Superconductivity in the surface state of noble metal gold and its Fermi level tuning by EuS dielectric

TL;DR

This paper demonstrates induced superconductivity in the surface state of gold thin films and shows how to tune its Fermi level using EuS dielectric, advancing the development of topological superconductors and Majorana bound states.

Contribution

It provides the first experimental evidence of superconductivity in gold surface states and demonstrates Fermi level tuning via EuS, enabling scalable topological quantum devices.

Findings

Superconductivity induced in Au(111) surface state via quasiparticle scattering.

Fermi level of surface state tunable from ~550 mV to ~34 mV using EuS.

Surface superconductivity achieved without direct interfacial Andreev reflection.

Abstract

The induced superconductivity (SC) in a robust and scalable quantum material with strong Rashba spin-orbit coupling is particularly attractive for generating topological superconductivity and Majorana bound states (MBS). Gold (111) thin film has been proposed as a promising candidate because of the large Rashba energy, the predicted topological nature and the possibility for large-scale MBS device fabrications. We experimentally demonstrate two important steps towards achieving such a goal. We successfully show induced SC in the Shockley surface state (SS) of ultrathin Au(111) layers grown over epitaxial vanadium films, which is easily achievable on a wafer scale. The emergence of SC in the SS, which is physically separated from a bulk superconductor, is attained by indirect quasiparticle scattering processes instead of by conventional interfacial Andreev reflections. We further show the ability to tune the SS Fermi level (E_F) by interfacing SS with a high-k dielectric ferromagnetic insulator EuS. The shift of E_F from ~ 550 mV to ~34mV in superconducting SS is an important step towards realizing MBS in this robust system.