Scanning tunneling spectroscopy of a magnetic atom on graphene in the Kondo regime

TL;DR

This paper investigates the Kondo effect in a magnetic atom on graphene using non-equilibrium Green functions, revealing two regimes in doped graphene and a critical condition in undoped graphene, with implications for scanning tunneling spectroscopy.

Contribution

It introduces a detailed theoretical analysis of the Kondo effect on graphene, highlighting the conditions for its presence and the impact of tip-graphene coupling.

Findings

Kondo phase exists at all times in doped graphene.

Two types of Kondo regimes are identified in doped graphene.

Kondo phase only appears beyond a critical energy level in undoped graphene.

Abstract

The Kondo effect in the system consisting of a magnetic adatom on the graphene is studied. By using the non-equilibrium Green function method with the slave-boson mean field approximation, the local density of state (LDOS) and the conductance are calculated. For a doped graphene, the Kondo phase is present at all time. Surprisingly, two kinds of Kondo regimes are revealed. But for the undoped graphene, the Kondo phase only exists if the adatom's energy level is beyond a critical value. The conductance is similar to the LDOS, thus, the Kondo peak in the LDOS can be observed with the scanning tunneling spectroscopy. In addition, in the presence of a direct coupling between the STM tip and the graphene, the conductance may be dramatically enhanced, depending on the coupling site.