Physics – Condensed Matter – Quantum Gases
Scientific paper
2010-10-23
Phys.Rev.A83:033621,2011
Physics
Condensed Matter
Quantum Gases
9 pages, 7 figures, added an appendix on the dynamical instability
Scientific paper
10.1103/PhysRevA.83.033621
We study the effects of an external periodic potential on the critical velocity of a superfluid Fermi gas in the crossover between the Bardeen-Cooper-Schrieffer (BCS) phase and Bose-Einstein condensation (BEC). We numerically solve the Bogoliubov-de Gennes equations to model a three-dimensional (3D) gas of ultracold atoms in the superfluid phase flowing through a 1D optical lattice. We find that when the recoil energy is comparable to the Fermi energy, the presence of the periodic potential reduces the effect of pair-breaking excitations. This behavior is a consequence of the peculiar band structure of the quasiparticle energy spectrum in the lattice. When the lattice height is much larger than the Fermi energy, the periodic potential makes pairs of atoms to be strongly bound even in the BCS regime and pair-breaking excitations are further suppressed. We have also found that when the recoil energy is comparable to or larger than the Fermi energy, the critical velocity due to long-wavelength phonon excitations shows a non-monotonic behavior along the BCS-BEC crossover.
Dalfovo Franco
Pitaevskii Lev P.
Stringari Sandro
Watanabe Gentaro
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