Proximity-induced Superconductivity in Epitaxial Topological Insulator/Iron Chalcogenide Heterostructure

Introducing superconductivity in the surface states of a topological insulator gives rise to exotic physics known as topological superconductivity. Surprisingly it was shown recently that superconductivity can arise at the interface of MBE-grown Bi2Te3/FeTe. In this work, we study whether this interfacial superconductivity can then proximitize the surface states of 8QL Bi2Te3/FeTe using four-terminal transport and transport tunneling spectroscopy. We fabricated lithography-free van der Waals tunnel junctions using AFM-etched graphite electrodes, thin hBN as a tunnel barrier, and dry transfer techniques to make the device inside a glovebox [Li, Cequn, et al. "Proximity-induced superconductivity in epitaxial topological insulator/graphene/gallium heterostructures." Nature Materials 22.5 (2023): 570-575]. Hall bar devices are also made on the same film. Transport studies show a superconducting transition temperature Tc~ 13K and a large critical field above 9T. Transport tunneling spectroscopy allows us to probe the density of states of the Bi2Te3/FeTe film. We observed a V-shaped dip in the differential conductance around zero bias with coherence peaks centered around 1.2 meV. These features weaken with increasing temperature and disappear around 13 K. We associate the tunneling spectra with a proximity-induced gap on the surface.