Locally enhanced Zeeman field in Au (111) for the creation of a topological superconductor*

Recent theory modeling has shown that applying a local Zeeman field on spin-helical surface states leads to topological superconductivity and Majorana zero modes. In this talk, we experimentally demonstrate how such a local Zeeman field can be generated in Au(111)-superconductor heterostructures in which the surface Rashaba band consists of two copies of spin-helical states. Our results consist of tunneling studies of epitaxial Nb/Au(111) heterostructures using a unique tunnel barrier material at milli-Kelvin temperatures. We have observed three features of interest. First, we have achieved an enhanced surface superconducting gap - much larger than that being reported before. Second, we are able to obtain a highly transparent tunnel barrier, which allows us to observe fine tunneling features within the superconducting gap such as the Andreev bound states. Third, the tunnel barrier is shown to have a large Lande g-factor which independently tunes the surface superconducting gap with respect to the bulk gap.

Acknowledgements: NSF CAREER DMR-2046648, NSF C-ACCL 2040620, MIT-Lincoln Lab Line fund; NSF C-Accel Track C grant 2040620, MIT-Lincoln Lab Line Proposal Fund, NSF CAREER grant 2046648