From tunneling to contact in a magnetic atom: the non-equilibrium Kondo effect

TL;DR

This study investigates the evolution of the Kondo effect in a magnetic atom using low-temperature STM, revealing how conductance features change from tunneling to contact regimes and analyzing the underlying physics.

Contribution

It combines experimental STM measurements with theoretical modeling to elucidate the non-equilibrium Kondo effect in a magnetic atom junction, highlighting the role of tip coupling.

Findings

The zero-bias anomaly (ZBA) shows asymmetric lineshape in tunneling and symmetrizes upon contact.

Linewidth broadening is mainly due to increased coupling to the tip.

Non-equilibrium effects influence the ZBA tails but not the main lineshape.

Abstract

A low-temperature scanning tunneling microscope was employed to study the differential conductance in an atomic junction formed by an adsorbed Co atom on a Cu(100) surface and a copper-covered tip. A zero-bias anomaly (ZBA) reveals spin scattering off the Co atom, which is assigned to a Kondo effect. The ZBA exhibits a characteristic asymmetric lineshape when electrons tunnel between tip and sample, while upon the tip-Co contact it symmetrizes and broadens. Through density functional theory calculations and the non-equilibrium non-crossing approximation we show that the lineshape broadening is mainly a consequence of the additional coupling to the tip, while non-equilibrium effects only modify the large-bias tails of the ZBA.