Uniform spin susceptibility and spin-gap phenomenon in the BCS-BEC-crossover regime of an ultracold Fermi gas

作者：Tajima Hiroyuki^*; Kashimura Takashi; Hanai Ryo; Watanabe Ryota; Ohashi Yoji

来源：Physical Review A, 2014, 89(3): 033617.

DOI：10.1103/PhysRevA.89.033617

We investigate the uniform spin susceptibility X-s in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an ultracold Fermi gas. Including pairing fluctuations within the framework of an extended T-matrix approximation, we show X-s exhibits nonmonotonic temperature dependence in the normal state. In particular, X-s is suppressed near the superfluid phase transition temperature T-c due to strong pairing fluctuations. To characterize this anomalous behavior, we introduce the spin-gap temperature T-s as the temperature at which X-s takes a maximum value. Determining T-s in the whole BCS-BEC crossover region, we identify the spingap regime in the phase diagram of a Fermi gas in terms of the temperature and the strength of a pairing interaction. We also clarify how the spin-gap phenomenon is related to the pseudogap phenomenon appearing in the singleparticle density of states. Our results indicate that an ultracold Fermi gas in the BCS-BEC crossover region is a very useful system to examine the pseudogap phenomenon and the spin-gap phenomenon in a unified manner.

• 出版日期2014-3-12