In the unitary regime, when the scattering amplitude greatly exceeds in magnitude the average interparticle separation, and below the critical temperature thermal properties of an atomic fermionic cloud are governed by the collective modes, specifically the Bogoliubov-Anderson sound modes. The specific heat of an atomic cloud in an elongated trap, in particular, has a rather complex temperature dependence, which changes from an exponential behavior at very low temperatures ($T\ll \hslash {\omega }_{\parallel }$), to $\propto T$ for $\hslash {\omega }_{\parallel }\ll T\ll \hslash {\omega }_{\perp }$ and then continuously to $\propto T^4$ at temperatures just below the critical temperature, when the surface modes play a dominant role. Only the low ($\hslash {\omega }_{\parallel }\ll T\ll \hslash {\omega }_{\perp }$) and high ($\hslash {\omega }_{\perp }\ll T<T_c$) temperature power laws are well defined. For the intermediate temperatures one can introduce at most a gradually increasing with temperature exponent.

• Received 1 March 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.140403