The Fano resonance for Anderson impurity systems

TL;DR

This paper develops a comprehensive theory for Fano resonance in Anderson impurity systems, emphasizing the role of impurity level broadening and interference effects, and successfully explains experimental observations for various impurities.

Contribution

It introduces a new theoretical framework accounting for impurity level broadening's impact on Fano resonance in Anderson systems, especially in the mixed valence regime.

Findings

The theory explains Fano lineshapes in Co and Ti impurities on Au and Ag surfaces.

Impurity level broadening significantly influences Fano resonance features.

Ti impurities are characterized as being in the mixed valence regime.

Abstract

We present a general theory for the Fano resonance in Anderson impurity systems. It is shown that the broadening of the impurity level leads to an additional and important contribution to the Fano resonance around the Fermi surface, especially in the mixed valence regime. This contribution results from the interference between the Kondo resonance and the broadened impurity level. Being applied to the scanning tunnelling microscopic experiments, we find that our theory gives a consistent and quantitative account for the Fano resonance lineshapes for both Co and Ti impurities on Au or Ag surfaces. The Ti systems are found to be in the mixed valence regime.