18 February 2021 Thu 4 pm

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The superconducting proximity effect induced in materials in close contact with a superconductor is now very well established. We reveal that similarly, the topologically protected surface states recently found on the surfaces of topological insulators can leak into appropriate adjoining materials. We bring these two effects into proximity and study how superconductivity and topologically protected surface states interact with each other, a situation of interest in the search for Majorana bound states. We consider generalities of the proximity effect in a contact between a conventional s-wave superconductor nano-island and a thin film of a topological insulator. A local hybridization coupling mechanism is considered and a corresponding model is corroborated that captures not only the induced unconventional superconductivity in a TI, but also predicts the spreading of topologically protected surface states into the superconducting over-layer. This dual nature of the proximity effect leads specifically to a modified description of topological superconductivity in these systems. Experimentally accessible signatures of this phenomenon are discussed in the context of scanning tunneling microscopy measurements. For this purpose an effective density of states is computed in both the superconductor and topological insulator. As a guiding example, practical applications are made for Nb islands deposited on a surface of Bi2Se3 and compared to experiments.