Renormalization of the superfluid density in the two-dimensional BCS-BEC crossover

Abstract

We analyze the theoretical derivation of the beyond-mean-field equation of state for a two-dimensional gas of dilute, ultracold alkali-metal atoms in the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover. We show that at zero temperature our theory -- considering Gaussian fluctuations on top of the mean-field equation of state -- is in very good agreement with experimental data. Subsequently, we investigate the superfluid density at finite temperature and its renormalization due to the proliferation of vortex-antivortex pairs. By doing so, we determine the Berezinskii-Kosterlitz-Thouless (BKT) critical temperature -- at which the renormalized superfluid density jumps to zero -- as a function of the inter-atomic potential strength. We find that the Nelson-Kosterlitz criterion overestimates the BKT temperature with respect to the renormalization group equations, this effect being particularly relevant in the intermediate regime of the crossover.

9 pages, 3 figures, presented to the International Conference "Electron correlation in superconductors and nanostructures", 17-20 August 2017, Odessa (Ukraine). To be published in the Proceedings

References in corpus (12)

• Extension of Bogoliubov theory to quasi-condensates
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• Zero-point energy of ultracold atoms
• Berezinskii-Kosterlitz-Thouless transition in trapped quasi-two-dimensional Fermi gas near a Feshbach resonance
• Condensate Fraction of a Two-Dimensional Attractive Fermi Gas
• Composite bosons in the 2D BCS-BEC crossover from Gaussian fluctuations
• Non-Universal Equation of State of the Two-Dimensional Bose Gas
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Cited by in corpus (5)

• Observation of superfluidity in a strongly correlated two-dimensional Fermi gas
• Density correlation functions and the spatial structure of the two-dimensional BEC-BCS crossover
• Dimensional crossover in ultracold Fermi gases from Functional Renormalisation
• First and second sound in two-dimensional bosonic and fermionic superfluids
• Correlated phases of moat-band excitons in two dimensions