Two Transitions in the Damping of a Unitary Fermi Gas

Abstract

We measure the temperature dependence of the radial breathing mode in an optically trapped, strongly-interacting Fermi gas of ${}^6$Li, just above the center of a broad Feshbach resonance. The frequency remains close to the unitary hydrodynamic value, while the damping rate reveals transitions at two well-separated temperatures, consistent with the existence of atom pairs above a superfluid transition.

5 pages, 2 figures