Modeling of gate controlled Kondo effect at carbon point-defects in graphene

TL;DR

This paper investigates the magnetic properties near a single carbon defect in graphene, modeling the Kondo effect with a two-orbital impurity approach and analyzing different magnetic regimes via numerical renormalization group calculations.

Contribution

It introduces a two-orbital impurity model including Coulomb and Hund's coupling to study the Kondo effect at graphene vacancies, incorporating realistic band structure effects.

Findings

Identification of three magnetic regimes depending on chemical potential and hybridization.

Qualitative agreement with experimental scanning tunneling spectra.

Demonstration of the impact of curvature-induced hybridization on magnetic properties.

Abstract

We study the magnetic properties in the vicinity of a single carbon defect in a monolayer of graphene. We include the unbound $\sigma$ orbital and the vacancy induced bound $\pi$ state in an effective two-orbital single impurity model. The local magnetic moments are stabilized by the Coulomb interaction as well as a significant ferromagnetic Hund's rule coupling between the orbitals predicted by a density functional theory calculation. A hybridization between the orbitals and the Dirac fermions is generated by the curvature of the graphene sheet in the vicinity of the vacancy. We present results for the local spectral function calculated using Wilson's numerical renormalization group approach for a realistic graphene band structure and find three different regimes depending on the filling, the controlling chemical potential, and the hybridization strength. These different regions are characterized by different magnetic properties. The calculated spectral functions qualitatively agree with recent scanning tunneling spectra on graphene vacancies.