Fractional-flux oscillations of Josephson critical currents in multi-gap superconductors: a test for unconventional superconductivity

TL;DR

This paper demonstrates that fractional flux oscillations in Josephson junctions can serve as a phase-sensitive probe for identifying multi-gap and unconventional superconducting states, including the $s_$-wave state.

Contribution

The authors extend Ginzburg-Landau theory to multi-gap superconductors, showing fractional flux oscillations as a signature of unconventional pairing symmetries.

Findings

Fractional flux oscillations occur in multi-gap superconductors.

These oscillations can identify unconventional pairing states.

The results suggest new experiments for emerging superconductors like nickelates.

Abstract

Josephson-junction interferometry has played a pivotal role in uncovering unconventional superconductivity in the cuprates. Using a Ginzburg-Landau-like approach, we generalize previous results to the genuine multi-gap case. Thus, we show that fractional flux oscillations of the Josephson critical current can arise as a direct consequence of multi-gap superconductivity. These oscillations reveal key information about the underlying superconducting states, including the unconventional $s_\pm$-wave state. Thus, our findings suggest new phase-sensitive experiments to characterize the Cooper pairing of new emerging superconductors such as the nickelates.