Localized Magnetic States And The Kondo Effect Of The Impurity Absorbed In Graphene

In this thesis, we study the localized magnetic states of adatom in graphene aswell as its scanning tunneling spectroscopy. The main results are summarized asfollows:1. For the graphene system with two impurities. We find that the inter-impurityinteraction brings about a significant modification for the impurity self-energy,which pushes the impurity energy across the zero energy point, and hence leadsto the splitting of the impurity magnetization boundary into the three peaks. Withincreasing the inter-impurity interaction strength, the two side peaks sharplydeviate away from the central one, and their amplitudes exhibit the differentdependence on interaction strength. For the fixed energy of some impurity, themagnetic region exhibits an asymmetry behavior between cases of the positiveand negative energy of another impurity. Additionally, we show that theinter-impurity interaction tends to suppress the local magnetic moment onimpurities.2. We present a theoretic study on scanning tunneling spectroscopy of a magneticadatom in graphene. Three typical configurations of adatoms on graphene areconsidered explicitly: the adatom is on the top of a carbon atom(AC), in asubstitutional site(SC), or above the center of the honeycomb hexagon(HC).Based on the nonequilibrium Green’s function method, we derive the local densityof state(LDOS) for the adatom and the differential conductance through thescanning tunneling microscopy device. It is found that in comparison with thecases of TC and SC, there exists an anomalous broadening of the local adatomenergy level in the HC, which pushes the adatom energy level to first cross theFermi level, leading to the appearance of an antiresonance in the LDOS due to theinterference between the Kondo scattering and the broadening adatom level.Correspondingly, the bias dependence of the differential conductance exhibits amore asymmetric sharp Kondo peak pinned to the gate voltage, and its height stillremains significantly large compared to that for the other two cases. Furthermore,with decreasing the gate voltage, the Kondo peak in the differential conductancegradually decays, and eventually vanishes in the absence of the gate voltage.