Thermal-assisted Anisotropy and Thermal-driven Instability in the Superfluidity state of Two-Species Polar Fermi Gas

TL;DR

This paper investigates how temperature and anisotropic interactions influence the superfluid state of two-species polar Fermi gases, revealing temperature-induced anisotropy and potential instability leading to FFLO states.

Contribution

It introduces a self-consistent approach considering Fock exchange and symmetry to analyze anisotropic superfluidity in dipolar Fermi gases, highlighting temperature effects and instability conditions.

Findings

Temperature increases pairing anisotropy unexpectedly.

Negative superfluid mass density component indicates instability.

Potential realization of FFLO state due to anisotropic superflow.

Abstract

We study the superfluid state of two-species heteronuclear Fermi gases with isotropic contact and anisotropic long-range dipolar interactions. By explicitly taking account of Fock exchange contribution, we derive self-consistent equations describing the pairing states in the system. Exploiting the symmetry of the system, we developed an efficient way of solving the self-consistent equations by exploiting the symmetries. We find that the temperature tends to increase the anisotropy of the pairing state, which is rather counterintuitive. We study the anisotropic properties of the system by examining the angular dependence of the number density distribution, the excitation spectrum and the pair correlation function. The competing effects of the contact interaction and the dipolar interaction upon the anisotropy are revealed. We derive and compute the superfluid mass density $\rho_{ij}$ for the system. Astonishingly, we find that $\rho_{zz}$ becomes negative above some certain temperature $T^*$($T<T_c$), signaling some instability of the system. This suggests that the elusive FFLO state may be observed in experiments, due to an anisotropic state with a spontaneously generated superflow.