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

G. S. Diniz, G. I. Luiz, A. Latgé, E. Vernek
2018 Physical review B  
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 Γ_imp in a hollow or top site configuration. In addition, the adatom is also weakly coupled to a metallic STM tip by a hybridization function Γ_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
more » ... mploying 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 zigazag graphene nanoribbon: (1) a weak coupling regime (Γ_imp≪Γ_tip), in which the edge states produce an enhancement of the Kondo temperature T_K and (2) a strong coupling regime (Γ_imp≫Γ_tip), in which a local singlet is formed, in detriment to 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 nanoribon (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.
doi:10.1103/physrevb.97.115444 fatcat:zww4hyx3izfjjaobhks7o6bxda