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arXiv · 1710.11171

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

G. Bighin·L. Salasnich
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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.

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G. Bighin, L. Salasnich. 2017-10-30. Renormalization of the superfluid density in the two-dimensional BCS-BEC crossover. https://doi.org/10.1142/s0217979218400222

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