Two Transitions in the Damping of a Unitary Fermi Gas

TL;DR

This study investigates how the damping of collective oscillations in a strongly-interacting Fermi gas changes with temperature, revealing two distinct transitions likely related to atom pairing phenomena.

Contribution

It provides the first detailed measurement of temperature-dependent damping in a unitary Fermi gas, identifying two separate transition points.

Findings

Damping rate exhibits two distinct transitions with temperature.

Frequency remains near the hydrodynamic value across temperatures.

Evidence suggests atom pairing above the superfluid transition.

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.