Three-dimensional spin–orbit coupled Fermi gases: Fulde–Ferrell pairing, Majorana fermions, Weyl fermions, and gapless topological superfluidity*
Liu Xia-Jia), Hu Huia), Pu Hanb),c)†
       
(a) Evolution of the superfluid phase with equally increasing in-plane and out-plane Zeeman fields, and with an imperfect Rashba spin–orbit coupling at the angle θ = π /8. The system evolves from a gapped FF superfluid to a gapped topologically nontrivial topo-FF4 state, and then to a gapless topologically non-trivial FF superfluid with either four (gapless topo-FF4) or two Weyl nodes/loops (gapless topo-FF2). The solid and dashed lines show the energy at k = 0 [ E 2+( k = 0)] and the minimum energy [min E 2+( k )] of the lower particle branch. (b) The pairing gap (solid line) and FF pairing momentum (dashed line) as a function of the Zeeman field. The thick and thin lines correspond to the cases with θ = π /8 and θ = π /4, respectively.