Ground-state thermodynamic quantities of homogeneous spin-$1/2$ fermions from the BCS region to the unitarity limit

Abstract

We experimentally determined various thermodynamic quantities of interacting two-component fermions at the zero-temperature limit from the Bardeen-Cooper-Schrieffer (BCS) region to the unitarity limit. The obtained results are very accurate in the sense that the systematic error is within 4% around the unitarity limit. Using this advantage, we can compare our data with various many-body theories. We found that an extended $T$-matrix approximation, which is a strong-coupling theory involving fluctuations in the Cooper channel, well reproduces our experimental results. We also found that the superfluid order parameter $\Delta$ calculated by solving the ordinary BCS gap equation with the chemical potential of interacting fermions is close to the binding energy of the paired fermions directly observed in a spectroscopic experiment and that obtained using a quantum Monte Carlo method. Since understanding the strong-coupling properties of a superfluid Fermi gas in the BCS-BEC (Bose-Einstein condensation) crossover region is a crucial issue in condensed matter physics and nuclear physics, the results of the present study are expected to be useful in the further development of these fields.

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• Normal-state Properties of a Unitary Bose-Fermi Mixture: A Combined Strong-coupling Approach with Universal Thermodynamics
• A model study on superfluidity of a unitary Fermi gas of atoms interacting with a finite-ranged potential
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