Abstract: The phase diagram of a homogenous ultracold Fermi gas with spin polarizationis studied at unitarity. In the framework of Landau's phase-transition theory, the thermodynamic grand potential is expanded to the sixth order in the order parameter, and coefficients of each order are determined. The tricritical point in the temperature-polarization plane is obtained. Abovethe critical point, the second-order phase-transition line between the super fluid and the normal phase is determined. Belowthe critical point, there is a phase-separation region between these two phases, and the first-order phase-transition line is obtained.

Key words: superfluid, tricritical point, polarized Fermi gas, phase diagram, resonance

摘要： 研究了超冷均匀极化的费米气体在共振区的相图。在朗道相变理论的框架下, 把热力学势展开到了序参量的六阶, 并且通过比较微观的推导结果与朗道的唯象理论确定出了这些展开项的系数。在温度和费米子极化的相图上得到了三相点的位置。在三相点温度以上, 超流和正常相之间有二级相变。在三相点温度以下, 存在着这两个相共存的相分离区域, 一阶相变的位置被确定下来。

关键词: 超流, 三相点, 极化费米子, 相图, 共振