Ferromagnetic induced Kondo effect in graphene with a magnetic impurity

TL;DR

This paper studies the unique Kondo effect induced by ferromagnetism in graphene with magnetic impurities, revealing unconventional behaviors such as increased Kondo temperature with spin polarization and spin-dependent Kondo resonances.

Contribution

It uncovers how ferromagnetic graphene exhibits novel Kondo physics, including the enhancement of Kondo temperature and spin-selective Kondo resonances, differing from traditional ferromagnetic materials.

Findings

Kondo correlations can emerge in ferromagnetic graphene due to band dispersion.

External magnetic fields can merge Kondo kinks into a full resonance.

Kondo temperature increases monotonically with spin polarization.

Abstract

We investigate the many-body effects of a magnetic adatom in ferromagnetic graphene by using the numerical renormalization group method. The nontrivial band dispersion of ferromagnetic graphene gives rise to interesting Kondo physics different from that in conventional ferromagnetic materials. For a half-filled impurity in undoped graphene, the presence of ferromagnetism can bring forth Kondo correlations, yielding two kink structures in the local spectral function near the Fermi energy. When the spin splitting of local occupations is compensated by an external magnetic field, the two Kondo kinks merge into a full Kondo resonance characterizing the fully screened ground state. Strikingly, we find the resulting Kondo temperature monotonically increases with the spin polarization of Dirac electrons, which violates the common sense that ferromagnetic bands are usually detrimental to Kondo correlations. Doped ferromagnetic graphene can behave as half metals, where its density of states at the Fermi energy linearly vanishes for one spin direction but keeps finite for the opposite direction. In this regime, we demonstrate an abnormal Kondo resonance that occurs in the first spin direction, while completely absent in the other one.