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

Abstract

We investigate the center-of-mass momentum distribution $n_{\mathbf{Q}}$ of Cooper pairs and their first-order correlation function $g_1(r)$ in a strongly interacting two-dimensional Fermi gas. Recently, the BKT (Berezinskii-Kosterlitz-Thouless) transition was reported in a two-dimensional ${}^6$Li Fermi gas, based on (1) the observations of anomalous enhancement of $n_{\mathbf{Q}=0}$ [M. G. Ries, et. al., Phys. Rev. Lett. 114, 230401 (2015)], as well as (2) a power-law behavior of $g_1(r)$ [P. A. Murthy, et. al., Phys. Rev. Lett. 115, 010401 (2015)]. However, including pairing fluctuations within a $T$-matrix approximation (TMA), we show that these results can still be explained as strong-coupling properties of a normal-state two-dimensional Fermi gas. Our results indicate the importance of further experimental observations, to definitely confirm the realization of the BKT transition in this system. Since the BKT transition has been realized in a two-dimensional ultracold Bose gas, our results would be useful for the achievement of this quasi-long range order in an ultracold Fermi gas.

arXiv comment22 pages, 7 figures

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• Reaching the continuum limit in finite-temperature ab initio field-theory computations in many-fermion systems
• Visualizing the BEC-BCS crossover in the two-dimensional Fermi gas: pairing gaps and dynamical response functions from ab initio computations
• Second sound in 2D Bose gas: from the weakly interacting to the strongly interacting regime
• Dynamical structure factors of a two-dimensional Fermi superfluid within random phase approximation
• Vortices and antivortices in two-dimensional ultracold Fermi gases
• Precision Many-Body Study of the Berezinskii-Kosterlitz-Thouless Transition and Temperature-Dependent Properties in the Two-Dimensional Fermi Gas
• Quantum fluctuations and vortex-antivortex unbinding in the 2D BCS-BEC crossover
• Pseudogap regime of a two-dimensional uniform Fermi gas
• Pseudogap phenomena near the BKT transition of a two-dimensional ultracold Fermi gas in the crossover region
• Quantitative Studies on the Quantum Critical Regime near Superfluid to Mott Insulator Transition