Strong Coupling Effects on the Specific Heat of an Ultracold Fermi Gas in the Unitarity Limit

We investigate strong-coupling corrections to the specific heat in the normal state of an ultracold Fermi gas in the BCS-BEC crossover region. A recent experiment on a Li unitary Fermi gas (Ku et. al. in Science 335:563 2012) shows that is remarkably amplified near the superfluid phase transition temperature , being similar to the well-known -structure observed in liquid He. Including pairing fluctuations within the framework of the strong-coupling theory developed by NoziSres and Schmitt-Rink, we show that strong pairing fluctuations are sufficient to explain the anomalous behavior of observed in a Li unitary Fermi gas near . We also show that there is no contribution from stable preformed Cooper pairs to at the unitarity. This indicates that the origin of the observed anomaly is fundamentally different from the case of liquid He, where stable He Bose atoms induce the -structure in near the superfluid instability. Instead, the origin is the suppression of the entropy S, near , due to the increase of metastable preformed Cooper pairs. Our results indicate that the specific heat is a useful quantity to study the effects of pairing fluctuations on the thermodynamic properties of an ultracold Fermi gas in the BCS-BEC crossover region.