Phase correlations and quasicondensate in a two-dimensional ultracold Fermi gas

TL;DR

This paper investigates phase correlations in a 2D ultracold Fermi gas, showing that Gaussian pair fluctuations capture the transition from exponential to algebraic decay, indicating quasicondensation consistent with BKT theory.

Contribution

It demonstrates that Gaussian pair fluctuation formalism effectively describes phase correlations and quasicondensate behavior in 2D Fermi gases, aligning with BKT theory predictions.

Findings

Correlation function exhibits exponential decay at short distances.

At large distances, correlation decays algebraically with BKT exponent.

Gaussian pair fluctuations capture quasi long-range order in 2D Fermi gases.

Abstract

The interplay between dimensionality, coherence and interaction in superfluid Fermi gases is analyzed by the phase correlation function of the field of fermionic pairs. We calculate this phase correlation function for a two-dimensional superfluid Fermi gas with $s$-wave interactions within the Gaussian pair fluctuation formalism. The spatial behavior of the correlation function is shown to exhibit a rapid (exponential) decay at short distances and a characteristic algebraic decay at large distances, with an exponent matching that expected from Berezinskii-Kosterlitz-Thouless theory of 2D Bose superfluids. We conclude that the Gaussian pair fluctuation approximation is able to capture the physics of quasi long-range order in two-dimensional Fermi gases.