Josephson junction

The proximity coupling of WSe₂ to graphene can create a large spin-orbit interaction (SOI) in graphene. In particular, for bilayer graphene (BLG) encapsulated in WSe₂ (WSe₂/BLG/WSe₂) it was shown that displacement fields can drive a topological phase transition at zero density due to Ising SOI [1]. Here we study the current-phase relation (CPR) of Josephson junctions created in such van der Waals heterostructures.  At zero (in-plane) magnetic field we find that the CPR is largely independent of carrier density and displacement field. However at finite magnetic fields (~ few hundred mT) we observe anomalous CPRs displaying large gate-dependent phase shifts. While phase shifts are in general expected in Josephson junctions with Rashba-type SOI, the effect we observe is significantly larger and cannot be accounted for by existing models.  Furthermore, we find that this effect is absent for WSe₂/SLG/WSe₂, BLG/WSe₂ and trivial BLG JJs, suggesting that it is possibly related to the specific band structure of WSe₂/BLG/WSe₂.

[1] J. O. Island, X. Cui, C. Lewandowski, J. Y. Khoo, E. M. Spanton, H. Zhou, D. Rhodes, J. C. Hone, T. Taniguchi, K. Watanabe, L. S. Levitov, M. P. Zaletel, and A. F. Young, Nature 571, 85 (2019).