Robust supercurrent in graphene Josephson junctions assisted by strong spin-orbit interaction

A magnetic field is known to destroy the spin-singlet Cooper pair via the Zeeman effect. But the orbital effect of a magnetic flux also destroys proximity-induced superconductivity. Since spin-orbit interactions (SOI) can moderate these effects thanks to the spin-momentum locking it provides, one can wonder if supercurrent can be made more robust to an orbital magnetic field in materials with enhanced spin-orbit interaction. To investigate this question, we compare Josephson junctions built with two different graphene-based systems, a hBN/G/hBN stack, or a hBN/WS2/G stack, in which strong SOI have been induced in graphene via the van der Waals-coupled WS2. We measure the supercurrent induced through these systems in varying perpendicular magnetic fields and for different junction lengths.
We find similar signatures of induced superconductivity in both systems when the junctions are short (100nm), for fields up to 1T.
However, signatures of induced superconductivity in the longest junctions (500 nm) are found only in the hBN/WS2/G –based junction. The signatures survive up to 7 T.
We argue that the robust superconducting signatures arise from the existence of quasi-ballistic edge states stabilized by strong SOI induced in graphene by WS2.