We investigate single-particle excitations and strong-coupling effects in a twodimensional Fermi gas. Including pairing fluctuations within a Gaussian fluctuation theory, we calculate the density of states ρ ( ω ) near the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature T BKT . Near T BKT , we show that superfluid fluctuations induce a pseudogap in ρ (ω). 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 twodimensional 40 K Fermi gas has recently been realized, our results would contribute to the understanding of single-particle properties near the BKT instability.
We investigate pseudogap phenomena in a two-dimensional Fermi gas. Including pairing fluctuations within a self-consistent
T-matrix approximation, we determine the pseudogap temperature
T∗ below which a dip appears in the density of states
ρ(ω) around the Fermi level. Evaluating
T∗, we identify the pseudogap region in the phase diagram of this system. We find that, while the observed BKT (Berezinskii-Kosterlitz-Thouless) transition temperature
TBKTexp in a
6Li Fermi gas is in the pseudogap regime, the detailed pseudogap structure in
ρ(ω) at
TBKTexp still differs from a fully-gapped one, indicating the importance of amplitude fluctuations in the Cooper channel there. Since the observed
TBKTexp in the weak-coupling regime cannot be explained by the recent BKT theory which only includes phase fluctuations, our results may provide a hint about how to improve this BKT theory. Although
ρ(ω) has not been measured in this system, we show that the assessment of our results is still possible by using the observable Tan's contact.