Spin susceptibility and fluctuation corrections in the BCS-BEC crossover regime of an ultracold Fermi gas

Abstract

We investigate magnetic properties and effects of pairing fluctuations in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an ultracold Fermi gas. Recently, Liu and Hu, and Parish, pointed out that the strong-coupling theory developed by Nozières and Schmitt-Rink (NSR), which has been extensively used to successfully clarify various physical properties of cold Fermi gases, unphysically gives negative spin susceptibility in the BCS-BEC crossover region. The same problem is found to also exist in the ordinary non-self-consistent T-matrix approximation. In this paper, we clarify that this serious problem comes from incomplete treatment in term of pseudogap phenomena originating from strong pairing fluctuations, as well as effects of spin fluctuations on the spin susceptibility. Including these two key issues, we construct an extended T-matrix theory which can overcome this problem. The resulting positive spin susceptibility agrees well with the recent experiment on a 6Li Fermi gas done by Sanner and co-workers. We also apply our theory to a polarized Fermi gas to examine the superfluid phase transition temperature Tc, as a function of the polarization rate. Since the spin susceptibility is an important physical quantity, especially in singlet Fermi superfluids, our results would be useful in considering how singlet pairs appear above and below Tc in the BCS-BEC crossover regime of cold Fermi gases.

21 pages, 9 figures

References in corpus (14)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
• Collective excitations of a degenerate gas at the BEC-BCS crossover
• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• Phase diagram of a two-component Fermi gas with resonant interactions
• Observation of pseudogap behavior in a strongly interacting Fermi gas
• Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
• BEC-BCS crossover, phase transitions and phase separation in polarized resonantly-paired superfluids
• Equation of state of a superfluid Fermi gas in the BCS-BEC crossover
• Virial expansion for a strongly correlated Fermi gas
• Evolution of the Normal State of a Strongly Interacting Fermi Gas from a Pseudogap Phase to a Molecular Bose Gas
• Speckle Imaging of Spin Fluctuations in a Strongly Interacting Fermi Gas
• Pseudo-gap pairing in ultracold Fermi atoms
• BCS-BEC crossover in an asymmetric two-component Fermi gas

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• Uniform spin susceptibility and spin-gap phenomenon in the BCS-BEC crossover regime of an ultracold Fermi gas
• Strong-coupling corrections to ground-state properties of a superfluid Fermi gas
• Thermal crossover, transition, and coexistence in Fermi polaronic spectroscopies
• Polaron Problems in Ultracold Atoms: Role of a Fermi Sea across Different Spatial Dimensions and Quantum Fluctuations of a Bose Medium
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• The pseudogap regime in the unitary Fermi gas
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• Local Photoemission Spectra and Effects of Spatial Inhomogeneity in the BCS-BEC Crossover Regime of a Trapped Ultracold Fermi Gas
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• Normal-state Properties of a Unitary Bose-Fermi Mixture: A Combined Strong-coupling Approach with Universal Thermodynamics
• Hidden Bose-Einstein Singularities in Correlated Electron Systems: II. Pseudogap Phase in the Weakly Attractive Hubbard Model
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