Composite bosons in the 2D BCS-BEC crossover from Gaussian fluctuations

Abstract

We study Gaussian fluctuations of the zero-temperature attractive Fermi gas in the 2D BCS-BEC crossover showing that they are crucial to get a reliable equation of state in the BEC regime of composite bosons, bound states of fermionic pairs. A low-momentum expansion up to the fourth order of the quadratic action of the fluctuating pairing field gives an ultraviolent divergent contribution of the Gaussian fluctuations to the grand potential. Performing dimensional regularization we evaluate the effective coupling constant in the beyond-mean-field grand potential. Remarkably, in the BEC regime our grand potential gives exactly the Popov's equation of state of 2D interacting bosons, and allows us to identify the scattering length $a_B$ of the interaction between composite bosons as $a_B=a_F/(2^{1/2}{e}^{1/4})=\mathrm{0.551...}{a}_F$, with $a_F$ is the scattering length of fermions. Remarkably, the value from our analytical relationship between the two scattering lengths is in full agreement with that obtained by recent Monte Carlo calculations.

5 pages, no figures, submitted for publication; typos corrected; to be published in Phys. Rev. A as a Rapid Communication

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Cited by in corpus (6)

• Pressure profiles of nonuniform two-dimensional atomic Fermi gases
• Josephson effect with superfluid fermions in the two-dimensional BCS-BEC crossover
• Quantum fluctuations and vortex-antivortex unbinding in the 2D BCS-BEC crossover
• Goldstone and Higgs Hydrodynamics in the BCS-BEC Crossover
• Scattering length of composite bosons in the 3D BCS-BEC crossover
• First and second sound in two-dimensional bosonic and fermionic superfluids