title: Collective excitations of a degenerate gas at the BEC-BCS crossover.
abstract: We study collective excitation modes of a fermionic gas of (6)Li atoms in the BEC-BCS crossover regime. While measurements of the axial compression mode in the cigar-shaped trap close to a Feshbach resonance confirm theoretical expectations, the radial compression mode shows surprising features. In the strongly interacting molecular BEC regime, we observe a negative frequency shift with increasing coupling strength. In the regime of a strongly interacting Fermi gas, an abrupt change in the collective excitation frequency occurs, which may be a signature for a transition from a superfluid to a collisionless phase.
authors.affiliation: Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria.
authors.forename: M
authors.initials: M
authors.lastname: Bartenstein
authors.forename: A
authors.initials: A
authors.lastname: Altmeyer
authors.forename: S
authors.initials: S
authors.lastname: Riedl
authors.forename: S
authors.initials: S
authors.lastname: Jochim
authors.forename: C
authors.initials: C
authors.lastname: Chin
authors.forename: J Hecker
authors.initials: JH
authors.lastname: Denschlag
authors.forename: R
authors.initials: R
authors.lastname: Grimm