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

• The phase correlation functions for an ultracold Fermi gas in 2D are calculated.
• The decay of the correlation functions is algebraic at long distances.
• The Gaussian pair fluctuation approach is shown to capture the quasicondensate physics in 2D Fermi gases.

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 the 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.