Comparison of strong-coupling theories for a two-dimensional Fermi gas

Understanding the formation of Cooper pairs and the resulting thermodynamic properties of a low-dimensional Fermi gas is an important area of research, elucidating our understanding of high temperature superconductors. In lower dimensions quantum fluctuations are expected to play an increasingly important role and the reliability of strong-coupling theories becomes questionable. Here, we present a comparison of recent thermodynamic measurements and theoretical predictions from different many-body $T$-matrix theories for a two-dimensional strongly interacting Fermi gas in the normal state. We find that the fully self-consistent $T$-matrix theory provides the best description of the experimental data over a wide range of temperatures and interatomic interactions. Our comparison reveals the crucial role played by the interactions between Cooper pairs and suggests that the future development of a quantitative strong-coupling theory for two-dimensional Fermi superfluids must explicitly take into account the diagrams that are responsible for pair-pair interactions.