Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture

TL;DR

This study uses radio-frequency spectroscopy to investigate pairing in an imbalanced Fermi gas, revealing that pairing can occur without superfluidity, challenging the assumption that mismatched Fermi surfaces prevent pairing.

Contribution

It demonstrates that fermion pairing can exist without superfluidity in imbalanced Fermi gases, showing that mismatched Fermi surfaces do not necessarily inhibit pairing.

Findings

Full pairing of minority atoms observed at high imbalance.

Mismatched Fermi surfaces do not prevent pairing.

Superfluidity can be quenched despite pairing presence.

Abstract

Radio-frequency spectroscopy is used to study pairing in the normal and superfluid phases of a strongly interacting Fermi gas with imbalanced spin populations. At high spin imbalances the system does not become superfluid even at zero temperature. In this normal phase full pairing of the minority atoms is observed. This demonstrates that mismatched Fermi surfaces do not prevent pairing but can quench the superfluid state, thus realizing a system of fermion pairs that do not condense even at the lowest temperature.