The Kondo effect of an adatom in graphene and its scanning tunneling spectroscopy

Abstract

We study the Kondo effect of a single magnetic adatom on the surface of graphene. 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 simply means that the Kondo resonance can be observed in a more wider parameter region than in the metallic host. The result indicates that the Kondo resonance indeed can form ranged from the Kondo regime, to the mixed valence, even to the empty orbital regime. While the Kondo resonance displays as a sharp peak in the first regime, it has a peak-dip structure and/or an anti-resonance in the remaining two regimes, which result from the Fano resonance due to the significant background leaded by dramatically 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 unusual large asymmetry factor in graphene. Our study indicates that the graphene is an ideal platform to study systematically the Kondo physics and these results are useful to further stimulate the relevant experimental studies on the system.

Nonequilibrium Kondo effect in a graphene-coupled quantum dot in the presence of a magnetic field

“…In addition, for µ α = 0 the Kondo peak does not show up in the DOS. This behavior of the DOS is agreement with the results of Li et al [67] for an adatom on the surface of graphene with U → ∞, and is a consequence of the zero DOS of graphene at the Dirac points.…”

“…The difference in height of the zero-bias peaks as a function of µ R results from the particle-hole asymmetry of the graphene electrodes. The behavior of the Kondo peak is in agreement with other theoretical results obtained for magnetic impurities in graphene [67,75]. Figure 7 shows the zero-bias peak as a function of the chemical potential µ R for eV = 0 at three different temperature values.…”

“…Here, for small values of |µ|, the Kondo temperature is independent of the sign of the chemical potential, namely T K ∝ |µ|. In the U → ∞ limit, an asymmetrical behavior of T K was reported in case the chemical potential is situated below or above the Dirac points of graphene with a magnetic adatom [67].…”

Prospects of spintronics based on 2D materials

“…It was predicted that magnetic impurities on free‐standing monolayer graphene exhibit the Kondo effect . However, this depends strongly on the DOS at the Fermi energy.…”

“…It was predicted that magnetic impurities on free-standing monolayer graphene exhibit the Kondo effect. 156,[171][172][173][174] However, this depends strongly on the DOS at the Fermi energy. Experimentally, Kondo resonance peak near the Fermi energy was observed from only Co adatoms on Ru(0001) substrate, at the edge of atop regions of the Moireì pattern.…”