Observation of the Pairing Gap in a Strongly Interacting Fermi Gas

TL;DR

This paper reports the observation of a pairing energy gap in a strongly interacting ultracold Fermi gas of lithium-6 atoms, demonstrating superfluidity and the dependence of the gap on interaction strength, temperature, and Fermi energy.

Contribution

It provides direct spectroscopic evidence of pairing gaps in a strongly interacting Fermi gas and explores their dependence on various physical parameters.

Findings

Observation of an energy gap in RF spectra

Dependence of the pairing gap on interaction strength and temperature

Evidence of superfluid state formation in the gas

Abstract

We study fermionic pairing in an ultracold two-component gas of $^6$Li atoms by observing an energy gap in the radio-frequency excitation spectra. With control of the two-body interactions via a Feshbach resonance we demonstrate the dependence of the pairing gap on coupling strength, temperature, and Fermi energy. The appearance of an energy gap with moderate evaporative cooling suggests that our full evaporation brings the strongly interacting system deep into a superfluid state.