From Kondo to local singlet state in graphene nanoribbons with magnetic impurities

Article

关键词: CARBON NANOTUBES;    RENORMALIZATION-GROUP;    ELECTRON TRANSISTOR;    TRANSPORT;    SYSTEMS;   

DOI  :  10.1103/PhysRevB.97.115444

来源: SCIE

【 摘 要 】

A detailed analysis of the Kondo effect of a magnetic impurity in a zigzag graphene nanoribbon is addressed. An adatom is coupled to the graphene nanoribbon via a hybridization amplitude Gamma(imp) in a hollow-or top-site configuration. In addition, the adatom is also weakly coupled to a metallic scanning tunnel microscope (STM) tip by a hybridization function Gamma(tip) that provides a Kondo screening of its magnetic moment. The entire system is described by an Anderson-like Hamiltonian whose low-temperature physics is accessed by employing the numerical renormalization-group approach, which allows us to obtain the thermodynamic properties used to compute the Kondo temperature of the system. We find two screening regimes when the adatom is close to the edge of the zigzag graphene nanoribbon: (1) a weak-coupling regime (Gamma(imp) << Gamma(tip)), in which the edge states produce an enhancement of the Kondo temperature T-K, and (2) a strong-coupling regime (Gamma(imp) >> Gamma(tip)), in which a local singlet is formed, to the detriment of the Kondo screening by the STM tip. These two regimes can be clearly distinguished by the dependence of their characteristic temperature T* on the coupling between the adatom and the carbon sites of the graphene nanoribbon V-imp. We observe that in the weak-coupling regime T* increases exponentially with V-imp(2). Differently, in the strong-coupling regime, T* increases linearly with V-imp(2).

【 授权许可】

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