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

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 $m^{\ast }$, a mean-field potential $U$, and a gap $\Delta$. Below the critical temperature $T_c=0.15{\epsilon }_F$ the results for $m^{\ast }$, $U$ 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 {$T^{\ast }\approx 0.20{\epsilon }_F>T_c$}.

Comments: 4 pages, 5 figures. Published version