Vortices and Superfluidity in a Strongly Interacting Fermi Gas

TL;DR

This paper reports the direct observation of vortices in a strongly interacting Fermi gas, providing definitive evidence of superfluidity and exploring the BEC-BCS crossover with implications for high-temperature superconductivity.

Contribution

It presents the first direct visualization of vortices in a strongly interacting Fermi gas, confirming superfluidity across the BEC-BCS crossover.

Findings

Vortex lattices observed in the Fermi gas.

Superfluidity confirmed in the strongly interacting regime.

Exploration of the BEC-BCS crossover dynamics.

Abstract

Quantum-degenerate Fermi gases provide a remarkable opportunity to study strongly interacting fermions. In contrast to other Fermi systems, such as superconductors, neutron stars or the quark-gluon plasma, these gases have low densities and their interactions can be precisely controlled over an enormous range. Here we report observations of vortices in such a gas that provide definitive evidence for superfluidity. By varying the pairing strength between two fermions near a Feshbach resonance, one can explore the crossover from a Bose-Einstein condensate (BEC) of molecules to a Bardeen-Cooper-Schrieffer (BCS) superfluid of loosely bound pairs whose size is comparable to, or even larger than, the interparticle spacing. The crossover realizes a novel form of high-T_C superfluidity and it may provide new insight for high-T_C superconductors. Previous experiments with Fermi gases have revealed condensation of fermion pairs. While these and other studies were consistent with predictions assuming superfluidity, the smoking gun for superfluid behavior has been elusive. Our observation of vortex lattices directly displays superfluid flow in a strongly interacting, rotating Fermi gas.