Momentum Distribution of Cooper Pairs and Strong-Coupling Effects in a Two-Dimensional Fermi Gas Near the Berezinskii–Kosterlitz–Thouless Transition

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• 作者：M. Matsumoto ; D. Inotani ; Y. Ohashi
• 关键词：Ultracold Fermi gas ; Two ; dimensional system ; BKT phase transition
• 刊名：Journal of Low Temperature Physics
• 出版年：2016
• 出版时间：May 2016
• 年：2016
• 卷：183
• 期：3-4
• 页码：199-207
• 全文大小：537 KB
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• 作者单位：M. Matsumoto (1)
  D. Inotani (1)
  Y. Ohashi (1)
  
  1. Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan
  
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Condensed Matter
  Characterization and Evaluation Materials
  Magnetism and Magnetic Materials
  
• 出版者：Springer Netherlands
• ISSN：1573-7357

文摘

We investigate strong-coupling properties of a two-dimensional ultracold Fermi gas in the normal state. Including pairing fluctuations within the framework of a T-matrix approximation, we calculate the distribution function \(n({\varvec{Q}})\) of Cooper pairs in terms of the center of mass momentum \({\varvec{Q}}\). In the strong-coupling regime, \(n({\varvec{Q}}=0)\) is shown to exhibit a remarkable increase with decreasing the temperature in the low temperature region, which agrees well with the recent experiment on a two-dimensional \(^6\)Li Fermi gas (Ries et al. in Phys Rev Lett 114:230401, 2015). Our result indicates that the observed remarkable increase of the number of Cooper pairs with zero center of mass momentum can be explained without assuming the Berezinskii–Kosterlitz–Thouless (BKT) transition, when one properly includes pairing fluctuations that are enhanced by the low-dimensionality of the system. Since the BKT transition is a crucial topic in two-dimensional Fermi systems, our results would be useful for the study toward the realization of this quasi-long-range order in an ultracold Fermi gas.