Finite-temperature equation of state of polarized fermions at unitarity

TL;DR

This paper investigates the thermodynamics of a polarized unitary Fermi gas at finite temperatures using the complex Langevin method, providing results consistent with existing theories and experiments across various regimes.

Contribution

It applies the complex Langevin method to study the thermodynamics of polarized Fermi gases at unitarity, offering nonperturbative insights across a wide temperature and polarization range.

Findings

Results agree with experimental data at zero polarization.

Excellent agreement with virial expansion at low fugacity.

Critical temperature for superfluidity weakly depends on polarization.

Abstract

We study in a nonperturbative fashion the thermodynamics of a unitary Fermi gas over a wide range of temperatures and spin polarizations. To this end, we use the complex Langevin method, a first principles approach for strongly coupled systems. Specifically, we show results for the density equation of state, the magnetization, and the magnetic susceptibility. At zero polarization, our results agree well with state-of-the art results for the density equation of state and with experimental data. At finite polarization and low fugacity, our results are in excellent agreement with the third-order virial expansion. In the fully quantum mechanical regime close to the balanced limit, the critical temperature for superfluidity appears to depend only weakly on the spin polarization.