods of maximum entropy and singular value decomposition. From $A(p,\omega)$ we determine the quasiparticle spectrum, which can be accurately parametrized by three functions of temperature: an effective mass $m^*$, a mean-field potential $U$, and a gap $\Delta$. Below the critical temperature $T_c=0.15\varepsilon_F$ the results for $m^*$, $U$ and $\Delta$ can be accurately reproduced using an independent quasiparticle model. We find evidence of a pseudogap in the fermionic excitation spectrum for temperatures up to {$T^*\approx 0.20\varepsilon_{F} > T_c$}.