Proximity-induced superconductivity and pairing in topological Sb₂Te₃ films on niobium

Topological insulator (TI) films interfaced with an elemental isotropic superconductor (SC) are theoretically fascinating systems hosting an exotic topological superconductor phase. Most prior studies on TI/SC neglect heavily p‑doped TIs, wherein the Fermi level is pinned to the bulk valence bands, but this property can tune the quantum‑mechanical coupling between bulk and surface states relevant to proximity effects. Using our novel cleavage‑based “flip‑chip” approach, we report the fabrication of topological Sb₂Te₃ thin films having predetermined layer thicknesses of 3‑7 quintuple layers on bulk superconducting Nb. With increasing Sb₂Te₃ layer thickness, we verify using angle‑resolved photoemission spectroscopy (ARPES) that the Fermi level crosses both the lower Dirac cone and bulk valence bands, yielding a heavily p-doped TI on an SC. Proximity‑induced superconducting gaps as a function of the Fermi surface wavevector in Sb₂Te₃/Nb are quantified using ultrahigh‑resolution laser ARPES, which are compared to those from our previous works on n‑doped TIs on Nb. Our results highlight approaches for tuning proximity‑induced superconductivity in TIs and for identifying the pairing relevant to quantum device applications.