Superfluid phase transition and effects of mass imbalance in the BCS-BEC crossover regime of an ultracold Fermi gas: A self-consistent T-matrix theory

We investigate a two-component Fermi gas with mass imbalance ($m_\uparrow\ne m_\downarrow$, where $m_\sigma$ is an atomic mass in the $\sigma$-component) in the BCS-BEC crossover region. Including pairing fluctuations within a self-consistent $T$-matrix theory, we examine how the superfluid instability is affected by the presence of mass imbalance. We determine the superfluid region in the phase diagram of a Fermi gas in terms of the temperature, the strength of a pairing interaction, and the ratio of mass imbalance. The superfluid phase transition is shown to always occur even when $m_\uparrow\ne m_\downarrow$.\footnote{R.Hanai and Y.Ohashi, J. Low Temp. Phys., DOI 10.1007/s10909-013-0909-3.} This behavior of $T_{\rm c}$ is quite different from the previous result in an extended $T$-matrix theory,\footnote{R.Hanai, \textit{et. al.}, Phys. Rev. A (2013) in press.} where $T_{\rm c}$ vanishes at a certain value of $m_\uparrow/m_\downarrow>0$ in the BCS regime. Since Fermi condensates with mass imbalance have been discussed in various systems, such as a cold Fermi gas, an exciton(polariton) condensate, as well as color superconductivity, our results would be useful for further understandings of these novel Fermi superfluids.