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 increasing out-of-plane Zeeman field at zero in-plane Zeeman field h in = 0. The system evolves from a standard BCS superfluid to a topological non-trivially superfluid with either four (topo-BCS4) or two Weyl nodes (topo-BCS2). 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. Panels (b) and (c) show the characteristic quasiparticle excitation spectrum E 2±( k x = 0, k y , k z ) in the topo-BCS4 ( h out = 0.4 E F) and topo-BCS2 phases ( h out = 0.5 E F), respectively. We note that the spectrum is symmetric with respect to k y and we plot only the left part with k y ≤ 0.