Critical velocity of superfluid flow through single barrier and periodic potentials

Details Critical velocity of superfluid flow through single barrier and periodic potentials Critical velocity of superfluid flow through single barrier and periodic potentials

2009-07-03

arxiv.org/abs/0907.0621v2

Phys. Rev. A 80, 053602 (2009)

Physics

Condensed Matter

Quantum Gases

10 pages, 6 figures; appendix extended, to appear in Phys. Rev. A

Scientific paper

10.1103/PhysRevA.80.053602

We investigate the problem of an ultracold atomic gas in the superfluid phase flowing in the presence of a potential barrier or a periodic potential. We use a hydrodynamic scheme in the local density approximation (LDA) to obtain an analytic expression for the critical current as a function of the barrier height or the lattice intensity, which applies to both Bose and Fermi superfluids. In this scheme, the stationary flow becomes energetically unstable when the local superfluid velocity is equal to the local sound velocity at the point where the external potential is maximum. We compare this prediction with the results of the numerical solutions of the Gross-Pitaevskii and Bogoliubov-de Gennes equations. We discuss the role of long wavelength excitations in determining the critical velocity. Our results allow one to identify the different regimes of superfluid flow, namely, the LDA hydrodynamic regime, the regime of quantum effects beyond LDA for weak barriers and the regime of tunneling between weakly coupled superfluids for strong barriers. We finally discuss the relevance of these results in the context of current experiments with ultracold gases.

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