Collisionless sound of bosonic superfluids in lower dimensions

Abstract

The superfluidity of low-temperature bosons is well established in the collisional regime. In the collisionless regime, however, the presence of superfluidity is not yet fully clarified, in particular in lower spatial dimensions. Here we compare the Vlasov-Landau equation, which does not take into account the superfluid nature of the bosonic system, with the Andreev-Khalatnikov equations, which instead explicitly contain a superfluid velocity. We show that recent experimental data of the sound mode in a two-dimensional collisionless Bose gas of ${}^{87}$Rb atoms are in good agreement with both theories but the sound damping is better reproduced by the Andreev -Khalatnikov equations below the Berezinskii-Kosterlitz-Thouless critical temperature $T_c$ while above $T_c$ the Vlasov-Landau results are closer to the experimental ones. For one dimensional bosonic fluids, where experimental data are not yet available, we find larger differences between the sound velocities predicted by the two transport theories and, also in this case, the existence of a superfluid velocity reduces the sound damping.

arXiv comment7 pages, 2 figures, improved version; to be published in Physical Review A

References in corpus (9)

• Critical Point of a Weakly Interacting Two-Dimensional Bose Gas
• Two-Dimensional Weakly Interacting Bose Gas in the Fluctuation Region
• Phase fluctuations in atomic Bose gases
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• Dynamical Kosterlitz-Thouless Theory for Two-Dimensional Ultracold Atomic Gases

Cited by in corpus (1)

• First and second sound in two-dimensional bosonic and fermionic superfluids