Observation of tunable single-atom Yu-Shiba-Rusinov states

TL;DR

This study investigates how single-atom Yu-Shiba-Rusinov states in superconductors can be tuned by analyzing Fe adatoms on Nb(110), revealing a site-dependent quantum phase transition influenced by Kondo screening.

Contribution

It provides the first detailed experimental and theoretical analysis of tunable YSR states at the single-atom level, highlighting the interplay between Kondo effect and superconductivity.

Findings

YSR states are strongly site-dependent.

A quantum phase transition occurs when Kondo temperature matches the superconducting gap.

Combined DFT and quantum Monte Carlo calculations explain experimental observations.

Abstract

The coupling of a spin to an underlying substrate is the basis for a plethora of phenomena. In the case of a metallic substrate, Kondo screening of the adatom magnetic moment can occur. As the substrate turns superconducting, an intriguing situation emerges where the pair breaking due to the adatom spins leads to Yu-Shiba-Rusinov bound states, but also intertwines with Kondo phenomena. Through scanning tunneling spectroscopy, we analyze the interdependence of Kondo screening and superconductivity. Our data obtained on single Fe adatoms on Nb(110) show that the coupling and the resulting YSR states are strongly adsorption site-dependent and reveal a quantum phase transition at a Kondo temperature comparable to the superconducting gap. The experimental signatures are rationalized by combined density functional theory and continuous-time quantum Monte-Carlo calculations to rigorously treat magnetic and hybridization effects on equal footing.