Quantifying the leading role of the surface state in the Kondo effect of Co/Ag(111)

TL;DR

This study demonstrates a nearly linear relationship between the Kondo temperature of Co atoms on Ag(111) and the surface state contribution to the local density of states, highlighting the surface state's role in Kondo physics.

Contribution

It provides the first systematic quantification of the surface state's influence on the Kondo effect using combined spectroscopy and manipulation techniques.

Findings

Nearly linear correlation between $T_K$ and surface state contribution $ ho_s$

At least 25% of impurity coupling occurs via surface state hybridization

Surface band onset near Fermi level crucial for observed behavior

Abstract

Using a combination of scanning tunneling spectroscopy and atomic lateral manipulation, we obtained a systematic variation of the Kondo temperature ($T_\mathrm K$) of Co atoms on Ag(111) as a function of the surface state contribution to the total density of states at the atom adsorption site ($\rho_s$). By sampling the $T_\mathrm K$ of a Co atom on positions where $\rho_s$ was spatially resolved beforehand, we obtain a nearly linear relationship between both magnitudes. We interpret the data on the basis of an Anderson model including orbital and spin degrees of freedom (SU(4)) in good agreement with the experimental findings. The fact that the onset of the surface band is near the Fermi level is crucial to lead to the observed linear behavior. In the light of this model, the quantitative analysis of the experimental data evidences that at least a quarter of the coupling of Co impurities with extended states takes place through the hybridization to surface states. This result is of fundamental relevance in the understanding of Kondo screening of magnetic impurities on noble metal surfaces, where bulk and surface electronic states coexist.