Effect of anisotropic spin-orbit coupling on condensation and superfluidity of a two-dimensional Fermi gases

We investigated the ground-state properties of a two-dimensional Fermi superfluid with an anisotropic spin-orbit coupling (SOC) using the path-integral field theoretical method. Within the framework of mean-field theory, we obtained the condensed fraction, including contributions from both singlet and triple pairing fields. We found that for small interaction parameters and large anisotropic parameters, the total condensed fraction changes non-monotonically when increasing the strength of SOC and has a global maximum. But this feature disappears when decreasing the anisotropic parameter and increasing the interaction parameter. However, the condensed fraction always decreases with increasing anisotropic parameters. Because of the anisotropy of the SOC, the superfluid fraction becomes a tensor. We obtained the superfluid fraction tensor by deriving the effective action of the phase field of the order parameter. Our numerical results show that for small interaction parameters and large anisotropic parameters, the superfluid fraction of the x component p(x) has a minimum as a function of the SOC strength. And this minimum of p(x) disappears when decreasing the anisotropic parameters. In the strong interaction regime, p(x) always decreases with increasing the strength of SOC. While for the y component of the superfluid fraction p(y), no matter how large the interaction parameters and anisotropic parameters are, it always has a minimum as a function of the SOC strength. As a function of the anisotropic parameter, for strong SOC strength, p(x)<p(y) with p(x ) having a minimum. For small SOC parameters, p(x)>p(y) with p(y) developing a minimum only in the weak interaction limit.