Abstract
We study the Kondo effect of a single magnetic adatom on the surface of graphene. The unique linear dispersion relation near the Dirac points in graphene makes it easier for the magnetic atom to form a local magnetic moment, which simply means that the Kondo resonance can be observed in a wider parameter region than in the metallic host. Our study indicates that the Kondo resonance, whenever the chemical potential is tuned away from the Dirac points, can indeed occur ranging from the Kondo regime, to the mixed valence, even to the empty orbital regime defined in the conventional metal host. While the Kondo resonance appears as a sharp peak in the Kondo regime, it has a peak-dip structure and/or an anti-resonance in the mixed valence and empty orbital regimes, which result from the Fano resonance due to the significant background due to dramatic broadening of the impurity level in graphene. We also study the scanning tunneling microscopy (STM) spectra of the adatom and they show obvious particle–hole asymmetry when the chemical potential is tuned by the gate voltages applied to the graphene. Finally, we explore the influence of the direct tunneling channel between the STM tip and the graphene on the Kondo resonance and find that the lineshape of the Kondo resonance is unaffected, which can be attributed to an unusually large asymmetry factor in graphene. Our study indicates that graphene is an ideal platform to systematically study Kondo physics and these results are useful to further stimulate relevant experimental studies on the system.
Highlights
The experimental realization of graphene[1,2] composed of a monolayer of carbon atoms trigged a new wave to study the carbon-based materials, both from fundamental physics and applications.[3,4,5] The graphene possesses perfect two-dimensional massless Dirac fermion behaviors, and the valence and conduction bands touch at two inequivalent Dirac points K− and K+ at the corner of the Brillouin zone
It was shown that the unique linear dispersion relation near the Dirac points in graphene makes it more easy to form the local magnetic moment, which means that the Kondo resonance can be observed in a more wider parameter region than in the metallic host
We study the scanning tunneling microscopy (STM) spectra of the adatom and they show obvious particle-hole asymmetry when the chemical potential is tuned by the gate voltages applied to the graphene
Summary
The experimental realization of graphene[1,2] composed of a monolayer of carbon atoms trigged a new wave to study the carbon-based materials, both from fundamental physics and applications.[3,4,5] The graphene possesses perfect two-dimensional massless Dirac fermion behaviors, and the valence and conduction bands touch at two inequivalent Dirac points K− and K+ at the corner of the Brillouin zone. When εd is above the Dirac points, the magnetic state extends to y < 0, which means that even the impurity level is located above the Fermi energy, it is possible that the localized magnetic moment exists This is quite different to that in usual metallic host. The Kondo temperature strongly but asymmetrically depends on the explicit position of the Fermi energy which is in agreement with reported in the literature.[23,26] Subsequently, we turn on the direct tunneling between the tip and the graphene to study its influence on the lineshape of the Kondo resonance, which is more realistic case.
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