Effects of periodic potentials on the critical velocity of superfluid Fermi gases in the BCS-BEC crossover

Year: 2011

Authors: Watanabe G., Dalfovo F., Pitaevskii L.P., Stringari S.

Autors Affiliation: Asia Pacific Center for Theoretical Physics (APCTP), POSTECH, San 31, Hyoja-dong, Nam-gu, Pohang, Gyeongbuk 790-784, Korea; Nishina Center, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan; INO-CNR BEC Center and Department of Physics, University of Trento, I-38123 Povo, Italy; Kapitza Institute for Physical Problems, 119334 Moscow, Russia

Abstract: 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 gas of ultracold atoms in the superfluid phase flowing through a one-dimensional 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 nonmonotonic behavior along the BCS-BEC crossover.


Volume: 83 (3)      Pages from: 033621  to: 033621

More Information: We thank Ki-Seok Kim, Chris Pethick, Robin G. Scott, and Tetsuya Takimoto for helpful discussions and comments. Calculations were performed on the RIKEN Integrated Cluster of Clusters (RICC) system, WIGLAF at the University of Trento, and BEN at ECT*. G. W. acknowledges the Max Planck Society (MPG), the Korea Ministry of Education, Science and Technology (MEST), Gyeongsangbuk-Do, and Pohang City for support from the Independent Junior Research Group at the Asia Pacific Center for Theoretical Physics (APCTP).
DOI: 10.1103/PhysRevA.83.033621

Citations: 9
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