Collective mode of homogeneous superfluid Fermi gases in the BEC-BCS crossover
- Laboratoire de Physique Statistique, Ecole Normale Superieure, 24 rue Lhomond, 75231 Paris Cedex 05, France and Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris (France)
- P. L. Kapitza Institute for Physical Problems, Kosygin street 2, Moscow 119334 (Russian Federation)
- Dipartimento di Fisica, Universita di Trento and BEC-INFM, I-38050 Povo (Italy)
We perform a detailed study of the collective mode across the whole crossover from the Bose-Einstein condensate (BEC)-to the BCS regime in fermionic gases at zero temperature, covering the whole range of energy beyond the linear regime. This is done on the basis of the dynamical BCS model. We recover first the results of the linear regime in a simple form. Then specific attention is paid to the nonlinear part of the dispersion relation and its interplay with the continuum of single-fermionic excitations. In particular we consider in detail the merging of the collective mode into the continuum of single-fermionic excitations. This occurs not only on the BCS side of the crossover, but also slightly beyond unitarity on the BEC side. Another remarkable feature is the very linear behavior of the dispersion relation in the vicinity of unitarity almost up to merging with the continuum. Finally, while on the BEC side the mode is quite analogous to the Bogoliubov mode, a difference appears at high wave vectors. On the basis of our results we determine the Landau critical velocity in the BEC-BCS crossover which is found to be largest close to unitarity. Our investigation has revealed interesting qualitative features which deserve experimental exploration as well as further theoretical studies by more sophisticated means.
- OSTI ID:
- 20857894
- Journal Information:
- Physical Review. A, Vol. 74, Issue 4; Other Information: DOI: 10.1103/PhysRevA.74.042717; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
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