Transport tunneling spectroscopy of the interface-induced superconductivity in Cr-doped Sb₂Te₃/FeTe heterostructures

Topological insulator/iron chalcogenide heterostructures are found to superconduct with a T_c of ~12 K although neither component superconducts on its own^1,2. Here we study the interplay between superconductivity and ferromagnetism in MBE-grown Cr-doped Sb₂Te₃ (CST)/FeTe thin films combining four-terminal transport and transport tunnelling spectroscopy. In transport studies, 4-10 quintuple-layer (QL) CST/FeTe films show a superconducting transition temperature of T_c ~11 K, and an upper critical field of H_c2 > 14 T at low temperatures. Below a curie temperature of ~20 K, ferromagnetism develops in the CST film. Following our previous work³, we made a lithography-free, van der Waals NbSe₂/CST/FeTe vertical superconductor-ferromagnet-superconductor junction to perform transport tunneling spectroscopy. Signatures of the superconducting gaps in NbSe₂ (Δ=1.1 meV) and of the interfacial superconductivity (Δ~2.4 meV) manifests in the tunneling spectra. The latter persists to B > 9 T and is consistent with the large Hc₂ of CST/FeTe obtained from four-terminal transport. We use similar device structure and measurement techniques to study thin CST/FeTe films, with the goal of observing proximity-induced superconductivity in the top surface of the CST/FeTe film and exploring the 0-π phase transition of the Josephson junction.

References:

[1] Q. L. He et al. Nat. Comm. 5, 4247 (2014).

[2] H. Yi et al. arXiv:2310.09190.

[3] C. Li et al. Nat. Mater. 22, 570–575 (2023).