Local Moment Formation of an Anderson Impurity on Graphene

TL;DR

This paper investigates how magnetic impurities on graphene form local moments due to the unique electronic structure of graphene, revealing conditions under which impurities are unscreened or Kondo screened.

Contribution

It introduces a Gutzwiller approximation analysis of impurity states on graphene, highlighting the parameter space for local moment formation distinct from conventional metals.

Findings

Local moments form in specific U-Ef parameter regions.

Impurity states transition between Kondo screened and local moment states.

Impurity level tuning causes re-entrant behavior between states.

Abstract

We study the property of a magnetic impurity on a single-layer graphene within an Anderson impurity model. Due to the vanishing local density of states at the Fermi level in graphene, the impurity spin cannot be effectively screened out. Treating the problem within the Gutzwiller approximation, we found a region in the parameter space of $U$-$E^f$ where the impurity is in the local moment state, which is characterized by a zero effective hybridization between the bath electron and the magnetic impurity. Here $U$ is the onsite Coulomb repulsion of the impurity electrons and $E^f$ the impurity energy level. The competition between $U$ and $E^f$ is also discussed. While larger $U$ reduces double occupation and favors local moment formation, a deeper impurity level prefers double occupation and a nonzero hybridization and thus a Kondo screened state. For a fixed $U$, by continuously lowering the impurity level, the impurity first enters from a Kondo screened state into a local moment state and then departs from this state and re-enters into the Kondo screened state.