Spin susceptibility and effects of a harmonic trap in the BCS-BEC crossover regime of an ultracold Fermi gas
Hiroyuki Tajima, Ryo Hanai, Yoji Ohashi
We theoretically investigate magnetic properties of a trapped ultracold Fermi gas. Including pairing fluctuations within the framework of an extended $T$-matrix approximation, as well as effects of a harmonic trap in the local density approximation, we calculate the local spin susceptibility ${\ensuremath{\chi}}_{\mathrm{t}}(r,T)$ in the Bardeen-Cooper-Schrieffer--Bose-Einstein condensation crossover region. We show that pairing fluctuations cause nonmonotonic temperature dependence of ${\ensuremath{\chi}}_{\mathrm{t}}(r,T)$. Although this behavior looks similar to the spin-gap phenomenon associated with pairing fluctuations in a uniform Fermi gas, the trapped case is found to also be influenced by the temperature-dependent density profile, in addition to pairing fluctuations. We demonstrate how to remove this extrinsic effect from ${\ensuremath{\chi}}_{\mathrm{t}}(r,T)$, to study the interesting spin-gap phenomenon purely originating from pairing fluctuations. Since experiments in cold-atom physics are always done in a trap, our results would be useful for the assessment of preformed pair scenario, from the viewpoint of spin-gap phenomenon.
arXiv:1706.05679•Physical Review A•Sep 11, 2017•7 citations