Gate-controlled Kondo screening in graphene: Quantum criticality and electron-hole asymmetry

¹  Institut für Theoretische Physik, Universität zu Köln - Zülpicher Str. 77, 50937 Köln, Germany, EU
²  Centro Atomico Bariloche - 8400 San Carlos de Bariloche, Argentina

Received: 16 February 2010
Accepted: 13 April 2010

Abstract

Magnetic impurities in neutral graphene provide a realization of the pseudogap Kondo model, which displays a quantum phase transition between phases with screened and unscreened impurity moment. Here, we present a detailed study of the pseudogap Kondo model with finite chemical potential μ. While carrier doping restores conventional Kondo screening at lowest energies, properties of the quantum critical fixed point turn out to influence the behavior over a large parameter range. Most importantly, the Kondo temperature T_K shows an extreme asymmetry between electron and hole doping. At criticality, depending on the sign of μ, T_K follows either the scaling prediction T_K |μ| with a universal prefactor, or T_K |μ|^x with x ≈ 2.6. This asymmetry between electron and hole doping extends well outside the quantum critical regime and also implies a qualitative difference in the shape of the tunneling spectra for both signs of μ.