Epitaxial growth of gold films on the elemental superconductors V(100), Nb(100) and Nb(110)

TL;DR

This study investigates the growth, composition, and superconducting properties of gold films on elemental superconductors vanadium and niobium, demonstrating their potential for quantum technology applications involving superconductivity and magnetism.

Contribution

It provides new insights into the epitaxial growth, surface properties, and superconducting proximity effects of gold films on V and Nb, highlighting their suitability for quantum device integration.

Findings

Gold films grow flat and oxygen-free at high annealing temperatures.

Proximitized superconducting gap observed at gold surface.

Gold films support magnetic molecules, enabling studies of magnetism-superconductivity interactions.

Abstract

Quantum technologies require a new generation of superconducting electronic devices and circuitry. However, the superconducting materials used to construct them are restricted to a class of bulk superconductors. Gold films grown in contact with superconducting materials can exhibit superconducting correlations through the proximity effect, with various possible implementations in quantum technology. Here, we study the growth of flat Au films on various surfaces of the elemental superconductors vanadium and niobium through a combination of low-temperature scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In particular, we investigate the growth morphology and composition as a function of temperature and coverage. We find that gold films can grow flat and oxygen-free when annealed to sufficiently high temperatures; however, they are also susceptible to partial intermixing with the substrate elements. Low-temperature scanning tunneling spectroscopy (STS) measurements elucidate the emergence of a proximitized superconducting gap at the gold surface. Additionally, we demonstrate the survival of the magnetic state of FeTPP-Cl molecules on the surface of these gold films, proving that they behave as a good support for probing molecular magnetism. We found that the exchange interaction between the molecular spin and the superconducting condensate can be inferred by the measurement of sub-gap Yu-Shiva-Rusinov states. Our work shows that proximitised Au films constitute a promising platform to explore on-superconducting-surface synthesis and the interaction between superconductivity and magnetism in a large spin-orbit coupling environment.