Enhancement and destruction of superfluidity: Unusual effects of population imbalance of atomic Fermi gases on a 1D optical lattice

We study the superfluid behavior of population imbalanced ultracold atomic Fermi gases with a short range attractive interaction on a 1D optical lattice, using a pairing fluctuation theory. Due to the lattice-continuum mixing in a 1D optical lattice, population imbalance now has highly unusual effects. While the transition Tc in the balanced case decreases and scales as k_Fa in the BEC regime, it approaches a constant BEC asymptote in imbalanced case. Therefore, population
imbalance may strongly enhance the superfluidity by raising Tc to the constant BEC asymptote. In addition to the destruction of superfluidity in some range of intermediate pairing strengths, the BEC regime may also become inaccessible when the lattice spacing d and the population imbalance p become large, and/or the lattice hopping integral t becomes small, in contrast to the 3D continuum or dilute 3D lattice case, for which the BEC regime is always accessible. Furthermore, even when the BEC regime is accessible, not all minority atoms are paired up in the BEC limit. Upon destruction of the superfluidity due to increasing (d,p) or decreasing t, only 50% of the minority atoms form pairs.