Kohn's theorem in a superfluid Fermi gas with a Feshbach resonance

Journal Article · Wed Dec 01 04:00:00 EST 2004 · Physical Review. A

DOI:https://doi.org/10.1103/PhysRevA.70.063613· OSTI ID:20649983

Ohashi, Y ^[1]

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1. Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305 (Japan)

We investigate the dipole mode in a superfluid gas of Fermi atoms trapped in a harmonic potential. According to Kohn's theorem, the frequency of this collective mode is not affected by an interaction between the atoms and is always equal to the trap frequency. This remarkable property, however, does not necessarily hold in an approximate theory. We explicitly prove that the Hartree-Fock-Bogoliubov generalized random phase approximation (HFB-GRPA), including a coupling between fluctuations in the density and Cooper channels, is consistent with both Kohn's theorem as well as Goldstone's theorem. This proof can be immediately extended to the strong-coupling superfluid theory developed by Nozieres and Schmitt-Rink (NSR), where the effect of superfluid fluctuations is included within the Gaussian level. As a result, the NSR-GRPA formalism can be used to study collective modes in the BCS-BEC crossover region in a manner which is consistent with Kohn's theorem. We also include the effect of a Feshbach resonance and a condensate of the associated molecular bound states. A detailed discussion is given of the unusual nature of the Kohn mode eigenfunctions in a Fermi superfluid, in the presence and absence of a Feshbach resonance. When the molecular bosons feel a different trap frequency from the Fermi atoms, the dipole frequency is shown to depend on the strength of effective interaction associated with the Feshbach resonance.

• OSTI ID: 20649983
• Journal Information: Physical Review. A, Journal Name: Physical Review. A Journal Issue: 6 Vol. 70; ISSN 1050-2947; ISSN PLRAAN
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ATOMS
BASIC INTERACTIONS
BOSONS
BOUND STATE
COUPLING
DENSITY
DIPOLES
EIGENFUNCTIONS
EIGENVALUES
FERMI GAS
FERMIONS
FLUCTUATIONS
HARMONIC POTENTIAL
HARTREE-FOCK-BOGOLYUBOV THEORY
RANDOM PHASE APPROXIMATION
RESONANCE
SUPERFLUIDITY
TRAPPING
TRAPS