Tunneling Transport of Unitary Fermions across the Superfluid Transition

We investigate the transport of a Fermi gas with unitarity-limited interactions across the superfluid phase transition, probing its response to a direct current (dc) drive through a tunnel junction. As the superfluid critical temperature is crossed from below, we observe the evolution from a highly nonlinear to an Ohmic conduction characteristic, associated with the critical breakdown of the Josephson dc current induced by pair condensate depletion. Moreover, we reveal a large and dominant anomalous contribution to resistive currents, which reaches its maximum at the lowest attained temperature, fostered by the tunnel coupling between the condensate and phononic Bogoliubov-Anderson excitations. Increasing the temperature, while the zeroing of supercurrents marks the transition to the normal phase, the conductance drops considerably but remains much larger than that of a normal, uncorrelated Fermi gas tunneling through the same junction. We attribute such enhanced transport to incoherent tunneling of sound modes, which remain weakly damped in the collisional hydrodynamic fluid of unpaired fermions at unitarity.

Automated summary

In this study, the transport of a Fermi gas with unitarity-limited interactions across the superfluid phase transition is investigated. It was found that as the critical temperature is crossed, the conductivity evolves from highly nonlinear to Ohmic characteristics, with the critical breakdown of the Josephson dc current induced by pair condensate depletion. Additionally, a large anomalous contribution to resistive currents was revealed, reaching its maximum at the lowest temperature due to tunnel coupling between the condensate and phononic Bogoliubov-Anderson excitations.