Momentum distribution of Cooper-pairs and strong-coupling effects in a two-dimensional Fermi gas near the Berezinskii-Kosterlitz-Thouless transition

Abstract

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 $n(\mathbf{Q})$ of Cooper pairs in terms of the center of mass momentum $\mathbf{Q}$. In the strong-coupling regime, $n(\mathbf{Q}=0)$ 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 [M. G. Ries, {\it et. al.}, Phys. Rev. Lett. {\bf 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.

7 pages, 4 figures, Proceedings of QFS2015

References in corpus (14)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
• Resonantly-paired fermionic superfluids
• Radiofrequency spectroscopy of a strongly interacting two-dimensional Fermi gas
• Observation of a two-dimensional Fermi gas of atoms
• Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas
• Observation of pair condensation in the quasi-2D BEC-BCS crossover
• Spin-Imbalanced Quasi-Two-Dimensional Fermi Gases
• Matter wave Fourier optics with a strongly interacting two-dimensional Fermi gas
• Pairing effects in the normal phase of a two-dimensional Fermi gas
• The effect of population imbalance on the Berezinskii-Kosterlitz-Thouless phase transition in a superfluid Fermi gas
• Pseudogap and preformed pairs in the imbalanced Fermi gas in two dimensions
• Pairing and radio-frequency spectroscopy in two-dimensional Fermi gases
• Pseudogap phenomena in a two-dimensional ultracold Fermi gas near the Berezinskii-Kosterlitz-Thouless transition

Cited by in corpus (2)

• Evolution of Cooper pairs with zero-center-of-mass momentum and their first-order correlation function in a two-dimensional ultracold Fermi gas near the observed Berezinskii-Kosterlitz-Thouless transition
• Two-dimensional spin-imbalanced Fermi gases at non-zero temperature: Phase separation of a non-condensate