Superconducting proximity effect in a topological insulator using Fe(Te,Se)

TL;DR

This study demonstrates a significant proximity-induced superconducting gap in a topological insulator using a high-Tc superconductor, revealing potential for high-temperature topological superconductivity.

Contribution

It reports the largest proximity-induced gap in Bi2Te3 with Fe(Te,Se), showing high-Tc superconductor's effectiveness for topological superconductivity.

Findings

Induced gap up to ~3.5 meV in Bi2Te3

Proximity effect persists across various thicknesses

Microscopic visualization of gapped surface states

Abstract

Interest in the superconducting proximity effect has recently been reignited by theoretical predictions that it could be used to achieve topological superconductivity. Low-T$_{c}$ superconductors have predominantly been used in this effort, but small energy scales of ~1 meV have hindered the characterization of the emergent electronic phase, limiting it to extremely low temperatures. In this work, we use molecular beam epitaxy to grow topological insulator Bi$_{2}$Te$_{3}$ in a range of thicknesses on top of a high-T$_{c}$ superconductor Fe(Te,Se). Using scanning tunneling microscopy and spectroscopy, we detect {\Delta}$_{ind}$ as high as ~3.5 meV, which is the largest reported gap induced by proximity to an s-wave superconductor to-date. We find that {\Delta}$_{ind}$ decays with Bi$_{2}$Te$_{3}$ thickness, but remains finite even after the topological surface states had been formed. Finally, by imaging the scattering and interference of surface state electrons, we provide a microscopic visualization of the fully gaped Bi$_{2}$Te$_{3}$ surface state due to Cooper pairing. Our results establish Fe-based high-T$_{c}$ superconductors as a promising new platform for realizing high-T$_{c}$ topological superconductivity.