Tuning a two-impurity Kondo system by a moir\'e superstructure

TL;DR

This study investigates how a moiré superstructure influences the Kondo effect and magnetic interactions of Mn adatoms on Au(111), revealing tunable exchange interactions and singlet-triplet splitting sensitive to the substrate pattern.

Contribution

It demonstrates control over two-impurity Kondo systems through moiré patterning, providing new insights into spin coupling and Kondo physics on engineered surfaces.

Findings

Kondo peaks vary with adatom location relative to moiré

Mn dimers show split Kondo resonances

Singlet-triplet splitting is highly sensitive to moiré structure

Abstract

Two-impurity Kondo models are paradigmatic for correlated spin-fermion systems. Working with Mn atoms on Au(111) covered by a monolayer of MoS$_2$, we tune the inter-adatom exchange via the adatom distance and the adatom-substrate exchange via the location relative to a moir\'e structure of the substrate. Differential-conductance measurements on isolated adatoms exhibit Kondo peaks with heights depending on the adatom location relative to the moir\'e structure. Mn dimers spaced by a few atomic lattice sites exhibit split Kondo resonances. In contrast, adatoms in closely spaced dimers couple antiferromagnetically, resulting in a molecular-singlet ground state. Exciting the singlet-triplet transition by tunneling electrons, we find that the singlet-triplet splitting is surprisingly sensitive to the moir\'e structure. We interpret our results theoretically by relating the variations in the singlet-triplet splitting to the heights of the Kondo peaks of single adatoms, finding evidence for coupling of the adatom spin to multiple conduction electron channels.