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

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 mu. 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 mu, T(K) follows either the scaling prediction T(K) alpha vertical bar mu vertical bar with a universal prefactor, or T(K) alpha vertical bar mu vertical bar(x) with x approximate to 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 mu. Copyright (C) EPLA, 2010