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

TL;DR

This paper investigates how gate-controlled doping affects Kondo screening in graphene with magnetic impurities, revealing quantum critical behavior and significant electron-hole asymmetry in the Kondo temperature and tunneling spectra.

Contribution

It provides a detailed analysis of the pseudogap Kondo model at finite chemical potential, highlighting the asymmetry in Kondo temperature scaling between electron and hole doping.

Findings

Kondo temperature T_K scales linearly with |mu| at criticality for one doping type.

T_K scales as |mu|^2.6 for the opposite doping type.

Electron-hole asymmetry affects tunneling spectra shape.

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 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 ~ |mu| with a universal prefactor, or T_K ~ |mu|^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 mu.