Transition and Damping of Collective Modes in a Trapped Fermi Gas between BCS and Unitary Limits near the Phase Transition.
Transition and Damping of Collective Modes in a Trapped Fermi Gas between BCS and Unitary Limits near the Phase Transition.
复制标题
相变附近 BCS 和酉极限之间困住费米气体中集体模式的转变和阻尼
DOI：
10.1038/srep15848
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发表时间：
2015-11-02
影响因子：
4.6
通讯作者：
Ma Y
中科院分区：
文献类型：
--
作者：
Dong H;Zhang W;Zhou L;Ma Y
本文结合正规相的t矩阵涨落理论和有序相的平均场理论，通过求解缩放形式的Boltzmann-Vlasov动力学方程，研究了捕获的单一费米气体中低能集体模的跃迁和阻尼。为了将多体Feshbach散射的微观描述和动力学描述联系起来，我们采用了一种现象学的双流体物理方法，推导了有序相的耦合常数。通过变分形式求解Boltzmann-Vlasov稳态方程，计算了费米子散射碰撞概率下的两种粘性松弛率，包括正常流体中的费米子和超流体中的费米子对。此外，通过考虑费米子的配对和依赖，我们得到了集体模式的频率和阻尼随温度和s波散射长度的变化结果。我们的理论结果与实验数据非常一致，特别是在无碰撞和流体动力行为之间的急剧转变以及在相变附近的BCS和单一极限之间的强阻尼之间。剧烈的跃迁源于费米子-费米子对碰撞在相变点产生的粘性弛豫速率最大值，而强阻尼源于集体模式频率从BCS极限到酉极限的快速变化。
We investigate the transition and damping of low-energy collective modes in a trapped unitary Fermi gas by solving the Boltzmann-Vlasov kinetic equation in a scaled form, which is combined with both the T-matrix fluctuation theory in normal phase and the mean-field theory in order phase. In order to connect the microscopic and kinetic descriptions of many-body Feshbach scattering, we adopt a phenomenological two-fluid physical approach, and derive the coupling constants in the order phase. By solving the Boltzmann-Vlasov steady-state equation in a variational form, we calculate two viscous relaxation rates with the collision probabilities of fermion’s scattering including fermions in the normal fluid and fermion pairs in the superfluid. Additionally, by considering the pairing and depairing of fermions, we get results of the frequency and damping of collective modes versus temperature and s-wave scattering length. Our theoretical results are in a remarkable agreement with the experimental data, particularly for the sharp transition between collisionless and hydrodynamic behaviour and strong damping between BCS and unitary limits near the phase transition. The sharp transition originates from the maximum of viscous relaxation rate caused by fermion-fermion pair collision at the phase transition point when the fermion depair, while the strong damping due to the fast varying of the frequency of collective modes from BCS limit to unitary limit.