Theory of Fano Resonances in Graphene: The Kondo effect probed by STM

TL;DR

This paper develops a theoretical understanding of Fano resonances and the Kondo effect in graphene with magnetic impurities, highlighting the role of orbital hybridization and quantum interference effects related to graphene's Berry phase.

Contribution

It provides a first-principles analysis of the Kondo effect and Fano resonances in graphene, identifying specific orbital contributions and explaining anomalous Fano factors due to quantum interference.

Findings

The $E_1$ orbital representation is key to Kondo screening in cobalt on graphene.

Anomalously large Fano $q$-factor (~80) observed for Co at the hexagon center.

Quantum interference related to graphene's Berry phase causes suppressed coupling and resonance anomalies.

Abstract

We consider the theory of Kondo effect and Fano factor energy dependence for magnetic impurity (Co) on graphene. We have performed a first principles calculation and find that the two dimensional $E_1$ representation made of $d_{xz},d_{yz}$ orbitals is likely to be responsible for the hybridization and ultimately Kondo screening for cobalt on graphene. There are few high symmetry sites where magnetic impurity atom can be adsorbed. For the case of Co atom in the middle of hexagon of carbon lattice we find anomalously large Fano $q$-factor, $q\approx 80$ and strongly suppressed coupling to conduction band. This anomaly is a striking example of quantum mechanical interference related to the Berry phase inherent to graphene band structure.