Strongly correlated superfluid order parameters from dc Josephson supercurrents

TL;DR

This study demonstrates the observation of dc Josephson supercurrents in strongly interacting fermionic superfluids, revealing insights into superfluid order parameters across the BCS-BEC crossover using phase-sensitive measurements.

Contribution

It provides the first experimental mapping of Josephson effects in strongly correlated fermionic superfluids, linking superfluid order parameters with Josephson critical currents across the BCS-BEC crossover.

Findings

Sinusoidal current-phase relation observed for strong barriers

Critical current behavior mapped across the BCS-BEC crossover

Determined pair condensate fraction in strongly interacting regime

Abstract

The dc Josephson effect provides a powerful phase-sensitive tool for investigating superfluid order parameters. We report on the observation of dc Josephson supercurrents in strongly interacting fermionic superfluids across a tunnelling barrier in the absence of any applied potential difference. For sufficiently strong barriers, we observe a sinusoidal current-phase relation, in agreement with Josephson's seminal prediction. We map out the zero-resistance state and its breakdown as a function of junction parameters, extracting the Josephson critical current behaviour. By comparing our results with an analytic model, we determine the pair condensate fraction throughout the Bardeen-Cooper-Schrieffer - Bose-Einstein Condensation crossover. Our work suggests that coherent Josephson transport may be used to pin down superfluid order parameters in diverse atomic systems, even in the presence of strong correlations.