Pseudogap phenomena in a two-dimensional ultracold Fermi gas near the Berezinskii-Kosterlitz-Thouless transition

Abstract

We investigate single-particle excitations and strong-coupling effects in a two-dimensional Fermi gas. Including pairing fluctuations within a Gaussian fluctuation theory, we calculate the density of states \(\rho(\omega)\) near the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature \(T_{\rm BKT}\). Near \(T_{\rm BKT}\), we show that superfluid fluctuations induce a pseudogap in \(\rho(\omega)\). The pseudogap structure is very similar to the BCS superfluid density of states, although the superfluid order parameter is absent in the present two-dimensional case. Since a two-dimensional \(^{40}\)K Fermi gas has recently been realized, our results would contribute to the understanding of single-particle properties near the BKT instability.