Figure 1: Pairing mechanism and phase diagram.
From: Topological Fulde–Ferrell–Larkin–Ovchinnikov states in spin–orbit-coupled Fermi gases
(a–c) Illustration of pairing mechanisms that give rise to different phases in the weak-coupling limit: (a) intra-branch pairing with a single Fermi surface, (b) intra-branch pairing with two Fermi surfaces and (c) inter-branch pairing. The filled areas with different colours represent the Fermi surfaces in the lower and upper helicity branches, and the black dot represents the origin of the momentum space. (d) Phase diagrams on the α−μ plane for Eb/h=0.5 and hx/h=0.1, where Eb is the binding energy of the two-body bound state in two dimensions without SOC. The solid curves are first-order boundaries, whereas the dash-dotted curves represent phase boundaries of continuous phase transitions. The dashed curves surrounding the normal region (N) are the threshold with ΔQ/h=10−3, whereas the dotted curves are the boundary against vacuum (VAC). In the weak-coupling limit, the tFF state corresponds to the pairing mechanism (a), the gapped FF (gFF) state and the nFF state correspond to the pairing mechanism (b), while (c) gives rise to a parameter region on the phase diagram where the global ground state is the result of competition between different FF states with centre-of-mass momentum in the x- or the y-direction (mixed). The out-of-plane Zeeman field h is taken to be the unit of energy, whereas the unit of momentum kh is defined through 
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