4π-periodic supercurrent tuned by an axial magnetic flux in topological insulator nanowires

Topological insulator (TI) nanowires in proximity to conventional superconductors have been proposed as a tunable platform to realize topological superconductivity and Majorana zero modes. The tuning is done using an axial magnetic flux ϕ which allows transforming the system from trivial at ϕ=0 to topologically nontrivial when half a magnetic flux quantum ϕ_{0}/2 threads the cross-section of the wire. Here, we explore the expected topological transition in TI-wire-based Josephson junctions as a function of magnetic flux by probing the 4π-periodic fraction of the supercurrent, which is considered an indicator of topological superconductivity. Our data suggest that this 4π-periodic supercurrent is at lower magnetic field largely of trivial origin but that, at magnetic fields above ∼ϕ_{0}/4, topological 4π-periodic supercurrents take over.