Transport in Superconductor-Topological Insulator-Superconductor 2D Arrays

Once coupled to s-wave superconducting material, three-dimensional topological insulators (TIs) – providing spin momentum locking of the electrons and spin polarized current at the surface – are expected to show novel properties and unconventional superconductivity. To probe the interplay between TI surface properties and superconductivity, we fabricated 2D superconducting island arrays on exfoliated flakes of the 3D TI Bi₂Se₃. Such two-dimensional junction arrays have been shown to undergo Kosterlitz-Thouless transitions toward a superconducting state. Transport and Fraunhofer spectroscopy measurements carried out on our devices show unusual, asymmetric behavior. In particular, the measurements provide evidence of charged vortices on the topological surface.