论文标题
SU（n） - 对称的费米气体在有限温度下的巡回铁磁学：一阶相变和时反转对称性
Itinerant Ferromagnetism in SU(N)-Symmetric Fermi Gases at Finite Temperature: First Order Phase Transitions and Time-Reversal Symmetry
论文作者
论文摘要
在远低于费米温度$ t_f $的温度下，磁波动与两个组成式费米气体中粒子孔激发的耦合使其过渡到流动的铁磁性是一阶相变。 Landau的相变理论的范式不描述这种效果，该理论假设自由能是顺序参数的分析函数，并预测了二阶相变。另一方面，尽管较大的对称性通常会在低洼状态中引入更大的退化性，但在这里我们表明，对于带有SU的费米气体（$ n> 2 $） - 在三个空间维度中的对称性，Ferromangotic Phopentions Transition The Ferromangotic Phase Transition首先是与Landau理论的预测[M. [M. A. Cazalilla \ emph {et al}。新J. of Phys。 {\ bf 11} 103033（2009）]。通过执行SU（$ n> 2 $）的无限制的Hartree-Fock计算 - 具有短距离交互的对称费米气体，我们发现顺序参数会在整个过渡中经历有限的跳跃。此外，我们没有观察到温度为$ t \ simeq 0.5 \：t_f $的任何三个临界点，而费米表面的热涂抹是底层的。超越平均场外，我们发现磁波和颗粒孔激发的耦合使过渡更加突然，并进一步增强了气体的趋势，以完全偏振$ n $的$ n $和气体参数$ k_f a_s $。在我们的研究中，我们还阐明了时间逆向对称性在微观汉密尔顿的作用，并获得了TAN接触的温度依赖性。对于后者而言，$ n = 2 $的三个临界点的存在导致过渡周围的温度依赖性比SU（$ n> 2 $） - 对称气体更为明显。
At temperatures well below the Fermi temperature $T_F$, the coupling of magnetic fluctuations to particle-hole excitations in a two-component Fermi gas makes the transition to itinerant ferromagnetism a first order phase transition. This effect is not described by the paradigm of Landau's theory of phase transitions, which assumes the free energy is an analytic function of the order parameter and predicts a second order phase transition. On the other hand, despite that larger symmetry often introduces larger degeneracies in the low-lying states, here we show that for a Fermi gas with SU($N > 2$)-symmetry in three space dimensions the ferromangetic phase transition is first order in agreement with the predictions of Landau's theory [M. A. Cazalilla \emph{et al}. New J. of Phys. {\bf 11} 103033 (2009)]. By performing unrestricted Hartree-Fock calculations for an SU($N > 2$)-symmetric Fermi gas with short range interactions, we find the order parameter undergoes a finite jump across the transition. In addition, we do not observe any tri-critical point up to temperatures $T \simeq 0.5\: T_F$, for which the thermal smearing of the Fermi surface is subtantial. Going beyond mean-field, we find that the coupling of magnetic fluctuations to particle-hole excitations makes the transition more abrupt and further enhances the tendency of the gas to become fully polarized for smaller values of $N$ and the gas parameter $k_F a_s$. In our study, we also clarify the role of time reversal symmetry in the microscopic Hamiltonian and obtain the temperature dependence of Tan's contact. For the latter, the presence of the tri-critical point for $N = 2$ leads to a more pronounced temperature dependence around the transition than for SU($N > 2$)-symmetric gases.
