Extrinsic nature of the "superconducting diode effect" in hybrid superconductors

We report observation of non-reciprocal critical current in Al/InAs nanowires in the presence of magnetic fields. Non-reciprocal component does not scale with the wire cross section pointing to the extrinsic nature of the effect. Moreover, field dependence of the non-reciprocal correction resembles variation of a critical current in asymmetric rings due to formation of persistent currents. Theoretical analysis shows that a conventional assumption of constant (zero) phase difference between Al and proximatized InAs layer cannot explain experimental observations. Spatial variation of phase difference results in inter-layer Josephson currents and formation of fractional Josephson vortices. In this setting non-reciprocity emerges in the presence of magnetic field even in the absence of spin-orbit interaction. This work can be relevant to the understanding of the recently reported “superconducting diode effect” in hybrid superconductors. It is also important to a search for non-abelian excitations because Al/InAs system is one of the leading candidates to realize a synthetic topological superconductor.