Hou Xu-Yang, Huang Ziwen, Guo Hao, He Yan, Chien Chih-Chun
Department of Physics, Southeast University, Jiulonghu Campus, Nanjing, 211189, China.
Department of Physics and Astronomy, Northwestern University, Evanston, IL, 60208, USA.
Sci Rep. 2018 Aug 10;8(1):11995. doi: 10.1038/s41598-018-30438-1.
The thermal field theory is applied to fermionic superfluids by doubling the degrees of freedom of the BCS theory. We construct the two-mode states and the corresponding Bogoliubov transformation to obtain the BCS thermal vacuum. The expectation values with respect to the BCS thermal vacuum produce the statistical average of the thermodynamic quantities. The BCS thermal vacuum allows a quantum-mechanical perturbation theory with the BCS theory serving as the unperturbed state. We evaluate the leading-order corrections to the order parameter and other physical quantities from the perturbation theory. A direct evaluation of the pairing correlation as a function of temperature shows the pseudogap phenomenon, where the pairing persists when the order parameter vanishes, emerges from the perturbation theory. The correspondence between the thermal vacuum and purification of the density matrix allows a unitary transformation, and we found the geometric phase associated with the transformation in the parameter space.
通过将BCS理论的自由度加倍，热场理论被应用于费米子超流体。我们构建双模态和相应的博戈留波夫变换以获得BCS热真空。关于BCS热真空的期望值产生了热力学量的统计平均值。BCS热真空允许以BCS理论作为未微扰态的量子力学微扰理论。我们从微扰理论评估对序参量和其他物理量的领先阶修正。对作为温度函数的配对关联的直接评估表明，当序参量消失时配对仍然存在的赝能隙现象，源自微扰理论。热真空与密度矩阵纯化之间的对应关系允许进行幺正变换，并且我们在参数空间中发现了与该变换相关的几何相位。
