2015/10/15 by Hiroyuki Tajima, H. Tajima, Ryo Hanai +3 · 20 citations
Physics and Astronomy · #Cold Atom Physics and Bose-Einstein Condensates #Condensed matter physics #Cooper pair #Cuprate #Electron #Fermi gas #Pairing #Physics #Physics of Superconductivity and Magnetism #Pseudogap #Quantum mechanics #Quantum, superfluid, helium dynamics #Spin (aerodynamics) #Superconductivity #Superfluidity #cond-mat.quant-gas
paper · pdf · doi:10.1103/physreva.93.013610
published in Physical Review A 93(1) (American Physical Society) · 24 pages, 8 figures
arxiv created 2015/10/15 · openalex publication_date 2016/01/12 · arxiv updated 2016/01/20 · openalex created_date 2016/07/22 · openalex updated_date 2026/08/05
We theoretically investigate the uniform spin susceptibility \ensuremathχ in the superfluid phase of an ultracold Fermi gas in the region of the Bardeen-Cooper-Schrieffer--Bose-Einstein-condensate (BCS-BEC) crossover. In our previous paper [H. Tajima et al., Phys. Rev. A 89, 033617 (2014)], including pairing fluctuations within an extended T-matrix approximation (ETMA), we showed that strong pairing fluctuations cause the so-called spin-gap phenomenon, where \ensuremathχ is anomalously suppressed even in the normal state near the superfluid phase transition temperature Tc. In this paper, we extend this work to the superfluid phase below Tc, to clarify how this many-body phenomenon is affected by the superfluid order. From the comparison of the ETMA \ensuremathχ with the Yosida function describing the spin susceptibility in a weak-coupling BCS superfluid, we identify the region where pairing fluctuations crucially affect this magnetic quantity below Tc in the phase diagram with respect to the strength of a pairing interaction and the temperature. This spin-gap regime is found to be consistent with the previous pseudogap regime determined from the pseudogapped density of states. We also compare our results with a recent experiment on a 6Li Fermi gas. Since the spin susceptibility is sensitive to the formation of spin-singlet preformed pairs, our results would be useful for the study of pseudogap physics in an ultracold Fermi gas on the viewpoint of the spin degrees of freedom.