Asymmetric Transport in Superconductor-Topological Insulator-Superconductor 2D Arrays

Three-dimensional topological insulators (TIs) are Dirac materials having spin momentum-locking of the electrons and showing evidence of spin-polarized currents at their surfaces. TIs proximity-coupled by s-wave superconducting materials are expected to display unconventional superconductivity. To probe the interplay between TI surface properties and superconductivity, we fabricated two-dimensional (2D) superconducting island arrays on exfoliated flakes of the three-dimensional TI Bi₂Se₃. Such 2D 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 behavior. They exhibit strong asymmetry in the field oscillations of the magnetoresistance suggestive of a spin-locked supercurrent.