2019/07/31 by Xiaoyu Wang, Qijin Chen, K. Levin +1
Materials Science · Physics and Astronomy · #Cold Atom Physics and Bose-Einstein Condensates #Crossover #Fermi Gamma-ray Space Telescope #Fermi gas #Iron-based superconductors research #Lattice (music) #Mean field theory #Pairing #Physics of Superconductivity and Magnetism #Quantum Monte Carlo #Superconductivity #Superfluidity #cond-mat.str-el #cond-mat.supr-con
paper · pdf · doi:10.1088/1367-2630/ab890b
published as 2020 New J. Phys. 22 063050 · 11 pages + 6 figures; updated version
openalex created_date 2019/09/19 · arxiv created 2020/02/14 · openalex publication_date 2020/04/14 · arxiv updated 2020/07/13 · openalex updated_date 2026/08/06
Abstract This paper addresses the transition from the normal to the superfluid state in strongly correlated two dimensional fermionic superconductors and Fermi gases. We arrive at the Berezinskii–Kosterlitz–Thouless (BKT) temperature T BKT as a function of attractive pairing strength by associating it with the onset of ‘quasi-condensation’ in the normal phase. Our approach builds on a criterion for determining the BKT transition temperature for atomic gases which is based on a well established quantum Monte Carlo analysis of the phase space density. This latter quantity, when derived from BCS–BEC crossover theory for fermions, leads to non-monotonic behavior for T BKT as a function of the attractive interaction or inverse scattering length. In Fermi gases, this implies a robust superconducting dome followed by a long tail from the flat BEC asymptote, rather similar to what is observed experimentally. For lattice systems we find that T BKT has an absolute maximum of the order of 0.1 E F . We discuss how our results compare with those derived from the Nelson–Kosterlitz criterion based on the mean field superfluid density and the approach to the transition from below. While there is agreement in the strict mean-field BCS regime at weak coupling, we find that at moderate pairing strength bosonic excitations cause a substantial increase in T BKT followed by an often dramatic decrease before the system enters the BEC regime.