Local tunneling spectroscopy measurements of sub-gap states in EuS nanowires coupled to Au(111) with induced superconductivity*

The noble metal surface states, such as those in Au(111), with induced superconductivity could host sub-gap states when coupled to a nanowire of a magnetic insulator such as EuS [1]. The sub-gap states are generated due to lateral Andreev reflections of quasiparticles at the edge of the EuS nanowire. The minimum energies of the sub-gap states could define the topological gap, which evolves with a magnetic field applied parallel to the wire and can lead to Majorana bound states at the ends of the wire. In this talk, we will present our progress on studying local tunneling spectroscopy of fabricated EuS nanowires on Au(111) using scalable planar tunnel junctions under milli-Kelvin temperatures. We will demonstrate the tunneling spectra at various locations along the nanowire. We will further discuss the evolution of these sub-gap states with planar magnetic fields applied along the wire and show that these states narrow into zero energy peaks which are limited by the thermal broadening. We will also compare the location dependance of these sub-gap states for various samples and discuss possible connections to topological superconductivity.

[1] Phys. Rev. Res. 3, 043086, (2021)