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