Gaussian fluctuations in the two-dimensional BCS-BEC crossover: finite temperature properties

Abstract

The role of fluctuations is enhanced in lower dimensionality systems: in a two dimensions off-diagonal long-range order is destroyed by the fluctuations at any finite temperature, drastically modifying the critical properties with respect to the three-dimensional counterpart. Recently two-dimensional systems of interacting fermions have been the subject of Montecarlo studies and experimental investigations, in particular an ultracold gas of attractive fermions with a widely tunable interaction due to a Feshbach resonance has been realized and the Berezinskii-Kosterlitz-Thouless transition has been observed. The present work deals with the theoretical description of an ultracold Fermi gas: we discuss the role of Gaussian fluctuations of the order parameter in the equation of state, in particular we take into account the first sound velocity, showing that the inclusion of order parameter fluctuations is needed in order to get the correct composite-boson limit in the strong-coupling regime. The theory is also compared with experimental data. Finally we focus on the superfluid density in the weak-coupling, intermediate and strong-coupling regimes at finite temperature, through which the Berezinskii-Kosterlitz-Thouless critical temperature is obtained.

7 pages, 3 figures, submitted to the proceedings of the 24th Annual International Laser Physics Workshop

References in corpus (9)

• Radiofrequency spectroscopy of a strongly interacting two-dimensional Fermi gas
• Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
• Observation of a two-dimensional Fermi gas of atoms
• Observation of the Berezinskii-Kosterlitz-Thouless Phase Transition in an Ultracold Fermi Gas
• Crossover from 2D to 3D in a weakly interacting Fermi gas
• Pairing fluctuations and the superfluid density through the BCS-BEC crossover
• Pressure, compressibility, and contact of the two-dimensional attractive Fermi gas
• Condensate Fraction of a Two-Dimensional Attractive Fermi Gas
• Low-temperature thermodynamics of the unitary Fermi gas: superfluid fraction, first sound and second sound

Cited by in corpus (1)

• Effect of Weak Disorder on the BCS-BEC crossover in a two-dimensional Fermi Gas