Spin-resolved spectroscopic evidence for spinarons in Co adatoms

TL;DR

This study provides experimental and theoretical evidence for the existence of spinarons, a new type of magnetic polaron, in Co adatoms on Cu(111), challenging the traditional Kondo effect interpretation of zero-bias anomalies.

Contribution

The paper presents the first combined experimental and ab-initio evidence for spinarons in Co adatoms, offering an alternative explanation to the Kondo resonance.

Findings

Disproved the Kondo resonance interpretation of ZBA in Co adatoms.

Provided evidence for multiple spinaronic states through spectroscopy and calculations.

Highlighted the potential of spinarons in designing hybrid many-body states in nanostructures.

Abstract

Single cobalt atoms on the (111) surfaces of noble metals were for a long time considered prototypical systems for the Kondo effect in scanning tunneling microscopy experiments. Yet, recent first-principle calculations suggest that the experimentally observed spectroscopic zero-bias anomaly (ZBA) should be interpreted in terms of excitations of the Co atom's spin and the formation of a novel quasiparticle, the spinaron, a magnetic polaron resulting from the interaction of spin excitations with conduction electrons, rather than in terms of a Kondo resonance. Here we present state-of-the-art spin-averaged and spin-polarized scanning tunneling spectroscopy measurements on Co atoms on the Cu(111) surface in magnetic fields of up to 12 T, that allow us to discriminate between the different theoretical models and to invalidate the prevailing Kondo-based interpretation of the ZBA. Employing extended ab-initio calculations, we instead provide strong evidence for multiple spinaronic states in the system. Our work opens a new avenue of research to explore the characteristics and consequences of these intriguing hybrid many-body states as well as their design in man-made nanostructures.