Specific heat and effects of pairing fluctuations in the BCS-BEC crossover regime of an ultracold Fermi gas

Abstract

We investigate the specific heat at constant volume $C_V$ in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an ultracold Fermi gas above the superfluid phase transition temperature $T_{\mathrm{c}}$. Within the framework of the strong-coupling theory developed by Nozières and Schmitt-Rink, we show that this thermodynamic quantity is sensitive to the stability of preformed Cooper pairs. That is, while $C_V(T\gesim T_{\rm c})$ in the unitary regime is remarkably enhanced by {\it metastable} preformed Cooper pairs or pairing fluctuations, it is well described by that of an ideal Bose gas of long-lived {\it stable} molecules in the strong-coupling BEC regime. Using these results, we identify the region where the system may be viewed as an almost ideal Bose gas of stable pairs, as well as the pseudogap regime where the system is dominated by metastable preformed Cooper pairs, in the phase diagram of an ultracold Fermi gas with respect to the strength of a pairing interaction and the temperature. We also show that the calculated specific heat agrees with the recent experiment on a ${}^6$Li unitary Fermi gas. Since the formation of preformed Cooper pairs is a crucial key in the BCS-BEC crossover phenomenon, our results would be helpful in considering how fluctuating preformed Cooper pairs appear in a Fermi gas, to eventually become stable, as one passes through the BCS-BEC crossover region.

21 pages, 8 figures

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• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
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Cited by in corpus (13)

• Thermodynamics of transition to BCS-BEC crossover superconductivity in FeSe${}_{1-x}$S${}_x$
• Pairing correlations across the superfluid phase transition in the unitary Fermi gas
• Magic gap ratio for optimally robust fermionic condensation and its implications for high-Tc superconductivity
• The pseudogap regime in the unitary Fermi gas
• Precursor of Superfluidity in a Strongly Interacting Fermi Gas with Negative Effective Range
• Strong-Coupling and Finite Temperature Effects on $p$-wave Contacts
• Pseudogap formation in organic superconductors
• Pseudogap regime of a strongly interacting two-dimensional Fermi gas with and without confinement-induced effect range of interactions
• Dip-hump temperature dependence of Specific Heat and Effects of Pairing Fluctuations in the Weak-coupling Side of a $p$-wave Interacting Fermi Gas
• Strong-coupling Properties of a $p$-wave Interacting Fermi Gas on the Viewpoint of Specific Heat at Constant Volume
• Isothermal compressibility and effects of multi-body molecular interactions in a strongly interacting ultracold Fermi gas
• Specific Heat and Effects of Uniaxial Anisotropy of a $p$-wave Pairing Interaction in a Strongly Interacting Ultracold Fermi Gas
• Strong coupling effects on specific heat in the BCS-BEC crossover